International Nuclear Information System (INIS)
Rothe, P.H.
1985-01-01
This book presents the papers given at a conference on fluid flow and hydraulics. Topics considered at the conference included a numerical study of pressure transients in a borehole due to pipe movement, laminar fluid transients in conduits of unconventional shape, water hammer analysis needs in nuclear power plant design, modeling blockage in unsteady slurry flow in conduits, and check valve slamming in a BWR feedwater system following a postulated pipe break
Computational aspects of unsteady flows
Cebeci, T.; Carr, L. W.; Khattab, A. A.; Schimke, S. M.
1985-01-01
The calculation of unsteady flows and the development of numerical methods for solving unsteady boundary layer equations and their application to the flows around important configurations such as oscillating airfoils are presented. A brief review of recent work is provided with emphasis on the need for numerical methods which can overcome possible problems associated with flow reversal and separation. The zig-zag and characteristic box schemes are described in this context, and when embodied in a method which permits interaction between solutions of inviscid and viscous equations, the characteristic box scheme is shown to avoid the singularity associated with boundary layer equations and prescribed pressure gradient. Calculations were performed for a cylinder started impulsively from rest and oscillating airfoils. The results are presented and discussed. It is conlcuded that turbulence models based on an algebraic specification of eddy viscosity can be adequate, that location of translation is important to the calculation of the location of flow separation and, therefore, to the overall lift of an oscillating airfoil.
NUMERICAL SIMULATION AND MODELING OF UNSTEADY FLOW ...
African Journals Online (AJOL)
2014-06-30
Jun 30, 2014 ... objective of this study is to control the simulation of unsteady flows around structures. ... Aerospace, our results were in good agreement with experimental .... Two-Equation Eddy-Viscosity Turbulence Models for Engineering.
Reynolds averaged simulation of unsteady separated flow
International Nuclear Information System (INIS)
Iaccarino, G.; Ooi, A.; Durbin, P.A.; Behnia, M.
2003-01-01
The accuracy of Reynolds averaged Navier-Stokes (RANS) turbulence models in predicting complex flows with separation is examined. The unsteady flow around square cylinder and over a wall-mounted cube are simulated and compared with experimental data. For the cube case, none of the previously published numerical predictions obtained by steady-state RANS produced a good match with experimental data. However, evidence exists that coherent vortex shedding occurs in this flow. Its presence demands unsteady RANS computation because the flow is not statistically stationary. The present study demonstrates that unsteady RANS does indeed predict periodic shedding, and leads to much better concurrence with available experimental data than has been achieved with steady computation
Unsteady flow over a decelerating rotating sphere
Turkyilmazoglu, M.
2018-03-01
Unsteady flow analysis induced by a decelerating rotating sphere is the main concern of this paper. A revolving sphere in a still fluid is supposed to slow down at an angular velocity rate that is inversely proportional to time. The governing partial differential equations of motion are scaled in accordance with the literature, reducing to the well-documented von Kármán equations in the special circumstance near the pole. Both numerical and perturbation approaches are pursued to identify the velocity fields, shear stresses, and suction velocity far above the sphere. It is detected that an induced flow surrounding the sphere acts accordingly to adapt to the motion of the sphere up to some critical unsteadiness parameters at certain latitudes. Afterward, the decay rate of rotation ceases such that the flow at the remaining azimuths starts revolving freely. At a critical unsteadiness parameter corresponding to s = -0.681, the decelerating sphere rotates freely and requires no more torque. At a value of s exactly matching the rotating disk flow at the pole identified in the literature, the entire flow field around the sphere starts revolving faster than the disk itself. Increasing values of -s almost diminish the radial outflow. This results in jet flows in both the latitudinal and meridional directions, concentrated near the wall region. The presented mean flow results will be useful for analyzing the instability features of the flow, whether of a convective or absolute nature.
Unsteady flow measurements in centrifugal compressors
International Nuclear Information System (INIS)
Bammert, K.; Mobarak, A.; Rautenberg, M.
1976-01-01
Centrifugal compressors and blowers are often used for recycling the coolant gas in gas-cooled reactors. To achieve the required high pressure ratios, highly loaded centrifugal compressors are built. The paper deals with unsteady flow measurements on highly loaded centrifugal impellers. Measurements of the approaching flow have been done with hot wires. The method of measurement enabled us to get the velocity distribution across the pitch ahead of the inducer. The static pressure signals along the shroud line has been discussed on the basis of some theoretical considerations. Accordingly the form of flow in the impeller and the wave flow or separation zones in the impeller can now be better interpreted. The importance of the unsteady nature of the relative flow, especially at impeller exit, is clearly demonstrated. Measurements with high responsive total pressure probes in the vicinity of impeller exit and the subsequent calculations have shown, that the instantaneous energy transfer at a certain point after the impeller may differ by more than 30% from the Euler work. Lastly, unsteady pressure measurements along the shroud line have been performed during surge and rotating stall. The surge signal have been analyzed in more detail and the mechanism of flow rupture and pressure recovery during a surge cycle is thoroughly discussed. (orig.) [de
Axisymmetric, Ventilated Supercavitation in Unsteady, Horizontal Flow
Kawakami, Ellison; Lee, Seung-Jae; Arndt, Roger
2012-11-01
Drag reduction and/or speed augmentation of marine vehicles by means of supercavitation is a topic of great interest. During the initial launch of a supercavitating vehicle, an artificial supercavity is required until the vehicle can reach conditions at which a natural supercavity can be sustained. Previous studies at Saint Anthony Falls Laboratory (SAFL) focused on the behavior of ventilated supercavities in steady horizontal flows. In open waters, vehicles can encounter unsteady flows, especially when traveling under waves. A study has been carried out at SAFL to investigate the effects of unsteady flow on axisymmetric supercavities. An attempt is made to duplicate sea states seen in open waters. In an effort to track cavity dimensions throughout a wave cycle, an automated cavity tracking script has been developed. Using a high speed camera and the proper software, it is possible to synchronize cavity dimensions with pressure measurements taken inside the cavity. Results regarding supercavity shape, ventilation demand, cavitation parameters and closure methods are presented. It was found that flow unsteadiness caused a decrease in the overall length of the supercavity while having only a minimal effect on the maximum diameter. The supercavity volume varied with cavitation number and a possible relationship between the two is being explored. (Supported by ONR)
Experimental study of unsteady thermally stratified flow
International Nuclear Information System (INIS)
Lee, Sang Jun; Chung, Myung Kyoon
1985-01-01
Unsteady thermally stratified flow caused by two-dimensional surface discharge of warm water into a oblong channel was investigated. Experimental study was focused on the rapidly developing thermal diffusion at small Richardson number. The basic objectives were to study the interfacial mixing between a flowing layer of warm water and an underlying body of cold water and to accumulate experimental data to test computational turbulence models. Mean velocity field measurements were carried out by using NMR-CT(Nuclear Magnetic Resonance-Computerized Tomography). It detects quantitative flow image of any desired section in any direction of flow in short time. Results show that at small Richardson number warm layer rapidly penetrates into the cold layer because of strong turbulent mixing and instability between the two layers. It is found that the transfer of heat across the interface is more vigorous than that of momentum. It is also proved that the NMR-CT technique is a very valuable tool to measure unsteady three dimensional flow field. (Author)
A modelling study of the multiphase leakage flow from pressurised CO{sub 2} pipeline
Energy Technology Data Exchange (ETDEWEB)
Zhou, Xuejin; Li, Kang [Department of Safety Science Engineering & State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei, Anhui 230026 (China); Tu, Ran [College of Mechanical Engineering and Automation, Huaqiao University, Jimei, Xiamen 361000 (China); Yi, Jianxin; Xie, Qiyuan [Department of Safety Science Engineering & State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei, Anhui 230026 (China); Jiang, Xi, E-mail: x.jiang@lancaster.ac.uk [Engineering Department, Lancaster University, Lancaster LA1 4YR (United Kingdom)
2016-04-05
Highlights: • A simplified model for CO{sub 2} decompression from high pressure pipelines is proposed. • The multiphase fluid was considered as a homogeneous equilibrium mixture. • Different real gas equations of state were incorporated into the model. • Detailed chocked flow calculation with capillary tube assumption was performed. • The model was validated against experimental data with discrepancies discussed. - Abstract: The accidental leakage is one of the main risks during the pipeline transportation of high pressure CO{sub 2}. The decompression process of high pressure CO{sub 2} involves complex phase transition and large variations of the pressure and temperature fields. A mathematical method based on the homogeneous equilibrium mixture assumption is presented for simulating the leakage flow through a nozzle in a pressurised CO{sub 2} pipeline. The decompression process is represented by two sub-models: the flow in the pipe is represented by the blowdown model, while the leakage flow through the nozzle is calculated with the capillary tube assumption. In the simulation, two kinds of real gas equations of state were employed in this model instead of the ideal gas equation of state. Moreover, results of the flow through the nozzle and measurement data obtained from laboratory experiments of pressurised CO{sub 2} pipeline leakage were compared for the purpose of validation. The thermodynamic processes of the fluid both in the pipeline and the nozzle were described and analysed.
COMPARATIVE EFFICIENCIES STUDY OF SLOT MODEL AND MOUSE MODEL IN PRESSURISED PIPE FLOW
Directory of Open Access Journals (Sweden)
Saroj K. Pandit
2014-01-01
Full Text Available The flow in sewers is unsteady and variable between free-surfac e to full pipe pressurized flow. Sewers are designed on the basis of free surf ace flow (gravity flow however they may carry pressurized flow. Preissmann Slot concep t is widely used numerical approach in unsteady free surface-pressurized flow as it provides the advantage of using free surface flow as a single type flow. Slo t concept uses the Saint- Venant’s equations as a basic equation for one-dimensional unst eady free surface flow. This paper includes two different numerical models using Saint Venant’s equations. The Saint Venant’s e quations of continuity and momen tum are solved by the Method of Characteristics and presented in forms for direct substitution into FORTRAN programming for numerical analysis in the first model. The MOUSE model carries out computation of unsteady flows which is founde d on an implicit, finite difference numerical solut ion of the basic one dimension al Saint Venant’s equations of free surface flow. The simulation results are comp ared to analyze the nature and degree of errors for further improvement.
Unsteady State Two Phase Flow Pressure Drop Calculations
Ayatollahi, Shahaboddin
1992-01-01
A method is presented to calculate unsteady state two phase flow in a gas-liquid line based on a quasi-steady state approach. A computer program for numerical solution of this method was prepared. Results of calculations using the computer program are presented for several unsteady state two phase flow systems
Development of a nonlinear unsteady transonic flow theory
Stahara, S. S.; Spreiter, J. R.
1973-01-01
A nonlinear, unsteady, small-disturbance theory capable of predicting inviscid transonic flows about aerodynamic configurations undergoing both rigid body and elastic oscillations was developed. The theory is based on the concept of dividing the flow into steady and unsteady components and then solving, by method of local linearization, the coupled differential equation for unsteady surface pressure distribution. The equations, valid at all frequencies, were derived for two-dimensional flows, numerical results, were obtained for two classses of airfoils and two types of oscillatory motions.
Implicit time accurate simulation of unsteady flow
van Buuren, René; Kuerten, Hans; Geurts, Bernard J.
2001-03-01
Implicit time integration was studied in the context of unsteady shock-boundary layer interaction flow. With an explicit second-order Runge-Kutta scheme, a reference solution to compare with the implicit second-order Crank-Nicolson scheme was determined. The time step in the explicit scheme is restricted by both temporal accuracy as well as stability requirements, whereas in the A-stable implicit scheme, the time step has to obey temporal resolution requirements and numerical convergence conditions. The non-linear discrete equations for each time step are solved iteratively by adding a pseudo-time derivative. The quasi-Newton approach is adopted and the linear systems that arise are approximately solved with a symmetric block Gauss-Seidel solver. As a guiding principle for properly setting numerical time integration parameters that yield an efficient time accurate capturing of the solution, the global error caused by the temporal integration is compared with the error resulting from the spatial discretization. Focus is on the sensitivity of properties of the solution in relation to the time step. Numerical simulations show that the time step needed for acceptable accuracy can be considerably larger than the explicit stability time step; typical ratios range from 20 to 80. At large time steps, convergence problems that are closely related to a highly complex structure of the basins of attraction of the iterative method may occur. Copyright
Flooding and non-equilibrium in counter-current flows with reference to pressurised water reactors
International Nuclear Information System (INIS)
Megahed, M.M.M.
1981-12-01
During the refill stage of a Loss of Coolant Accident (LOCA) in a Pressurised Water Reactor (PWR) the effectiveness with which the emergency coolant penetrates to the lower plenum, and hence to the core, is of paramount importance. Results of experimental and theoretical work carried out at the University of Strathclyde on two 1/10 scale planar test sections of a PWR downcomer annulus are presented. The experiments involved the countercurrent flows of air and water and the data were compared with existing flooding correlations for tubes. It was found experimentally that, as the inlet air flowed upwards against two opposing waterfalls, an increase in air flowrate caused the waterfalls to mover closer together until a critical air flowrate was reached where the waterfalls collapsed. A theoretical model defined this collapse condition. It was shown to be analogous to the choked flow of air through a nozzle whose cross sectional area varied with pressure. Previous experimental results for steam-water mixtures on similar test sections and the present air-water data were used to study condensation effects. Non-equilibrium effects were isolated and correlated against the dependent parameters of inlet water flowrate, inlet subcooling and downcomer wall temperature. A theoretical model giving good qualitative and quantitative agreement with experiment was developed. (author)
Transition of unsteady velocity profiles with reverse flow
Das, Debopam; Arakeri, Jaywant H
1998-01-01
This paper deals with the stability and transition to turbulence of wall-bounded unsteady velocity profiles with reverse flow. Such flows occur, for example, during unsteady boundary layer separation and in oscillating pipe flow. The main focus is on results from experiments in time-developing flow in a long pipe, which is decelerated rapidly. The flow is generated by the controlled motion of a piston. We obtain analytical solutions for laminar flow in the pipe and in a two-dimensional channe...
Dan MATEESCU
2015-01-01
This paper presents the analysis of the unsteady flows past stationary airfoils equipped with Gurney flaps at low Reynolds numbers, aiming to study the unsteady behavior of the aerodynamic coefficients due to the flow separations occurring at these Reynolds numbers. The Gurney flaps are simple but very efficient lift-increasing devices, which due to their mechanical simplicity are of particular interest for the small size micro-air-vehicles (MAV) flying at low speed and very low Reynolds numb...
Unsteady Flow in a Supersonic Turbine with Variable Specific Heats
Dorney, Daniel J.; Griffin, Lisa W.; Huber, Frank; Sondak, Douglas L.; Turner, James (Technical Monitor)
2001-01-01
Modern high-work turbines can be compact, transonic, supersonic, counter-rotating, or use a dense drive gas. The vast majority of modern rocket turbine designs fall into these Categories. These turbines usually have large temperature variations across a given stage, and are characterized by large amounts of flow unsteadiness. The flow unsteadiness can have a major impact on the turbine performance and durability. For example, the Space Transportation Main Engine (STME) fuel turbine, a high work, transonic design, was found to have an unsteady inter-row shock which reduced efficiency by 2 points and increased dynamic loading by 24 percent. The Revolutionary Reusable Technology Turbopump (RRTT), which uses full flow oxygen for its drive gas, was found to shed vortices with such energy as to raise serious blade durability concerns. In both cases, the sources of the problems were uncovered (before turbopump testing) with the application of validated, unsteady computational fluid dynamics (CFD) to the designs. In the case of the RRTT and the Alternate Turbopump Development (ATD) turbines, the unsteady CFD codes have been used not just to identify problems, but to guide designs which mitigate problems due to unsteadiness. Using unsteady flow analyses as a part of the design process has led to turbine designs with higher performance (which affects temperature and mass flow rate) and fewer dynamics problems. One of the many assumptions made during the design and analysis of supersonic turbine stages is that the values of the specific heats are constant. In some analyses the value is based on an average of the expected upstream and downstream temperatures. In stages where the temperature can vary by 300 to 500 K, however, the assumption of constant fluid properties may lead to erroneous performance and durability predictions. In this study the suitability of assuming constant specific heats has been investigated by performing three-dimensional unsteady Navier
Theory and Low-Order Modeling of Unsteady Airfoil Flows
Ramesh, Kiran
Unsteady flow phenomena are prevalent in a wide range of problems in nature and engineering. These include, but are not limited to, aerodynamics of insect flight, dynamic stall in rotorcraft and wind turbines, leading-edge vortices in delta wings, micro-air vehicle (MAV) design, gust handling and flow control. The most significant characteristics of unsteady flows are rapid changes in the circulation of the airfoil, apparent-mass effects, flow separation and the leading-edge vortex (LEV) phenomenon. Although experimental techniques and computational fluid dynamics (CFD) methods have enabled the detailed study of unsteady flows and their underlying features, a reliable and inexpensive loworder method for fast prediction and for use in control and design is still required. In this research, a low-order methodology based on physical principles rather than empirical fitting is proposed. The objective of such an approach is to enable insights into unsteady phenomena while developing approaches to model them. The basis of the low-order model developed here is unsteady thin-airfoil theory. A time-stepping approach is used to solve for the vorticity on an airfoil camberline, allowing for large amplitudes and nonplanar wakes. On comparing lift coefficients from this method against data from CFD and experiments for some unsteady test cases, it is seen that the method predicts well so long as LEV formation does not occur and flow over the airfoil is attached. The formation of leading-edge vortices (LEVs) in unsteady flows is initiated by flow separation and the formation of a shear layer at the airfoil's leading edge. This phenomenon has been observed to have both detrimental (dynamic stall in helicopters) and beneficial (high-lift flight in insects) effects. To predict the formation of LEVs in unsteady flows, a Leading Edge Suction Parameter (LESP) is proposed. This parameter is calculated from inviscid theory and is a measure of the suction at the airfoil's leading edge. It
Experimental validation of an ultrasonic flowmeter for unsteady flows
Leontidis, V.; Cuvier, C.; Caignaert, G.; Dupont, P.; Roussette, O.; Fammery, S.; Nivet, P.; Dazin, A.
2018-04-01
An ultrasonic flowmeter was developed for further applications in cryogenic conditions and for measuring flow rate fluctuations in the range of 0 to 70 Hz. The prototype was installed in a flow test rig, and was validated experimentally both in steady and unsteady water flow conditions. A Coriolis flowmeter was used for the calibration under steady state conditions, whereas in the unsteady case the validation was done simultaneously against two methods: particle image velocimetry (PIV), and with pressure transducers installed flush on the wall of the pipe. The results show that the developed flowmeter and the proposed methodology can accurately measure the frequency and amplitude of unsteady fluctuations in the experimental range of 0-9 l s-1 of the mean main flow rate and 0-70 Hz of the imposed disturbances.
Unsteady Viscous Flow Past an Impulsively Started Porous Vertical ...
African Journals Online (AJOL)
This paper presents a new numerical approach for solving unsteady two dimensional boundary layer flow past an infinite vertical porous surface with the flow generated by Newtonian heating and impulsive motion in the presence of viscous dissipation and temperature dependent viscosity. The viscosity of the fluid under ...
Unsteady MHD stagnation flow over a moving wall
International Nuclear Information System (INIS)
Kumari, M.; Nath, G.
2006-01-01
The unsteady viscous stagnation flow of an electrically conducting fluid over a continuously moving wall with an applied magnetic field has been investigated when the free stream and wall velocities increase arbitrarily with time. The flow is initially (t = 0) steady and at time t > 0, it becomes unsteady. The semi-similar solution of the unsteady Navier-Stokes equations along with the energy equation governing the flow and heat transfer has been obtained numerically. Also the self-similar solution is obtained when the surface and free stream velocities vary inversely as a linear function of time. The shear stress and the heat transfer increase with time and magnetic field. The surface shear stress vanishes for certain value of the ratio of the wall velocity to the free stream velocity. (author)
Directory of Open Access Journals (Sweden)
Dan MATEESCU
2015-12-01
Full Text Available This paper presents the analysis of the unsteady flows past stationary airfoils equipped with Gurney flaps at low Reynolds numbers, aiming to study the unsteady behavior of the aerodynamic coefficients due to the flow separations occurring at these Reynolds numbers. The Gurney flaps are simple but very efficient lift-increasing devices, which due to their mechanical simplicity are of particular interest for the small size micro-air-vehicles (MAV flying at low speed and very low Reynolds number. The unsteady aerodynamic analysis is performed with an efficient time-accurate numerical method developed for the solution of the Navier-Stokes equations at low Reynolds numbers, which is second-order-accurate in time and space. The paper presents solutions for the unsteady aerodynamic coefficients of lift and drag and for the lift-to-drag ratio of several symmetric and cambered airfoils with Gurney flaps. It was found that although the airfoil is considered stationary, starting from a relatively small incidence (about 8 degrees the flow becomes unsteady due to the unsteadiness of the flow separations occurring at low Reynolds numbers, and the aerodynamic coefficients display periodic oscillations in time. A detailed study is presented in the paper on the influence of various geometric and flow parameters, such as the Gurney flap height, Reynolds number, airfoil relative thickness and relative camber, on the aerodynamic coefficients of lift, drag and lift-to-drag ratio. The flow separation is also studied with the aid of flow visualizations illustrating the changes in the flow pattern at various moments in time.
Unsteady potential flow past a propeller blade section
Takallu, M. A.
1990-01-01
An analytical study was conducted to predict the effect of an oscillating stream on the time dependent sectional pressure and lift coefficients of a model propeller blade. The assumption is that as the blade sections encounter a wake, the actual angles of attack vary in a sinusoidal manner through the wake, thus each blade is exposed to an unsteady stream oscillating about a mean value at a certain reduced frequency. On the other hand, an isolated propeller at some angle of attack can experience periodic changes in the value of the flow angle causing unsteady loads on the blades. Such a flow condition requires the inclusion of new expressions in the formulation of the unsteady potential flow around the blade sections. These expressions account for time variation of angle of attack and total shed vortices in the wake of each airfoil section. It was found that the final expressions for the unsteady pressure distribution on each blade section are periodic and that the unsteady circulation and lift coefficients exhibit a hysteresis loop.
Unsteady flow model for circulation-control airfoils
Rao, B. M.
1979-01-01
An analysis and a numerical lifting surface method are developed for predicting the unsteady airloads on two-dimensional circulation control airfoils in incompressible flow. The analysis and the computer program are validated by correlating the computed unsteady airloads with test data and also with other theoretical solutions. Additionally, a mathematical model for predicting the bending-torsion flutter of a two-dimensional airfoil (a reference section of a wing or rotor blade) and a computer program using an iterative scheme are developed. The flutter program has a provision for using the CC airfoil airloads program or the Theodorsen hard flap solution to compute the unsteady lift and moment used in the flutter equations. The adopted mathematical model and the iterative scheme are used to perform a flutter analysis of a typical CC rotor blade reference section. The program seems to work well within the basic assumption of the incompressible flow.
Flow Measurements of a Plunging Wing in Unsteady Environment
Wengel, Jesse; Nathan, Rungun; Cheng, Bo; Eslam-Panah, Azar
2017-11-01
Despite the great progress in their design and control, Unmanned Aerial Vehicles (UAVs) are tremendously troubled while flying in turbulent environments, which are common in the lower atmospheric boundary layer (ABL). A nominally 2D plunging wing was developed and tested in the presence of unsteady wake to investigate the effect of the flow disturbances on vorticity fields. The experiments were conducted in a water channel facility with test section width of 0.76 m, and a water depth of 0.6 m. The unsteady wake in the form of von Kármán Vortex Street was generated by a cylinder located upstream of the plunging wing. The plunge amplitude and frequency of the oscillation were adjusted to bracket the range of Strouhal numbers relevant to the biological locomotion (0.25PIV) was employed to quantitatively study the effect of unsteady wake on the flow measurements of the plunging wing.
Unsteady axisymmetric flow of a micropolar fluid between the ...
African Journals Online (AJOL)
The influence of several parameters on dimensionless velocities is presented through plots. The behavior of skin friction and couple stress coefficients is tabulated against various values of the pertinent parameters. Keywords: Unsteady flow, micropolar fluid, radial stretching, skin friction coefficient, couple stress coefficient
Simulating unsteady conduit flows with smoothed particle hydrodynamics
Hou, Q.
2012-01-01
Pipelines are widely used for transport and cooling in industries such as oil and gas, chemical, water supply and sewerage, and hydro, fossil-fuel and nuclear power plants. Unsteady pipe flows with large pressure variations may cause a range of problems such as pipe rapture, support failure, pipe
The Unsteady Variable – Viscosity Free Convection Flow on a ...
African Journals Online (AJOL)
The unsteady variable-viscosity free convection flow of a viscous incompressible fluid near an infinite vertical plate (or wall) is investigated under an arbitrary timedependent heating of the plates, and the governing equations of motion and energy transformed into ordinary differential equations. Employing asymptotic ...
The flows structure in unsteady gas flow in pipes with different cross-sections
Plotnikov Leonid; Nevolin Alexandr; Nikolaev Dmitrij
2017-01-01
The results of numerical simulation and experimental study of the structure of unsteady flows in pipes with different cross sections are presented in the article. It is shown that the unsteady gas flow in a circular pipe is axisymmetric without secondary currents. Steady vortex structures (secondary flows) are observed in pipes with cross sections in the form of a square and an equilateral triangle. It was found that these secondary flows have a significant impact on gas flows in pipes of com...
Investigation into the behaviors of ventilated supercavities in unsteady flow
Shao, Siyao; Wu, Yue; Haynes, Joseph; Arndt, Roger E. A.; Hong, Jiarong
2018-05-01
A systematic investigation of ventilated supercavitation behaviors in an unsteady flow is conducted using a high-speed water tunnel at the Saint Anthony Falls Laboratory. The cavity is generated with a forward facing model under varying ventilation rates and cavitator sizes. The unsteady flow is produced by a gust generator consisting of two hydrofoils flapping in unison with a varying angle of attack (AoA) and frequency (fg). The current experiment reveals five distinct cavity states, namely, the stable state, wavy state, pulsating state I, pulsating state II, and collapsing state, based on the variation of cavity geometry and pressure signatures inside the cavity. The distribution of cavity states over a broad range of unsteady conditions is summarized in a cavity state map. It shows that the transition of the supercavity from the stable state to pulsating and collapsing states is primarily induced by increasing AoA while the transition to the wavy state triggers largely by increasing fg. Remarkably, the state map over the non-dimensionalized half wavelength and wave amplitude of the perturbation indicates that the supercavity loses its stability and transitions to pulsating or collapsing states when the level of its distortion induced by the flow unsteadiness exceeds the cavity dimension under a steady condition. The state maps under different ventilation rates and cavitator sizes yield similar distribution but show that the occurrence of the cavity collapse can be suppressed with increasing ventilation coefficient or cavitator size. Such knowledge can be integrated into designing control strategies for the supercavitating devices operating under different unsteady conditions.
Transition of unsteady velocity profiles with reverse flow
Das, Debopam; Arakeri, Jaywant H.
1998-11-01
This paper deals with the stability and transition to turbulence of wall-bounded unsteady velocity profiles with reverse flow. Such flows occur, for example, during unsteady boundary layer separation and in oscillating pipe flow. The main focus is on results from experiments in time-developing flow in a long pipe, which is decelerated rapidly. The flow is generated by the controlled motion of a piston. We obtain analytical solutions for laminar flow in the pipe and in a two-dimensional channel for arbitrary piston motions. By changing the piston speed and the length of piston travel we cover a range of values of Reynolds number and boundary layer thickness. The velocity profiles during the decay of the flow are unsteady with reverse flow near the wall, and are highly unstable due to their inflectional nature. In the pipe, we observe from flow visualization that the flow becomes unstable with the formation of what appears to be a helical vortex. The wavelength of the instability [simeq R: similar, equals]3[delta] where [delta] is the average boundary layer thickness, the average being taken over the time the flow is unstable. The time of formation of the vortices scales with the average convective time scale and is [simeq R: similar, equals]39/([Delta]u/[delta]), where [Delta]u=(umax[minus sign]umin) and umax, umin and [delta] are the maximum velocity, minimum velocity and boundary layer thickness respectively at each instant of time. The time to transition to turbulence is [simeq R: similar, equals]33/([Delta]u/[delta]). Quasi-steady linear stability analysis of the velocity profiles brings out two important results. First that the stability characteristics of velocity profiles with reverse flow near the wall collapse when scaled with the above variables. Second that the wavenumber corresponding to maximum growth does not change much during the instability even though the velocity profile does change substantially. Using the results from the experiments and the
Suppressing unsteady flow in arterio-venous fistulae
Grechy, L.; Iori, F.; Corbett, R. W.; Shurey, S.; Gedroyc, W.; Duncan, N.; Caro, C. G.; Vincent, P. E.
2017-10-01
Arterio-Venous Fistulae (AVF) are regarded as the "gold standard" method of vascular access for patients with end-stage renal disease who require haemodialysis. However, a large proportion of AVF do not mature, and hence fail, as a result of various pathologies such as Intimal Hyperplasia (IH). Unphysiological flow patterns, including high-frequency flow unsteadiness, associated with the unnatural and often complex geometries of AVF are believed to be implicated in the development of IH. In the present study, we employ a Mesh Adaptive Direct Search optimisation framework, computational fluid dynamics simulations, and a new cost function to design a novel non-planar AVF configuration that can suppress high-frequency unsteady flow. A prototype device for holding an AVF in the optimal configuration is then fabricated, and proof-of-concept is demonstrated in a porcine model. Results constitute the first use of numerical optimisation to design a device for suppressing potentially pathological high-frequency flow unsteadiness in AVF.
Numerical method for the unsteady potential flow about pitching airfoils
International Nuclear Information System (INIS)
Parrouffe, J.-M.; Paraschivoiu, I.
1985-01-01
This paper presents a numerical method for the unsteady potential flow about an aerodynamic profile and in its wake. This study has many applications such as airplane wings and propellers, guide vanes, subcavitant hydrofoils and wind turbine blades. Typical of such nonstationary configurations is the rotor of the Darrieus vertical-axis wind turbine whose blades are exposed to cyclic aerodynamic loads in the operating state
Observations and Measurements on Unsteady Cloud Cavitation Flow Structures
Gu, L. X.; Yan, G. J.; Huang, B.
2015-12-01
The objectives of this paper are to investigate the unsteady structures and hydrodynamics of cavitating flows. Experimental results are presented for a Clark-Y hydrofoil, which is fixed at α=0°, 5° and 8°. The high-speed video camera and Particle Image Velocimetry (PIV) are applied to investigate the transient flow structures. The dynamic measurement system is used to record the dynamic characteristics. The cloud cavitation exhibits noticeable unsteady characteristics. For the case of α=0°, there exit strong interactions between the attached cavity and the re-entrant flow. While for the case of α=8°, the re-entrant flow is relatively thin and the interaction between the cavity and re-entrant flow is limited. The results also present that the periodic collapse and shedding of the large-scale cloud cavitation, which leads to substantial increase of turbulent velocity fluctuations in the cavity region. Experimental evidence indicates that the hydrodynamics are clearly affected by the cavitating flow structures, the amplitude of load fluctuation are much higher for the cloud cavitating cases.
Observations and Measurements on Unsteady Cloud Cavitation Flow Structures
International Nuclear Information System (INIS)
Gu, L X; Yan, G J; Huang, B
2015-01-01
The objectives of this paper are to investigate the unsteady structures and hydrodynamics of cavitating flows. Experimental results are presented for a Clark-Y hydrofoil, which is fixed at α=0°, 5° and 8°. The high-speed video camera and Particle Image Velocimetry (PIV) are applied to investigate the transient flow structures. The dynamic measurement system is used to record the dynamic characteristics. The cloud cavitation exhibits noticeable unsteady characteristics. For the case of α=0°, there exit strong interactions between the attached cavity and the re-entrant flow. While for the case of α=8°, the re-entrant flow is relatively thin and the interaction between the cavity and re-entrant flow is limited. The results also present that the periodic collapse and shedding of the large-scale cloud cavitation, which leads to substantial increase of turbulent velocity fluctuations in the cavity region. Experimental evidence indicates that the hydrodynamics are clearly affected by the cavitating flow structures, the amplitude of load fluctuation are much higher for the cloud cavitating cases. (paper)
Prediction of unsteady separated flows on oscillating airfoils
Mccroskey, W. J.
1978-01-01
Techniques for calculating high Reynolds number flow around an airfoil undergoing dynamic stall are reviewed. Emphasis is placed on predicting the values of lift, drag, and pitching moments. Methods discussed include: the discrete potential vortex method; thin boundary layer method; strong interaction between inviscid and viscous flows; and solutions to the Navier-Stokes equations. Empirical methods for estimating unsteady airloads on oscillating airfoils are also described. These methods correlate force and moment data from wind tunnel tests to indicate the effects of various parameters, such as airfoil shape, Mach number, amplitude and frequency of sinosoidal oscillations, mean angle, and type of motion.
Unsteady resurgence flows in karstic media
Adler, Pierre; Drygas, Piotr; Mityushev, Vladimir
2017-04-01
Geological porous media are heterogeneous materials which in addition contain discontinuities such as fractures and conduits which facilitate fluid transport. Fractures are relatively plane objects which strongly interact with the surrounding porous medium because of their large contact surface. A different situation occurs in karsts where distant regions of the medium can be connected by relatively thin conduits which have little if any hydrodynamic interaction with the porous medium that they cross, except at their ends. This phenomenon is called resurgence because of the obvious analogy with rivers which suddenly disappear underground and go out at the ground surface again. Similar ideas have already been developed in other fields, such as Physics with random networks and Geophysics with electrical tomography. Media with resurgences are addressed in the following way. They consist of a double structure. The first one is the continuous porous medium described by the classical Darcy law. The second one is composed by the resurgences modeled by conduits with impermeable walls which relate distant points of the continuous medium. When non steady regimes are considered, it appears necessary to confer a capacity to these conduits in addition to their hydrodynamic resistance. Therefore, the conduits are able to store some quantity of fluid. In addition, two kinds of resurgence are addressed, namely punctual and extended; in the second case, the dimensions of the ends of the conduit are not negligible compared to the characteristic length scales of the embedding porous medium. Capacities and extended resurgences are new features which were not taken into account in our previous studies. The punctual resurgence is described by a spatial network with a finite number of conduits embedded in a continuous porous medium. The flow in the network is described by the classical Kirchhoff law (including capacities). The equations for flow in the network and in the continuous
Viscosity measurement in the capillary tube viscometer under unsteady flow
International Nuclear Information System (INIS)
Park, Heung Jun; Yoo, Sang Sin; Suh, Sang Ho
2000-01-01
The objective of the present study is to develop a new device that the viscous characteristics of fluids are determined by applying the unsteady flow concept to the traditional capillary tube viscometer. The capillary tube viscometer consists of a small cylindrical reservoir, capillary tube, a load cell system that measures the mass flow rate, interfaces, and computer. Due to the small size of the reservoir the height of liquid in the reservoir decreases as soon as the liquid in the reservoir drains out through the capillary and the mass flow rate in the capillary decreases as the hydrostatic pressure in the reservoir decreases resulting in a decrease of the shear rate in the capillary tube. The instantaneous shear rate and driving force in the capillary tube are determined by measuring the mass flow rate through the capillary, and the fluid viscosity is determined from the measured flow rate and the driving force
Unsteady coupling effects of wet steam in steam turbines flows
International Nuclear Information System (INIS)
Blondel, Frederic
2014-01-01
In addition to conventional turbomachinery problems, both the behavior and performances of steam turbines are highly dependent on the vapour thermodynamic state and the presence of a liquid phase. EDF, the main French electricity producer, is interested in further developing its' modelling capabilities and expertise in this area to allow for operational studies and long-term planning. This PhD thesis explores the modelling of wetness formation and growth in a steam turbine and an analysis of the coupling between the liquid phase and the main flow unsteadiness. To this end, the work in this thesis took the following approach. Wetness was accounted for using a homogeneous model coupled with transport equations to take into account the effects of non-equilibrium phenomena, such as the growth of the liquid phase and nucleation. The real gas attributes of the problem demanded adapted numerical methods. Before their implementation in the 3D elsA solver, the accuracy of the chosen models was tested using a developed one-dimensional nozzle code. In this manner, various condensation models were considered, including both poly-dispersed and monodispersed behaviours of the steam. Finally, unsteady coupling effects were observed from several perspectives (1D, 1D - 3D, 3D), demonstrating the ability of the method of moments to sustain unsteady phenomena which were not apparent in a simple monodispersed model. (author)
Efficient Unsteady Flow Visualization with High-Order Access Dependencies
Energy Technology Data Exchange (ETDEWEB)
Zhang, Jiang; Guo, Hanqi; Yuan, Xiaoru
2016-04-19
We present a novel high-order access dependencies based model for efficient pathline computation in unsteady flow visualization. By taking longer access sequences into account to model more sophisticated data access patterns in particle tracing, our method greatly improves the accuracy and reliability in data access prediction. In our work, high-order access dependencies are calculated by tracing uniformly-seeded pathlines in both forward and backward directions in a preprocessing stage. The effectiveness of our proposed approach is demonstrated through a parallel particle tracing framework with high-order data prefetching. Results show that our method achieves higher data locality and hence improves the efficiency of pathline computation.
Unsteady flow characteristics through a human nasal airway.
Lee, Jong-Hoon; Na, Yang; Kim, Sung-Kyun; Chung, Seung-Kyu
2010-07-31
Time-dependent characteristics of the flow in a human nasal airway constructed from the CT image of a healthy volunteer were investigated using a computational fluid dynamics (CFD) technique. To capture the time-varying nature of the flow as well as pressure and temperature fields, the large eddy simulation (LES) technique instead of the RANS (Reynolds Averaged Navier-Stokes) approach was adopted. To make the present analysis more relevant to a real human breathing cycle, the flow was designed to be induced by the pressure difference and the time-varying pressure at the end of trachea was described to reproduce the flow rate data from the measurement. Comparison of the present results with those of typical steady simulations showed that the difference in flow characteristics is magnified in the expiration phase. This fact may suggest that the inertial effect associated with unsteady flow is more important during the expiration period. Also, the fact that the distribution of the flow rate in a given cross-section of the airway changes significantly with time implies the importance of unsteady data for clinical decision. The wall shear stress was found to have relatively high values at the locations near nasopharynx and larynx but the magnitude changes with time during the whole respiratory cycle. Analysis of the temperature field showed that most of the temperature change occurs in the nasal cavity when the air is incoming and thus, the nasal cavity acts as a very efficient heat exchanger during an inspiration period. Copyright 2010 Elsevier B.V. All rights reserved.
Perbandingan Hasil Pemodelan Aliran Satu Dimensi Unsteady Flow dan Steady Flow pada Banjir Kota
Directory of Open Access Journals (Sweden)
Andreas Tigor Oktaga
2016-06-01
Full Text Available One dimensional flow is often used as a flood simulation for the planning capacity of the river. Flood is a type of unsteady non-uniform flow, that can be simulated using HEC-RAS. HEC-RAS software is often used for flood modeling with a one-dimensional flow method. Unsteady flow modeling results in HEC-RAS sometimes refer to error and warning due to unstable analysis program. The stability program among others influenced bend in the river flow, the steep slope of the river bottom, and changes in cross-section shape. Because the flood handling required maximum discharge and maximum flood water level, then a steady flow is often used as an alternative to simulate the flood flow. This study aimed to determine the advantages and disadvantages of modeling unsteady non-uniform and steady non-uniform flow. The research location in the Kanal Banjir Barat, in the Semarang City. Hydraulics modeling uses HEC-RAS 4.1 and for discharge the plan is obtained from the HEC-HMS 3.5. Results of the comparison modeling hydraulics the modeling of steady non-uniform flow has a tendency water level is higher and modeling of unsteady non-uniform flow takes longer to analyze. Results of the comparison the average flood water level maximun is less than 15% (± 0,3 meters, that is 0.27 meters (13.16% for Q50, 0.25 meters (11.56% for Q100, dan 0.16 meters (4.73% for Q200. So the modeling steady non-uniform flow can still be used as a companion version the modeling unsteady non-uniform flow.
Numerical flow analysis of axial flow compressor for steady and unsteady flow cases
Prabhudev, B. M.; Satish kumar, S.; Rajanna, D.
2017-07-01
Performance of jet engine is dependent on the performance of compressor. This paper gives numerical study of performance characteristics for axial compressor. The test rig is present at CSIR LAB Bangalore. Flow domains are meshed and fluid dynamic equations are solved using ANSYS package. Analysis is done for six different speeds and for operating conditions like choke, maximum efficiency & before stall point. Different plots are compared and results are discussed. Shock displacement, vortex flows, leakage patterns are presented along with unsteady FFT plot and time step plot.
Deep learning of unsteady laminar flow over a cylinder
Lee, Sangseung; You, Donghyun
2017-11-01
Unsteady flow over a circular cylinder is reconstructed using deep learning with a particular emphasis on elucidating the potential of learning the solution of the Navier-Stokes equations. A deep neural network (DNN) is employed for deep learning, while numerical simulations are conducted to produce training database. Instantaneous and mean flow fields which are reconstructed by deep learning are compared with the simulation results. Fourier transform of flow variables has been conducted to validate the ability of DNN to capture both amplitudes and frequencies of flow motions. Basis decomposition of learned flow is performed to understand the underlying mechanisms of learning flow through DNN. The present study suggests that a deep learning technique can be utilized for reconstruction and, potentially, for prediction of fluid flow instead of solving the Navier-Stokes equations. This work was supported by the National Research Foundation of Korea(NRF) Grant funded by the Korea government(Ministry of Science, ICT and Future Planning) (No. 2014R1A2A1A11049599, No. 2015R1A2A1A15056086, No. 2016R1E1A2A01939553).
Numerical Modeling of Unsteady Flow in Steam Turbine Stage
Czech Academy of Sciences Publication Activity Database
Halama, Jan; Dobeš, J.; Fořt, Jaroslav; Fürst, J.; Kozel, Karel
2010-01-01
Roč. 234, č. 7 (2010), s. 2336-2341 ISSN 0377-0427 Grant - others:GA ČR(CZ) GA201/08/0012 Program:GA Institutional research plan: CEZ:AV0Z20760514 Keywords : stator-rotor interaction * unsteady flow * two - phase flow Subject RIV: BK - Fluid Dynamics Impact factor: 1.029, year: 2010 http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6TYH-4X1J73B-M-W&_cdi=5619&_user=640952&_pii=S0377042709005718&_origin=search&_coverDate=08%2F01%2F2010&_sk=997659992&view=c&wchp=dGLzVlz-zSkzS&md5=36ee785371868aebdcc6bd0d17263fc4&ie=/sdarticle.pdf
Investigation of Unsteady Flow Behavior in Transonic Compressor Rotors with LES and PIV Measurements
Hah, Chunill; Voges, Melanie; Mueller, Martin; Schiffer, Heinz-Peter
2009-01-01
In the present study, unsteady flow behavior in a modern transonic axial compressor rotor is studied in detail with large eddy simulation (LES) and particle image velocimetry (PIV). The main purpose of the study is to advance the current understanding of the flow field near the blade tip in an axial transonic compressor rotor near the stall and peak-efficiency conditions. Flow interaction between the tip leakage vortex and the passage shock is inherently unsteady in a transonic compressor. Casing-mounted unsteady pressure transducers have been widely applied to investigate steady and unsteady flow behavior near the casing. Although many aspects of flow have been revealed, flow structures below the casing cannot be studied with casing-mounted pressure transducers. In the present study, unsteady velocity fields are measured with a PIV system and the measured unsteady flow fields are compared with LES simulations. The currently applied PIV measurements indicate that the flow near the tip region is not steady even at the design condition. This self-induced unsteadiness increases significantly as the compressor rotor operates near the stall condition. Measured data from PIV show that the tip clearance vortex oscillates substantially near stall. The calculated unsteady characteristics of the flow from LES agree well with the PIV measurements. Calculated unsteady flow fields show that the formation of the tip clearance vortex is intermittent and the concept of vortex breakdown from steady flow analysis does not seem to apply in the current flow field. Fluid with low momentum near the pressure side of the blade close to the leading edge periodically spills over into the adjacent blade passage. The present study indicates that stall inception is heavily dependent on unsteady behavior of the flow field near the leading edge of the blade tip section for the present transonic compressor rotor.
Stratified steady and unsteady two-phase flows between two parallel plates
International Nuclear Information System (INIS)
Sim, Woo Gun
2006-01-01
To understand fluid dynamic forces acting on a structure subjected to two-phase flow, it is essential to get detailed information about the characteristics of two-phase flow. Stratified steady and unsteady two-phase flows between two parallel plates have been studied to investigate the general characteristics of the flow related to flow-induced vibration. Based on the spectral collocation method, a numerical approach has been developed for the unsteady two-phase flow. The method is validated by comparing numerical result to analytical one given for a simple harmonic two-phase flow. The flow parameters for the steady two-phase flow, such as void fraction and two-phase frictional multiplier, are evaluated. The dynamic characteristics of the unsteady two-phase flow, including the void fraction effect on the complex unsteady pressure, are illustrated
Parallel Computation of Unsteady Flows on a Network of Workstations
1997-01-01
Parallel computation of unsteady flows requires significant computational resources. The utilization of a network of workstations seems an efficient solution to the problem where large problems can be treated at a reasonable cost. This approach requires the solution of several problems: 1) the partitioning and distribution of the problem over a network of workstation, 2) efficient communication tools, 3) managing the system efficiently for a given problem. Of course, there is the question of the efficiency of any given numerical algorithm to such a computing system. NPARC code was chosen as a sample for the application. For the explicit version of the NPARC code both two- and three-dimensional problems were studied. Again both steady and unsteady problems were investigated. The issues studied as a part of the research program were: 1) how to distribute the data between the workstations, 2) how to compute and how to communicate at each node efficiently, 3) how to balance the load distribution. In the following, a summary of these activities is presented. Details of the work have been presented and published as referenced.
Contribution to the study of unsteady condensation in transonic flow
International Nuclear Information System (INIS)
Collignan, B.; Laali, A.R.
1993-12-01
The aim of this thesis is the study of transonic steam flows with condensation, especially at high pressure. This study includes a numerical part an experimental one. The modelling has consisted of introducing a spontaneous condensation model in a one-dimensional Euler code using steam-water thermodynamic tables. Calculations, performed with this code, are in good agreement with experimental results at low pressure. The experimental study has been undertaken on a high pressure experimental loop installed at the Bugey nuclear power plant. We have studied steam flows in nozzles. The results obtained show that a partial heterogeneous condensation occurs in these flows. This proportion is stronger if the expansion rate of the flow is low and if the inlet pressure is high. However, a correction factor is obtained for high pressure nucleation rate model from experimental results. No unsteady condensation has been observed for flows between 15 bars and 50 bars with the steam available at Bugey power plant. (authors). figs., 71 refs., 6 annexes
Prediction of unsteady airfoil flows at large angles of incidence
Cebeci, Tuncer; Jang, H. M.; Chen, H. H.
1992-01-01
The effect of the unsteady motion of an airfoil on its stall behavior is of considerable interest to many practical applications including the blades of helicopter rotors and of axial compressors and turbines. Experiments with oscillating airfoils, for example, have shown that the flow can remain attached for angles of attack greater than those which would cause stall to occur in a stationary system. This result appears to stem from the formation of a vortex close to the surface of the airfoil which continues to provide lift. It is also evident that the onset of dynamic stall depends strongly on the airfoil section, and as a result, great care is required in the development of a calculation method which will accurately predict this behavior.
Unsteady interfacial coupling of two-phase flow models
International Nuclear Information System (INIS)
Hurisse, O.
2006-01-01
The primary coolant circuit in a nuclear power plant contains several distinct components (vessel, core, pipes,...). For all components, specific codes based on the discretization of partial differential equations have already been developed. In order to obtain simulations for the whole circuit, the interfacial coupling of these codes is required. The approach examined within this work consists in coupling codes by providing unsteady information through the coupling interface. The numerical technique relies on the use of an interface model, which is combined with the basic strategy that was introduced by Greenberg and Leroux in order to compute approximations of steady solutions of non-homogeneous hyperbolic systems. Three different coupling cases have been examined: (i) the coupling of a one-dimensional Euler system with a two-dimensional Euler system; (ii) the coupling of two distinct homogeneous two-phase flow models; (iii) the coupling of a four-equation homogeneous model with the standard two-fluid model. (author)
Unsteady flow analysis of combustion processes in a Davis gun
Energy Technology Data Exchange (ETDEWEB)
Cho, H.-C.; Shin, H.D. [Korea Advanced Inst. of Science and Technology, Mechanical Engineering Dept., Taejon (Korea, Republic of); Yoon, J.-K. [Hansung Univ., School of Industrial and System Engineering, Seoul (Korea, Republic of)
1999-09-01
The Davis gun, a type of recoilless gun, had the advantages of requiring less rear area and less powder than a conventional recoilless gun. The unsteady pressure and flow fields of a Davis gun were numerically simulated by using a two-phase fluid dynamic model. Numerical simulation results were compared with experimental values to evaluate the feasibility of the interior ballistic model. The interior ballistics in a Davis gun with a simple countermass were predicted with the computational model. It was shown that the pressure-time curves matched well between experimental data and numerical analysis except in the vicinity of the peak pressure and steep pressure gradient. The predicted muzzle velocity of projectile and countermass was closely similar to the experimental one. In this study, large pressure waves were not observed since the initial porosity was relatively high ({phi}{sub 0}0.867) and the charge was ignited at the centre of the granular bed. (Author)
Numerical solutions of unsteady flows with low inlet Mach numbers
Czech Academy of Sciences Publication Activity Database
Punčochářová, Petra; Furst, Jiří; Horáček, Jaromír; Kozel, Karel
2010-01-01
Roč. 80, č. 8 (2010), s. 1795-1805 ISSN 0378-4754 R&D Projects: GA AV ČR IAA200760613 Institutional research plan: CEZ:AV0Z20760514 Keywords : finite volume method * unsteady flow * low Mach number * viscous compressible fluid Subject RIV: BI - Acoustics Impact factor: 0.812, year: 2010 http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6V0T-4Y0D67D-1-R&_cdi=5655&_user=640952&_pii=S0378475409003607&_origin=search&_coverDate=04%2F30%2F2010&_sk=999199991&view=c&wchp=dGLbVlb-zSkzk&md5=ed6eaf0a050968ee978714fd54e7f131&ie=/sdarticle.pdf
Viscous-inviscid method for the simulation of turbulent unsteady wind turbine airfoil flow
Energy Technology Data Exchange (ETDEWEB)
Bermudez, L.; Velazquez, A.; Matesanz, A. [Thermal Engineering Area, Carlos III University of Madrid, Avd. Universidad 30, 28911 Leganes, Madrid (Spain)
2002-06-01
A Viscous-inviscid interaction method is presented that allows for the simulation of unsteady airfoil flow in the context of wind turbine applications. The method couples a 2-D external unsteady potential flow to a 2-D unsteady turbulent boundary layer. The separation point on the airfoil leeward side is determined in a self-consistent way from the boundary-layer equations, and the separated flow region is modelled independently. Wake shape and motion are also determined in a self-consistent way, while an unsteady Kutta condition is implemented. The method is able to deal with attached flow and light stall situations characterised by unsteady turbulent boundary-layer separation size up to 50% of the airfoil chord length. The results of the validation campaign show that the method could be used for industrial design purposes because of its numerical robustness, reasonable accuracy, and limited computational time demands.
Unsteady Flow Interactions Between Pitching Wings In Schooling Arrangements
Kurt, Melike; Moored, Keith
2017-11-01
In nature, many fish aggregate into large groups or schools for protection against predators, for social interactions and to save energy during migrations. Regardless of their prime motivation, fish experience three-dimensional flow interactions amongst themselves that can improve or hamper swimming performance and give rise to fluid-mediated forces between individuals. To date, the unsteady, three-dimensional flow interactions among schooling fish remains relatively unexplored. In order to study these interactions, the caudal fins of two interacting fish are idealized as two finite span pitching wings arranged in mixtures of canonical in-line and side-by-side arrangements. The forces and moments acting on the wings in the streamwise and cross-stream directions are quantified as the arrangement and the phase delay between the wings is altered. Particle image velocimetry is employed to characterize the flow physics during high efficiency locomotion. Finally, the forces and flowfields of two-dimensional pitching wings are compared with three-dimensional wings to distinguish how three-dimensionality alters the flow interactions in schools of fish.
Unsteady 3D flow simulations in cranial arterial tree
Grinberg, Leopold; Anor, Tomer; Madsen, Joseph; Karniadakis, George
2008-11-01
High resolution unsteady 3D flow simulations in major cranial arteries have been performed. Two cases were considered: 1) a healthy volunteer with a complete Circle of Willis (CoW); and 2) a patient with hydrocephalus and an incomplete CoW. Computation was performed on 3344 processors of the new half petaflop supercomputer in TACC. Two new numerical approaches were developed and implemented: 1) a new two-level domain decomposition method, which couples continuous and discontinuous Galerkin discretization of the computational domain; and 2) a new type of outflow boundary conditions, which imposes, in an accurate and computationally efficient manner, clinically measured flow rates. In the first simulation, a geometric model of 65 cranial arteries was reconstructed. Our simulation reveals a high degree of asymmetry in the flow at the left and right parts of the CoW and the presence of swirling flow in most of the CoW arteries. In the second simulation, one of the main findings was a high pressure drop at the right anterior communicating artery (PCA). Due to the incompleteness of the CoW and the pressure drop at the PCA, the right internal carotid artery supplies blood to most regions of the brain.
Energy Technology Data Exchange (ETDEWEB)
Seidel, Tobias; Vallee, Christophe; Lucas, Dirk; Beyer, Matthias; Deendarlianto
2011-09-15
In order to investigate the two-phase flow behaviour in a complex reactor-typical geometry and to supply suitable data for CFD code validation, a model of the hot leg of a pressurised water reactor was built at FZD. The hot leg model is operated in the pressure chamber of the TOPFLOW test facility, which is used to perform high-pressure experiments under pressure equilibrium with the inside atmosphere of the chamber. This technique makes it possible to visualise the two-phase flow through large windows, also at reactor-typical pressure levels. In order to optimise the optical observation possibilities, the test section was designed with a rectangular cross-section. Experiments were performed with air and water at 1.5 and 3.0 bar at room temperature as well as with steam and water at 15, 30 and 50 bar and the corresponding saturation temperature (i.e. up to 264 C). The total of 194 runs are divided into 4 types of experiments covering stationary co-current flow, counter-current flow, flow without water circulation and transient counter-current flow limitation (CCFL) experiments. This report provides a detailed documentation of the experiments including information on the experimental setup, experimental procedure, test matrix and on the calibration of the measuring devices. The available data is described and data sheets were arranged for each experiment in order to give an overview of the most important parameters. For the cocurrent flow experiments, water level histograms were arranged and used to characterise the flow in the hot leg. In fact, the form of the probability distribution was found to be sensitive to the boundary conditions and, therefore, is useful for the CFD comparison. Furthermore, the flooding characteristics of the hot leg model plotted in terms of the classical Wallis parameter or Kutateladze number were found to fail to properly correlate the data of the air/water and steam/water series. Therefore, a modified Wallis parameter is proposed, which
International Nuclear Information System (INIS)
Seidel, Tobias; Vallee, Christophe; Lucas, Dirk; Beyer, Matthias; Deendarlianto
2011-09-01
In order to investigate the two-phase flow behaviour in a complex reactor-typical geometry and to supply suitable data for CFD code validation, a model of the hot leg of a pressurised water reactor was built at FZD. The hot leg model is operated in the pressure chamber of the TOPFLOW test facility, which is used to perform high-pressure experiments under pressure equilibrium with the inside atmosphere of the chamber. This technique makes it possible to visualise the two-phase flow through large windows, also at reactor-typical pressure levels. In order to optimise the optical observation possibilities, the test section was designed with a rectangular cross-section. Experiments were performed with air and water at 1.5 and 3.0 bar at room temperature as well as with steam and water at 15, 30 and 50 bar and the corresponding saturation temperature (i.e. up to 264 C). The total of 194 runs are divided into 4 types of experiments covering stationary co-current flow, counter-current flow, flow without water circulation and transient counter-current flow limitation (CCFL) experiments. This report provides a detailed documentation of the experiments including information on the experimental setup, experimental procedure, test matrix and on the calibration of the measuring devices. The available data is described and data sheets were arranged for each experiment in order to give an overview of the most important parameters. For the cocurrent flow experiments, water level histograms were arranged and used to characterise the flow in the hot leg. In fact, the form of the probability distribution was found to be sensitive to the boundary conditions and, therefore, is useful for the CFD comparison. Furthermore, the flooding characteristics of the hot leg model plotted in terms of the classical Wallis parameter or Kutateladze number were found to fail to properly correlate the data of the air/water and steam/water series. Therefore, a modified Wallis parameter is proposed, which
NUMERICAL SIMULATION AND MODELING OF UNSTEADY FLOW AROUND AN AIRFOIL. (AERODYNAMIC FORM
Directory of Open Access Journals (Sweden)
M. Y. Habib
2015-07-01
Full Text Available During this work, we simulated an unsteady flow around an airfoil type NACA0012 using the Fluent software. The objective is to control the code on the one hand and on the other hand the simulation of unsteady flows. By simulating an unsteady flow Reynolds number (Re = 6.85 * 106 and Mach number (M = 0.3, we have the flowing with a grid (mesh adequate numerical results and experimental data are in good agreement. To represent the results of the simulation we have validated by comparing the values of aerodynamic coefficients with those of experimental data.
Unsteady characteristics of a slat-cove flow field
Pascioni, Kyle A.; Cattafesta, Louis N.
2018-03-01
The leading-edge slat of a multielement wing is a significant contributor to the acoustic signature of an aircraft during the approach phase of the flight path. An experimental study of the two-dimensional 30P30N geometry is undertaken to further understand the flow physics and specific noise source mechanisms. The mean statistics from particle image velocimetry (PIV) shows the differences in the flow field with angle of attack, including the interaction between the cove and trailing-edge flow. Phase-locked PIV successfully links narrow-band peaks found in the surface pressure spectrum to shear layer instabilities and also reveals that a bulk cove oscillation at a Strouhal number based on a slat chord of 0.15 exists, indicative of shear layer flapping. Unsteady surface pressure measurements are documented and used to estimate spanwise coherence length scales. A narrow-band frequency prediction scheme is also tested and found to agree well with the data. Furthermore, higher-order spectral analysis suggests that nonlinear effects cause additional peaks to arise in the power spectrum, particularly at low angles of attack.
International Nuclear Information System (INIS)
Gueguen, J.
2013-01-01
This study is a contribution to the modelling of multidimensional high pressure boiling flows relative to PWR. Numerical simulation of such two-phase flows is considered to be an interesting way for the DNB understanding. The first part of this study exposes a two-dimensional steady state two-phase flows model able to predict velocity and temperature profiles in tube. The mixture balanced equations are used with the eddy diffusivity concept to close the turbulent transport terms. The second part is devoted to the development of the model in the general two dimensional case. Contrary to the steady state model, this model is independent of experimental data and implies the use of an original local homogeneous relaxation model (HRM). The results obtained from the comparison with the data bank DEBORA reveals that in a mixture approach two sub models are sufficient to obtain a physical good description of turbulent boiling flows. Some limitations appear at conditions close to DNB conditions. The turbulent closures and the relaxation time in the HRM model have been clearly identified as the most important and sensitive parameters in the model. (author) [fr
Unsteady Flows Control Hydrologic Turnover Rates in Antarctic Hyporheic Zones
Wlostowski, A. N.; Gooseff, M. N.; McKnight, D. M.; Lyons, W. B.; Saelens, E.
2016-12-01
Hydrologic turnover of the hyporheic zone (HZ) is the process of HZ flowpaths receiving water and solutes from the stream channel while simultaneously contributing water and solutes from the HZ back to the stream channel. The influence of hydrologic turnover on HZ solute storage depends on the relative magnitude of hyporheic exchange rates (i.e. physical transport) and biogeochemical reaction rates. Because both exchange rates and reaction rates are unsteady in natural systems, the availability of solutes in the HZ is controlled by the legacy of hydraulic and biological conditions. In this study, we quantify the influence of unsteady flows on hydrologic turnover of the HZ. We study a glacial melt stream in the McMurdo Dry Valleys of Antarctica (MDVs). The MDVs provide an ideal setting for investigating hydrologic and chemical storage characteristics of HZs, because nearly all streamflow is generated from glacier melt and the HZ is vertically bounded by continuous permafrost. A dense network of shallow groundwater wells and piezometers was installed along a 60-meter reach of Von Guerard Stream. 12 days of continuous water level data in each well was used to compute the magnitude and direction of 2D hydraulic gradients between the stream channel and lateral hyporheic aquifer. Piezometers were sampled daily for stable isotope abundances. The direction and magnitude of the cross-valley (CV), perpendicular to the thalweg, component of hydraulic gradients is sensitive to daily flood events and exhibits significant spatial heterogeneity. CV gradients are consistently oriented from the hyporheic aquifer towards the stream channel on 2 sections of the study reach, whereas CV gradients are consistently oriented from the stream channel towards the hyporheic aquifer on 1 section. Three sections show diel changes in orientation of CV gradients, coincident with the passage of daily flood events. During a 4-day period of low flows, the HZ is isotopically distinct from the stream
Numerical study of unsteady viscous flow past oscillating airfoil
Energy Technology Data Exchange (ETDEWEB)
Jin Yan; Yuan Xin [Tsinghua Univ., Dept. of Thermal Engineering, Beijing (China)
2001-07-01
Accurate simulation of the dynamic stall of an oscillating airfoil is of major importance to wing and wind turbine blade design. However, dynamic stall is complicated and influenced by many factors, such as geometry shape of the airfoil, reduced frequency, etc. The difficulties of simulation are both mathematical (numerical method) and physical (turbulence model). The present paper has introduced a new numerical method (new LU-type scheme and fourth-order higher resolution MUSCL TVD scheme) and q-{omega} turbulence modelling to calculate the unsteady flowfields of an oscillating NACA0015 airfoil. The test targets include attached flow, light-stall and deep-stall of the airfoil. The calculated results for attached flow and light-stall are in good agreement with those of experiments. The calculated results for deep-stall also show improvement, especially during the downstroke of the oscillation. However, there is still a significant difference between the results of calculation and experiment in the hysteresis curves of the drag coefficient. One reason is that the q-{omega} turbulence model still has limitations. Another is that the drag coefficient is difficult to measure and the experiments are not reliable. (Author)
Validation of a CFD code for Unsteady Flows with cyclic boundary Conditions
International Nuclear Information System (INIS)
Kim, Jong-Tae; Kim, Sang-Baik; Lee, Won-Jae
2006-01-01
Currently Lilac code is under development to analyze thermo-hydraulics of a high-temperature gas-cooled reactor (GCR). Interesting thermo-hydraulic phenomena in a nuclear reactor are usually unsteady and turbulent. The analysis of the unsteady flows by using a three dimension CFD code is time-consuming if the flow domain is very large. Hopefully, flow domains commonly encountered in the nuclear thermo-hydraulics is periodic. So it is better to use the geometrical characteristics in order to reduce the computational resources. To get the benefits from reducing the computation domains especially for the calculations of unsteady flows, the cyclic boundary conditions are implemented in the parallelized CFD code LILAC. In this study, the parallelized cyclic boundary conditions are validated by solving unsteady laminar and turbulent flows past a circular cylinder
Unsteady airfoil flows with application to aeroelastic stability
Energy Technology Data Exchange (ETDEWEB)
Johansen, Jeppe
1999-09-01
The present report describes numerical investigation of two-dimensional unsteady airfoil flows with application to aeroelastic stability. The report is divided in two parts. Part A describes the purely aerodynamic part, while Part B includes the aeroelastic part. In Part A a transition prediction algorithm based on a simplified version of the e{sup n} method is proposed. Laminar Boundary Layer instability data are stored in a database from which stability characteristics can be extracted by interpolation. Input to the database are laminar integral boundary layer parameters. These are computed from an integral boundary layer formulation coupled to a Navier-Stokes flow solver. Five different airfoils are considered at fixed angle of attack, and the flow is computed assuming both fully turbulent and transitional flow and compared with experimental data. Results indicate that using a transition model the drag prediction is improved considerably. Also the lift is slightly improved. At high angles of attack transition will affect leading edge separation which again will affect the overall vortex shedding. If the transition point is not properly predicted this will affect the whole hysteresis curve. The transition model developed in the present work showed more stable predictions compared to the empirical transition model. In Part B a simple three degrees-of-freedom (DOF) structural dynamics model is developed and coupled to the aerodynamics models from Part A. A 2nd order accurate time integration scheme is used to solve the equations of motion. Two airfoils are investigated. The aeroelastic models predict stable conditions well at low angle of attack. But at high angles of attack, and where unstable behaviour is expected, only the Navier-Stokes solver predict correct aeroelastic response. The semi-empirical dynamic stall model does not predict vortex shedding and moment correctly leading to an erroneous aerodynamic damping. (au) 5 tabs.; 55 ills., 52 refs.
National Research Council Canada - National Science Library
Barakos, G
1998-01-01
The numerical simulation of unsteady separated turbulent flows around moving lifting surfaces is fueled by the industrial need to analyse and understand flow phenomena associated with the behaviour...
Q-factor of coolant flow in the primary circuit of NPP with pressurised water reactors
International Nuclear Information System (INIS)
Proskuryakov, K.N.; Belikov, S.O.; Novikov, K.S.
2011-01-01
Systems of preoperational vibration dynamic monitoring in of WWER are presented. The results of measurements during commission of NPP with WWER are presented. The paper provides the result of the research, that estimation of coolant fluctuations caused by pulse perturbation of pressure in the primary circuit NPP. It is shown that results could be received at known value of a Q - factor of acoustical oscillatory system only. The research demonstrates the results of dependence of the sound speed from the mass steam content in the coolant flow thru reactor core. The worked out results can be used for identification of the reasons of abnormal growth of level of vibrations of fuel assembly, fuel rod, equipment and internals, and for forecasting the operation conditions which provide of vibration - acoustical resonances in the primary loop equipment. (author)
Modeling of Unsteady Flow through the Canals by Semiexact Method
Directory of Open Access Journals (Sweden)
Farshad Ehsani
2014-01-01
Full Text Available The study of free-surface and pressurized water flows in channels has many interesting application, one of the most important being the modeling of the phenomena in the area of natural water systems (rivers, estuaries as well as in that of man-made systems (canals, pipes. For the development of major river engineering projects, such as flood prevention and flood control, there is an essential need to have an instrument that be able to model and predict the consequences of any possible phenomenon on the environment and in particular the new hydraulic characteristics of the system. The basic equations expressing hydraulic principles were formulated in the 19th century by Barre de Saint Venant and Valentin Joseph Boussinesq. The original hydraulic model of the Saint Venant equations is written in the form of a system of two partial differential equations and it is derived under the assumption that the flow is one-dimensional, the cross-sectional velocity is uniform, the streamline curvature is small and the pressure distribution is hydrostatic. The St. Venant equations must be solved with continuity equation at the same time. Until now no analytical solution for Saint Venant equations is presented. In this paper the Saint Venant equations and continuity equation are solved with homotopy perturbation method (HPM and comparison by explicit forward finite difference method (FDM. For decreasing the present error between HPM and FDM, the st.venant equations and continuity equation are solved by HAM. The homotopy analysis method (HAM contains the auxiliary parameter ħ that allows us to adjust and control the convergence region of solution series. The study has highlighted the efficiency and capability of HAM in solving Saint Venant equations and modeling of unsteady flow through the rectangular canal that is the goal of this paper and other kinds of canals.
Scott, James R.; Atassi, Hafiz M.
1990-01-01
A linearized unsteady aerodynamic analysis is presented for unsteady, subsonic vortical flows around lifting airfoils. The analysis fully accounts for the distortion effects of the nonuniform mean flow on the imposed vortical disturbances. A frequency domain numerical scheme which implements this linearized approach is described, and numerical results are presented for a large variety of flow configurations. The results demonstrate the effects of airfoil thickness, angle of attack, camber, and Mach number on the unsteady lift and moment of airfoils subjected to periodic vortical gusts. The results show that mean flow distortion can have a very strong effect on the airfoil unsteady response, and that the effect depends strongly upon the reduced frequency, Mach number, and gust wave numbers.
Soret and Hall effects on unsteady MHD free convection flow of ...
African Journals Online (AJOL)
International Journal of Engineering, Science and Technology ... effects on unsteady MHD free convection flow of radiating and chemically reactive fluid ... Expressions for shear stress, rate of heat transfer and rate of mass transfer at the plate ...
A High Order Accuracy Computational Tool for Unsteady Turbulent Flows and Acoustics, Phase I
National Aeronautics and Space Administration — The main objective of this research effort is to develop a higher order unsteady turbulent flow solver based on the FDV method, and to exploit its attributes of...
Rule-Based Multidisciplinary Tool for Unsteady Reacting Real-Fluid Flows, Phase I
National Aeronautics and Space Administration — A design and analysis computational tool is proposed for simulating unsteady reacting flows in combustor devices used in reusable launch vehicles. Key aspects...
Unsteady flow phenomena in human undulatory swimming: a numerical approach.
Pacholak, Steffen; Hochstein, Stefan; Rudert, Alexander; Brücker, Christoph
2014-06-01
The undulatory underwater sequence is one of the most important phases in competitive swimming. An understanding of the recurrent vortex dynamics around the human body and their generation could therefore be used to improve swimming techniques. In order to produce a dynamic model, we applied human joint kinematics to three-dimensional (3D) body scans of a female swimmer. The flow around this dynamic model was then calculated using computational fluid dynamics with the aid of moving 3D meshes. Evaluation of the numerical results delivered by the various motion cycles identified characteristic vortex structures for each of the cycles, which exhibited increasing intensity and drag influence. At maximum thrust, drag forces appear to be 12 times higher than those of a passive gliding swimmer. As far as we know, this is the first disclosure of vortex rings merging into vortex tubes in the wake after vortex recapturing. All unsteady structures were visualized using a modified Q-criterion also incorporated into our methods. At the very least, our approach is likely to be suited to further studies examining swimmers engaging in undulatory swimming during training or competition.
Numerical Simulation of Unsteady Large Scale Separated Flow around Oscillating Airfoil
Isogai, Koji; 磯貝, 紘二
1991-01-01
Numerical simulations of dynamic stall phenomenon of NACA0012 airfoil oscillating in pitch near static stalling angle are performed by using the compressible Navier-Stokes equations. In the present computations, a TVD scheme and an algebraic turbulence model are employed for the simulations of the unsteady separated flows at Reynolds number of 1.1x105. The hysteresis loops of the unsteady pitching moment during dynamic stall are compared with the existing experimental data. The flow pattern a...
Energy Technology Data Exchange (ETDEWEB)
Wu, Denghao; Ren, Yun; Mou, Jiegang; Gu, Yunqing [Zhejiang University of Technology, Hangzhou (China)
2017-05-15
Circulator pumps have wide engineering applications but the acoustics, vibration and unsteady flow structures of the circulator pump are still not fully understood. We investigated the noise and vibration characteristics and unsteady flow structures in a circulator pump at different flow rates. Three-dimensional, unsteady RANS equations were solved on high-quality structured meshes with SST k-ω turbulence model numerically. Measurements were made in a semi-anechoic chamber to get an overview of noise and vibration level of a pump at different flow rates. The 1/3 octave-band filter technique was applied to obtain the explicit frequency spectra of sound, pressure fluctuations and vibration signals and their principal frequencies were identified successfully. The air-borne noise level of the designed condition is lower than that of the off-design conditions, and the highest sound pressure level is found at part-load condition. The acoustic emission from the pump is mainly caused by unsteady flow structures and pressure fluctuations. In addition, both the link between air- borne noise and pressure fluctuation, and the correlation between vibration and unsteady hydrodynamic forces, were quantitatively examined and verified. This work offers good data to understand noise and vibration characteristics of circulator pumps and the relationships among the noise, vibration and unsteady flow structures.
International Nuclear Information System (INIS)
Shirani, E.; Zirak, S.
2001-01-01
Compressible flows for unsteady, inviscid and viscous cases have been studied. Important features of flows such as formation of shock waves across the flow in an unsteady flow as well as interaction of shock waves with boundary layers and their effects on the flow around the blades have been analyzed. Jameson control volume approach was used to spatially integrate the flow equations and the fourth order Runge-Kutta method was used for time integration. The obtained finite difference equations were used to simulate inviscid and viscous flows in V KI cascades and the effects of viscosity, angle of attack, bal de pitches and back pressure on the flow were obtained. It was shown that when the flow was assumed inviscid, the error on the distribution of pressure on the blades were about ten percent. Finally, unsteady flow were simulated and formation of shock waves and their motions were analyzed
Numerical Investigations of Unsteady Flow in a Centrifugal Pump with a Vaned Diffuser
Directory of Open Access Journals (Sweden)
Olivier Petit
2013-01-01
Full Text Available Computational fluid dynamics (CFD analyses were made to study the unsteady three-dimensional turbulence in the ERCOFTAC centrifugal pump test case. The simulations were carried out using the OpenFOAM Open Source CFD software. The test case consists of an unshrouded centrifugal impeller with seven blades and a radial vaned diffuser with 12 vanes. A large number of measurements are available in the radial gap between the impeller and the diffuse, making this case ideal for validating numerical methods. Results of steady and unsteady calculations of the flow in the pump are compared with the experimental ones, and four different turbulent models are analyzed. The steady simulation uses the frozen rotor concept, while the unsteady simulation uses a fully resolved sliding grid approach. The comparisons show that the unsteady numerical results accurately predict the unsteadiness of the flow, demonstrating the validity and applicability of that methodology for unsteady incompressible turbomachinery flow computations. The steady approach is less accurate, with an unphysical advection of the impeller wakes, but accurate enough for a crude approximation. The different turbulence models predict the flow at the same level of accuracy, with slightly different results.
Numerical investigation on vibration and noise induced by unsteady flow in an axial-flow pump
Energy Technology Data Exchange (ETDEWEB)
Chen, Eryun; Ma, Zui Ling; Yang, Ai Ling; Nan, Guo Fang [School of Energy and Power Engineering, University of Shanghai for Science and Technology, Shanghai (China); Zhao, Gai Ping [School of Medical Instruments and Food Engineering, University of Shanghai for Science and Technology, Shanghai (China); Li, Guo Ping [Shanghai Marine Equipment Research Institute, Shanghai (China)
2016-12-15
Full-scale structural vibration and noise induced by flow in an axial-flow pump was simulated by a hybrid numerical method. An unsteady flow field was solved by a large eddy simulation-based computational fluid dynamics commercial code, Fluent. An experimental validation on pressure fluctuations was performed to impose an appropriate vibration exciting source. The consistency between the computed results and experimental tests were interesting. The modes of the axial-flow pump were computed by the finite element method. After that, the pump vibration and sound field were solved using a coupled vibro-acoustic model. The numerical results indicated that the the blade-passing frequency was the dominant frequency of the vibration acceleration of the pump. This result was consistent with frequency spectral characteristics of unsteady pressure fluctuation. Finally, comparisons of the vibration acceleration between the computed results and the experimental test were conducted. These comparisons validated the computed results. This study shows that using the hybrid numerical method to evaluate the flow-induced vibration and noise generated in an axial-flow pump is feasible.
The flows structure in unsteady gas flow in pipes with different cross-sections
Plotnikov, Leonid; Nevolin, Alexandr; Nikolaev, Dmitrij
2017-10-01
The results of numerical simulation and experimental study of the structure of unsteady flows in pipes with different cross sections are presented in the article. It is shown that the unsteady gas flow in a circular pipe is axisymmetric without secondary currents. Steady vortex structures (secondary flows) are observed in pipes with cross sections in the form of a square and an equilateral triangle. It was found that these secondary flows have a significant impact on gas flows in pipes of complex configuration. On the basis of experimental researches it is established that the strong oscillatory phenomena exist in the inlet pipe of the piston engine arising after the closing of the intake valve. The placement of the profiled plots (with a cross section of a square or an equilateral triangle) in the intake pipe leads to the damping of the oscillatory phenomena and a more rapid stabilization of pulsating flow. This is due to the stabilizing effect of the vortex structures formed in the corners of this configuration.
The flows structure in unsteady gas flow in pipes with different cross-sections
Directory of Open Access Journals (Sweden)
Plotnikov Leonid
2017-01-01
Full Text Available The results of numerical simulation and experimental study of the structure of unsteady flows in pipes with different cross sections are presented in the article. It is shown that the unsteady gas flow in a circular pipe is axisymmetric without secondary currents. Steady vortex structures (secondary flows are observed in pipes with cross sections in the form of a square and an equilateral triangle. It was found that these secondary flows have a significant impact on gas flows in pipes of complex configuration. On the basis of experimental researches it is established that the strong oscillatory phenomena exist in the inlet pipe of the piston engine arising after the closing of the intake valve. The placement of the profiled plots (with a cross section of a square or an equilateral triangle in the intake pipe leads to the damping of the oscillatory phenomena and a more rapid stabilization of pulsating flow. This is due to the stabilizing effect of the vortex structures formed in the corners of this configuration.
Applications of Coupled Explicit–Implicit Solution of SWEs for Unsteady Flow in Yangtze River
Directory of Open Access Journals (Sweden)
Yufei Ding
2017-02-01
Full Text Available In engineering practice, the unsteady flows generated from the operation of hydropower station in the upstream region could significantly change the navigation system of waterways located in the middle-lower reaches of the river. In order to study the complex propagation, convergence and superposition characteristics of unsteady flows in a long channel with flow confluence, a numerical model based on the coupling of implicit and explicit solution algorithms of Shallow Water Equations (SWEs has been applied to two large rivers in the reach of Yangtze River, China, which covers the distance from Yibin to Chongqing located upstream side of the Three Gorges Dam. The accuracy of numerical model has been validated by both the steady and unsteady flows using the prototype hydrological data. It is found that the unsteady flows show much more complex water level and discharge behaviors than the steady ones. The studied unsteady flows arising from the water regulation of two upstream hydropower stations could influence the region as far as Zhutuo hydrologic station, which is close to the city of Chongqing. Meanwhile, the computed stage–discharge rating curves at all observation stations demonstrate multi-value loop patterns because of the presence of additional water surface gradient. The present numerical model proves to be robust for simulating complex flows in very long engineering rivers up to 400 km.
A novel method for unsteady flow field segmentation based on stochastic similarity of direction
Omata, Noriyasu; Shirayama, Susumu
2018-04-01
Recent developments in fluid dynamics research have opened up the possibility for the detailed quantitative understanding of unsteady flow fields. However, the visualization techniques currently in use generally provide only qualitative insights. A method for dividing the flow field into physically relevant regions of interest can help researchers quantify unsteady fluid behaviors. Most methods at present compare the trajectories of virtual Lagrangian particles. The time-invariant features of an unsteady flow are also frequently of interest, but the Lagrangian specification only reveals time-variant features. To address these challenges, we propose a novel method for the time-invariant spatial segmentation of an unsteady flow field. This segmentation method does not require Lagrangian particle tracking but instead quantitatively compares the stochastic models of the direction of the flow at each observed point. The proposed method is validated with several clustering tests for 3D flows past a sphere. Results show that the proposed method reveals the time-invariant, physically relevant structures of an unsteady flow.
International Nuclear Information System (INIS)
Huang, W D; Fan, H G; Chen, N X
2012-01-01
To study the interaction between the transient flow in pipe and the unsteady turbulent flow in turbine, a coupled model of the transient flow in the pipe and three-dimensional unsteady flow in the turbine is developed based on the method of characteristics and the fluid governing equation in the accelerated rotational relative coordinate. The load-rejection process under the closing of guide vanes of the hydraulic power plant is simulated by the coupled method, the traditional transient simulation method and traditional three-dimensional unsteady flow calculation method respectively and the results are compared. The pressure, unit flux and rotation speed calculated by three methods show a similar change trend. However, because the elastic water hammer in the pipe and the pressure fluctuation in the turbine have been considered in the coupled method, the increase of pressure at spiral inlet is higher and the pressure fluctuation in turbine is stronger.
Huang, W. D.; Fan, H. G.; Chen, N. X.
2012-11-01
To study the interaction between the transient flow in pipe and the unsteady turbulent flow in turbine, a coupled model of the transient flow in the pipe and three-dimensional unsteady flow in the turbine is developed based on the method of characteristics and the fluid governing equation in the accelerated rotational relative coordinate. The load-rejection process under the closing of guide vanes of the hydraulic power plant is simulated by the coupled method, the traditional transient simulation method and traditional three-dimensional unsteady flow calculation method respectively and the results are compared. The pressure, unit flux and rotation speed calculated by three methods show a similar change trend. However, because the elastic water hammer in the pipe and the pressure fluctuation in the turbine have been considered in the coupled method, the increase of pressure at spiral inlet is higher and the pressure fluctuation in turbine is stronger.
Heat transfer analysis for unsteady MHD flow past a non-isothermal stretching surface
International Nuclear Information System (INIS)
Mukhopadhyay, Swati
2011-01-01
Highlights: ► Unsteady boundary layer flow and heat transfer over a non-isothermal stretching sheet in a magnetic field are studied. ► Fluid velocity and temperature decrease for increasing unsteadiness parameter. ► Fluid velocity decreases but temperature increases with the increasing values of the Hartman number. ► The sheet temperature in respect of distance and time has analogous effects on the heat transfer. - Abstract: An analysis is made for the unsteady two-dimensional magneto-hydrodynamic flow of an incompressible viscous and electrically conducting fluid over a stretching surface having a variable and general form of surface temperature which removes the restrictions of the particular forms of prescribed surface temperature. Similarity solutions for the transformed governing equations are obtained. The transformed boundary layer equations are solved numerically for some values of the involved parameters, namely the unsteadiness parameter, magnetic parameter, the temperature exponent parameters. The features of the flow and heat transfer characteristics for different values of the governing parameters are analysed and discussed. It is found that the fluid velocity and temperature decrease for increasing unsteadiness parameter. Fluid velocity decreases with the increasing values of the Hartman number resulting an increase in the temperature field in steady as well in unsteady case. It is observed that the variation of the sheet temperature in respect of distance and time has analogous effects both on the free surface temperature and on the heat transfer rate (Nusselt number) at the sheet.
Matthews, Megan; Sponberg, Simon
2017-11-01
Birds, insects, and many animals use unsteady aerodynamic mechanisms to achieve stable hovering flight. Natural environments are often characterized by unsteady flows causing animals to dynamically respond to perturbations while performing complex tasks, such as foraging. Little is known about how unsteady flow around an animal interacts with already unsteady flow in the environment or how this impacts performance. We study how the environment impacts maneuverability to reveal any coupling between body dynamics and aerodynamics for hawkmoths, Manduca sexta,tracking a 3D-printed robotic flower in a wind tunnel. We also observe the leading-edge vortex (LEV), a known lift-generating mechanism for insect flight with smoke visualization. Moths in still and unsteady air exhibit near perfect tracking at low frequencies, but tracking in the flower wake results in larger overshoot at mid-range. Smoke visualization of the flower wake shows that the dominant vortex shedding corresponds to the same frequency band as the increased overshoot. Despite the large effect on flight dynamics, the LEV remains bound to the wing and thorax throughout the wingstroke. In general, unsteady wind seems to decrease maneuverability, but LEV stability seems decoupled from changes in flight dynamics.
Numerical simulation of unsteady free surface flow and dynamic performance for a Pelton turbine
International Nuclear Information System (INIS)
Xiao, Y X; Wang, Z W; Yan, Z G; Cui, T
2012-01-01
Different from the reaction turbines, the hydraulic performance of the Pelton turbine is dynamic due to the unsteady free surface flow in the rotating buckets in time and space. This paper aims to present the results of investigations conducted on the free surface flow in a Pelton turbine rotating buckets. The unsteady numerical simulations were performed with the CFX code by using the Realizable k-ε turbulence model coupling the two-phase flow volume of fluid method. The unsteady free surface flow patterns and torque varying with the bucket rotating were analysed. The predicted relative performance at five operating conditions was compared with the field test results. The study was also conducted the interactions between the bucket rear and the water jet.
Numerical simulation of unsteady free surface flow and dynamic performance for a Pelton turbine
Xiao, Y. X.; Cui, T.; Wang, Z. W.; Yan, Z. G.
2012-11-01
Different from the reaction turbines, the hydraulic performance of the Pelton turbine is dynamic due to the unsteady free surface flow in the rotating buckets in time and space. This paper aims to present the results of investigations conducted on the free surface flow in a Pelton turbine rotating buckets. The unsteady numerical simulations were performed with the CFX code by using the Realizable k-ε turbulence model coupling the two-phase flow volume of fluid method. The unsteady free surface flow patterns and torque varying with the bucket rotating were analysed. The predicted relative performance at five operating conditions was compared with the field test results. The study was also conducted the interactions between the bucket rear and the water jet.
Characterization of the unsteady flow in the nacelle region of a modern wind turbine
DEFF Research Database (Denmark)
Zahle, Frederik; Sørensen, Niels N.
2011-01-01
A three-dimensional Navier–Stokes solver has been used to investigate the flow in the nacelle region of a wind turbine where anemometers are typically placed to measure the flow speed and the turbine yaw angle. A 500 kW turbine was modelled with rotor and nacelle geometry in order to capture...... the complex separated flow in the blade root region of the rotor. A number of steady state and unsteady simulations were carried out for wind speeds ranging from 6 m s−1 to 16 m s−1 as well as two yaw and tilt angles. The flow in the nacelle region was found to be highly unsteady, dominated by unsteady vortex...... anemometry showed significant dependence on both yaw and tilt angles with yaw errors of up to 10 degrees when operating in a tilted inflow. Copyright © 2010 John Wiley & Sons, Ltd....
Topology optimization of unsteady flow problems using the lattice Boltzmann method
DEFF Research Database (Denmark)
Nørgaard, Sebastian Arlund; Sigmund, Ole; Lazarov, Boyan Stefanov
2016-01-01
This article demonstrates and discusses topology optimization for unsteady incompressible fluid flows. The fluid flows are simulated using the lattice Boltzmann method, and a partial bounceback model is implemented to model the transition between fluid and solid phases in the optimization problems...
Unsteady flow damping force prediction of MR dampers subjected to sinusoidal loading
Yu, M.; Wang, S. Q.; Fu, J.; Peng, Y. X.
2013-02-01
So far quasi-steady models are usually used to design magnetorheological (MR) dampers, but these models are not sufficient to describe the MR damper behavior under unsteady dynamic loading, for fluid inertia is neglected in quasi-steady models, which will bring more error between computer simulation and experimental results. Under unsteady flow model, the fluid inertia terms will bring error calculated upto 10%, so it is necessary to be considered in the governing equation. In this paper, force-stroke behavior of MR damper with flow mode due to sinusoidal loading excitation is mainly investigated, to simplify the analysis, the one-dimensional axisymmetric annular duct geometry of MR dampers is approximated as a rectangular duct. The rectangular duct can be divided into 3 regions for the velocity profile of the incompressible MR fluid flow, in each region, a partial differential equation is composed of by Navier-Stokes equations, boundary conditions and initial conditions to determine the velocity solution. In addition, in this work, not only Bingham plastic model but the Herschel—Bulkley model is adopted to analyze the MR damper performance. The damping force resulting from the pressure drop of unsteady MR dampers can be obtained and used to design or size MR dampers. Compared with the quasi-steady flow damping force, the damping force of unsteady MR dampers is more close to practice, particularly for the high-speed unsteady movement of MR dampers.
Unsteady flow damping force prediction of MR dampers subjected to sinusoidal loading
International Nuclear Information System (INIS)
Yu, M; Fu, J; Wang, S Q; Peng, Y X
2013-01-01
So far quasi-steady models are usually used to design magnetorheological (MR) dampers, but these models are not sufficient to describe the MR damper behavior under unsteady dynamic loading, for fluid inertia is neglected in quasi-steady models, which will bring more error between computer simulation and experimental results. Under unsteady flow model, the fluid inertia terms will bring error calculated upto 10%, so it is necessary to be considered in the governing equation. In this paper, force-stroke behavior of MR damper with flow mode due to sinusoidal loading excitation is mainly investigated, to simplify the analysis, the one-dimensional axisymmetric annular duct geometry of MR dampers is approximated as a rectangular duct. The rectangular duct can be divided into 3 regions for the velocity profile of the incompressible MR fluid flow, in each region, a partial differential equation is composed of by Navier-Stokes equations, boundary conditions and initial conditions to determine the velocity solution. In addition, in this work, not only Bingham plastic model but the Herschel—Bulkley model is adopted to analyze the MR damper performance. The damping force resulting from the pressure drop of unsteady MR dampers can be obtained and used to design or size MR dampers. Compared with the quasi-steady flow damping force, the damping force of unsteady MR dampers is more close to practice, particularly for the high-speed unsteady movement of MR dampers.
An improved water cooled nuclear reactor and pressuriser assembly
International Nuclear Information System (INIS)
Gardner, F.J.; Strong, R.
1991-01-01
A water cooled nuclear reactor is described which comprises a reactor core, a primary water coolant circuit and a pressuriser arranged as an integral unit in a pressure vessel. The pressure vessel is divided into an upper and a lower chamber by a casing. The reactor core and primary water coolant circuit are arranged in the lower chamber and the pressuriser is arranged in the upper chamber. A plurality of spray pipes interconnect a steam space of the pressuriser with the downcomer of the primary water coolant circuit below a heat exchanger. A plurality of surge ports interconnect a water space of the pressuriser with the primary water coolant circuit. The surge ports have hydraulic diodes so that there is a low flow resistance for water from the water space of the pressuriser to the primary water coolant circuit and high flow resistance in the opposite direction. The spray pipes provide a desuperheating spray of cooled water into the pressuriser during positive volume surges of the primary water coolant. The pressuriser arrangement may also be applied to integral water cooled reactors with separate pressurisers and to dispersed pressurised water reactors. The surge ports also allow water to flow by gravity to the core in an emergency. (author)
Installations having pressurised fluid circuits
International Nuclear Information System (INIS)
Rigg, S.; Grant, J.
1977-01-01
Reference is made to nuclear installations having pressurised coolant flow circuits. Breaches in such circuits may quickly result in much damage to the plant. Devices such as non-return valves, orifice plates, and automatically operated shut-off valves have been provided to prevent or reduce fluid flow through a breached pipe line, but such devices have several disadvantages; they may present large restrictions to normal flow of coolant, and may depend on the operation of ancillary equipment, with consequent delay in bringing them into operation in an emergency. Other expedients that have been adopted to prevent or reduce reverse flow through an upstream breach comprise various forms of hydraulic counter flow brakes. The arrangement described has at least one variable fluid brake comprising a fluidic device connected into a duct in the pressurised circuit, the device having an inlet, an outlet, a vortex chamber between the inlet and outlet, a control jet for introducing fluid into the vortex chamber, connections communicating the inlet and the outlet into one part of the circuit and the control jet into another region at a complementary pressure so that, in the event of a breach in the circuit in one region, fluid passes from the other region to enter the vortex chamber to stimulate pressure to create a flow restricting vortex in the chamber that reduces flow through the breach. The system finds particular application to stream generating pressure tube reactors, such as the steam generating heavy water reactor at UKAEA, Winfrith. (U.K.)
Examination of forced unsteady separated flow fields on a rotating wind turbine blade
Energy Technology Data Exchange (ETDEWEB)
Huyer, S [Univ. of Colorado, Boulder, CO (US)
1993-04-01
The wind turbine industry faces many problems regarding the construction of efficient and predictable wind turbine machines. Steady state, two-dimensional wind tunnel data are generally used to predict aerodynamic loads on wind turbine blades. Preliminary experimental evidence indicates that some of the underlying fluid dynamic phenomena could be attributed to dynamic stall, or more specifically to generation of forced unsteady separated flow fields. A collaborative research effort between the University of Colorado and the National Renewable Energy Laboratory was conducted to systematically categorize the local and global effects of three- dimensional forced unsteady flow fields.
Experimental Study of Unsteady Flow Separation in a Laminar Boundary Layer
Bonacci, Andrew; Lang, Amy; Wahidi, Redha; Santos, Leonardo
2017-11-01
Flow separation, caused by an adverse pressure gradient, is a major problem in many applications. Reversing flow near the wall is the first sign of incipient separation and can bristle shark scales which may be linked to a passive, flow actuated separation control mechanism. An investigation of how this backflow forms and how it interacts with shark skin is of interest due to the fact that this could be used as a bioinspired means of initiating flow control. A water tunnel experiment aims to study unsteady separation with a focus on the reversing flow development near the wall within a flat plate laminar boundary layer (Re on order of 105) as an increasing adverse pressure gradient is induced by a rotating cylinder. Unsteady reversing flow development is documented using DPIV. Funding was provided by the National Science Foundation under the Research Experience for Undergraduates (REU) program (EEC 1659710) and the Army Research Office.
Directory of Open Access Journals (Sweden)
M. Younsi
2007-01-01
Full Text Available The aim of this study is to evaluate the influence of design parameters on the unsteady flow in a forward-curved centrifugal fan and their impact on the aeroacoustic behavior. To do so, numerical and experimental studies have been carried out on four centrifugal impellers designed with various geometrical parameters. The same volute casing has been used to study these impellers. The effects on the unsteady flow behavior related to irregular blade spacing, blade count and radial distance between the impeller periphery and the volute tongue have been studied. The numerical simulations of the unsteady flow have been carried out using computational fluid dynamics (CFD tools based on the unsteady Reynolds averaged Navier Stokes (URANS approach. The study is focused on the unsteadiness induced by the aerodynamic interaction between the volute and the rotating impeller blades. In order to predict the acoustic pressure at far field, the unsteady flow variables provided by the CFD calculations have been used as inputs in the Ffowcs Williams-Hawkings equations (FW-H. The experimental part of this work concerns measurement of aerodynamic performance of the fans using a test bench built according to ISO 5801 (1997 standard. In addition to this, pressure microphones have been flush mounted on the volute tongue surface in order to measure the wall pressure fluctuations. The sound pressure level (SPL measurements have been carried out in an anechoic room in order to remove undesired noise reflections. Finally, the numerical results have been compared with the experimental measurements and a correlation between the wall pressure fluctuations and the far field noise signals has been found.
computational study of Couette flow between parallel plates for steady and unsteady cases
International Nuclear Information System (INIS)
Rihan, Y.
2008-01-01
Couette flow between parallel plates is a classical problem that has important applications in various industrial processing. In this investigation an analytical solution was obtained to predict the steady and unsteady Couette flow between parallel plates. One of the plates was stationary and the other plate moved with constant velocity. The governing partial differential equations were solved numerically using Crank-Nicolson implicit method to represent the flow behavior of the fluid
Exact solution for flow in a porous pipe with unsteady wall suction and/or injection
Tsangaris, S.; Kondaxakis, D.; Vlachakis, N. W.
2007-10-01
This paper presents an extension of the exact solution of the steady laminar axisymmetric flow in a straight pipe of circular cross section with porous wall, given by R.M. Terrill, to the case of unsteady wall injection and/or suction. The cases of the pulsating parabolic profile and of the developed pulsating flow are investigated as examples. The pulsating flow in porous ducts has many applications in biomedical engineering and in other engineering areas.
Flow and axial dispersion in a sinusoidal-walled tube: Effects of inertial and unsteady flows
Richmond, Marshall C.; Perkins, William A.; Scheibe, Timothy D.; Lambert, Adam; Wood, Brian D.
2013-12-01
In this work, we consider a sinusoidal-walled tube (a three-dimensional tube with sinusoidally-varying diameter) as a simplified conceptualization of flow in porous media. Direct numerical simulation using computational fluid dynamics (CFD) methods was used to compute velocity fields by solving the Navier-Stokes equations, and also to numerically solve the volume averaging closure problem, for a range of Reynolds numbers (Re) spanning the low-Re to inertial flow regimes, including one simulation at Re=449 for which unsteady flow was observed. The longitudinal dispersion observed for the flow was computed using a random walk particle tracking method, and this was compared to the longitudinal dispersion predicted from a volume-averaged macroscopic mass balance using the method of volume averaging; the results of the two methods were consistent. Our results are compared to experimental measurements of dispersion in porous media and to previous theoretical results for both the low-Re, Stokes flow regime and for values of Re representing the steady inertial regime. In the steady inertial regime, a power-law increase in the effective longitudinal dispersion (DL) with Re was found, and this is consistent with previous results. This rapid rate of increase is caused by trapping of solute in expansions due to flow separation (eddies). One unsteady (but non-turbulent) flow case (Re=449) was also examined. For this case, the rate of increase of DL with Re was smaller than that observed at lower Re. Velocity fluctuations in this regime lead to increased rates of solute mass transfer between the core flow and separated flow regions, thus diminishing the amount of tailing caused by solute trapping in eddies and thereby reducing longitudinal dispersion. The observed tailing was further explored through analysis of concentration skewness (third moment) and its assymptotic convergence to conventional advection-dispersion behavior (skewness = 0). The method of volume averaging was
The Chimera Method of Simulation for Unsteady Three-Dimensional Viscous Flow
Meakin, Robert L.
1996-01-01
The Chimera overset grid method is reviewed and discussed in the context of a method of solution and analysis of unsteady three-dimensional viscous flows. The state of maturity of the various pieces of support software required to use the approach is discussed. A variety of recent applications of the method is presented. Current limitations of the approach are defined.
Numerical simulation of unsteady compressible low Mach number flow in a channel
Czech Academy of Sciences Publication Activity Database
Punčochářová-Pořízková, P.; Kozel, Karel; Horáček, Jaromír; Fürst, J.
2010-01-01
Roč. 17, č. 2 (2010), s. 83-97 ISSN 1802-1484 R&D Projects: GA MŠk OC09019 Institutional research plan: CEZ:AV0Z20760514 Keywords : CFD * finite volume method * unsteady flow * low Mach number Subject RIV: BI - Acoustics
Unsteady free convection MHD flow between two heated vertical parallel conducting plates
International Nuclear Information System (INIS)
Sanyal, D.C.; Adhikari, A.
2006-01-01
Unsteady free convection flow of a viscous incompressible electrically conducting fluid between two heated conducting vertical parallel plates subjected to a uniform transverse magnetic field is considered. The approximate analytical solutions for velocity, induced field and temperature distribution are obtained for small and large values of magnetic Reynolds number. The problem is also extended to thermometric case. (author)
A Note on Unsteady Temperature Equation For Gravity Flow of A ...
African Journals Online (AJOL)
We present an analytical study of unsteady temperature energy equation for gravity of a fluid with non – Newtonian behaviour through a porous medium. For the case of radial axisymmetric flow, the governing partial differential equation is transformed into an ordinary differential equation through similarity variables.
Analytical Solution of Unsteady Gravity Flows of A Power-Law Fluid ...
African Journals Online (AJOL)
We present an analytical study of unsteady non-linear rheological effects of a power-law fluid under gravity. The fluid flows through a porous medium. The governing equations are derived and similarity solutions are determined. The results show the existence of traveling waves. It is assumed that the viscosity is temperature ...
Asymptotic expansion of unsteady gravity flow of a power-law fluid ...
African Journals Online (AJOL)
We present a paper on the asymptotic expansion of unsteady non-linear rheological effects of a power-law fluid under gravity. The fluid flows through a porous medium. The asymptotic expansion is employed to obtain solution of the nonlinear problem. The results show the existence of traveling waves. It is assumed that the ...
Numerical simulation of 3D unsteady flow in a rotating pump by dynamic mesh technique
International Nuclear Information System (INIS)
Huang, S; Guo, J; Yang, F X
2013-01-01
In this paper, the numerical simulation of unsteady flow for three kinds of typical rotating pumps, roots blower, roto-jet pump and centrifugal pump, were performed using the three-dimensional Dynamic Mesh technique. In the unsteady simulation, all the computational domains, as stationary, were set in one inertial reference frame. The motions of the solid boundaries were defined by the Profile file in FLUENT commercial code, in which the rotational orientation and speed of the rotors were specified. Three methods (Spring-based Smoothing, Dynamic Layering and Local Re-meshing) were used to achieve mesh deformation and re-meshing. The unsteady solutions of flow field and pressure distribution were solved. After a start-up stage, the flow parameters exhibit time-periodic behaviour corresponding to blade passing frequency of rotor. This work shows that Dynamic Mesh technique could achieve numerical simulation of three-dimensional unsteady flow field in various kinds of rotating pumps and have a strong versatility and broad application prospects
Formation of coherent structures in a class of realistic 3D unsteady flows
Speetjens, M.F.M.; Clercx, H.J.H.; Klapp, J.; Medina, A.; Cros, A.; Vargas, C.
2013-01-01
The formation of coherent structures in three-dimensional (3D) unsteady laminar flows in a cylindrical cavity is reviewed. The discussion concentrates on two main topics: the role of symmetries and fluid inertia in the formation of coherent structures and the ramifications for the Lagrangian
Effects of Unsteady Flow Past An Infinite Vertical Plate With Variable ...
African Journals Online (AJOL)
The effects of unsteady flow past an infinite vertical plate with variable temperature and constant mass flux are investigated. Laplace transform technique is used to obtain velocity and concentration fields. The computation of the results indicates that the velocity profiles increase with increase in Grashof numbers, mass ...
High Fidelity Simulations for Unsteady Flow Through the Orbiter LH2 Feedline Flowliner
Kiris, Cetin C.; Kwak, Dochan; Chan, William; Housman, Jeffrey
2005-01-01
High fidelity computations were carried out to analyze the orbiter M2 feedline flowliner. Various computational models were used to characterize the unsteady flow features in the turbopump, including the orbiter Low-Pressure-Fuel-Turbopump (LPFTP) inducer, the orbiter manifold and a test article used to represent the manifold. Unsteady flow originating from the orbiter LPFTP inducer is one of the major contributors to the high frequency cyclic loading that results in high cycle fatigue damage to the gimbal flowliners just upstream of the LPFTP. The flow fields for the orbiter manifold and representative test article are computed and analyzed for similarities and differences. An incompressible Navier-Stokes flow solver INS3D, based on the artificial compressibility method, was used to compute the flow of liquid hydrogen in each test article.
Unsteady two-dimensional potential-flow model for thin variable geometry airfoils
DEFF Research Database (Denmark)
Gaunaa, Mac
2010-01-01
In the present work, analytical expressions for distributed and integral unsteady two-dimensional forces on a variable geometry airfoil undergoing arbitrary motion are derived under the assumption of incompressible, irrotational, inviscid flow. The airfoil is represented by its camber line...... in their equivalent state-space form, allowing for use of the present theory in problems employing the eigenvalue approach, such as stability analysis. The analytical expressions for the integral forces can be reduced to Munk's steady and Theodorsen's unsteady results for thin airfoils, and numerical evaluation shows...
Unsteady axisymmetric flow and heat transfer over time-dependent radially stretching sheet
Directory of Open Access Journals (Sweden)
Azeem Shahzad
2017-03-01
Full Text Available This article address the boundary layer flow and heat transfer of unsteady and incompressible viscous fluid over an unsteady stretching permeable surface. First of all modeled nonlinear partial differential equations are transformed to a system of ordinary differential equations by using similarity transformations. Analytic solution of the reduced problem is constructed by using homotopy analysis method (HAM. To validate the constructed series solution a numerical counterpart is developed using shooting algorithm based on Runge-Kutta method. Both schemes are in an excellent agreement. The effects of the pertinent parameters on the velocity and energy profile are shown graphically and examined in detail.
Unsteady flow field in a mini VAWT with relative rotation blades: analysis of temporal results
International Nuclear Information System (INIS)
Bayeul-Lainé, A C; Simonet, S; Bois, G
2013-01-01
The present wind turbine is a small one which can be used on roofs or in gardens. This turbine has a vertical axis. Each turbine blade combines a rotating movement around its own axis and around the main rotor axis. Due to this combination of movements, flow around this turbine is highly unsteady and needs to be modelled by unsteady calculation. The present work is an extended study starting in 2009. The benefits of combined rotating blades have been shown. The performance coefficient of this kind of turbine is very good for some blade stagger angles. Spectral analysis of unsteady results on specific points in the domain and temporal forces on blades was already presented for elliptic blades. The main aim here is to compare two kinds of blades in case of the best performances
Helicopter Rotor Blade Computation in Unsteady Flows Using Moving Overset Grids
Ahmad, Jasim; Duque, Earl P. N.
1996-01-01
An overset grid thin-layer Navier-Stokes code has been extended to include dynamic motion of helicopter rotor blades through relative grid motion. The unsteady flowfield and airloads on an AH-IG rotor in forward flight were computed to verify the methodology and to demonstrate the method's potential usefulness towards comprehensive helicopter codes. In addition, the method uses the blade's first harmonics measured in the flight test to prescribe the blade motion. The solution was impulsively started and became periodic in less than three rotor revolutions. Detailed unsteady numerical flow visualization techniques were applied to the entire unsteady data set of five rotor revolutions and exhibited flowfield features such as blade vortex interaction and wake roll-up. The unsteady blade loads and surface pressures compare well against those from flight measurements. Details of the method, a discussion of the resulting predicted flowfield, and requirements for future work are presented. Overall, given the proper blade dynamics, this method can compute the unsteady flowfield of a general helicopter rotor in forward flight.
International Nuclear Information System (INIS)
Rothe, P.H.
1984-01-01
Several devices involving unsteady flows are characterized, along with methods of modeling the flows. Analyses are presented of wave rotor propulsive device cycles, MHD channel flow in the presence of magnetic field transients, and propellant sloshing on board spacecraft. The influence of the wing nose radius on unsteady phenomena in large scale flows is examined and a collocation-finite element method is defined for solving the two-dimensional Navier-Stokes equations
Airfoil optimization for unsteady flows with application to high-lift noise reduction
Rumpfkeil, Markus Peer
The use of steady-state aerodynamic optimization methods in the computational fluid dynamic (CFD) community is fairly well established. In particular, the use of adjoint methods has proven to be very beneficial because their cost is independent of the number of design variables. The application of numerical optimization to airframe-generated noise, however, has not received as much attention, but with the significant quieting of modern engines, airframe noise now competes with engine noise. Optimal control techniques for unsteady flows are needed in order to be able to reduce airframe-generated noise. In this thesis, a general framework is formulated to calculate the gradient of a cost function in a nonlinear unsteady flow environment via the discrete adjoint method. The unsteady optimization algorithm developed in this work utilizes a Newton-Krylov approach since the gradient-based optimizer uses the quasi-Newton method BFGS, Newton's method is applied to the nonlinear flow problem, GMRES is used to solve the resulting linear problem inexactly, and last but not least the linear adjoint problem is solved using Bi-CGSTAB. The flow is governed by the unsteady two-dimensional compressible Navier-Stokes equations in conjunction with a one-equation turbulence model, which are discretized using structured grids and a finite difference approach. The effectiveness of the unsteady optimization algorithm is demonstrated by applying it to several problems of interest including shocktubes, pulses in converging-diverging nozzles, rotating cylinders, transonic buffeting, and an unsteady trailing-edge flow. In order to address radiated far-field noise, an acoustic wave propagation program based on the Ffowcs Williams and Hawkings (FW-H) formulation is implemented and validated. The general framework is then used to derive the adjoint equations for a novel hybrid URANS/FW-H optimization algorithm in order to be able to optimize the shape of airfoils based on their calculated far
Sjogreen, Bjoern; Yee, H. C.
2007-01-01
Flows containing steady or nearly steady strong shocks in parts of the flow field, and unsteady turbulence with shocklets on other parts of the flow field are difficult to capture accurately and efficiently employing the same numerical scheme even under the multiblock grid or adaptive grid refinement framework. On one hand, sixth-order or higher shock-capturing methods are appropriate for unsteady turbulence with shocklets. On the other hand, lower order shock-capturing methods are more effective for strong steady shocks in terms of convergence. In order to minimize the shortcomings of low order and high order shock-capturing schemes for the subject flows,a multi- block overlapping grid with different orders of accuracy on different blocks is proposed. Test cases to illustrate the performance of the new solver are included.
Unsteady Flow in a Horizontal Double-Sided Symmetric Thin Liquid Films
Directory of Open Access Journals (Sweden)
Joseph G. ABDULAHAD
2017-06-01
Full Text Available In this paper a mathematical model is constructed to describe a two dimensional incompressible flow in a symmetric horizontal thin liquid film for unsteadies flow. We apply the Navier-Stokes equations with specified boundary conditions and we obtain the equation of the film thickness by using the similarity method in which we can isolate the explicit time dependence and then the shape of the film will depend on one variable only.
International Nuclear Information System (INIS)
Chakraborty, S.; Borkakati, A.K.
1999-01-01
An unsteady viscous incompressible free convection flow of an electrically conducting fluid between two heated vertical parallel plates is considered in presence of a uniform magnetic field applied transversely to the flow. The approximate analytical solutions for velocity, induced field and temperature distributions are obtained for small and large magnetic Reynolds number. The skin-friction on the two plates are obtained and plotted graphically. The problem is extended for thermometric case. (author)
Unsteady Flow Dynamics and Acoustics of Two-Outlet Centrifugal Fan Design
Wong, I. Y. W.; Leung, R. C. K.; Law, A. K. Y.
2011-09-01
In this study, a centrifugal fan design with two flow outlets is investigated. This design aims to provide high mass flow rate but low noise performance. Two dimensional unsteady flow simulation with CFD code (FLUENT 6.3) is carried out to analyze the fan flow dynamics and its acoustics. The calculations were done using the unsteady Reynolds averaged Navier Stokes (URANS) approach in which effects of turbulence were accounted for using κ-ɛ model. This work aims to provide an insight how the dominant noise source mechanisms vary with a key fan geometrical paramters, namely, the ratio between cutoff distance and the radius of curvature of the fan housing. Four new fan designs were calculated. Simulation results show that the unsteady flow-induced forces on the fan blades are found to be the main noise sources. The blade force coefficients are then used to build the dipole source terms in Ffowcs Williams and Hawkings (FW-H) Equation for estimating their noise effects. It is found that one design is able to deliver a mass flow 34% more, but with sound pressure level (SPL) 10 dB lower, than the existing design .
Directory of Open Access Journals (Sweden)
Cui Michael M.
2005-01-01
Full Text Available To reduce vibration and noise level, the impeller and diffuser blade numbers inside an industrial compressor are typically chosen without common divisors. The shapes of volutes or collectors in these compressors are also not axis-symmetric. When impeller blades pass these asymmetric structures, the flow field in the compressor is time-dependent and three-dimensional. To obtain a fundamental physical understanding of these three-dimensional unsteady flow fields and assess their impact on the compressor performance, the flow field inside the compressors needs to be studied as a whole to include asymmetric and unsteady interaction between the compressor components. In the current study, a unified three-dimensional numerical model was built for a transonic centrifugal compressor including impeller, diffusers, and volute. HFC 134a was used as the working fluid. The thermodynamic and transport properties of the refrigerant gas were modeled by the Martin-Hou equation of state and power laws, respectively. The three-dimensional unsteady flow field was simulated with a Navier-Stokes solver using the k−ϵ turbulent model. The overall performance parameters are obtained by integrating the field quantities. Both the unsteady flow field and the overall performance are analyzed comparatively for each component. The compressor was tested in a water chiller system instrumented to obtain both the overall performance data and local flow-field quantities. The experimental and numerical results agree well. The correlation between the overall compressor performance and local flow-field quantities is defined. The methodology developed and data obtained in these studies can be applied to the centrifugal compressor design and optimization.
Energy Technology Data Exchange (ETDEWEB)
Paik, Joongcheol [University of Minnesota; Sotiropoulos, Fotis [University of Minnesota; Sale, Michael J [ORNL
2005-06-01
A numerical method is developed for carrying out unsteady Reynolds-averaged Navier-Stokes (URANS) simulations and detached-eddy simulations (DESs) in complex 3D geometries. The method is applied to simulate incompressible swirling flow in a typical hydroturbine draft tube, which consists of a strongly curved 90 degree elbow and two piers. The governing equations are solved with a second-order-accurate, finite-volume, dual-time-stepping artificial compressibility approach for a Reynolds number of 1.1 million on a mesh with 1.8 million nodes. The geometrical complexities of the draft tube are handled using domain decomposition with overset (chimera) grids. Numerical simulations show that unsteady statistical turbulence models can capture very complex 3D flow phenomena dominated by geometry-induced, large-scale instabilities and unsteady coherent structures such as the onset of vortex breakdown and the formation of the unsteady rope vortex downstream of the turbine runner. Both URANS and DES appear to yield the general shape and magnitude of mean velocity profiles in reasonable agreement with measurements. Significant discrepancies among the DES and URANS predictions of the turbulence statistics are also observed in the straight downstream diffuser.
Unsteady Simulations of the Flow in a Channel Flow and a Ventilated Room Using the SST-SAS Model
DEFF Research Database (Denmark)
Davidson, Lars; Nielsen, Peter V.
The SAS model (Scale Adapted Simulation) was invented by Menter and his co-workers. The idea behind the SST-SAS model is to add an additional production term - the SAS term - in the w equation which is sensitive to resolved (i.e. unsteady) fluctuations. In regions where the flow is on the limit...
Discrete Adjoint-Based Design Optimization of Unsteady Turbulent Flows on Dynamic Unstructured Grids
Nielsen, Eric J.; Diskin, Boris; Yamaleev, Nail K.
2009-01-01
An adjoint-based methodology for design optimization of unsteady turbulent flows on dynamic unstructured grids is described. The implementation relies on an existing unsteady three-dimensional unstructured grid solver capable of dynamic mesh simulations and discrete adjoint capabilities previously developed for steady flows. The discrete equations for the primal and adjoint systems are presented for the backward-difference family of time-integration schemes on both static and dynamic grids. The consistency of sensitivity derivatives is established via comparisons with complex-variable computations. The current work is believed to be the first verified implementation of an adjoint-based optimization methodology for the true time-dependent formulation of the Navier-Stokes equations in a practical computational code. Large-scale shape optimizations are demonstrated for turbulent flows over a tiltrotor geometry and a simulated aeroelastic motion of a fighter jet.
Study of the flow unsteadiness in the human airway using large eddy simulation
Bernate, Jorge A.; Geisler, Taylor S.; Padhy, Sourav; Shaqfeh, Eric S. G.; Iaccarino, Gianluca
2017-08-01
The unsteady flow in a patient-specific geometry of the airways is studied. The geometry comprises the oral cavity, orophrarynx, larynx, trachea, and the bronchial tree extending to generations 5-8. Simulations are carried out for a constant inspiratory flow rate of 60 liters/min, corresponding to a Reynolds number of 4213 for a nominal tracheal diameter of 2 cm. The computed mean flow field is compared extensively with magnetic resonance velocimetry measurements by Banko et al. [Exp. Fluids 56, 117 (2015), 10.1007/s00348-015-1966-y] carried out in the same computed-tomography-based geometry, showing good agreement. In particular, we focus on the dynamics of the flow in the bronchial tree. After becoming unsteady at a constriction in the oropharynx, the flow is found to be chaotic, exhibiting fluctuations with broad-band spectra even at the most distal airways in which the Reynolds numbers are as low as 300. An inertial range signature is present in the trachea but not in the bronchial tree where a narrower range of scales is observed. The unsteadiness is attributed to the convection of turbulent structures produced at the larynx as well as to local kinetic energy production throughout the bronchial tree. Production occurs predominantly at shear layers bounding geometry-induced separation regions.
Performance Characteristics of a Cross-Flow Hydrokinetic Turbine under Unsteady Conditions
Flack, Karen; Lust, Ethan; Bailin, Ben
2017-11-01
Performance characteristics are presented for a cross-flow hydrokinetic turbine designed for use in a riverine environment. The test turbine is a 1:6 scale model of a three-bladed device (9.5 m span, 6.5 m diameter) that has been proposed by the Department of Energy. Experiments are conducted in the large towing tank (116 m long, 7.9 m wide, 5 m deep) at the United States Naval Academy. The turbine is towed beneath a moving carriage at a constant speed in combination with a shaft motor to achieve the desired tip speed ratio (TSR) range. The measured quantities of turbine thrust, torque and RPM result in power and thrust coefficients for a range of TSR. Results will be presented for cases with quiescent flow at a range of Reynolds numbers and flow with mild surface waves, representative of riverine environments. The impact of unsteady flow conditions on the average turbine performance was not significant. Unsteady flow conditions did have an impact on instantaneous turbine performance which operationally would result in unsteady blade loading and instantaneous power quality.
Minnowbrook IV: 2003 Workshop on Transition and Unsteady Aspects of Turbomachinery Flows
LaGraff, John E. (Editor); Ashpis, David E.
2004-01-01
This Minnowbrook IV 2003 workshop on Transition and Unsteady Aspects of Turbomachinery Flows includes the following topics: 1) Current Issues in Unsteady Turbomachinery Flows; 2) Global Instability and Control of Low-Pressure Turbine Flows; 3) Influence of End Wall Leakage on Secondary Flow Development in Axial Turbines; 4) Active and Passive Flow Control on Low Pressure Turbine Airfoils; 5) Experimental and Numerical Investigation of Transitional Flows as Affected by Passing Wakes; 6) Effects of Freestream Turbulence on Turbine Blade Heat Transfer; 7) Bypass Transition Via Continuous Modes and Unsteady Effects on Film Cooling; 8) High Frequency Surface Heat Flux Imaging of Bypass Transition; 9) Skin Friction and Heat Flux Oscillations in Upstream Moving Wave Packets; 10) Transition Mechanisms and Use of Surface Roughness to Enhance the Benefits of Wake Passing in LP Turbines; 11) Transient Growth Approach to Roughness-Induced Transition; 12) Roughness- and Freestream-Turbulence-Induced Transient Growth as a Bypass Transition Mechanism; 13) Receptivity Calculations as a Means to Predicting Transition; 14) On Streamwise Vortices in a Curved Wall Jet and Their Effect on the Mean Flow; 15) Plasma Actuators for Separation Control of Low Pressure Turbine Blades; 16) Boundary-Layer Separation Control Under Low-Pressure-Turbine Conditions Using Glow-Discharge Plasma Actuators; 17) Control of Separation for Low Pressure Turbine Blades: Numerical Simulation; 18) Effects of Elevated Free-Stream Turbulence on Active Control of a Separation Bubble; 19) Wakes, Calming and Transition Under Strong Adverse Pressure Gradients; 20) Transitional Bubble in Periodic Flow Phase Shift; 21) Modelling Spots: The Calmed Region, Pressure Gradient Effects and Background; 22) Modeling of Unsteady Transitional Flow on Axial Compressor Blades; 23) Challenges in Predicting Component Efficiencies in Turbomachines With Low Reynolds Number Blading; 24) Observations on the Causal Relationship Between
Hypersonic and Unsteady Flow Science Issues for Explosively Formed Penetrators
2006-08-01
under going real- time dynamic deformation. ACCOMPLISHMENTS/RESULTS • Completed initial assessment of flow chemistry • Completed initial stability... flow chemistry during rapid deformation •Cannot use static boundary conditions in CFD codes •Interfaces one approach to coupling with hydrocodes
Simulation of three-demensional unsteady flow in hydraulic pumps
van Esch, B.P.M.; van Esch, Bartholomeus Petrus Maria
1997-01-01
In this thesis it is shown that the flow in hydraulic pumps of the radial and mixedflow type, operating at conditions not too far from design point, can be considered as an incompressible potential flow, where the influence of viscosity is restricted to thin boundary layers, wakes and mixing areas.
Rubinato, Matteo; Martins, Ricardo; Kesserwani, Georges; Leandro, Jorge; Djordjević, Slobodan; Shucksmith, James
2017-09-01
The linkage between sewer pipe flow and floodplain flow is recognised to induce an important source of uncertainty within two-dimensional (2D) urban flood models. This uncertainty is often attributed to the use of empirical hydraulic formulae (the one-dimensional (1D) weir and orifice steady flow equations) to achieve data-connectivity at the linking interface, which require the determination of discharge coefficients. Because of the paucity of high resolution localised data for this type of flows, the current understanding and quantification of a suitable range for those discharge coefficients is somewhat lacking. To fulfil this gap, this work presents the results acquired from an instrumented physical model designed to study the interaction between a pipe network flow and a floodplain flow. The full range of sewer-to-surface and surface-to-sewer flow conditions at the exchange zone are experimentally analysed in both steady and unsteady flow regimes. Steady state measured discharges are first analysed considering the relationship between the energy heads from the sewer flow and the floodplain flow; these results show that existing weir and orifice formulae are valid for describing the flow exchange for the present physical model, and yield new calibrated discharge coefficients for each of the flow conditions. The measured exchange discharges are also integrated (as a source term) within a 2D numerical flood model (a finite volume solver to the 2D Shallow Water Equations (SWE)), which is shown to reproduce the observed coefficients. This calibrated numerical model is then used to simulate a series of unsteady flow tests reproduced within the experimental facility. Results show that the numerical model overestimated the values of mean surcharge flow rate. This suggests the occurrence of additional head losses in unsteady conditions which are not currently accounted for within flood models calibrated in steady flow conditions.
Unsteady flow characteristic analysis of turbine based combined cycle (TBCC inlet mode transition
Directory of Open Access Journals (Sweden)
Jun Liu
2015-09-01
Full Text Available A turbine based combined cycle (TBCC propulsion system uses a turbine-based engine to accelerate the vehicle from takeoff to the mode transition flight condition, at which point, the propulsion system performs a “mode transition” from the turbine to ramjet engine. Smooth inlet mode transition is accomplished when flow is diverted from one flowpath to the other, without experiencing unstart or buzz. The smooth inlet mode transition is a complex unsteady process and it is one of the enabling technologies for combined cycle engine to become a functional reality. In order to unveil the unsteady process of inlet mode transition, the research of over/under TBCC inlet mode transition was conducted through a numerical simulation. It shows that during the mode transition the terminal shock oscillates in the inlet. During the process of inlet mode transition mass flow rate and Mach number of turbojet flowpath reduce with oscillation. While in ramjet flowpath the flow field is non-uniform at the beginning of inlet mode transition. The speed of mode transition and the operation states of the turbojet and ramjet engines will affect the motion of terminal shock. The result obtained in present paper can help us realize the unsteady flow characteristic during the mode transition and provide some suggestions for TBCC inlet mode transition based on the smooth transition of thrust.
Wall modeling for the simulation of highly non-isothermal unsteady flows
International Nuclear Information System (INIS)
Devesa, A.
2006-12-01
Nuclear industry flows are most of the time characterized by their high Reynolds number, density variations (at low Mach numbers) and a highly unsteady behaviour (low to moderate frequencies). High Reynolds numbers are un-affordable by direct simulation (DNS), and simulations must either be performed by solving averaged equations (RANS), or by solving only the large eddies (LES), both using a wall model. A first investigation of this thesis dealt with the derivation and test of two variable density wall models: an algebraic law (CWM) and a zonal approach dedicated to LES (TBLE-ρ). These models were validated in quasi-isothermal cases, before being used in academic and industrial non-isothermal flows with satisfactory results. Then, a numerical experiment of pulsed passive scalars was performed by DNS, were two forcing conditions were considered: oscillations are imposed in the outer flow; oscillations come from the wall. Several frequencies and amplitudes of oscillations were taken into account in order to gain insights in unsteady effects in the boundary layer, and to create a database for validating wall models in such context. The temporal behaviour of two wall models (algebraic and zonal wall models) were studied and showed that a zonal model produced better results when used in the simulation of unsteady flows. (author)
Unsteady hydrodynamic forces acting on a robotic hand and its flow field.
Takagi, Hideki; Nakashima, Motomu; Ozaki, Takashi; Matsuuchi, Kazuo
2013-07-26
This study aims to clarify the mechanism of generating unsteady hydrodynamic forces acting on a hand during swimming in order to directly measure the forces, pressure distribution, and flow field around the hand by using a robotic arm and particle image velocimetry (PIV). The robotic arm consisted of the trunk, shoulder, upper arm, forearm, and hand, and it was independently computer controllable in five degrees of freedom. The elbow-joint angle of the robotic arm was fixed at 90°, and the arm was moved in semicircles around the shoulder joint in a plane perpendicular to the water surface. Two-component PIV was used for flow visualization around the hand. The data of the forces and pressure acting on the hand were sampled at 200Hz and stored on a PC. When the maximum resultant force acting on the hand was observed, a pair of counter-rotating vortices appeared on the dorsal surface of the hand. A vortex attached to the hand increased the flow velocity, which led to decreased surface pressure, increasing the hydrodynamic forces. This phenomenon is known as the unsteady mechanism of force generation. We found that the drag force was 72% greater and the lift force was 4.8 times greater than the values estimated under steady flow conditions. Therefore, it is presumable that swimmers receive the benefits of this unsteady hydrodynamic force. Copyright © 2013 Elsevier Ltd. All rights reserved.
Unsteady hydrodynamic forces acting on a hand and its flow field during sculling motion.
Takagi, Hideki; Shimada, Shohei; Miwa, Takahiro; Kudo, Shigetada; Sanders, Ross; Matsuuchi, Kazuo
2014-12-01
The goal of this research is to clarify the mechanism by which unsteady forces are generated during sculling by a skilled swimmer and thereby to contribute to improving propulsive techniques. We used particle image velocimetry (PIV) to acquire data on the kinematics of the hand during sculling, such as fluid forces and flow field. By investigating the correlations between these data, we expected to find a new propulsion mechanism. The experiment was performed in a flow-controlled water channel. The participant executed sculling motions to remain at a fixed position despite constant water flow. PIV was used to visualize the flow-field cross-section in the plane of hand motion. Moreover, the fluid forces acting on the hand were estimated from pressure distribution measurements performed on the hand and simultaneous three-dimensional motion analysis. By executing the sculling motion, a skilled swimmer produces large unsteady fluid forces when the leading-edge vortex occurs on the dorsal side of the hand and wake capture occurs on the palm side. By using a new approach, we observed interesting unsteady fluid phenomena similar to those of flying insects. The study indicates that it is essential for swimmers to fully exploit vortices. A better understanding of these phenomena might lead to an improvement in sculling techniques. Copyright © 2014 Elsevier B.V. All rights reserved.
Effects of flow unsteadiness on the wall shear stress
International Nuclear Information System (INIS)
Amiri, K; Cervantes, M J; Raisee, M
2012-01-01
Measurements were performed on pulsating fully turbulent flows in a pipe test rig with a diameter of 100 mm. Sinusoidal oscillatory flow at different frequencies was superimposed on a mean flow of averaged Reynolds number Re=20000 based on the pipe diameter. The measurements have been performed at different forcing frequencies (0.001 + < 0.08) covering all the oscillatory regimes; quasi-steady, relaxation, quasi laminar and high frequency. The amplitude of the flow oscillation was small enough to allow a linear response in the measurements, i.e., all flow parameters showed an oscillatory behavior at the frequency of the flow. The amplitude of the oscillatory flow was about 10% of the mean velocity in all cases. The results include mean and phase averaged values of different parameters. The centerline velocity was measured by a 2D LDA system. Hot film and constant temperature anemometry system was used to determine the wall shear stress. Bulk velocity and pressure gradient along the pipe were also acquired. The results showed a good agreement with the previous analytical, experimental and numerical results available in the literature.
Unconfined Unsteady Laminar Flow of a Power-Law Fluid across a Square Cylinder
Directory of Open Access Journals (Sweden)
Asterios Pantokratoras
2016-11-01
Full Text Available The flow of a non-Newtonian, power-law fluid, directed normally to a horizontal cylinder with square cross-section (two-dimensional flow is considered in the present paper. The problem is investigated numerically with a very large calculation domain in order that the flow could be considered unconfined. The investigation covers the power-law index from 0.1 up to 2 and the Reynolds number ranges from 60 to 160. Over this range of Reynolds numbers the flow is unsteady. It is found that the drag coefficient and the Strouhal number are higher in a confined flow compared to those of an unconfined flow. In addition some flow characteristics are lost in a confined flow. Complete results for the drag coefficient and Strouhal number in the entire shear-thinning and shear-thickening region have been produced. In shear-thinning fluids chaotic structures exist which diminish at higher values of power-law index. This study represents the first investigation of unsteady, non-Newtonian power-law flow past a square cylinder in an unconfined field.
Unsteady MHD flow in porous media past over exponentially ...
African Journals Online (AJOL)
International Journal of Engineering, Science and Technology ... rotation and magnetic field on the flow past an exponentially accelerated vertical plate with ... Let (u, v, w) be the components of the velocity vector V. Then using the equation.
Unsteady MHD free convective flow past a vertical porous plate ...
African Journals Online (AJOL)
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International Journal of Engineering, Science and Technology .... dimensional MHD boundary layer on the body with time varying temperature. ... flow of an electrically conducting fluid past an infinite vertical porous flat plate coinciding with.
Shear stress from hot-film sensors in unsteady gas flow
International Nuclear Information System (INIS)
Cole, K.D.
1991-01-01
In this paper a data analysis procedure is proposed for obtaining unsteady wall shear stress from flush-mounted hot-film anemometer measurements. The method is based on a two-dimensional heat transfer model of the unsteady heat transfer in both the hot-film sensor and in the gas flow. The sensor thermal properties are found from preliminary calibration experiments at zero flow. Numerical experiments are used to demonstrate the data analysis method using simulated sensor signals that are corrupted with noise. The numerical experiments show that noise in the data propagates into the results so that data smoothing may be important in analyzing experimental data. Because the data analysis procedure is linear, a linear digital filter is constructed that could be used for processing large amounts of experimental data. However, further refinements will be needed before the method can be applied to experimental data
Schairer, Edward T.; Heineck, James T.; Walker, Louise Ann; Kushner, Laura Kathryn; Zilliac, Gregory
2010-01-01
This paper describes simultaneous, synchronized, high-frequency measurements of both unsteady flow in the wake of a tension-cone decelerator in subsonic flow (by PIV) and the unsteady shape of the decelerator (by photogrammetry). The purpose of these measurements was to develop the test techniques necessary to validate numerical methods for computing fluid-structure interactions of flexible decelerators. A critical need for this effort is to map fabric surfaces that have buckled or wrinkled so that code developers can accurately represent them. This paper describes a new photogrammetric technique that performs this measurement. The work was done in support of the Entry, Descent, and Landing discipline within the Supersonics Project of NASA s Fundamental Aeronautics Program.
Pressurised water reactor operation
International Nuclear Information System (INIS)
Birnie, S.; Lamonby, J.K.
1987-01-01
The operation of a pressurized water reactor (PWR) is described with respect to the procedure for a unit start-up. The systems details and numerical data are for a four loop PWR station of the design proposed for Sizewell-'B', United Kingdom. A description is given of: the initial conditions, filling the reactor coolant system (RCS), heat-up and pressurisation of the RCS, secondary system preparations, reactor start-up, and reactivity control at power. (UK)
Frequency effects of upstream wake and blade interaction on the unsteady boundary layer flow
International Nuclear Information System (INIS)
Kang, Dong Jin; Bae, Sang Su
2002-01-01
Effects of the reduced frequency of upstream wake on downstream unsteady boundary layer flow were simulated by using a Navier-Stokes code. The Navier-Stokes code is based on an unstructured finite volume method and uses a low Reynolds number turbulence model to close the momentum equations. The geometry used in this paper is the MIT flapping foil experimental set-up and the reduced frequency of the upstream wake is varied in the range of 0.91 to 10.86 to study its effect on the unsteady boundary layer flow. Numerical solutions show that they can be divided into two categories. One is so called the low frequency solution, and behaves quite similar to a Stokes layer. Its characteristics is found to be quite similar to those due to either a temporal or spatial wave. The low frequency solutions are observed clearly when reduced frequency is smaller than 3.26. The other one is the high frequency solution. It is observed for the reduced frequency larger than 7.24. It shows a sudden shift of the phase angle of the unsteady velocity around the edge of the boundary layer. The shift of phase angle is about 180 degree, and leads to separation of the boundary layer flow from corresponding outer flow. The high frequency solution shows the characteristics of a temporal wave whose wave length is half of the upstream frequency. This characteristics of the high frequency solution is found to be caused by the strong interaction between unsteady vortices. This strong interaction also leads to destroy of the upstream wake stripe inside the viscous sublayer as well as the buffer layer
Czech Academy of Sciences Publication Activity Database
Punčochářová-Pořízková, P.; Kozel, K.; Horáček, Jaromír
2011-01-01
Roč. 46, č. 1 (2011), s. 404-410 ISSN 0045-7930 R&D Projects: GA MŠk OC09019 Institutional research plan: CEZ:AV0Z20760514 Keywords : finite volume method * unsteady flow * low Mach number * viscous compressible fluid Subject RIV: BI - Acoustics Impact factor: 1.810, year: 2011 http://www.sciencedirect.com/science/article/pii/S0045793010003439
Five-point Element Scheme of Finite Analytic Method for Unsteady Groundwater Flow
Institute of Scientific and Technical Information of China (English)
Xiang Bo; Mi Xiao; Ji Changming; Luo Qingsong
2007-01-01
In order to improve the finite analytic method's adaptability for irregular unit, by using coordinates rotation technique this paper establishes a five-point element scheme of finite analytic method. It not only solves unsteady groundwater flow equation but also gives the boundary condition. This method can be used to calculate the three typical questions of groundwater. By compared with predecessor's computed result, the result of this method is more satisfactory.
Dynamic lift on an artificial static armor layer during highly unsteady open channel flow
Spiller, Stephan Mark; Ruther, Nils; Friedrich, Heide
2015-01-01
The dynamic lift acting on a 100 mm × 100 mm section of a static armor layer during unsteady flow is directly measured in a series of physical experiments. The static armor layer is represented by an artificial streambed mold, made from an actual gravel bed. Data from a total of 190 experiments are presented, undertaken in identical conditions. Results show that during rapid discharge increases, the dynamic lift on the streambed repeatedly exhibits three clear peaks. The magnitude of the obse...
Unsteady flow of an incompressible fluid in a horizontal porous medium with suction
International Nuclear Information System (INIS)
Bestman, A.R.
1988-04-01
A theoretical analysis of two-dimensional unsteady flow in a porous medium bounded by a horizontal wall is presented as a perturbation on a basic flow. It is assumed that the perturbation is occasioned by a sudden suction at the wall. Even for a highly permeable medium the characteristic Reynolds number in porous media flow is usually small and asymptotic solutions are developed by the Laplace transform technique. It is observed that the perturbed shear stress at the wall decays exponentially with time. (author). 5 refs
Unsteady supercritical/critical dual flowpath inlet flow and its control methods
Directory of Open Access Journals (Sweden)
Jun LIU
2017-12-01
Full Text Available The characteristics of unsteady flow in a dual-flowpath inlet, which was designed for a Turbine Based Combined Cycle (TBCC propulsion system, and the control methods of unsteady flow were investigated experimentally and numerically. It was characterized by large-amplitude pressure oscillations and traveling shock waves. As the inlet operated in supercritical condition, namely the terminal shock located in the throat, the shock oscillated, and the period of oscillation was about 50â¯ms, while the amplitude was 6â¯mm. The shock oscillation was caused by separation in the diffuser. This shock oscillation can be controlled by extending the length of diffuser which reduces pressure gradient along the flowpath. As the inlet operated in critical condition, namely the terminal shock located at the shoulder of the third compression ramp, the shock oscillated, and the period of oscillation was about 7.5â¯ms, while the amplitude was 12â¯mm. At this condition, the shock oscillation was caused by an incompatible backpressure in the bleed region. It can be controlled by increasing the backpressure of the bleed region. Keywords: Airbreathing hypersonic vehicle, Dual flowpath inlet, Terminal shock oscillation, Turbine based combined cycle, Unsteady flow
Unsteady flow simulations of Pelton turbine at different rotational speeds
Directory of Open Access Journals (Sweden)
Minsuk Choi
2015-11-01
Full Text Available This article presents numerical simulations of a small Pelton turbine suitable for desalination system. A commercial flow solver was adopted to resolve difficulties in the numerical simulation for Pelton turbine such as the relative motion of the turbine runner to the injector and two-phase flow of water and air. To decrease the numerical diffusion of the water jet, a new topology with only hexagonal mesh was suggested for the computational mesh around the complex geometry of a bucket. The predicted flow coefficient, net head coefficient, and overall efficiency showed a good agreement with the experimental data. Based on the validation of the numerical results, the pattern of wet area on the bucket inner surface has been analyzed at different rotational speeds, and an attempt to find the connection between rotational speeds, torque, and efficiency has been made.
Unsteady transonic flow analysis for low aspect ratio, pointed wings.
Kimble, K. R.; Ruo, S. Y.; Wu, J. M.; Liu, D. Y.
1973-01-01
Oswatitsch and Keune's parabolic method for steady transonic flow is applied and extended to thin slender wings oscillating in the sonic flow field. The parabolic constant for the wing was determined from the equivalent body of revolution. Laplace transform methods were used to derive the asymptotic equations for pressure coefficient, and the Adams-Sears iterative procedure was employed to solve the equations. A computer program was developed to find the pressure distributions, generalized force coefficients, and stability derivatives for delta, convex, and concave wing planforms.
Visualisation of heat transfer in unsteady laminar flows
Speetjens, M.F.M.; Steenhoven, van A.A.
2011-01-01
Heat transfer in fluid flows traditionally is examined in terms of temperature fields and heat-transfer coefficients. However, heat transfer may alternatively be considered as the transport of thermal energy by the total convective-conductive heat flux in a way analogous to the transport of fluid by
Visualisation of heat transfer in 3D unsteady flows
Speetjens, M.F.M.; Steenhoven, van A.A.
2010-01-01
Heat transfer in fluid flows traditionally is examined in terms oftemperature field and heat-transfer coefficients at non-adiabaticwalls. However, heat transfer may alternatively be considered asthe transport of thermal energy by the total convective-conductiveheat flux in a way analogous to the
Partially Ventilated Transom Flow Elevations-Unsteady Analysis
2016-06-30
questions or concerns relating to this submittal. Sincerely ~o~"L Richard A. Royce, Ph.D. Director of Research James J. Henry Professor of Naval...Symposium on Naval Hydrodynamics, Rome, Italy, September 2006. O’Dea, J. , Jenkins , D., and Nagle, T. "Flow Characteristics of a Transom Stem Ship
Unsteady MHD free convection flow and heat transfer along an ...
African Journals Online (AJOL)
Steady free convection flow of an electrically conducting fluid along an infinite vertical porous plate under Arrhenius kinetics are investigated in the presence of strong transverse magnetic field imposed perpendicularly to the plate .A similarity parameter length scale (h) as a function of time and the suction velocity are ...
Unsteady hydromagnetic Couette flow within a porous channel with ...
African Journals Online (AJOL)
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International Journal of Engineering, Science and Technology. Vol. ... long parallel porous plates, taking Hall current into account, in the presence of a transverse ..... modified Hartmann boundary layer and the decaying oscillations excited by the ...... On flow of electrically conducting fluid over a flat plate in the presence of a ...
Energy Technology Data Exchange (ETDEWEB)
Rusanov, A V; Yershov, S V [Institute of Mechanical Engineering Problems of National Academy of Sciences of Ukraine Kharkov (Ukraine)
1998-12-31
The numerical method is suggested for the calculation of the 3D periodically unsteady viscous cascade flow evoked by the aerodynamics interaction of blade rows. Such flow is described by the thin-layer Reynolds-averaged unsteady Navier-Stokes equations. The turbulent effects are simulated with the modified Baldwin-Lomax turbulence model. The problem statement allows to consider an unsteady flow through either a single turbo-machine stage or a multi stage turbomachine. The sliding mesh techniques and the time-space non-oscillatory square interpolation are used in axial spacings to calculate the flow in a computational domain that contains the reciprocally moving elements. The gasdynamical equations are integrated numerically with the implicit quasi-monotonous Godunov`s type ENO scheme of the second or third order of accuracy. The suggested numerical method is incorporated in the FlowER code developed by authors for calculations of the 3D viscous compressible flows through multi stage turbomachines. The numerical results are presented for unsteady turbine stage throughflows. The method suggested is shown to simulate qualitatively properly the main unsteady cascade effects in particular the periodically blade loadings, the propagation of stator wakes through rotor blade passage and the unsteady temperature flowfields for stages with cooled stator blades. (author) 21 refs.
Energy Technology Data Exchange (ETDEWEB)
Rusanov, A.V.; Yershov, S.V. [Institute of Mechanical Engineering Problems of National Academy of Sciences of Ukraine Kharkov (Ukraine)
1997-12-31
The numerical method is suggested for the calculation of the 3D periodically unsteady viscous cascade flow evoked by the aerodynamics interaction of blade rows. Such flow is described by the thin-layer Reynolds-averaged unsteady Navier-Stokes equations. The turbulent effects are simulated with the modified Baldwin-Lomax turbulence model. The problem statement allows to consider an unsteady flow through either a single turbo-machine stage or a multi stage turbomachine. The sliding mesh techniques and the time-space non-oscillatory square interpolation are used in axial spacings to calculate the flow in a computational domain that contains the reciprocally moving elements. The gasdynamical equations are integrated numerically with the implicit quasi-monotonous Godunov`s type ENO scheme of the second or third order of accuracy. The suggested numerical method is incorporated in the FlowER code developed by authors for calculations of the 3D viscous compressible flows through multi stage turbomachines. The numerical results are presented for unsteady turbine stage throughflows. The method suggested is shown to simulate qualitatively properly the main unsteady cascade effects in particular the periodically blade loadings, the propagation of stator wakes through rotor blade passage and the unsteady temperature flowfields for stages with cooled stator blades. (author) 21 refs.
Energy Technology Data Exchange (ETDEWEB)
Mondal, Rabindra Nath, E-mail: rnmondal71@yahoo.com; Shaha, Poly Rani [Department of Mathematics, Jagannath University, Dhaka-1100 (Bangladesh); Roy, Titob [Department of Mathematics, Vikarunnesa Nun School and College, Boshundhara, Dhaka (Bangladesh); Yanase, Shinichiro, E-mail: yanase@okayama-u.ac.jp [Department of Mechanical and Systems Engineering, Okayama University, Okayama 700-8530 (Japan)
2016-07-12
Unsteady laminar flow with convective heat transfer through a curved square duct rotating at a constant angular velocity about the center of curvature is investigated numerically by using a spectral method, and covering a wide range of the Taylor number −300≤Tr≤1000 for the Dean number Dn = 1000. A temperature difference is applied across the vertical sidewalls for the Grashof number Gr = 100, where the outer wall is heated and the inner wall cooled, the top and bottom walls being adiabatic. Flow characteristics are investigated with the effects of rotational parameter, Tr, and the pressure-driven parameter, Dn, for the constant curvature 0.001. Time evolution calculations as well as their phase spaces show that the unsteady flow undergoes through various flow instabilities in the scenario ‘multi-periodic → chaotic → steady-state → periodic → multi-periodic → chaotic’, if Tr is increased in the positive direction. For negative rotation, however, time evolution calculations show that the flow undergoes in the scenario ‘multi-periodic → periodic → steady-state’, if Tr is increased in the negative direction. Typical contours of secondary flow patterns and temperature profiles are obtained at several values of Tr, and it is found that the unsteady flow consists of two- to six-vortex solutions if the duct rotation is involved. External heating is shown to generate a significant temperature gradient at the outer wall of the duct. This study also shows that there is a strong interaction between the heating-induced buoyancy force and the centrifugal-Coriolis instability in the curved channel that stimulates fluid mixing and consequently enhances heat transfer in the fluid.
METHOD FOR NUMERICAL MODELING OF UNSTEADY SEPARATED FLOW AROUND AIRFOILS MOVING CLOSE TO FLAT SCREEN
Directory of Open Access Journals (Sweden)
V. Pogrebnaya Tamara
2017-01-01
Full Text Available In this article an attempt is made to explain the nature of differences in measurements of forces and moments, which influence an aircraft at take-off and landing when testing on different types of stands. An algorithm for numerical simulation of unsteady separated flow around airfoil is given. The algorithm is based on the combination of discrete vortex method and turbulent boundary layer equations. An unsteady flow separation modeling has been used. At each interval vortex method was used to calculate the potential flow around airfoils located near a screen. Calculated pressures and velocities were then used in boundary layer calculations to determine flow separation points and separated vortex in- tensities. After that calculation were made to determine free vortex positions to next time step and the process was fulfilled for next time step. The proposed algorithm allows using numeric visualization to understand physical picture of flow around airfoil moving close to screen. Three different ways of flow modeling (mirror method, fixed or movable screens were tested. In each case the flow separation process, which determines pressure distribution over airfoil surface and influ- ences aerodynamic performance, was viewed. The results of the calculations showed that at low atitudes of airfoil over screen mirror method over predicts lift force compared with movable screen, while fixed screen under predicts it. The data obtained can be used when designing equipment for testing in wind tunnels.
MODELING AND ANALYSIS OF UNSTEADY FLOW BEHAVIOR IN DEEPWATER CONTROLLED MUD-CAP DRILLING
Directory of Open Access Journals (Sweden)
Jiwei Li
Full Text Available Abstract A new mathematical model was developed in this study to simulate the unsteady flow in controlled mud-cap drilling systems. The model can predict the time-dependent flow inside the drill string and annulus after a circulation break. This model consists of the continuity and momentum equations solved using the explicit Euler method. The model considers both Newtonian and non-Newtonian fluids flowing inside the drill string and annular space. The model predicts the transient flow velocity of mud, the equilibrium time, and the change in the bottom hole pressure (BHP during the unsteady flow. The model was verified using data from U-tube flow experiments reported in the literature. The result shows that the model is accurate, with a maximum average error of 3.56% for the velocity prediction. Together with the measured data, the computed transient flow behavior can be used to better detect well kick and a loss of circulation after the mud pump is shut down. The model sensitivity analysis show that the water depth, mud density and drill string size are the three major factors affecting the fluctuation of the BHP after a circulation break. These factors should be carefully examined in well design and drilling operations to minimize BHP fluctuation and well kick. This study provides the fundamentals for designing a safe system in controlled mud-cap drilling operati.
Efficient self-consistent viscous-inviscid solutions for unsteady transonic flow
Howlett, J. T.
1985-01-01
An improved method is presented for coupling a boundary layer code with an unsteady inviscid transonic computer code in a quasi-steady fashion. At each fixed time step, the boundary layer and inviscid equations are successively solved until the process converges. An explicit coupling of the equations is described which greatly accelerates the convergence process. Computer times for converged viscous-inviscid solutions are about 1.8 times the comparable inviscid values. Comparison of the results obtained with experimental data on three airfoils are presented. These comparisons demonstrate that the explicitly coupled viscous-inviscid solutions can provide efficient predictions of pressure distributions and lift for unsteady two-dimensional transonic flows.
A fully unsteady prescribed wake model for HAWT performance prediction in yawed flow
Energy Technology Data Exchange (ETDEWEB)
Coton, F.N.; Tongguang, Wang; Galbraith, R.A.M.; Lee, D. [Univ. of Glasgow (United Kingdom)
1997-12-31
This paper describes the development of a fast, accurate, aerodynamic prediction scheme for yawed flow on horizontal axis wind turbines (HAWTs). The method is a fully unsteady three-dimensional model which has been developed over several years and is still being enhanced in a number of key areas. The paper illustrates the current ability of the method by comparison with field data from the NREL combined experiment and also describes the developmental work in progress. In particular, an experimental test programme designed to yield quantitative wake convection information is summarised together with modifications to the numerical model which are necessary for meaningful comparison with the experiments. Finally, current and future work on aspects such as tower-shadow and improved unsteady aerodynamic modelling are discussed.
Computation of steady and unsteady compressible quasi-axisymmetric vortex flow and breakdown
Kandil, Osama A.; Kandil, Hamdy A.; Liu, C. H.
1991-01-01
The unsteady, compressible Navier-Stokes equations are used to compute and analyze compressible quasi-axisymmetric isolated vortices. The Navier-Stokes equations are solved using an implicit, upwind, flux-difference splitting finite-volume scheme. The developed three-dimensional solver has been verified by comparing its solution profiles with those of a slender, quasi-axisymmetric vortex solver for a subsonic, isolated quasi-axisymmetric vortex in an unbounded domain. The Navier-Stokes solver is then used to solve for a supersonic quasi-axisymmetric vortex flow in a configured circular duct. Steady and unsteady vortex-shock interactions and breakdown have been captured. The problem has also been calculated using the Euler solver of the same code and the results are compared with those of the Navier-Stokes solver. The effect of the initial swirl has been tentatively studied.
A modified hydrodynamic model for routing unsteady flow in a river having piedmont zone
Directory of Open Access Journals (Sweden)
Patowary Sudarshan
2017-03-01
Full Text Available Existence of piedmont zone in a river bed is a critical parameter from among numerous variations of topographical, geological and geographical conditions that can significantly influence the river flow scenario. Downstream flow situation assessed by routing of upstream hydrograph may yield higher flow depth if existence of such high infiltration zone is ignored and therefore it is a matter of concern for water resources planning and flood management. This work proposes a novel modified hydrodynamic model that has the potential to accurately determine the flow scenario in presence of piedmont zone. The model has been developed using unsteady free surface flow equations, coupled with Green-Ampt infiltration equation as governing equation. For solution of the governing equations Beam and Warming implicit finite difference scheme has been used. The proposed model was first validated from the field data of Trout Creek River showing excellent agreement. The validated model was then applied to a hypothetical river reach commensurate with the size of major tributaries of Brahmaputra Basin of India. Results indicated a 10% and 14% difference in the maximum value of discharge and depth hydrograph in presence and absence of piedmont zone respectively. Overall this model was successfully used to accurately predict the effect of piedmont zone on the unsteady flow in a river.
Hall effects on unsteady MHD flow between two rotating disks with non-coincident parallel axes
Energy Technology Data Exchange (ETDEWEB)
Barik, R.N., E-mail: barik.rabinarayan@rediffmail.com [Department of Mathematics, Trident Academy of Technology, Bhubaneswar (India); Dash, G.C., E-mail: gcdash@indiatimes.com [Department of Mathematics, S.O.A. University, Bhubaneswar (India); Rath, P.K., E-mail: pkrath_1967@yahoo.in [Department of Mathematics, B.R.M. International Institute of Technology, Bhubaneswar (India)
2013-01-15
Hall effects on the unsteady MHD rotating flow of a viscous incompressible electrically conducting fluid between two rotating disks with non-coincident parallel axes have been studied. There exists an axisymmetric solution to this problem. The governing equations are solved by applying Laplace transform method. It is found that the torque experienced by the disks decreases with an increase in either the Hall parameter, m or the rotation parameter, S{sup 2}. Further, the axis of rotation has no effect on the fluid flow. (author)
Hall effects on unsteady MHD flow between two rotating disks with non-coincident parallel axes
International Nuclear Information System (INIS)
Barik, R.N.; Dash, G.C.; Rath, P.K.
2013-01-01
Hall effects on the unsteady MHD rotating flow of a viscous incompressible electrically conducting fluid between two rotating disks with non-coincident parallel axes have been studied. There exists an axisymmetric solution to this problem. The governing equations are solved by applying Laplace transform method. It is found that the torque experienced by the disks decreases with an increase in either the Hall parameter, m or the rotation parameter, S 2 . Further, the axis of rotation has no effect on the fluid flow. (author)
Unsteady thin film flow of a fourth grade fluid over a vertical moving and oscillating belt
Directory of Open Access Journals (Sweden)
Taza Gul
2016-09-01
Full Text Available This article studies the unsteady thin film flow of a fourth grade fluid over a moving and oscillating vertical belt. The problem is modeled in terms of non-nonlinear partial differential equations with some physical conditions. Both problems of lift and drainage are studied. Two different techniques namely the adomian decomposition method (ADM and the optimal homotopy asymptotic method (OHAM are used for finding the analytical solutions. These solutions are compared and found in excellent agreement. For the physical analysis of the problem, graphical results are provided and discussed for various embedded flow parameters.
Effects of Oscillation Frequency and Amplitude on Separation in an Unsteady Turbulent Flow.
1980-09-01
be performed with much of the aircraft immersed in turbulent flow. When in operation near the ground or landing platform , unsteady, turbulent flow...34 - .-,...i ,aXa. 8O- IDa I"l N 0 N( ’A0 a r. 0 a 0.a " - M - if l’ . t 1 - o t I.- I.- I I I Ni ilNl 1i * 11 it O ag 0) - -i "NUm M CA myp WiX ~ U’iCL
Control of unsteady separated flow associated with the dynamic pitching of airfoils
Ahmed, Sajeer
1991-01-01
Although studies have been done to understand the dependence of parameters for the occurrence of deep stall, studies to control the flow for sustaining lift for a longer time has been little. To sustain the lift for a longer time, an understanding of the development of the flow over the airfoil is essential. Studies at high speed are required to study how the flow behavior is dictated by the effects of compressibility. When the airfoil is pitched up in ramp motion or during the upstroke of an oscillatory cycle, the flow development on the upper surface of the airfoil and the formation of the vortex dictates the increase in lift behavior. Vortex shedding past the training edge decreases the lift. It is not clear what is the mechanism associated with the unsteady separation and vortex formation in present unsteady environment. To develop any flow control device, to suppress the vortex formation or delay separation, it is important that this mechanism be properly understood. The research activities directed toward understanding these questions are presented and the results are summarized.
Predicted and experimental steady and unsteady transonic flows about a biconvex airfoil
Levy, L. L., Jr.
1981-01-01
Results of computer code time dependent solutions of the two dimensional compressible Navier-Stokes equations and the results of independent experiments are compared to verify the Mach number range for instabilities in the transonic flow field about a 14 percent thick biconvex airfoil at an angle of attack of 0 deg and a Reynolds number of 7 million. The experiments were conducted in a transonic, slotted wall wind tunnel. The computer code included an algebraic eddy viscosity turbulence model developed for steady flows, and all computations were made using free flight boundary conditions. All of the features documented experimentally for both steady and unsteady flows were predicted qualitatively; even with the above simplifications, the predictions were, on the whole, in good quantitative agreement with experiment. In particular, predicted time histories of shock wave position, surface pressures, lift, and pitching moment were found to be in very good agreement with experiment for an unsteady flow. Depending upon the free stream Mach number for steady flows, the surface pressure downstream of the shock wave or the shock wave location was not well predicted.
Unsteady numerical simulation of the flow in the U9 Kaplan turbine model
Javadi, Ardalan; Nilsson, Håkan
2014-03-01
The Reynolds-averaged Navier-Stokes equations with the RNG k-ε turbulence model closure are utilized to simulate the unsteady turbulent flow throughout the whole flow passage of the U9 Kaplan turbine model. The U9 Kaplan turbine model comprises 20 stationary guide vanes and 6 rotating blades (696.3 RPM), working at best efficiency load (0.71 m3/s). The computations are conducted using a general finite volume method, using the OpenFOAM CFD code. A dynamic mesh is used together with a sliding GGI interface to include the effect of the rotating runner. The clearance is included in the guide vane. The hub and tip clearances are also included in the runner. An analysis is conducted of the unsteady behavior of the flow field, the pressure fluctuation in the draft tube, and the coherent structures of the flow. The tangential and axial velocity distributions at three sections in the draft tube are compared against LDV measurements. The numerical result is in reasonable agreement with the experimental data, and the important flow physics close to the hub in the draft tube is captured. The hub and tip vortices and an on-axis forced vortex are captured. The numerical results show that the frequency of the forced vortex in 1/5 of the runner rotation.
Unsteady numerical simulation of the flow in the U9 Kaplan turbine model
International Nuclear Information System (INIS)
Javadi, Ardalan; Nilsson, Håkan
2014-01-01
The Reynolds-averaged Navier-Stokes equations with the RNG k-ε turbulence model closure are utilized to simulate the unsteady turbulent flow throughout the whole flow passage of the U9 Kaplan turbine model. The U9 Kaplan turbine model comprises 20 stationary guide vanes and 6 rotating blades (696.3 RPM), working at best efficiency load (0.71 m 3 /s). The computations are conducted using a general finite volume method, using the OpenFOAM CFD code. A dynamic mesh is used together with a sliding GGI interface to include the effect of the rotating runner. The clearance is included in the guide vane. The hub and tip clearances are also included in the runner. An analysis is conducted of the unsteady behavior of the flow field, the pressure fluctuation in the draft tube, and the coherent structures of the flow. The tangential and axial velocity distributions at three sections in the draft tube are compared against LDV measurements. The numerical result is in reasonable agreement with the experimental data, and the important flow physics close to the hub in the draft tube is captured. The hub and tip vortices and an on-axis forced vortex are captured. The numerical results show that the frequency of the forced vortex in 1/5 of the runner rotation
An efficient parallel simulation of unsteady blood flows in patient-specific pulmonary artery.
Kong, Fande; Kheyfets, Vitaly; Finol, Ender; Cai, Xiao-Chuan
2018-04-01
Simulation of blood flows in the pulmonary artery provides some insight into certain diseases by examining the relationship between some continuum metrics, eg, the wall shear stress acting on the vascular endothelium, which responds to flow-induced mechanical forces by releasing vasodilators/constrictors. V. Kheyfets, in his previous work, studies numerically a patient-specific pulmonary circulation to show that decreasing wall shear stress is correlated with increasing pulmonary vascular impedance. In this paper, we develop a scalable parallel algorithm based on domain decomposition methods to investigate an unsteady model with patient-specific pulsatile waveforms as the inlet boundary condition. The unsteady model offers tremendously more information about the dynamic behavior of the flow field, but computationally speaking, the simulation is a lot more expensive since a problem which is similar to the steady-state problem has to be solved many times, and therefore, the traditional sequential approach is not suitable anymore. We show computationally that simulations using the proposed parallel approach with up to 10 000 processor cores can be obtained with much reduced compute time. This makes the technology potentially usable for the routine study of the dynamic behavior of blood flows in the pulmonary artery, in particular, the changes of the blood flows and the wall shear stress in the spatial and temporal dimensions. Copyright © 2017 John Wiley & Sons, Ltd.
Redolfi, M.; Bertoldi, W.; Tubino, M.; Welber, M.
2018-02-01
Measurement and estimation of bed load transport in gravel bed rivers are highly affected by its temporal fluctuations. Such variability is primarily driven by the flow regime but is also associated with a variety of inherent channel processes, such as flow turbulence, grain entrainment, and bed forms migration. These internal and external controls often act at comparable time scales, and are therefore difficult to disentangle, thus hindering the study of bed load variability under unsteady flow regime. In this paper, we report on laboratory experiments performed in a large, mobile bed flume where typical hydromorphological conditions of gravel bed rivers were reproduced. Data from a large number of replicated runs, including triangular and square-wave hydrographs, were used to build a statistically sound description of sediment transport processes. We found that the inherent variability of bed load flux strongly depends on the sampling interval, and it is significantly higher in complex, wandering or braided channels. This variability can be filtered out by computing the mean response over the experimental replicates, which allows us to highlight two distinctive phenomena: (i) an overshooting (undershooting) response of the mean bed load flux to a sudden increase (decrease) of discharge, and (ii) a clockwise hysteresis in the sediment rating curve. We then provide an interpretation of these findings through a conceptual mathematical model, showing how both phenomena are associated with a lagging morphological adaptation to unsteady flow. Overall, this work provides basic information for evaluating, monitoring, and managing gravel transport in morphologically active rivers.
Problems of unsteady temperature measurements in a pulsating flow of gas
International Nuclear Information System (INIS)
Olczyk, A
2008-01-01
Unsteady flow temperature is one of the most difficult and complex flow parameters to measure. Main problems concern insufficient dynamic properties of applied sensors and an interpretation of recorded signals, composed of static and dynamic temperatures. An attempt is made to solve these two problems in the case of measurements conducted in a pulsating flow of gas in the 0–200 Hz range of frequencies, which corresponds to real conditions found in exhaust pipes of modern diesel engines. As far as sensor dynamics is concerned, an analysis of requirements related to the thermometer was made, showing that there was no possibility of assuring such a high frequency band within existing solutions. Therefore, a method of double-channel correction of sensor dynamics was proposed and experimentally tested. The results correspond well with the calculations made by means of the proposed model of sensor dynamics. In the case of interpretation of the measured temperature signal, a method for distinguishing its two components was proposed. This decomposition considerably helps with a correct interpretation of unsteady flow phenomena in pipes
Unsteady motion and transition to turbulence in developing curved duct flow
International Nuclear Information System (INIS)
Arnal, M.; Firmino, F.; Humphrey, J.A.C.
1987-01-01
An experiment was performed to further the understanding of developing flows in curved ducts of square cross-section. Unlike most earlier works, attention was paid to investigating the time-dependent character of the motion. Mean and unsteady flow characteristics were determined using flow visualization and a laser-Doppler velocimeter. Only one velocity component, that aligned in the longitudinal (streamwise) coordinate direction, was measured. Notwithstanding, the time histories, autocorrelations and spectra derived reveal a time-periodic motion that becomes turbulent with increasing Reynolds number. The results are of intrinsic fundamental value and also illustrate the danger of imposing symmetry of the conservation equations on numerical solutions of this flow. 24 references
Dynamics of an inline tube array in steam-water flow. Part 2: Unsteady fluid forces
International Nuclear Information System (INIS)
Mureithi, N.W.; Nakamura, T.; Hirota, K.; Murata, M.; Utsumi, S.
1996-01-01
The existence of fluidelastic instability in two-phase flow has been confirmed by a number of investigators to date. In essentially homogeneous two-phase flow, e.g., bubbly flow, it appears that the mechanisms underlying fluidelastic instability and the instability phenomenon are the same as those observed in single phase flow. The more general case of non-homogeneous two-phase flow, e.g., slug flow, is less amenable to straight forward interpretation by direct comparison with single phase flow mechanisms. In this paper, experimental results of unsteady fluid force measurement are reported. Important deviations of the measured fluid force from their single phase flow counterparts were uncovered. Most importantly, the resulting force coefficients are not simple functions of the reduced velocity U/fD, as is the case for single phase flow. Test results at 0.5 MPa challenge the basic assumption of the existence of a time invariant linear transfer function between tube displacement and the resulting fluid forces. Time-frequency analysis using Wignerville transforms shows that the phase difference between tube displacement and the fluid force (an indicator of stabilizing or destabilizing fluid effects) undergoes significant variation under what may be considered steady flow conditions. This variation may explain the previously reported phenomenon of intermittent fluidelastic instability in two-phase flows
Experimental study on unsteady open channel flow and bedload transport based on a physical model
Cao, W.
2015-12-01
Flow in a nature river are usually unsteady, while nearly all the theories about bedload transport are on the basis of steady, uniform flow, and also with supposed equilibrium state of sediment transport. This is may be one of the main reasons why the bedload transport formulas are notoriously poor accuracy to predict the bedload. The aim of this research is to shed light on the effect of unsteadiness on the bedload transport based on experimental studies. The novel of this study is that the experiments were not carried out in a conventional flume but in a physical model, which are more similar to the actual river. On the other hand, in our experiments, multiple consecutive flood wave were reproduced in the physical model, and all the flow and sediment parameters are based on a large number of data obtained from many of identical flood waves. This method allow us to get more data for one flood, efficiently avoids the uncertainty of bedload rate only for one single flood wave, due to the stochastic fluctuation of the bedload transport. Three different flood waves were selected in the experiments. During each run of experiment, the water level of five different positions along the model were measured by ultrasonic water level gauge, flow velocity at the middle of the channel were measured by two dimensional electromagnetic current meter. Moreover, the bedload transport rate was measured by a unique automatic trap collecting and weighing system at the end of the physical model. The results shows that the celerity of flood wave propagate varies for different flow conditions. The velocity distribution was approximately accord with log-law profile during the entire rising and falling limb of flood. The bedload transport rate show intensity fluctuation in all the experiments, moreover, for different flood waves, the moment when the shear stress reaches its maximum value is not the exact moment when the sediment transport rate reaches its maximum value, which indicates
Unsteady 2D potential-flow forces on a thin variable geometry airfoil undergoing arbitrary motion
DEFF Research Database (Denmark)
Gaunaa, M.
2006-01-01
In this report analytical expressions for the unsteady 2D force distribution on a variable geometry airfoil undergoing arbitrary motion are derived under the assumption of incompressible, irrotational, inviscid flow. The airfoil is represented by itscamberline as in classic thin-airfoil theory...... using an indicial function approach, making the practical calculation of the aerodynamic response numerically very efficient by use ofDuhamel superposition. Furthermore, the indicial function expressions for the time-lag terms are formulated in their equivalent state-space form, allowing for use...
Directory of Open Access Journals (Sweden)
Mohammad Mehdi Rashidi
2008-01-01
Full Text Available The flow of a viscous incompressible fluid between two parallel plates due to the normal motion of the plates is investigated. The unsteady Navier-Stokes equations are reduced to a nonlinear fourth-order differential equation by using similarity solutions. Homotopy analysis method (HAM is used to solve this nonlinear equation analytically. The convergence of the obtained series solution is carefully analyzed. The validity of our solutions is verified by the numerical results obtained by fourth-order Runge-Kutta.
Unsteady natural convection flow past an accelerated vertical plate in a thermally stratified fluid
Directory of Open Access Journals (Sweden)
Deka Rudra Kt.
2009-01-01
Full Text Available An exact solution to one-dimensional unsteady natural convection flow past an infinite vertical accelerated plate, immersed in a viscous thermally stratified fluid is investigated. Pressure work term and the vertical temperature advection are considered in the thermodynamic energy equation. The dimensionless governing equations are solved by Laplace Transform techniques for the Prandtl number unity. The velocity and temperature profiles as well as the skin-friction and the rate of heat transfer are presented graphically and discussed the effects of the Grashof number Gr, stratification parameter S at various times t.
Unsteady response of flow system around balance piston in a rocket pump
Kawasaki, S.; Shimura, T.; Uchiumi, M.; Hayashi, M.; Matsui, J.
2013-03-01
In the rocket engine turbopump, a self-balancing type of axial thrust balancing system using a balance piston is often applied. In this study, the balancing system in liquid-hydrogen (LH2) rocket pump was modeled combining the mechanical structure and the flow system, and the unsteady response of the balance piston was investigated. The axial vibration characteristics of the balance piston with a large amplitude were determined, sweeping the frequency of the pressure fluctuation on the inlet of the balance piston. This vibration was significantly affected by the compressibility of LH2.
Numerical Leak Detection in a Pipeline Network of Complex Structure with Unsteady Flow
Aida-zade, K. R.; Ashrafova, E. R.
2017-12-01
An inverse problem for a pipeline network of complex loopback structure is solved numerically. The problem is to determine the locations and amounts of leaks from unsteady flow characteristics measured at some pipeline points. The features of the problem include impulse functions involved in a system of hyperbolic differential equations, the absence of classical initial conditions, and boundary conditions specified as nonseparated relations between the states at the endpoints of adjacent pipeline segments. The problem is reduced to a parametric optimal control problem without initial conditions, but with nonseparated boundary conditions. The latter problem is solved by applying first-order optimization methods. Results of numerical experiments are presented.
Energy Technology Data Exchange (ETDEWEB)
Salah, Anis Bousbia; Vlassenbroeck, Jacques [Bel V - Subsidiary of the Belgian Federal Agency for Nuclear Contro, Brussels (Belize)
2017-04-15
Coolant mixing under natural circulation flow regime constitutes a key parameter that may play a role in the course of an accidental transient in a nuclear pressurized water reactor. This issue has motivated some experimental investigations carried out within the OECD/NEA PKL projects. The aim was to assess the coolant mixing phenomenon in the reactor pressure vessel downcomer and the core lower plenum under several asymmetric steady and unsteady flow conditions, and to provide experimental data for code validations. Former studies addressed the mixing phenomenon using, on the one hand, one-dimensional computational approaches with cross flows that are not fully validated under transient conditions and, on the other hand, expensive computational fluid dynamic tools that are not always justified for large-scale macroscopic phenomena. In the current framework, an unsteady coolant mixing experiment carried out in the Rossendorf coolant mixing test facility is simulated using the three-dimensional porous media capabilities of the thermal–hydraulic system CATHARE code. The current study allows highlighting the current capabilities of these codes and their suitability for reproducing the main phenomena occurring during asymmetric transient natural circulation mixing conditions.
Directory of Open Access Journals (Sweden)
Ibukun Sarah Oyelakin
2016-06-01
Full Text Available In this paper we report on combined Dufour and Soret effects on the heat and mass transfer in a Casson nanofluid flow over an unsteady stretching sheet with thermal radiation and heat generation. The effects of partial slip on the velocity at the boundary, convective thermal boundary condition, Brownian and thermophoresis diffusion coefficients on the concentration boundary condition are investigated. The model equations are solved using the spectral relaxation method. The results indicate that the fluid flow, temperature and concentration profiles are significantly influenced by the fluid unsteadiness, the Casson parameter, magnetic parameter and the velocity slip. The effect of increasing the Casson parameter is to suppress the velocity and temperature growth. An increase in the Dufour parameter reduces the flow temperature, while an increase in the value of the Soret parameter causes increase in the concentration of the fluid. Again, increasing the velocity slip parameter reduces the velocity profile whereas increasing the heat generation parameter increases the temperature profile. A validation of the work is presented by comparing the current results with existing literature.
Investigation of Unsteady Flow Interaction Between an Ultra-Compact Inlet and a Transonic Fan
Hah, Chunill; Rabe, Douglas; Scribben, Angie
2015-01-01
In the present study, unsteady flow interaction between an ultra-compact inlet and a transonic fan stage is investigated. Future combat aircraft require ultra-compact inlet ducts as part of an integrated, advanced propulsion system to improve air vehicle capability and effectiveness to meet future mission needs. The main purpose of the study is to advance the current understanding of the flow interaction between two different ultra-compact inlets and a transonic fan for future design applications. Both URANS and LES approaches are used to calculate the unsteady flow field and are compared with the available measured data. The present study indicates that stall inception is mildly affected by the distortion pattern generated by the inlet with the current test set-up. The numerical study indicates that the inlet distortion pattern decays significantly before it reaches the fan face for the current configuration. Numerical results with a shorter distance between the inlet and fan show that counter-rotating vortices near the rotor tip due to the serpentine diffuser affects fan characteristics significantly.
Unsteady CFD modeling of micro-adaptive flow control for an axisymmetric body
International Nuclear Information System (INIS)
Sahu, J.; Heavey, K.R.
2005-01-01
This paper describes a computational study undertaken, as part of a grand challenge project, to consider the aerodynamic effect of micro-adaptive flow control as a means to provide the divert authority needed to maneuver a projectile at a low subsonic speed. A time-accurate Navier-Stokes computational technique has been used to obtain numerical solutions for the unsteady microjet-interaction flow field for the axisymmetric projectile body at subsonic speeds, Mach = 0.11 and 0.24 and angles of attack, 0 o to 4 o . Numerical solutions have been obtained using both Renolds-Averaged Navier-Stokes (RANS) and a hybrid RANS/Large Eddy Simulation (LES) turbulence models. Unsteady numerical results show the effect of the jet on the flow field and the aerodynamic coefficients, in particular the lift force. This research has provided an increased fundamental understanding of the complex, three-dimensional, time-dependent, aerodynamic interactions associated with micro-jet control for yawing spin-stabilized munitions. (author)
Unsteady CFD modeling of micro-adaptive flow control for an axisymmetric body
Energy Technology Data Exchange (ETDEWEB)
Sahu, J.; Heavey, K.R. [U.S. Army Research Laboratory, Aberdeen Proving Ground, MD (United States)]. E-mail: sahu@arl.army.mil
2005-07-01
This paper describes a computational study undertaken, as part of a grand challenge project, to consider the aerodynamic effect of micro-adaptive flow control as a means to provide the divert authority needed to maneuver a projectile at a low subsonic speed. A time-accurate Navier-Stokes computational technique has been used to obtain numerical solutions for the unsteady microjet-interaction flow field for the axisymmetric projectile body at subsonic speeds, Mach = 0.11 and 0.24 and angles of attack, 0{sup o} to 4{sup o}. Numerical solutions have been obtained using both Renolds-Averaged Navier-Stokes (RANS) and a hybrid RANS/Large Eddy Simulation (LES) turbulence models. Unsteady numerical results show the effect of the jet on the flow field and the aerodynamic coefficients, in particular the lift force. This research has provided an increased fundamental understanding of the complex, three-dimensional, time-dependent, aerodynamic interactions associated with micro-jet control for yawing spin-stabilized munitions. (author)
Dorney, Suzanne; Dorney, Daniel J.; Huber, Frank; Sheffler, David A.; Turner, James E. (Technical Monitor)
2001-01-01
The advent of advanced computer architectures and parallel computing have led to a revolutionary change in the design process for turbomachinery components. Two- and three-dimensional steady-state computational flow procedures are now routinely used in the early stages of design. Unsteady flow analyses, however, are just beginning to be incorporated into design systems. This paper outlines the transition of a three-dimensional unsteady viscous flow analysis from the research environment into the design environment. The test case used to demonstrate the analysis is the full turbine system (high-pressure turbine, inter-turbine duct and low-pressure turbine) from an advanced turboprop engine.
An autonomous dynamical system captures all LCSs in three-dimensional unsteady flows.
Oettinger, David; Haller, George
2016-10-01
Lagrangian coherent structures (LCSs) are material surfaces that shape the finite-time tracer patterns in flows with arbitrary time dependence. Depending on their deformation properties, elliptic and hyperbolic LCSs have been identified from different variational principles, solving different equations. Here we observe that, in three dimensions, initial positions of all variational LCSs are invariant manifolds of the same autonomous dynamical system, generated by the intermediate eigenvector field, ξ 2 (x 0 ), of the Cauchy-Green strain tensor. This ξ 2 -system allows for the detection of LCSs in any unsteady flow by classical methods, such as Poincaré maps, developed for autonomous dynamical systems. As examples, we consider both steady and time-aperiodic flows, and use their dual ξ 2 -system to uncover both hyperbolic and elliptic LCSs from a single computation.
Unsteady magnetohydrodynamics mixed convection flow in a rotating medium with double diffusion
Energy Technology Data Exchange (ETDEWEB)
Jiann, Lim Yeou; Ismail, Zulkhibri; Khan, Ilyas; Shafie, Sharidan [Department of Mathematical Sciences, Faculty of Science, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor (Malaysia)
2015-05-15
Exact solutions of an unsteady Magnetohydrodynamics (MHD) flow over an impulsively started vertical plate in a rotating medium are presented. The effects of thermal radiative and thermal diffusion on the fluid flow are also considered. The governing equations are modelled and solved for velocity, temperature and concentration using Laplace transforms technique. Expressions of velocity, temperature and concentration profiles are obtained and their numerical results are presented graphically. Skin friction, Sherwood number and Nusselt number are also computed and presented in tabular forms. The determined solutions can generate a large class of solutions as special cases corresponding to different motions with technical relevance. The results obtained herein may be used to verify the validation of obtained numerical solutions for more complicated fluid flow problems.
Extreme-Scale Stochastic Particle Tracing for Uncertain Unsteady Flow Analysis
Energy Technology Data Exchange (ETDEWEB)
Guo, Hanqi; He, Wenbin; Seo, Sangmin; Shen, Han-Wei; Peterka, Tom
2016-11-13
We present an efficient and scalable solution to estimate uncertain transport behaviors using stochastic flow maps (SFM,) for visualizing and analyzing uncertain unsteady flows. SFM computation is extremely expensive because it requires many Monte Carlo runs to trace densely seeded particles in the flow. We alleviate the computational cost by decoupling the time dependencies in SFMs so that we can process adjacent time steps independently and then compose them together for longer time periods. Adaptive refinement is also used to reduce the number of runs for each location. We then parallelize over tasks—packets of particles in our design—to achieve high efficiency in MPI/thread hybrid programming. Such a task model also enables CPU/GPU coprocessing. We show the scalability on two supercomputers, Mira (up to 1M Blue Gene/Q cores) and Titan (up to 128K Opteron cores and 8K GPUs), that can trace billions of particles in seconds.
Unsteady MHD blood flow through porous medium in a parallel plate channel
Latha, R.; Rushi Kumar, B.
2017-11-01
In this study, we have analyzed heat and mass transfer effects on unsteady blood flow through parallel plate channel in a saturated porous medium in the presence of a transverse magnetic field with thermal radiation. The governing higher order nonlinear PDE’S are converted to dimensionless equations using dimensionless variables. The dimensionless equations are then solved analytically using boundary conditions by choosing the axial flow transport and the fields of concentration and temperature apart from the normal velocity as a function of y and t. The effects of different pertinent parameters appeared in this model viz thermal radiation, Prandtl number, Heat source parameter, Hartmann number, Permeability parameter, Decay parameter on axial flow transport and the normal velocity are analyzed in detail.
Directory of Open Access Journals (Sweden)
Jawad Ahmed
Full Text Available This paper examines the boundary layer flow and heat transfer characteristic in power law fluid model over unsteady radially stretching sheet under the influence of convective boundary conditions. A uniform magnetic field is applied transversely to the direction of the flow. The governing time dependent nonlinear boundary layer equations are reduced into nonlinear ordinary differential equations with the help of similarity transformations. The transformed coupled ordinary differential equations are then solved analytically by homotopy analysis method (HAM and numerically by shooting procedure. Effects of various governing parameters like, power law index n, magnetic parameter M, unsteadiness A, suction/injection S, Biot number γ and generalized Prandtl number Pr on velocity, temperature, local skin friction and the local Nusselt number are studied and discussed. It is found from the analysis that the magnetic parameter diminishes the velocity profile and the corresponding thermal boundary layer thickness. Keywords: Axisymmetric flow, Power law fluid, Unsteady stretching, Convective boundary conditions
Energy Technology Data Exchange (ETDEWEB)
Li, Ying, E-mail: 13110290008@fudan.edu.cn [Department of Mechanics and Engineering Science, Fudan University, Shanghai 200433 (China); Shen, Xiangying, E-mail: 13110190068@fudan.edu.cn [Department of Physics, State Key Laboratory of Surface Physics, and Collaborative Innovation Center of Advanced Microstructures, Fudan University, Shanghai 200433 (China); Huang, Jiping, E-mail: jphuang@fudan.edu.cn [Department of Physics, State Key Laboratory of Surface Physics, and Collaborative Innovation Center of Advanced Microstructures, Fudan University, Shanghai 200433 (China); Ni, Yushan, E-mail: niyushan@fudan.edu.cn [Department of Mechanics and Engineering Science, Fudan University, Shanghai 200433 (China)
2016-04-22
For manipulating heat flow efficiently, recently we established a theory of temperature-dependent transformation thermotics which holds for steady-state cases. Here, we develop the theory to unsteady-state cases by considering the generalized Fourier's law for transient thermal conduction. As a result, we are allowed to propose a new class of intelligent thermal metamaterial — switchable concentrator, which is made of inhomogeneous anisotropic materials. When environmental temperature is below or above a critical value, the concentrator is automatically switched on, namely, it helps to focus heat flux in a specific region. However, the focusing does not affect the distribution pattern of temperature outside the concentrator. We also perform finite-element simulations to confirm the switching effect according to the effective medium theory by assembling homogeneous isotropic materials, which bring more convenience for experimental fabrication than inhomogeneous anisotropic materials. This work may help to figure out new intelligent thermal devices, which provide more flexibility in controlling heat flow, and it may also be useful in other fields that are sensitive to temperature gradient, such as the Seebeck effect. - Highlights: • Established the unsteady-state temperature dependent transformation thermotics. • A thermal concentrator with switchable functionality. • An effective-medium design for experimental realization.
Twin Tail/Delta Wing Configuration Buffet Due to Unsteady Vortex Breakdown Flow
Kandil, Osama A.; Sheta, Essam F.; Massey, Steven J.
1996-01-01
The buffet response of the twin-tail configuration of the F/A-18 aircraft; a multidisciplinary problem, is investigated using three sets of equations on a multi-block grid structure. The first set is the unsteady, compressible, full Navier-Stokes equations. The second set is the coupled aeroelastic equations for bending and torsional twin-tail responses. The third set is the grid-displacement equations which are used to update the grid coordinates due to the tail deflections. The computational model consists of a 76 deg-swept back, sharp edged delta wing of aspect ratio of one and a swept-back F/A-18 twin-tails. The configuration is pitched at 32 deg angle of attack and the freestream Mach number and Reynolds number are 0.2 and 0.75 x 10(exp 6) respectively. The problem is solved for the initial flow conditions with the twin tail kept rigid. Next, the aeroelastic equations of the tails are turned on along with the grid-displacement equations to solve for the uncoupled bending and torsional tails response due to the unsteady loads produced by the vortex breakdown flow of the vortex cores of the delta wing. Two lateral locations of the twin tail are investigated. These locations are called the midspan and inboard locations.
Numerical and experimental research on unsteady cavitating flow around NACA 2412 hydrofoil
International Nuclear Information System (INIS)
Sedlář, M; Komárek, M; Rudolf, P; Kozák, J; Huzlík, R
2015-01-01
This work deals with the numerical and experimental investigation of unsteady cavitating flow around a prismatic NACA 2412 hydrofoil. The main attention is focussed on the dependence of cavitation dynamics on the cavitation number at high incidence angles. The experimental research is carried out in the cavitation water tunnel the rectangular test section of which has inner dimensions 150×150×500 mm. Currently tested hydrofoils have a chord length of 120 mm and are equipped with pressure transducers at the leading edge and on the suction side. The PVDF hydrophone enables to measure high-frequency pressure pulses behind the hydrofoil trailing edge. The visualizations are based on two simultaneous high-speed cameras, recording the hydrofoil from the top and from one side. A comprehensive CFD analysis has been done with the ANSYS CFX package for a wide range of flow regimes. Different turbulence models including SAS-SST and Reynolds-stress models have been tested to capture highly unsteady phenomena on the hydrofoil. The numerical simulations show, that the dominant frequency of the cavity oscillation depends on the cavitation number and that there is a certain range of this number in which the 'resonance' effect can be reached. In such regime the amplitudes of the pressure pulses on the suction side of the hydrofoil dramatically increase. The calculated results have been verified by both the visualizations and the pressure measurements carried out at the hydrofoil incidence angle of 8 degrees
Directory of Open Access Journals (Sweden)
I. J. Uwanta
2014-01-01
Full Text Available This study investigates the unsteady natural convection and mass transfer flow of viscous reactive, heat generating/absorbing fluid in a vertical channel formed by two infinite parallel porous plates having temperature dependent thermal conductivity. The motion of the fluid is induced due to natural convection caused by the reactive property as well as the heat generating/absorbing nature of the fluid. The solutions for unsteady state temperature, concentration, and velocity fields are obtained using semi-implicit finite difference schemes. Perturbation techniques are used to get steady state expressions of velocity, concentration, temperature, skin friction, Nusselt number, and Sherwood number. The effects of various flow parameters such as suction/injection (γ, heat source/sinks (S, Soret number (Sr, variable thermal conductivity δ, Frank-Kamenetskii parameter λ, Prandtl number (Pr, and nondimensional time t on the dynamics are analyzed. The skin friction, heat transfer coefficients, and Sherwood number are graphically presented for a range of values of the said parameters.
Characterization of Unsteady Flow Structures Near Leading-Edge Slat. Part 1; PIV Measurements
Jenkins, Luther N.; Khorrami, Mehdi R.; Choudhari, Meelan
2004-01-01
A comprehensive computational and experimental study has been performed at the NASA Langley Research Center as part of the Quiet Aircraft Technology (QAT) Program to investigate the unsteady flow near a leading-edge slat of a two-dimensional, high-lift system. This paper focuses on the experimental effort conducted in the NASA Langley Basic Aerodynamics Research Tunnel (BART) where Particle Image Velocimetry (PIV) data was acquired in the slat cove and at the slat trailing edge of a three-element, high-lift model at 4, 6, and 8 degrees angle of attack and a freestream Mach Number of 0.17. Instantaneous velocities obtained from PIV images are used to obtain mean and fluctuating components of velocity and vorticity. The data show the recirculation in the cove, reattachment of the shear layer on the slat lower surface, and discrete vortical structures within the shear layer emanating from the slat cusp and slat trailing edge. Detailed measurements are used to examine the shear layer formation at the slat cusp, vortex shedding at the slat trailing edge, and convection of vortical structures through the slat gap. Selected results are discussed and compared with unsteady, Reynolds-Averaged Navier-Stokes (URANS) computations for the same configuration in a companion paper by Khorrami, Choudhari, and Jenkins (2004). The experimental dataset provides essential flow-field information for the validation of near-field inputs to noise prediction tools.
Flow structure and unsteadiness in the supersonic wake of a generic space launcher
Schreyer, Anne-Marie; Stephan, Sören; Radespiel, Rolf
2015-11-01
At the junction between the rocket engine and the main body of a classical space launcher, a separation-dominated and highly unstable flow field develops and induces strong wall-pressure oscillations. These can excite structural vibrations detrimental to the launcher. It is desirable to minimize these effects, for which a better understanding of the flow field is required. We study the wake flow of a generic axisymmetric space-launcher model with and without propulsive jet (cold air). Experimental investigations are performed at Mach 2.9 and a Reynolds number ReD = 1 . 3 .106 based on model diameter D. The jet exits the nozzle at Mach 2.5. Velocity measurements by means of Particle Image Velocimetry and mean and unsteady wall-pressure measurements on the main-body base are performed simultaneously. Additionally, we performed hot-wire measurements at selected points in the wake. We can thus observe the evolution of the wake flow along with its spectral content. We describe the mean and turbulent flow topology and evolution of the structures in the wake flow and discuss the origin of characteristic frequencies observed in the pressure signal at the launcher base. The influence of a propulsive jet on the evolution and topology of the wake flow is discussed in detail. The German Research Foundation DFG is gratefully acknowledged for funding this research within the SFB-TR40 ``Technological foundations for the design of thermally and mechanically highly loaded components of future space transportation systems.''
Discrete Adjoint-Based Design for Unsteady Turbulent Flows On Dynamic Overset Unstructured Grids
Nielsen, Eric J.; Diskin, Boris
2012-01-01
A discrete adjoint-based design methodology for unsteady turbulent flows on three-dimensional dynamic overset unstructured grids is formulated, implemented, and verified. The methodology supports both compressible and incompressible flows and is amenable to massively parallel computing environments. The approach provides a general framework for performing highly efficient and discretely consistent sensitivity analysis for problems involving arbitrary combinations of overset unstructured grids which may be static, undergoing rigid or deforming motions, or any combination thereof. General parent-child motions are also accommodated, and the accuracy of the implementation is established using an independent verification based on a complex-variable approach. The methodology is used to demonstrate aerodynamic optimizations of a wind turbine geometry, a biologically-inspired flapping wing, and a complex helicopter configuration subject to trimming constraints. The objective function for each problem is successfully reduced and all specified constraints are satisfied.
Flow field analysis of a pentagonal-shaped bridge deck by unsteady RANS
Directory of Open Access Journals (Sweden)
Md. Naimul Haque
2016-01-01
Full Text Available Long-span cable-stayed bridges are susceptible to dynamic wind effects due to their inherent flexibility. The fluid flow around the bridge deck should be well understood for the efficient design of an aerodynamically stable long-span bridge system. In this work, the aerodynamic features of a pentagonal-shaped bridge deck are explored numerically. The analytical results are compared with past experimental work to assess the capability of two-dimensional unsteady RANS simulation for predicting the aerodynamic features of this type of deck. The influence of the bottom plate slope on aerodynamic response and flow features was investigated. By varying the Reynolds number (2 × 104 to 20 × 104 the aerodynamic behavior at high wind speeds is clarified.
Numerical studies of unsteady coherent structures and transport in two-dimensional flows
Energy Technology Data Exchange (ETDEWEB)
Hesthaven, J.S.
1995-08-01
The dynamics of unsteady two-dimensional coherent structures in various physical systems is studied through direct numerical solution of the dynamical equations using spectral methods. The relation between the Eulerian and the Lagrangian auto-correlation functions in two-dimensional homogeneous, isotropic turbulence is studied. A simple analytic expression for the Eulerian and Lagrangian auto-correlation function for the fluctuating velocity field is derived solely on the basis of the one-dimensional power spectrum. The long-time evolution of monopolar and dipolar vortices in anisotropic systems relevant for geophysics and plasma physics is studied by direct numerical solution. Transport properties and spatial reorganization of vortical structures are found to depend strongly on the initial conditions. Special attention is given to the dynamics of strong monopoles and the development of unsteady tripolar structures. The development of coherent structures in fluid flows, incompressible as well as compressible, is studied by novel numerical schemes. The emphasis is on the development of spectral methods sufficiently advanced as to allow for detailed and accurate studies of the self-organizing processes. (au) 1 ill., 94 refs.
Directory of Open Access Journals (Sweden)
N. Sandeep
2016-03-01
Full Text Available We analyzed the unsteady magnetohydrodynamic radiative flow and heat transfer characteristics of a dusty nanofluid over an exponentially permeable stretching surface in presence of volume fraction of dust and nano particles. We considered two types of nanofluids namely Cu-water and CuO-water embedded with conducting dust particles. The governing equations are transformed into nonlinear ordinary differential equations by using similarity transformation and solved numerically using Runge–Kutta based shooting technique. The effects of non-dimensional governing parameters namely magneticfield parameter, mass concentration of dust particles, fluid particle interaction parameter, volume fraction of dust particles, volume fraction of nano particles, unsteadiness parameter, exponential parameter, radiation parameter and suction/injection parameter on velocity profiles for fluid phase, dust phase and temperature profiles are discussed and presented through graphs. Also, friction factor and Nusselt numbers are discussed and presented for two dusty nanofluids separately. Comparisons of the present study were made with existing studies under some special assumptions. The present results have an excellent agreement with existing studies. Results indicated that the enhancement in fluid particle interaction increases the heat transfer rate and depreciates the wall friction. Also, radiation parameter has the tendency to increase the temperature profiles of the dusty nanofluid.
Unsteady 2D potential-flow forces and a thin variable geometry airfoil undergoing arbitrary motion
Energy Technology Data Exchange (ETDEWEB)
Gaunaa, M.
2006-07-15
In this report analytical expressions for the unsteady 2D force distribution on a variable geometry airfoil undergoing arbitrary motion are derived under the assumption of incompressible, irrotational, inviscid flow. The airfoil is represented by its camberline as in classic thin-airfoil theory, and the deflection of the airfoil is given by superposition of chordwise deflection mode shapes. It is shown from the expressions for the forces, that the influence from the shed vorticity in the wake is described by the same time-lag for all chordwise positions on the airfoil. This time-lag term can be approximated using an indicial function approach, making the practical calculation of the aerodynamic response numerically very efficient by use of Duhamel superposition. Furthermore, the indicial function expressions for the time-lag terms are formulated in their equivalent state-space form, allowing for use of the present theory in problems employing the eigenvalue approach, such as stability analysis. The analytical expressions for the forces simplify to all previously known steady and unsteady thin-airfoil solutions. Apart from the obvious applications within active load control/reduction, the current theory can be used for various applications which up to now have been possible only using much more computational costly methods. The propulsive performance of a soft heaving propulsor, and the influence of airfoil camberline elasticity on the flutter limit are two computational examples given in the report that highlight this feature. (au)
Energy Technology Data Exchange (ETDEWEB)
Kim, Nak-Geun; Lee, Kye-Bock [Chungbuk National University, Cheongju (Korea, Republic of); Cho, Yong [Korea Water Resources Corporation, Daejeon (Korea, Republic of)
2017-07-15
Numerical analysis on the flow induced vibration and flow characteristics in the water gate has been carried out by 2-dimensional unsteady CFD simulation when sea water flows into the port in the river. Effect of gate opening on the frequency and the mean velocity and the vortex shedding under the water gate were studied. The streamlines were compared for various gate openings. To get the frequency spectrum, Fourier transform should be performed. Spectral analysis of the excitation force signals permitted identification of the main characteristics of the interaction process. The results show that the sources of disturbed frequency are the vortex shedding from under the water gate. As the gate opening ratio increases, the predicted vibration frequency decreases. The bottom scouring occurs for large gate opening rather than smaller one. The unstable operation conditions can be estimated by using the CFD results and the Strouhal number results for various gate opening gaps.
International Nuclear Information System (INIS)
Kim, Nak-Geun; Lee, Kye-Bock; Cho, Yong
2017-01-01
Numerical analysis on the flow induced vibration and flow characteristics in the water gate has been carried out by 2-dimensional unsteady CFD simulation when sea water flows into the port in the river. Effect of gate opening on the frequency and the mean velocity and the vortex shedding under the water gate were studied. The streamlines were compared for various gate openings. To get the frequency spectrum, Fourier transform should be performed. Spectral analysis of the excitation force signals permitted identification of the main characteristics of the interaction process. The results show that the sources of disturbed frequency are the vortex shedding from under the water gate. As the gate opening ratio increases, the predicted vibration frequency decreases. The bottom scouring occurs for large gate opening rather than smaller one. The unstable operation conditions can be estimated by using the CFD results and the Strouhal number results for various gate opening gaps.
Directory of Open Access Journals (Sweden)
A. S. Laskin
2015-01-01
Full Text Available The article presents the results of numerical investigation of kinetic energy (KE loss and blading efficiency of the single-stage axial turbine under different operating conditions, characterized by the ratio u/C0. The calculations are performed by stationary (Stage method and nonstationary (Transient method methods using ANSYS CFX. The novelty of this work lies in the fact that the numerical simulation of steady and unsteady flows in a turbine stage is conducted, and the results are obtained to determine the loss of KE, both separately by the elements of the flow range and their total values, in the stage efficiency as well. The results obtained are compared with the calculated efficiency according to one-dimensional theory.To solve these problems was selected model of axial turbine stage with D/l = 13, blade profiles of rotor and stator of constant cross-section, similar to tested ones in inverted turbine when = 0.3. The degree of reactivity ρ = 0.27, the rotor speed was varied within the range 1000 ÷ 1800 rev/min.Results obtained allow us to draw the following conclusions:1. The level of averaged coefficients of total KE losses in the range of from 0.48 to 0.75 is from 18% to 21% when calculating by the Stage method and from 21% to 25% by the Transient one.2. The level of averaged coefficients of KE losses with the output speed of in the specified range is from 9% to 13%, and almost the same when in calculating by Stage and Transient methods.3. Levels of averaged coefficients of KE loss in blade tips (relative to the differential enthalpies per stage are changed in the range: from 4% to 3% (Stage and are stored to be equal to 5% (Transient; from 5% to 6% (Stage and from 6% to 8% (Transient.4. Coefficients of KE losses in blade tips GV and RB are higher in calculations of the model stage using the Transient method than the Stage one, respectively, by = 1.5 ÷ 2.5% and = 4 ÷ 5% of the absolute values. These are values to characterize the KE
International Nuclear Information System (INIS)
Michel, A.; Heinecke, E.; Decken, C.B. von der.
1986-01-01
Unsteady flow forces arising in heat exchangers with cross-flow may lead to serious vibrations of the tubes. These vibrations can destroy the tubes in the end supports or in the baffles, which would require expensive repairs. The flow forces reach unexpectedly by high values if the vibration of the tube intensifies these forces. To clear up this coupling mechanism the flow forces and the vibration amplitude were measured simultaneously in a staggered and in an inline tube bundle. Considering the tube as a one-mass oscillator excited by the flow force, the main parameters can be derived, i.e. dynamic pressure, reduced mass, eigenfrequency and damping. These parameters form a dimensionless model number describing the coherence of the vibration amplitude and the force coefficient. The validity of this number has been confirmed by varying the test conditions. With the aid of this model number, the expected force coefficient can be calculated and then using a finite-element program information can be obtained about mechanical tensions and the lifetime of the heat exchanger tubes. With this model number the results of other authors, who measured the vibration amplitude only, could be confirmed in good agreement. The experiments were carried out in air with Reynolds numbers 10 4 5 . (orig.) [de
Pratomo, Rizky Verdyanto; Widodo, Basuki; Adzkiya, Dieky
2017-12-01
Research about fluid flow was very interesting because have a lot of advantages and it can be applied in many aspects of life. The study on fluid flow which is now widely studied is on magnetohydrodynamic (MHD). Magnetohydrodynamic is a conductive and electrical in a magnetic field. This paper considers the effect of unsteady magnetic fields on the flow of magneto-hydrodynamic fluid on the boundary layer that flows past a sphere in micropolar fluid influenced by magnetic field. Our approach is as follows. First, we construct a mathematical model and then the system of equations obtained will be solved numerically using the Keller-Box scheme. Then the system is simulated to assess its effect on the fluid flow velocity profile and the profile of microrotation particles. The result of this research indicates, that when the magnetic parameters increase, then velocity profile increases. If material parameters increase, then velocity profile decreases and magnetic parameters increase for n = 0. For n = 0.5, if magnetic parameters increase, then microrotation profile decreases.
Lawless, Patrick B.; Fleeter, Sanford
1991-01-01
A mathematical model is developed to analyze the suppression of rotating stall in an incompressible flow centrifugal compressor with a vaned diffuser, thereby addressing the important need for centrifugal compressor rotating stall and surge control. In this model, the precursor to to instability is a weak rotating potential velocity perturbation in the inlet flow field that eventually develops into a finite disturbance. To suppress the growth of this potential disturbance, a rotating control vortical velocity disturbance is introduced into the impeller inlet flow. The effectiveness of this control is analyzed by matching the perturbation pressure in the compressor inlet and exit flow fields with a model for the unsteady behavior of the compressor. To demonstrate instability control, this model is then used to predict the control effectiveness for centrifugal compressor geometries based on a low speed research centrifugal compressor. These results indicate that reductions of 10 to 15 percent in the mean inlet flow coefficient at instability are possible with control waveforms of half the magnitude of the total disturbance at the inlet.
International Nuclear Information System (INIS)
Li, R N; Wang, H Y; Han, W; Shen, Z J; Ma, W
2013-01-01
The screw centrifugal pump is used as an object, and the unsteady numerical simulation of solid-liquid two-phase flow is carried out under different flow rate conditions in one circle by choosing the two-phase flow of sand and water as medium, using the software FLUENT based on the URANS equations, combining with sliding mesh method, and choosing the Mixture multiphase flow model and the SIMPLE algorithm. The results show that, with the flow rate increasing, the change trends for the pressure on volute outlet are almost constant, the fluctuation trends of the impeller axial force have a little change, the pressure and the axial force turn to decrease on the whole, the radial force gradually increases when the impeller maximum radius passes by half a cycle near the volute outlet, and the radial force gradually decreases when the maximum radius passes by the other half a cycle in a rotation cycle. The distributions of the solid particles are very uneven under a small flow rate condition on the face. The solid particles under a big flow rate condition are distributed more evenly than the ones under a small flow rate condition on the back. The theoretical basis and reference are provided for improving its working performance
Angelidis, Dionysios; Chawdhary, Saurabh; Sotiropoulos, Fotis
2016-11-01
A novel numerical method is developed for solving the 3D, unsteady, incompressible Navier-Stokes equations on locally refined fully unstructured Cartesian grids in domains with arbitrarily complex immersed boundaries. Owing to the utilization of the fractional step method on an unstructured Cartesian hybrid staggered/non-staggered grid layout, flux mismatch and pressure discontinuity issues are avoided and the divergence free constraint is inherently satisfied to machine zero. Auxiliary/hanging nodes are used to facilitate the discretization of the governing equations. The second-order accuracy of the solver is ensured by using multi-dimension Lagrange interpolation operators and appropriate differencing schemes at the interface of regions with different levels of refinement. The sharp interface immersed boundary method is augmented with local near-boundary refinement to handle arbitrarily complex boundaries. The discrete momentum equation is solved with the matrix free Newton-Krylov method and the Krylov-subspace method is employed to solve the Poisson equation. The second-order accuracy of the proposed method on unstructured Cartesian grids is demonstrated by solving the Poisson equation with a known analytical solution. A number of three-dimensional laminar flow simulations of increasing complexity illustrate the ability of the method to handle flows across a range of Reynolds numbers and flow regimes. Laminar steady and unsteady flows past a sphere and the oblique vortex shedding from a circular cylinder mounted between two end walls demonstrate the accuracy, the efficiency and the smooth transition of scales and coherent structures across refinement levels. Large-eddy simulation (LES) past a miniature wind turbine rotor, parameterized using the actuator line approach, indicates the ability of the fully unstructured solver to simulate complex turbulent flows. Finally, a geometry resolving LES of turbulent flow past a complete hydrokinetic turbine illustrates
Similarity solutions for unsteady free-convection flow from a continuous moving vertical surface
Abd-El-Malek, Mina B.; Kassem, Magda M.; Mekky, Mohammad L.
2004-03-01
The transformation group theoretic approach is applied to present an analysis of the problem of unsteady free convection flow over a continuous moving vertical sheet in an ambient fluid. The thermal boundary layer induced within a vertical semi-infinite layer of Boussinseq fluid by a constant heated bounding plate. The application of two-parameter groups reduces the number of independent variables by two, and consequently the system of governing partial differential equations with the boundary conditions reduces to a system of ordinary differential equations with appropriate boundary conditions. The obtained ordinary differential equations are solved analytically for the temperature and numerically for the velocity using the shooting method. Effect of Prandtl number on the thermal boundary-layer and velocity boundary-layer are studied and plotted in curves.
Unsteady free convection flow of a micropolar fluid with Newtonian heating: Closed form solution
Directory of Open Access Journals (Sweden)
Hussanan Abid
2017-01-01
Full Text Available This article investigates the unsteady free convection flow of a micropolar fluid over a vertical plate oscillating in its own plane with Newtonian heating condition. The problem is modelled in terms of partial differential equations with some physical conditions. Closed form solutions in terms of exponential and complementary error functions of Gauss are obtained by using the Laplace transform technique. They satisfy the governing equations and impose boundary and initial conditions. The present solution in the absence of microrotation reduces to well-known solutions of Newtonian fluid. Graphs are plotted to study the effects of various physical parameters on velocity and microrotation. Numerical results for skin friction and wall couple stress is computed in tables. Apart from the engineering point of view, the present article has strong advantage over the published literature as the exact solutions obtained here can be used as a benchmark for comparison with numerical/ approximate solutions and experimental data.
Unsteady cavity flow around a rectangular cylinder; Kakuchu mawari no hiteijo cavitation nagare
Energy Technology Data Exchange (ETDEWEB)
Takahashi, T.; Kaga, T.; Ota, T. [Tohoku University, Sendai (Japan). Faculty of Engineering; Mori, T. [Hachinohe Institute of Technology, Aomori (Japan)
1995-08-25
Unsteady cavity flow around a rectangular cylinder was observed using a high-speed camera. To clarify the correlation between the cavity behavior and fluid dynamic characteristics in the transitional region and supercavitation, fluctuating forces and surface pressures on the cylinder surface were recorded simultaneously. The tested cylinder has a critical width-to-height ration 2.8, in which the shear layer separated from the leading edge intermittently reattaches near the trailing edge. Bubbly cloud originating from the separated region near the leading edge causes fluctuation of cavity termination and induces large oscillations of fluid forces and pressures. As the cavitation number decreases, the low-frequency fluctuation of the cavity developing downstream of the rear surface increases in the fluid dynamic behavior. 24 refs., 12 figs.
An investigation of noise produced by unsteady gas flow through silencer elements
Mawhinney, Graeme Hugh
This thesis presents an investigation of the noise produced by unsteady gas flow through silencer elements. The central aim of the research project was to produce a tool for assistance in the design of the exhaust systems of diesel powered electrical generator sets, with the modelling techniques developed having a much wider application in reciprocating internal combustion engine exhaust systems. An automotive cylinder head was incorporated in a purpose built test rig to supply exhaust pulses, typical of those found in the exhaust system of four stroke diesel engines, to various experimental exhaust systems. Exhaust silencer elements evaluated included expansion, re- entrant, concentric tube resonator and absorptive elements. Measurements taken on the test rig included, unsteady superposition pressure in the exhaust ducting, cyclically averaged mass flow rate through the system and exhaust noise levels radiated into a semi-anechoic measurement chamber. The entire test rig was modelled using the 1D finite volume method developed previously developed at Queen's University Belfast. Various boundary conditions, developed over the years, were used to model the various silencer elements being evaluated. The 1D gas dynamic simulation thus estimated the mass flux history at the open end of the exhaust system. The mass flux history was then broken into its harmonic components and an acoustic radiation model was developed to model the sound pressure level produced by an acoustic monopole over a reflecting plane. The accuracy of the simulation technique was evaluated by correlation of measured and simulated superposition pressure and noise data. In general correlation of superposition pressure was excellent for all of the silencer elements tested. Predicted sound pressure level radiated from the open end of the exhaust tailpipe was seen to be accurate in the 100 Hz to 1 kHz frequency range for all of the silencer elements tested.
Hydrodynamic pressure sensing with an artificial lateral line in steady and unsteady flows
International Nuclear Information System (INIS)
Venturelli, Roberto; Akanyeti, Otar; Visentin, Francesco; Fiorini, Paolo; Ježov, Jaas; Toming, Gert; Kruusmaa, Maarja; Chambers, Lily D; Brown, Jennifer; Megill, William M
2012-01-01
With the overall goal being a better understanding of the sensing environment from the local perspective of a situated agent, we studied uniform flows and Kármán vortex streets in a frame of reference relevant to a fish or swimming robot. We visualized each flow regime with digital particle image velocimetry and then took local measurements using a rigid body with laterally distributed parallel pressure sensor arrays. Time and frequency domain methods were used to characterize hydrodynamically relevant scenarios in steady and unsteady flows for control applications. Here we report that a distributed pressure sensing mechanism has the capability to discriminate Kármán vortex streets from uniform flows, and determine the orientation and position of the platform with respect to the incoming flow and the centre axis of the Kármán vortex street. It also enables the computation of hydrodynamic features which may be relevant for a robot while interacting with the flow, such as vortex shedding frequency, vortex travelling speed and downstream distance between vortices. A Kármán vortex street was distinguished in this study from uniform flows by analysing the magnitude of fluctuations present in the sensor measurements and the number of sensors detecting the same dominant frequency. In the Kármán vortex street the turbulence intensity was 30% higher than that in the uniform flow and the sensors collectively sensed the vortex shedding frequency as the dominant frequency. The position and orientation of the sensor platform were determined via a comparative analysis between laterally distributed sensor arrays; the vortex travelling speed was estimated via a cross-correlation analysis among the sensors. (paper)
Unsteady Magnetized Flow and Heat Transfer of a Viscoelastic fluid over a Stretching Surface
Ghosh, Sushil Kumar
2017-12-01
This paper is to study the flow of heated ferro-fluid over a stretching sheet under the influence of magnetic field. The fluid considered in the present investigation is a mixture of blood as well as fluid-dispersed magnetic nano particles and under this context blood is found to be the appropriate choice of viscoelastic, Walter's B fluid. The objective of the present work is to study the effect of various parameters found in the mathematical analysis. Taking into account the blood has zero electrical conductivity, magnetization effect has been considered in the governing equation of the present study with the use of ferro-fluid dynamics principle. By introducing appropriate non-dimensional variables into the governing equations of unsteady two-dimensional flow of viscoelastic fluid with heat transfer are converted to a set of ordinary differential equations with appropriate boundary conditions. Newton's linearization technique has been employed for the solution of non-linear ordinary differential equations. Important results found in the present investigation are the substantial influence of ferro-magnetic parameter, Prandlt number and the parameter associated with the thermal conductivity on the flow and heat transfer. It is observed that the presence of magnetic dipole essentially reduces the flow velocity in the vertical direction and that helps to damage the cancer cells in the tumor region.
Studies of the process of an unsteady formation of hard nitride coatings in an arc plasma flow
International Nuclear Information System (INIS)
Zake, M.
1996-01-01
The kinetic studies of an unsteady formation of hard ZrN and TiN coatings on the surface of metallic (Zr, Ti) samples in an Ar-N plasma flow are carried out. The obtained result is that at the initial stage of an unsteady heating of titanium samples nitrogen atoms penetrate into metal lattice and form interstitial compounds of hard nitrogen solutions in α-phase of Ti. This process is followed by a growth of thin surface layers of titanium nitrides with subsequent changes of surface radiance of exposed samples. Unsteady formation of ZrN is a similar two-stage process which includes the ZrN film growth and formation of a α-hard solution with subsequent changes of total normal emissivity of the surface. (author). 1 ref., 1 fig
Energy Technology Data Exchange (ETDEWEB)
Shaha, Poly Rani; Poddar, Nayan Kumar; Mondal, Rabindra Nath, E-mail: rnmondal71@yahoo.com [Department of Mathematics, Jagannath University, Dhaka-1100 (Bangladesh); Rudro, Sajal Kanti [Department of Mathematics, Notredame Colleage, Motijheel, Dhaka (Bangladesh)
2016-07-12
The study of flows through coiled ducts and channels has attracted considerable attention not only because of their ample applications in Chemical, Mechanical, Civil, Nuclear and Biomechanical engineering but also because of their ample applications in other areas, such as blood flow in the veins and arteries of human and other animals. In this paper, a numerical study is presented for the fully developed two-dimensional flow of viscous incompressible fluid through a loosely coiled rectangular duct of large aspect ratio. Numerical calculations are carried out by using a spectral method, and covering a wide range of the Dean number, Dn, for two types of curvatures of the duct. The main concern of the present study is to find out effects of curvature as well as formation of secondary vortices on unsteady solutions whether the unsteady flow is steady-state, periodic, multi-periodic or chaotic, if Dn is increased. Time evolution calculations as well as their phase spaces are performed with a view to study the non-linear behavior of the unsteady solutions, and it is found that the steady-state flow turns into chaotic flow through various flow instabilities, if Dn is increased no matter what the curvature is. It is found that the unsteady flow is a steady-state solution for small Dn’s and oscillates periodically or non-periodically (chaotic) between two- and twelve-vortex solutions, if Dn is increased. It is also found that the chaotic solution is weak for small Dn’s but strong as Dn becomes large. Axial flow distribution is also investigated and shown in contour plots.
International Nuclear Information System (INIS)
Shaha, Poly Rani; Poddar, Nayan Kumar; Mondal, Rabindra Nath; Rudro, Sajal Kanti
2016-01-01
The study of flows through coiled ducts and channels has attracted considerable attention not only because of their ample applications in Chemical, Mechanical, Civil, Nuclear and Biomechanical engineering but also because of their ample applications in other areas, such as blood flow in the veins and arteries of human and other animals. In this paper, a numerical study is presented for the fully developed two-dimensional flow of viscous incompressible fluid through a loosely coiled rectangular duct of large aspect ratio. Numerical calculations are carried out by using a spectral method, and covering a wide range of the Dean number, Dn, for two types of curvatures of the duct. The main concern of the present study is to find out effects of curvature as well as formation of secondary vortices on unsteady solutions whether the unsteady flow is steady-state, periodic, multi-periodic or chaotic, if Dn is increased. Time evolution calculations as well as their phase spaces are performed with a view to study the non-linear behavior of the unsteady solutions, and it is found that the steady-state flow turns into chaotic flow through various flow instabilities, if Dn is increased no matter what the curvature is. It is found that the unsteady flow is a steady-state solution for small Dn’s and oscillates periodically or non-periodically (chaotic) between two- and twelve-vortex solutions, if Dn is increased. It is also found that the chaotic solution is weak for small Dn’s but strong as Dn becomes large. Axial flow distribution is also investigated and shown in contour plots.
Water Flow Testing and Unsteady Pressure Analysis of a Two-Bladed Liquid Oxidizer Pump Inducer
Schwarz, Jordan B.; Mulder, Andrew; Zoladz, Thomas
2011-01-01
The unsteady fluid dynamic performance of a cavitating two-bladed oxidizer turbopump inducer was characterized through sub-scale water flow testing. While testing a novel inlet duct design that included a cavitation suppression groove, unusual high-frequency pressure oscillations were observed. With potential implications for inducer blade loads, these high-frequency components were analyzed extensively in order to understand their origins and impacts to blade loading. Water flow testing provides a technique to determine pump performance without the costs and hazards associated with handling cryogenic propellants. Water has a similar density and Reynolds number to liquid oxygen. In a 70%-scale water flow test, the inducer-only pump performance was evaluated. Over a range of flow rates, the pump inlet pressure was gradually reduced, causing the flow to cavitate near the pump inducer. A nominal, smooth inducer inlet was tested, followed by an inlet duct with a circumferential groove designed to suppress cavitation. A subsequent 52%-scale water flow test in another facility evaluated the combined inducer-impeller pump performance. With the nominal inlet design, the inducer showed traditional cavitation and surge characteristics. Significant bearing loads were created by large side loads on the inducer during synchronous cavitation. The grooved inlet successfully mitigated these loads by greatly reducing synchronous cavitation, however high-frequency pressure oscillations were observed over a range of frequencies. Analytical signal processing techniques showed these oscillations to be created by a rotating, multi-celled train of pressure pulses, and subsequent CFD analysis suggested that such pulses could be created by the interaction of rotating inducer blades with fluid trapped in a cavitation suppression groove. Despite their relatively low amplitude, these high-frequency pressure oscillations posed a design concern due to their sensitivity to flow conditions and
Pyrometric fuel particle measurements in pressurised reactors
Energy Technology Data Exchange (ETDEWEB)
Hernberg, R.; Joutsenoja, T. [Tampere Univ. of Technology (Finland)
1996-12-01
A fiberoptic two-colour pyrometric technique for fuel particle temperature and size measurement is modified and applied to three pressurized reactors of different type in Finland, Germany and France. A modification of the pyrometric method for simultaneous in situ measurement of the temperature and size of individual pulverized coal particles at the pressurized entrained flow reactor in Jyvaeskylae was developed and several series of measurements were made. In Orleans a fiberoptic pyrometric device was installed to a pressurised thermogravimetric reactor and the two-colour temperatures of fuel samples were measured. Some results of these measurements are presented. The project belongs to EU`s Joule 2 extension research programme. (author)
Tumuklu, Ozgur; Levin, Deborah A.; Theofilis, Vassilis
2018-04-01
Shock-dominated hypersonic laminar flows over a double cone are investigated using time accurate direct simulation Monte Carlo combined with the residuals algorithm for unit Reynolds numbers gradually increasing from 9.35 × 104 to 3.74 × 105 m-1 at a Mach number of about 16. The main flow features, such as the strong bow-shock, location of the separation shock, the triple point, and the entire laminar separated region, show a time-dependent behavior. Although the separation shock angle is found to be similar for all Re numbers, the effects of Reynolds number on the structure and extent of the separation region are profound. As the Reynolds number is increased, larger pressure values in the under-expanded jet region due to strong shock interactions form more prominent λ-shocklets in the supersonic region between two contact surfaces. Likewise, the surface parameters, especially on the second cone surface, show a strong dependence on the Reynolds number, with skin friction, pressure, and surface heating rates increasing and velocity slip and temperature jump values decreasing for increasing Re number. A Kelvin-Helmholtz instability arising at the shear layer results in an unsteady flow for the highest Reynolds number. These findings suggest that consideration of experimental measurement times is important when it comes to determining the steady state surface parameters even for a relatively simple double cone geometry at moderately large Reynolds numbers.
Experimental investigation of the unsteady one-phase flow through perforated plates
International Nuclear Information System (INIS)
Casadei, F.
1982-07-01
The flow of the coolant through the perforated dip-plate during a hypothetical core-disruptive accident in a sodium-cooled fast breeder reactor was simulated in a one-dimensional model. Several experiments with water as fluid and with various perforation ratios of the dip-plate and different initial heights of the fluid head over the dip plate were run. The pressure drop through the dip-plate and the forces acting on the dip-plate and on the upper plug of the reactor vessel in a wide range of the Reynolds and Strouhal numbers were measured. The flow pattern downstreams the perforated plate was filmed with high-speed cameras. The resistance coefficients for the unsteady flow of the coolant through the perforated plate were obtained as a function of the acceleration. The forces acting on the upper plug and their time integral were compared with those acting on the dip-plate. Finally, using the high-speed film pictures the formation of fluid jets downstream the dip-plate was investigated. (orig.) [de
Energy Technology Data Exchange (ETDEWEB)
Lok, Y.Y. [Center for Academic Services, Kolej Universiti Teknikal Kebangsaan Malaysia, 75450 Ayer Keroh, Melaka (Malaysia); Amin, N. [Department of Mathematics, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor (Malaysia); Pop, I. [Faculty of Mathematics, University of Cluj, R-3400 Cluj, CP 253 (Romania)
2006-12-15
The unsteady mixed convection boundary-layer flow of a micro-polar fluid near the region of the stagnation point on a double-infinite vertical flat plate is studied. It is assumed that the unsteadiness is caused by the impulsive motion of the free stream velocity and by sudden increase or sudden decrease in the surface temperature from the uniform ambient temperature. The problem is reduced to a system of non-dimensional partial differential equations, which is solved numerically using the Keller-box method. This method may present well-behaved solutions for the transient (small time) solution and those of the steady-state flow (large time) solution. It was found that there is a smooth transition from the small-time solution (initial unsteady-state flow) to the large-time solution (final steady-state flow). Further, it is shown that for both assisting and opposing cases and a fixed value of the Prandtl number, the reduced steady-state skin friction and the steady-state heat transfer from the wall (or Nusselt number) decrease with the increase of the material parameter. On the other hand, it is shown that with the increase of the Prandtl number and a fixed value of the material parameter, the reduced steady-state skin friction decreases when the flow is assisting and it increases when the flow is opposing. (author)
Di Nucci, Carmine
2018-05-01
This note examines the two-dimensional unsteady isothermal free surface flow of an incompressible fluid in a non-deformable, homogeneous, isotropic, and saturated porous medium (with zero recharge and neglecting capillary effects). Coupling a Boussinesq-type model for nonlinear water waves with Darcy's law, the two-dimensional flow problem is solved using one-dimensional model equations including vertical effects and seepage face. In order to take into account the seepage face development, the system equations (given by the continuity and momentum equations) are completed by an integral relation (deduced from the Cauchy theorem). After testing the model against data sets available in the literature, some numerical simulations, concerning the unsteady flow through a rectangular dam (with an impermeable horizontal bottom), are presented and discussed.
Ramesh, Kiran; Granlund, Kenneth; Ol, Michael V.; Gopalarathnam, Ashok; Edwards, Jack R.
2018-04-01
A leading-edge suction parameter (LESP) that is derived from potential flow theory as a measure of suction at the airfoil leading edge is used to study initiation of leading-edge vortex (LEV) formation in this article. The LESP hypothesis is presented, which states that LEV formation in unsteady flows for specified airfoil shape and Reynolds number occurs at a critical constant value of LESP, regardless of motion kinematics. This hypothesis is tested and validated against a large set of data from CFD and experimental studies of flows with LEV formation. The hypothesis is seen to hold except in cases with slow-rate kinematics which evince significant trailing-edge separation (which refers here to separation leading to reversed flow on the aft portion of the upper surface), thereby establishing the envelope of validity. The implication is that the critical LESP value for an airfoil-Reynolds number combination may be calibrated using CFD or experiment for just one motion and then employed to predict LEV initiation for any other (fast-rate) motion. It is also shown that the LESP concept may be used in an inverse mode to generate motion kinematics that would either prevent LEV formation or trigger the same as per aerodynamic requirements.
Development of a Robust and Efficient Parallel Solver for Unsteady Turbomachinery Flows
West, Jeff; Wright, Jeffrey; Thakur, Siddharth; Luke, Ed; Grinstead, Nathan
2012-01-01
The traditional design and analysis practice for advanced propulsion systems relies heavily on expensive full-scale prototype development and testing. Over the past decade, use of high-fidelity analysis and design tools such as CFD early in the product development cycle has been identified as one way to alleviate testing costs and to develop these devices better, faster and cheaper. In the design of advanced propulsion systems, CFD plays a major role in defining the required performance over the entire flight regime, as well as in testing the sensitivity of the design to the different modes of operation. Increased emphasis is being placed on developing and applying CFD models to simulate the flow field environments and performance of advanced propulsion systems. This necessitates the development of next generation computational tools which can be used effectively and reliably in a design environment. The turbomachinery simulation capability presented here is being developed in a computational tool called Loci-STREAM [1]. It integrates proven numerical methods for generalized grids and state-of-the-art physical models in a novel rule-based programming framework called Loci [2] which allows: (a) seamless integration of multidisciplinary physics in a unified manner, and (b) automatic handling of massively parallel computing. The objective is to be able to routinely simulate problems involving complex geometries requiring large unstructured grids and complex multidisciplinary physics. An immediate application of interest is simulation of unsteady flows in rocket turbopumps, particularly in cryogenic liquid rocket engines. The key components of the overall methodology presented in this paper are the following: (a) high fidelity unsteady simulation capability based on Detached Eddy Simulation (DES) in conjunction with second-order temporal discretization, (b) compliance with Geometric Conservation Law (GCL) in order to maintain conservative property on moving meshes for
Dholey, S.
2018-04-01
In this paper, we have investigated numerically the laminar unsteady separated stagnation-point flow and heat transfer of a viscous fluid over a moving flat surface in the presence of a time dependent free stream velocity which causes the unsteadiness of this flow problem. The plate is assumed to move in the same or opposite direction of the free stream velocity. The flow is therefore governed by the velocity ratio parameter λ (ratio of the plate velocity to the free stream velocity) and the unsteadiness parameter β. When the plate surface moves in the same direction of the free stream velocity (i.e., when λ > 0), the solution of this flow problem continues for any given value of β. On the other hand, when they move in opposite directions (i.e., when λ heat transfer analysis is that for a given value of λ(= 0), first the heat transfer rate increases with the increase of the Prandtl number Pr and after attaining a maximum value, it decreases and finally tends to be zero for large values of Pr depending upon the values of β > 0. On the contrary, for a given value of β(≤ 0), the rate of heat transfer increases consistently with the increase of Pr.
International Nuclear Information System (INIS)
Gedik, Engin; Recebli, Ziyaddin; Kurt, Hueseyin; Kecebas, Ali
2012-01-01
The unsteady viscous incompressible and electrically conducting of two-phase fluid flow in circular pipes with external magnetic and electrical field is considered in this present study. Effects of both uniform transverse external magnetic and electrical fields applied perpendicular to the fluid and each other on the two-phase (solid/liquid) unsteady flow is investigated numerically. While iron powders are being used as the first phase of two-phase fluid, pure water was used as the second phase. The system of the derived governing equations, which are based on the Navier-Stokes equations including Maxwell equations, are solved numerically by using Pdex4 function on the Matlab for both phases. The originality of this study is that, in addition to magnetic field, the effect of electrical field on two-phase unsteady fluids is being examined. The magnetic field which is applied on flow decreases the velocity of both phases, whereas the electrical field applied along with magnetic field acted to increase and decrease the velocity values depending on the direction of electrical field. Electrical field alone did not display any impact on two-phase flow. On the other hand, analytical and numerical results are compared and favorable agreements have been obtained. (authors)
Directory of Open Access Journals (Sweden)
A. M. Berta
2010-05-01
Full Text Available During the floods, the effects of sediment transport in river beds are particulary significant and can be studied through the evolution of the water-sediment layer which moves in the lower part of a flow, named "moving layer". Moving layer variations along rivers lead to depositions and erosions and are typically unsteady, but are often tackled with expressions developed for steady (equilibrium conditions. In this paper, we develop an expression for the moving layer in unsteady conditions and calibrate it with experimental data. During laboratory tests, we have in fact reproduced a rapidly changing unsteady flow by the erosion of a granular steep slope. Results have shown a clear tendency of the moving layer, for fixed discharges, toward equilibrium conditions. Knowing the equilibrium achievement has presented many difficulties, being influenced by the choice of the equilibrium expression and moreover by the estimation of the parameters involved (for example friction angle. Since we used only data relevant to hyper-concentrated mono-dimensional flows for the calibration – occurring for slope gradients in the range 0.03–0.20 – our model can be applied both on open channels and on embankments/dams, providing that the flows can be modelled as mono-dimensional, and that slopes and applied shear stress levels fall within the considered ranges.
Pyrometric fuel particle measurements in pressurised reactors
Energy Technology Data Exchange (ETDEWEB)
Hernberg, R; Joutsenoja, T [Tampere Univ. of Technology (Finland)
1997-10-01
A fibre-optic two-colour pyrometric technique for fuel particle temperature and size measurement is modified and applied to three pressurised reactors of different type in Finland, Germany and France. A modification of the pyrometric method for simultaneous in situ measurement of the temperature and size of individual pulverised coal particles at the pressurised entrained flow reactor of VTT Energy in Jyvaeskylae was developed and several series of measurements were made in order to study the effects of oxygen concentration (3-30 vol%) and pressure (0.2-1.0 MPa) on the particle temperature. The fuels used in the experiments were Westerholt, Polish and Goettelborn hvb coals, Gardanne lignite and Niederberg anthracite. The initial nominal fuel particle size varied in the experiments from 70 to 250 ,{mu}m and the gas temperature was typically 1173 K. For the anthracite also the effects of gas temperature (1073-1423K) and CO{sub 2} concentration (6-80 vol%) were studied. In Orleans a fibreoptic pyrometric device was installed to a pressurised thermogravimetric reactor of CNRS and the two-colour temperatures of fuel samples were measured. The fuel in the experiments was pulverised Goettelborn char. The reliability of optical temperature measurement in this particular application was analysed. In Essen a fibre-optic pyrometric technique that is capable to measure bed and fuel particle temperatures was applied to an atmospheric fluidised bed reactor of DMT. The effects of oxygen concentration (3-8 vol%) and bed temperature (1123-1193 K) on the fuel particle temperature were studied. The fuels in these were Westerholt coal and char and EBV-coal. Some results of these measurements are presented. The project belonged to EU`s Joule 2 extension research programme (contract JOU2-CT93-0331). (orig.)
Characterisation of fuels for advanced pressurised combustion
Energy Technology Data Exchange (ETDEWEB)
Zevenhoven, R; Hupa, M; Backman, P; Forssen, M; Karlsson, M; Kullberg, M; Sorvari, V; Uusikartano, T [Aabo Akademi, Turku (Finland). Combustion Chemistry Research Group; Nurk, M [Tallinskij Politekhnicheskij Inst., Tallinn (Estonia)
1997-10-01
The objective of the research was to determine a set of fuel characteristics which quantify the behaviour of a fuel in a typical pressurised combustor or gasifier environment, especially in hybrid processes such as second generation PFBC. One specific aspect was to cover a wide range of fuels, including several coal types and several grades of peat and biomasses: 7 types of coal, 2 types of peat, 2 types of wood, 2 types of black liquor, Estonian oil shale and Venezuelan Orimulsion were studied. The laboratory facilities used are a pressurised thermogravimetric reactor (PTGR), a pressurised grid heater (PGH) and an atmospheric entrained flow quartz tube reactor, with gas analysis, which can be operated as a fixed bed reactor. A major part of the work was related to fuel devolatilisation in the PGH and sequential devolatilisation and char gasification (with carbon dioxide or steam) in the PTGR. The final part of that work is reported here, with the combustion of Estonian oil shale at AFBC or PFBC conditions as additional subject. Devolatilisation of the fuels at atmospheric pressure in nitrogen while monitoring gaseous exhausts, followed by ultimate analysis of the chars has been reported earlier. Here, results on the analysis of the reduction of NO (with and without CO) on chars at atmospheric pressure in a fixed bed reactor are reported. Finally, a comparison is given between experimental results and direct numerical simulation with several computer codes, i.e. PyroSim, developed at TU Graz, Austria, and the codes Partikkeli, Pisara and Cogas, which were provided by VTT Energy, Jyvaeskylae
Directory of Open Access Journals (Sweden)
Yonghui Xie
2013-01-01
Full Text Available Air turbines are widely used to convert kinetic energy into power output in power engineering. The unsteady performance of air turbines with partial admission not only influences the aerodynamic performance and thermodynamic efficiency of turbine but also generates strong excitation force on blades to impair the turbine safely operating. Based on three-dimensional viscous compressible Navier-stokes equations, the present study employs RNG (Renormalization group k-ε turbulence model with finite volume discretization on air turbine with partial admission. Numerical models of four different admission rates with full annulus are built and analyzed via CFD (computational fluid dynamics modeling unsteady flows. Results indicate that the unsteady time-averaged isentropic efficiency is lower than the steady isentropic efficiency, and this difference rises as unsteady isentropic efficiency fluctuates stronger when the admission rate is reduced. The rotor axial and tangential forces with time are provided for all four admission rates. The low frequency excitation forces generated by partial admission are extraordinarily higher than the high frequency excitation forces by stator wakes.
Directory of Open Access Journals (Sweden)
Hyun Ju Jung
2009-12-01
Full Text Available The two-dimensional unsteady flow around a vertical axis turbine for tidal stream energy conversion was investigated using a computational fluid dynamics tool solving the Reynolds-Averaged Navier-Stokes equations. The geometry of the turbine blade section was NACA653-018 airfoil. The computational analysis was done at several different angles of attack and the results were compared with the corresponding experimental data for validation and calibration. Simulations were then carried out for the two-dimensional cross section of a vertical axis turbine. The simulation results demonstrated the usefulness of the method for the typical unsteady flows around vertical axis turbines. The optimum turbine efficiency was achieved for carefully selected combinations of the number of blades and tip speed ratios.
Alesbe, Israa; Abdel-Maksoud, Moustafa; Aljabair, Sattar
2017-06-01
Environmental effects have an important influence on Offshore Wind Turbine (OWT) power generation efficiency and the structural stability of such turbines. In this study, we use an in-house Boundary Element (BEM)— panMARE code—to simulate the unsteady flow behavior of a full OWT with various combinations of aerodynamic and hydrodynamic loads in the time domain. This code is implemented to simulate potential flows for different applications and is based on a three-dimensional first-order panel method. Three different OWT configurations consisting of a generic 5 MW NREL rotor with three different types of foundations (Monopile, Tripod, and Jacket) are investigated. These three configurations are analyzed using the RANSE solver which is carried out using ANSYS CFX for validating the corresponding results. The simulations are performed under the same environmental atmospheric wind shear and rotor angular velocity, and the wave properties are wave height of 4 m and wave period of 7.16 s. In the present work, wave environmental effects were investigated firstly for the two solvers, and good agreement is achieved. Moreover, pressure distribution in each OWT case is presented, including detailed information about local flow fields. The time history of the forces at inflow direction and its moments around the mudline at each OWT part are presented in a dimensionless form with respect to the mean value of the last three loads and the moment amplitudes obtained from the BEM code, where the contribution of rotor force is lower in the tripod case and higher in the jacket case and the calculated hydrodynamic load that effect on jacket foundation type is lower than other two cases.
Institute of Scientific and Technical Information of China (English)
Israa Alesbe; Moustafa Abdel-Maksoud; Sattar Aljabair
2017-01-01
Environmental effects have an important influence on Offshore Wind Turbine (OWT) power generation efficiency and the structural stability of such turbines.In this study,we use an in-house Boundary Element (BEM)-panMARE code-to simulate the unsteady flow behavior of a full OWT with various combinations of aerodynamic and hydrodynamic loads in the time domain.This code is implemented to simulate potential flows for different applications and is based on a three-dimensional first-order panel method.Three different OWT configurations consisting of a generic 5 MW NREL rotor with three different types of foundations (Monopile,Tripod,and Jacket) are investigated.These three configurations are analyzed using the RANSE solver which is carried out using ANSYS CFX for validating the corresponding results.The simulations are performed under the same environmental atmospheric wind shear and rotor angular velocity,and the wave properties are wave height of 4 m and wave period of 7.16 s.In the present work,wave environmental effects were investigated firstly for the two solvers,and good agreement is achieved.Moreover,pressure distribution in each OWT case is presented,including detailed information about local flow fields.The time history of the forces at inflow direction and its moments around the mudline at each OWT part are presented in a dimensionless form with respect to the mean value of the last three loads and the moment amplitudes obtained from the BEM code,where the contribution of rotor force is lower in the tripod case and higher in the jacket case and the calculated hydrodynamic load that effect on jacket foundation type is lower than other two cases.
ali shokrgozar abbasi; Asghar Baradaran Rahimi; Hamidreza Mozayeni
2016-01-01
General formulation and solution of Navier-Stokes and energy equations are sought in the study of threedimensional axisymmetric unsteady stagnation-point flow and heat transfer impinging on a flat plate when the plate is moving with variable velocity and acceleration towards the main stream or away from it. As an application, among others, this accelerated plate can be assumed as a solidification front which is being formed with variable velocity. An external fluid, along z - directi...
Energy Technology Data Exchange (ETDEWEB)
Isa, Sharena Mohamad; Ali, Anati [Department of Mathematical Sciences, Faculty of Science Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia sharena-ina@yahoo.com, anati@utm.my (Malaysia)
2015-10-22
In this paper, the hydromagnetic flow of dusty fluid over a vertical stretching sheet with thermal radiation is investigated. The governing partial differential equations are reduced to nonlinear ordinary differential equations using similarity transformation. These nonlinear ordinary differential equations are solved numerically using Runge-Kutta Fehlberg fourth-fifth order method (RKF45 Method). The behavior of velocity and temperature profiles of hydromagnetic fluid flow of dusty fluid is analyzed and discussed for different parameters of interest such as unsteady parameter, fluid-particle interaction parameter, the magnetic parameter, radiation parameter and Prandtl number on the flow.
Unsteady convection flow and heat transfer over a vertical stretching surface.
Cai, Wenli; Su, Ning; Liu, Xiangdong
2014-01-01
This paper investigates the effect of thermal radiation on unsteady convection flow and heat transfer over a vertical permeable stretching surface in porous medium, where the effects of temperature dependent viscosity and thermal conductivity are also considered. By using a similarity transformation, the governing time-dependent boundary layer equations for momentum and thermal energy are first transformed into coupled, non-linear ordinary differential equations with variable coefficients. Numerical solutions to these equations subject to appropriate boundary conditions are obtained by the numerical shooting technique with fourth-fifth order Runge-Kutta scheme. Numerical results show that as viscosity variation parameter increases both the absolute value of the surface friction coefficient and the absolute value of the surface temperature gradient increase whereas the temperature decreases slightly. With the increase of viscosity variation parameter, the velocity decreases near the sheet surface but increases far away from the surface of the sheet in the boundary layer. The increase in permeability parameter leads to the decrease in both the temperature and the absolute value of the surface friction coefficient, and the increase in both the velocity and the absolute value of the surface temperature gradient.
Directory of Open Access Journals (Sweden)
Khan A.
2017-12-01
Full Text Available An exact solution and analysis of an initial unsteady two dimensional free convection flow, heat and mass transfer in the presence of thermal radiation along an infinite fixed vertical plate when the plate temperature is instantaneously raised, is presented. The fluid considered is a gray, absorbing emitting radiation but a nonscattering medium. Three cases have been discussed, in particular, namely, (i when, the plate temperature is instantaneously raised to a higher constant value, (ii when, the plate temperature varies linearly with time and (iii when, the plate temperature varies non-linearly with time. A close form general solution for all the cases has been obtained in terms of repeated integrals of error functions. In two particular cases, the solutions in terms of the repeated integrals of error functions have been further simplified to forms containing only error functions. It is observed that for an increase in the radiation parameter N or a decrease in the Grashof number Gr or Gm, there is a fall in the velocity or temperature, but compared to the no radiation case or no diffusing species, there is a rise in the velocity and temperature of the fluid.
International Nuclear Information System (INIS)
Chatterjee, Dipankar; Biswas, Gautam; Amiroudine, Sakir
2009-01-01
This paper presents the unsteady laminar forced convection heat transfer from a row of five isothermal square cylinders placed in a side-by-side arrangement at a Reynolds number of 150. The numerical simulations are performed using a finite volume code based on the PISO algorithm in a collocated grid system. Special attention is paid to investigate the effect of the spacing between the cylinders on the overall transport processes for the separation ratios (spacing to size ratio) between 0.2 and 10. No significant interaction between the wakes is observed for spacing greater than four times the diameter at this Reynolds number. However, at smaller spacing, the wakes interact in a complicated manner resulting different thermo-hydrodynamic regimes. The vortex structures and isotherm patterns obtained are systematically presented and discussed for different separation ratios. In addition, the mean and instantaneous drag and lift coefficients, mean and local Nusselt number and Strouhal number are determined and discussed for various separation ratios. A new correlation is derived for mean Nusselt number as a function of separation ratio for such flows.
Gohari, Iman; Korobenko, Artem; Yan, Jinhui; Bazilevs, Yuri; Sarkar, Sutanu
2016-11-01
Wind is a renewable energy resource that offers several advantages including low pollutant emission and inexpensive construction. Wind turbines operate in conditions dictated by the Atmospheric Boundary Layer (ABL) and that motivates the study of coupling ABL simulations with wind turbine dynamics. The ABL simulations can be used for realistic modeling of the environment which, with the use of fluid-structure interaction, can give realistic predictions of extracted power, rotor loading, and blade structural response. The ABL simulations provide inflow boundary conditions to the wind-turbine simulator which uses arbitrary Lagrangian-Eulerian variational multiscale formulation. In the present work, ABL simulations are performed to examine two different scenarios: (i) A neutral ABL with zero heat-flux and inversion layer at 350m, in which the wind turbine experiences maximum mean shear; (2) A shallow ABL with the surface cooling-rate of -1 K/hr, in which the wind turbine experiences maximum mean velocity at the low-level-jet nose height. We will discuss differences in the unsteady flow between the two different ABL conditions and their impact on the performance of the wind turbine cluster in the coupled ABL-wind turbine simulations.
Plasma assisted measurements of alkali metal concentrations in pressurised combustion processes
Energy Technology Data Exchange (ETDEWEB)
Hernberg, R; Haeyrinen, V [Tampere Univ. of Technology (Finland)
1997-10-01
In this project the continuous alkali measurement method plasma excited alkali resonance line spectroscopy (PEARLS) was developed, tested and demonstrated in pressurised combustion facilities. The PEARLS method has been developed at Tampere University of Technology (TUT). During 1994-1996 the PEARLS method was developed from the laboratory level to an industrial prototype. The alkali measuring instrument has been tested and used for regular measurements in four different pressurised combustion installations ranging up to industrial pilot scale. The installations are: (1) a pressurised entrained flow reactor (PEFR) at VTT Energy in Jyvaeskylae, Finland (2) a pressurised fluidised bed combustion facility, called FRED, at DMT in Essen, Germany. (3) a 10 MW pressurised circulating fluidised bed combustion pilot plant at Foster Wheeler Energia Oy in Karhula, Finland (4) PFBC Research Facility at ABB Carbon in Finspaang, Sweden
Extracting quantitative three-dimensional unsteady flow direction from tuft flow visualizations
Energy Technology Data Exchange (ETDEWEB)
Omata, Noriyasu; Shirayama, Susumu, E-mail: omata@nakl.t.u-tokyo.ac.jp, E-mail: sirayama@sys.t.u-tokyo.ac.jp [Department of Systems Innovation, School of Engineering, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo, 113-8656 (Japan)
2017-10-15
We focus on the qualitative but widely used method of tuft flow visualization, and propose a method for quantifying it using information technology. By applying stereo image processing and computer vision, the three-dimensional (3D) flow direction in a real environment can be obtained quantitatively. In addition, we show that the flow can be divided temporally by performing appropriate machine learning on the data. Acquisition of flow information in real environments is important for design development, but it is generally considered difficult to apply simulations or quantitative experiments to such environments. Hence, qualitative methods including the tuft method are still in use today. Although attempts have been made previously to quantify such methods, it has not been possible to acquire 3D information. Furthermore, even if quantitative data could be acquired, analysis was often performed empirically or qualitatively. In contrast, we show that our method can acquire 3D information and analyze the measured data quantitatively. (paper)
Extracting quantitative three-dimensional unsteady flow direction from tuft flow visualizations
International Nuclear Information System (INIS)
Omata, Noriyasu; Shirayama, Susumu
2017-01-01
We focus on the qualitative but widely used method of tuft flow visualization, and propose a method for quantifying it using information technology. By applying stereo image processing and computer vision, the three-dimensional (3D) flow direction in a real environment can be obtained quantitatively. In addition, we show that the flow can be divided temporally by performing appropriate machine learning on the data. Acquisition of flow information in real environments is important for design development, but it is generally considered difficult to apply simulations or quantitative experiments to such environments. Hence, qualitative methods including the tuft method are still in use today. Although attempts have been made previously to quantify such methods, it has not been possible to acquire 3D information. Furthermore, even if quantitative data could be acquired, analysis was often performed empirically or qualitatively. In contrast, we show that our method can acquire 3D information and analyze the measured data quantitatively. (paper)
International Nuclear Information System (INIS)
Choi, Hyeon Kyeong; Park, Jong Woon
2013-01-01
In this work, behavior of unsteady and oscillating flow through a typical tube bundle array are analyzed by unsteady computations: 2D unsteady Reynolds averaged Navier-Stokes (URANS) and 3D Large Eddy Simulation (LES) and the results are compared with existing experimental data. In order to confirm appropriateness and limitations of CFD applications in the Korean VHTR design, two types of unsteady computations are performed such as 2D unsteady Reynolds averaged Navier-Stokes (URANS) and 3D Large Eddy Simulation (LES) for the existing tube bundle array. The velocity component profiles are compared with the experimental data and it is concluded that the URANS with the standard k-ω model is reasonably appropriate for cost-effective VHTR lower plenum analysis. Nevertheless, if more accurate results are needed, the LES-Smagorinsky computation is recommended considering limitations in the time averaged RANS in capturing small eddies
Nakamura, S.; Scott, J. N.
1993-01-01
A two-dimensional model to solve compressible Navier-Stokes equations for the flow through stator and rotor blades of a turbine is developed. The flow domains for the stator and rotor blades are coupled by the Chimera method that makes grid generation easy and enhances accuracy because the area of the grid that have high turning of grid lines or high skewness can be eliminated from the computational domain after the grids are generated. The results of flow computations show various important features of unsteady flows including the acoustic waves interacting with boundary layers, Karman vortex shedding from the trailing edge of the stator blades, pulsating incoming flow to a rotor blade from passing stator blades, and flow separation from both suction and pressure sides of the rotor blades.
A complete second-order theory for the unsteady flow about an airfoil due to a periodic gust
Goldstein, M. E.; Atassi, H.
1976-01-01
A uniformly valid second-order theory is developed for calculating the unsteady incompressible flow that occurs when an airfoil is subjected to a convected sinusoidal gust. Explicit formulas for the airfoil response functions (i.e., fluctuating lift) are given. The theory accounts for the effect of the distortion of the gust by the steady-state potential flow around the airfoil, and this effect is found to have an important influence on the response functions. A number of results relevant to the general theory of the scattering of vorticity waves by solid objects are also presented.
International Nuclear Information System (INIS)
Kroshilin, A.E.; Kroshilin, V.E.; Nigmatulin, B.I.
1984-01-01
A one-dimensional unsteady hydrodynamic model of vapour-liquid disperse-annular flows in channels with heated fuel rod clusters has been constructed. Regularities in the appearance of critical heat transfer due to the dryout of a near-wall liquid film on rod surfaces in such channels are investigated. The model developed takes into account the main flow regularities in the channels with heated rod clusters. The calculations made have shown that the time before crisis appearance agrees satisfactorily with the experimental data
Kassem, M.
2006-03-01
The problem of heat and mass transfer in an unsteady free-convection flow over a continuous moving vertical sheet in an ambient fluid is investigated for constant heat flux using the group theoretical method. The nonlinear coupled partial differential equation governing the flow and the boundary conditions are transformed to a system of ordinary differential equations with appropriate boundary conditions. The obtained ordinary differential equations are solved numerically using the shooting method. The effect of Prandlt number on the velocity and temperature of the boundary-layer is plotted in curves. A comparison with previous work is presented.
International Nuclear Information System (INIS)
Bestman, A.R.; Adjepong, S.K.
1987-11-01
We study the unsteady free convection flow near a moving infinite flat plate in a rotating medium by imposing a time dependent perturbation on a constant plate temperature. The temperatures involved are assumed to be very large so that radiative heat transfer is significant, which renders the problem very nonlinear even on the assumption of a differential approximation for the radiative flux. When the perturbation is small, the transient flow is tackled by the Laplace transform technique. Complete first order solutions are deduced for an impulsive motion. (author). 12 refs, 2 figs
Newman, James C., III
1995-01-01
The limiting factor in simulating flows past realistic configurations of interest has been the discretization of the physical domain on which the governing equations of fluid flow may be solved. In an attempt to circumvent this problem, many Computational Fluid Dynamic (CFD) methodologies that are based on different grid generation and domain decomposition techniques have been developed. However, due to the costs involved and expertise required, very few comparative studies between these methods have been performed. In the present work, the two CFD methodologies which show the most promise for treating complex three-dimensional configurations as well as unsteady moving boundary problems are evaluated. These are namely the structured-overlapped and the unstructured grid schemes. Both methods use a cell centered, finite volume, upwind approach. The structured-overlapped algorithm uses an approximately factored, alternating direction implicit scheme to perform the time integration, whereas, the unstructured algorithm uses an explicit Runge-Kutta method. To examine the accuracy, efficiency, and limitations of each scheme, they are applied to the same steady complex multicomponent configurations and unsteady moving boundary problems. The steady complex cases consist of computing the subsonic flow about a two-dimensional high-lift multielement airfoil and the transonic flow about a three-dimensional wing/pylon/finned store assembly. The unsteady moving boundary problems are a forced pitching oscillation of an airfoil in a transonic freestream and a two-dimensional, subsonic airfoil/store separation sequence. Accuracy was accessed through the comparison of computed and experimentally measured pressure coefficient data on several of the wing/pylon/finned store assembly's components and at numerous angles-of-attack for the pitching airfoil. From this study, it was found that both the structured-overlapped and the unstructured grid schemes yielded flow solutions of
Unsteady fluid flow in a slightly curved annular pipe: The impact of the annulus on the flow physics
Messaris, Gerasimos A. T.; Karahalios, George T.
2017-02-01
The motivation of the present study is threefold. Mainly, the etiological explanation of the Womersley number based on physical reasoning. Next, the extension of a previous work [Messaris, Hadjinicolaou, and Karahalios, "Unsteady fluid flow in a slightly curved pipe: A comparative study of a matched asymptotic expansions solution with a single analytical solution," Phys. Fluids 28, 081901 (2016)] to the annular pipe flow. Finally, the discussion of the effect of the additional stresses generated by a catheter in an artery and exerted on the arterial wall during an in vivo catheterization. As it is known, the square of the Womersley number may be interpreted as an oscillatory Reynolds number which equals to the ratio of the inertial to the viscous forces. The adoption of a modified Womersley number in terms of the annular gap width seems therefore more appropriate to the description of the annular flow than an ordinary Womersley number defined in terms of the pipe radius. On this ground, the non-dimensional equations of motion are approximately solved by two analytical methods: a matched asymptotic expansions method and a single. In the first method, which is valid for very large values of the Womersley number, the flow region consists of the main core and the two boundary layers formed at the inner and outer boundaries. In the second, the fluid is considered as one region and the Womersley number can vary from finite values, such that they fit to the blood flow in the aorta and the main arteries, to infinity. The single solution predicts increasing circumferential and decreasing axial stresses with increasing catheter radius at a prescribed value of the Womersley parameter in agreement with analogous results from other theoretical and numerical solutions. It also predicts the formation of pinches on the secondary flow streamlines and a third boundary layer, additional to those formed at the boundary walls. Finally, we show that the insertion of a catheter in an
Mirels, Harold
1959-01-01
A source distribution method is presented for obtaining flow perturbations due to small unsteady area variations, mass, momentum, and heat additions in a basic uniform (or piecewise uniform) one-dimensional flow. First, the perturbations due to an elemental area variation, mass, momentum, and heat addition are found. The general solution is then represented by a spatial and temporal distribution of these elemental (source) solutions. Emphasis is placed on discussing the physical nature of the flow phenomena. The method is illustrated by several examples. These include the determination of perturbations in basic flows consisting of (1) a shock propagating through a nonuniform tube, (2) a constant-velocity piston driving a shock, (3) ideal shock-tube flows, and (4) deflagrations initiated at a closed end. The method is particularly applicable for finding the perturbations due to relatively thin wall boundary layers.
Experimental investigations of the unsteady flow in a Francis turbine draft tube cone
International Nuclear Information System (INIS)
Baya, A; Muntean, S; Campian, V C; Cuzmos, A; Diaconescu, M; Balan, G
2010-01-01
Operating Francis turbines at partial discharge is often hindered by the development of the helical vortex (so-called vortex rope) downstream the runner, in the draft tube cone. The unsteady pressure field induced by precessing vortex rope leads to pressure fluctuations. The paper presents the experimental investigations of the unsteady pressure field generated by precessing vortex rope and its associated pressure fluctuations into a draft tube of the Francis turbine operating at partial discharge. In situ measurements are performed in order to evaluate the pressure fluctuations and vortex rope frequency at partial load operation. Three pressure taps are installed on the cone wall of the draft tube in order to record the unsteady pressure. As a result, the Fourier spectra are obtained in order to evaluate the amplitude of pressure fluctuations and vortex rope frequency. Moreover, the wall pressure recovery along to the draft tube cone is acquired. Finally, conclusions are drawn in order to present the vortex rope effects.
Experimental investigations of the unsteady flow in a Francis turbine draft tube cone
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Baya, A [Department of Hydraulic Machinery, ' Politehnica' University of Timisoara Bv. Mihai Viteazu 1, RO-300222, Timisoara (Romania); Muntean, S [Centre of Advanced Research in Engineering Sciences, Romanian Academy - Timisoara Branch Bv. Mihai Viteazu 24, RO-300223, Timisoara (Romania); Campian, V C; Cuzmos, A [Research Center in Hydraulics, Automation and Heat Transfer, ' Eftimie Murgu' University of Resita P-ta. Traian Vuia 1-4, RO-320085, Resita (Romania); Diaconescu, M; Balan, G, E-mail: abaya@mh.mec.upt.r [Ramnicu Valcea Subsidiary, S.C. Hidroelectrica S.A. Str. Decebal 11, RO-240255, Ramnicu Valcea (Romania)
2010-08-15
Operating Francis turbines at partial discharge is often hindered by the development of the helical vortex (so-called vortex rope) downstream the runner, in the draft tube cone. The unsteady pressure field induced by precessing vortex rope leads to pressure fluctuations. The paper presents the experimental investigations of the unsteady pressure field generated by precessing vortex rope and its associated pressure fluctuations into a draft tube of the Francis turbine operating at partial discharge. In situ measurements are performed in order to evaluate the pressure fluctuations and vortex rope frequency at partial load operation. Three pressure taps are installed on the cone wall of the draft tube in order to record the unsteady pressure. As a result, the Fourier spectra are obtained in order to evaluate the amplitude of pressure fluctuations and vortex rope frequency. Moreover, the wall pressure recovery along to the draft tube cone is acquired. Finally, conclusions are drawn in order to present the vortex rope effects.
El-Asrag, Hossam A.; Ghoniem, Ahmed F.
2011-01-01
simulation, one must introduce a dynamic subgrid model that accounts for the multiscale nature of the problem using information available on a resolvable grid. Here, we discuss a model that captures unsteady flow-flame interactions- including extinction, re
Sviridenkov, A. A.; Toktaliev, P. D.; Tretyakov, V. V.
2018-03-01
Numerical and experimental research of atomization and propagation of drop-liquid phase in swirling flow behind the frontal device of combustion chamber was performed. Numerical procedure was based on steady and unsteady Reynolds equations solution. It's shown that better agreement with experimental data could be obtained with unsteady approach. Fractional time step method was implemented to solve Reynolds equations. Models of primary and secondary breakup of liquid fuel jet in swirling flows are formulated and tested. Typical mean sizes of fuel droplets for base operational regime of swirling device and combustion chamber were calculated. Comparison of main features of internal swirling flow in combustion chamber with unbounded swirling flow was made.
Energy Technology Data Exchange (ETDEWEB)
Belkheir, N. [Khemis Miliana Univ., Ain Defla (Algeria); Dizene, R. [Univ. des Sciences et de la Technologie Houari Boumediene, Algiers (Algeria). Laboratoire de Mecanique Avancee; Khelladi, S.; Massouh, F.; Dobrev, I. [Arts et Metiers Paris Tech., Paris (France)
2010-07-01
The shape of an airfoil is designed to achieve the best aerodynamic performance. An aerofoil section undergoes dynamic stall when subjected to any form of unsteady angle of pitch. The study of a horizontal-axis wind turbine (HAWT) under wind operating conditions is complex because it is subject to instantaneous speed and wind direction variation. When turbine blades are driven into a dynamic stall, the lift coefficient drops suddenly resulting in a degradation in aerodynamic performance. This study presented steady and unsteady wind load predictions over an oscillating S809 airfoil tested in a subsonic wind tunnel. A model of sinusoidal pitch oscillations was used. The values for the angles of attack in steady state ranged from -20 to +40 degrees. The model considered 3 frequencies and 2 amplitudes. The two-dimensional numerical model simulated the instantaneous change of wind direction with respect to the turbine blade. Results were compared with data measurements of S809 aerofoil. Reasonable deviations were obtained between the predicted and experimental results for pitch oscillations. The URANS approach was used to predict the stall while the software FLUENT was used for the numerical solution. It was concluded that the behaviour of the unsteady flow in the wind farm must be considered in order to obtain an accurate estimate of the wind turbine aerodynamic load. 12 refs., 5 figs.
International Nuclear Information System (INIS)
Banerjee, I.; Mahendra, A.K.; Chandresh, B.G.; Srikanthan, M.R.; Bera, T.K.
2010-01-01
A spiral pump uses two interleaved spirals (it can be involutes of a circle, involutes of a square, hybrid wraps, Archimedean spiral, logarithmic spirals and so on). Interleaved spiral orbits eccentrically without rotation around a fixed scroll, thereby trapping and compressing pockets of fluids between the spirals. Another method of providing the compression motion is by virtue of co-rotating the spirals synchronously with an offset in centers of rotation thereby providing relative motion similar to orbiting. Recently spiral pumps for low-pressure application have become popular. Since spiral pumps contain gas volumes, whose shapes and size change continuously, the flow fields inside the pumps is time dependent. The unsteadiness controls the mechanisms responsible for the behavior of the spiral pump components. To improve the spiral pump design for better performance as per our process requirement and reliability, information is required to understand the detailed physics of the unsteady flows inside the spiral pumps. The unsteady flows in a pump are studied numerically. The system simulated includes one side gap between fixed and moving spirals as the other side lies just in the reverse symmetry of the one side. Heavy molecular weight, condensable gas is used as the moving fluid. The mesh free Least Square Kinetic Upwind Method (LSKUM) for moving node is applied for numerical analysis of wobbling spiral. Nodes and boundaries change their positions, for every real time step hence at every iteration nodes take new coordinates. Our work consists of identifying various spiral dimensions and geometry, geometric modeling of suction process, identifying the eccentric orbiting motion of the moving spiral, formation of variable velocity moving nodes. Flow analysis of the spiral pump is done with a view to design and develop new pump as per our requirement. Experimental data from an existing spiral pump is used to carryout validation of the code. (author)
1987-03-01
MACHI, K. 1905 Unsteady Plow in a Turbine Rotor, VDI -Berichte 572.2p 1 9,5, pp. 273-292. FRANSSON, T.1!. and SUTER, P. 1983 Two-Dimensional and...Schaufelreihen in Axialverdichtern und Axialturbinen, VDI -Berichte No. 361, pp. 33-43. I[;RA, T. and RANNIE, W.D. 1953 Observations of Propagating Stall in...NASA-CR-3940. VICTORY, M. 1943 Flutter at High Incidence. Brit. A.R.C. R & M 2048 . VOGELER, K. 1984 The Unsteady Pressure Distribution on Parabolic
Influence of a k-type Roughness on the Behaviour of Turbulence in an Unsteady Channel Flow
International Nuclear Information System (INIS)
Seddighi, Mehdi; He Shuisheng; Vardy, Alan E; Orlandi, Paolo
2011-01-01
Direct Numerical Simulations (DNS) have been carried out for a spatially fully developed turbulent channel flow with one smooth wall and one k-type rough-wall surface to study the influence of a square bar roughness on the behaviour of unsteady turbulent flow. The flow state under investigation is a uniform acceleration from an initially steady turbulent flow. Results are compared with simulations of flows in a smooth wall channel undergoing a similar acceleration, and with quasi-steady behaviour obtained using steady flow simulations. The turbulence in the wall region and the buffer layer of an accelerating flow with a rough wall shows strikingly different behaviour from that of corresponding flows with smooth walls. The characteristic long delays in the response of the streamwise turbulent velocity and the different behaviours of the three turbulent velocity components that are exhibited in smooth wall flows are not seen in the rough wall flow. This is attributed to different turbulent production mechanisms in the two types of flows. Important differences are also seen in the wall shear stress responses one wall is rough and when both walls are smooth.
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Boričić Zoran
2005-01-01
Full Text Available This paper deals with laminar, unsteady flow of viscous, incompressible and electro conductive fluid caused by variable motion of flat plate. Fluid electro conductivity is variable. Velocity of the plate is time function. Plate moves in its own plane and in "still" fluid. Present external magnetic filed is perpendicular to the plate. Plate temperature is a function of longitudinal coordinate and time. Viscous dissipation, Joule heat, Hole and polarization effects are neglected. For obtaining of universal equations system general similarity method is used as well as impulse and energy equation of described problem.
Piezoelectric pump and pressurised circuit provided therewith
Van Es, Johannes; Wits, Wessel Willems
2015-01-01
A piezoelectric pump for use in a pressurised circuit is provided, comprising a pump chamber (5) with an inlet (6) provided with a one way inlet valve (7), for connection to a feeding line (8) of the pressurised circuit and an outlet (9) provided with a one way outlet valve (10), for connection to a
International Nuclear Information System (INIS)
Singh, K.; Rawat, S. K.; Kumar, M.
2016-01-01
Heat and mass transfer behavior of unsteady flow of squeezing between two parallel plates in the sight of uniform magnetic field with slip velocity effect is investigated. The governing equations representing fluid flow have been transformed into nonlinear ordinary differential equations using similarity transformation. The equations thus obtained have been solved numerically using Runge-Kutta-Fehlberg method with shooting technique. Effects on the behavior of velocity, temperature, and concentration for various values of relevant parameters are illustrated graphically. The skin-friction coefficient and heat and mass transfer rate are also tabulated for various governing parameters. The results indicate that, for nano fluid flow, the rates of heat and mass transfer are inversely proportional to nanoparticle volume fraction and magnetic parameter. The rate of mass transfer increases with increasing values of Schmidt number and squeeze number.
Unsteady Magnetohydrodynamic Flow of Liquid Through a Channel Variable Pressure Gradient
International Nuclear Information System (INIS)
Singh, C.B.
1998-01-01
The article studies the unsteady motion of an electrically conducting, viscous incompressible fluid along a channel in the presence of imposed transverse magnetic field, when the walls do not conduct current, under the influence of pressure gradient which varies linearly with respect to time. Analytical expressions for the velocity of the fluid for various values of Hartman numbers and at different times has been obtained
(YIP 2011) Unsteady Output-based Adaptive Simulation of Separated and Transitional Flows
2015-03-19
Investigator Aerospace Eng. U. Michigan Marco Ceze Ph.D. student/postdoctoral associate Aerospace Eng. U. Michigan Steven Kast Ph.D. student Aerospace...13] S. M. Kast , M. A. Ceze, and K. J. Fidkowski. Output-adaptive solution strategies for unsteady aerodynamics on deformable domains. Seventh...International Conference on Computational Fluid Dynamics ICCFD7-3802, 2012. [14] S. M. Kast and K. J. Fidkowski. Output-based mesh adaptation for high order
Czech Academy of Sciences Publication Activity Database
Pořízková, P.; Kozel, Karel; Horáček, Jaromír
2014-01-01
Roč. 270, November (2014), s. 323-329 ISSN 0377-0427 R&D Projects: GA ČR(CZ) GAP101/11/0207; GA ČR(CZ) GAP101/10/1329 Institutional support: RVO:61388998 Keywords : compressible * incompressible * unsteady * CFD * acoustic * vocal tract Subject RIV: BI - Acoustics Impact factor: 1.266, year: 2014 http://www.sciencedirect.com/science/article/pii/S0377042713007188#
Energy Technology Data Exchange (ETDEWEB)
Ginter, F.
1997-12-31
The unsteady flow in a hydraulic machinery, affected by the interaction between guide vane and impeller, is simulated by a Finite-Element program. Based on the standard-k-{epsilon}-model modifications are investigated to model the turbulent flow. The low-Re-model of Lam-Brenhorst and a two-layer model is implemented for the calculation of the boundary layer. An algebraic Reynolds stress model is investigated for the simulation of the anisotropy of the turbulence structure. The turbulence models are compared by flows with characteristic properties. The pressure field of the incompressible flow is calculated by the mixed formulation and by solving the Poisson equation. The mixed formulation shows oscillations for the pressure field using elements with bilinear shape functions for the velocity and constant shape functions for the pressure, which are eliminated with a smoothing algorithm. An algorithm is implemented for the calculation of the unsteady interaction between fixed and moved blade rows, based on the method of overlapping regions, and is applied to the two-dimensional flow in an axial expansion turbine. (orig.) [Deutsch] Die instationaere Stroemung in einer hydraulischen Stroemungsmaschine, beruhend auf den Wechselwirkungen zwischen Leitrad und Laufrad, wird mit einem Finite-Elemente-Programm berechnet. Ausgehend vom Standard-k-{epsilon}-Modell werden Erweiterungen zur Modellierung der turbulenten Stroemung untersucht. Fuer die Berechnung der Grenzschicht werden das Low-Re-Modell nach Lam-Brenhorst und ein Zweischichtenmodell implementiert. Zur Erfassung der Anisotropie der Turbulenzstruktur wird ein algebraisches Reynoldsspannungsmodell untersucht. Die Turbulenzmodelle werden anhand von Stroemungen mit charakterischen Eigenschaften verglichen. Die Druckberechnung der inkompressiblen Stroemung erfolgt auf der Bais der gemischten Formulierung bzw. durch Loesung der Poissongleichung. Fuer die gemischte Formulierung zeigt das Druckfeld Oszillationen fuer
Shyam, Vikram; Ameri, Ali; Luk, Daniel F.; Chen, Jen-Ping
2010-01-01
Unsteady three-dimensional RANS simulations have been performed on a highly loaded transonic turbine stage and results are compared to steady calculations as well as experiment. A low Reynolds number k- turbulence model is employed to provide closure for the RANS system. A phase-lag boundary condition is used in the periodic direction. This allows the unsteady simulation to be performed by using only one blade from each of the two rows. The objective of this paper is to study the effect of unsteadiness on rotor heat transfer and to glean any insight into unsteady flow physics. The role of the stator wake passing on the pressure distribution at the leading edge is also studied. The simulated heat transfer and pressure results agreed favorably with experiment. The time-averaged heat transfer predicted by the unsteady simulation is higher than the heat transfer predicted by the steady simulation everywhere except at the leading edge. The shock structure formed due to stator-rotor interaction was analyzed. Heat transfer and pressure at the hub and casing were also studied. Thermal segregation was observed that leads to the heat transfer patterns predicted by steady and unsteady simulations to be different.
Boutsioukis, C; Verhaagen, B; Versluis, M; Kastrinakis, E; van der Sluis, L W M
2010-05-01
To compare the results of a Computational Fluid Dynamics (CFD) simulation of the irrigant flow within a prepared root canal, during final irrigation with a syringe and a needle, with experimental high-speed visualizations and theoretical calculations of an identical geometry and to evaluate the effect of off-centre positioning of the needle inside the root canal. A CFD model was created to simulate irrigant flow from a side-vented needle inside a prepared root canal. Calculations were carried out for four different positions of the needle inside a prepared root canal. An identical root canal model was made from poly-dimethyl-siloxane (PDMS). High-speed imaging of the flow seeded with particles and Particle Image Velocimetry (PIV) were combined to obtain the velocity field inside the root canal experimentally. Computational, theoretical and experimental results were compared to assess the validity of the computational model. Comparison between CFD computations and experiments revealed good agreement in the velocity magnitude and vortex location and size. Small lateral displacements of the needle inside the canal had a limited effect on the flow field. High-speed imaging experiments together with PIV of the flow inside a simulated root canal showed a good agreement with the CFD model, even though the flow was unsteady. Therefore, the CFD model is able to predict reliably the flow in similar domains.
Directory of Open Access Journals (Sweden)
Asma Khalid
2015-01-01
Full Text Available The unsteady free flow of a Casson fluid past an oscillating vertical plate with constant wall temperature has been studied. The Casson fluid model is used to distinguish the non-Newtonian fluid behaviour. The governing partial differential equations corresponding to the momentum and energy equations are transformed into linear ordinary differential equations by using nondimensional variables. Laplace transform method is used to find the exact solutions of these equations. Expressions for shear stress in terms of skin friction and the rate of heat transfer in terms of Nusselt number are also obtained. Numerical results of velocity and temperature profiles with various values of embedded flow parameters are shown graphically and their effects are discussed in detail.
Directory of Open Access Journals (Sweden)
Abid Hussanan
Full Text Available In this paper, the heat transfer effect on the unsteady boundary layer flow of a Casson fluid past an infinite oscillating vertical plate with Newtonian heating is investigated. The governing equations are transformed to a systems of linear partial differential equations using appropriate non-dimensional variables. The resulting equations are solved analytically by using the Laplace transform method and the expressions for velocity and temperature are obtained. They satisfy all imposed initial and boundary conditions and reduce to some well-known solutions for Newtonian fluids. Numerical results for velocity, temperature, skin friction and Nusselt number are shown in various graphs and discussed for embedded flow parameters. It is found that velocity decreases as Casson parameters increases and thermal boundary layer thickness increases with increasing Newtonian heating parameter.
Rawi, N. A.; Ilias, M. R.; Lim, Y. J.; Isa, Z. M.; Shafie, S.
2017-09-01
The influence of nanoparticles on the unsteady mixed convection flow of Casson fluid past an inclined stretching sheet is investigated in this paper. The effect of gravity modulation on the flow is also considered. Carboxymethyl cellulose solution (CMC) is chosen as the base fluid and copper as nanoparticles. The basic governing nonlinear partial differential equations are transformed using appropriate similarity transformation and solved numerically using an implicit finite difference scheme by means of the Keller-box method. The effect of nanoparticles volume fraction together with the effect of inclination angle and Casson parameter on the enhancement of heat transfer of Casson nanofluid is discussed in details. The velocity and temperature profiles as well as the skin friction coefficient and the Nusselt number are presented and analyzed.
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Isaac Lare Animasaun
2016-06-01
Full Text Available The problem of unsteady convective with thermophoresis, chemical reaction and radiative heat transfer in a micropolar fluid flow past a vertical porous surface moving through binary mixture considering temperature dependent dynamic viscosity and constant vortex viscosity has been investigated theoretically. For proper and correct analysis of fluid flow along vertical surface with a temperature lesser than that of the free stream, Boussinesq approximation and temperature dependent viscosity model were modified and incorporated into the governing equations. The governing equations are converted to systems of ordinary differential equations by applying suitable similarity transformations and solved numerically using fourth-order Runge–Kutta method along with shooting technique. The results of the numerical solution are presented graphically and in tabular forms for different values of parameters. Velocity profile increases with temperature dependent variable fluid viscosity parameter. Increase of suction parameter corresponds to an increase in both temperature and concentration within the thin boundary layer.
Javed, T.; Ghaffari, A.; Ahmad, H.
2016-05-01
The unsteady stagnation point flow impinging obliquely on a flat plate in presence of a uniform applied magnetic field due to an oscillating stream has been studied. The governing partial differential equations are transformed into dimensionless form and the stream function is expressed in terms of Hiemenz and tangential components. The dimensionless partial differential equations are solved numerically by using well-known implicit finite difference scheme named as Keller-box method. The obtained results are compared with those available in the literature. It is observed that the results are in excellent agreement with the previous studies. The effects of pertinent parameters involved in the problem namely magnetic parameter, Prandtl number and impinging angle on flow and heat transfer characteristics are illustrated through graphs. It is observed that the influence of magnetic field strength increases the fluid velocity and by the increase of obliqueness parameter, the skin friction increases.
Khan, Kashif Ali; Butt, Asma Rashid; Raza, Nauman
2018-03-01
In this study, an endeavor is to observe the unsteady two-dimensional boundary layer flow with heat and mass transfer behavior of Casson fluid past a stretching sheet in presence of wall mass transfer by ignoring the effects of viscous dissipation. Chemical reaction of linear order is also invoked here. Similarity transformation have been applied to reduce the governing equations of momentum, energy and mass into non-linear ordinary differential equations; then Homotopy analysis method (HAM) is applied to solve these equations. Numerical work is done carefully with a well-known software MATHEMATICA for the examination of non-dimensional velocity, temperature, and concentration profiles, and then results are presented graphically. The skin friction (viscous drag), local Nusselt number (rate of heat transfer) and Sherwood number (rate of mass transfer) are discussed and presented in tabular form for several factors which are monitoring the flow model.
Hussanan, Abid; Zuki Salleh, Mohd; Tahar, Razman Mat; Khan, Ilyas
2014-01-01
In this paper, the heat transfer effect on the unsteady boundary layer flow of a Casson fluid past an infinite oscillating vertical plate with Newtonian heating is investigated. The governing equations are transformed to a systems of linear partial differential equations using appropriate non-dimensional variables. The resulting equations are solved analytically by using the Laplace transform method and the expressions for velocity and temperature are obtained. They satisfy all imposed initial and boundary conditions and reduce to some well-known solutions for Newtonian fluids. Numerical results for velocity, temperature, skin friction and Nusselt number are shown in various graphs and discussed for embedded flow parameters. It is found that velocity decreases as Casson parameters increases and thermal boundary layer thickness increases with increasing Newtonian heating parameter.
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Taza Gul
Full Text Available This article aims to study the thin film layer flowing on a vertical oscillating belt. The flow is considered to satisfy the constitutive equation of unsteady second grade fluid. The governing equation for velocity and temperature fields with subjected initial and boundary conditions are solved by two analytical techniques namely Adomian Decomposition Method (ADM and Optimal Homotopy Asymptotic Method (OHAM. The comparisons of ADM and OHAM solutions for velocity and temperature fields are shown numerically and graphically for both the lift and drainage problems. It is found that both these solutions are identical. In order to understand the physical behavior of the embedded parameters such as Stock number, frequency parameter, magnetic parameter, Brinkman number and Prandtl number, the analytical results are plotted graphically and discussed.
Gul, Taza; Islam, Saeed; Shah, Rehan Ali; Khan, Ilyas; Khalid, Asma; Shafie, Sharidan
2014-01-01
This article aims to study the thin film layer flowing on a vertical oscillating belt. The flow is considered to satisfy the constitutive equation of unsteady second grade fluid. The governing equation for velocity and temperature fields with subjected initial and boundary conditions are solved by two analytical techniques namely Adomian Decomposition Method (ADM) and Optimal Homotopy Asymptotic Method (OHAM). The comparisons of ADM and OHAM solutions for velocity and temperature fields are shown numerically and graphically for both the lift and drainage problems. It is found that both these solutions are identical. In order to understand the physical behavior of the embedded parameters such as Stock number, frequency parameter, magnetic parameter, Brinkman number and Prandtl number, the analytical results are plotted graphically and discussed. PMID:25383797
Narahari, Marneni
2018-04-01
The unsteady free convective flow of nanofluids past a semi-infinite vertical plate with uniform heat flux has been investigated numerically. An implicit finite difference technique of Crank-Nicolson scheme has been employed to solve the governing partial differential equations. Five different types of water based nanofluids containing Cu, Ag, Al2O3, CuO and TiO2 nanoparticles are considered to study the fluid flow characteristics with various time and solid volume fraction parameters. It is found that the local as well as the average Nusselt number for nanofluids is higher than the pure fluid (water). The local skin-friction is higher for pure fluid as compared to the nanofluids. The present numerical results obtained for local Nusselt number are validated with the previously published correlation results for a limiting case and it is found that the results are in good agreement.
Mettot, Clément; Sipp, Denis; Bézard, Hervé
2014-04-01
This article presents a quasi-laminar stability approach to identify in high-Reynolds number flows the dominant low-frequencies and to design passive control means to shift these frequencies. The approach is based on a global linear stability analysis of mean-flows, which correspond to the time-average of the unsteady flows. Contrary to the previous work by Meliga et al. ["Sensitivity of 2-D turbulent flow past a D-shaped cylinder using global stability," Phys. Fluids 24, 061701 (2012)], we use the linearized Navier-Stokes equations based solely on the molecular viscosity (leaving aside any turbulence model and any eddy viscosity) to extract the least stable direct and adjoint global modes of the flow. Then, we compute the frequency sensitivity maps of these modes, so as to predict before hand where a small control cylinder optimally shifts the frequency of the flow. In the case of the D-shaped cylinder studied by Parezanović and Cadot [J. Fluid Mech. 693, 115 (2012)], we show that the present approach well captures the frequency of the flow and recovers accurately the frequency control maps obtained experimentally. The results are close to those already obtained by Meliga et al., who used a more complex approach in which turbulence models played a central role. The present approach is simpler and may be applied to a broader range of flows since it is tractable as soon as mean-flows — which can be obtained either numerically from simulations (Direct Numerical Simulation (DNS), Large Eddy Simulation (LES), unsteady Reynolds-Averaged-Navier-Stokes (RANS), steady RANS) or from experimental measurements (Particle Image Velocimetry - PIV) — are available. We also discuss how the influence of the control cylinder on the mean-flow may be more accurately predicted by determining an eddy-viscosity from numerical simulations or experimental measurements. From a technical point of view, we finally show how an existing compressible numerical simulation code may be used in
Energy Technology Data Exchange (ETDEWEB)
Eulitz, F
2000-04-01
The present work is devoted to the development of a computational technique for the Reynolds-averaged, time-resolved simulation of the undsteady, viscous flow in turbomachinery. After identification of model criteria, a novel turbulence and transition model, based on the extension of a one-equation turbulence model, is derived in order to incorporate the Reynolds-averaged effects of boundary-layer transition in unsteady turbomachinery flow. Preserving low numerical dissipation and dispersion errors, the explicit time integration method is accelerated through a time-consistent two-grid approach to allow for an efficient use of parallel computers. The model development is carefully assessed by considering various test cases of steady and unsteady turbine flow with various transition modes or of transonic channel flow with self-excited shock-oscillation. The application of the computational technique is demonstrated for the case of a single-stage, transonic compressor component and of a three-stage low-pressure turbine at low Reynolds-number operation. (orig.) [German] In dieser Arbeit wird ein numerisches Verfahren zur zeitgenauen Simulation der instationaeren, reibungsbehafteten Stroemung in Turbomaschinen auf Grundlage der Reynolds-gemittelten Navier-Stokes-Gleichungen entwickelt. Nach Aufarbeitung der Modellierungsanforderungen wird basierend auf einem Eingleichungsturbulenzmodell ein neuartiges Turbulenz- und Transitionsmodell abgeleitet, mit dem verschiedene Transitionsmoden der instationaeren Turbomaschinenstroemung in ihrer Reynolds-gemittelten Wirkung beschrieben werden koennen. Durch einen zeitkonsistenten Zweigitter-Ansatz wird die Zeitintegration fuer Navier-Stokes-Simulationen auf Parallelrechnern unter Wahrung geringer numerischer Phasen- und Amplitudenfehler beschleunigt. Die Entwicklung wird an einer Reihe von Testfaellen, zur stationaeren und instationaeren Turbinenstroemung mit unterschiedlicher Grenzschichttransition oder zur transsonischen
Hamid, Aamir; Hashim; Khan, Masood
2018-06-01
The main concern of this communication is to investigate the two-layer flow of a non-Newtonian rheological fluid past a wedge-shaped geometry. One remarkable aspect of this article is the mathematical formulation for two-dimensional flow of Williamson fluid by incorporating the effect of infinite shear rate viscosity. The impacts of heat transfer mechanism on time-dependent flow field are further studied. At first, we employ the suitable non-dimensional variables to transmute the time-dependent governing flow equations into a system of non-linear ordinary differential equations. The converted conservation equations are numerically integrated subject to physically suitable boundary conditions with the aid of Runge-Kutta Fehlberg integration procedure. The effects of involved pertinent parameters, such as, moving wedge parameter, wedge angle parameter, local Weissenberg number, unsteadiness parameter and Prandtl number on the non-dimensional velocity and temperature distributions have been evaluated. In addition, the numerical values of the local skin friction coefficient and the local Nusselt number are compared and presented through tables. The outcomes of this study indicate that the rate of heat transfer increases with the growth of both wedge angle parameter and unsteadiness parameter. Moreover, a substantial rise in the fluid velocity is observed with enhancement in the viscosity ratio parameter while an opposite trend is true for the non-dimensional temperature field. A comparison is presented between the current study and already published works and results found to be in outstanding agreement. Finally, the main findings of this article are highlighted in the last section.
Force-deflection analysis of offset indentations on pressurised pipes
International Nuclear Information System (INIS)
Hyde, T.H.; Luo, R.; Becker, A.A.
2007-01-01
The indenter force vs. deflection characteristics of pressurised pipes with long offset indentations under plane strain conditions have been investigated using finite element (FE) and analytical methods with four experimental tests performed on aluminium rings. Two different materials and five different geometries were used to investigate their effects on the elastic-plastic behaviour. A comparison of the experimental, FE and the analytical results indicates that the analytical formulation developed in this paper, for predicting the force-deflection curves for pressurised pipes with offset indenters, is reasonably accurate. Also, all of the analyses presented in this paper indicate that by using a representative flow stress, which is defined as the average of the yield and ultimate tensile stresses, the analytical method can accurately predict the force-deflection curves
Exact solution of unsteady flow generated by sinusoidal pressure gradient in a capillary tube
Directory of Open Access Journals (Sweden)
M. Abdulhameed
2015-12-01
Full Text Available In this paper, the mathematical modeling of unsteady second grade fluid in a capillary tube with sinusoidal pressure gradient is developed with non-homogenous boundary conditions. Exact analytical solutions for the velocity profiles have been obtained in explicit forms. These solutions are written as the sum of the steady and transient solutions for small and large times. For growing times, the starting solution reduces to the well-known periodic solution that coincides with the corresponding solution of a Newtonian fluid. Graphs representing the solutions are discussed.
Reddy, G. Janardhana; Hiremath, Ashwini; Kumar, Mahesh
2018-03-01
The present paper aims to investigate the effect of Prandtl number for unsteady third-grade fluid flow over a uniformly heated vertical cylinder using Bejan's heat function concept. The mathematical model of this problem is given by highly time-dependent non-linear coupled equations and are resolved by an efficient unconditionally stable implicit scheme. The time histories of average values of momentum and heat transport coefficients as well as the steady-state flow variables are displayed graphically for distinct values of non-dimensional control parameters arising in the system. As the non-dimensional parameter value gets amplified, the time taken for the fluid flow variables to attain the time-independent state is decreasing. The dimensionless heat function values are closely associated with an overall rate of heat transfer. Thermal energy transfer visualization implies that the heat function contours are compact in the neighborhood of the leading edge of the hot cylindrical wall. It is noticed that the deviations of flow-field variables from the hot wall for a non-Newtonian third-grade fluid flow are significant compared to the usual Newtonian fluid flow.
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M. Das
2015-12-01
Full Text Available The influence of Newtonian heating on heat and mass transfer in unsteady hydromagnetic flow of a Casson fluid past a vertical plate in the presence of thermal radiation and chemical reaction is studied. The Casson fluid model is used to distinguish the non-Newtonian fluid behavior. The fluid flow is induced due to periodic oscillations of the plate along its length and a uniform transverse magnetic field is applied in a direction which is normal to the direction of fluid flow. The partial differential equations governing the flow, heat, and mass transfer are transformed to non-dimensional form using suitable non-dimensional variables which are then solved analytically by using Laplace transform technique. The numerical values of the fluid velocity, fluid temperature, and species concentration are depicted graphically whereas the values of skin-friction, Nusselt number, and Sherwood number are presented in tabular form. It is noticed that the fluid velocity and temperature decrease with increasing values of Casson parameter while concentration decreases with increasing values of chemical reaction parameter and Schmidt number. Such a fluid flow model has several industrial and medical applications such as in glass manufacturing, paper production, purification of crude oil and study of blood flow in the cardiovascular system.
Directory of Open Access Journals (Sweden)
G. Revathi
2014-12-01
Full Text Available Non-similar solutions are found numerically to a system of coupled non-linear partial differential equations indicating, unsteady laminar water boundary layer flow over yawed cylinder using implicit finite difference scheme along with Quasi-linearization technique. The fluid properties such as viscosity and Prandtl number are considered as an inverse function of temperature. Unsteadiness is caused by upstream velocity in and directions and non-uniform mass transfer (suction/injection which is applied through slot on the surface of the geometry. The effect of yaw angle, variable fluid properties and non-uniform mass transfer on skin friction and heat transfer coefficients is analyzed. It is found that non-uniform slot suction and downstream movement of the slot cause the point of vanishing skin friction moves downstream, but non-uniform slot injection produces the opposite result of that corresponding to the suction case. When the yaw angle increases, both the skin friction coefficient in the – direction and the heat transfer coefficient decrease but the skin friction coefficient in the – direction increases for all times. The effect of the yaw angle is very little on the point of vanishing skin friction.
Unsteady Stokes equations: Some complete general solutions
Indian Academy of Sciences (India)
R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22
homogeneous unsteady Stokes equations are examined. A necessary and sufficient condition for a divergence-free vector to represent the velocity field of a possible unsteady Stokes flow in the absence of body forces is derived. Keywords. Complete ...
Simulation of a 3D unsteady flow in an axial turbine stage
Directory of Open Access Journals (Sweden)
Straka Petr
2012-04-01
Full Text Available The contribution deals with a numerical simulation of an unsteady ﬂow in an axial turbine stage. The solution is performed using an in-house numerical code developed in the Aeronautical and Test Institute, Plc. in Prague. The numerical code is based on a ﬁnite volume discretization of governing equations (Favre averaged Navier-Stokes equations and a two-equations turbulence model. The temporal integration is based on the implicit second-order backward Euler formula, which is realized through the iteration process in dual time. The proposed numerical method is used for solution of the 3D, unsteady, viscous turbulent ﬂow of a perfect gas in the axial turbine stage. The ﬂow path consists of an input nozzle, stator blade-wheel, rotor blade-wheel, a shroud-seal gap and a diffuser. Attention is paid to the inﬂuence of a secondary ﬂow structures, such as generated vortices and ﬂow in shroud-seal gap.
Manideep, P.; Raju, R. Srinivasa; Rao, T. Siva Nageswar; Reddy, G. Jithender
2018-05-01
This paper deals, an unsteady magnetohydrodynamic heat transfer natural convection flow of non-Newtonian Casson fluid over an inclined vertical plate embedded in a porous media with the presence of boundary conditions such as oscillating velocity, constant wall temperature. The governing dimensionless boundary layer partial differential equations are reduced to simultaneous algebraic linear equation for velocity, temperature of Casson fluid through finite element method. Those equations are solved by Thomas algorithm after imposing the boundary conditions through MATLAB for analyzing the behavior of Casson fluid velocity and temperature with various physical parameters. Also analyzed the local skin-friction and rate of heat transfer. Compared the present results with earlier reported studies, the results are comprehensively authenticated and robust FEM.
Rana, B. M. Jewel; Ahmed, Rubel; Ahmmed, S. F.
2017-06-01
Unsteady MHD free convection flow past a vertical porous plate in porous medium with radiation, diffusion thermo, thermal diffusion and heat source are analyzed. The governing non-linear, partial differential equations are transformed into dimensionless by using non-dimensional quantities. Then the resultant dimensionless equations are solved numerically by applying an efficient, accurate and conditionally stable finite difference scheme of explicit type with the help of a computer programming language Compaq Visual Fortran. The stability and convergence analysis has been carried out to establish the effect of velocity, temperature, concentration, skin friction, Nusselt number, Sherwood number, stream lines and isotherms line. Finally, the effects of various parameters are presented graphically and discussed qualitatively.
Ahmed, Rubel; Rana, B. M. Jewel; Ahmmed, S. F.
2017-06-01
The effects of magnetic, radiation and chemical reaction parameters on the unsteady heat and mass transfer boundary layer flow past an oscillating cylinder is considered. The dimensionless momentum, energy and concentration equations are solved numerically by using explicit finite difference method with the help of a computer programming language Compaq visual FORTRAN 6.6a. The obtained results of this study have been discussed for different values of well-known parameters with different time steps. The effect of these parameters on the velocity field, temperature field and concentration field, skin-friction, Nusselt number, streamlines and isotherms has been studied and results are presented by graphically represented by the tabular form quantitatively. The stability and convergence analysis of the solution parameters that have been used in the mathematical model have been tested.
Devakar, M.; Raje, Ankush
2018-05-01
The unsteady flow of two immiscible micropolar and Newtonian fluids through a horizontal channel is considered. In addition to the classical no-slip and hyper-stick conditions at the boundary, it is assumed that the fluid velocities and shear stresses are continuous across the fluid-fluid interface. Three cases for the applied pressure gradient are considered to study the problem: one with constant pressure gradient and the other two cases with time-dependent pressure gradients, viz. periodic and decaying pressure gradient. The Crank-Nicolson approach has been used to obtain numerical solutions for fluid velocity and microrotation for diverse sets of fluid parameters. The nature of fluid velocities and microrotation with various values of pressure gradient, Reynolds number, ratio of viscosities, micropolarity parameter and time is illustrated through graphs. It has been observed that micropolarity parameter and ratio of viscosities reduce the fluid velocities.
Colera, Manuel; Pérez-Saborid, Miguel
2017-09-01
A finite differences scheme is proposed in this work to compute in the time domain the compressible, subsonic, unsteady flow past an aerodynamic airfoil using the linearized potential theory. It improves and extends the original method proposed in this journal by Hariharan, Ping and Scott [1] by considering: (i) a non-uniform mesh, (ii) an implicit time integration algorithm, (iii) a vectorized implementation and (iv) the coupled airfoil dynamics and fluid dynamic loads. First, we have formulated the method for cases in which the airfoil motion is given. The scheme has been tested on well known problems in unsteady aerodynamics -such as the response to a sudden change of the angle of attack and to a harmonic motion of the airfoil- and has been proved to be more accurate and efficient than other finite differences and vortex-lattice methods found in the literature. Secondly, we have coupled our method to the equations governing the airfoil dynamics in order to numerically solve problems where the airfoil motion is unknown a priori as happens, for example, in the cases of the flutter and the divergence of a typical section of a wing or of a flexible panel. Apparently, this is the first self-consistent and easy-to-implement numerical analysis in the time domain of the compressible, linearized coupled dynamics of the (generally flexible) airfoil-fluid system carried out in the literature. The results for the particular case of a rigid airfoil show excellent agreement with those reported by other authors, whereas those obtained for the case of a cantilevered flexible airfoil in compressible flow seem to be original or, at least, not well-known.
Sajben, Miklos; Freund, Donald D.
1998-01-01
The ability to predict the dynamics of integrated inlet/compressor systems is an important part of designing high-speed propulsion systems. The boundaries of the performance envelope are often defined by undesirable transient phenomena in the inlet (unstart, buzz, etc.) in response to disturbances originated either in the engine or in the atmosphere. Stability margins used to compensate for the inability to accurately predict such processes lead to weight and performance penalties, which translate into a reduction in vehicle range. The prediction of transients in an inlet/compressor system requires either the coupling of two complex, unsteady codes (one for the inlet and one for the engine) or else a reliable characterization of the inlet/compressor interface, by specifying a boundary condition. In the context of engineering development programs, only the second option is viable economically. Computations of unsteady inlet flows invariably rely on simple compressor-face boundary conditions (CFBC's). Currently, customary conditions include choked flow, constant static pressure, constant axial velocity, constant Mach number or constant mass flow per unit area. These conditions are straightforward extensions of practices that are valid for and work well with steady inlet flows. Unfortunately, it is not at all likely that any flow property would stay constant during a complex system transient. At the start of this effort, no experimental observation existed that could be used to formulate of verify any of the CFBC'S. This lack of hard information represented a risk for a development program that has been recognized to be unacceptably large. The goal of the present effort was to generate such data. Disturbances reaching the compressor face in flight may have complex spatial structures and temporal histories. Small amplitude disturbances may be decomposed into acoustic, vorticity and entropy contributions that are uncoupled if the undisturbed flow is uniform. This study
Lightbody, A.; Sotiropoulos, F.; Kang, S.; Diplas, P.
2009-12-01
Despite their widespread application to prevent lateral river migration, stabilize banks, and promote aquatic habitat, shallow transverse flow training structures such as rock vanes and stream barbs lack quantitative design guidelines. Due to the lack of fundamental knowledge about the interaction of the flow field with the sediment bed, existing engineering standards are typically based on various subjective criteria or on cross-sectionally-averaged shear stresses rather than local values. Here, we examine the performance and stability of in-stream structures within a field-scale single-threaded sand-bed meandering stream channel in the newly developed Outdoor StreamLab (OSL) at the St. Anthony Falls Laboratory (SAFL). Before and after the installation of a rock vane along the outer bank of the middle meander bend, high-resolution topography data were obtained for the entire 50-m-long reach at 1-cm spatial scale in the horizontal and sub-millimeter spatial scale in the vertical. In addition, detailed measurements of flow and turbulence were obtained using acoustic Doppler velocimetry at twelve cross-sections focused on the vicinity of the structure. Measurements were repeated at a range of extreme events, including in-bank flows with an approximate flow rate of 44 L/s (1.4 cfs) and bankfull floods with an approximate flow rate of 280 L/s (10 cfs). Under both flow rates, the structure reduced near-bank shear stresses and resulted in both a deeper thalweg and near-bank aggradation. The resulting comprehensive dataset has been used to validate a large eddy simulation carried out by SAFL’s computational fluid dynamics model, the Virtual StreamLab (VSL). This versatile computational framework is able to efficiently simulate 3D unsteady turbulent flows in natural streams with complex in-stream structures and as a result holds promise for the development of much-needed quantitative design guidelines.
Directory of Open Access Journals (Sweden)
O. D. Makinde
2014-01-01
Full Text Available This paper investigates the unsteady hydromagnetic-free convection of an incompressible electrical conducting Boussinesq’s radiating fluid past a moving vertical plate in an optically thin environment with the Navier slip, viscous dissipation, and Ohmic and Newtonian heating. The nonlinear partial differential equations governing the transient problem are obtained and tackled numerically using a semidiscretization finite difference method coupled with Runge-Kutta Fehlberg integration technique. Numerical data for the local skin friction coefficient and the Nusselt number have been tabulated for various values of parametric conditions. Graphical results for the fluid velocity, temperature, skin friction, and the Nusselt number are presented and discussed. The results indicate that the skin friction coefficient decreases while the heat transfer rate at the plate surface increases as the slip parameter and Newtonian heating increase.
Energy Technology Data Exchange (ETDEWEB)
Janetzky, B.
2001-07-01
A numerical model for the transient, free surface flow is implemented in a Finite-Element program for the unsteady calculation of incompressible flow with free surface. The program is used to calculate the flow in different components of a hydraulic turbine, the Pelton turbine. The movement of the fluid with free surface is described mathematically by introducing a partial differential equation for the volume fraction. This equation is simply a transport equation for f, i.e. the volume fraction is advected with the flow in time. The equations is solved numerically. (orig.) [German] Es wird ein Verfahren zur Modellierung von veraenderlichen, freien Oberflaechen vorgestellt und in einem Finite-Elemente-Programm zur numerischen Berechnung von instationaeren, inkompressiblen Stroemungen implementiert. Die veraenderliche, freie Oberflaeche wird mit einem Volume-Of-Fluid Ansatz erfasst. Zur Approximierung der freien Oberflaeche werden stueckweise konstante oder gestufte Verlaeufe im Element angesetzt. Es werden die Eigenschaften des Verfahrens an ausgewaehlten Beispielen mit freier Oberflaeche untersucht. Das erweiterte Programm wird auf instationaere Stroemungen mit freier Oberflaeche in einer hydraulischen Maschine, der Peltonturbine, angewandt. (orig.)
Kang, Seokkoo; Borazjani, Iman; Sotiropoulos, Fotis
2008-11-01
Unsteady 3D simulations of flows in natural streams is a challenging task due to the complexity of the bathymetry, the shallowness of the flow, and the presence of multiple nature- and man-made obstacles. This work is motivated by the need to develop a powerful numerical method for simulating such flows using coherent-structure-resolving turbulence models. We employ the curvilinear immersed boundary method of Ge and Sotiropoulos (Journal of Computational Physics, 2007) and address the critical issue of numerical efficiency in large aspect ratio computational domains and grids such as those encountered in long and shallow open channels. We show that the matrix-free Newton-Krylov method for solving the momentum equations coupled with an algebraic multigrid method with incomplete LU preconditioner for solving the Poisson equation yield a robust and efficient procedure for obtaining time-accurate solutions in such problems. We demonstrate the potential of the numerical approach by carrying out a direct numerical simulation of flow in a long and shallow meandering stream with multiple hydraulic structures.
Hah, Chunill; Hathaway, Michael; Katz, Joseph; Tan, David
2015-01-01
The primary focus of this paper is to investigate how a rotor's unsteady tip clearance flow structure changes in a low speed one and half stage axial compressor when the rotor tip gap size is increased from 0.5 mm (0.49% of rotor tip blade chord, 2% of blade span) to 2.4 mm (2.34% chord, 4% span) at the design condition are investigated. The changes in unsteady tip clearance flow with the 0.62 % tip gap as the flow rate is reduced to near stall condition are also investigated. A Large Eddy Simulation (LES) is applied to calculate the unsteady flow field at these three flow conditions. Detailed Stereoscopic PIV (SPIV) measurements of the current flow fields were also performed at the Johns Hopkins University in a refractive index-matched test facility which renders the compressor blades and casing optically transparent. With this setup, the unsteady velocity field in the entire flow domain, including the flow inside the tip gap, can be measured. Unsteady tip clearance flow fields from LES are compared with the PIV measurements and both LES and PIV results are used to study changes in tip clearance flow structures. The current study shows that the tip clearance vortex is not a single structure as traditionally perceived. The tip clearance vortex is formed by multiple interlaced vorticities. Therefore, the tip clearance vortex is inherently unsteady. The multiple interlaced vortices never roll up to form a single structure. When phased-averaged, the tip clearance vortex appears as a single structure. When flow rate is reduced with the same tip gap, the tip clearance vortex rolls further upstream and the tip clearance vortex moves further radially inward and away from the suction side of the blade. When the tip gap size is increased at the design flow condition, the overall tip clearance vortex becomes stronger and it stays closer to the blade suction side and the vortex core extends all the way to the exit of the blade passage. Measured and calculated unsteady flow
Grid-converged solution and analysis of the unsteady viscous flow in a two-dimensional shock tube
Zhou, Guangzhao; Xu, Kun; Liu, Feng
2018-01-01
The flow in a shock tube is extremely complex with dynamic multi-scale structures of sharp fronts, flow separation, and vortices due to the interaction of the shock wave, the contact surface, and the boundary layer over the side wall of the tube. Prediction and understanding of the complex fluid dynamics are of theoretical and practical importance. It is also an extremely challenging problem for numerical simulation, especially at relatively high Reynolds numbers. Daru and Tenaud ["Evaluation of TVD high resolution schemes for unsteady viscous shocked flows," Comput. Fluids 30, 89-113 (2001)] proposed a two-dimensional model problem as a numerical test case for high-resolution schemes to simulate the flow field in a square closed shock tube. Though many researchers attempted this problem using a variety of computational methods, there is not yet an agreed-upon grid-converged solution of the problem at the Reynolds number of 1000. This paper presents a rigorous grid-convergence study and the resulting grid-converged solutions for this problem by using a newly developed, efficient, and high-order gas-kinetic scheme. Critical data extracted from the converged solutions are documented as benchmark data. The complex fluid dynamics of the flow at Re = 1000 are discussed and analyzed in detail. Major phenomena revealed by the numerical computations include the downward concentration of the fluid through the curved shock, the formation of the vortices, the mechanism of the shock wave bifurcation, the structure of the jet along the bottom wall, and the Kelvin-Helmholtz instability near the contact surface. Presentation and analysis of those flow processes provide important physical insight into the complex flow physics occurring in a shock tube.
2017-07-31
ultimately, may lead to revolutionary practical methods for the prediction and control of unsteady and turbulent flow. Recent work suggests a class...Recent work suggests a class of exact Navier-Stokes solutions termed “Exact Coherent Structures” (ECS) [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12] may...velocimetry. In the Taylor-Couette geometry, walls are always in close proximity to the flows of interest; thus, interrogation of fluorescing particles
Schobeiri, M. T.; Ozturk, B.; Ashpis, David E.
2007-01-01
The paper experimentally studies the effects of periodic unsteady wake flow and different Reynolds numbers on boundary layer development, separation and re-attachment along the suction surface of a low pressure turbine blade. The experimental investigations were performed on a large scale, subsonic unsteady turbine cascade research facility at Turbomachinery Performance and Flow Research Laboratory (TPFL) of Texas A&M University. The experiments were carried out at Reynolds numbers of 110,000 and 150,000 (based on suction surface length and exit velocity). One steady and two different unsteady inlet flow conditions with the corresponding passing frequencies, wake velocities, and turbulence intensities were investigated. The reduced frequencies chosen cover the operating range of LP turbines. In addition to the unsteady boundary layer measurements, surface pressure measurements were performed. The inception, onset, and the extent of the separation bubble information collected from the pressure measurements were compared with the hot wire measurements. The results presented in ensemble-averaged, and the contour plot forms help to understand the physics of the separation phenomenon under periodic unsteady wake flow and different Reynolds number. It was found that the suction surface displayed a strong separation bubble for these three different reduced frequencies. For each condition, the locations defining the separation bubble were determined carefully analyzing and examining the pressure and mean velocity profile data. The location of the boundary layer separation was dependent of the Reynolds number. It is observed that starting point of the separation bubble and the re-attachment point move further downstream by increasing Reynolds number from 110,000 to 150,000. Also, the size of the separation bubble is smaller when compared to that for Re=110,000.
Directory of Open Access Journals (Sweden)
Nor Athirah Mohd Zin
Full Text Available In this article, the influence of thermal radiation on unsteady magnetohydrodynamics (MHD free convection flow of rotating Jeffrey nanofluid passing through a porous medium is studied. The silver nanoparticles (AgNPs are dispersed in the Kerosene Oil (KO which is chosen as conventional base fluid. Appropriate dimensionless variables are used and the system of equations is transformed into dimensionless form. The resulting problem is solved using the Laplace transform technique. The impact of pertinent parameters including volume fraction Ï, material parameters of Jeffrey fluid Î»1, Î», rotation parameter r, Hartmann number Ha, permeability parameter K, Grashof number Gr, Prandtl number Pr, radiation parameter Rd and dimensionless time t on velocity and temperature profiles are presented graphically with comprehensive discussions. It is observed that, the rotation parameter, due to the Coriolis force, tends to decrease the primary velocity but reverse effect is observed in the secondary velocity. It is also observed that, the Lorentz force retards the fluid flow for both primary and secondary velocities. The expressions for skin friction and Nusselt number are also evaluated for different values of emerging parameters. A comparative study with the existing published work is provided in order to verify the present results. An excellent agreement is found. Keywords: Jeffrey nanofluid, AgNPs, MHD and Porosity, Rotating flow, Laplace transform technique
Rumsey, Christopher L.; Greenblatt, David
2007-01-01
This is an expanded version of a limited-length paper that appeared at the 5th International Symposium on Turbulence and Shear Flow Phenomena by the same authors. A computational study was performed for steady and oscillatory flow control over a hump model with flow separation to assess how well the steady and unsteady Reynolds-averaged Navier-Stokes equations predict trends due to Reynolds number, control magnitude, and control frequency. As demonstrated in earlier studies, the hump model case is useful because it clearly demonstrates a failing in all known turbulence models: they under-predict the turbulent shear stress in the separated region and consequently reattachment occurs too far downstream. In spite of this known failing, three different turbulence models were employed to determine if trends can be captured even though absolute levels are not. Overall the three turbulence models showed very similar trends as experiment for steady suction, but only agreed qualitatively with some of the trends for oscillatory control.
Suresh Babu, Arun Vishnu; Ramesh, Kiran; Gopalarathnam, Ashok
2017-11-01
In previous research, Ramesh et al. (JFM,2014) developed a low-order discrete vortex method for modeling unsteady airfoil flows with intermittent leading edge vortex (LEV) shedding using a leading edge suction parameter (LESP). LEV shedding is initiated using discrete vortices (DVs) whenever the Leading Edge Suction Parameter (LESP) exceeds a critical value. In subsequent research, the method was successfully employed by Ramesh et al. (JFS, 2015) to predict aeroelastic limit-cycle oscillations in airfoil flows dominated by intermittent LEV shedding. When applied to flows that require large number of time steps, the computational cost increases due to the increasing vortex count. In this research, we apply an amalgamation strategy to actively control the DV count, and thereby reduce simulation time. A pair each of LEVs and TEVs are amalgamated at every time step. The ideal pairs for amalgamation are identified based on the requirement that the flowfield in the vicinity of the airfoil is least affected (Spalart, 1988). Instead of placing the amalgamated vortex at the centroid, we place it at an optimal location to ensure that the leading-edge suction and the airfoil bound circulation are conserved. Results of the initial study are promising.
On the One-Dimensional Steady and Unsteady Porous Flow Equation
DEFF Research Database (Denmark)
Andersen, O. H.; Burcharth, H. F.
1995-01-01
Porous flow in coarse granular media is discussed theoretically with special concern given to the variation of the flow resistance with the porosity. For steady state flow, the Navier-Stokes equation is applied as a basis for the derivations. A turbulent flow equation is suggested. Alternative...... derivations based on dimensional analysis and a pipe analogy, respectively, are discussed. For non-steady state flow, the derivations are based on a cylinder/sphere analogy leading to a virtual mass coefficient. For the fully turbulent flow regime, existing experimental data values of the quadratic flow...... resistance coefficients are presented. Moreover, a simple formula for estimation of the turbulent flow coefficient is given. Virtual mass coefficients based on existing data are presented, however, no definite conclusions can be given due to the scarce data available....
Fatin Jamil, Dzuliana; Roslan, Rozaini; Abdulhameed, Mohammed; Che-Him, Norziha; Sufahani, Suliadi; Mohamad, Mahathir; Ghazali Kamardan, Muhamad
2018-04-01
The effects of nanoparticles such as Fe 3O4,TiO2, and Cu on blood flow inside a stenosed artery are studied. In this study, blood was modelled as non-Newtonian Bingham plastic fluid subjected to periodic body acceleration and slip velocity. The flow governing equations were solved analytically by using the perturbation method. By using the numerical approaches, the physiological parameters were analyzed, and the blood flow velocity distributions were generated graphically and discussed. From the flow results, the flow speed increases as slip velocity increases and decreases as the values of yield stress increases.
International Nuclear Information System (INIS)
Huang, Si; Su, Xianghui; Guo, Jing; Yue, Le
2014-01-01
Highlights: • The transient gas–liquid two-phase flow fields in the self-priming centrifugal pump are simulated. • The self-priming time and performance are estimated. • The air void fraction and two phase distribution are obtained.· The hole on the volute plays a significant role for gas exhausting. • The frequency of the impulsive pressure basically conforms to that of the air exhausted out of the pump. - Abstract: Self-priming pumps start up without pre-irrigation, and then work as common pumps when air in the pump is exhausted. The transient gas–liquid flow at the start-up stage inside a self-priming pump is an interesting process which greatly influences performance of the pump. In this paper, a conventional vertical self-priming centrifugal pump was selected as the object. Using unsteady numerical simulation, the authors investigated the transient gas–liquid two-phase flow in the self-priming centrifugal pump during the self-priming process. The main innovation in the simulation was that a section of the suction pipe filled with air was set as the initial condition, which conformed to the actual self-priming conditions. The gas–liquid two-phase distribution, the pressure and velocity in relation to time were computed and analyzed. Flow rates of both phases with time at the pump inlet and outlet were obtained based on the simulation, which could be used to estimate the self-priming time and other performance parameters. Finally, the numerical method and results for gas–liquid two-phase flow in the self-priming pump was partly validated by the pump performance test
The effect of inlet distorted flow on steady and unsteady performance of a centrifugal compressor
International Nuclear Information System (INIS)
Park, Jae Hyoung; Kang, Shin Hyoung
2005-01-01
Effects of inlet distorted flow on performance, stall and surge are experimentally investigated for a high-speed centrifugal compressor. Tested results for the distorted inlet flow cases are compared with the result of the undistorted one. The performance of compressor is slightly deteriorated due to the inlet distortion. The inlet distortion does not affect the number of stall cell and the propagation velocity. It also does not change stall inception flow rate. However, as the distortion increases, stall starts at the higher flow rate for low speed at the lower flow rate for high speed. For 50,000 rpm stall occurs as the flow rate decreases, however disappears for the smaller flow rate. This is due to the interaction of surge and stall. After the stall and surge interact, the number of stall cell decreases
Directory of Open Access Journals (Sweden)
Costanza Aricò
2018-01-01
Full Text Available The shallow water equations are a mathematical tool widely applied for the simulation of flow routing in rivers and floodplains, as well as for flood inundation mapping. The interest of many researchers has been focused on the study of simplified forms of the original set of equations. One of the most commonly applied simplifications consists of neglecting the inertial terms. The effects of such a choice on the outputs of the simulations of flooding events are controversial and are an important topic of debate. In the present paper, two numerical models recently proposed for the solution of the complete and zero-inertia forms of the shallow water equations, are applied to several unsteady flow routing scenarios. We simulate synthetic and laboratory scenarios of unsteady flow routing, starting from very simple geometries and gradually moving towards complex topographies. Unlike the studies of the range of validity of the zero-inertia model, based on a small perturbation of the linearized flow model, in unsteady flow propagation over irregular topographies, it is more difficult to specify criteria for the applicability of the simplified set of equations. In analyzing the role of the terms in the momentum equations, we try to understand the effect of neglecting the inertial terms in the zero-inertia formulation. We also analyze the computational costs.
Vermeire, B. C.; Witherden, F. D.; Vincent, P. E.
2017-04-01
First- and second-order accurate numerical methods, implemented for CPUs, underpin the majority of industrial CFD solvers. Whilst this technology has proven very successful at solving steady-state problems via a Reynolds Averaged Navier-Stokes approach, its utility for undertaking scale-resolving simulations of unsteady flows is less clear. High-order methods for unstructured grids and GPU accelerators have been proposed as an enabling technology for unsteady scale-resolving simulations of flow over complex geometries. In this study we systematically compare accuracy and cost of the high-order Flux Reconstruction solver PyFR running on GPUs and the industry-standard solver STAR-CCM+ running on CPUs when applied to a range of unsteady flow problems. Specifically, we perform comparisons of accuracy and cost for isentropic vortex advection (EV), decay of the Taylor-Green vortex (TGV), turbulent flow over a circular cylinder, and turbulent flow over an SD7003 aerofoil. We consider two configurations of STAR-CCM+: a second-order configuration, and a third-order configuration, where the latter was recommended by CD-adapco for more effective computation of unsteady flow problems. Results from both PyFR and STAR-CCM+ demonstrate that third-order schemes can be more accurate than second-order schemes for a given cost e.g. going from second- to third-order, the PyFR simulations of the EV and TGV achieve 75× and 3× error reduction respectively for the same or reduced cost, and STAR-CCM+ simulations of the cylinder recovered wake statistics significantly more accurately for only twice the cost. Moreover, advancing to higher-order schemes on GPUs with PyFR was found to offer even further accuracy vs. cost benefits relative to industry-standard tools.
Energy Technology Data Exchange (ETDEWEB)
Vermeire, B.C., E-mail: brian.vermeire@concordia.ca; Witherden, F.D.; Vincent, P.E.
2017-04-01
First- and second-order accurate numerical methods, implemented for CPUs, underpin the majority of industrial CFD solvers. Whilst this technology has proven very successful at solving steady-state problems via a Reynolds Averaged Navier–Stokes approach, its utility for undertaking scale-resolving simulations of unsteady flows is less clear. High-order methods for unstructured grids and GPU accelerators have been proposed as an enabling technology for unsteady scale-resolving simulations of flow over complex geometries. In this study we systematically compare accuracy and cost of the high-order Flux Reconstruction solver PyFR running on GPUs and the industry-standard solver STAR-CCM+ running on CPUs when applied to a range of unsteady flow problems. Specifically, we perform comparisons of accuracy and cost for isentropic vortex advection (EV), decay of the Taylor–Green vortex (TGV), turbulent flow over a circular cylinder, and turbulent flow over an SD7003 aerofoil. We consider two configurations of STAR-CCM+: a second-order configuration, and a third-order configuration, where the latter was recommended by CD-adapco for more effective computation of unsteady flow problems. Results from both PyFR and STAR-CCM+ demonstrate that third-order schemes can be more accurate than second-order schemes for a given cost e.g. going from second- to third-order, the PyFR simulations of the EV and TGV achieve 75× and 3× error reduction respectively for the same or reduced cost, and STAR-CCM+ simulations of the cylinder recovered wake statistics significantly more accurately for only twice the cost. Moreover, advancing to higher-order schemes on GPUs with PyFR was found to offer even further accuracy vs. cost benefits relative to industry-standard tools.
International Nuclear Information System (INIS)
Vermeire, B.C.; Witherden, F.D.; Vincent, P.E.
2017-01-01
First- and second-order accurate numerical methods, implemented for CPUs, underpin the majority of industrial CFD solvers. Whilst this technology has proven very successful at solving steady-state problems via a Reynolds Averaged Navier–Stokes approach, its utility for undertaking scale-resolving simulations of unsteady flows is less clear. High-order methods for unstructured grids and GPU accelerators have been proposed as an enabling technology for unsteady scale-resolving simulations of flow over complex geometries. In this study we systematically compare accuracy and cost of the high-order Flux Reconstruction solver PyFR running on GPUs and the industry-standard solver STAR-CCM+ running on CPUs when applied to a range of unsteady flow problems. Specifically, we perform comparisons of accuracy and cost for isentropic vortex advection (EV), decay of the Taylor–Green vortex (TGV), turbulent flow over a circular cylinder, and turbulent flow over an SD7003 aerofoil. We consider two configurations of STAR-CCM+: a second-order configuration, and a third-order configuration, where the latter was recommended by CD-adapco for more effective computation of unsteady flow problems. Results from both PyFR and STAR-CCM+ demonstrate that third-order schemes can be more accurate than second-order schemes for a given cost e.g. going from second- to third-order, the PyFR simulations of the EV and TGV achieve 75× and 3× error reduction respectively for the same or reduced cost, and STAR-CCM+ simulations of the cylinder recovered wake statistics significantly more accurately for only twice the cost. Moreover, advancing to higher-order schemes on GPUs with PyFR was found to offer even further accuracy vs. cost benefits relative to industry-standard tools.
Gordon, Kathryn; Morris, Scott; Jemcov, Aleksandar; Cameron, Joshua
2013-11-01
The interaction of components in a compressible, internal flow often results in unsteady interactions between the wakes and moving blades. A prime example in which this flow feature is of interest is the interaction between the downstream rotor blades in a transonic axial compressor with the wake vortices shed from the upstream inlet guide vane (IGV). Previous work shows that a double row of counter-rotating vortices convects downstream into the rotor passage as a result of the rotor blade bow shock impinging on the IGV. The rotor-relative time-mean total pressure distribution has a region of high total pressure corresponding to the pathline of the vortices. The present work focuses on the relationship between the magnitude of the time-mean rotor-relative total pressure profile and the axial spacing between the IGV and the rotor. A survey of different axial gap sizes is performed in a two-dimensional computational study to obtain the sensitivity of the pressure profile amplitude to IGV-rotor axial spacing.
The unsteady flow of a nanofluid in the stagnation point region of a time-dependent rotating sphere
Directory of Open Access Journals (Sweden)
Malvandi Amir
2015-01-01
Full Text Available This paper deals with the unsteady boundary layer flow and heat transfer of nanofluid over a time-dependent rotating sphere where the free stream velocity varies continuously with time. The boundary layer equations were normalized via similarity variables and solved numerically. Best accuracy of the results has been obtained for regular fluid with previous studies. The nanofluid is treated as a two-component mixture (base fluid+nanoparticles that incorporates the effects of Brownian diffusion and thermophoresis simultaneously as the two most important mechanisms of slip velocity in laminar flows. Our outcomes indicated that as A and λ increase, surface shear stresses, heat transfer and concentration rates, climb up. Also, Increasing the thermophoresis Nt is found to decrease in the both values of heat transfer and concentration rates. This decrease supresses for higher thermophoresis number. In addition, it was observed that unlike the heat transfer rate, a rise in Brownian motion Nb, leads to an increase in concentration rate.
Visualization and PIV measurement of unsteady flow around a darrieus wind turbine in dynamic stall
Energy Technology Data Exchange (ETDEWEB)
Shibuya, Satoshi; Fujisawa, Nobuyuki; Takano, Tsuyoshi [Dept. of Mechanical and Production Engineering, Niigata Univ., Niigata (Japan)
1999-07-01
Flow around a Darrieus wind turbine in dynamic stall is studied by flow visualization and PIV (particle image velocimeter) measurement in a rotating frame of reference, which allows the successive observation of the dynamic stall over the blade. The qualitative features of the flow field in dynamic stall observed by the flow visualization, such as the formation and shedding of the stall vortices, are quantitatively reproduced in the instantaneous velocity distributions near the blade by using PIV. These results indicate that two pairs of stall vortices are generated from the blade during one rotation of the blade and that the size and the generating blade angle of the stall vortices are enlarged as the tip-speed ratio decreases. These stall vortices are produced by the in-flow motion from the outer surface to the inner surface through the trailing edge of the blade and the flow separation over the inner surface of the blade. (author)
Unsteady Flow Simulation of a Sweeping Jet Actuator Using a Lattice-Boltzmann Method
Duda, B.; Wessels, M.; Fares, E.; Vatsa, V.
2016-01-01
Active flow control technology is increasingly used in aerospace applications to control flow separation and to improve aerodynamic performance. In this paper, PowerFLOW is used to simulate the flow through a sweeping jet actuator at two different pressure ratios. The lower pressure ratio leads to a high subsonic flow, whereas the high pressure ratio produces a choked flow condition. Comparison of numerical results with experimental data is shown, which includes qualitatively good agreement of pressure histories and spectra. PIV measurements are also available but the simulation overestimates mean and fluctuation quantities outside the actuator. If supply pressure is matched at one point inside the mixing chamber a good qualitative agreement is achieved at all other monitor points.
Spatial Harmonic Decomposition as a tool for unsteady flow phenomena analysis
International Nuclear Information System (INIS)
Duparchy, A; Guillozet, J; De Colombel, T; Bornard, L
2014-01-01
Hydropower is already the largest single renewable electricity source today but its further development will face new deployment constraints such as large-scale projects in emerging economies and the growth of intermittent renewable energy technologies. The potential role of hydropower as a grid stabilizer leads to operating hydro power plants in ''off-design'' zones. As a result, new methods of analyzing associated unsteady phenomena are needed to improve the design of hydraulic turbines. The key idea of the development is to compute a spatial description of a phenomenon by using a combination from several sensor signals. The spatial harmonic decomposition (SHD) extends the concept of so-called synchronous and asynchronous pulsations by projecting sensor signals on a linearly independent set of a modal scheme. This mathematical approach is very generic as it can be applied on any linear distribution of a scalar quantity defined on a closed curve. After a mathematical description of SHD, this paper will discuss the impact of instrumentation and provide tools to understand SHD signals. Then, as an example of a practical application, SHD is applied on a model test measurement in order to capture and describe dynamic pressure fields. Particularly, the spatial description of the phenomena provides new tools to separate the part of pressure fluctuations that contribute to output power instability or mechanical stresses. The study of the machine stability in partial load operating range in turbine mode or the comparison between the gap pressure field and radial thrust behavior during turbine brake operation are both relevant illustrations of SHD contribution
Pressurised water reactor in the UK
International Nuclear Information System (INIS)
Anon.
1982-01-01
Since the Three Mile Island accident there has been much debate about the safety considerations of Pressurised Water Reactors. Their development will continue throughout the world but it will be based upon the lessons learned from that unfortunate accident. In the United Kingdom there is a public enquiry discussing all aspects of the reactor. The papers given in this book provide an informed addition to the literature. The design, safety and licensing and construction of a pressurised water reactor system are discussed in detail. Considerations stemming from the Three Mile Island accident are presented
Energy Technology Data Exchange (ETDEWEB)
Devesa, A
2006-12-15
Nuclear industry flows are most of the time characterized by their high Reynolds number, density variations (at low Mach numbers) and a highly unsteady behaviour (low to moderate frequencies). High Reynolds numbers are un-affordable by direct simulation (DNS), and simulations must either be performed by solving averaged equations (RANS), or by solving only the large eddies (LES), both using a wall model. A first investigation of this thesis dealt with the derivation and test of two variable density wall models: an algebraic law (CWM) and a zonal approach dedicated to LES (TBLE-{rho}). These models were validated in quasi-isothermal cases, before being used in academic and industrial non-isothermal flows with satisfactory results. Then, a numerical experiment of pulsed passive scalars was performed by DNS, were two forcing conditions were considered: oscillations are imposed in the outer flow; oscillations come from the wall. Several frequencies and amplitudes of oscillations were taken into account in order to gain insights in unsteady effects in the boundary layer, and to create a database for validating wall models in such context. The temporal behaviour of two wall models (algebraic and zonal wall models) were studied and showed that a zonal model produced better results when used in the simulation of unsteady flows. (author)
On unsteady two-phase fluid flow due to eccentric rotation of a disk
Directory of Open Access Journals (Sweden)
A. K. Ghosh
2003-01-01
in a double-disk configuration, a result which is the reverse to that of solid-body rotation. Finally, the results are presented graphically to determine the quantitative response of the particle on the flow.
Zonal Detached-Eddy Simulation of Turbulent Unsteady Flow over Iced Airfoils
Zhang, Yue; Habashi, Wagdi G.; Khurram, Rooh Ul Amin
2015-01-01
scales to the grid (resolved) scales. The stabilization terms arise naturally and are free of userdefined stability parameters. Validation of the method is accomplished via the turbulent flow over tandem cylinders. The boundary-layer separation, free
Unsteady Helical Flows of a Size-Dependent Couple-Stress Fluid
Rubbab, Qammar; Mirza, Itrat Abbas; Siddique, Imran; Irshad, Saadia
2017-01-01
The helical flows of couple-stress fluids in a straight circular cylinder are studied in the framework of the newly developed, fully determinate linear couple-stress theory. The fluid flow is generated by the helical motion of the cylinder with time-dependent velocity. Also, the couple-stress vector is given on the cylindrical surface and the nonslip condition is considered. Using the integral transform method, analytical solutions to the axial velocity, azimuthal velocity, nonsymmetric force...
High-Order Multioperator Compact Schemes for Numerical Simulation of Unsteady Subsonic Airfoil Flow
Savel'ev, A. D.
2018-02-01
On the basis of high-order schemes, the viscous gas flow over the NACA2212 airfoil is numerically simulated at a free-stream Mach number of 0.3 and Reynolds numbers ranging from 103 to 107. Flow regimes sequentially varying due to variations in the free-stream viscosity are considered. Vortex structures developing on the airfoil surface are investigated, and a physical interpretation of this phenomenon is given.
The role of unsteady effusion rates on inflation in long-lived lava flow fields
Rader, E.; Vanderkluysen, L.; Clarke, A.
2017-11-01
The emission of volcanic gases and particles can have global and lasting environmental effects, but their timing, tempo, and duration can be problematic to quantify for ancient eruptions where real-time measurements are absent. Lava flows, for example, may be long-lasting, and their impact is controlled by the rate, tempo, and vigor of effusion. These factors are currently difficult to derive from the geologic record but can have large implications for the atmospheric impact of an eruption. We conducted a set of analogue experiments on lava flow inflation aiming at connecting lava morphologies preserved in the rock record to eruption tempo and dynamics through pulsating effusion rates. Inflation, a process where molten material is injected beneath the crust of an active lava flow and lifts it upwards, is a common phenomenon in basaltic volcanic systems. This mechanism requires three components: a) a coherent, insulating crust; b) a wide-spread molten core; and c) pressure built up beneath the crust from a sustained supply of molten material. Inflation can result in a lava flow growing tens of meters thick, even in flow fields that expand hundreds of square kilometers. It has been documented that rapid effusion rates tend to create channels and tubes, isolating the active part of the flow from the stagnant part, while slow effusion rates may cause crust to form quickly and seize up, forcing lava to overtop the crust. However, the conditions that allow for inflation of large flow fields have not previously been evaluated in terms of effusion rate. By using PEG 600 wax and a programmable pump, we observe how, by pulsating effusion rate, inflation occurs even in very low viscosity basaltic eruptions. We show that observations from inflating Hawaiian lava flows correlate well with experimental data and indicate that instantaneous effusion rates may have been 3 times higher than average effusion rates during the emplacement of the 23 January 1988 flow at Kīlauea (Hawai
A. Sinha; J.C. Misra; G.C. Shit
2016-01-01
This paper presents a theoretical analysis of blood flow and heat transfer in a permeable vessel in the presence of an external magnetic field. The unsteadiness in the coupled flow and temperature fields is considered to be caused due to the time-dependent stretching velocity and the surface temperature of the vessel. The non-uniform heat source/sink effect on blood flow and heat transfer is taken into account. This study is of potential value in the clinical treatment of cardiovascular disor...
Irfan, M.; Khan, M.; Khan, W. A.
Inspired by modern deeds of nanotechnology and nanoscience and their abundant applications in the field of science and engineering, we establish a mathematical relation for unsteady 3D forced convective flow of Carreau nanofluid over a bidirectional stretched surface. Heat transfer phenomena of Carreau nanofluid is inspected through the variable thermal conductivity and heat generation/absorption impact. Furthermore, this research paper presents a more convincing approach for heat and mass transfer phenomenon of nanoliquid by utilizing new mass flux condition. Practically, zero mass flux condition is more adequate because in this approach we assume nanoparticle amends itself accordingly on the boundaries. Now the features of Buongiorno's relation for Carreau nanofluid can be applied in a more efficient way. An appropriate transformation is vacant to alter the PDEs into ODEs and then tackled numerically by employing bvp4c scheme. The numerous consequence of scheming parameters on the Carreau nanoliquid velocity components, temperature and concentration fields are portrayed graphically and deliberated in detail. The numerical outcomes for local skin friction and the wall temperature gradient for nanoliquid are intended and vacant through tables. The outcomes conveyed here manifest that impact of Brownian motion parameter Nb on the rate of heat transfer for nanoliquids becomes negligible for the recently recommended revised relation. Addationally, for authentication of the present relation, the achieved results are distinguished with earlier research works in specific cases and marvelous agreement has been noted.
Directory of Open Access Journals (Sweden)
M.J. Uddin
2016-09-01
Full Text Available The two-dimensional unsteady laminar free convective heat and mass transfer fluid flow of a non-Newtonian fluid adjacent to a vertical plate has been analyzed numerically. The two parameters Lie group transformation method that transforms the three independent variables into a single variable is used to transform the continuity, the momentum, the energy and the concentration equations into a set of coupled similarity equations. The transformed equations have been solved by the Runge–Kutta–Fehlberg fourth-fifth order numerical method with shooting technique. Numerical calculations were carried out for the various parameters entering into the problem. The dimensionless velocity, temperature and concentration profiles were shown graphically and the skin friction, heat and mass transfer rates were given in tables. It is found that friction factor and heat transfer (mass transfer rate for methanol are higher (lower than those of hydrogen and water vapor. Friction factor decreases while heat and mass transfer rate increase as the Prandtl number increases. Friction (heat and mass transfer rate factor of Newtonian fluid is higher (lower than the dilatant fluid.
Directory of Open Access Journals (Sweden)
C. Sulochana
2016-02-01
Full Text Available We analyzed the momentum and heat transfer characteristics of unsteady MHD flow of a dusty nanofluid over a vertical stretching surface in presence of volume fraction of dust and nano particles with non uniform heat source/sink. We considered two types of nanofluids namely Ag-water and Cu-water embedded with conducting dust particles. The governing equations are transformed in to nonlinear ordinary differential equations by using similarity transformation and solved numerically using Shooting technique. The effects of non-dimensional governing parameters on velocity and temperature profiles for fluid and dust phases are discussed and presented through graphs. Also, the skin friction coefficient and Nusselt number are discussed and presented for two dusty nanofluids separately in tabular form. Results indicate that an increase in the volume fraction of dust particles enhances the heat transfer in Cu-water nanofluid compared with Ag-water nanofluid and a raise in the volume fraction of nano particles shows uniform heat transfer in both Cu-water and Ag-water nanofluids.
International Nuclear Information System (INIS)
Kaznacheev, A; Kuznetsov, I
2014-01-01
The measurements and video observation of unsteady flow in the draft tube cone of the pump-turbine model were conducted in the Laboratory of Water Turbines, property of OJSC ''Power machines'' - ''LMZ''. The prototype head was about 250 m. The experiments were performed for the turbine mode of operation. Measurements were taken for the unit speed value n11 corresponding to rated head in the generating mode of operation, for a wide range of guide vanes openings at loads ranging from partial to maximum value. The researches of the velocity field in function of the Thoma number were carried out in some operating conditions. The mean values and RMS deviations of the velocity components were the results of laser measurements. The curves of the intensity of the vortex versus the guide vane opening and the Thoma number were plotted. The energy velocity spectra were presented for the points at which the most pronounced frequency precession of the helical axial vortex was observed. Video recording and laser Doppler anemometry were made in the operating conditions of the developed cavitation. Based on the results of video observations and energy spectra obtained via LDA, vortex frequencies were determined i.e. the frequencies of the vortex precession under the runner in the draft tube cone
Directory of Open Access Journals (Sweden)
Dong Yan
2017-01-01
Full Text Available Strong shock waves can be generated by pulse discharge in water, and the characteristics due to the shock wave normal reflection from rigid walls have important significance to many fields, such as industrial production and defense construction. This paper investigates the effects of hydrostatic pressures and perturbation of wave source (i.e., charging voltage on normal reflection of one-dimensional unsteady flow shock waves. Basic properties of the incidence and reflection waves were analyzed theoretically and experimentally to identify the reflection mechanisms and hence the influencing factors and characteristics. The results indicated that increased perturbation (i.e., charging voltage leads to increased peak pressure and velocity of the reflected shock wave, whereas increased hydrostatic pressure obviously inhibited superposition of the reflection waves close to the rigid wall. The perturbation of wave source influence on the reflected wave was much lower than that on the incident wave, while the hydrostatic pressure obviously affected both incident and reflection waves. The reflection wave from the rigid wall in water exhibited the characteristics of a weak shock wave, and with increased hydrostatic pressure, these weak shock wave characteristics became more obvious.
Computation of unsteady flow and aerodynamic noise of NACA0018 airfoil using large-eddy simulation
Energy Technology Data Exchange (ETDEWEB)
Kim, H.-J. [Department of Mechanical Engineering, Inha University, 253 Yonghyun-dong, Nam-gu, Incheon 402-751 (Korea, Republic of); Lee, S. [Department of Mechanical Engineering, Inha University, 253 Yonghyun-dong, Nam-gu, Incheon 402-751 (Korea, Republic of)]. E-mail: sbaelee@inha.ac.kr; Fujisawa, N. [Department of Mechanical and Production Engineering, Niigata University, 8050 Ikarashi-2, Niigata 950-2181 (Japan)
2006-04-15
The flow field around a symmetrical NACA airfoil in the uniform flow under generation of noise was numerically studied. The numerical simulation was carried out by a large-eddy simulation that employs a deductive dynamic model as the subgrid-scale model. The results at small angle of attack {alpha} = 3-6{sup o} indicate that the discrete frequency noise is generated when the separated laminar flow reattaches near the trailing edge of pressure side and the strong instability thereafter affects positive vortices shed near the trailing edge. The quasi-periodic behavior of negative vortex formation on the suction side is affected by the strength and the periodicity of positive vortices near the trailing edge. The computation using aero-acoustic analogy indicates the primary discrete peak at the Strouhal frequency (=2f . {delta}/U ) of 0.15 by the vortex shedding from the trailing edge, which is in a close agreement with the experiment.
Particle image velocimetry investigation of flow over unsteady airfoil with trailing-edge strip
Energy Technology Data Exchange (ETDEWEB)
Gerontakos, P.; Lee, T. [McGill University, Montreal, QC (Canada)
2008-04-15
The flow over a flapped NACA 0012 airfoil, oscillated slightly through the static-stall angle, was investigated by using particle image velocimetry, and was supplemented by surface pressure and dynamic-load measurements. A significant increase in the dynamic lift force and nose-down pitching moment was observed. The most pronounced flow phenomenon was the formation and detachment of an energetic leading-edge vortex compared to the no-flapped airfoil. The details of the underlying physical mechanisms responsible for the various light-stall flow processes were provided via the instantaneous velocity and vorticity fields measurements. In contrast to the Gurney flap, the inverted trailing-edge strip led to an improved negative damping while a reduced lift force. The addition of an inverted strip always led to the appearance of a Karman-type vortex shedding street immediately downstream of the strip over the entire oscillation cycle. (orig.)
CSIR Research Space (South Africa)
Dunn, Dwain I
2011-08-01
Full Text Available with the rotor leading edge, i.e. the location that the wake impinges on the leading edge of the rotor. It can be seen that there was not much fluctuation in time in the pressure profiles. With regards to the annular case the pressure surface shows... and lighter for a given b) (1) (A) (b) (1) (A) 2 thrust rating, the stronger secondary flows become. Therefore a reduction in secondary flow leads to an increase in performance of the turbine engine. One of the methods currently being investigated...
Studies on unsteady pressure fields in the region of separating and reattaching flows
Govinda Ram, H. S.; Arakeri, V. H.
1990-12-01
Experimental studies on the measurement of pressure fields in the region of separating and reattaching flows behind several two-dimensional fore-bodies and one axisymmetric body are reported. In particular, extensive measurements of mean pressure, surface pressure fluctuation, and pressure fluctuation within the flow were made for a series of two-dimensional fore-body shapes consisting of triangular nose with varying included angle. The measurements from different bodies are compared and one of the important findings is that the maximum values of rms pressure fluctuation levels in the shear layer approaching reattachment are almost equal to the maximum value of the surface fluctuation levels.
Rubino, A.; Pini, M.; Colonna di Paliano, Piero; Dossena, V.; Guardone, A.; Astolfi, M.
2017-01-01
Currently, turbomachinery design optimization methodologies are mainly restricted to steady state approaches, due to the high computational cost associated with time-accurate shape optimization algorithms. However, the possibility to include unsteady effects in turbomachinery optimization can
Sensitivity Analysis of Unsteady Flow Fields and Impact of Measurement Strategy
Directory of Open Access Journals (Sweden)
Takashi Misaka
2014-01-01
Full Text Available Difficulty of data assimilation arises from a large difference between the sizes of a state vector to be determined, that is, the number of spatiotemporal mesh points of a discretized numerical model and a measurement vector, that is, the amount of measurement data. Flow variables on a large number of mesh points are hardly defined by spatiotemporally limited measurements, which poses an underdetermined problem. In this study we conduct the sensitivity analysis of two- and three-dimensional vortical flow fields within a framework of data assimilation. The impact of measurement strategy, which is evaluated by the sensitivity of the 4D-Var cost function with respect to measurements, is investigated to effectively determine a flow field by limited measurements. The assimilation experiment shows that the error defined by the difference between the reference and assimilated flow fields is reduced by using the sensitivity information to locate the limited number of measurement points. To conduct data assimilation for a long time period, the 4D-Var data assimilation and the sensitivity analysis are repeated with a short assimilation window.
A way to visualise heat transfer in 3D unsteady flows
Speetjens, M.F.M.
2009-01-01
Heat transfer in fluid flows traditionally is examined in terms of temperature field and heat-transfer coefficients. However, heat transfer may alternatively be considered as the transport of thermal energy by the total convective-conductive heat flux in a way analogous to the transport of fluid by
Gulping phenomena in transient countercurrent two-phase flow
International Nuclear Information System (INIS)
Tehrani, Ali A.K.
2001-04-01
Apart from previous work on countercurrent gas-liquid flow, transient tank drainage through horizontal off-take pipes is described, including experimental procedure, flow pattern on observations and countercurrent flow limitation results. A separate chapter is devoted to countercurrent two-phase flow in a pressurised water reactor hot-leg scaled model. Results concerning low head flooding, high head and loss of bowl flooding, transient draining of the steam generator and pressure variation and bubble detachment are presented. The following subjects are covered as well: draining of sealed tanks of vertical pipes, unsteady draining of closed vessel via vertical tube, unsteady filling of a closed vessel via vertical tube from a constant head reservoir. Practical significance of the results obtained is discussed
Directory of Open Access Journals (Sweden)
Govindarajan Arunachalam
2014-01-01
Full Text Available An investigation of unsteady MHD free convective flow and mass transfer during the motion of a viscous incompressible fluid through a porous medium, bounded by an infinite vertical porous surface, in a rotating system is presented. The porous plane surface and the porous medium are assumed to rotate in a solid body rotation. The vertical surface is subjected to uniform constant suction perpendicular to it and the temperature at this surface fluctuates in time about a non-zero constant mean. Analytical expressions for the velocity, temperature and concentration fields are obtained using the perturbation technique. The effects of R (rotation parameter, k0 (permeability parameter, M (Hartmann number and w (frequency parameter on the flow characteristics are discussed. It is observed that the primary velocity component decreases with the increase in either of the rotation parameter R, the permeability parameter k0, or the Hartmann number M. It is also noted that the primary skin friction increases whenever there is an increase in the Grashof number Gr or the modified Grashof number Gm. It is clear that the heat transfer coefficient in terms of the Nusselt number decreases in the case of both air and water when there is an increase in the Hartmann number M. It is observed that the magnitude of the secondary velocity profiles increases whenever there is an increase in either of the Grashof number or the modified Grashof number for mass transfer or the permeability of the porous media. Concentration profiles decreases with an increase in the Schmidt number.
A monitoring device for pressurised-air-driven diaphragm-based artificial heart assist devices
Hoeben, F.P.; Hoeben, F.P.; de Mul, F.F.M.; Stokkink, J.S.D.; Stokkink, H.S.D.; Koelink, M.H.; Koelink, M.H.; Greve, Jan
1992-01-01
A non-invasive device has been developed to monitor the diaphragm position and the blood flow in artificial heart assist devices equipped with a pressurised-air-driven diaphragm. Light scattering from the diaphragm is used as a mechanism for measuring. Information about the position of several
Directory of Open Access Journals (Sweden)
Yannick Bousquet
2014-01-01
Full Text Available This study concerns a 2.5 pressure ratio centrifugal compressor stage consisting of a splittered unshrouded impeller and a vaned diffuser. The aim of this paper is to investigate the modifications of the flow structure when the operating point moves from peak efficiency to near stall. The investigations are based on the results of unsteady three-dimensional simulations, in a calculation domain comprising all the blade. A detailed analysis is given in the impeller inducer and in the vaned diffuser entry region through time-averaged and unsteady flow field. In the impeller inducer, this study demonstrates that the mass flow reduction from peak efficiency to near stall leads to intensification of the secondary flow effects. The low momentum fluid accumulated near the shroud interacts with the main flow through a shear layer zone. At near stall condition, the interface between the two flow structures becomes unstable leading to vortices development. In the diffuser entry region, by reducing the mass flow, the high incidence angle from the impeller exit induces a separation on the diffuser vane suction side. At near stall operating point, vorticity from the separation is shed into vortex cores which are periodically formed and convected downstream along the suction side.
Feedback control for unsteady flow and its application to the stochastic Burgers equation
Choi, Haecheon; Temam, Roger; Moin, Parviz; Kim, John
1993-01-01
The study applies mathematical methods of control theory to the problem of control of fluid flow with the long-range objective of developing effective methods for the control of turbulent flows. Model problems are employed through the formalism and language of control theory to present the procedure of how to cast the problem of controlling turbulence into a problem in optimal control theory. Methods of calculus of variations through the adjoint state and gradient algorithms are used to present a suboptimal control and feedback procedure for stationary and time-dependent problems. Two types of controls are investigated: distributed and boundary controls. Several cases of both controls are numerically simulated to investigate the performances of the control algorithm. Most cases considered show significant reductions of the costs to be minimized. The dependence of the control algorithm on the time-descretization method is discussed.
Numerical simulations of unsteady flows past two-bladed rotors in forward-flight conditions
International Nuclear Information System (INIS)
Xu, H.; Mamou, M.; Khalid, M.
2004-01-01
The current paper presents time-accurate numerical simulations of compressible flows past two-bladed rotor configurations using a Chimera moving grid approach. The simulations are performed for a variety of flow conditions and various blade aspect ratios. The rotor blades are rectangular, untapered and untwisted planforms. Their cross-sections are built using the NACA 0012 airfoil profile. The aerodynamic performance of the rotor is investigated using the Euler equations. The CFD-FASTRAN code was used for the computations. The pressure distributions are benchmarked against the experimental data from Caradonna and Tung and a number of previous Euler calculations by Agarwal and Deese and Chen et al. The comparisons indicate that the current simulations for the forward flight conditions can reproduce the pressure distributions on the blade surfaces and the prediction of shockwave locations with reasonably good accuracy. (author)
Numerical simulations of unsteady flows past two-bladed rotors in forward-flight conditions
Energy Technology Data Exchange (ETDEWEB)
Xu, H.; Mamou, M.; Khalid, M. [National Research Council, Inst. for Aerospace Research, Ottawa, Ontario (Canada)]. E-mail: Hongyi.Xu@nrc.ca
2004-07-01
The current paper presents time-accurate numerical simulations of compressible flows past two-bladed rotor configurations using a Chimera moving grid approach. The simulations are performed for a variety of flow conditions and various blade aspect ratios. The rotor blades are rectangular, untapered and untwisted planforms. Their cross-sections are built using the NACA 0012 airfoil profile. The aerodynamic performance of the rotor is investigated using the Euler equations. The CFD-FASTRAN code was used for the computations. The pressure distributions are benchmarked against the experimental data from Caradonna and Tung and a number of previous Euler calculations by Agarwal and Deese and Chen et al. The comparisons indicate that the current simulations for the forward flight conditions can reproduce the pressure distributions on the blade surfaces and the prediction of shockwave locations with reasonably good accuracy. (author)
Unsteady flow of fractional Oldroyd-B fluids through rotating annulus
Tahir, Madeeha; Naeem, Muhammad Nawaz; Javaid, Maria; Younas, Muhammad; Imran, Muhammad; Sadiq, Naeem; Safdar, Rabia
2018-04-01
In this paper exact solutions corresponding to the rotational flow of a fractional Oldroyd-B fluid, in an annulus, are determined by applying integral transforms. The fluid starts moving after t = 0+ when pipes start rotating about their axis. The final solutions are presented in the form of usual Bessel and hypergeometric functions, true for initial and boundary conditions. The limiting cases for the solutions for ordinary Oldroyd-B, fractional Maxwell and Maxwell and Newtonian fluids are obtained. Moreover, the solution is obtained for the fluid when one pipe is rotating and the other one is at rest. At the end of this paper some characteristics of fluid motion, the effect of the physical parameters on the flow and a correlation between different fluid models are discussed. Finally, graphical representations confirm the above affirmation.
CFD Analysis of 2D Unsteady Flow Past a Square Cylinder at Low Reynolds Numbers
Directory of Open Access Journals (Sweden)
Li Zhenquan
2018-01-01
Full Text Available A study of the behaviour of flow past a square cylinder for Reynolds numbers 10 and 20 is presented. Open source software Navier2d in Matlab is used in this study. The investigation starts from a uniform initial mesh and then refine the initial mesh using a mesh refinement method which was proposed based on both qualitative theory of differential equations and the finite volume method implemented in Navier2d. The horizontal and vertical velocity component profiles and pressures are shown on the once refined meshes. The comparisons between the profiles and pressures are conducted to show the variations from Reynolds number 10 to 20. The twice refined meshes are also presented and these refined meshes provide the information where the behaviour of flow is complex.
Numerical study of unsteady flows past oscillating airfoils using direct zonal coupling method
International Nuclear Information System (INIS)
Zhang, F.; Khalid, M.
2005-01-01
A direct zonal coupling method was proposed for solving the flows past oscillating airfoils in this study. The entire computational domain was divided into inner and outer zones. The grid in the inner zone is moving with the oscillation of the airfoil, whereas the grid in the outer zone is artificially adjusted to the position consistent with the inner zone grid. The governing equations in the moving frame (the rotation potential energy is included) and those under the stationary frame were applied to inner and outer zones, respectively. By using this kind of treatment, the grid on the zonal interface is 1-to-1 matched. The coupling between the two zones is direct. Both the geometric and flow conservations are entirely satisfied. The NACA0012 and NLR7301 airfoils with oscillations were used as the test cases. The accuracy of the proposed method was demonstrated by the computational results compared with the experimental data.(author)
Directory of Open Access Journals (Sweden)
Sami Ul Haq
2015-01-01
Full Text Available The objective of this study is to explore the influence of wall slip condition on a free convection flow of an incompressible viscous fluid with heat transfer and ramped wall temperature. Exact solution of the problem is obtained by using Laplace transform technique. Graphical results to see the effects of Prandtl number Pr, time t, and slip parameter η on velocity and skin friction for the case of ramped and constant temperature of the plate are provided and discussed.
Numerical Simulation of Unsteady Compressible Flow in Convergent Channel: Pressure Spectral Analysis
Czech Academy of Sciences Publication Activity Database
Pořízková, P.; Kozel, Karel; Horáček, Jaromír
2012-01-01
Roč. 2012, č. 545120 (2012), s. 1-9 ISSN 1110-757X R&D Projects: GA ČR(CZ) GAP101/11/0207 Institutional research plan: CEZ:AV0Z20760514 Keywords : finite volume method * simulation of flow in vibrating glottis * biomechanics of voice Subject RIV: BI - Acoustics Impact factor: 0.834, year: 2012 http://www.hindawi.com/journals/jam/2012/545120/
Contribution to the verification and the validation of an unsteady two-phase flow model
International Nuclear Information System (INIS)
Liu, Yujie
2013-01-01
This thesis contributes to the verification and the validation of the Baer-Nunziato (BN) model, to model water hammer phenomena in industrial piping systems. It consists of two parts, the first is to model water hammer flows with the BN model in Eulerian representation and the second is to extend this model to the ALE (Arbitrary Lagrangian Eulerian) formalism so as to take into account fluid-structure interaction (FSI). To model water hammer flows, closure laws of the BN model concerning the interfacial/source terms and the equations of state (EOS) were first studied. Then the whole system was simulated with a fractional step method including two steps, one for the resolution of the convective part, the other for the source terms. For the convective part, the Rusanov scheme was first checked, and some stability problems have been observed. Thus a more stable fractional step scheme has been proposed and verified. Regarding the source terms, four non-instantaneous relaxation schemes which represent the return to equilibrium of pressure, the transfers of momentum, heat and mass were successively applied. These schemes have been extended to 'generalized Stiffened Gas' EOS in order to represent phase-change. After regaining some typical phenomena associated with water hammer flows, the BN model was validated with the Simpson experiment, a classical water hammer test case, and the Canon experience, a rapid decompression of fluid in a high pressure duct. Moreover, the model was compared with two homogeneous models on these two experiments. Finally, an ALE version of the BN model was implemented, and verified on a case of wave propagation in a 'single' phase flow and a two-phase flow in a flexible pipe. The variation of wave propagation speed due to the coupling between the fluid and the structure has been well retrieved. The validation was performed on an experiment which examines the response of a pipe filled with water, subjected to a violent pressure peak (140 bar
Franz, Delbert D.; Melching, Charles S.
1997-01-01
The Full EQuations (FEQ) model is a computer program for solution of the full, dynamic equations of motion for one-dimensional unsteady flow in open channels and through control structures. A stream system that is simulated by application of FEQ is subdivided into stream reaches (branches), parts of the stream system for which complete information on flow and depth are not required (dummy branches), and level-pool reservoirs. These components are connected by special features; that is, hydraulic control structures, including junctions, bridges, culverts, dams, waterfalls, spillways, weirs, side weirs, and pumps. The principles of conservation of mass and conservation of momentum are used to calculate the flow and depth throughout the stream system resulting from known initial and boundary conditions by means of an implicit finite-difference approximation at fixed points (computational nodes). The hydraulic characteristics of (1) branches including top width, area, first moment of area with respect to the water surface, conveyance, and flux coefficients and (2) special features (relations between flow and headwater and (or) tail-water elevations, including the operation of variable-geometry structures) are stored in function tables calculated in the companion program, Full EQuations UTiLities (FEQUTL). Function tables containing other information used in unsteady-flow simulation (boundary conditions, tributary inflows or outflows, gate settings, correction factors, characteristics of dummy branches and level-pool reservoirs, and wind speed and direction) are prepared by the user as detailed in this report. In the iterative solution scheme for flow and depth throughout the stream system, an interpolation of the function tables corresponding to the computational nodes throughout the stream system is done in the model. FEQ can be applied in the simulation of a wide range of stream configurations (including loops), lateral-inflow conditions, and special features. The
Tellez Alvarez, Jackson David; Redondo, Jose Manuel; Sanchez, Jesu Mary
2016-04-01
The improvements in experimental methods and high resolution image analysis are nowadays able to detect subtle changes in the structure of the turbulence over a wide range of temporal and spatial scales [1], we compare the scaling shown by different mixing fronts driven by buoyancy that form convective driven mixing. We use PIV and density front tracking in several experimental configurations akin to geophysical overturning [2, 3]. We parametrize the role of unstable stratification by means of the Rayleigh and Atwood numbers and compare the scaling and the multifractal structure functions of the different markers used to visualize the non-homogeneous. Both reactive and passive scalar tracers are used to investigate the mixing structure and the intermittency of the flow. Different initial conditions are compared and the mixing efficiency of the overall turbulent process is evaluated [4 - 6]. Diffusion is measured in the transition from a homogeneous linearly stratified fluid to a cellular or layered structure by means of Thermoelectric generated heating and cooling [2, 4]. Patterns arise by setting up a convective flow generated by a buoyant heat flux either in the base or in a side wall of the convective enclosure [1, 6]. The experiments described here investigate high Prandtl number mixing using brine or sugar solutions and fresh water in order to form a density interface and low Prandtl number mixing with only temperature gradients [7]. The set of dimensionless parameters define conditions of numeric and small scale laboratory modeling of environmental flows. Fields of velocity, density and their gradients were computed and visualized [8, 9]. When convective heating and cooling takes place the combination of internal waves and buoyant turbulence is much more complicated if the Rayleigh and Reynolds numbers are high in order to study entrainment and mixing. The experiments described here investigate high Prandtl number mixing using salt or sugar solutions and
International Nuclear Information System (INIS)
Mukhopadhyay, Swati; Arif, M. Golam; Pk M Wazed Ali
2013-01-01
The aim of this article is to present the effects of transpiration on the unsteady two-dimensional boundary layer flow of non-Newtonian fluid passing through a stretching sheet in the presence of a first order constructive/destructive chemical reaction. The upper-convected Maxwell (UCM) model is used here to characterize the non-Newtonian behavior of the fluid. Using similarity solutions, the governing nonlinear partial differential equations are transformed into ordinary ones and are then solved numerically by the shooting method. The flow fields and mass transfer are significantly influenced by the governing parameters. The fluid velocity initially decreases as the unsteadiness parameter increases and the concentration decreases significantly due to the increase in the unsteadiness. The effect of increasing values of transpiration (suction) and the Maxwell parameter is to suppress the velocity field; however, the concentration is enhanced as transpiration (suction) and the Maxwell parameter increase. Also, it is found that the fluid velocity decreases as the magnetic parameter increases; however, the concentration increases in this case. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)
Explicit evaluation of discontinuities in 2-D unsteady flows solved by the method of characteristics
Osnaghi, C.
When shock waves appear in the numerical solution of flows, a choice is necessary between shock capturing techniques, possible when equations are written in conservative form, and shock fitting techniques. If the second one is preferred, e.g. in order to obtain better definition and more physical description of the shock evolution in time, the method of characteristics is advantageous in the vicinity of the shock and it seems natural to use this method everywhere. This choice requires to improve the efficiency of the numerical scheme in order to produce competitive codes, preserving accuracy and flexibility, which are intrinsic features of the method: this is the goal of the present work.
Lee, Daniel H.
The impact blade row interactions can have on the performance of compressor rotors has been well documented. It is also well known that rotor tip clearance flows can have a large effect on compressor performance and stall margin and recent research has shown that tip leakage flows can exhibit self-excited unsteadiness at near stall conditions. However, the impact of tip leakage flow on the performance and operating range of a compressor rotor, relative to other important flow features such as upstream stator wakes or downstream potential effects, has not been explored. To this end, a numerical investigation has been conducted to determine the effects of self-excited tip flow unsteadiness, upstream stator wakes, and downstream blade row interactions on the performance prediction of low speed and transonic compressor rotors. Calculations included a single blade-row rotor configuration as well as two multi-blade row configurations: one where the rotor was modeled with an upstream stator and a second where the rotor was modeled with a downstream stator. Steady-state and time accurate calculations were performed using a RANS solver and the results were compared with detailed experimental data obtained in the GE Low Speed Research Compressor and the Notre Dame Transonic Rig at several operating conditions including near stall. Differences in the performance predictions between the three configurations were then used to determine the effect of the upstream stator wakes and the downstream blade row interactions. Results obtained show that for both the low speed and transonic research compressors used in this investigation time-accurate RANS analysis is necessary to accurately predict the stalling character of the rotor. Additionally, for the first time it is demonstrated that capturing the unsteady tip flow can have a larger impact on rotor performance predictions than adjacent blade row interactions.
Directory of Open Access Journals (Sweden)
Qingkai Zhao
2017-01-01
Full Text Available The time-dependent mixed bioconvection flow of an electrically conducting fluid between two infinite parallel plates in the presence of a magnetic field and a first-order chemical reaction is investigated. The fully coupled nonlinear systems describing the total mass, momentum, thermal energy, mass diffusion, and microorganisms equations are reduced to a set of ordinary differential equations via a set of new similarity transformations. The detailed analysis illustrating the influences of various physical parameters such as the magnetic, squeezing, and chemical reaction parameters and the Schmidt and Prandtl numbers on the distributions of temperature and microorganisms as well as the skin friction and the Nusselt number is presented. The conclusion is drawn that the flow field, temperature, and chemical reaction profiles are significantly influenced by magnetic parameter, heat generation/absorption parameter, and chemical parameter. Some examples of potential applications of such bioconvection could be found in pharmaceutical industry, microfluidic devices, microbial enhanced oil recovery, modeling oil, and gas-bearing sedimentary basins.
Experimental investigation of the unsteady two-phase flow through perforated plates
International Nuclear Information System (INIS)
Tartaglia, G.P.
1985-07-01
The coolant flow across the perforated dip-plate during a hypothetical core disruptive accident (HCDA) in a liquid metal fast breeder reactor was simulated in a one-dimensional model. Experiments with a water-air mixture as fluid were run by varying the following parameters: geometry of the dip-plate (perforation ratio, number of the holes), height of the fluid head over the dip-plate, air volumetric fraction, size of the air bubbles, acceleration of the fluid. The pressure drop across the dip-plate, the forces acting on the dip-plate and on the upper plate, acceleration and displacement of the piston, the air volumetric fraction and the size of the air bubbles were measured in a wide range of Strouhal and acceleration numbers. The flow pattern downstream the dip-plate was filmed with a high-speed camera. The following correlations were investigated: resistance coefficients as a function of the acceleration and Strouhal number, time delay of the force on the upper plate as a function of the cavitation number, and forces and impulses acting on the upper plate compared with those acting on the dip-plate. Finally, using high-speed film pictures, the formation of fluid jets downstream the dip-plate was investigated. The following relations were obtained: displacement of the mixture surface and of the jets as a function of the perforation ratio and of the air volumetric fraction, and cavitation volume as a function of the cavitation number. (orig.) [de
Zonal Detached-Eddy Simulation of Turbulent Unsteady Flow over Iced Airfoils
Zhang, Yue
2015-07-23
This paper presentsamultiscale finite-element formulation for the second modeofzonal detached-eddy simulation. The multiscale formulation corrects the lack of stability of the standard Galerkin formulation by incorporating the effect of unresolved scales to the grid (resolved) scales. The stabilization terms arise naturally and are free of userdefined stability parameters. Validation of the method is accomplished via the turbulent flow over tandem cylinders. The boundary-layer separation, free shear-layer rollup, vortex shedding from the upstream cylinder, and interaction with the downstream cylinder are well reproduced. Good agreement with experimental measurements gives credence to the accuracy of zonal detached-eddy simulation in modeling turbulent separated flows. A comprehensive study is then conducted on the performance degradation of ice-contaminated airfoils. NACA 23012 airfoil with a spanwise ice ridge and Gates Learjet Corporation-305 airfoil with a leading-edge horn-shape glaze ice are selected for investigation. Appropriate spanwise domain size and sufficient grid density are determined to enhance the reliability of the simulations. A comparison of lift coefficient and flowfield variables demonstrates the added advantage that the zonal detached-eddy simulation model brings to the Spalart-Allmaras turbulence model. Spectral analysis and instantaneous visualization of turbulent structures are also highlighted via zonal detached-eddy simulation. Copyright © 2015 by the CFD Lab of McGill University. Published by the American Institute of Aeronautics and Astronautics, Inc.
Directory of Open Access Journals (Sweden)
Shivaiah S.
2012-01-01
Full Text Available The objective of this paper is to analyze the effect of chemical reaction on unsteady magneto hydrodynamic free convective fluid flow past a vertical porous plate in the presence of suction or injection. The governing equations of the flow field are solved numerically by a finite element method. The effects of the various parameters on the velocity, temperature and concentration profiles are presented graphically and values of skin-friction coefficient, Nusselt number and Sherwood number for various values of physical parameters are presented through tables.
Magnetohydrodynamic unsteady flow of a Maxwell fluid past a flat plate
International Nuclear Information System (INIS)
Khandpur, S.L.; Ravi Kant
1979-01-01
A study of the equations describing the flow pattern set up in a linear electrically conducting viscoelastic fluid past an infinite flat plate in the presence of a transverse magnetic field has been made, when the plate is moving parallel to itself with an arbitrary time dependent velocity. The pressure is assumed to be uniform with initial velocity distribution in an exponential form. Operational methods are used to obtain the exact solutions for the velocity profiles. The effects of relaxation parameter of the fluid and magnetic field have been studied. Several particular cases are easily deduced of which two cases: (i) when the plate is moving in its own plane harmonically with time, and (ii) when the velocity of the plate is decaying exponentially with time, are discussed. (auth.)
Method and Apparatus for Predicting Unsteady Pressure and Flow Rate Distribution in a Fluid Network
Majumdar, Alok K. (Inventor)
2009-01-01
A method and apparatus for analyzing steady state and transient flow in a complex fluid network, modeling phase changes, compressibility, mixture thermodynamics, external body forces such as gravity and centrifugal force and conjugate heat transfer. In some embodiments, a graphical user interface provides for the interactive development of a fluid network simulation having nodes and branches. In some embodiments, mass, energy, and specific conservation equations are solved at the nodes, and momentum conservation equations are solved in the branches. In some embodiments, contained herein are data objects for computing thermodynamic and thermophysical properties for fluids. In some embodiments, the systems of equations describing the fluid network are solved by a hybrid numerical method that is a combination of the Newton-Raphson and successive substitution methods.
Self-Similar Unsteady Flow of a Sisko Fluid in a Cylindrical Tube Undergoing Translation
Directory of Open Access Journals (Sweden)
M. Khan
2015-01-01
Full Text Available The governing nonlinear equation for unidirectional flow of a Sisko fluid in a cylindrical tube due to translation of the tube wall is modelled in cylindrical polar coordinates. The exact steady-state solution for the nonlinear problem is obtained. The reduction of the nonlinear initial value problem is carried out by using a similarity transformation. The partial differential equation is transformed into an ordinary differential equation, which is integrated numerically taking into account the influence of the exponent n and the material parameter b of the Sisko fluid. The initial approximation for the fluid velocity on the axis of the cylinder is obtained by matching inner and outer expansions for the fluid velocity. A comparison of the velocity, vorticity, and shear stress of Newtonian and Sisko fluids is presented.
Directory of Open Access Journals (Sweden)
Modesto Pérez-Sánchez
2018-04-01
Full Text Available The knowledge of transient conditions in water pressurized networks equipped with pump as turbines (PATs is of the utmost importance and necessary for the design and correct implementation of these new renewable solutions. This research characterizes the water hammer phenomenon in the design of PAT systems, emphasizing the transient events that can occur during a normal operation. This is based on project concerns towards a stable and efficient operation associated with the normal dynamic behaviour of flow control valve closure or by the induced overspeed effect. Basic concepts of mathematical modelling, characterization of control valve behaviour, damping effects in the wave propagation and runaway conditions of PATs are currently related to an inadequate design. The precise evaluation of basic operating rules depends upon the system and component type, as well as the required safety level during each operation.
Filtration behaviors of rod-shaped bacterial broths in unsteady-state phase of cross-flow filtration
Energy Technology Data Exchange (ETDEWEB)
Tanaka, T.; Usui, K.; Koda, K.; Nakanishi, K. [Okayama University, Okayama (Japan). Faculty of Engineering
1996-12-20
Filtration behaviors in the unsteady-state phase of crossflow filtration of broths of Bacillus subtilis, Escherichia coli, and Lactobacillus delbrueckii, which are rod-shaped, were studied from the viewpoint of the changes in the specific resistance and in the structure of the microbial cake formed on the membrane surface. The permeation flux followed the cake filtration law at the initial stage of the crossflow filtration of the broths of B. subtilis and E. coli, where the cells deposited randomly on the membrane. In the case of the crossflow filtration of a L. delbrueckii broth, the period of random deposition was shorter. The specific resistance for the cake formed at the initial stage agreed with that measured in dead-end filtration. Then, the specific resistance started to increase in comparison with that measured in dead-end filtration due to shear-induced arrangement of the cells. The extent of the increase in specific resistance became higher and the time taken to start the cell arrangement became shorter with increasing circulation flow rate. The increase in specific resistance due to the shear-induced arrangement was more appreciable in the crossflow filtration of the broth of L. delbrueckii than that of B. subtilis and E. coli. The average permeation flux was increased considerably by applying periodical backwashing with appropriate time intervals. The permeation flux was well predicted by the cake filtration law, since the cells deposited in a way similar to that for dead-end filtration during a sufficiently short period of crossflow filtration in a backwashing mode. 21 refs., 11 figs.
Pressurised-water reactor plant
International Nuclear Information System (INIS)
Bergloeff, D.
1976-01-01
This additional patent improves the plant described in main patent 2244562 where the primary coolant pump is built into the housing of the steam raising unit, by overcoming certain difficulties in the transition from the specially extensive tube floor of the steam raising unit to the narrow crossection of the pump penetration. This is achieved by the formation of an unsymmetrical inlet funnel between the tube floor of the steam raising unit and the suction side of the pump. A side wall of the funnel forms the separating wall between the inlet and the outlet chamber below the tube floor of the steam raising unit. The crossection of the inlet funnel is reduced towards the pump by 2/3 to 1/3. Even laminar flow conditions are obtained at all flow velocities. Erosion, which disturbs flow and causes cavitation, no longer occurs. (ORU) [de
Numerical modelling of unsteady flow behaviour in the rectangular jets with oblique opening
Directory of Open Access Journals (Sweden)
James T. Hart
2016-09-01
Full Text Available Vortex shedding in a bank of three rectangular burner-jets was investigated using a CFD model. The jets were angled to the wall and the whole burner was recessed into a cavity in the wall; the ratio of velocities between the jets varied from 1 to 3. The model was validated against experimentally measured velocity profiles and wall pressure tapings from a physical model of the same burner geometry, and was generally found to reproduce the mean flow field faithfully. The CFD model showed that vortex shedding was induced by a combination of an adverse pressure gradient, resulting from the diffuser-like geometry of the recess, and the entrainment of fluid into the spaces separating the jets. The asymmetry of the burner, a consequence of being angled to the wall, introduced a cross-stream component into the adverse pressure gradient that forced the jets to bend away from their geometric axes, the extent of which depended upon the jet velocity. The vortex shedding was also found to occur in different jets depending on the jet velocity ratio.
Unsteady-state analysis of a counter-flow dew point evaporative cooling system
Lin, J.
2016-07-19
Understanding the dynamic behavior of the dew point evaporative cooler is crucial in achieving efficient cooling for real applications. This paper details the development of a transient model for a counter-flow dew point evaporative cooling system. The transient model approaching steady conditions agreed well with the steady state model. Additionally, it is able to accurately predict the experimental data within 4.3% discrepancy. The transient responses of the cooling system were investigated under different inlet air conditions. Temporal temperature and humidity profiles were analyzed for different transient and step responses. The key findings from this study include: (1) the response trend and settling time is markedly dependent on the inlet air temperature, humidity and velocity; (2) the settling time of the transient response ranges from 50 s to 300 s when the system operates under different inlet conditions; and (3) the average transient wet bulb effectiveness (1.00–1.06) of the system is observed to be higher than the steady state wet bulb effectiveness (1.01) for our range of study. © 2016 Elsevier Ltd
PIV study of flow around unsteady airfoil with dynamic trailing-edge flap deflection
Energy Technology Data Exchange (ETDEWEB)
Gerontakos, P.; Lee, T. [McGill University, Department of Mechanical Engineering, Montreal, Quebec (Canada)
2008-12-15
The flow around an oscillating NACA 0015 airfoil with prescheduled trailing-edge flap motion control was investigated by using particle image velocimetry (PIV). Aerodynamic load coefficients, obtained via surface pressure measurements, were also acquired to supplement the PIV results. The results demonstrate that upward flap deflections led to an improved negative peak pitching moment coefficient C{sub m,peak}, mainly as a consequence of the increased suction pressure on the lower surface of the flap. The behavior of the leading-edge vortex (LEV) was largely unaffected. Its strength was, however, reduced slightly compared to that of the uncontrolled airfoil. No trailing-edge vortex was observed. For downward flap deflection, the strength of the LEV was found to be slightly increased. A favorable increase in C{sub l,max}, as a consequence of downward flap-induced positive camber effects, accompanied by a detrimental increase in the nose-down C{sub m,peak}, due to the large pressure increase on the lower surface of the flap, was also observed. (orig.)
Comparative Field Tests of Pressurised Rover Prototypes
Mann, G. A.; Wood, N. B.; Clarke, J. D.; Piechochinski, S.; Bamsey, M.; Laing, J. H.
The conceptual designs, interior layouts and operational performances of three pressurised rover prototypes - Aonia, ARES and Everest - were field tested during a recent simulation at the Mars Desert Research Station in Utah. A human factors experiment, in which the same crew of three executed the same simulated science mission in each of the three vehicles, yielded comparative data on the capacity of each vehicle to safely and comfortably carry explorers away from the main base, enter and exit the vehicle in spacesuits, perform science tasks in the field, and manage geological and biological samples. As well as offering recommendations for design improvements for specific vehicles, the results suggest that a conventional Sports Utility Vehicle (SUV) would not be suitable for analog field work; that a pressurised docking tunnel to the main habitat is essential; that better provisions for spacesuit storage are required; and that a crew consisting of one driver/navigator and two field science crew specialists may be optimal. From a field operations viewpoint, a recurring conflict between rover and habitat crews at the time of return to the habitat was observed. An analysis of these incidents leads to proposed refinements of operational protocols, specific crew training for rover returns and again points to the need for a pressurised docking tunnel. Sound field testing, circulating of results, and building the lessons learned into new vehicles is advocated as a way of producing ever higher fidelity rover analogues.
International Nuclear Information System (INIS)
Cahuzac, A; Boudet, J; Borgnat, P; Lévêque, E
2011-01-01
A dynamic method based on Kalman filtering is presented to isolate low-frequency unsteadiness from turbulent fluctuations in the large-eddy simulation (LES) of unsteady turbulent flows. The method can be viewed as an adaptive exponential smoothing, in which the smoothing factor adapts itself dynamically to the local behavior of the flow. Interestingly, the proposed method does not require any empirical tuning. In practice, it is used to estimate a shear-improved Smagorinsky viscosity, in which the low-frequency component of the velocity field is used to estimate a correction term to the Smagorinsky viscosity. The LES of the flow past a circular cylinder at Reynolds number Re D = 4.7 × 10 4 is examined as a challenging test case. Good comparisons are obtained with the experimental results, indicating the relevance of the shear-improved Smagorinsky model and the efficiency of the Kalman filtering. Finally, the adaptive cut-off of the Kalman filter is investigated, and shown to adapt locally and instantaneously to the complex flow around the cylinder.
Unsteady Double Wake Model for the Simulation of Stalled Airfoils
DEFF Research Database (Denmark)
Ramos García, Néstor; Cayron, Antoine; Sørensen, Jens Nørkær
2015-01-01
In the present work, the recent developed Unsteady Double Wake Model, USDWM, is used to simulate separated flows past a wind turbine airfoil at high angles of attack. The solver is basically an unsteady two-dimensional panel method which uses the unsteady double wake technique to model flow separ...
Energy Technology Data Exchange (ETDEWEB)
Dano, C.
2003-01-15
The objective of this thesis is to evaluate k-e, k-l and k-w low Reynolds two equation turbulence models for. A quadratic nonlinear k-l model is also implemented in this study. We analyze the two equation turbulence models capacity to predict the turbomachinery flows and the wakes. We are interested more particularly in the unsteady three dimensional configuration with rotor-stator interactions. A Gaussian distribution reproduces the upstream wake. This analysis is carried out in term of prediction quality but also in term of numerical behavior. Turbines and compressors configurations are tested. (author)
Directory of Open Access Journals (Sweden)
Sandeep Naramgari
2014-01-01
Full Text Available We analyse the effects of aligned magnetic field, radiation, and rotation on unsteady hydromagnetic free convection flow of a viscous incompressible electrically conducting fluid past an impulsively moving vertical plate in a porous medium in presence of heat source. An exact solution of the governing equations in dimensionless form is obtained by Laplace transform technique in ramped temperature case. To compare the results obtained in this case with that of isothermal plate, the exact solution of the governing equations is also obtained for isothermal plate and results are discussed graphically in both ramped temperature and isothermal cases.
Directory of Open Access Journals (Sweden)
A. Sinha
2016-09-01
Full Text Available This paper presents a theoretical analysis of blood flow and heat transfer in a permeable vessel in the presence of an external magnetic field. The unsteadiness in the coupled flow and temperature fields is considered to be caused due to the time-dependent stretching velocity and the surface temperature of the vessel. The non-uniform heat source/sink effect on blood flow and heat transfer is taken into account. This study is of potential value in the clinical treatment of cardiovascular disorders accompanied by accelerated circulation. The problem is treated mathematically by reducing it to a system of coupled nonlinear differential equations, which have been solved by using similarity transformation and boundary layer approximation. The resulting nonlinear coupled ordinary differential equations are solved numerically by using an implicit finite difference scheme. Computational results are obtained for the velocity, temperature, the skin-friction coefficient and the rate of heat transfer in the vessel. The estimated results are compared with another analytical study reported earlier in scientific literatures. The present study reveals that the heat transfer rate is enhanced as the value of the unsteadiness parameter increases, but it reduces as the space-dependence parameter for heat source/sink increases.
Sudalaimuthu, Vignesh; Liu, Xiaofeng
2017-11-01
A series of wind tunnel aerodynamic force measurements have been conducted on a 2D hollow cylinder with perforated holes uniformly-distributed on its surface to evaluate the efficacy of perforation as a means of passive flow control in reducing unsteady aerodynamic forces. Both smooth and perforated cylinders were tested for comparison at Reynolds numbers ranging from 50,000 to 200,000 corresponding to free stream velocities varying from 5 to 20 m/s (at an increment of 5 m/s) and a cylinder diameter of 0.152 m. The aerodynamic forces acting on the testing model were measured using a 6-component load cell. For each tunnel speed, the test has been repeated for 10 runs at a sampling rate of 10 kHz for 60 seconds each, with a total of 6,000,000 samples acquired for each test. Both mean and r.m.s. values of the lift and drag coefficients were calculated. Power spectral density distributions of the unsteady aerodynamic force loading was analyzed to investigate the effect of the perforation on the frequency composition. Comparisons indicate that the perforated cylinder with a 8% porosity and a hole diameter of about 2% of that of the cylinder gives both substantially less unsteady drag and lift than those of the smooth cylinder for the entire Reynolds number range tested, with the r.m.s. force reduction from 8% to 82% for the drag and 64% to 85% for the lift, confirming a corresponding beneficial reduction in flow-induced cylinder vibration as observed during the experiments. Sponsor: San Diego State University.
Directory of Open Access Journals (Sweden)
Mohammad Ishaq
2018-05-01
Full Text Available This research paper investigates entropy generation analysis on two-dimensional nanofluid film flow of Eyring–Powell fluid with heat amd mass transmission over an unsteady porous stretching sheet in the existence of uniform magnetic field (MHD. The flow of liquid films are taken under the impact of thermal radiation. The basic time dependent equations of heat transfer, momentum and mass transfer are modeled and converted to a system of differential equations by employing appropriate similarity transformation with unsteady dimensionless parameters. Entropy analysis is the main focus in this work and the impact of physical parameters on the entropy profile are discussed in detail. The influence of thermophoresis and Brownian motion has been taken in the nanofluids model. An optima approach has been applied to acquire the solution of modeled problem. The convergence of the HAM (Homotopy Analysis Method has been presented numerically. The disparity of the Nusslet number, Skin friction, Sherwood number and their influence on the velocity, heat and concentration fields has been scrutinized. Moreover, for comprehension, the physical presentation of the embedded parameters are explored analytically for entropy generation and discussed.
International Nuclear Information System (INIS)
Azimi, Mohammadreza
2017-01-01
Investigation for unsteady squeezing viscous flow is one of the most important research topics due to its wide range of engineering applications such as polymer processing and lubrication systems. The aim of the present paper is to study the unsteady squeezing viscous graphene oxide-water nanofluid flow with heat transfer between two infinite parallel plates. The governing equations, continuity, momentum and energy for this problem are reduced to coupled nonlinear ordinary differential equations using a similarity transformation. The transmuted model is shown to be controlled by a number of thermo-physical parameters, viz., moving parameter, graphene oxide nanoparticles solid volume fraction, Eckert and Prandtl numbers. Nusselt number and skin friction parameter are obtained for various values of GO solid volume fraction and Eckert number. Comparison between analytical results and numerical ones achieved by fourth order Runge-Kutta method revealed that our analytical method can be a simple, powerful and efficient technique for finding analytical solutions in science and engineering nonlinear differential equations. (author)
Energy Technology Data Exchange (ETDEWEB)
Lim, Tae Gyun; Jeon, Wan Ho [Technical Research Lab., CEDIC Co., Seoul (Korea, Republic of); Minorikawa, Gaku [Dept. of f Mechanical Engineering, Faculty of Science and Engineering, Hosei University, Tokyo (Japan)
2016-10-15
The recent development of small and lightweight rack mount servers and computers has resulted in the decrease of the size of cooling fans. However, internal fans still need to achieve a high performance to release the heat generated from interior parts, and they should emit low noise. On the contrary, measurement data, such as flow properties and flow visualizations, cannot be obtained easily when cooling fans are small. Thus, a numerical analysis approach is necessary for the performance evaluation and noise reduction of small cooling fans. In this study, the noise of a small cooling fan used for computers or servers was measured and then compared with the aeroacoustic noise result based on a numerical analysis. Three-dimensional Navier-Stokes equations were solved to predict the unsteady flow field and surface pressure fluctuation according to the blades and casing surface used. The simplified Ffowcs Williams and Hawkings equation was used to predict aeroacoustic noise by assuming that a dipole is the major cause of fan noise. Results of the aeroacoustic noise analysis agreed well with that of the experiment, and a tonal noise whose frequency was lower than the first blade passing frequency could be identified in the noise spectrum. This phenomenon is caused by the shape of the bell mouth. A coherence analysis was performed to examine the correlation between the shape of the cooling fan and the noise.
International Nuclear Information System (INIS)
Lim, Tae Gyun; Jeon, Wan Ho; Minorikawa, Gaku
2016-01-01
The recent development of small and lightweight rack mount servers and computers has resulted in the decrease of the size of cooling fans. However, internal fans still need to achieve a high performance to release the heat generated from interior parts, and they should emit low noise. On the contrary, measurement data, such as flow properties and flow visualizations, cannot be obtained easily when cooling fans are small. Thus, a numerical analysis approach is necessary for the performance evaluation and noise reduction of small cooling fans. In this study, the noise of a small cooling fan used for computers or servers was measured and then compared with the aeroacoustic noise result based on a numerical analysis. Three-dimensional Navier-Stokes equations were solved to predict the unsteady flow field and surface pressure fluctuation according to the blades and casing surface used. The simplified Ffowcs Williams and Hawkings equation was used to predict aeroacoustic noise by assuming that a dipole is the major cause of fan noise. Results of the aeroacoustic noise analysis agreed well with that of the experiment, and a tonal noise whose frequency was lower than the first blade passing frequency could be identified in the noise spectrum. This phenomenon is caused by the shape of the bell mouth. A coherence analysis was performed to examine the correlation between the shape of the cooling fan and the noise
El-Asrag, Hossam A.
2011-01-01
Direct simulation of all the length and time scales relevant to practical combustion processes is computationally prohibitive. When combustion processes are driven by reaction and transport phenomena occurring at the unresolved scales of a numerical simulation, one must introduce a dynamic subgrid model that accounts for the multiscale nature of the problem using information available on a resolvable grid. Here, we discuss a model that captures unsteady flow-flame interactions- including extinction, re-ignition, and history effects-via embedded simulations at the subgrid level. The model efficiently accounts for subgrid flame structure and incorporates detailed chemistry and transport, allowing more accurate prediction of the stretch effect and the heat release. In this chapter we first review the work done in the past thirty years to develop the flame embedding concept. Next we present a formulation for the same concept that is compatible with Large Eddy Simulation in the flamelet regimes. The unsteady flame embedding approach (UFE) treats the flame as an ensemble of locally one-dimensional flames, similar to the flamelet approach. However, a set of elemental one-dimensional flames is used to describe the turbulent flame structure directly at the subgrid level. The calculations employ a one-dimensional unsteady flame model that incorporates unsteady strain rate, curvature, and mixture boundary conditions imposed by the resolved scales. The model is used for closure of the subgrid terms in the context of large eddy simulation. Direct numerical simulation (DNS) data from a flame-vortex interaction problem is used for comparison. © Springer Science+Business Media B.V. 2011.
Directory of Open Access Journals (Sweden)
N. Sandeep
2015-12-01
Full Text Available The aim of the present study is to investigate the influence of non-uniform heat source/sink, mass transfer and chemical reaction on an unsteady mixed convection boundary layer flow of a magneto-micropolar fluid past a stretching/shrinking sheet in the presence of viscous dissipation and suction/injection. The governing equations of the flow, heat and mass transfer are transformed into system of nonlinear ordinary differential equations by using similarity transformation and then solved numerically using Shooting technique with Matlab Package. The influence of non-dimensional governing parameters on velocity, microrotation, temperature and concentration profiles are discussed and presented with the help of their graphical representations. Also, friction factor, heat and mass transfer rates have been computed and presented through tables. Under some special conditions, present results are compared with the existed results to check the accuracy and validity of the present study. An excellent agreement is observed with the existed results.
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Mohammed Almakki
2017-07-01
Full Text Available The entropy generation in unsteady three-dimensional axisymmetric magnetohydrodynamics (MHD nanofluid flow over a non-linearly stretching sheet is investigated. The flow is subject to thermal radiation and a chemical reaction. The conservation equations are solved using the spectral quasi-linearization method. The novelty of the work is in the study of entropy generation in three-dimensional axisymmetric MHD nanofluid and the choice of the spectral quasi-linearization method as the solution method. The effects of Brownian motion and thermophoresis are also taken into account. The nanofluid particle volume fraction on the boundary is passively controlled. The results show that as the Hartmann number increases, both the Nusselt number and the Sherwood number decrease, whereas the skin friction increases. It is further shown that an increase in the thermal radiation parameter corresponds to a decrease in the Nusselt number. Moreover, entropy generation increases with respect to some physical parameters.
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Motsa Sandile Sydney
2015-01-01
Full Text Available The behaviour of unsteady non-Darcian magnetohydrodynamic fluid flow past an impulsively started vertical porous surface is investigated. The effect of thermophoresis due to migration of colloidal particles in response to a macroscopic temperature gradient is taken into account. It is assumed that both dynamic viscosity and thermal conductivity are linear functions of temperature. The governing equations are non-dimensionalized by using suitable similarity transformation which can unravel the behaviour of the flow at short time and long time periods. A novel iteration scheme, called bivariate spectral local linearization method is developed for solving the corresponding systems of highly non-linear partial differential equations. The results of the numerical solutions obtained are presented graphically and analyzed for the effects of the various important parameters entering into the problem on velocity, temperature, and concentration field within the boundary layer.
Hessenius, K. A.; Goorjian, P. M.
1981-01-01
A high frequency extension of the unsteady, transonic code LTRAN2 was created and is evaluated by comparisons with experimental results. The experimental test case is a NACA 64A010 airfoil in pitching motion at a Mach number of 0.8 over a range of reduced frequencies. Comparisons indicate that the modified code is an improvement of the original LTRAN2 and provides closer agreement with experimental lift and moment coefficients. A discussion of the code modifications, which involve the addition of high frequency terms of the boundary conditions of the numerical algorithm, is included.
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Zhiyin Yang
2014-12-01
Full Text Available A complex flow field is created when a vertical/short take-off and landing aircraft is operating near ground. One major concern for this kind of aircraft in ground effect is the possibility of ingestion of hot gases from the jet engine exhausts back into the engine, known as hot gas ingestion, which can increase the intake air temperature and also reduce the oxygen content in the intake air, potentially leading to compressor stall, low combustion efficiency and causing a dramatic loss of lift. This flow field can be represented by the configuration of twin impinging jets in a cross-flow. Accurate prediction of this complicated flow field under the Reynolds averaged Navier–Stokes (RANS approach (current practise in industry is a great challenge as previous studies suggest that some important flow features cannot be captured by the Steady-RANS (SRANS approach even with a second-order Reynolds stress model (RSM. This paper presents a numerical study of this flow using the Unsteady-RANS (URANS approach with a RSM and the results clearly indicate that the URANS approach is superior than the SRANS approach but still the predictions of Reynolds stress are not accurate enough.
Water relations in silver birch during springtime: How is sap pressurised?
Hölttä, T; Dominguez Carrasco, M D R; Salmon, Y; Aalto, J; Vanhatalo, A; Bäck, J; Lintunen, A
2018-05-06
Positive sap pressures are produced in the xylem of birch trees in boreal conditions during the time between the thawing of the soil and bud break. During this period, xylem embolisms accumulated during wintertime are refilled with water. The mechanism for xylem sap pressurization and its environmental drivers are not well known. We measured xylem sap flow, xylem sap pressure, xylem sap osmotic concentration, xylem and whole stem diameter changes, and stem and root non-structural carbohydrate concentrations, along with meteorological conditions at two sites in Finland during and after the sap pressurisation period. The diurnal dynamics of xylem sap pressure and sap flow during the sap pressurisation period varied, but were more often opposite to the diurnal pattern after bud burst, i.e. sap pressure increased and sap flow rate mostly decreased when temperature increased. Net conversion of soluble sugars to starch in the stem and roots occurred during the sap pressurisation period. Xylem sap osmotic pressure was small in comparison to total sap pressure, and it did not follow changes in environmental conditions or tree water relations. Based on these findings, we suggest that xylem sap pressurisation and embolism refilling occur gradually over a few weeks through water transfer from parenchyma cells to xylem vessels during daytime, and then the parenchyma are refilled mostly during nighttime by water uptake from soil. Possible drivers for water transfer from parenchyma cells to vessels are discussed. Also the functioning of thermal dissipation probes in conditions of changing stem water content is discussed. © 2018 German Society for Plant Sciences and The Royal Botanical Society of the Netherlands.
Energy Technology Data Exchange (ETDEWEB)
Maity, S., E-mail: susantamaiti@gmail.com [Department of Mathematics, National Institute of Technology, Arunachal Pradesh, Yupia, Papumpare 791112 (India); Singh, S.K. [Engineering Mechanics Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore 560064 (India); Kumar, A.V. [Department of Mathematics, National Institute of Technology, Arunachal Pradesh, Yupia, Papumpare 791112 (India)
2016-12-01
Three dimensional flow of thin Casson liquid film over a porous unsteady stretching sheet is investigated under assumption of initial uniform film thickness. The effects of the uniform transverse magnetic field, suction and injection are also considered for investigation. The nonlinear governing set of equations and film evolution equation are solved analytically by using singular perturbation technique. It is found that the film thickness decreases with the increasing values of the Casson parameter. The Hartmann number and porosity parameter resist the film thinning process. It is also observed that the film thickness increases with the increasing values of the suction velocity whereas it decreases for increasing values of the injection velocity at the stretching surface.
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Khilap Singh
2016-01-01
Full Text Available A numerical model is developed to examine the effects of thermal radiation on unsteady mixed convection flow of a viscous dissipating incompressible micropolar fluid adjacent to a heated vertical stretching surface in the presence of the buoyancy force and heat generation/absorption. The Rosseland approximation is used to describe the radiative heat flux in the energy equation. The model contains nonlinear coupled partial differential equations which have been converted into ordinary differential equation by using the similarity transformations. The dimensionless governing equations for this investigation are solved by Runge-Kutta-Fehlberg fourth fifth-order method with shooting technique. Numerical solutions are then obtained and investigated in detail for different interesting parameters such as the local skin-friction coefficient, wall couple stress, and Nusselt number as well as other parametric values such as the velocity, angular velocity, and temperature.
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Prasad Ramachandra V.
2007-01-01
Full Text Available An unsteady, two-dimensional, hydromagnetic, laminar free convective boundary-layer flow of an incompressible, Newtonian, electrically-conducting and radiating fluid past an infinite heated vertical porous plate with heat and mass transfer is analyzed, by taking into account the effect of viscous dissipation. The dimensionless governing equations for this investigation are solved analytically using two-term harmonic and non-harmonic functions. Numerical evaluation of the analytical results is performed and graphical results for velocity, temperature and concentration profiles within the boundary layer and tabulated results for the skin-friction coefficient, Nusselt number and Sherwood number are presented and discussed. It is observed that, when the radiation parameter increases, the velocity and temperature decrease in the boundary layer, whereas when thermal and solutal Grashof increases the velocity increases.
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Reddy G.J.
2017-02-01
Full Text Available An unsteady magnetohydromagnetic natural convection on the Couette flow of electrically conducting water at 4°C (Pr = 11.40 in a rotating system has been considered. A Finite Element Method (FEM was employed to find the numerical solutions of the dimensionless governing coupled boundary layer partial differential equations. The primary velocity, secondary velocity and temperature of water at 4°C as well as shear stresses and rate of heat transfer have been obtained for both ramped temperature and isothermal plates. The results are independent of the mesh (grid size and the present numerical solutions through the Finite Element Method (FEM are in good agreement with the existing analytical solutions by the Laplace Transform Technique (LTT. These are shown in tabular and graphical forms.
International Nuclear Information System (INIS)
Chiem, Kok Siong; Zhao Yong
2004-01-01
In this study, a high-resolution characteristic-based finite-volume (FV) method on unstructured grids [Int. J. Numer. Method Eng. 50 (2001) 11; Int. J. Heat Fluid Flow 21 (2000) 432] is extended by a matrix-free implicit dual-time stepping scheme for the numerical simulation of steady and unsteady flow and heat transfer with porous media. The method has been used to study the characteristics of a complex problem: flow and heat transfer in a channel with multiple discrete porous blocks, which was originally proposed by Huang and Vafai [J. Thermophys. Heat Transfer 8 (3) (1994) 563]. In addition, flow and heat transfer in a channel partially or fully filled with porous layers and containing solid protruding blocks with constant heat flux on its lower surface are also investigated in details. Hydrodynamic and heat transfer results are reported for both steady and transient flow cases. In particular, the effects of Darcy and Reynolds numbers on heat transfer augmentation and pressure loss are studied. An in-depth discussion of the formation and variation of recirculation is presented and the existence of optimum porous insert is demonstrated. At high Reynolds numbers the flow in the porous channel exhibits a cyclic characteristics although unlike the non-porous channel flow, the cyclic vortex development is only restricted to a small area behind the last solid block, while temperature changes more slowly and does not exhibit cyclic variations over a long period of time. It is shown that for all the cases studied altering some parametric values can have significant and interesting effects on both flow pattern as well as heat transfer characteristics
Energy Technology Data Exchange (ETDEWEB)
Das, S.S. [Department of Physics, K B D A V College, Nirakarpur, Khurda-752 019 (Orissa) (India); Tripathy, R.K. [Department of Physics, D R Nayapalli College, Bhubaneswar-751 012 (Orissa) (India); Padhy, R.K. [Department of Physics, D A V Public School, Chandrasekharpur, Bhubaneswar-751 021 (Orissa) (India); Sahu, M. [Department of Physics, Jupiter +2 Women’s Science College, IRC Village, Bhubaneswar-751 015 (Orissa) (India)
2012-07-01
This paper theoretically investigates the combined natural convection and mass transfer effects on unsteady flow of a viscous incompressible fluid past an infinite vertical porous plate embedded in a porous medium with heat source. The governing equations of the flow field are solved analytically for velocity, temperature, concentration distribution, skin friction and the rate of heat transfer using multi parameter perturbation technique and the effects of the flow parameters such as permeability parameter Kp, Grashof number for heat and mass transfer Gr, Gc; heat source parameter S, Schmidt number Sc, Prandtl number Pr etc. on the flow field are analyzed and discussed with the help of figures and tables. The permeability parameter Kp is reported to accelerate the transient velocity of the flow field at all points for small values of Kp (£1) and for higher values the effect reverses. The effect of increasing Grashof numbers for heat and mass transfer or heat source parameter is to enhance the transient velocity of the flow field at all points while a growing Schmidt number retards its effect at all points. A growing permeability parameter or heat source parameter increases the transient temperature of the flow field at all points, while a growing Prandtl number shows reverse effect. The effect of increasing Schmidt number is to decrease the concentration boundary layer thickness of the flow field at all points. Further, a growing permeability parameter enhances the skin friction at the wall and a growing Prandtl number shows reverse effect. The effect of increasing Prandtl number or permeability parameter leads to increase the magnitude of the rate of heat transfer at the wall.
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V. Rajesh
2014-08-01
Full Text Available The interaction of free convection with thermal radiation of a viscous incompressible unsteady flow past a vertical plate with ramped wall temperature and mass diffusion is presented here, taking into account the homogeneous chemical reaction of first order. The fluid is gray, absorbing-emitting but non-scattering medium and the Rosseland approximation is used to describe the radiative flux in the energy equation. The dimensionless governing equations are solved using an implicit finite-difference method of the Crank-Nicolson type, which is stable and convergent. The velocity profiles are compared with the available theoretical solution and are found to be in good agreement. Numerical results for the velocity, the temperature, the concentration, the local and average skin friction, the Nusselt number and Sherwood number are shown graphically. This work has wide application in chemical and power engineering and also in the study of vertical air flow into the atmosphere. The present results can be applied to an important class of flows in which the driving force for the flow is provided by combination of the thermal and chemical species diffusion effects.
International Nuclear Information System (INIS)
Le Coq, G.; Boudsocq, G.; Raymond, P.
1983-03-01
The Control Variable Method is extended to multidimensional fluid flow transient computations. In this paper basic principles of the method are given. The method uses a fully implicit space discretization and is based on the decomposition of the momentum flux tensor into scalar, vectorial, and tensorial, terms. Finally some computations about viscous-driven flow and buoyancy-driven flow in cavity are presented
Transient dynamic crack propagation in gas pressurised pipelines
International Nuclear Information System (INIS)
Caldis, E.S.; Owen, D.R.J.; Taylor, C.
1983-01-01
The prime limitation of dynamic fracture analysis is the lack of a fundamental crack advance theory which can be easily and economically adopted for use with numerical models. The necessity for the inclusion of inertia effects in the solution of certain problem classes is now evident, but most transient dynamic fracture models considered to date include (of necessity) some intuitive/empirical parameters with a frequent need of a priori knowledge of experimental solutions. The particular problem considered in this study is Mode I transient dynamic crack propagation in gas pressurised pipelines. The steel pipe is modelled using thin shell Semiloof finite elements and its transient response is coupled to a one-dimensional finite element model of the compressible gas equations, incorporating a lateral gas flow parameter. The pipe is governed by the usual dynamic equilibrium equation which is discretised in the time domain by a central difference explicit algorithm. The compressible gas response is modelled by the Continuity and Momentum equations and time discretisation is performed by means of a fully backward difference scheme in time. (orig./GL)
Heat and mass transfer in air-fed pressurised suits
International Nuclear Information System (INIS)
Tesch, K.; Collins, M.W.; Karayiannis, T.G.; Atherton, M.A.; Edwards, P.
2009-01-01
Air-fed pressurised suits are used to protect workers against contamination and hazardous environments. The specific application here is the necessity for regular clean-up maintenance within the torus chamber of fusion reactors. The current design of suiting has been developed empirically. It is, therefore, very desirable to formulate a thermo-fluids model, which will be able to define optimum designs and operating parameters. Two factors indicate that the modelling should be as comprehensive as possible. Firstly, the overall thermo-fluids problem is three-dimensional and includes mass as well as heat transfer. The fluid field is complex, bounded on one side by the human body and on the other by what may be distensible, porous and multi-layer clothing. In this paper, we report firstly the modelling necessary for the additional mass and heat transport processes. This involves the use of Fick's and Fourier's laws and conjugate heat transfer. The results of an initial validation study are presented. Temperatures at the outlet of the suits were obtained experimentally and compared with those predicted by the overall CFD model. Realistic three-dimensional geometries were used for the suit and human body. Calculations were for turbulent flow with single- and two-component (species) models
International Nuclear Information System (INIS)
Ford, C L; Winroth, M; Alfredsson, P H
2016-01-01
An entirely pressure-based vortex-shedding meter has been designed for use in practical time-dependent flows. The meter is capable of measuring mass-flow rate in variable density gases in spite of the fact that fluid temperature is not directly measured. Unlike other vortex meters, a pressure based meter is incredibly robust and may be used in industrial type flows; an environment wholly unsuitable for hot-wires for example. The meter has been tested in a number of static and dynamic flow cases, across a range of mass-flow rates and pressures. The accuracy of the meter is typically better than about 3% in a static flow and resolves the fluctuating mass-flow with an accuracy that is better than or equivalent to a hot-wire method. (paper)
Mahmoud, Mostafa A. A.; Megahed, Ahmed M.
2017-10-01
Theoretical and numerical outcomes of the non-Newtonian Casson liquid thin film fluid flow owing to an unsteady stretching sheet which exposed to a magnetic field, Ohmic heating and slip velocity phenomena is reported here. The non-Newtonian thermal conductivity is imposed and treated as it vary with temperature. The nonlinear partial differential equations governing the non-Newtonian Casson thin film fluid are simplified into a group of highly nonlinear ordinary differential equations by using an adequate dimensionless transformations. With this in mind, the numerical solutions for the ordinary conservation equations are found using an accurate shooting iteration technique together with the Runge-Kutta algorithm. The lineaments of the thin film flow and the heat transfer characteristics for the pertinent parameters are discussed through graphs. The results obtained here detect many concern for the local Nusselt number and the local skin-friction coefficient in which they may be beneficial for the material processing industries. Furthermore, in some special conditions, the present problem has an excellent agreement with previously published work.
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Farhad Ali
2013-01-01
Full Text Available The focus of this paper is to analyze the influence of thermal radiation on some unsteady magnetohydrodynamic (MHD free convection flows of an incompressible Brinkman type fluid past a vertical flat plate embedded in a porous medium with the Newtonian heating boundary condition. The fluid is considered as a gray absorbing-emitting but nonscattering medium and the Rosseland approximation in the energy equations is used to describe the radiative heat flux for optically thick fluid. For a detailed analysis of the problem, four important situations of flow due to (i impulsive motion of the plate (ii uniform acceleration of the plate (iii nonuniform acceleration of the plate, and (iv highly nonuniform acceleration of the plate are considered. The governing equations are first transformed into a system of dimensionless equations and then solved analytically using the Laplace transform technique. Numerical results for temperature and velocity are shown graphically, while skin friction and Nusselt number are computed in tables. The results show that temperature and velocity increase on increasing radiation and Newtonian heating parameters. However, the results of magnetic and porosity parameters on velocity are found quite opposite.
Energy Technology Data Exchange (ETDEWEB)
Gentner, C.
2000-07-01
The periodic instationary flow in guidevanes and runner of an axial hydraulic turbine is examined experimentally and numerically. The study is carried out at three different points of operation. The experimental study comprises the measurement of the velocity of the flow at midspan using a single channel Laser Doppler Velocimeter and the acquisition of the ozillating pressure at several locations in the casing. The unsteady numerical examination is carried out in a two dimensional plane at midspan of the runnerblades. The interaction between guidevanes and runner is taken into account by exchanging the flow properties at the adjoining edges of the two calculation grids. Further the influence of the tip clearance flow on the characteristics of the turbine is studied numerically by means of a three dimensional steady state calculation. The comparison of the results of measurement and calculation shows the abilities and the limitations of the applied numerical method. Moreover the results are helpful for the optimisation of the turbine with regard to higher efficiency and reduced cavitation. (orig.) [German] Die periodisch instationaere Stroemung in Leit- und Laufrad einer hydraulischen Axialturbine zur Druckentspannung in Rohrleitungssystemen wird fuer drei Betriebspunkte experimentell und rechnerisch untersucht. Die experimentelle Untersuchung umfasst die zeitaufgeloeste Messung der Stroemungsgeschwindigkeiten mit einem Laser-Doppler-Velozimeter im Mittelschnitt und die Erfassung des periodisch schwankenden Drucks an mehreren Punkten an der Gehaeusewand. Die instationaere numerische Untersuchung erfolgt in einem zweidimensionalen Zylinderschnitt im mittleren Durchmesser der Laufschaufeln. Die Wechselwirkung zwischen Leit- und Laufrad wird druch den Austausch der Stroemungsgroessen mittels eines Kopplungsalgorithmus an der Stossflaeche zwischen den zwei gegeneinander bewegten Berechnungsgittern erfasst. Darueber hinaus wird in einer dreidimensionalen stationaeren
Sibra, A.; Dupays, J.; Murrone, A.; Laurent, F.; Massot, M.
2017-06-01
In this paper, we tackle the issue of the accurate simulation of evaporating and reactive polydisperse sprays strongly coupled to unsteady gaseous flows. In solid propulsion, aluminum particles are included in the propellant to improve the global performances but the distributed combustion of these droplets in the chamber is suspected to be a driving mechanism of hydrodynamic and acoustic instabilities. The faithful prediction of two-phase interactions is a determining step for future solid rocket motor optimization. When looking at saving computational ressources as required for industrial applications, performing reliable simulations of two-phase flow instabilities appears as a challenge for both modeling and scientific computing. The size polydispersity, which conditions the droplet dynamics, is a key parameter that has to be accounted for. For moderately dense sprays, a kinetic approach based on a statistical point of view is particularly appropriate. The spray is described by a number density function and its evolution follows a Williams-Boltzmann transport equation. To solve it, we use Eulerian Multi-Fluid methods, based on a continuous discretization of the size phase space into sections, which offer an accurate treatment of the polydispersion. The objective of this paper is threefold: first to derive a new Two Size Moment Multi-Fluid model that is able to tackle evaporating polydisperse sprays at low cost while accurately describing the main driving mechanisms, second to develop a dedicated evaporation scheme to treat simultaneously mass, moment and energy exchanges with the gas and between the sections. Finally, to design a time splitting operator strategy respecting both reactive two-phase flow physics and cost/accuracy ratio required for industrial computations. Using a research code, we provide 0D validations of the new scheme before assessing the splitting technique's ability on a reference two-phase flow acoustic case. Implemented in the industrial
Unsteady Aerodynamics of Deformable Thin Airfoils
Walker, William Paul
2009-01-01
Unsteady aerodynamic theories are essential in the analysis of bird and insect flight. The study of these types of locomotion is vital in the development of flapping wing aircraft. This paper uses potential flow aerodynamics to extend the unsteady aerodynamic theory of Theodorsen and Garrick (which is restricted to rigid airfoil motion) to deformable thin airfoils. Frequency-domain lift, pitching moment and thrust expressions are derived for an airfoil undergoing harmonic oscillations and def...
International Nuclear Information System (INIS)
Song, P P; Wei, M S; Shi, L; Ma, C C
2013-01-01
Three-dimensional numerical simulations of a scroll expander were performed with dynamic mesh technology. R245fa was selected as the working fluid in the simulations. The PISO algorithm was applied to solve the governing equations with RNG k-ε turbulent model. The distribution and variation of three-dimensional flow field inside the scroll expander were obtained. The research indicates that the flow field is nonuniform and asymmetrical distributions exist inside the expander. Vortex flows also exist in some working chambers. Dynamic clearance leakage flows and inlet orifice throttling have great effects on the flow field distribution. Transient output torque and the mass flux have periodic fluctuations during the working cycles
Jodko, Daniel; Obidowski, Damian; Reorowicz, Piotr; Jóźwik, Krzysztof
2016-01-01
The aim of this study was to investigate the blood flow in the end-to-side arteriovenous (a-v) fistula, taking into account its pulsating nature and the patient-specific geometry of blood vessels. Computational Fluid Dynamics (CFD) methods were used for this analysis. DICOM images of the fistula, obtained from the angio-computed tomography, were a source of the data applied to develop a 3D geometrical model of the fistula. The model was meshed, then the ANSYS CFX v. 15.0 code was used to perform simulations of the flow in the vessels under analysis. Mesh independence tests were conducted. The non-Newtonian rheological model of blood and the Shear Stress Transport model of turbulence were employed. Blood vessel walls were assumed to be rigid. Flow patterns, velocity fields, the volume flow rate, the wall shear stress (WSS) propagation on particular blood vessel walls were shown versus time. The maximal value of the blood velocity was identified in the anastomosis - the place where the artery is connected to the vein. The flow rate was calculated for all veins receiving blood. The blood flow in the geometrically complicated a-v fistula was simulated. The values and oscillations of the WSS are the largest in the anastomosis, much lower in the artery and the lowest in the cephalic vein. A strong influence of the mesh on the results concerning the maximal and area-averaged WSS was shown. The relation between simulations of the pulsating and stationary flow under time-averaged flow conditions was presented.
Yanase, Kazutaka; Saarenrinne, Pentti
2016-12-15
The boundary layers of rainbow trout, Oncorhynchus mykiss [0.231±0.016 m total body length (L) (mean±s.d.); N=6], swimming at 1.6±0.09 L s -1 (N=6) in an experimental flow channel (Reynolds number, Re=4×10 5 ) with medium turbulence (5.6% intensity) were examined using the particle image velocimetry technique. The tangential flow velocity distributions in the pectoral and pelvic surface regions (arc length from the rostrum, l x =71±8 mm, N=3, and l x =110±13 mm, N=4, respectively) were approximated by a laminar boundary layer model, the Falkner-Skan equation. The flow regime over the pectoral and pelvic surfaces was regarded as a laminar flow, which could create less skin-friction drag than would be the case with turbulent flow. Flow separation was postponed until vortex shedding occurred over the posterior surface (l x =163±22 mm, N=3). The ratio of the body-wave velocity to the swimming speed was in the order of 1.2. This was consistent with the condition of the boundary layer laminarization that had been confirmed earlier using a mechanical model. These findings suggest an energy-efficient swimming strategy for rainbow trout in a turbulent environment. © 2016. Published by The Company of Biologists Ltd.
2010-04-01
Characteristics associated with “Free Flight” Shroud and Stage Separation and Mode Switching in LENS II Michael S. Holden, PhD CUBRC , Inc. 4455 Genesee...ADDRESS(ES) CUBRC , Inc. 4455 Genesee Street Buffalo, NY 14225, USA 8. PERFORMING ORGANIZATION REPORT NUMBER 9. SPONSORING/MONITORING AGENCY NAME(S) AND...switching and inlet-starting validation • Validation to CFD community ( CUBRC /UM) Figure 32: Numerical Simulation of the Unsteady Flow Dynamics during
Directory of Open Access Journals (Sweden)
B.I. Olajuwon
2014-12-01
Full Text Available Heat and mass transfer effects on unsteady flow of a viscoelastic micropolar fluid over an infinite moving permeable plate in a saturated porous medium in the presence of a transverse magnetic field with Hall effect and thermal radiation are studied. The governing system of partial differential equations is transformed to dimensionless equations using dimensionless variables. The dimensionless equations are then solved analytically using perturbation technique to obtain the expressions for velocity, microrotation, temperature and concentration. With the help of graphs, the effects of magnetic field parameter M, thermal radiation parameter Nr, Hall current parameter m, K, viscoelastic parameter a, and slip parameter h on the velocity, microrotation, temperature and concentration fields within the boundary layer are discussed. The result showed that increase in Nr and m increases translational velocity across the boundary layer while (a decreases translational velocity in the vicinity of the plate but the reverse happens when away from the plate. As h increases the translational velocity across the boundary layer increases. The higher the values of Nr, the higher the micro-rotational velocity effect while m lowers it. Also the effects n, a, m, Nr, Pr and Sc on the skin friction coefficient, Nusselt number and Sherwood numbers are presented numerically in tabular form. The result also revealed that increase in n reduces the skin friction coefficient. Pr enhances the rate of heat transfer while Sc enhances the rate of mass transfer.
Kumaresan, E.; Vijaya Kumar, A. G.; Rushi Kumar, B.
2017-11-01
This article studies, an exact solution of unsteady MHD free convection boundary-layer flow of a silver nanofluid past an exponentially accelerated moving vertical plate through aporous medium in the presence of thermal radiation, transverse applied amagnetic field, radiation absorption and Heat generation or absorption with chemical reaction are investigated theoretically. We consider nanofluids contain spherical shaped nanoparticle of silverwith a nanoparticle volume concentration range smaller than or equal to 0.04. This phenomenon is modeled in the form of partial differential equations with initial boundary conditions. Some suitable dimensional variables are introduced. The corresponding dimensionless equations with boundary conditions are solved by using Laplace transform technique. The exact solutions for velocity, energy, and species are obtained, also the corresponding numerical values of nanofluid velocity, temperature and concentration profiles are represented graphically. The expressions for skin friction coefficient, the rate of heat transfer and mass transfer are derived. The present study finds applications involving heat transfer, enhancement of thermal conductivity and other applications like transportation, industrial cooling applications, heating buildings and reducing pollution, energy applications and solar absorption. The effect of heat transfer is found to be more pronounced in a silver-water nanofluid than in the other nanofluids.
Energy Technology Data Exchange (ETDEWEB)
Verdonk, G. [GEC Alsthom Rateau, 93 - La Courneuve (France); Naudin, M. [Framatome Thermodyn, 71 - Le Creusot (France); Pluviose, M. [CNAM, 75 - Paris (France); Sankale, H. [CETIM, 44 - Nantes (France)
1998-06-01
The blades of turbomachinery undergo unsteady flow forces, created principally by the presence of a series of stator or diffuser blades prior to a series of rotor blades. The stage geometry is the main factor which defines the magnitude of these forces. The influence of both geometric and thermodynamic parameters is currently being analysed using a model representing the turbine blades and by applying the hydraulic analogy technique. The study is being conducted at CETIM in Nantes amongst a working group including manufacturers, research organisms, and technical center. Work is in progress and initial results have proved sufficiently encouraging for presentation at the forthcoming Symposium on multidisciplinary turbomachinery issues organised by the Societe Francaise des Mecaniciens. The study should eventually facilitate the optimisation of rotor blade dimensioning for total and partial injection turbine applications and furthermore to reduce the risk of blade failure. Following quantitative study, results obtained for a given geometry of total injection turbine are presented in this paper. (authors) 16 refs.
Assessment of RANS CFD modelling for pressurised thermal shock analysis
International Nuclear Information System (INIS)
Sander M Willemsen; Ed MJ Komen; Sander Willemsen
2005-01-01
Full text of publication follows: The most severe Pressurised Thermal Shock (PTS) scenario is a cold water Emergency Core Coolant (ECC) injection into the cold leg during a LOCA. The injected ECC water mixes with the hot fluid present in the cold leg and flows towards the downcomer where further mixing takes place. When the cold mixture comes into contact with the Reactor Pressure Vessel (RPV) wall, it may lead to large temperature gradients and consequently to high stresses in the RPV wall. Knowledge of these thermal loads is important for RPV remnant life assessments. The existing thermal-hydraulic system codes currently applied for this purpose are based on one-dimensional approximations and can, therefore, not predict the complex three-dimensional flows occurring during ECC injection. Computational Fluid Dynamics (CFD) can be applied to predict these phenomena, with the ultimate benefit of improved remnant RPV life assessment. The present paper presents an assessment of various Reynolds Averaged Navier Stokes (RANS) CFD approaches for modeling the complex mixing phenomena occurring during ECC injection. This assessment has been performed by comparing the numerical results obtained using advanced turbulence models available in the CFX 5.6 CFD code in combination with a hybrid meshing strategy with experimental results of the Upper Plenum Test Facility (UPTF). The UPTF was a full-scale 'simulation' of the primary system of the four loop 1300 MWe Siemens/KWU Pressurised Water Reactor at Grafenrheinfeld. The test vessel upper plenum internals, downcomer and primary coolant piping were replicas of the reference plant, while other components, such as core, coolant pump and steam generators were replaced by simulators. From the extensive test programme, a single-phase fluid-fluid mixing experiment in the cold leg and downcomer was selected. Prediction of the mixing and stratification is assessed by comparison with the measured temperature profiles at several locations
Tripathi, Dharmendra; Bég, O Anwar
2012-08-01
Magnetohydrodynamic peristaltic flows arise in controlled magnetic drug targeting, hybrid haemodynamic pumps and biomagnetic phenomena interacting with the human digestive system. Motivated by the objective of improving an understanding of the complex fluid dynamics in such flows, we consider in the present article the transient magneto-fluid flow and heat transfer through a finite length channel by peristaltic pumping. Reynolds number is small enough and the wavelength to diameter ratio is large enough to negate inertial effects. Analytical solutions for temperature field, axial velocity, transverse velocity, pressure gradient, local wall shear stress, volume flowrate and averaged volume flowrate are obtained. The effects of the transverse magnetic field, Grashof number and thermal conductivity on the flow patterns induced by peristaltic waves (sinusoidal propagation along the length of channel) are studied using graphical plots. The present study identifies that greater pressure is required to propel the magneto-fluid by peristaltic pumping in comparison to a non-conducting Newtonian fluid, whereas, a lower pressure is required if heat transfer is effective. The analytical solutions further provide an important benchmark for future numerical simulations.
Gasification of sawdust in pressurised internally circulating fluidized bed
Energy Technology Data Exchange (ETDEWEB)
Maartensson, R.; Lindblom, M. [Lund Univ. (Sweden). Dept. of Chemical Engineering
1996-12-31
A test plant for pressurised gasification of biofuels in a internally circulating fluidized bed has been built at the department of Chemical Engineering II at the University of Lund. The design performance is set to maximum 20 bar and 1 050 deg C at a thermal input of 100 kW or a maximum fuel input of 18 kg/in. The primary task is to study pressurised gasification of biofuels in relation to process requirements of the IGCC concept (integrated gasification combined cycle processes), which includes studies in different areas of hot gas clean-up in reducing atmosphere for gas turbine applications. (orig.)
Gasification of sawdust in pressurised internally circulating fluidized bed
Energy Technology Data Exchange (ETDEWEB)
Maartensson, R; Lindblom, M [Lund Univ. (Sweden). Dept. of Chemical Engineering
1997-12-31
A test plant for pressurised gasification of biofuels in a internally circulating fluidized bed has been built at the department of Chemical Engineering II at the University of Lund. The design performance is set to maximum 20 bar and 1 050 deg C at a thermal input of 100 kW or a maximum fuel input of 18 kg/in. The primary task is to study pressurised gasification of biofuels in relation to process requirements of the IGCC concept (integrated gasification combined cycle processes), which includes studies in different areas of hot gas clean-up in reducing atmosphere for gas turbine applications. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Zhang, Desheng; Shi, Lei; Zhao, Ruijie; Shi, Weidong; Pan, Qiang [Jiangsu University, Zhenjiang (China); Esch, B. P. [Eindhoven University of Technology, Eindhoven (Netherlands)
2017-02-15
The aim of the present investigation is to simulate and analyze the tip leakage flow structure and instantaneous evolution of tip vortex cavitation in a scaled axial-flow pump model. The improved filter-based turbulence model based on the density correction and a homogeneous cavitation model were used for implementing this work. The results show that when entering into the tip clearance, the backward flow separates from the blade tip near the pressure side, resulting in the generation of a corner vortex with high magnitude of turbulence kinetic energy. Then, at the exit of the tip clearance, the leakage jets would re-attach on the blade tip wall. Moreover, the maximum swirling strength method was employed in identifying the TLV core and a counter-rotating induced vortex near the end-wall successfully. The three dimensional cavitation patterns and in-plain cavitation structures obtained by the improved numerical method agree well with the experimental results. At the sheet cavitation trailing edge in the tip region, the perpendicular cavitation cloud induced by TLV sheds and migrates toward the pressure side of the neighboring blade. During its migration, it breaks down abruptly and generates a large number of smallscale cavities, leading to severe degradation of the pump performance, which is similar with the phenomenon observed by Tan et al.
Multi-GPU unsteady 2D flow simulation coupled with a state-to-state chemical kinetics
Tuttafesta, Michele; Pascazio, Giuseppe; Colonna, Gianpiero
2016-10-01
In this work we are presenting a GPU version of a CFD code for high enthalpy reacting flow, using the state-to-state approach. In supersonic and hypersonic flows, thermal and chemical non-equilibrium is one of the fundamental aspects that must be taken into account for the accurate characterization of the plasma and state-to-state kinetics is the most accurate approach used for this kind of problems. This model consists in writing a continuity equation for the population of each vibrational level of the molecules in the mixture, determining at the same time the species densities and the distribution of the population in internal levels. An explicit scheme is employed here to integrate the governing equations, so as to exploit the GPU structure and obtain an efficient algorithm. The best performances are obtained for reacting flows in state-to-state approach, reaching speedups of the order of 100, thanks to the use of an operator splitting scheme for the kinetics equations.
Turbine-99 unsteady simulations - Validation
International Nuclear Information System (INIS)
Cervantes, M J; Andersson, U; Loevgren, H M
2010-01-01
The Turbine-99 test case, a Kaplan draft tube model, aimed to determine the state of the art within draft tube simulation. Three workshops were organized on the matter in 1999, 2001 and 2005 where the geometry and experimental data were provided as boundary conditions to the participants. Since the last workshop, computational power and flow modelling have been developed and the available data completed with unsteady pressure measurements and phase resolved velocity measurements in the cone. Such new set of data together with the corresponding phase resolved velocity boundary conditions offer new possibilities to validate unsteady numerical simulations in Kaplan draft tube. The present work presents simulation of the Turbine-99 test case with time dependent angular resolved inlet velocity boundary conditions. Different grids and time steps are investigated. The results are compared to experimental time dependent pressure and velocity measurements.
Turbine-99 unsteady simulations - Validation
Cervantes, M. J.; Andersson, U.; Lövgren, H. M.
2010-08-01
The Turbine-99 test case, a Kaplan draft tube model, aimed to determine the state of the art within draft tube simulation. Three workshops were organized on the matter in 1999, 2001 and 2005 where the geometry and experimental data were provided as boundary conditions to the participants. Since the last workshop, computational power and flow modelling have been developed and the available data completed with unsteady pressure measurements and phase resolved velocity measurements in the cone. Such new set of data together with the corresponding phase resolved velocity boundary conditions offer new possibilities to validate unsteady numerical simulations in Kaplan draft tube. The present work presents simulation of the Turbine-99 test case with time dependent angular resolved inlet velocity boundary conditions. Different grids and time steps are investigated. The results are compared to experimental time dependent pressure and velocity measurements.
Fundamentals of modern unsteady aerodynamics
Gülçat, Ülgen
2016-01-01
In this book, the author introduces the concept of unsteady aerodynamics and its underlying principles. He provides the readers with a comprehensive review of the fundamental physics of free and forced unsteadiness, the terminology and basic equations of aerodynamics ranging from incompressible flow to hypersonics. The book also covers modern topics related to the developments made in recent years, especially in relation to wing flapping for propulsion. The book is written for graduate and senior year undergraduate students in aerodynamics and also serves as a reference for experienced researchers. Each chapter includes ample examples, questions, problems and relevant references. The treatment of these modern topics has been completely revised end expanded for the new edition. It now includes new numerical examples, a section on the ground effect, and state-space representation.
Directory of Open Access Journals (Sweden)
R. Kandasamy
2016-03-01
Full Text Available The objective of the present work was to investigate theoretically the effect of single walled carbon nanotubes (SWCNTs in the presence of water and seawater with variable stream condition due to solar radiation energy. The conclusion is drawn that the flow motion and the temperature field for SWCNTs in the presence of base fluid are significantly influenced by magnetic field, convective radiation and thermal stratification. Thermal boundary layer of SWCNTs-water is compared to that of Cu-water, absorbs the incident solar radiation and transits it to the working fluid by convection.
International Nuclear Information System (INIS)
Bestman, A.R.; Adjepong, S.K.
1987-11-01
This paper investigates transient effect on the flow of a thermally radiating and electrically conducting compressible gas in a rotating medium bounded by a vertical flat plate. The transience is provoked by a time dependent perturbation on a constant plate temperature. The problem particularly focusses on an optically thick gas and a gas of arbitrary optical thickness when the difference between the wall and free stream temperatures is small. Analytical results are possible only for limiting values of time and these results are discussed quantitatively. Indeed the assumption of small temperature difference is more appropriate for plates which are opaque rather than transparent. (author). 3 refs
Krishna, M. Veera; Swarnalathamma, B. V.
2017-07-01
We considered the transient MHD flow of a reactive second grade fluid through porous medium between two infinitely long horizontal parallel plates when one of the plate is set into uniform accelerated motion in the presence of a uniform transverse magnetic field under Arrhenius reaction rate. The governing equations are solved by Laplace transform technique. The effects of the pertinent parameters on the velocity, temperature are discussed in detail. The shear stress and Nusselt number at the plates are also obtained analytically and computationally discussed with reference to governing parameters.
International Nuclear Information System (INIS)
Amaya, J.; Cabrit, O.; Poitou, D.; Cuenot, B.; El Hafi, M.
2010-01-01
Direct numerical simulations (DNS) of an anisothermal reacting turbulent channel flow with and without radiative source terms have been performed to study the influence of the radiative heat transfer on the optically non-homogeneous boundary layer structure. A methodology for the study of the emitting/absorbing turbulent boundary layer (TBL) is presented. Details on the coupling strategy and the parallelization techniques are exposed. An analysis of the first order statistics is then carried out. It is shown that, in the studied configuration, the global structure of the thermal boundary layer is not significantly modified by radiation. However, the radiative transfer mechanism is not negligible and contributes to the heat losses at the walls. The classical law-of-the-wall for temperature can thus be improved for RANS/LES simulations taking into account the radiative contribution.
Chlorine decay under steady and unsteady-state hydraulic conditions
DEFF Research Database (Denmark)
Stoianov, Ivan; Aisopou, Angeliki
2014-01-01
This paper describes a simulation framework for the scale-adaptive hydraulic and chlorine decay modelling under steady and unsteady-state flows. Bulk flow and pipe wall reaction coefficients are replaced with steady and unsteady-state reaction coefficients. An unsteady decay coefficient is defined...... which depends upon the absolute value of shear stress and the rate of change of shear stress for quasi-unsteady and unsteady-state flows. A preliminary experimental and analytical investigation was carried out in a water transmission main. The results were used to model monochloramine decay...... and these demonstrate that the dynamic hydraulic conditions have a significant impact on water quality deterioration and the rapid loss of disinfectant residual. © 2013 The Authors....
A Coordinate Transformation for Unsteady Boundary Layer Equations
Directory of Open Access Journals (Sweden)
Paul G. A. CIZMAS
2011-12-01
Full Text Available This paper presents a new coordinate transformation for unsteady, incompressible boundary layer equations that applies to both laminar and turbulent flows. A generalization of this coordinate transformation is also proposed. The unsteady boundary layer equations are subsequently derived. In addition, the boundary layer equations are derived using a time linearization approach and assuming harmonically varying small disturbances.
International Nuclear Information System (INIS)
Pedemonte, A.A.; Traverso, A.; Massardo, A.F.
2008-01-01
One of the most interesting methods of water introduction in a gas turbine circuit is represented by the humid air turbine cycle (HAT). In the HAT cycle, the humidification can be provided by a pressurised saturator (i.e. humidification tower or saturation tower), this solution being known to offer several attractive features. This part A is focused on an experimental study of a pressurised humidification tower, with structured packing inside. After a description of the test rig employed to carry out the measuring campaign, the results relating to the thermodynamic process are presented and discussed. The experimental campaign was carried out over 162 working points, covering a relatively wide range of possible operating conditions. Details about measured data are provided in the appendix. It is shown that the saturator's behaviour, in terms of air outlet humidity and temperature, is primarily driven by, in decreasing order of relevance, the inlet water temperature, the inlet water over inlet dry air mass flow ratio and the inlet air temperature. Finally, the exit relative humidity is shown to be consistently over 100%, which may be explained partially by measurement accuracy and droplet entrainment, and partially by the non-ideal behaviour of air-steam mixtures close to saturation
Ullah, Imran; Bhattacharyya, Krishnendu; Shafie, Sharidan; Khan, Ilyas
2016-01-01
Numerical results are presented for the effect of first order chemical reaction and thermal radiation on mixed convection flow of Casson fluid in the presence of magnetic field. The flow is generated due to unsteady nonlinearly stretching sheet placed inside a porous medium. Convective conditions on wall temperature and wall concentration are also employed in the investigation. The governing partial differential equations are converted to ordinary differential equations using suitable transformations and then solved numerically via Keller-box method. It is noticed that fluid velocity rises with increase in radiation parameter in the case of assisting flow and is opposite in the case of opposing fluid while radiation parameter has no effect on fluid velocity in the forced convection. It is also seen that fluid velocity and concentration enhances in the case of generative chemical reaction whereas both profiles reduces in the case of destructive chemical reaction. Further, increase in local unsteadiness parameter reduces fluid velocity, temperature and concentration. Over all the effects of physical parameters on fluid velocity, temperature and concentration distribution as well as on the wall shear stress, heat and mass transfer rates are discussed in detail.
Wind Turbines: Unsteady Aerodynamics and Inflow Noise
DEFF Research Database (Denmark)
Broe, Brian Riget
in order to estimate the lift fluctuations due to unsteady aerodynamics (Sears, W. R.: 1941, Some aspects of non-stationary airfoil theory and its practical application; Goldstein, M. E. and Atassi, H. M.: 1976, A complete second-order theory for the unsteady flow about an airfoil due to a periodic gust...... (Sears, W. R.: 1941; and Graham, J. M. R.: 1970). An acoustic model is investigated using a model for the lift distribution as input (Amiet, R. K.: 1975, Acoustic radiation from an airfoil in a turbulent stream). The two models for lift distribution are used in the acoustic model. One of the models...
Directory of Open Access Journals (Sweden)
Pandit K. K.
2017-12-01
Full Text Available An investigation of the effects of a chemical reaction and thermal radiation on unsteady MHD free convection heat and mass transfer flow of an electrically conducting, viscous, incompressible fluid past a vertical infinite flat plate embedded in a porous medium is carried out. The flow is induced by a general time-dependent movement of the vertical plate, and the cases of ramped temperature and isothermal plates are studied. An exact solution of the governing equations is obtained in closed form by the Laplace Transform technique. Some applications of practical interest for different types of plate motions are discussed. The numerical values of fluid velocity, temperature and species concentration are displayed graphically whereas the numerical values of skin friction, Nusselt number and Sherwood number are presented in a tabular form for various values of pertinent flow parameters for both ramped temperature and isothermal plates.
Pandit, K. K.; Sarma, D.; Singh, S. I.
2017-12-01
An investigation of the effects of a chemical reaction and thermal radiation on unsteady MHD free convection heat and mass transfer flow of an electrically conducting, viscous, incompressible fluid past a vertical infinite flat plate embedded in a porous medium is carried out. The flow is induced by a general time-dependent movement of the vertical plate, and the cases of ramped temperature and isothermal plates are studied. An exact solution of the governing equations is obtained in closed form by the Laplace Transform technique. Some applications of practical interest for different types of plate motions are discussed. The numerical values of fluid velocity, temperature and species concentration are displayed graphically whereas the numerical values of skin friction, Nusselt number and Sherwood number are presented in a tabular form for various values of pertinent flow parameters for both ramped temperature and isothermal plates.
Unsteady computational fluid dynamics in aeronautics
Tucker, P G
2014-01-01
The field of Large Eddy Simulation (LES) and hybrids is a vibrant research area. This book runs through all the potential unsteady modelling fidelity ranges, from low-order to LES. The latter is probably the highest fidelity for practical aerospace systems modelling. Cutting edge new frontiers are defined. One example of a pressing environmental concern is noise. For the accurate prediction of this, unsteady modelling is needed. Hence computational aeroacoustics is explored. It is also emerging that there is a critical need for coupled simulations. Hence, this area is also considered and the tensions of utilizing such simulations with the already expensive LES. This work has relevance to the general field of CFD and LES and to a wide variety of non-aerospace aerodynamic systems (e.g. cars, submarines, ships, electronics, buildings). Topics treated include unsteady flow techniques; LES and hybrids; general numerical methods; computational aeroacoustics; computational aeroelasticity; coupled simulations and...
Safety aspects of pressurised water reactors
International Nuclear Information System (INIS)
1985-01-01
This submission to the Health and Safety Executive has been prepared by the Institution of Professional Civil Servants (IPCS) as a contribution to the debate on safety aspects associated with Pressurized Water Reactors (PWRs). Although supporting an energy policy which includes the development of nuclear power, assurances are sought on a number of safety issues if it is decided that this should be generated by a PWR-type reactor. These issues are listed. In particular the following are mentioned: the wider publication of design information, the use of elastic-plastic fracture mechanics as the basis for determining pressure vessel integrity, the failure rate of steam generating units, water coolant quality control, greater investigation of two-phase flow accident conditions, the components of the reactor cooling system and training of reactor personnel in the understanding of LOCA effects. (U.K.)
International Nuclear Information System (INIS)
Rodliffe, R.S.; Polley, M.V.; Thornton, E.W.
1985-05-01
The redistribution of corrosion products from the primary circuit surfaces of a water reactor can result in increased flow resistance, poorer heat transfer performance, fuel failure and radioactive contamination of circuit surfaces. The environment is generally sufficiently well controlled to ensure that the first three effects are not limiting. The last effect is of particular importance since radioactive corrosion products are major contributors to shutdown fields and since it is necessary to ensure that the radiation exposure of personnel is as low as reasonably achievable. This review focusses attention on the principles which must form the basis for any mechanistic model describing the formation, transport and deposition of radioactive corrosion products. It is relevant to all water reactors in which the primary heat transfer medium is predominantly single-phase water and in which steam is generated in a secondary circuit, i.e. including CANDU pressurised heavy water reactors, Sovient VVERs, etc. (author)
Energy Technology Data Exchange (ETDEWEB)
Bauer, C.
2001-07-01
The objective of this study is the development of an algorithm enabling coupling of nonmatching computational grids to carry out calculations of an unsteady flow through a hydraulic axial turbine with reference to interaction between stator and rotor. The algorithm should offer the possibility to operate the computational grids in a fixed position relative to each other as well as in relative movement. Furthermore, the calculation should be feasible with separate grids in parallel and different frames of reference. Employing selected examples this method is investigated in detail the results are compared with performed measurements. The unsteady numerical examination of the coupling process is carried out with different examples; especially the interaction effects between stator, rotor and draft tube of a hydraulic axial turbine are observed. In addition, the effect of tip clearance of the mean flow is described. Extensive model tests using the axial turbine have been performed at the Institute for Fluid Mechanics and Hydraulic Machinery, IHS. Flow time dependent velocities have been measured with a Laser Doppler Velocimeter placed at midspan of the blading. Periodical changes in static pressure have been recorded at different locations near the wall of the turbine casing. These measurements serve as reference for the comparison with results derived from the unsteady calculations. The confrontation of the time-dependent fluctuations of the flow quantities and the calculation of the efficiency of the turbine resulting from the simulation results allow a comparison in absolute terms. (orig.) [German] Fuer die instationaere Berechnung einer hydraulischen Axialturbine unter Beruecksichtigung der Interaktion zwischen Leit- und Laufrad wird ein Algorithmus zum Koppeln von nichtpassenden Berechnungsnetzen entwickelt. Diese Berechnungsnetze sollen zueinander ortsfest sein oder auch eine Relativbewegung zueinander haben koennen. Sie sollen ausserdem und in unterschiedlichen
Sandeep, N.; Animasaun, I. L.
2017-06-01
Within the last few decades, experts and scientists dealing with the flow of non-Newtonian fluids (most especially Casson fluid) have confirmed the existence of such flow on a stretchable surface with low heat energy (i.e. absolute zero of temperature). This article presents the motion of a three-dimensional of such fluid. Influence of uniform space dependent internal heat source on the intermolecular forces holding the molecules of Casson fluid is investigated. It is assumed that the stagnation flow was induced by an external force (pressure gradient) together with impulsive. Based on these assumptions, variable thermophysical properties are most suitable; hence modified kinematic viscosity model is presented. The system of governing equations of 3-dimensional unsteady Casson fluid was non-dimensionalized using suitable similarity transformation which unravels the behavior of the flow at full fledge short period. The numerical solution of the corresponding boundary value problem (ODE) was obtained using Runge-Kutta fourth order along with shooting technique. The intermolecular forces holding the molecules of Casson fluid flow in both horizontal directions when magnitude of velocity ratio parameters are greater than unity breaks continuously with an increase in Casson parameter and this leads to an increase in velocity profiles in both directions.
Directory of Open Access Journals (Sweden)
Sandeep N.
2017-06-01
Full Text Available Within the last few decades, experts and scientists dealing with the flow of non-Newtonian fluids (most especially Casson fluid have confirmed the existence of such flow on a stretchable surface with low heat energy (i.e. absolute zero of temperature. This article presents the motion of a three-dimensional of such fluid. Influence of uniform space dependent internal heat source on the intermolecular forces holding the molecules of Casson fluid is investigated. It is assumed that the stagnation flow was induced by an external force (pressure gradient together with impulsive. Based on these assumptions, variable thermophysical properties are most suitable; hence modified kinematic viscosity model is presented. The system of governing equations of 3-dimensional unsteady Casson fluid was non-dimensionalized using suitable similarity transformation which unravels the behavior of the flow at full fledge short period. The numerical solution of the corresponding boundary value problem (ODE was obtained using Runge-Kutta fourth order along with shooting technique. The intermolecular forces holding the molecules of Casson fluid flow in both horizontal directions when magnitude of velocity ratio parameters are greater than unity breaks continuously with an increase in Casson parameter and this leads to an increase in velocity profiles in both directions.
Unsteady wake of a rotating tire
Lombard, Jean-Eloi; Moxey, Dave; Xu, Hui; Sherwin, Spencer; Sherwin Lab Team
2015-11-01
For open wheel race-cars, such as IndyCar and Formula One, the wheels are responsible for 40% of the total drag. For road cars drag associated to the wheels and under-carriage can represent 60% of total drag at highway cruise speeds. Experimental observations have reported two or three pairs of counter rotating vortices, the relative importance of which still remains an open question, that interact to form a complex wake. Traditional RANS based methods are typically not well equipped to deal with such highly unsteady flows which motivates research into more physical, unsteady models. Leveraging a high-fidelity spectral/hp element based method a Large Eddy Simulation is performed to give further insight into unsteady characteristics of the wake. In particular the unsteady nature of both the jetting and top vortex pair is reported as well as the time and length scales associated with the vortex core trajectories. Correlation with experimentally obtained particle image velocimetry is presented. The authors acknowledge support from the United Kingdom Turbulence Consortium (UKTC) as well as from the Engineering and Physical Sciences Research Council (EPSRC) for access to ARCHER UK National Supercomputing Service.
Koehl, M. A. R.
2016-02-01
When animals swim in marine habitats, the water through which they move is usually flowing. Therefore, an important part of understanding the physics of how animals swim in nature is determining how they interact with the fluctuating turbulent water currents in their environment. The research systems we have been using to address this question are microscopic marine animals swimming in turbulent, wavy water flow over spatially-complex communities of organisms growing on surfaces. Field measurements of water motion were used to design realistic turbulent flow in a laboratory wave-flume over different substrata, particle-image velocimetry was used to measure fine-scale, rapidly-varying water velocity vector fields, and planar laser-induced fluorescence was used to measure concentrations of chemical cues from the substratum. We used individual-based models of small animals swimming in this unsteady flow to determine how their trajectories and contacts with substrata were affected by their locomotion through the water, rotation by local shear, response to odors, and transport by ambient flow. We found that the shears, accelerations, and odor concentrations encountered by small swimmers fluctuate rapidly, with peaks much higher than mean values lasting fractions of a second. We identified ways in which the behavior of small, weak swimmers can bias how they are transported by ambient flow (e.g. sinking during brief encounters with shear or odor enhances settlement onto substrata below, whereas constant swimming enhances contact with surfaces above or beside larvae). Although microscopic organisms swim slowly relative to ambient water flow, their locomotory behavior in response to the rapidly-fluctuating shears and odors they encounter can affect where they are transported by ambient water movement.
Energy Technology Data Exchange (ETDEWEB)
Boudesocque-Dubois, C.; Gauthier, S.; Clarisse, J.M
2007-07-01
We exhibit and detail the properties of exact self-similar solutions for inviscid compressible ablative flows in slab symmetry with nonlinear heat conduction relevant to inertial confinement fusion (ICF). These solutions have been found after several contributions over the last four decades. We first derived the set of ODEs that governs the self-similar solutions by using the invariance of the Euler's equations with nonlinear heat conduction under the two-parameter Lie group symmetry. A sub-family that leaves the density invariant is detailed since this is the most relevant case for ICF. A physical analysis of these unsteady ablation flows is then provided where the associated dimensionless numbers (Mach, Froude and P let numbers) are calculated. Finally we show that these solutions do not satisfy the constraints of the low Mach number approximation that means that ablation fronts generated within the framework of the present hypotheses (electronic conduction, growing heat flux at the boundary, etc.) cannot be approximated by a steady quasi-incompressible flow as it is often assumed in ICF. Two particular solutions of this family have been recently used for studying stability properties of ablation fronts, since they are representative of the flows that should be reached on the future French Laser MegaJoule. (authors)
Energy Technology Data Exchange (ETDEWEB)
Rodriguez, Jose Fernando; Garcia, Marcelo Horacio [Universidad de Illinois (United States); Admiraal, David Mark [Universidad de Nebraska en Lincoln (United States)
2001-06-01
In order to compute the total amount and vertical distribution of suspended sediment, a reference concentration near the bed or entrainment function is needed, and considerable research effort has been dedicated to obtain such formulae. Several entrainment functions are available in the literature, but all of them have been developed for steady, uniform flow conditions. The ability of such relationships to predict entrainment rates in unsteady flows has not been demonstrated, nor has there been any attempt to develop a general formulation that work for both steady and unsteady flow conditions. The traditional approach relates the entrainment of sediment to the wall shear stress associated with skin friction in a deterministic way, providing only a relation between mean values. An alternative is to consider both the shear stress and the entrainment as stochastic turbulent quantities and to express them in terms of their probability density functions (PDFs). In this way, statistics of the entrainment can be obtained from measured shear stress PDFs, either in steady or unsteady situations, since the effect of unsteadiness is embedded in the PDF. This new methodology was used to estimate sediment entrainment produced by the passage of vessels in the Mississippi River and the Illinois River. Using a low order cumulant expansion to describe the PDF of the shear stress and a generalized version of Garcia and Parker's entrainment relationship, an expression for the average of the entrainment as a function of the average, variance, skewness of the shear stress distribution was obtained. Predictions compared favourably with values reported in the literature. [Spanish] Para calcular la cantidad total y distribucion vertical de sedimento en suspension es preciso conocer una concentracion de referencia cerca del lecho o funcion de incorporacion, para lo cual se ha hecho un considerable esfuerzo por obtener dichas formulas. Existen varias funciones de incorporacion en la
Numerical simulation of the unsteady progress in centrifuge
International Nuclear Information System (INIS)
Wei Chunlin; Zeng Shi
2006-01-01
Unsteady flow equations for the centrifuge are solved on a staggered grid by a finite volume method. The transient process that the axial flow in the centrifuge is established under a steady thermal driving. It can be concluded that the influence which causes the perturbing fluid is different at the beginning and the end of the processing. The flow is caused by the imbalance of temperature which turns to be caused by the imbalance of pressure. The results show that the numerical simulation is effective at the unsteady fluid in a centrifuge. (authors)
Li, Gaohua; Fu, Xiang; Wang, Fuxin
2017-10-01
The low-dissipation high-order accurate hybrid up-winding/central scheme based on fifth-order weighted essentially non-oscillatory (WENO) and sixth-order central schemes, along with the Spalart-Allmaras (SA)-based delayed detached eddy simulation (DDES) turbulence model, and the flow feature-based adaptive mesh refinement (AMR), are implemented into a dual-mesh overset grid infrastructure with parallel computing capabilities, for the purpose of simulating vortex-dominated unsteady detached wake flows with high spatial resolutions. The overset grid assembly (OGA) process based on collection detection theory and implicit hole-cutting algorithm achieves an automatic coupling for the near-body and off-body solvers, and the error-and-try method is used for obtaining a globally balanced load distribution among the composed multiple codes. The results of flows over high Reynolds cylinder and two-bladed helicopter rotor show that the combination of high-order hybrid scheme, advanced turbulence model, and overset adaptive mesh refinement can effectively enhance the spatial resolution for the simulation of turbulent wake eddies.
International Nuclear Information System (INIS)
Korpela, T.; Hippinen, I.; Konkola, M.
1996-01-01
The influence of operating conditions on gaseous emissions in pressurised fluidised-bed combustion have been studied. The research objectives have been behaviour of sulphur absorbents and reduction of sulphur dioxide emissions, reduction of nitrogen oxide emissions, release of vapour-phase alkalimetals and carbon monoxide emissions. The sulphur capture capacities of calcium-based sorbents under PFBC conditions have been studied at a pressurised fluidised-bed reactor and at a pressurised thermogravimetric apparatus. The project has also connected results of the experimental PFBC at HUT/EVO. (author)
International Nuclear Information System (INIS)
Anand Rao, J.; Prabhakar Reddy, B.
2010-01-01
The numerical solution of unsteady hydro-magnetic natural convection heat and mass transfer flow of a rotating, incompressible, viscous Boussinesq fluid is presented in this study in the presence of radiative heat transfer and a first order chemical reaction between the fluid and diffusing species. The Rosseland approximation for an optically thick fluid is invoked to describe the radiative flux. The solutions for velocity, temperature and concentration fields have been obtained by using Ritz finite element method. The results obtained are discussed for Grashof number(G r > 0) corresponding to cooling of the plate and (G r r , Sc, M, N, K, G r , G c and t with the help of graphs and tables. The numerical values of skin-friction coefficient entered in the tables. Results obtained show that a decrease in the temperature boundary layer occurs when the Prandtl number and the radiation parameter are increased and the flow velocity approaches steady state as the time parameter t, is increased. These findings are in quantitative agreement with earlier reported studies. (author)
Unsteady fluid dynamics around a hovering wing
Krishna, Swathi; Green, Melissa; Mulleners, Karen
2017-11-01
The unsteady flow around a hovering flat plate wing has been investigated experimentally using particle image velocimetry and direct force measurements. The measurements are conducted on a wing that rotates symmetrically about the stroke reversal at a reduced frequency of k = 0.32 and Reynolds number of Re = 220 . The Lagrangian finite-time Lyapunov exponent method is used to analyse the unsteady flow fields by identifying dynamically relevant flow features such as the primary leading edge vortex (LEV), secondary vortices, and topological saddles, and their evolution within a flapping cycle. The flow evolution is divided into four stages that are characterised by the LEV (a)emergence, (b)growth, (c)lift-off, and (d)breakdown and decay. Tracking saddle points is shown to be helpful in defining the LEV lift-off which occurs at the maximum stroke velocity. The flow fields are correlated with the aerodynamic forces revealing that the maximum lift and drag are observed just before LEV lift-off. The end of wing rotation in the beginning of the stroke stimulates a change in the direction of the LEV growth and the start of rotation at the end of the stroke triggers the breakdown of the LEV.
Review of the physics of enhancing vortex lift by unsteady excitation
Wu, J. Z.; Vakili, A. D.; Wu, J. M.
1991-01-01
A review aimed at providing a physical understanding of the crucial mechanisms for obtaining super lift by means of unsteady excitations is presented. Particular attention is given to physical problems, including rolled-up vortex layer instability and receptivity, wave-vortex interaction and resonance, nonlinear streaming, instability of vortices behind bluff bodies and their shedding, and vortex breakdown. A general theoretical framework suitable for handling the unsteady vortex flows is introduced. It is suggested that wings with swept and sharp leading edges, equipped with devices for unsteady excitations, could yield the first breakthrough of the unsteady separation barrier and provide super lift at post-stall angle of attack.
Evolution of Surface Nanopores in Pressurised Gyrospun Polymeric Microfibers
Directory of Open Access Journals (Sweden)
U. Eranka Illangakoon
2017-10-01
Full Text Available The selection of a solvent or solvent system and the ensuing polymer–solvent interactions are crucial factors affecting the preparation of fibers with multiple morphologies. A range of poly(methylmethacrylate fibers were prepared by pressurised gyration using acetone, chloroform, N,N-dimethylformamide (DMF, ethyl acetate and dichloromethane as solvents. It was found that microscale fibers with surface nanopores were formed when using chloroform, ethyl acetate and dichloromethane and poreless fibers were formed when using acetone and DMF as the solvent. These observations are explained on the basis of the physical properties of the solvents and mechanisms of pore formation. The formation of porous fibers is caused by many solvent properties such as volatility, solubility parameters, vapour pressure and surface tension. Cross-sectional images show that the nanopores are only on the surface of the fibers and they were not inter-connected. Further, the results show that fibers with desired nanopores (40–400 nm can be prepared by carefully selecting the solvent and applied pressure in the gyration process.
Design and Verification of Critical Pressurised Windows for Manned Spaceflight
Lamoure, Richard; Busto, Lara; Novo, Francisco; Sinnema, Gerben; Leal, Mendes M.
2014-06-01
The Window Design for Manned Spaceflight (WDMS) project was tasked with establishing the state-of-art and explore possible improvements to the current structural integrity verification and fracture control methodologies for manned spacecraft windows.A critical review of the state-of-art in spacecraft window design, materials and verification practice was conducted. Shortcomings of the methodology in terms of analysis, inspection and testing were identified. Schemes for improving verification practices and reducing conservatism whilst maintaining the required safety levels were then proposed.An experimental materials characterisation programme was defined and carried out with the support of the 'Glass and Façade Technology Research Group', at the University of Cambridge. Results of the sample testing campaign were analysed, post-processed and subsequently applied to the design of a breadboard window demonstrator.Two Fused Silica glass window panes were procured and subjected to dedicated analyses, inspection and testing comprising both qualification and acceptance programmes specifically tailored to the objectives of the activity.Finally, main outcomes have been compiled into a Structural Verification Guide for Pressurised Windows in manned spacecraft, incorporating best practices and lessons learned throughout this project.
Directory of Open Access Journals (Sweden)
Mohammadreza Azimi
2015-03-01
Full Text Available In the current research, the unsteady two dimensional Graphene Oxide water based nanofluid heat transfer between two moving parallel plates is analyzed using an intelligent black-box identifier. The developed intelligent tool is known as evolvable evolutionary fuzzy inference system (EE-FIS which is based on the integration of low-level fuzzy programming and hyper-level evolutionary computing concepts. Here, the authors propose the use of a modified evolutionary algorithm (EA which is called hybrid genetic mutable smart bee algorithm (HGMSBA. The proposed HGMSBA is used to evolve both antecedent and consequent parts of fuzzy rule base. Besides, it tries to prune the rule base of fuzzy inference system (FIS to decrease its computational complexity and increase its interpretability. By considering the prediction error of the fuzzy identifier as the objective function of HGMSBA, an automatic soft interpolation machine is developed which can intuitively increase the robustness and accuracy of the final model. Here, HGMSBA-FIS is used to provide a nonlinear map between inputs, i.e. nanoparticles solid volume fraction (ϕ, Eckert number (Ec and a moving parameter which describes the movements of plates (S, and output, i.e. Nusselt number (Nu. Prior to proceeding with the modeling process, a comprehensive numerical comparative study is performed to investigate the potentials of the proposed model for nonlinear system identification. After demonstrating the efficacy of HGMSBA for training the FIS, the system is applied to the considered problem. Based on the obtained results, it can be inferred that the developed HGMSBA-FIS black-box identifier can be used as a very authentic tool with respect to accuracy and robustness. Besides, as the proposed black-box is not a physics-based identifier, it frees experts from the cumbersome mathematical formulations, and can be used for advanced real-time applications such as model-based control. The simulations
Energy Technology Data Exchange (ETDEWEB)
Bastin, G.
2004-09-15
The aim of this study concerns the use of numerical methods for the resolution of the Reynolds Averaged Navier Stokes equations adapted to the simulation of the cooling of the trailing edge of a stator in a high pressure turbine. These methods, based on the elsA solver developed at ONERA, use a four steps Runge Kutta time discretization scheme and a Jameson centered space discretization scheme. The scheme is applied through a finite volume approach on control volume centered on the cells of a multi-block structured mesh. Turbulence is simulated either through the algebraic Michel model, or through the one-transport-equation Spalart-Allmaras model, or through the two-transport-equations k 1, k {omega} and k {epsilon} models, and through ASM model. A simulation of the flow in a bidimensional stator, without cooling, is carried out. The cooling, which is realized with trailing edge slots, is then simulated on a bidimensional stator. Because the slot is represented by meshes overlapping the mesh of the smooth blade, the Chimera method is chosen. This method makes it possible computations with overlapping meshes. The comparison with the experimental data, on these two first computations has validated this strategy to represent such slots. The tridimensional simulation of a single stator with taking account of the cooling is then realized. It showed the complex and tridimensional aspects of the main flow with focus on the influence of the cooling system. Finally two steady computations, without and with cooling, and an unsteady computation without cooling are carried out on a high pressure turbine stage. The comparison with the experimental data obtained in the frame of the European Brite-Euram program is made. These results make it possible to determine the effect of the cooling on the flow in a turbine stage. (authors)
Unsteady bio-fluid dynamics in flying and swimming
Liu, Hao; Kolomenskiy, Dmitry; Nakata, Toshiyuki; Li, Gen
2017-08-01
Flying and swimming in nature present sophisticated and exciting ventures in biomimetics, which seeks sustainable solutions and solves practical problems by emulating nature's time-tested patterns, functions, and strategies. Bio-fluids in insect and bird flight, as well as in fish swimming are highly dynamic and unsteady; however, they have been studied mostly with a focus on the phenomena associated with a body or wings moving in a steady flow. Characterized by unsteady wing flapping and body undulation, fluid-structure interactions, flexible wings and bodies, turbulent environments, and complex maneuver, bio-fluid dynamics normally have challenges associated with low Reynolds number regime and high unsteadiness in modeling and analysis of flow physics. In this article, we review and highlight recent advances in unsteady bio-fluid dynamics in terms of leading-edge vortices, passive mechanisms in flexible wings and hinges, flapping flight in unsteady environments, and micro-structured aerodynamics in flapping flight, as well as undulatory swimming, flapping-fin hydrodynamics, body-fin interaction, C-start and maneuvering, swimming in turbulence, collective swimming, and micro-structured hydrodynamics in swimming. We further give a perspective outlook on future challenges and tasks of several key issues of the field.
AERFORCE: Subroutine package for unsteady blade-element/momentum calculations
Energy Technology Data Exchange (ETDEWEB)
Bjoerck, Anders
2000-05-01
A subroutine package, called AERFORCE, for the calculation of aerodynamic forces of wind turbine rotors has been written. The subroutines are written in FORTRAN. AERFORCE requires the input of airfoil aerodynamic data via tables as function of angle of attack, the turbine blade and rotor geometry and wind and blade velocities as input. The method is intended for use in an aeroelastic code. Wind and blade velocities are given at a sequence of time steps and blade forces are returned. The aerodynamic method is basically a Blade-Element/Momentum method. The method is fast and coded to be used in time simulations. In order to obtain a steady state solution a time simulation to steady state conditions has to be carried out. The BEM-method in AERFORCE includes extensions for: Dynamic inflow: Unsteady modeling of the inflow for cases with unsteady blade loading or unsteady wind. Extensions to BEM-theory for inclined flow to the rotor disc (yaw model). Unsteady blade aerodynamics: The inclusion of 2D attached flow unsteady aerodynamics and a semi-empirical model for 2D dynamic stall.
Fundamentals of modern unsteady aerodynamics
Gülçat, Ülgen
2010-01-01
This introduction to the principles of unsteady aerodynamics covers all the core concepts, provides readers with a review of the fundamental physics, terminology and basic equations, and covers hot new topics such as the use of flapping wings for propulsion.
Nath, G.; Pathak, R. P.; Dutta, Mrityunjoy
2018-01-01
Similarity solutions for the flow of a non-ideal gas behind a strong exponential shock driven out by a piston (cylindrical or spherical) moving with time according to an exponential law is obtained. Solutions are obtained, in both the cases, when the flow between the shock and the piston is isothermal or adiabatic. The shock wave is driven by a piston moving with time according to an exponential law. Similarity solutions exist only when the surrounding medium is of constant density. The effects of variation of ambient magnetic field, non-idealness of the gas, adiabatic exponent and gravitational parameter are worked out in detail. It is shown that the increase in the non-idealness of the gas or the adiabatic exponent of the gas or presence of magnetic field have decaying effect on the shock wave. Consideration of the isothermal flow and the self-gravitational field increase the shock strength. Also, the consideration of isothermal flow or the presence of magnetic field removes the singularity in the density distribution, which arises in the case of adiabatic flow. The result of our study may be used to interpret measurements carried out by space craft in the solar wind and in neighborhood of the Earth's magnetosphere.
International Nuclear Information System (INIS)
Messaris, Gerasimos A. T.; Hadjinicolaou, Maria; Karahalios, George T.
2016-01-01
The present work is motivated by the fact that blood flow in the aorta and the main arteries is governed by large finite values of the Womersley number α and for such values of α there is not any analytical solution in the literature. The existing numerical solutions, although accurate, give limited information about the factors that affect the flow, whereas an analytical approach has an advantage in that it can provide physical insight to the flow mechanism. Having this in mind, we seek analytical solution to the equations of the fluid flow driven by a sinusoidal pressure gradient in a slightly curved pipe of circular cross section when the Womersley number varies from small finite to infinite values. Initially the equations of motion are expanded in terms of the curvature ratio δ and the resulting linearized equations are solved analytically in two ways. In the first, we match the solution for the main core to that for the Stokes boundary layer. This solution is valid for very large values of α. In the second, we derive a straightforward single solution valid to the entire flow region and for 8 ≤ α < ∞, a range which includes the values of α that refer to the physiological flows. Each solution contains expressions for the axial velocity, the stream function, and the wall stresses and is compared to the analogous forms presented in other studies. The two solutions give identical results to each other regarding the axial flow but differ in the secondary flow and the circumferential wall stress, due to the approximations employed in the matched asymptotic expansion process. The results on the stream function from the second solution are in agreement with analogous results from other numerical solutions. The second solution predicts that the atherosclerotic plaques may develop in any location around the cross section of the aortic wall unlike to the prescribed locations predicted by the first solution. In addition, it gives circumferential wall stresses
Energy Technology Data Exchange (ETDEWEB)
Messaris, Gerasimos A. T., E-mail: messaris@upatras.gr [Department of Physics, Division of Theoretical Physics, University of Patras, GR 265 04 Rion (Greece); School of Science and Technology, Hellenic Open University, 11 Sahtouri Street, GR 262 22 Patras (Greece); Hadjinicolaou, Maria [School of Science and Technology, Hellenic Open University, 11 Sahtouri Street, GR 262 22 Patras (Greece); Karahalios, George T. [Department of Physics, Division of Theoretical Physics, University of Patras, GR 265 04 Rion (Greece)
2016-08-15
The present work is motivated by the fact that blood flow in the aorta and the main arteries is governed by large finite values of the Womersley number α and for such values of α there is not any analytical solution in the literature. The existing numerical solutions, although accurate, give limited information about the factors that affect the flow, whereas an analytical approach has an advantage in that it can provide physical insight to the flow mechanism. Having this in mind, we seek analytical solution to the equations of the fluid flow driven by a sinusoidal pressure gradient in a slightly curved pipe of circular cross section when the Womersley number varies from small finite to infinite values. Initially the equations of motion are expanded in terms of the curvature ratio δ and the resulting linearized equations are solved analytically in two ways. In the first, we match the solution for the main core to that for the Stokes boundary layer. This solution is valid for very large values of α. In the second, we derive a straightforward single solution valid to the entire flow region and for 8 ≤ α < ∞, a range which includes the values of α that refer to the physiological flows. Each solution contains expressions for the axial velocity, the stream function, and the wall stresses and is compared to the analogous forms presented in other studies. The two solutions give identical results to each other regarding the axial flow but differ in the secondary flow and the circumferential wall stress, due to the approximations employed in the matched asymptotic expansion process. The results on the stream function from the second solution are in agreement with analogous results from other numerical solutions. The second solution predicts that the atherosclerotic plaques may develop in any location around the cross section of the aortic wall unlike to the prescribed locations predicted by the first solution. In addition, it gives circumferential wall stresses
Directory of Open Access Journals (Sweden)
I-Chung Liu
2012-01-01
Full Text Available We have analyzed the effects of variable heat flux and internal heat generation on the flow and heat transfer in a thin film on a horizontal sheet in the presence of thermal radiation. Similarity transformations are used to transform the governing equations to a set of coupled nonlinear ordinary differential equations. The obtained differential equations are solved approximately by the homotopy perturbation method (HPM. The effects of various parameters governing the flow and heat transfer in this study are discussed and presented graphically. Comparison of numerical results is made with the earlier published results under limiting cases.
Messaris, Gerasimos A. T.; Hadjinicolaou, Maria; Karahalios, George T.
2016-08-01
The present work is motivated by the fact that blood flow in the aorta and the main arteries is governed by large finite values of the Womersley number α and for such values of α there is not any analytical solution in the literature. The existing numerical solutions, although accurate, give limited information about the factors that affect the flow, whereas an analytical approach has an advantage in that it can provide physical insight to the flow mechanism. Having this in mind, we seek analytical solution to the equations of the fluid flow driven by a sinusoidal pressure gradient in a slightly curved pipe of circular cross section when the Womersley number varies from small finite to infinite values. Initially the equations of motion are expanded in terms of the curvature ratio δ and the resulting linearized equations are solved analytically in two ways. In the first, we match the solution for the main core to that for the Stokes boundary layer. This solution is valid for very large values of α. In the second, we derive a straightforward single solution valid to the entire flow region and for 8 ≤ α flows. Each solution contains expressions for the axial velocity, the stream function, and the wall stresses and is compared to the analogous forms presented in other studies. The two solutions give identical results to each other regarding the axial flow but differ in the secondary flow and the circumferential wall stress, due to the approximations employed in the matched asymptotic expansion process. The results on the stream function from the second solution are in agreement with analogous results from other numerical solutions. The second solution predicts that the atherosclerotic plaques may develop in any location around the cross section of the aortic wall unlike to the prescribed locations predicted by the first solution. In addition, it gives circumferential wall stresses augmented by approximately 100% with respect to the matched asymptotic expansions
Energy Technology Data Exchange (ETDEWEB)
Fottner, L.; Teusch, R.; Kampitsch, M.
2000-09-01
For the aerodynamic design of turbomachine blades current methods generally apply steady flow theory and consider unsteady effects like blade row interaction, shock-boundary layer interaction, potential effects and secondary flow effects only by means of empirical or semi-empirical correlations. In the context of a modern, cost-oriented blade design efforts are made to increase the aerodynamic blade loading by considering these unsteady effects whereby efficiency and performance are kept constant. This results in a blade count reduction and consequently a weight reduction, but entails a highly three-dimensional and unsteady flow field, which makes great demands on numerical design codes. The primary goals of this work was to investigate the unsteady flow behavior in compressor cascades with controlled diffusion blading under the influence of upstream wakes and to obtain a detailed insight into the physics of unsteady boundary layer behavior. With the obtained data base a validation of unsteady codes should be conducted. The investigated cascades V110 and V111 are representative for the mid section of stator blades in a high pressure compressors. At the investigated low Reynolds number a loss reduction up to 20% was observed, while at the high Reynolds number a loss increase up to 30% compared to the steady flow case was noted. The numerical results obtained by the unsteady Reynolds-averaged Navier-Stokes code TRACE{sub U} which includes a transition correlation showed a very good agreement with the experimental results. Further on indications for new design criteria considering unsteady flow effects were provided. (orig.) [German] Bei der aerodynamischen Auslegung von Turbomaschinenbeschaufelungen beruecksichtigten bisherige Verfahren instationaere Stroemungseffekte wie Schaufelreihen-Interaktion, Stoss-Grenzschicht-Wechselwirkung, Einfluss des Potentialfeldes und Sekundaerstroemungseffekte nur partiell ueber empirische und halbempirische Korrelationen. Im Rahmen
Heat and mass transfer in the unsteady hydromagnetic free ...
African Journals Online (AJOL)
Heat and mass transfer in the unsteady hydromagnetic free-convection flow in a rotating binary fluid I. ... By imposing a time dependent perturbation on the constant plate temperature and concentration and assuming a differential approximation for the radiative flux, the coupled non linear problem is solved for the ...
Unsteady force estimation using a Lagrangian drift-volume approach
McPhaden, Cameron J.; Rival, David E.
2018-04-01
A novel Lagrangian force estimation technique for unsteady fluid flows has been developed, using the concept of a Darwinian drift volume to measure unsteady forces on accelerating bodies. The construct of added mass in viscous flows, calculated from a series of drift volumes, is used to calculate the reaction force on an accelerating circular flat plate, containing highly-separated, vortical flow. The net displacement of fluid contained within the drift volumes is, through Darwin's drift-volume added-mass proposition, equal to the added mass of the plate and provides the reaction force of the fluid on the body. The resultant unsteady force estimates from the proposed technique are shown to align with the measured drag force associated with a rapid acceleration. The critical aspects of understanding unsteady flows, relating to peak and time-resolved forces, often lie within the acceleration phase of the motions, which are well-captured by the drift-volume approach. Therefore, this Lagrangian added-mass estimation technique opens the door to fluid-dynamic analyses in areas that, until now, were inaccessible by conventional means.
Unsteady Sail Dynamics in Olympic Class Sailboats
Williamson, Charles; Schutt, Riley
2016-11-01
Unsteady sailing techniques have evolved in competitive sailboat fleets, in cases where the relative weight of the sailor is sufficient to impart unsteady motions to the boat and sails. We will discuss three types of motion that are used by athletes to propel their boats on an Olympic race course faster than using the wind alone. In all of our cases, body weight movements induce unsteady sail motion, increasing driving force and speed through the water. In this research, we explore the dynamics of an Olympic class Laser sailboat equipped with a GPS, IMU, wind sensor, and a 6-GoPro camera array. We shall briefly discuss "sail flicking", whereby the helmsman periodically rolls the sail into the apparent wind, at an angle which is distinct from classical heave (in our case, the oscillations are not normal to the apparent flow). We also demonstrate "roll tacking", where there are considerable advantages to rolling the boat during such a maneuver, especially in light wind. In both of the above examples from on-the-water studies, corresponding experiments using a towing tank exhibit increases in the driving force, associated with the formation of strong vortex pairs into the flow. Finally, we focus on a technique known as "S-curving" in the case where the boat sails downwind. In contrast to the previous cases, it is drag force rather than lift force that the sailor is trying to maximise as the boat follows a zig-zag trajectory. The augmented apparent wind strength due to the oscillatory sail motion, and the growth of strong synchronised low-pressure wake vortices on the low-pressure side of the sail, contribute to the increase in driving force, and velocity-made-good downwind.
International Nuclear Information System (INIS)
Sattar, M.A.
1990-12-01
A similar solution for the flow past a vertical plate started impulsively in its own plane in a viscous incompressible fluid is presented on taking into account the effects of variable suction and/or injection and mass transfer. To solve the momentum, energy and concentration equations, a time dependent length scale is introduced, which leads to the driving parameters γ(=G r /R σ 2 ) and γ*(=G r */R σ 2 ), where G r and G r * are respectively the Grashof and modified Grashof numbers while R σ is the Reynolds number. The resulting locally similar momentum equation is then solved by the method of superposition. The effects of the parameters and that of suction/injection on the flow and on the wall shear-stress of the plate are shown graphically for different values of Schmidt number and transpiration parameter. (author). 24 refs, 11 figs
Modeling of Unsteady Sheet Cavitation on Marine Propeller Blades
Directory of Open Access Journals (Sweden)
Spyros A. Kinnas
2003-01-01
Full Text Available Unsteady sheet cavitation is very common on marine propulsor blades. The authors summarize a lifting-surface and a surface-panel model to solve for the unsteady cavitating flow around a propeller that is subject to nonaxisymmetric inflow. The time-dependent extent and thickness of the cavity were determined by using an iterative method. The cavity detachment was determined by applying the smooth detachment criterion in an iterative manner. A nonzeroradius developed vortex cavity model was utilized at the tip of the blade, and the trailing wake geometry was determined using a fully unsteady wake-alignment process. Comparisons of predictions by the two models and measurements from several experiments are given.
Unsteady load on an oscillating Kaplan turbine runner
Puolakka, O.; Keto-Tokoi, J.; Matusiak, J.
2013-02-01
A Kaplan turbine runner oscillating in turbine waterways is subjected to a varying hydrodynamic load. Numerical simulation of the related unsteady flow is time-consuming and research is very limited. In this study, a simplified method based on unsteady airfoil theory is presented for evaluation of the unsteady load for vibration analyses of the turbine shaft line. The runner is assumed to oscillate as a rigid body in spin and axial heave, and the reaction force is resolved into added masses and dampings. The method is applied on three Kaplan runners at nominal operating conditions. Estimates for added masses and dampings are considered to be of a magnitude significant for shaft line vibration. Moderate variation in the added masses and minor variation in the added dampings is found in the frequency range of interest. Reference results for added masses are derived by solving the boundary value problem for small motions of inviscid fluid using the finite element method. Good correspondence is found in the added mass estimates of the two methods. The unsteady airfoil method is considered accurate enough for design purposes. Experimental results are needed for validation of unsteady load analyses.
A Wind Tunnel Model to Explore Unsteady Circulation Control for General Aviation Applications
Cagle, Christopher M.; Jones, Gregory S.
2002-01-01
Circulation Control airfoils have been demonstrated to provide substantial improvements in lift over conventional airfoils. The General Aviation Circular Control model is an attempt to address some of the concerns of this technique. The primary focus is to substantially reduce the amount of air mass flow by implementing unsteady flow. This paper describes a wind tunnel model that implements unsteady circulation control by pulsing internal pneumatic valves and details some preliminary results from the first test entry.
Thomas, M.; Petford, N.; Bromhead, E. N.
2003-04-01
Since the events at mount St Helens during May 1980, there has been considerable attention focused on the mechanisms and consequences of volcanic edifice collapse. As a result catastrophic edifice failure is now recognised as perhaps the most socially devastating natural disaster associated with volcanic activity. The tendency of volcanic edifices to fail appears ubiquitous behaviour, and a number of failure precursors and more importantly triggers have been suggested, of which magmagenic (e.g. thermal and mechanical pore pressure increases) and seismogenic (e.g. tectonic or volcanic earthquakes) are common. Despite the increased interest in this field, large-scale, deep seated catastrophic edifice failure has still only be successfully modelled in the most extreme of cases, which does not account for the volume of field evidence of edifice collapse. One possible reason for this is the way that pore pressures are considered. For pore fluids that are entering the system from the surface (e.g. rain water) there is a set volume and therefore a set pressure that the system can accommodate, as once the edifice becomes saturated, any new fluids to fall on the surface of the edifice simply run off. If we consider internal pore fluid pressurisation from magmatic gasses, then the pressurising fluid is already in the system and the only limit to how much pressure can be accommodated is the strength of the edifice itself. The failure to fully consider the strength and deformability of a rock mass compared to an intact laboratory sample of a volcanic rock may result in a misleading assessment of edifice strength. An intact laboratory sample of basalt may yield a strength of 100--350 MPa (from uniaxial compression tests), a volcanic edifice however is not an intact rock, and is cut through by many discontinuities, including; faults, fractures and layering from discrete lava flows. A better approximation of the true strength can be determined from the rock mass rating (RMR
Unsteady Aerodynamics of Flapping Wing of a Bird
Directory of Open Access Journals (Sweden)
M. Agoes Moelyadi
2013-04-01
Full Text Available The unsteady flow behavior and time-dependent aerodynamic characteristics of the flapping motion of a bird’s wing were investigated using a computational method. During flapping, aerodynamic interactions between bird wing surfaces and surrounding flow may occur, generating local time-dependent flow changes in the flow field and aerodynamic load of birds. To study the effect of flapping speed on unsteady aerodynamic load, two kinds of computational simulations were carried out, namely a quasi-steady and an unsteady simulation. To mimic the movement of the down-stroke and the upstroke of a bird, the flapping path accorded to a sinus function, with the wing attitude changing in dihedral angle and time. The computations of time-dependent viscous flow were based on the solution of the Reynolds Averaged Navier-Stokes equations by applying the k-e turbulence model. In addition, the discretization for the computational domain around the model used multi-block structured grid to provide more accuracy in capturing viscous flow, especially in the vicinity of the wing and body surfaces, to obtain a proper wing-body geometry model. For this research, the seagull bird was chosen, which has high aspect ratio wings with pointed wing-tips and a high camber wing section. The results include mesh movement, velocity contours as well as aerodynamic coefficients of the flapping motion of the bird at various flapping frequencies.
Citeau, M; Olivier, J; Mahmoud, A; Vaxelaire, J; Larue, O; Vorobiev, E
2012-09-15
Pressurised electro-osmotic dewatering (PEOD) of two sewage sludges (activated and anaerobically digested) was studied under constant electric current (C.C.) and constant voltage (C.V.) with a laboratory chamber simulating closely an industrial filter. The influence of sludge characteristics, process parameters, and electrode/filter cloth position was investigated. The next parameters were tested: 40 and 80 A/m², 20, 30, and 50 V-for digested sludge dewatering; and 20, 40 and 80 A/m², 20, 30, and 50 V-for activated sludge dewatering. Effects of filter cloth electric resistance and initial cake thickness were also investigated. The application of PEOD provides a gain of 12 points of dry solids content for the digested sludge (47.0% w/w) and for the activated sludge (31.7% w/w). In PEOD processed at C.C. or at C.V., the dewatering flow rate was similar for the same electric field intensity. In C.C. mode, both the electric resistance of cake and voltage increase, causing a temperature rise by ohmic effect. In C.V. mode, a current intensity peak was observed in the earlier dewatering period. Applying at first a constant current and later on a constant voltage, permitted to have better control of ohmic heating effect. The dewatering rate was not significantly affected by the presence of filter cloth on electrodes, but the use of a thin filter cloth reduced remarkably the energy consumption compared to a thicker one: 69% of reduction energy input at 45% w/w of dry solids content. The reduction of the initial cake thickness is advantageous to increase the final dry solids content. Copyright © 2012 Elsevier Ltd. All rights reserved.
A Broyden numerical Kutta condition for an unsteady panel method
International Nuclear Information System (INIS)
Liu, P.; Bose, N.; Colbourne, B.
2003-01-01
In panel methods, numerical Kutta conditions are applied in order to ensure that pressure differences between the surfaces at the trailing edges of lifting surface elements are close to zero. Previous numerical Kutta conditions for 3-D panel methods have focused on use of the Newton-Raphson iterative procedure. For extreme unsteady motions, such as for oscillating hydrofoils or for a propeller behind a blockage, the Newton-Raphson procedure can have severe convergence difficulties. The Broyden iteration, a modified Newton-Raphson iteration procedure, is applied here to obtain improved convergence behavior. Using the Broyden iteration increases the reliability, robustness and in many cases computing efficiency for unsteady, multi-body interactive flows. This method was tested in a time domain code for an ice class propeller in both open water flow and during interaction with a nearby ice blockage. Predictions showed that the method was effective in these extreme flows. (author)
Shock unsteadiness in a thrust optimized parabolic nozzle
Verma, S. B.
2009-07-01
This paper discusses the nature of shock unsteadiness, in an overexpanded thrust optimized parabolic nozzle, prevalent in various flow separation modes experienced during start up {(δ P0 /δ t > 0)} and shut down {(δ P0/δ t The results are based on simultaneously acquired data from real-time wall pressure measurements using Kulite pressure transducers, high-speed schlieren (2 kHz) of the exhaust flow-field and from strain-gauges installed on the nozzle bending tube. Shock unsteadiness in the separation region is seen to increase significantly just before the onset of each flow transition, even during steady nozzle operation. The intensity of this measure ( rms level) is seen to be strongly influenced by relative locations of normal and overexpansion shock, the decrease in radial size of re-circulation zone in the back-flow region, and finally, the local nozzle wall contour. During restricted shock separation, the pressure fluctuations in separation region exhibit periodic characteristics rather than the usually observed characteristics of intermittent separation. The possible physical mechanisms responsible for the generation of flow unsteadiness in various separation modes are discussed. The results are from an experimental study conducted in P6.2 cold-gas subscale test facility using a thrust optimized parabolic nozzle of area-ratio 30.
Pressurisation of IP-SOFC technology for second generation hybrid application
Energy Technology Data Exchange (ETDEWEB)
Jones, L.
2005-07-01
The Integrated Planar Solid Oxide Fuel Cell (IP-SOFC) technology developed by Rolls-Royce plc is a hybrid fuel cell technology considered highly suitable for the distributed power generation market. This report presents the results of a project to examine the technical viability of the IP-SOFC technology and some of the associated hybrid system component technologies under pressurised conditions and to investigate the validity of the predicted pressurisation phenomena. The work included: identification of critical material specifications, construction processes, control parameters, etc; the design and commissioning of two pressurised IP-SOFC test rigs at Rolls Royce in Derby; testing two multi-bundle strips at high temperature and atmospheric pressure; testing an active IP-SOFC bundle at high temperature and pressure; testing an experimental steam reforming unit at high temperature and pressure; testing a novel low pressure drop, off-gas combustor concept under atmospheric and pressurised conditions; design studies to identify key parameters affecting the successful integration and packaging of the fuel cell stack with certain associated hybrid components; and designing a hybrid system experimental verification rig. Significant progress was made in addressing the development challenges associated with the IP-SOFC of leakage, performance, durability, yield and geometry, the reaction rate of steam reforming and emissions from the off-gas combustor. Recommendations for future work are made.
Quantification of four ionophores in soil, sediment and manure using pressurised liquid extraction
DEFF Research Database (Denmark)
Bak, Søren Alex; Hansen, Martin; Pedersen, Kenneth Munk
2013-01-01
A multi-residue pressurised liquid extraction (PLE) methodology has been established for the determination of the four ionophores: lasalocid, monensin, salinomycin and narasin in solid environmental matrices. The PLE methodology is combined with solid phase extraction as clean-up using liquid...
Directory of Open Access Journals (Sweden)
Mihai Leonida NICULESCU
2013-03-01
Full Text Available In this paper, Proper Orthogonal Decomposition (POD is applied to the analysis of the unsteady rotor-stator interaction in a low-pressure centrifugal compressor. Numerical simulations are carried out through finite volumes method using the Unsteady Reynolds-Averaged Navier-Stokes Equations (URANS model. Proper Orthogonal Decomposition allows an accurate reconstruction of flow field using only a small number of modes; therefore, this method is one of the best tools for data storage. The POD results and the data obtained by the Adamczyk decomposition are compared. Both decompositions show the behavior of unsteady rotor-stator interaction, but the POD modes allow quantifying better the numerical errors.
Unsteady aerodynamic modelling of wind turbines
Energy Technology Data Exchange (ETDEWEB)
Coton, F.N.; Galbraith, R.A. [Univ. og Glasgow, Dept. of Aerospace Engineering, Glasgow (United Kingdom)
1997-08-01
The following current and future work is discussed: Collaborative wind tunnel based PIV project to study wind turbine wake structures in head-on and yawed flow. Prescribed wake model has been embedded in a source panel representation of the wind tunnel walls to allow comparison with experiment; Modelling of tower shadow using high resolution but efficient vortex model in tower shadow domain; Extension of model to yawing flow; Upgrading and tuning of unsteady aerodynamic model for low speed, thick airfoil flows. Glasgow has a considerable collection of low speed dynamic stall data. Currently, the Leishman - Beddoes model is not ideally suited to such flows. For example: Range of stall onset criteria used for dynamic stall prediction including Beddoes. Wide variation of stall onset prediction. Beddoes representation was developed primarily with reference to compressible flows. Analyses of low speed data from Glasgow indicate deficiencies in the current model; Predicted versus measured response during ramp down motion. Modification of the Beddoes representation is required to obtain a fit with the measured data. (EG)
Stamhuis, EJ; Videler, JJ; van Duren, LA; Muller, UK
2002-01-01
Digital particle image velocimetry (DPIV) has been applied to animal-generated flows since 1993 to map the flow patterns and vortex wakes produced by a range of feeding and swimming aquatic animals, covering a Re range of 10(-2)-10(5). In this paper, the special circumstances, problems and some
Efficient Parallel Algorithms for Unsteady Incompressible Flows
Guermond, Jean-Luc; Minev, Peter D.
2013-01-01
The objective of this paper is to give an overview of recent developments on splitting schemes for solving the time-dependent incompressible Navier–Stokes equations and to discuss possible extensions to the variable density/viscosity case. A particular attention is given to algorithms that can be implemented efficiently on large parallel clusters.
Workshop II On Unsteady Separated Flow Proceedings
1988-07-28
particularly for the higher incidence around finite-aspect-ratio wings using a angles, cannot be divorced from the wing as an two-dimensional approximation is...in Pitch", AIAA Paper No. 87-2493, presented at the AIAA Atmospheric Flight Mechanics Conference, Monterrey , CA., August 17-19, 1987. 6. Malcolm, G
Wind turbine noise propagation modelling: An unsteady approach
DEFF Research Database (Denmark)
Barlas, Emre; Zhu, Wei Jun; Shen, Wen Zhong
2016-01-01
Wind turbine sound generation and propagation phenomena are inherently time dependent, hence tools that incorporate the dynamic nature of these two issues are needed for accurate modelling. In this paper, we investigate the sound propagation from a wind turbine by considering the effects of unste...... Pressure Level (SPL).......Wind turbine sound generation and propagation phenomena are inherently time dependent, hence tools that incorporate the dynamic nature of these two issues are needed for accurate modelling. In this paper, we investigate the sound propagation from a wind turbine by considering the effects...... of unsteady flow around it and time dependent source characteristics. For the acoustics modelling we employ the Parabolic Equation (PE) method while Large Eddy Simulation (LES) as well as synthetically generated turbulence fields are used to generate the medium flow upon which sound propagates. Unsteady...
ERCOFTAC Symposium on Unsteady Separation in Fluid-Structure Interaction
Bottaro, Alessandro; Thompson, Mark
2016-01-01
This book addresses flow separation within the context of fluid-structure interaction phenomena. Here, new findings from two research communities focusing on fluids and structures are brought together, emphasizing the importance of a unified multidisciplinary approach. The book covers the theory, experimental findings, numerical simulations, and modeling in fluid dynamics and structural mechanics for both incompressible and compressible separated unsteady flows. There is a focus on the morphing of lifting structures in order to increase their aerodynamic and/or hydrodynamic performances, to control separation and to reduce noise, as well as to inspire the design of novel structures. The different chapters are based on contributions presented at the ERCOFTAC Symposium on Unsteady Separation in Fluid-Structure Interaction held in Mykonos, Greece, 17-21 June, 2013 and include extended discussions and new highlights. The book is intended for students, researchers and practitioners in the broad field of computatio...
Vortex scale of unsteady separation on a pitching airfoil.
Fuchiwaki, Masaki; Tanaka, Kazuhiro
2002-10-01
The streaklines of unsteady separation on two kinds of pitching airfoils, the NACA65-0910 and a blunt trailing edge airfoil, were studied by dye flow visualization and by the Schlieren method. The latter visualized the discrete vortices shed from the leading edge. The results of these visualization studies allow a comparison between the dynamic behavior of the streakline of unsteady separation and that of the discrete vortices shed from the leading edge. The influence of the airfoil configuration on the flow characteristics was also examined. Furthermore, the scale of a discrete vortex forming the recirculation region was investigated. The non-dimensional pitching rate was k = 0.377, the angle of attack alpha(m) = 16 degrees and the pitching amplitude was fixed to A = +/-6 degrees for Re = 4.0 x 10(3) in this experiment.
DEFF Research Database (Denmark)
Aisopou, Angeliki; Stoianov, Ivan; Graham, Nigel
2013-01-01
This paper investigates the impact of the dynamic hydraulic conditions on the kinetics of chlorine decay in water supply systems. A simulation framework has been developed for the scale-adaptive hydraulic and chlorine decay modelling under steady- and unsteady-state flows. An unsteady decay coeff...... of experimental data provides new insights for the near real-time modelling and management of water quality as well as highlighting the uncertainty and challenges of accurately modelling the loss of disinfectant in water supply networks.......This paper investigates the impact of the dynamic hydraulic conditions on the kinetics of chlorine decay in water supply systems. A simulation framework has been developed for the scale-adaptive hydraulic and chlorine decay modelling under steady- and unsteady-state flows. An unsteady decay...... coefficient is defined which depends upon the absolute value of shear stress and the rate of change of shear stress for quasi-unsteady and unsteady-state flows. By coupling novel instrumentation technologies for continuous hydraulic monitoring and water quality sensors for in-pipe water quality sensing...
Unsteady aerodynamic coefficients obtained by a compressible vortex lattice method.
Fabiano Hernandes
2009-01-01
Unsteady solutions for the aerodynamic coefficients of a thin airfoil in compressible subsonic or supersonic flows are studied. The lift, the pitch moment, and pressure coefficients are obtained numerically for the following motions: the indicial response (unit step function) of the airfoil, i.e., a sudden change in the angle of attack; a thin airfoil penetrating into a sharp edge gust (for several gust speed ratios); a thin airfoil penetrating into a one-minus-cosine gust and sinusoidal gust...
New methodology of measurement the unsteady thermal cooling of objects
Winczek, Jerzy
2018-04-01
The problems of measurements of unsteady thermal turbulent flow affect a many of domains, such as heat energy, manufacturing technologies, and many others. The subject of the study is focused on the analysis of current state of the problem, overview of the design solutions and methods to measure non-stationary thermal phenomena, presentation, and choice of adequate design of the cylinder, development of the method to measure and calculate basic values that characterize the process of heat exchange on the model surface.
Implementing unsteady friction in pressure-time measurements
Jonsson, Pontus; Ramdal, Jorgen; Cervantes, Michel; Nielsen, Torbjørn Kristian
2012-01-01
Laboratory measurements using the pressure‐time method showed a velocity or Reynolds number dependent error of the flow estimate. It was suspected that the quasi steady friction formulation of the method was the cause. This was investigated, and it was proved that implementing a model for unsteady friction into the calculations improved the result. This paper presents the process of this investigation, and proposes a new method for treatment of the friction term in the pressure‐time method.
Measurement of unsteady airflow velocity at nozzle outlet
Pyszko, René; MachÅ¯, Mário
2017-09-01
The paper deals with a method of measuring and evaluating the cooling air flow velocity at the outlet of the flat nozzle for cooling a rolled steel product. The selected properties of the Prandtl and Pitot sensing tubes were measured and compared. A Pitot tube was used for operational measurements of unsteady dynamic pressure of the air flowing from nozzles to abtain the flow velocity. The article also discusses the effects of air temperature, pressure and relative air humidity on air density, as well as the influence of dynamic pressure filtering on the error of averaged velocity.
International Nuclear Information System (INIS)
Joemon, V.; Sinha, R.K.
1993-01-01
Indian Pressurised Heavy Water Reactors are natural uranium fuelled heavy water moderated and cooled reactors. As per the conventional scheme, the moderator enters through one or more inlet nozzles penetrating the calandria shell and flows out through outlet nozzles. Baffles are fixed at the inlet nozzles for proper distribution of moderator in the calandria and to avoid the impact of the jet on the neighbouring calandria tubes. An alternate scheme for moderator inlet has been conceived and engineered in which three lower peripheral lattice locations of the reactor are converted into moderator inlets. This is achieved by moderator sparger channels each containing a 5 m long perforated zircaloy-2 sparger tube rolled to the calandria tube sheets and extended by stainless steel tubular components (inserts) at both ends of a sparger channel. Moderator enters the sparger channel at both ends and flows into the calandria. In the absence of standard codes for design of rolled joints, it was requires to develop these joints based on trials followed by various tests. this paper discusses the details of the rolled joint developed for this purpose, the details of the trials with test results and optimization of rolling parameters for these joints
Unsteady Particle Deposition in a Human Nasal Cavity during Inhalation
Directory of Open Access Journals (Sweden)
Camby M.K. Se
2010-12-01
Full Text Available The present study investigates the deposition efficiency during the unsteady inhalation cycle by using Computational Fluid Dynamics (CFD. The unsteady inhalation profile was applied at the outlet of nasopharynx, which had a maximum flow rate of 40.3L/min which corresponds to an equivalent steady inhalation tidal volume flow rate of 24.6L/min. Aerodynamic particle sizes of 5μm and 20μm were studied in order to reflect contrasting Stokes numbered particle behaviour. Two particle deposition efficiencies in the nasal cavity versus time are presented. In general, the deposition of 5μm particles was much less than 20μm particles. The first 0.2 second of the inhalation cycle was found to be significant to the particle transport, since the majority of particles were deposited during this period (i.e. its residence time. Comparisons were also made with its equivalent steady inhalation flow rate which found that the unsteady inhalation produced lower deposition efficiency for both particle sizes.
DEFF Research Database (Denmark)
Runnqvist, Hannah; Bak, Søren Alex; Hansen, Martin
2010-01-01
Pressurised liquid extraction (PLE) is now a well established and extensively applied extraction technique in environmental analysis for pollutants such as persistent organic pollutants (POPs). During the past decade, an emerging group of environmentally interesting analytes are pharmaceuticals...
Pressurised combustion of biomass-derived, low calorific value, fuel gas
Energy Technology Data Exchange (ETDEWEB)
Andries, J.; Hoppesteyn, P.D.J.; Hein, K.R.G. [Lab. for Thermal Power Engineering, Dept. of Mechanical Engineering and Marine Technology, Delft Univ. of Technology (Netherlands)
1996-12-31
The Laboratory for Thermal Power Engineering of the Delft University of Technology is participating in an EU-funded, international R + D project which is designed to aid European industry in addressing issues regarding pressurised combustion of biomass-derived, low calorific flue fuel gas. The objects of the project are: To design, manufacture and test a pressurised, high temperature gas turbine combustor for biomass derived LCV fuel gas; to develop a steady-state and dynamic model describing a combustor using biomass-derived, low calorific value fuel gases; to gather reliable experimental data on the steady-state and dynamic characteristics of the combustor; to study the steady-state and dynamic plant behaviour using a plant layout wich incorporates a model of a gas turbine suitable for operation on low calorific value fuel gas. (orig)
Pressurised combustion of biomass-derived, low calorific value, fuel gas
Energy Technology Data Exchange (ETDEWEB)
Andries, J; Hoppesteyn, P D.J.; Hein, K R.G. [Lab. for Thermal Power Engineering, Dept. of Mechanical Engineering and Marine Technology, Delft Univ. of Technology (Netherlands)
1997-12-31
The Laboratory for Thermal Power Engineering of the Delft University of Technology is participating in an EU-funded, international R + D project which is designed to aid European industry in addressing issues regarding pressurised combustion of biomass-derived, low calorific flue fuel gas. The objects of the project are: To design, manufacture and test a pressurised, high temperature gas turbine combustor for biomass derived LCV fuel gas; to develop a steady-state and dynamic model describing a combustor using biomass-derived, low calorific value fuel gases; to gather reliable experimental data on the steady-state and dynamic characteristics of the combustor; to study the steady-state and dynamic plant behaviour using a plant layout wich incorporates a model of a gas turbine suitable for operation on low calorific value fuel gas. (orig)
Tseng, K.; Morino, L.
1975-01-01
A general theory for study, oscillatory or fully unsteady potential compressible aerodynamics around complex configurations is presented. Using the finite-element method to discretize the space problem, one obtains a set of differential-delay equations in time relating the potential to its normal derivative which is expressed in terms of the generalized coordinates of the structure. For oscillatory flow, the motion consists of sinusoidal oscillations around a steady, subsonic or supersonic flow. For fully unsteady flow, the motion is assumed to consist of constant subsonic or supersonic speed for time t or = 0 and of small perturbations around the steady state for time t 0.
Real-Time Unsteady Loads Measurements Using Hot-Film Sensors
Mangalam, Arun S.; Moes, Timothy R.
2004-01-01
Several flight-critical aerodynamic problems such as buffet, flutter, stall, and wing rock are strongly affected or caused by abrupt changes in unsteady aerodynamic loads and moments. Advanced sensing and flow diagnostic techniques have made possible simultaneous identification and tracking, in realtime, of the critical surface, viscosity-related aerodynamic phenomena under both steady and unsteady flight conditions. The wind tunnel study reported here correlates surface hot-film measurements of leading edge stagnation point and separation point, with unsteady aerodynamic loads on a NACA 0015 airfoil. Lift predicted from the correlation model matches lift obtained from pressure sensors for an airfoil undergoing harmonic pitchup and pitchdown motions. An analytical model was developed that demonstrates expected stall trends for pitchup and pitchdown motions. This report demonstrates an ability to obtain unsteady aerodynamic loads in real time, which could lead to advances in air vehicle safety, performance, ride-quality, control, and health management.
Induced Seismicity in pressurised single fractures: a numerical approach
Piris, Guillem; Griera, Albert; Gómez Rivas, Enrique; Herms, Ignasi; Goula, Xavier
2017-01-01
The exploration and exploitation of deep geothermal reservoirs hass ig nificantly increased during the last years. These reservoirs use heat exchange to produce heat or electricity. The so-called Enhanced Geothermal Systems (EGS) are characterize by a stimulation phase that aims to increase fluid flow and heat transfer between wells by increasing the permeability and transitivit y of the reservoir. This is achieved by injecting high-pressure fluids (normally water) in order to increase the a...
Lee, Eun Seok
2000-10-01
An improved aerodynamics performance of a turbine cascade shape can be achieved by an understanding of the flow-field associated with the stator-rotor interaction. In this research, an axial gas turbine airfoil cascade shape is optimized for improved aerodynamic performance by using an unsteady Navier-Stokes solver and a parallel genetic algorithm. The objective of the research is twofold: (1) to develop a computational fluid dynamics code having faster convergence rate and unsteady flow simulation capabilities, and (2) to optimize a turbine airfoil cascade shape with unsteady passing wakes for improved aerodynamic performance. The computer code solves the Reynolds averaged Navier-Stokes equations. It is based on the explicit, finite difference, Runge-Kutta time marching scheme and the Diagonalized Alternating Direction Implicit (DADI) scheme, with the Baldwin-Lomax algebraic and k-epsilon turbulence modeling. Improvements in the code focused on the cascade shape design capability, convergence acceleration and unsteady formulation. First, the inverse shape design method was implemented in the code to provide the design capability, where a surface transpiration concept was employed as an inverse technique to modify the geometry satisfying the user specified pressure distribution on the airfoil surface. Second, an approximation storage multigrid method was implemented as an acceleration technique. Third, the preconditioning method was adopted to speed up the convergence rate in solving the low Mach number flows. Finally, the implicit dual time stepping method was incorporated in order to simulate the unsteady flow-fields. For the unsteady code validation, the Stokes's 2nd problem and the Poiseuille flow were chosen and compared with the computed results and analytic solutions. To test the code's ability to capture the natural unsteady flow phenomena, vortex shedding past a cylinder and the shock oscillation over a bicircular airfoil were simulated and compared with