The drift force on an object in an inviscid weakly-varying rotational flow
Energy Technology Data Exchange (ETDEWEB)
Wallis, G.B. [Dartmouth College, Hanover, NH (United States)
1995-12-31
The force on any stationary object in an inviscid incompressible extensive steady flow is derived in terms of the added mass tensor and gradient of velocity of the undisturbed fluid. Taylor`s theorem is extended to flows with weak vorticity. There are possible applications to constitutive equations for two-phase flow.
Childs, Peter R N
2010-01-01
Rotating flow is critically important across a wide range of scientific, engineering and product applications, providing design and modeling capability for diverse products such as jet engines, pumps and vacuum cleaners, as well as geophysical flows. Developed over the course of 20 years' research into rotating fluids and associated heat transfer at the University of Sussex Thermo-Fluid Mechanics Research Centre (TFMRC), Rotating Flow is an indispensable reference and resource for all those working within the gas turbine and rotating machinery industries. Traditional fluid and flow dynamics
Rotationally symmetric viscous gas flows
Weigant, W.; Plotnikov, P. I.
2017-03-01
The Dirichlet boundary value problem for the Navier-Stokes equations of a barotropic viscous compressible fluid is considered. The flow region and the data of the problem are assumed to be invariant under rotations about a fixed axis. The existence of rotationally symmetric weak solutions for all adiabatic exponents from the interval (γ*,∞) with a critical exponent γ* < 4/3 is proved.
FLUID FLOW IN ROTATING HELICAL SQUARE DUCTS
Institute of Scientific and Technical Information of China (English)
Chen Hua-jun; Zhang Ben-zhao; Zhang Jin-suo
2003-01-01
A numerical study is made for a fully developed laminar flow in rotating helical pipes.Due to the rotation, the Coriolis force can also contribute to the secondary flow.The interaction between rotation, torsion, and curvature complicates the flow characteristics.The effects of rotation and torsion on the flow transitions are studied in details.The results show that there are obvious differences between the flow in rotating ducts and in helical ducts without rotation.Certain hitherto unknown flow patterns are found.The effects of rotation and torsion on the friction factor are also examined.Present results show the characteristics of the fluid flow in rotating helical square ducts.
Oscillatory Couette flow of rotating Sisko fluid
Institute of Scientific and Technical Information of China (English)
T.HAYAT; S.ABELMAN; M.HAMESE
2014-01-01
The oscillatory Couette flow of a magnetohydrodynamic (MHD) Sisko fluid between two infinite non-conducting parallel plates is explored in a rotating frame. The lower plate is fixed, and the upper plate is oscillating in its own plane. Using MATLAB, a numerical solution to the resulting nonlinear system is presented. The influence of the physical parameters on the velocity components is analyzed. It is found that the effect of rotation on the primary velocity is more significant than that on the secondary velocity. Further, the oscillatory character in the flow is also induced by rotation. The considered flow situation behaves inertialess when the Reynolds number is small.
Hydromagnetic Flow between Two Rotating Coaxial Discs
Directory of Open Access Journals (Sweden)
Abdul Aleem Khan
1970-01-01
Full Text Available This paper relates to the steady flow of an electrically incompressible viscous fluid between two parallel coaxial rotating discs with a transverse magnetic field when the discs are rotating in the same direction with the same velocity and there is a source at the centre.
Hydromagnetic rotating flow of third grade fluid
Institute of Scientific and Technical Information of China (English)
T. HAYAT; R. NAZ; A. ALSAEDI; M. M. RASHIDI
2013-01-01
This work investigates the flow of a third grade fluid in a rotating frame of reference. The fluid is incompressible and magnetohydrodynamic (MHD). The flow is bounded between two porous plates, the lower of which is shrinking linearly. Mathematical modelling of the considered flow leads to a nonlinear problem. The solution of this nonlinear problem is computed by the homotopy analysis method (HAM). Graphs are presented to demonstrate the effect of several emerging parameters, which clearly describe the flow characteristics.
THE FLOW IN ROTATING CURVED CIRCULAR PIPE
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
The combined effects of the system rotation (Coriolis force) and curvature (centrifugal force) on the flow in rotating curved circular pipe with small curvature are examined by perturbation method. A second-order perturbation solution is presented. The secondary flow structure and the primary axial velocity distributions are studied in detail. The loops of the secondary flow are more complex than those in a curved pipe without rotation or a rotating straight pipe. Its numbers depend on the body force ratio F which represents the ratio of the Coriolis to the centrifugal force. The maximum of the axial velocity is pushed to either outer bend or inner bend, which is also determined by F. The results are confirmed by the results of other authors who studied the same problem by different methods.
Stochastically driven instability in rotating shear flows
Mukhopadhyay, Banibrata
2012-01-01
Origin of hydrodynamic turbulence in rotating shear flows is investigated. The particular emphasis is the flows whose angular velocity decreases but specific angular momentum increases with increasing radial coordinate. Such flows are Rayleigh stable, but must be turbulent in order to explain observed data. Such a mismatch between the linear theory and observations/experiments is more severe when any hydromagnetic/magnetohydrodynamic instability and then the corresponding turbulence therein is ruled out. The present work explores the effect of stochastic noise on such hydrodynamic flows. We essentially concentrate on a small section of such a flow which is nothing but a plane shear flow supplemented by the Coriolis effect. This also mimics a small section of an astrophysical accretion disk. It is found that such stochastically driven flows exhibit large temporal and spatial correlations of perturbation velocities, and hence large energy dissipations of perturbation, which presumably generate instability. A ra...
Rotating electrical machines: Poynting flow
Donaghy-Spargo, C.
2017-09-01
This paper presents a complementary approach to the traditional Lorentz and Faraday approaches that are typically adopted in the classroom when teaching the fundamentals of electrical machines—motors and generators. The approach adopted is based upon the Poynting vector, which illustrates the ‘flow’ of electromagnetic energy. It is shown through simple vector analysis that the energy-flux density flow approach can provide insight into the operation of electrical machines and it is also shown that the results are in agreement with conventional Maxwell stress-based theory. The advantage of this approach is its complementary completion of the physical picture regarding the electromechanical energy conversion process—it is also a means of maintaining student interest in this subject and as an unconventional application of the Poynting vector during normal study of electromagnetism.
Kawata, Takuya; Alfredsson, P. Henrik
2016-07-01
Plane Couette flow under spanwise, anticyclonic system rotation [rotating plane Couette flow (RPCF)] is studied experimentally using stereoscopic particle image velocimetry for different Reynolds and rotation numbers in the fully turbulent regime. Similar to the laminar regime, the turbulent flow in RPCF is characterized by roll cells, however both instantaneous snapshots of the velocity field and space correlations show that the roll cell structure varies with the rotation number. All three velocity components are measured and both the mean flow and all four nonzero Reynolds stresses are obtained across the central parts of the channel. This also allows us to determine the wall shear stress from the viscous stress and the Reynolds stress in the center of the channel, and for low rotation rates the wall shear stress increases with increasing rotation rate as expected. The results show that zero absolute vorticity is established in the central parts of the channel of turbulent RPCF for high enough rotation rates, but also that the mean velocity profile for certain parameter ranges shows an S shape giving rise to a negative velocity gradient in the center of the channel. We find that from an analysis of the Reynolds stress transport equation using the present data there is a transport of the Reynolds shear stress towards the center of the channel, which may then result in a negative mean velocity gradient there.
Flow structure on a rotating plate
Energy Technology Data Exchange (ETDEWEB)
Ozen, C.A.; Rockwell, D. [Lehigh University, Department of Mechanical Engineering and Mechanics, Bethlehem, PA (United States)
2012-01-15
The flow structure on a rotating plate of low aspect ratio is characterized well after the onset of motion, such that transient effects are not significant, and only centripetal and Coriolis accelerations are present. Patterns of vorticity, velocity contours, and streamline topology are determined via quantitative imaging, in order to characterize the leading-edge vortex in relation to the overall flow structure. A stable leading-edge vortex is maintained over effective angles of attack from 30 to 75 , and at each angle of attack, its sectional structure at midspan is relatively insensitive to Reynolds number over the range from 3,600 to 14,500. The streamline topology, vorticity distribution, and circulation of the leading-edge vortex are determined as a function of angle of attack, and related to the velocity field oriented toward, and extending along, the leeward surface of the plate. The structure of the leading-edge vortex is classified into basic regimes along the span of the plate. Images of these regimes are complemented by patterns on crossflow planes, which indicate the influence of root and tip swirl, and spanwise flow along the leeward surface of the plate. Comparison with the equivalent of the purely translating plate, which does not induce the foregoing flow structure, further clarifies the effects of rotation. (orig.)
Flow in a rotating membrane plasma separator.
Lueptow, R M; Hajiloo, A
1995-01-01
Rotating filter separators are very effective in the separation of plasma from whole blood, but details of the flow field in the device have not been investigated. The flow in a commercial device has been modeled computationally using the finite element code FIDAP. Taylor vortices appear in the upstream end of the annulus but disappear in the downstream end because of increasing blood viscosity as plasma is removed. Fluid transport at the upstream end of the annulus results from both translation of Taylor vortices and fluid winding around the vortices. If the inertial effects of the axial flow are reduced, less fluid winds around the vortices and more fluid is transported by the translation of the vortices. The pressure at the membrane is nonuniform in the region where vortices appear, although the relative magnitude of the fluctuations is small.
Magnetohydrodynamic Flow Between Concentric Rotating Porous Cylinders
Directory of Open Access Journals (Sweden)
S. N. Dube
1971-10-01
Full Text Available An attempt has been made to study the steady laminar flow of a incompressible electrically conducting fluid between infinitely long concentric rotating porous cylinders under the influence of radial magnetic field. A solution has been obtained under the assumption of uniform conditions along the axis of the cylinders. The cylinders being porous, a hyperbolic radial velocity distribution has been superimposed over the circumferential velocity produced due to rotation. There is a Bernoulli type pressure variation in the radial in the direction. When the inner cylinder is at rest the shearing stress at it and the torque transmitted to it decrease as R (=v/Sub/1y/Sub1/v= v/Sub2y/Sub2/v increases and the magnetic parameter lambda (=4sigma mue/sube/sup2A/Sup2/Mue will further decrease them.
Topological Structures in Rotating Stratified Flows
Redondo, J. M.; Carrillo, A.; Perez, E.
2003-04-01
Detailled 2D Particle traking and PIV visualizations performed on a series of large scale laboratory experiments at the Coriolis Platform of the SINTEF in Trondheim have revealed several resonances which scale on the Strouhal, the Rossby and the Richardson numbers. More than 100 experiments spanned a wide range of Rossby Deformation Radii and the topological structures (Parabolic /Eliptic /Hyperbolic) of the quasi-balanced stratified-rotating flows were studied when stirring (akin to coastal mixing) occured at a side of the tank. The strong asymetry favored by the total vorticity produces a wealth of mixing patterns.
Flow Structure and Heat Transfer Between Two Disks Rotating Independently
Institute of Scientific and Technical Information of China (English)
Chyi-Yeou Soong
2003-01-01
In the present paper, fluid flow and convective heat transfer between two co-axial disks rotating independently are dealt with mainly based on the author's recent research on that topic. Three rotational modes, i.e. co-rotation, rotor-stator, and counter-rotation, are considered. Theory of rotating non-isothermal fluids with the presence of disk rotation and thermal effects is addressed. Rotational buoyancy effects on the flow structure development are highlighted. Results of flow visualization and heat transfer measurements are discussed to explore the thermal flow mechanisms involved in the two-disk flows at various rotational and geometric conditions. Potential issues open to the future investigation are also proposed.
Simulation of flow around rotating Savonius rotors
Ishimatsu, Katsuya; Shinohara, Toshio
1993-09-01
Flow around Savonius rotors was simulated by solving 2-D (two-dimensional) Navier-Stokes equations. The equations were discretized by finite volume method for space and fractional step method for time. Convection terms were specially discretized by an upwinding scheme for unstructured grid. Only rotating rotors were simulated in this report. The values of parameters were as follows: Reynolds number, 10(exp 5); overlap ratio, zero and 0.16; and tip speed ratio, 0.25 to 1.75. Results showed good agreement with experimental data for the following points: optimum tip speed ratio is 0.75 to 1.0; overlapping is effective to increase power coefficient. Moreover, simulated flow fields showed that vortex shedding occur at not only tips of bucket but back of bucket and the shed vortex decrease torque.
An improved turbulence model for rotating shear flows*
Nagano, Yasutaka; Hattori, Hirofumi
2002-01-01
In the present study, we construct a turbulence model based on a low-Reynolds-number non-linear k e model for turbulent flows in a rotating channel. Two-equation models, in particular the non-linear k e model, are very effective for solving various flow problems encountered in technological applications. In channel flows with rotation, however, the explicit effects of rotation only appear in the Reynolds stress components. The exact equations for k and e do not have any explicit terms concerned with the rotation effects. Moreover, the Coriolis force vanishes in the momentum equation for a fully developed channel flow with spanwise rotation. Consequently, in order to predict rotating channel flows, after proper revision the Reynolds stress equation model or the non-linear eddy viscosity model should be used. In this study, we improve the non-linear k e model so as to predict rotating channel flows. In the modelling, the wall-limiting behaviour of turbulence is also considered. First, we evaluated the non-linear k e model using the direct numerical simulation (DNS) database for a fully developed rotating turbulent channel flow. Next, we assessed the non-linear k e model at various rotation numbers. Finally, on the basis of these assessments, we reconstruct the non-linear k e model to calculate rotating shear flows, and the proposed model is tested on various rotation number channel flows. The agreement with DNS and experiment data is quite satisfactory.
Energetics of geostrophic adjustment in rotating flow
Juan, Fang; Rongsheng, Wu
2002-09-01
Energetics of geostrophic adjustment in rotating flow is examined in detail with a linear shallow water model. The initial unbalanced flow considered first falls tinder two classes. The first is similar to that adopted by Gill and is here referred to as a mass imbalance model, for the flow is initially motionless but with a sea surface displacement. The other is the same as that considered by Rossby and is referred to as a momentum imbalance model since there is only a velocity perturbation in the initial field. The significant feature of the energetics of geostrophic adjustment for the above two extreme models is that although the energy conversion ratio has a large case-to-case variability for different initial conditions, its value is bounded below by 0 and above by 1 / 2. Based on the discussion of the above extreme models, the energetics of adjustment for an arbitrary initial condition is investigated. It is found that the characteristics of the energetics of geostrophic adjustment mentioned above are also applicable to adjustment of the general unbalanced flow under the condition that the energy conversion ratio is redefined as the conversion ratio between the change of kinetic energy and potential energy of the deviational fields.
Particle rotation in a Couette flow
Ye, J.; Roco, M. C.
1992-02-01
The rotational velocity of neutrally buoyant particles was measured in a planar Couette flow. The flow cross section is rectangular with a 4-to-1 (200 mm/50 mm) aspect ratio. The mixtures consist of uniform polystyrene spheres and a glycerol-water solution of specific density 1.052. Four sphere sizes have been tested: 3, 4.76, 6.35, and 7.94 mm. Particle motion in turbulent flow was recorded with a high-speed SP-2000 motion analysis system. The characteristics of particle motion, including particle spin, were measured as a function of the distance from the wall, at three shear rates corresponding to Re=4.6, 6.8, and 9.2×104. It was found that the particle angular velocity normalized by shear rate is a function of the normalized distance to the moving and stationary walls. The flow conditions are defined with measurements on mean velocities, particle velocity fluctuations, kinetic energy, inertial stresses, and diffusion coefficients.
Modeling Rotating Turbulent Flows with the Body Force Potential Model.
Bhattacharya, Amitabh; Perot, Blair
2000-11-01
Like a Reynolds Stress Transport equation model, the turbulent potential model has an explicit Coriolis acceleration term that appears in the model that accounts for rotation effects. In this work the additional secondary effects that system rotation has on the dissipation rate, return-to-isotropy, and fast pressure strain terms are also included in the model. The resulting model is tested in the context of rotating isotropic turbulence, rotating homogeneous shear flow, rotating channel flow, and swirling pipe flow. Many of the model changes are applicable to Reynolds stress transport equation models. All model modifications are frame indifferent.
Fluid flow and heat transfer in rotating porous media
Vadasz, Peter
2016-01-01
This Book concentrates the available knowledge on rotating fluid flow and heat transfer in porous media in one single reference. Dr. Vadasz develops the fundamental theory of rotating flow and heat transfer in porous media and introduces systematic classification and identification of the relevant problems. An initial distinction between rotating flows in isothermal heterogeneous porous systems and natural convection in homogeneous non-‐isothermal porous systems provides the two major classes of problems to be considered. A few examples of solutions to selected problems are presented, highlighting the significant impact of rotation on the flow in porous media.
UNSTEADY INTERMITTENT FLOW IN A ROTATING CURVED PIPE
Institute of Scientific and Technical Information of China (English)
YIN Jian-an; SHEN Xin-rong; CHEN Hua-jun; ZHANG Ben-zhao
2004-01-01
The effects of rotation and intermittent fre quency on the flow transition of secondary flow and, main flow were examined in detail. Certain hitherto unknown flow patterns were found. A numerical study was performed to study the characteristics of unsteady intermittent flow in a rotating curved pipe. Due to the rotation, both the Coriolis force and the centrifugal force could contribute to the unsteady intermittent flow and some complicated phenomena can be found. The results indicate that the unsteady intermittent flow are mainly characterized by five parameters: the Dean number Dn , the curvatureκ, the maximal force ratio F (of the Coriolis force to the centrifugal force in a cycle), the intermittent frequency parameter η(the ratio of a pulslating time to the cycle period), and the Womersley number α. Present works shows the natures of the unsteady intermittent flow in a rotating curved pipe.
Modelling of convective heat and mass transfer in rotating flows
Shevchuk, Igor V
2016-01-01
This monograph presents results of the analytical and numerical modeling of convective heat and mass transfer in different rotating flows caused by (i) system rotation, (ii) swirl flows due to swirl generators, and (iii) surface curvature in turns and bends. Volume forces (i.e. centrifugal and Coriolis forces), which influence the flow pattern, emerge in all of these rotating flows. The main part of this work deals with rotating flows caused by system rotation, which includes several rotating-disk configurations and straight pipes rotating about a parallel axis. Swirl flows are studied in some of the configurations mentioned above. Curvilinear flows are investigated in different geometries of two-pass ribbed and smooth channels with 180° bends. The author demonstrates that the complex phenomena of fluid flow and convective heat transfer in rotating flows can be successfully simulated using not only the universal CFD methodology, but in certain cases by means of the integral methods, self-similar and analyt...
Effects of spanwise rotation on turbulent channel flow
Brethouwer, Geert
2016-01-01
A study of fully developed plane turbulent channel flow subject to spanwise system rotation through direct numerical simulations is presented. In order to study both the influence of the Reynolds number and spanwise rotation on channel flow, the Reynolds number $Re = U_b h/\
Effects of symmetrically alternative rotating flow on flocculation
Institute of Scientific and Technical Information of China (English)
徐继润; 张育新; 邢军; 孙永正; 徐海燕; 刘正宁; 康勇
2003-01-01
A symmetrically alternative rotating flow pattern was designed for flocculation process in order to produce large and dense flocs. The special effects of a symmetrically alternative rotating flow on the diameter and density of flocs were investigated. The results show that under the new fluid conditions, the primary particles on the outer part of the formed flocs may be cut down and the flocs contract at the end of the original rotating direction; then fluid changes its rotating direction, an opposite shearing is imposed to the flocs and makes some primary particles slide along the floc surface, leading to a denser floc; meanwhile, the broken and unflocculated particles on the trajectory may have opportunities to penetrate into or cohere to the flocs. Compared with the conventional rotating flow, the new-designed flow pattern can not only keep the floc size (even enlarge the floc diameter if a suitable flow is chosen) but also increase the floc density effectively.
Algebraic disturbances and their consequences in rotating channel flow transition
Jose, Sharath; Pier, Benoît; Govindarajan, Rama
2016-01-01
It is now established that subcritical mechanisms play a crucial role in the transition to turbulence of non-rotating plane shear flows. The role of these mechanisms in rotating channel flow is examined here in the linear and nonlinear stages. Distinct patterns of behaviour are found: the transient growth leading to nonlinearity at low rotation rates $Ro$, a highly chaotic intermediate $Ro$ regime, a localised weak chaos at higher $Ro$, and complete stabilization of transient disturbances at very high $Ro$. At very low $Ro$, the transient growth amplitudes are close to those for non-rotating flow, but Coriolis forces already assert themselves by producing distinct asymmetry about the channel centreline. Nonlinear processes are then triggered, in a streak-breakdown mode of transition. The high $Ro$ regimes do not show these signatures, here the leading eigenmode emerges as dominant in the early stages. Elongated structures plastered close to one wall are seen at higher rotation rates. Rotation is shown to redu...
Instability of Taylor-Couette Flow between Concentric Rotating Cylinders
Dou, H S; Phan-Thien, N; Yeo, K S; Dou, Hua-Shu; Khoo, Boo Cheong; Phan-Thien, Nhan; Yeo, Koon Seng
2005-01-01
The energy gradient theory is used to study the instability of Taylor-Couette flow between concentric rotating cylinders. In our previous studies, the energy gradient theory was demonstrated to be applicable for wall bounded parallel flows. It was found that the critical value of the energy gradient parameter K at subcritical transition is about 370-389 for wall bounded parallel flows (which include plane Poiseuille flow, pipe Poiseuille flow and plane Couette flow) below which no turbulence occurs. In this paper, the detailed derivation for the calculation of the energy gradient parameter in the flow between concentric rotating cylinders is provided. The theoretical results for the critical condition of primary instability obtained are in very good agreement with the experiments found in literature. The mechanism of spiral vortices generation for counter-rotating of two cylinders is also explained using the energy gradient theory. The energy gradient theory can also serve to relate the condition of flow tran...
Rotation of melting ice disks due to melt fluid flow.
Dorbolo, S; Adami, N; Dubois, C; Caps, H; Vandewalle, N; Darbois-Texier, B
2016-03-01
We report experiments concerning the melting of ice disks (85 mm in diameter and 14 mm in height) at the surface of a thermalized water bath. During the melting, the ice disks undergo translational and rotational motions. In particular, the disks rotate. The rotation speed has been found to increase with the bath temperature. We investigated the flow under the bottom face of the ice disks by a particle image velocimetry technique. We find that the flow goes downwards and also rotates horizontally, so that a vertical vortex is generated under the ice disk. The proposed mechanism is the following. In the vicinity of the bottom face of the disk, the water eventually reaches the temperature of 4 °C for which the water density is maximum. The 4 °C water sinks and generates a downwards plume. The observed vertical vorticity results from the flow in the plume. Finally, by viscous entrainment, the horizontal rotation of the flow induces the solid rotation of the ice block. This mechanism seems generic: any vertical flow that generates a vortex will induce the rotation of a floating object.
Rotating thermal flows in natural and industrial processes
Lappa, Marcello
2012-01-01
Rotating Thermal Flows in Natural and Industrial Processes provides the reader with a systematic description of the different types of thermal convection and flow instabilities in rotating systems, as present in materials, crystal growth, thermal engineering, meteorology, oceanography, geophysics and astrophysics. It expressly shows how the isomorphism between small and large scale phenomena becomes beneficial to the definition and ensuing development of an integrated comprehensive framework. This allows the reader to understand and assimilate the underlying, quintessential mechanisms withou
Dynamic Characteristics of Rotating Stall in Mixed Flow Pump
Directory of Open Access Journals (Sweden)
Xiaojun Li
2013-01-01
Full Text Available Rotating stall, a phenomenon that causes flow instabilities and pressure hysteresis by propagating at some fraction of the impeller rotational speed, can occur in centrifugal impellers, mixed impellers, radial diffusers, or axial diffusers. Despite considerable efforts devoted to the study of rotating stall in pumps, the mechanics of this phenomenon are not sufficiently understood. The propagation mechanism and onset of rotating stall are not only affected by inlet flow but also by outlet flow as well as the pressure gradient in the flow passage. As such, the complexity of these concepts is not covered by the classical explanation. To bridge this research gap, the current study investigated prerotation generated at the upstream of the impeller, leakage flow at the tip clearance between the casing and the impeller, and strong reserve flow at the inlet of the diffuser. Understanding these areas will clarify the origin of the positive slope of the head-flow performance curve for a mixed flow pump. Nonuniform pressure distribution and adverse pressure gradient were also introduced to evaluate the onset and development of rotating stall within the diffuser.
EXACT SOLUTIONS FOR MAGNETOHYDRODYNAMIC FLOW IN A ROTATING FLUID
Institute of Scientific and Technical Information of China (English)
S.Asghar; Masood Khan; A.M.Siddiqui; T.Hayat
2002-01-01
An analytical solution is obtained for the flow due to solid-body rotations of an oscillating porous disk and of a fluid at infinity. Neglecting the induced magnetic field, the effects of the transversely applied magnetic field on the flow are studied. Further, the flow confined between two disks is also discussed. It is found that an infinite number of solutions exist for the flow confined between two disks.
Flow in a Narrow Gap Along an Enclosed Rotating disk with Through-Flow
黒川, 淳一; 佐久問, 真人
1988-01-01
Flow in a narrow gap along an enclosed rotating disk superimposed with through-flow is studied theoretically and experimentally. When the axial gap is narrow, or a large outward through-flow is imposed, the boundary layers on the rotating and the stationary walls interfere with each other. The present study proposes an analytical model for such interference of gap flow and gives a theoretical analysis which is easily applicable to various boundary conditions. For non-interference of gap flow,...
Experimental investigation of a rapidly rotating turbulent duct flow
Energy Technology Data Exchange (ETDEWEB)
Maartensson, G.E.; Johansson, A.V. [Department of Mechanics, KTH, 10044 Stockholm (Sweden); Gunnarsson, J. [Bombardier Transportation, Vaesteraas (Sweden); Moberg, H. [Alfa Laval, 14780 Tumba (Sweden)
2002-09-01
Rapidly rotating duct flow is studied experimentally with Rotation numbers in the interval. To achieve this, in combination with relatively high Reynolds numbers (5,000-30,000 based on the hydraulic radius), water was used as the working medium. Square and rectangular duct cross-sections were used and the angle between the rotation vector and the main axis of the duct was varied. The influence of the rotation on the pressure drop in the duct was investigated and suitable scalings of this quantity were studied. (orig.)
Topographic instability of flow in a rotating fluid
Directory of Open Access Journals (Sweden)
K. I. Patarashvili
2006-01-01
Full Text Available Here are presented the results of experimental and theoretical studies on a stability of zonal geostrophic flows in the rotating layer of the shallow water. In the experiments, a special apparatus by Abastumani Astrophysical Observatory Georgian Academy of Science was used. This apparatus represents a paraboloid of rotation, which can be set in a regulable rotation around the vertical axis. Maximal diameter of the paraboloid is 1.2 m, radius of curvature in the pole is 0.698 m. In the paraboloid, water spreads on walls as a layer uniform on height under the period of rotation 1.677 s. Against a background of the rotating fluid, the zonal flows are formed by the source-sink system. It consists of two concentric circular perforations on the paraboloid bottom (width is 0.3 cm, radiuses are 8.4 and 57.3 cm, respectively; water can be pumped through them with various velocities and in all directions. It has been established that under constant vertical depth of the rotating fluid the zonal flows are stable. There are given the measurements of the radial profiles for the water level and velocity in the stationary regime. It has been found that zonal flows may lose stability under the presence of the radial gradient of full depth formed by a change of angular velocity of paraboloid rotation. An instability origin results in the loss of flow axial symmetry and in the appearance of self-excited oscillations in the zonal flow. At the given angular velocity of rotation, instability is observed only in the definite range of intensities of the source-sink system. The theoretical estimations are performed in the framework of the equations of the shallow water theory, including the terms describing the bottom friction. It has been shown that the instability of zonal flows found experimentally has a topographical nature and is related with non-monotone dependence of the potential vorticity on radius.
Effects of uniform rotational flow on predator-prey system
Lee, Sang-Hee
2012-12-01
Rotational flow is often observed in lotic ecosystems, such as streams and rivers. For example, when an obstacle interrupts water flowing in a stream, energy dissipation and momentum transfer can result in the formation of rotational flow, or a vortex. In this study, I examined how rotational flow affects a predator-prey system by constructing a spatially explicit lattice model consisting of predators, prey, and plants. A predation relationship existed between the species. The species densities in the model were given as S (for predator), P (for prey), and G (for plant). A predator (prey) had a probability of giving birth to an offspring when it ate prey (plant). When a predator or prey was first introduced, or born, its health state was assigned an initial value of 20 that subsequently decreased by one with every time step. The predator (prey) was removed from the system when the health state decreased to less than zero. The degree of flow rotation was characterized by the variable, R. A higher R indicates a higher tendency that predators and prey move along circular paths. Plants were not affected by the flow because they were assumed to be attached to the streambed. Results showed that R positively affected both predator and prey survival, while its effect on plants was negligible. Flow rotation facilitated disturbances in individuals’ movements, which consequently strengthens the predator and prey relationship and prevents death from starvation. An increase in S accelerated the extinction of predators and prey.
Natures of Rotating Stall Cell in a Diagonal Flow Fan
Institute of Scientific and Technical Information of China (English)
N. SHIOMI; K. KANEKO; T. SETOGUCHI
2005-01-01
In order to clarify the natures of a rotating stall cell, the experimental investigation was carried out in a high specific-speed diagonal flow fan. The pressure field on the casing wall and the velocity fields at the rotor inlet and outlet were measured under rotating stall condition with a fast response pressure transducer and a single slant hot-wire probe, respectively. The data were processed using the "Double Phase-Locked Averaging (DPLA)"technique, which enabled to obtain the unsteady flow field with a rotating stall cell in the relative co-ordinate system fixed to the rotor. As a result, the structure and behavior of the rotating stall cell in a high specific-speed diagonal flow fan were shown.
Axisymmetric rotational stagnation-point flow impinging on a rotating disk
Weidman, Patrick
2015-12-01
Agrawal's (Q J Mech Appl Math, 10:42-44, 1957) stagnation-point flow problem is extended to flow impingement normal to a uniformly rotating disk. This is the analog of the extension of Homann's (Z Angew Math Mech (ZAMM), 16:153-164, 1936) stagnation flow when impinging on a rotating disk as reported by Hannah (Rep Mem Aerosp Res Coun Lond 2772, 1947). While both oncoming stagnation flows are axisymmetric, in the far field Homann's stagnation flow is irrotational while Agrawal's is rotational. A similarity reduction of the Navier-Stokes equations yields a pair of coupled ordinary differential equations governed by a dimensionless rotation rate σ. Integrations were carried out up to σ = 30 beyond which the equations become stiff and solution independence of integration length cannot be ensured. Results for the radial and azimuthal shear stresses are presented along with the strength of the flow induced into the boundary layer and the thickness of the azimuthal flow boundary layer. Analytic results found at σ = 0 are shown to be in excellent agreement with the numerical calculations. Sample velocity profiles for the radial and azimuthal flows are presented.
A study of Impinging Flow on a Rotating Disc
Directory of Open Access Journals (Sweden)
Horia DUMITRESCU
2014-09-01
Full Text Available This paper focuses on the behavior of the boundary-layer laminar flow produced by a large radius no-thickness disc which rotates inside an axial stream. Some early solutions are only known for the upstream flow field, but the details of the flow behind the disc are still obscure. A better understanding of the mechanisms and the properties of the shear layer close to disc is sought through the development of an analytic theory and then is completed by CFD computations. This article also shows that the basic flow on the leeward side of disc is mostly rotational-inviscid and only on in the neighborhood of the disc surface there is a viscous layer which rotates drawn by disc. The viscous layer containing a thin Ekman sublayer and a thicker essentially inviscid superlayer, governed by Taylor-Proudman theorem, can carry three possible actions: centrifugal (pumping mode, neutral mode and centripetal (suction mode. The action type depends on the relative importance of effects given by translation of the fluid (W and rotation of the disc (ΩR, defined by a rotating parameter (W/ΩR. The existence of such modes is connected to the amount of angular momentum transferred outside the Ekman sublayer. A CFD analysis was used to identify the vortex structure which is responsible for the angular momentum transfer from the rotating disc to an axial stream.
Large Scale Magnetohydrodynamic Dynamos from Cylindrical Differentially Rotating Flows
Ebrahimi, F
2015-01-01
For cylindrical differentially rotating plasmas threaded with a uniform vertical magnetic field, we study large-scale magnetic field generation from finite amplitude perturbations using analytic theory and direct numerical simulations. Analytically, we impose helical fluctuations, a seed field, and a background flow and use quasi-linear theory for a single mode. The predicted large-scale field growth agrees with numerical simulations in which the magnetorotational instability (MRI) arises naturally. The vertically and azimuthally averaged toroidal field is generated by a fluctuation-induced EMF that depends on differential rotation. Given fluctuations, the method also predicts large-scale field growth for MRI-stable rotation profiles and flows with no rotation but shear.
Gulshani, Parviz
2016-01-01
We derive in a simple manner and from first principles the Inglis semi-classical phenomenological cranking model for nuclear collective rotation. The derivation transforms the nuclear Schrodinger equation (instead of the Hamiltonian) to a rotating frame using a product wavefunction and imposing no constraints on either the wavefunction or the nucleon motion. The difference from Inglis model is that the frame rotation is driven by the motions of the nucleons and not externally. Consequently, the transformed Schrodinger equation is time-reversal invariant, and the total angular momentum is the sum of those of the intrinsic system and rotating frame. In this article, we choose the rotation of the frame to be given by a combination of rigid and irrotational flows. The dynamic angular velocity of the rotating frame is determined by the angular momentum of the frame and by a moment of inertia that is determined by the nature of the flow combination. The intrinsic-system and rotating-frame angular momenta emerge to ...
Hydrodynamic turbulence in quasi-Keplerian rotating flows
Shi, Liang; Hof, Björn; Rampp, Markus; Avila, Marc
2017-04-01
We report a direct-numerical-simulation study of the Taylor-Couette flow in the quasi-Keplerian regime at shear Reynolds numbers up to O (105) . Quasi-Keplerian rotating flow has been investigated for decades as a simplified model system to study the origin of turbulence in accretion disks that is not fully understood. The flow in this study is axially periodic and thus the experimental end-wall effects on the stability of the flow are avoided. Using optimal linear perturbations as initial conditions, our simulations find no sustained turbulence: the strong initial perturbations distort the velocity profile and trigger turbulence that eventually decays.
Mean flow generation in rotating anelastic two-dimensional convection
Currie, Laura K
2016-01-01
We investigate the processes that lead to the generation of mean flows in two-dimensional anelastic convection. The simple model consists of a plane layer that is rotating about an axis inclined to gravity. The results are two-fold: firstly we numerically investigate the onset of convection in three-dimensions, paying particular attention to the role of stratification and highlight a curious symmetry. Secondly, we investigate the mechanisms that drive both zonal and meridional flows in two dimensions. We find that, in general, non-trivial Reynolds stresses can lead to systematic flows and, using statistical measures, we quantify the role of stratification in modifying the coherence of these flows.
Turbulent Compressible Convection with Rotation. 2; Mean Flows and Differential Rotation
Brummell, Nicholas H.; Hurlburt, Neal E.; Toomre, Juri
1998-01-01
The effects of rotation on turbulent, compressible convection within stellar envelopes are studied through three-dimensional numerical simulations conducted within a local f-plane model. This work seeks to understand the types of differential rotation that can be established in convective envelopes of stars like the Sun, for which recent helioseismic observations suggest an angular velocity profile with depth and latitude at variance with many theoretical predictions. This paper analyzes the mechanisms that are responsible for the mean (horizontally averaged) zonal and meridional flows that are produced by convection influenced by Coriolis forces. The compressible convection is considered for a range of Rayleigh, Taylor, and Prandtl (and thus Rossby) numbers encompassing both laminar and turbulent flow conditions under weak and strong rotational constraints. When the nonlinearities are moderate, the effects of rotation on the resulting laminar cellular convection leads to distinctive tilts of the cell boundaries away from the vertical. These yield correlations between vertical and horizontal motions that generate Reynolds stresses that can drive mean flows, interpretable as differential rotation and meridional circulations. Under more vigorous forcing, the resulting turbulent convection involves complicated and contorted fluid particle trajectories, with few clear correlations between vertical and horizontal motions, punctuated by an evolving and intricate downflow network that can extend over much of the depth of the layer. Within such networks are some coherent structures of vortical downflow that tend to align with the rotation axis. These yield a novel turbulent alignment mechanism, distinct from the laminar tilting of cellular boundaries, that can provide the principal correlated motions and thus Reynolds stresses and subsequently mean flows. The emergence of such coherent structures that can persist amidst more random motions is a characteristic of turbulence
Bubble Pinch-Off in a Rotating Flow
DEFF Research Database (Denmark)
Bergmann, Raymond; Andersen, Anders Peter; van der Meer, Devaraj
2009-01-01
We create air bubbles at the tip of a "bathtub vortex" which reaches to a finite depth. The bathtub vortex is formed by letting water drain through a small hole at the bottom of a rotating cylindrical container. The tip of the needlelike surface dip is unstable at high rotation rates and releases...... bubbles which are carried down by the flow. Using high-speed imaging we find that the minimal neck radius of the unstable tip decreases in time as a power law with an exponent close to 1/3. This exponent was found by Gordillo et al. [Phys. Rev. Lett. 95, 194501 (2005)] to govern gas flow driven pinch......-off, and indeed we find that the volume oscillations of the tip creates a considerable air flow through the neck. We argue that the Bernoulli pressure reduction caused by this air flow can become sufficient to overcome the centrifugal forces and cause the final pinch-off....
Flow of viscoplastic fluids in a rotating concentric annulus
DEFF Research Database (Denmark)
Hassager, Ole; Bittleston, Simon H.
1992-01-01
pressure gradient is small compared to the yield stress of the fluid then the full solution predicts the existence of plugs attached to the outer wall of the annulus. The slot approximation fails to predict this feature. For larger pressure gradients the two solutions are in good agreement. The analytical......A difficulty in any flow calculation with viscoplastic fluids such as Bingham fluids is the determination of possible plug zones in which no deformation occurs. This paper investigates the flow in a concentric annulus when there is both an axial and tangential flow, the tangent flow arising from...... rotation of the inner cylinder of the annulus. The flow is analyzed by considering flow in a slot, for which an analytical solution is given, and by solving the full problem numerically. It is shown that when the boundary is set in motion an applied pressure gradient will always cause flow. If the applied...
Effective diffusivity of passive scalars in rotating flow
Imazio, P Rodriguez
2012-01-01
We use direct numerical simulations to compute turbulent transport coefficients for passive scalars in turbulent rotating flows. Effective diffusion coefficients in the directions parallel and perpendicular to the rotations axis are obtained by studying the diffusion of an imposed initial profile for the passive scalar, and calculated by measuring the scalar average concentration and average spatial flux as a function of time. The Rossby and Schmidt numbers are varied to quantify their effect on the effective diffusion. It is find that rotation reduces scalar diffusivity in the perpendicular direction. The perpendicular diffusion can be estimated from mixing length arguments using the characteristic velocities and lengths perpendicular to the rotation axis. Deviations are observed for small Schmidt numbers, for which turbulent transport decreases and molecular diffusion becomes more significant.
Numerical and experimental study of rotating jet flows
Shin, Seungwon; Che, Zhizhao; Kahouadji, Lyes; Matar, Omar; Chergui, Jalel; Juric, Damir
2015-11-01
Rotating jets are investigated through experimental measurements and numerical simulations. The experiments are performed on a rotating jet rig and the effects of a range of parameters controlling the liquid jet are investigated, e.g. jet flow rate, rotation speed, jet diameter, etc. Different regimes of the jet morphology are identified, and the dependence on several dimensionless numbers is studied, e.g. Reynolds number, Weber number, etc. The breakup process of droplets is visualized through high speed imaging. Full three-dimensional direct numerical simulations are performed using BLUE, a massively parallel two-phase flow code. The novel interface algorithms in BLUE track the gas-liquid interface through a wide dynamic range including ligament formation, break up and rupture. EPSRC Programme Grant, MEMPHIS, EP/K0039761/1.
Rotating polygon instability of a swirling free surface flow
DEFF Research Database (Denmark)
Tophøj, Laust Emil Hjerrild; Bohr, Tomas; Mougel, J.;
2013-01-01
an analytically soluble model, which, together with estimates of the circulation based on angular momentum balance, reproduces the main features of the experimental phase diagram. The generality of our arguments implies that the instability should not be limited to flows with a rotating bottom (implying singular...
Generation of zonal flows in rotating fluids and magnetized plasmas
DEFF Research Database (Denmark)
Juul Rasmussen, J.; Garcia, O.E.; Naulin, V.
2006-01-01
contribution the generation of zonal flows will be illustrated in a simple fluid experiment performed in a rotating container with radial symmetric bottom topography. An effective mixing that homogenizes the potential vorticity in the fluid layer will lead to the replacement of the high-potential vorticity...
Polygon formation and surface flow on a rotating fluid surface
DEFF Research Database (Denmark)
Bergmann, Raymond; Tophøj, Laust Emil Hjerrild; Homan, T. A. M.;
2011-01-01
We present a study of polygons forming on the free surface of a water flow confined to a stationary cylinder and driven by a rotating bottom plate as described by Jansson et al. (Phys. Rev. Lett., vol. 96, 2006, 174502). In particular, we study the case of a triangular structure, either completel...
Dynamics of granular flows down rotating semi-cylindrical chutes
Shirsath, S.S.; Padding, J.T.; Clercx, H.J.H.; Kuipers, J.A.M.; Han, Yongshen; Ge, Wei; Wang, Junwu; Wang, Limin; Liu, Xinhua
2015-01-01
The behavior of spherical particles flowing down a three-dimensional chute, inclined at fixed angle, is commonly simulated by a discrete element method (DEM). DEM is nowadays a standard tool for numerical studies of e.g. gas-solid fluidized beds. We have modified DEM for the simulation of rotating g
Structure parameters in rotating Couette-Poiseuille channel flow
Knightly, George H.; Sather, D.
1986-01-01
It is well-known that a number of steady state problems in fluid mechanics involving systems of nonlinear partial differential equations can be reduced to the problem of solving a single operator equation of the form: v + lambda Av + lambda B(v) = 0, v is the summation of H, lambda is the summation of one-dimensional Euclid space, where H is an appropriate (real or complex) Hilbert space. Here lambda is a typical load parameter, e.g., the Reynolds number, A is a linear operator, and B is a quadratic operator generated by a bilinear form. In this setting many bifurcation and stability results for problems were obtained. A rotating Couette-Poiseuille channel flow was studied, and it showed that, in general, the superposition of a Poiseuille flow on a rotating Couette channel flow is destabilizing.
Internal Flow of Contra-Rotating Small Hydroturbine at Off- Design Flow Rates
SHIGEMITSU, Toru; TAKESHIMA, Yasutoshi; OGAWA, Yuya; FUKUTOMI, Junichiro
2016-11-01
Small hydropower generation is one of important alternative energy, and enormous potential lie in the small hydropower. However, efficiency of small hydroturbines is lower than that of large one. Then, there are demands for small hydroturbines to keep high performance in wide flow rate range. Therefore, we adopted contra-rotating rotors, which can be expected to achieve high performance. In this research, performance of the contra-rotating small hydroturbine with 60mm casing diameter was investigated by an experiment and numerical analysis. Efficiency of the contra-rotating small hydroturbine was high in pico-hydroturbine and high efficiency could be kept in wide flow rate range, however the performance of a rear rotor decreased significantly in partial flow rates. Then, internal flow condition, which was difficult to measure experimentally, was investigated by the numerical flow analysis. Then, a relation between the performance and internal flow condition was considered by the numerical analysis result.
Flow structure in turbulent rotating Rayleigh-Bénard convection
Kunnen, Rudie; Corre, Yoann; Clercx, Herman
2012-11-01
Turbulent Rayleigh-Bénard convection is usually studied in an upright cylinder. The addition of axial rotation has profound effects on the flow structuring. The well-known large-scale circulation (LSC) of the non-rotating case is still found at low rotation rates but is replaced by an irregular array of vertically aligned vortical plumes at higher rotation rates. We report PIV measurements of turbulent rotating convection in a cylindrical cell of diameter-to-height aspect ratio Γ = 1 / 2 at Rayleigh number Ra = 4 . 5 ×109 and at many rotation rates covering both the LSC and the vortical-plume regime. We focus on: (i) the azimuthal precession of the LSC, (ii) collective motions of the vortical plumes, and (iii) the sidewall boundary layers. With these results we can clarify remarkable differences between the Γ = 1 and Γ = 1 / 2 cases reported recently in the literature. Traineeship project carried out in Eindhoven as part of Master's Degree at Université Paris-Sud, France.
Dynamics and Statistical Mechanics of Rotating and non-Rotating Vortical Flows
Energy Technology Data Exchange (ETDEWEB)
Lim, Chjan [RPI
2013-12-18
Three projects were analyzed with the overall aim of developing a computational/analytical model for estimating values of the energy, angular momentum, enstrophy and total variation of fluid height at phase transitions between disordered and self-organized flow states in planetary atmospheres. It is believed that these transitions in equilibrium statistical mechanics models play a role in the construction of large-scale, stable structures including super-rotation in the Venusian atmosphere and the formation of the Great Red Spot on Jupiter. Exact solutions of the spherical energy-enstrophy models for rotating planetary atmospheres by Kac's method of steepest descent predicted phase transitions to super-rotating solid-body flows at high energy to enstrophy ratio for all planetary spins and to sub-rotating modes if the planetary spin is large enough. These canonical statistical ensembles are well-defined for the long-range energy interactions that arise from 2D fluid flows on compact oriented manifolds such as the surface of the sphere and torus. This is because in Fourier space available through Hodge theory, the energy terms are exactly diagonalizable and hence has zero range, leading to well-defined heat baths.
Compressibility effects on the flow past a rotating cylinder
Teymourtash, A. R.; Salimipour, S. E.
2017-01-01
In this paper, laminar flow past a rotating circular cylinder placed in a compressible uniform stream is investigated via a two-dimensional numerical simulation and the compressibility effects due to the combination of the free-stream and cylinder rotation on the flow pattern such as forming, shedding, and removing of vortices and also the lift and drag coefficients are studied. The numerical simulation of the flow is based on the discretization of convective fluxes of the unsteady Navier-Stokes equations by second-order Roe's scheme and an explicit finite volume method. Because of the importance of the time dependent parameters in the solution, the second-order time accurate is applied by a dual time stepping approach. In order to validate the operation of a computer program, some results are compared with previous experimental and numerical data. The results of this study show that the effects due to flow compressibility such as normal shock wave caused the interesting variations on the flow around the cylinder even at a free-stream with a low Mach number. At incompressible flow around the rotating cylinder, increasing the speed ratio, α (ratio of the surface speed to free-stream velocity), causes the ongoing increase in the lift coefficient, but in compressible flow for each free-stream Mach number, increasing the speed ratio results in obtaining a limited lift coefficient (a maximum mean lift coefficient). In addition, results from the compressible flow indicate that by increasing the free-stream Mach number, the maximum mean lift coefficient is decreased, while the mean drag coefficient is increased. It is also found that by increasing the Reynolds number at low Mach numbers, the maximum mean lift coefficient and critical speed ratio are decreased and the mean drag coefficient and Strouhal number are increased. However at the higher Mach numbers, these parameters become independent of the Reynolds number.
Bubble Pinch-Off in a Rotating Flow
Bergmann, Raymond; Andersen, Anders Peter; van der Meer, Devaraj; Bohr, Tomas
2009-01-01
We create air bubbles at the tip of a "bathtub vortex" which reaches to a finite depth. The bathtub vortex is formed by letting water drain through a small hole at the bottom of a rotating cylindrical container. The tip of the needlelike surface dip is unstable at high rotation rates and releases bubbles which are carried down by the flow. Using high-speed imaging we find that the minimal neck radius of the unstable tip decreases in time as a power law with an exponent close to 1/3. This expo...
Bubble Pinch-Off in a Rotating Flow
Bergmann, Raymond; Andersen, Anders; Meer, van der, D
2009-01-01
We create air bubbles at the tip of a “bathtub vortex” which reaches to a finite depth. The bathtub vortex is formed by letting water drain through a small hole at the bottom of a rotating cylindrical container. The tip of the needlelike surface dip is unstable at high rotation rates and releases bubbles which are carried down by the flow. Using high-speed imaging we find that the minimal neck radius of the unstable tip decreases in time as a power law with an exponent close to 1/3. This expo...
Renormalization Group Analysis of Weakly Rotating Turbulent Flows
Institute of Scientific and Technical Information of China (English)
王晓宏; 周全
2011-01-01
Dynamic renormalization group (RNG) analysis is applied to the investigation of the behavior of the infrared limits of weakly rotating turbulence. For turbulent How subject to weak rotation, the anisotropic part in the renormalized propagation is considered to be a perturbation of the isotropic part. Then, with a low-order approximation, the coarsening procedure of RNG transformation is performed. After implementing the coarsening and rescaling procedures, the RNG analysis suggests that the spherically averaged energy spectrum has the scaling behavior E(k) ∝ k11/5 for weakly rotating turbulence. It is also shown that the Coriolis force will disturb the stability of the Kolmogorov -5/3 energy spectrum and will change the scaling behavior even in the case of weak rotation.%Dynamic renormalization group(RNG)analysis is applied to the investigation of the behavior of the infrared limits of weakly rotating turbulence.For turbulent flow subject to weak rotation,the anisotropic part in the renormalized propagation is considered to be a perturbation of the isotropic part.Then,with a low-order approximation,the coarsening procedure of RNG transformation is performed.After implementing the coarsening and rescaling procedures,the RNG analysis suggests that the spherically averaged energy spectrum has the scaling behavior E(k)∝ k-11/5 for weakly rotating turbulence.It is also shown that the Coriolis force will disturb the stability of the Kolmogorov-5/3 energy spectrum and will change the scaling behavior even in the case of weak rotation.
Flow electrification characteristics of transformer oil by rotating electrode systems
Energy Technology Data Exchange (ETDEWEB)
Jagadish, R.; Poovamma, P.K. [Central Power Research Inst., Bangalore (India)
1995-07-01
Flow electrification has been found to be the principal cause of a number of failures of forced oil cooled power transformers. Flow charging characteristics of oil/cellulose system with factors like electrode configuration, electrode material, presence of Benzotriazole (BTA), metallic contaminants and Copper coils were investigated for paraffinic oil by employing rotating electrode system. A few hydrodynamic parameters viz. Reynolds number, boundary layer thickness and friction factor were correlated with flow charging characteristics of oil for varying temperatures and concentrations of BTA. With lower concentrations of BTA in oil viz. 10 ppm and 25 ppm a marginal reduction in flow charging of oil was noticed, but about 40% reduction was observed with 150 ppm of BTA. A significant reduction in the flow charging characteristics of untreated and BTA treated oils was also observed in the presence of Copper coils and metallic particle contaminants.
Rotating permanent magnet excitation for blood flow measurement.
Nair, Sarath S; Vinodkumar, V; Sreedevi, V; Nagesh, D S
2015-11-01
A compact, portable and improved blood flow measurement system for an extracorporeal circuit having a rotating permanent magnetic excitation scheme is described in this paper. The system consists of a set of permanent magnets rotating near blood or any conductive fluid to create high-intensity alternating magnetic field in it and inducing a sinusoidal varying voltage across the column of fluid. The induced voltage signal is acquired, conditioned and processed to determine its flow rate. Performance analysis shows that a sensitivity of more than 250 mV/lpm can be obtained, which is more than five times higher than conventional flow measurement systems. Choice of rotating permanent magnet instead of an electromagnetic core generates alternate magnetic field of smooth sinusoidal nature which in turn reduces switching and interference noises. These results in reduction in complex electronic circuitry required for processing the signal to a great extent and enable the flow measuring device to be much less costlier, portable and light weight. The signal remains steady even with changes in environmental conditions and has an accuracy of greater than 95%. This paper also describes the construction details of the prototype, the factors affecting sensitivity and detailed performance analysis at various operating conditions.
Experimental studies of magnetorotational instability in differentially rotating cylindrical flows
Brawn, Barbara; Lathrop, Daniel
2006-11-01
Given the ubiquity of rotating disks in the observable universe (e.g., galaxies, planetary rings, protoplanetary disks and accretion disks around compact objects), understanding differentially rotating, electrically conducting flows is of considerable astrophysical interest. Theoretical and numerical studies indicate that infall and accretion of orbiting material can result from a so-called magnetorotational instability (MRI) arising in such flows. Recent experimental work suggests that MRI is observable in a laboratory setting; inspired by these observations, we are building a sodium Taylor-Couette experiment, comprised of a stationary 30 cm diameter outer cylinder and a rotating 15 cm diameter inner cylinder, with liquid sodium filling the gap between the cylinders. Numerical studies indicate that MRI arises in this geometry in the presence of an external magnetic field; we will impose on the sodium flow a uniform axial magnetic field produced by Helmholtz coils at either end of the experiment. We will use ultrasound Doppler velocimetry to examine the turbulent sodium flow, and a Hall probe array to examine the induced magnetic field of the system, and will relate our observations to theoretical and numerical expectations.
Coherent Structures and Extreme Events in Rotating Multiphase Turbulent Flows
Directory of Open Access Journals (Sweden)
L. Biferale
2016-11-01
Full Text Available By using direct numerical simulations (DNS at unprecedented resolution, we study turbulence under rotation in the presence of simultaneous direct and inverse cascades. The accumulation of energy at large scale leads to the formation of vertical coherent regions with high vorticity oriented along the rotation axis. By seeding the flow with millions of inertial particles, we quantify—for the first time—the effects of those coherent vertical structures on the preferential concentration of light and heavy particles. Furthermore, we quantitatively show that extreme fluctuations, leading to deviations from a normal-distributed statistics, result from the entangled interaction of the vertical structures with the turbulent background. Finally, we present the first-ever measurement of the relative importance between Stokes drag, Coriolis force, and centripetal force along the trajectories of inertial particles. We discover that vortical coherent structures lead to unexpected diffusion properties for heavy and light particles in the directions parallel and perpendicular to the rotation axis.
Coherent Structures and Extreme Events in Rotating Multiphase Turbulent Flows
Biferale, L.; Bonaccorso, F.; Mazzitelli, I. M.; van Hinsberg, M. A. T.; Lanotte, A. S.; Musacchio, S.; Perlekar, P.; Toschi, F.
2016-10-01
By using direct numerical simulations (DNS) at unprecedented resolution, we study turbulence under rotation in the presence of simultaneous direct and inverse cascades. The accumulation of energy at large scale leads to the formation of vertical coherent regions with high vorticity oriented along the rotation axis. By seeding the flow with millions of inertial particles, we quantify—for the first time—the effects of those coherent vertical structures on the preferential concentration of light and heavy particles. Furthermore, we quantitatively show that extreme fluctuations, leading to deviations from a normal-distributed statistics, result from the entangled interaction of the vertical structures with the turbulent background. Finally, we present the first-ever measurement of the relative importance between Stokes drag, Coriolis force, and centripetal force along the trajectories of inertial particles. We discover that vortical coherent structures lead to unexpected diffusion properties for heavy and light particles in the directions parallel and perpendicular to the rotation axis.
Theory of rotating electrohydrodynamic flows in a liquid film.
Shiryaeva, E V; Vladimirov, V A; Zhukov, M Yu
2009-10-01
The mathematical model of rotating electrohydrodynamic flows in a thin suspended liquid film is proposed and studied. The flows are driven by the given difference of potentials in one direction and constant external electric field E(out) in another direction in the plane of a film. To derive the model, we employ the spatial averaging over the normal coordinate to a film that leads to the average Reynolds stress that is proportional to |E(out)|3. This stress generates tangential velocity in the vicinity of the edges of a film that, in turn, causes the rotational motion of a liquid. The proposed model is used to explain the experimental observations of the liquid film motor.
On soft stability loss in rotating turbulent MHD flows
Energy Technology Data Exchange (ETDEWEB)
Kapusta, Arkady [Center for MHD Studies, Ben-Gurion University of the Negev PO Box 653, Beer-Sheva 84105 (Israel); Mikhailovich, Boris, E-mail: borismic@bgu.ac.il [Department of Mechanical Engineering, Ben-Gurion University of the Negev PO Box 653, Beer-Sheva 84105 (Israel)
2014-08-01
The problem of the stability of turbulent flows of liquid metal in a cylindrical cavity against small velocity disturbances under the action of a rotating magnetic field (RMF) has been studied. The flow is considered in the induction-free approximation using the ‘external’ friction model. A system of dimensionless equations is examined in cylindrical coordinates. The results of computations performed on the basis of this mathematical model using the exchange of stabilities principle have shown a good consistency between the critical values of computed and experimental Reynolds numbers. (paper)
Aerodynamic structures and processes in rotationally augmented flow fields
DEFF Research Database (Denmark)
Schreck, S.J.; Sørensen, Niels N.; Robinson, M.C.
2007-01-01
. Experimental measurements consisted of surface pressure data statistics used to infer sectional boundary layer state and to quantify normal force levels. Computed predictions included high-resolution boundary layer topologies and detailed above-surface flow field structures. This synergy was exploited...... to reliably identify and track pertinent features in the rotating blade boundary layer topology as they evolved in response to varying wind speed. Subsequently, boundary layer state was linked to above-surface flow field structure and used to deduce mechanisms; underlying augmented aerodynamic force...
Directory of Open Access Journals (Sweden)
Tu Cheng-Xu
2014-01-01
Full Text Available The field characteristics of two side-by-side rotating circular cylinders in a cross-flow is investigated under different rotation types, at T/D = 1.11,1.6, and 3, respectively (T is the center spacing between the cylinders, and D is the cylinder diameter. A similar flow pattern which is the most efficient to narrow the lowpressure area is identified for rotation type A, independent of T/D ratio, and two typical flow patterns are found under different spacings for rotation type B and type C, respectively. It is confirmed that there is an optimal rotational speed of 1.7-2, under rotation type A to attenuate the vortices, velocity drop, and turbulence intensity tremendously. As rotational speed increases to the optimal value, both the velocity drop and turbulence intensity decrease and their distributions are smooth. The results indicate that the shear layers which are accelerated following the free-stream direction would have significant influence on the flow modification, and different rotation types actually arrange these shear layers in diverse ways to change the flow pattern. Pitch ratio is capable to transform the gap flow, which is usually including the shear layers referred, thus this parameter can modify the wake of the two cylinders at different rotation types.
Numerical Simulation and Flow Behaviors of Taylor Flow in Co-Axial Rotating Cylinder
Directory of Open Access Journals (Sweden)
Sheng Chung Tzeng
2014-04-01
Full Text Available This work uses the incense as the trace of flow to perform flow visualization of Taylor-Couette flow. The test section was made of a rotational inner cylinder and a stationary outer cylinder. Two modes of inner cylinder were employed. One had a smooth wall, and the other had an annular ribbed wall. Clear and complete Taylor vortices were investigated in both smooth and ribbed wall of co-axial rotating cylinder. Besides, a steady-state, axis-symmetrical numerical model was provided to simulate the present flow field. The Taylor vortices could be also successfully predicted. However, the assumption of steady-state flow might reduce some flow perturbations, resulting in an over-predicted critical Taylor number. A transient simulation is suggested to be performed in the future.
Turbulent statistics and flow structures in spanwise-rotating turbulent plane Couette flows
Gai, Jie; Xia, Zhenhua; Cai, Qingdong; Chen, Shiyi
2016-09-01
A series of direct numerical simulations of spanwise-rotating turbulent plane Couette flows at a Reynolds number of 1300 with rotation numbers Ro between 0 and 0.9 is carried out to investigate the effects of anticyclonic rotation on turbulent statistics and flow structures. Several typical turbulent statistics are presented, including the mean shear rate at the centerline, the wall-friction Reynolds number, and volume-averaged kinetic energies with respect to the secondary flow field, turbulent field, and total fluctuation field. Our results show that the rotation changes these quantities in different manners. Volume-averaged balance equations for kinetic energy are analyzed and it turns out that the interaction term acts as a kinetic energy bridge that transfers energy from the secondary flow to the turbulent fluctuations. Several typical flow regimes are identified based on the correlation functions across the whole channel and flow visualizations. The two-dimensional roll cells are observed at weak rotation Ro=0.01 , where alternant clustering of vortices appears. Three-dimensional roll cells emerge around Ro≈0.02 , where the clustering of vortices shows the meandering and bifurcating behavior. For moderate rotation 0.07 ≲Ro≲0.36 , well-organized structures are observed, where the herringbonelike vortices are clustered between streaks from the top view of three-dimensional flow visualization and form annuluses. More importantly, the vortices are rather confined to one side of the walls when Ro≤0.02 and are inclined from the bottom to upper walls when Ro≥0.07 .
Unsteady Flow Produced by Oscillations of Eccentric Rotating Disks
Directory of Open Access Journals (Sweden)
H. Volkan Ersoy
2012-01-01
Full Text Available While the disks are initially rotating eccentrically, the unsteady flow caused by their oscillations in their own planes and in the opposite directions is studied. The analytical solutions to the problem are obtained for both small and large times, and thus the velocity field is determined for every value of time. The variations of all the parameters on the flow are scrutinized by means of the graphical representations. In particular, the effect of the ratio of the frequency of oscillation to the angular velocity of the disks is analyzed. The dependence of the oscillations in both - and -directions on the flow is examined. The influence of the Reynolds number is also investigated.
Axisymmetric compressible flow in a rotating cylinder with axial convection
Ungarish, M.; Israeli, M.
1985-05-01
The steady compressible flow of an ideal gas in a rotating annulus with thermally conducting walls is considered for small Rossby number epsilon and Ekman number E and moderate rotational Mach numbers M. Attention is focused on nonlinear effects which show up when sigma and epsilon M-squared are not small (sigma = epsilon/H square root of E, H is the dimensionless height of the container). These effects are not properly predicted by the classical linear perturbation analysis, and are treated here by quasi-linear extensions. The extra work required by these extensions is only the numerical solution of one ordinary differential equation for the pressure. Numerical solutions of the full Navier-Stokes equations in the nonlinear range are presented, and the validity of the present approach is confirmed.
Coherent structures and extreme events in rotating multiphase turbulent flows
Biferale, Luca; Mazzitelli, Irene M; van Hinsberg, Michel A T; Lanotte, Alessandra S; Musacchio, Stefano; Perlekar, Prasad; Toschi, Federico
2016-01-01
By using direct numerical simulations (DNS) at unprecedented resolution we study turbulence under rotation in the presence of simultaneous direct and inverse cascades. The accumulation of energy at large scale leads to the formation of vertical coherent regions with high vorticity oriented along the rotation axis. By seeding the flow with millions of inertial particles, we quantify -for the first time- the effects of those coherent vertical structures on the preferential concentration of light and heavy particles. Furthermore, we quantitatively show that extreme fluctuations, leading to deviations from a normal-distributed statistics, result from the entangled interaction of the vertical structures with the turbulent background. Finally, we present the first-ever measurement of the relative importance between Stokes drag, Coriolis force and centripetal forces along the trajectories of inertial particles. We discover that vortical coherent structures lead to unexpected diffusion properties for heavy and light ...
A rotational compressible inverse design method for internal flow configurations
Dedoussis, V.; Chaviaropoulos, P.; Papailiou, K. D.
The development of a rotational inviscid compressible inverse design method for two-dimensional internal flow configurations is described. Rotationality is due to an incoming entropy gradient, while total enthalpy is considered to be constant throughout the flowfield. The method is based on the potential function-streamfunction formulation. A novel procedure based on differential geometry arguments is employed to derive the governing equation for velocity by requiring the curvature of the two-dimensional Euclidean space to be zero. The velocity equation solved in conjunction with a transport equation for a thermal drift function provide the flowfield without any geometry feedback. An auxiliary orthogonal computational grid adapted to the solution is employed. Geometry is determined by integrating Frenet equations of the grid lines. Inverse calculation results are compared with results of direct reproduction calculations.
Performance Test and Flow Measurement of Contra-Rotating Axial Flow Pump
Institute of Scientific and Technical Information of China (English)
Akinori Furukawa; Toru Shigemitsu; Satoshi Watanabe
2007-01-01
An application of contra-rotating rotors has been proposed against a demand for developing higher specific speed axial flow pump. In the present paper, the advantage and disadvantage of using contra-rotating rotors are described in comparison with conventional type of rotor-stator, based on theoretical and experimental investigations. The advantages are as follows: (1) The pump is inherently designed as smaller sized and at lower rotational speed. (2) A stable head-characteristic curve for flow rate with negative slope appears. (3)As the rear rotor rotational speed is varied as independent control of front rotor, the wider range of high performance operation is obtained by rear rotor speed control in addition to front rotor speed control. The disadvantages are as follows: (1) The structure of double shaft system becomes complex. (2) The pump performance is inferior at over flow rate as the rear rotor loading is weakened. (3) The blade rows interaction from rear rotor to front rotor more strongly appears. Then the rear rotor design is a key to achieve higher pump performance. Some methods to overcome these disadvantages will be discussed in more details toward wider usage of contra-rotating axial flow pump in various industrial fields.
Extraction of coherent structures in a rotating turbulent flow experiment
Ruppert-Felsot, J E; Sharon, E; Swinney, H L; Ruppert-Felsot, Jori E.; Praud, Olivier; Sharon, Eran; Swinney, Harry L.
2004-01-01
The discrete wavelet packet transform (DWPT) and discrete wavelet transform (DWT) are used to extract and study the dynamics of coherent structures in a turbulent rotating fluid. Three-dimensional (3D) turbulence is generated by strong pumping through tubes at the bottom of a rotating tank (48.4 cm high, 39.4 cm diameter). This flow evolves toward two-dimensional (2D) turbulence with increasing height in the tank. Particle Image Velocimetry (PIV) measurements on the quasi-2D flow reveal many long-lived coherent vortices with a wide range of sizes. The vorticity fields exhibit vortex birth, merger, scattering, and destruction. We separate the flow into a low-entropy ``coherent'' and a high-entropy ``incoherent'' component by thresholding the coefficients of the DWPT and DWT of the vorticity fields. Similar thresholdings using the Fourier transform and JPEG compression together with the Okubo-Weiss criterion are also tested for comparison. We find that the DWPT and DWT yield similar results and are much more ef...
Coupling Onset of Cyclone Upward and Rotation Flows in a Little Bottle
Kawata, Shigeo
2012-01-01
A coupling onset of the cyclone upward and rotation flows is experimentally demonstrated in a little bottle. The rotating flow provides a pressure increase in the outer part of the rotating flow by its centrifugal force. When a gradient of the fluid rotation appears along the rotation axis, the higher-pressure area is localized and pushes the fluid in a low pressure. Then the fluid staying in the central area of the rotation is pushed up along the rotation axis, and the upward wind is enhanced. In this coupling mechanism the rotation gradient is the key; the coupling of the rotation and the upward fluid flow is essentially important for a cyclone buildup, and is well explained experimentally and theoretically.
FLOW OF OLDROYD-B FLUID IN ROTATING CURVED SQUARE DUCTS
Institute of Scientific and Technical Information of China (English)
ZHANG Ming-kan; SHEN Xin-rong; MA Jian-feng; ZHANG Ben-zhao
2007-01-01
The fully developed Oldroyd-B fluid flow through rotating square ducts was numerically studied. The effects of the rotation on secondary flow, axial velocity, and axial normal stress were examined in detail. The results indicated that all of the secondary flow, the axial flow, and the axial normal stress were evidently affected by the rotation. The Taylor-Proudman phenomenon could be observed in the flow. For the secondary flow, the four vortices structure and the six vortices structure were described. Recent studies also showed the effects of rotation on the axial normal stress.
Sengupta, Tapan K.; Gullapalli, Atchyut
2016-11-01
Spinning cylinder rotating about its axis experiences a transverse force/lift, an account of this basic aerodynamic phenomenon is known as the Robins-Magnus effect in text books. Prandtl studied this flow by an inviscid irrotational model and postulated an upper limit of the lift experienced by the cylinder for a critical rotation rate. This non-dimensional rate is the ratio of oncoming free stream speed and the surface speed due to rotation. Prandtl predicted a maximum lift coefficient as CLmax = 4π for the critical rotation rate of two. In recent times, evidences show the violation of this upper limit, as in the experiments of Tokumaru and Dimotakis ["The lift of a cylinder executing rotary motions in a uniform flow," J. Fluid Mech. 255, 1-10 (1993)] and in the computed solution in Sengupta et al. ["Temporal flow instability for Magnus-robins effect at high rotation rates," J. Fluids Struct. 17, 941-953 (2003)]. In the latter reference, this was explained as the temporal instability affecting the flow at higher Reynolds number and rotation rates (>2). Here, we analyze the flow past a rotating cylinder at a super-critical rotation rate (=2.5) by the enstrophy-based proper orthogonal decomposition (POD) of direct simulation results. POD identifies the most energetic modes and helps flow field reconstruction by reduced number of modes. One of the motivations for the present study is to explain the shedding of puffs of vortices at low Reynolds number (Re = 60), for the high rotation rate, due to an instability originating in the vicinity of the cylinder, using the computed Navier-Stokes equation (NSE) from t = 0 to t = 300 following an impulsive start. This instability is also explained through the disturbance mechanical energy equation, which has been established earlier in Sengupta et al. ["Temporal flow instability for Magnus-robins effect at high rotation rates," J. Fluids Struct. 17, 941-953 (2003)].
Inverse cascades in turbulence and the case of rotating flows
Pouquet, A; Rosenberg, D; Mininni, P D; Baerenzung, J
2012-01-01
We first summarize briefly several properties concerning the dynamics of two-dimensional (2D) turbulence, with an emphasis on the inverse cascade of energy to the largest accessible scale of the system. In order to study a similar phenomenon in three-dimensional (3D) turbulence undergoing strong solid-body rotation, we test a previously developed Large Eddy Simulation (LES) model against a high-resolution direct numerical simulation of rotating turbulence on a grid of $3072^3$ points. We then describe new numerical results on the inverse energy cascade in rotating flows using this LES model and contrast the case of 2D versus 3D forcing, as well as non-helical forcing (i.e., with weak overall alignment between velocity and vorticity) versus the fully helical Beltrami case, both for deterministic and random forcing. The different scaling of the inverse energy cascade can be attributed to the dimensionality of the forcing, with, in general, either a $k_{\\perp}^{-3}$ or a $k_{\\perp}^{-5/3}$ energy spectrum of slo...
Trailing edge noise theory for rotating blades in uniform flow
Sinayoko, Samuel; Agarwal, Anurag
2013-01-01
This paper presents a new formulation for trailing edge noise radiation from rotating blades based on an analytical solution of the convective wave equation. It accounts for distributed loading and the effect of mean flow and spanwise wavenumber. A commonly used theory due to Schlinker and Amiet (1981) predicts trailing edge noise radiation from rotating blades. However, different versions of the theory exist; it is not known which version is the correct one and what the range of validity of the theory is. This paper addresses both questions by deriving Schlinker and Amiet's theory in a simple way and by comparing it to the new formulation, using model blade elements representative of a wind turbine, a cooling fan and an aircraft propeller. The correct form of Schlinker and Amiet's theory (1981) is identified. It is valid at high enough frequency, i.e. for a Helmholtz number relative to chord greater than one and a rotational frequency much smaller than the angular frequency of the noise sources.
Optic Flow Information Influencing Heading Perception during Rotation
Directory of Open Access Journals (Sweden)
Diederick C. Niehorster
2011-05-01
Full Text Available We investigated what roles global spatial frequency, surface structure, and foreground motion play in heading perception during simulated rotation from optic flow. The display (110°Hx94°V simulated walking on a straight path over a ground plane (depth range: 1.4–50 m at 2 m/s while fixating a target off to one side (mean R/T ratios: ±1, ±2, ±3 under six display conditions. Four displays consisted of nonexpanding dots that were distributed so as to manipulate the amount of foreground motion and the presence of surface structure. In one further display the ground was covered with disks that expanded during the trial and lastly a textured ground display was created with the same spatial frequency power spectrum as the disk ground. At the end of each 1s trial, observers indicated their perceived heading along a line at the display's center. Mean heading biases were smaller for the textured than for the disk ground, for the displays with more foreground motion and for the displays with surface structure defined by dot motion than without. We conclude that while spatial frequency content is not a crucial factor, dense motion parallax and surface structure in optic flow are important for accurate heading perception during rotation.
Elastic fingering in rotating Hele-Shaw flows
Carvalho, Gabriel D.
2014-05-21
The centrifugally driven viscous fingering problem arises when two immiscible fluids of different densities flow in a rotating Hele-Shaw cell. In this conventional setting an interplay between capillary and centrifugal forces makes the fluid-fluid interface unstable, leading to the formation of fingered structures that compete dynamically and reach different lengths. In this context, it is known that finger competition is very sensitive to changes in the viscosity contrast between the fluids. We study a variant of such a rotating flow problem where the fluids react and produce a gellike phase at their separating boundary. This interface is assumed to be elastic, presenting a curvature-dependent bending rigidity. A perturbative weakly nonlinear approach is used to investigate how the elastic nature of the interface affects finger competition events. Our results unveil a very different dynamic scenario, in which finger length variability is not regulated by the viscosity contrast, but rather determined by two controlling quantities: a characteristic radius and a rigidity fraction parameter. By properly tuning these quantities one can describe a whole range of finger competition behaviors even if the viscosity contrast is kept unchanged. © 2014 American Physical Society.
Zhong, Jin-Qiang; Wang, Xue-ying
2016-01-01
We present measurements of the azimuthal orientation {\\theta}(t) and thermal amplitude {\\delta}(t) of the large-scale circulation (LSC) of turbulent rotating convection within an unprecedented large Rossby number range 170. We identify the mechanism through which the mean retrograde rotation speed can be enhanced by stochastic cessations in the presence of weak Coriolis force, and show that a low-dimensional, stochastic model provides predictions of the observed large-scale flow dynamics and interprets its retrograde rotation.
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
The instability of forced flow in a rotating cylindrical pool with a differentially rotating disk on the free surface is investigated through a series of unsteady three-dimensional numerical simulations.The results show that the basic flow state of this system is axisymmetric and steady,but has rich structures at the meridian plane.However,when the rotation Reynolds number exceeds a critical value,the flow will undergo a transition to three-dimensional oscillatory flow,characterized by the velocity fluctuation waves traveling in the azimuthal direction.The main characteristics of the flow patterns are presented,including the propagating direction,velocity,amplitude and wave number,which depend on the rotation rates and directions of the disk and the cylindrical pool,and the critical conditions for the onset of oscillatory flow are also determined.For the case of disk-only rotation,the centrifugal instability is responsible for the flow transition,and when the disk isoand counter-rotates with the cylindrical pool,the mechanisms for the transition are elliptic and of circular shear instabilities,respectively.
FLOW PAST TWO ROTATING CIRCULAR CYLINDERS IN A SIDE-BY-SIDE ARRANGEMENT
Institute of Scientific and Technical Information of China (English)
GUO Xiao-hui; LIN Jian-zhong; TU Cheng-xu; WANG Hao-li
2009-01-01
Measurements were performed using Particle Image Velocimetry (PIV) to analyze the modification of flow by the combined effects of the rotation and the Reynolds number on the flow past two rotating circular cylinders in a side-by-side-arrangement at a range of , (α is the rotational speed) at one gap spacing of (T and d are the distance between the centers of two cylinders and the cylinder diameter, respectively). A new Immersed-Lattice Boltzmann Method (ILBM) scheme was used to study the effect of the gap spacing on the flow. The results show that the vortex shedding is suppressed as rotational speed increases. The flow reaches a steady state when the vortex shedding for both cylinders is completely suppressed at critical rotational speed. As the rotational speed further increases, the separation phenomenon in the boundary layers disappears at the attachment rotational speed. The critical rotational speed and attachment rotational speed become small as Reynolds number increases. The absolute rotational speed of cylinders should be large at same critical rotational speed and attachment rotational speed in the case of large Reynolds number. The gap spacing has an important role in changing the pattern of vortex shedding. It is very different in the mechanism of vortex shedding suppression for the flows around two rotating cylinders and single rotating cylinder.
Statistical equilibria of the coupled barotropic flow and shallow water flow on a rotating sphere
Ding, Xueru
The motivation of this research is to build equilibrium statistical models that can apply to explain two enigmatic phenomena in the atmospheres of the solar system's planets: (1) the super-rotation of the atmospheres of slowly-rotating terrestrial planets---namely Venus and Titan, and (2) the persistent anticyclonic large vortex storms on the gas giants, such as the Great Red Spot (GRS) on Jupiter. My thesis is composed of two main parts: the first part focuses on the statistical equilibrium of the coupled barotropic vorticity flow (non-divergent) on a rotating sphere; the other one has to do with the divergent shallow water flow rotating sphere system. The statistical equilibria of these two systems are simulated in a wide range of parameter space by Monte Carlo methods based on recent energy-relative enstrophy theory and extended energy-relative enstrophy theory. These kind of models remove the low temperatures defect in the old classical doubly canonical energy-enstrophy theory which cannot support any phase transitions. The other big difference of our research from previous work is that we work on the coupled fluid-sphere system, which consists of a rotating high density rigid sphere, enveloped by a thin shell of fluid. The sphere is considered to have infinite mass and angular momentum; therefore, it can serve as a reservoir of angular momentum. Unlike the fluid sphere system itself, the coupled fluid sphere system allows for the exchange of angular momentum between the atmosphere and the solid planet. This exchange is the key point in any model that is expected to capture coherent structures such as the super-rotation and GRS-like vortices problems in planetary atmospheres. We discovered that slowly-rotating planets can have super-rotation at high energy state. All known slowly-rotating cases in the solar system---Venus and Titan---have super-rotation. Moreover, we showed that the anticyclonicity in the GRS-like structures is closely associated with the
Zonal flow regimes in rotating anelastic spherical shells (Invited)
Gastine, T.; Wicht, J.; Aurnou, J. M.; Heimpel, M. H.
2013-12-01
The surface zonal winds observed in the giant planets form a complex jet pattern with alternating prograde and retrograde direction. While the main equatorial band is prograde on the gas giants, both ice giants have a pronounced retrograde equatorial jet. The depth of these jets is however poorly known and highly debated. Theoretical scenarios range from "shallow models", that assume that these zonal flows are restricted to the outer stably stratified layer; to "deep models" that hypothesise that the surface winds are the signature of deep-seated convection. Most of the numerical models supporting the latter idea employed the Boussinesq approximation where compressibility effects are ignored. While this approximation is suitable for modelling the liquid iron core of terrestrial planets, this becomes questionable in the gas giants interiors, where density increases by several orders of magnitude. To tackle this problem, several numerical models using the "anelastic approximation" have been recently developed to study the compressibility effects while filtering out the fast acoustic waves. Here, we consider such anelastic models of rapidly-rotating spherical shells to explore the properties of the zonal winds in different regimes where either rotation or buoyancy dominates the force balance. We conduct several parameter studies to quantify the dependence of zonal flows on the background density stratification and the driving of convection. We find that the direction of the equatorial wind is controlled by the ratio of buoyancy and Coriolis force. The prograde equatorial band maintained by Reynolds stresses is found in the rotation-dominated regime. At low Ekman numbers, several alternating jets form at high latitude in a similar way to some previous Boussinesq calculations. In cases where buoyancy dominates Coriolis force, the angular momentum per unit mass is homogenised and the equatorial band is retrograde, reminiscent to those observed in the ice giants
Directory of Open Access Journals (Sweden)
Norimasa Shiomi
2003-01-01
Full Text Available We carried out investigations for the purpose of clarifying the rotor outlet flow fields with rotating stall cell in a diagonal-flow fan. The test fan was a high–specific-speed (ns=1620 type of diagonal-flow fan that had 6 rotor blades and 11 stator blades. It has been shown that the number of the stall cell is 1, and its propagating speed is approximately 80% of its rotor speed, although little has been known about the behavior of the stall cell because a flow field with a rotating stall cell is essentially unsteady. In order to capture the behavior of the stall cell at the rotor outlet flow fields, hot-wire surveys were performed using a single-slant hotwire probe. The data obtained by these surveys were processed by means of a double phase-locked averaging technique, which enabled us to capture the flow field with the rotating stall cell in the reference coordinate system fixed to the rotor. As a result, time-dependent ensemble averages of the three-dimensional velocity components at the rotor outlet flow fields were obtained. The behavior of the stall cell was shown for each velocity component, and the flow patterns on the meridional planes were illustrated.
Stochastic Rotation Dynamics simulations of wetting multi-phase flows
Hiller, Thomas; Sanchez de La Lama, Marta; Brinkmann, Martin
2016-06-01
Multi-color Stochastic Rotation Dynamics (SRDmc) has been introduced by Inoue et al. [1,2] as a particle based simulation method to study the flow of emulsion droplets in non-wetting microchannels. In this work, we extend the multi-color method to also account for different wetting conditions. This is achieved by assigning the color information not only to fluid particles but also to virtual wall particles that are required to enforce proper no-slip boundary conditions. To extend the scope of the original SRDmc algorithm to e.g. immiscible two-phase flow with viscosity contrast we implement an angular momentum conserving scheme (SRD+mc). We perform extensive benchmark simulations to show that a mono-phase SRDmc fluid exhibits bulk properties identical to a standard SRD fluid and that SRDmc fluids are applicable to a wide range of immiscible two-phase flows. To quantify the adhesion of a SRD+mc fluid in contact to the walls we measure the apparent contact angle from sessile droplets in mechanical equilibrium. For a further verification of our wettability implementation we compare the dewetting of a liquid film from a wetting stripe to experimental and numerical studies of interfacial morphologies on chemically structured surfaces.
Magnetohydrodynamics flow over a rapidly rotating axisymmetric wavy disk
Energy Technology Data Exchange (ETDEWEB)
Yoon, Myung Sup [Korea Testing Laboratory, 222-13 Guro3-dong Guro-gu, Seoul 152-718 (Korea, Republic of); Park, Jun Sang [Department of Mechanical Engineering, Halla University, Halla dae 1-gil, HeungUp, Wonju, Kangwon-do 220-712 (Korea, Republic of); Hyun, Jae Min, E-mail: jspark@halla.ac.kr [Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, 373-1 Kusong-dong, Yusong-gu, Taejon 305-701 (Korea, Republic of)
2011-08-15
A numerical study of Magnetohydrodynamics boundary layer flow over a rapidly rotating wavy disc was performed under which magnetic fields are imposed by a circular electric coil. The shape of the disc is assumed to be axisymmetric and sinusoidal in the radial direction, and semi-infinite space over the disc steadily rotating is occupied by an electrically conducting fluid. The study was conducted for the case where the representative Reynolds number is very large and the magnetic Reynolds number is negligibly small. The effect of Lorentz force on fluid motion was precisely investigated as the main external controlling force. The generalized boundary layer equation, including both magnetic field and heat flux, is derived to examine interactions among the effects of wavy surface shape, magnetic field and heat flux from the disc surface. Two cases of uniform magnetic field, much studied in previous research, and of non-uniform magnetic field, realized by a circular coil, have been scrutinized. Details of velocity profile, skin friction coefficient and heat transfer coefficient are given.
Microscale flow and heat transfer between rotating disks
Energy Technology Data Exchange (ETDEWEB)
Jiji, Latif M., E-mail: jiji@ccny.cuny.ed [Department of Mechanical Engineering, City College of the City University of New York, New York, NY 10031 (United States); Ganatos, Peter, E-mail: ganatos@ccny.cuny.ed [Department of Mechanical Engineering, City College of the City University of New York, New York, NY 10031 (United States)
2010-08-15
In this paper we consider steady laminar flow and heat transfer generated by two infinite parallel disks separated by a gas-filled micro-gap {delta}. One disk rotates with angular velocity {Omega} and the second with angular velocity s{Omega}. The analysis takes into consideration velocity slip, temperature jump, rarefaction and dissipation. A solution based on similarity transformation is obtained and used to examine the effects of the governing parameters on the velocity field, temperature distribution, disks' torque and power, and Nusselt number. The solution requires numerical integration of the resulting coupled ordinary non-linear differential equations. An exact analytical solution is obtained for the limiting case of small Reynolds numbers.
Two-dimensionalization of the flow driven by a slowly rotating impeller in a rapidly rotating fluid
Machicoane, Nathanaël; Cortet, Pierre-Philippe
2016-01-01
We characterize the two-dimensionalization process in the turbulent flow produced by an impeller rotating at a rate $\\omega$ in a fluid rotating at a rate $\\Omega$ around the same axis for Rossby number $Ro=\\omega/\\Omega$ down to $10^{-2}$. The flow can be described as the superposition of a large-scale vertically invariant global rotation and small-scale shear layers detached from the impeller blades. As $Ro$ decreases, the large-scale flow is subjected to azimuthal modulations. In this regime, the shear layers can be described in terms of wakes of inertial waves traveling with the blades, originating from the velocity difference between the non-axisymmetric large-scale flow and the blade rotation. The wakes are well defined and stable at low Rossby number, but they become disordered at $Ro$ of order of 1. This experiment provides insight into the route towards pure two-dimensionalization induced by a background rotation for flows driven by a non-axisymmetric rotating forcing.
Renouf, M.; Bonamy, D.; Dubois, F.; Alart, P.
2005-10-01
The rheology of two-dimensional steady surface flow of cohesionless cylinders in a rotating drum is investigated through nonsmooth contact dynamics simulations. Profiles of volume fraction, translational and angular velocity, rms velocity, strain rate, and stress tensor are measured at the midpoint along the length of the surface-flowing layer, where the flow is generally considered as steady and homogeneous. Analysis of these data and their interrelations suggest the local inertial number—defined as the ratio between local inertial forces and local confinement forces—to be the relevant dimensionless parameter to describe the transition from the quasistatic part of the packing to the flowing part at the surface of the heap. Variations of the components of the stress tensor as well as the ones of rms velocity as a function of the inertial number are analyzed within both the quasistatic and the flowing phases. Their implications are discussed.
Effective slip for flow in a rotating channel bounded by stick-slip walls
Ng, Chiu-On
2016-12-01
This paper aims to look into how system rotation may modify the role played by boundary slip in controlling flow through a rotating channel bounded by stick-slip walls. A semianalytical model is developed for pressure-driven flow in a slit channel that rotates about an axis perpendicular to its walls, which are superhydrophobic surfaces patterned with periodic alternating no-shear and no-slip stripes. The cases where the flow is driven by a pressure gradient parallel or normal to the stripes are considered. The effects of the no-shear area fraction on the velocities and effective slip lengths for the primary and secondary flows are investigated as functions of the rotation rate and the channel height. It is mathematically proved that the secondary flow rate is exactly the same in the two cases, irrespective of whether the primary flow is parallel or normal to the wall stripes. For any rotation speed, there is an optimal value of the no-shear area fraction at which the primary flow rate is maximum. This is a consequence of two competing effects: the no-shear part of the wall may serve to reduce the wall resistance, thereby enhancing the flow especially at low rotation, but it also weakens the formation of the near-wall Ekman layer, which is responsible for pumping the flow especially at high rotation. Wall slip in a rotating environment is to affect flow in the Ekman layer, but not flow in the geostrophic core.
Numerical simulation of turbulent flow between shrouded contra-rotating disks
Directory of Open Access Journals (Sweden)
Shu-Xian Chen
2016-06-01
Full Text Available The turbulent flow between shrouded contra-rotating disks was numerically studied with a two-layer turbulence model and a modified Launder–Sharma low-Reynolds number k-ε model. The dissipation rate decrease caused by solid body rotation was considered in the second model. The comparisons of the effectiveness between these two turbulence models for capturing the critical radius of flow structure transition and reproducing the flow velocity measurements data were presented. For the flow between shrouded disks rotating at the same speed but in opposite senses, that is, the angular velocity ratio of the two disks equals to −1, the Stewartson-type flow structure is found in the cavity. For the flow with one disk rotating more slowly than the other, Stewartson-type flow coexists with Batchelor-type flow, that is, Batchelor-type flow occurs radially outward of the stagnation point where two opposing boundary layer flows meet, and Stewartson-type flow occurs radially inward. The stagnation points near the slower disk move radially outward as the angular velocity ratio decreases toward −1. Theory of rotating fluids with the presence of centrifugal and Coriolis forces stemming from the disk rotation is employed to manifest the flow structure transition mechanisms as the rotation ratio of the disks is varied. The source of the earlier transition to turbulent flow in counter-rotating disk cavity compared with rotor-stator disk cavity is also explained through the research of instability of the flowing free shear layer formed by the counter secondary circulations. With the aid of the numerical results obtained from the two turbulence models, it is found that a more turbulent flow in the core can destroy the Batchelor-type flow and creates a larger Stewartson-type flow region.
Institute of Scientific and Technical Information of China (English)
GAO Zhen-yu; LIN Jian-zhong; LI Jun
2007-01-01
The rotational dispersion coefficient of the fiber in the turbulent shear flow of fiber suspension was studied theoretically. The function of correlation moment between the different fluctuating velocity gradients of the flow was built firstly. Then the expression, dependent on the characteristic length, time, velocity and a dimensionless parameter related to the effect of wall, of rotational dispersion coefficient is derived. The derived expression of rotational dispersion coefficient can be employed to the inhomogeneous and non-isotropic turbulent flows. Furthermore it can be expanded to three-dimensional turbulent flows and serves the theoretical basis for solving the turbulent flow of fiber suspension.
Process and apparatus for recovery from rotating stall in axial flow fans and compressors
1997-01-01
Active recovery from a rotating stall operating condition in an axial flow compression system is accomplished by altering the temperature and/or density of the working fluid flowing in the inlet of the compression system once rotating stall is detected. A burner is used to increase the compressor inlet flow temperature and concomitantly reduce the inlet flow density. Alternatively, a low density gas such as helium is injected into the compressor inlet. The ingestion of high temperature gases ...
Cho, Lee-Sang; Cha, Bong-Jun; Cho, Jin-Soo
The counter-rotating axial flow fan shows that the complex flow characteristics with three-dimensional, viscous, and unsteady flow fields. For the understanding of the entire core flow in counter-rotating axial flow fan, it is necessary to investigate the three-dimensional unsteady flow field between the rotors. This information is also essential for the improvement of the aerodynamic characteristics, the reduction of the aerodynamic noise level and vibration characteristics of the counter-rotating axial flow fan. The purpose of this study is, therefore, to present the periodic characteristics of the blade passage flow, the wake and the tip vortex, which are utilized for the blade design data for the improvement of the aerodynamic characteristics, the reduction of the aerodynamic noise level and vibration characteristics of the counter-rotating axial flow fan. In this paper, the three-dimensional unsteady flow by the rotor-rotor interaction of the CRF were investigated at the design point(peak efficiency operating point). Unsteady flow fields in the CRF are measured at the cross-sectional planes of the upstream, between and downstream of each rotor using the 45° inclined hot-wire probe. The stationary hot-wire technique used the 45° inclined hot-wire probe, which rotates successively with 120 degrees increments about its own axis. And, the sampling data of unsteady flow fields were phase-locked averaged to remove the random components.
On the Nature of Magnetic Turbulence in Rotating, Shearing Flows
Walker, Justin; Boldyrev, Stanislav
2015-01-01
The local properties of turbulence driven by the magnetorotational instability (MRI) in rotating, shearing flows are studied in the framework of a shearing-box model. Based on numerical simulations, we propose that the MRI-driven turbulence comprises two components: the large-scale shear-aligned strong magnetic field and the small-scale fluctuations resembling magnetohydrodynamic (MHD) turbulence. The energy spectrum of the large-scale component is close to $k^{-2}$, whereas the spectrum of the small-scale component agrees with the spectrum of strong MHD turbulence $k^{-3/2}$. While the spectrum of the fluctuations is universal, the outer-scale characteristics of the turbulence are not; they depend on the parameters of the system, such as the net magnetic flux. However, there is remarkable universality among the allowed turbulent states -- their intensity $v_0$ and their outer scale $\\lambda_0$ satisfy the balance condition $v_0/\\lambda_0\\sim \\mathrm d\\Omega/\\mathrm d\\ln r$, where $\\mathrm d\\Omega/\\mathrm d\\l...
The effect of diamagnetic flows on turbulent driven ion toroidal rotation
Energy Technology Data Exchange (ETDEWEB)
Lee, J. P. [Courant Institute of Mathematical Sciences, New York University, New York, New York 10003 (United States); Barnes, M. [Institute for Fusion Studies, The University of Texas at Austin, Austin, Texas 78712 (United States); Parra, F. I. [Rudolf Peierls Centre for Theoretical Physics, Oxford University, Oxford OX1 3NP (United Kingdom); Belli, E. A.; Candy, J. [General Atomics, San Diego, California 92121 (United States)
2014-05-15
Turbulent momentum redistribution determines the radial profile of rotation in a tokamak. The momentum transport driven by diamagnetic flow effects is an important piece of the radial momentum transport for sub-sonic rotation, which is often observed in experiments. In a non-rotating state, the diamagnetic flow and the E × B flow must cancel. The diamagnetic flow and the E × B flow have different effects on the turbulent momentum flux, and this difference in behavior induces intrinsic rotation. The momentum flux is evaluated using gyrokinetic equations that are corrected to higher order in the ratio of the poloidal Larmor radius to the minor radius, which requires evaluation of the diamagnetic corrections to Maxwellian equilibria. To study the momentum transport due to diamagnetic flow effects, three experimental observations of ion rotation are examined. First, a strong pressure gradient at the plasma edge is shown to result in a significant inward momentum transport due to the diamagnetic effect, which may explain the observed peaking of rotation in a high confinement mode. Second, the direction of momentum transport is shown to change as collisionality increases, which is qualitatively consistent with the observed reversal of intrinsic rotation by varying plasma density and current. Last, the dependence of the intrinsic momentum flux on the magnetic shear is found, and it may explain the observed rotation changes in the presence of lower hybrid current drive.
The effects of flow multiplicity on GaN deposition in a rotating disk CVD reactor
Gkinis, P. A.; Aviziotis, I. G.; Koronaki, E. D.; Gakis, G. P.; Boudouvis, A. G.
2017-01-01
The effect of gas flow multiplicity, i.e. the possibility of two very different flow regimes prevailing at random in a rotating disk metalorganic chemical vapor deposition (MOCVD) reactor, on the deposited GaN film is investigated. A transport model coupled with a system of chemical reactions in the gas phase and on the wafer where the film is formed, is implemented in the parameter regions where multiple flows are possible. In the region of multiplicity where either plug flow, imposed by forced convection, or buoyancy-dominated flow is possible, the results in the latter case indicate high deposition rate and decreased uniformity. In the former case, increasing the pressure and the rotation rate has a favorable effect on the deposition rate without sacrificing uniformity. In the parameter window of multiplicity where either rotation or combined rotation/buoyancy may prevail, the effects of buoyancy lead to higher deposition rate at the center of the wafer and reduced uniformity. The Arrhenius plots in the regions of multiplicity for exactly the same operating conditions reveal that the system operates in a diffusion-limited regime in the plug flow and in the rotation-dominated flow, in the first and second region of multiplicity respectively. In contrast, in the buoyancy-dominated flow and the combined rotation/buoyancy flow (first and second region of multiplicity respectively) the process shifts into the kinetics-limited regime.
Bubble Pinch-Off in a Rotating Flow
Bergmann, Raymond; Andersen, Anders; Meer, van der Devaraj
2009-01-01
We create air bubbles at the tip of a “bathtub vortex” which reaches to a finite depth. The bathtub vortex is formed by letting water drain through a small hole at the bottom of a rotating cylindrical container. The tip of the needlelike surface dip is unstable at high rotation rates and releases bu
The Origin of Ekman Flow in a Cavity Subject to Impulsive Rotational Motions
Directory of Open Access Journals (Sweden)
Wen-Jei Yang
2001-01-01
Full Text Available An experimental study is performed to disclose the origin of Ekman flow on the surfaces of a rotating drum resulting from fluid-structure interaction after an impulsive start of motion (referred to as the spin-up process or an impulsive stop (the spin-down process. Laser Doppler velocimetry (LDV is employed to determine instantaneous distribution of both the radial and angular velocity components in the flow field inside the rotating drum. From these results, the secondary flow and the time history of the Ekman boundary layer thickness are determined. The tracer/light sheet method is also engaged to enable real-time visualization of flow patterns. Fluid viscosity, drum size and rotational speed are varied to determine their effects on fluid-structure interactions. Results may be applied to cavity flow in rotating machinery.
Combined free and forced convection flow in a rotating channel with ...
African Journals Online (AJOL)
user
Heat transfer characteristics of the flow is considered taking viscous and Joule ... flow of a viscous incompressible electrically conducting fluid between two ... with the fundamental equations of magnetohydrodynamics in a rotating medium. ..... The non-dimensional mass flow rates Qx/ρυ and Qy/ρυ, in the primary and ...
Flow of viscoplastic fluids in a rotating concentric annulus
DEFF Research Database (Denmark)
Hassager, Ole; Bittleston, Simon H.
1992-01-01
A difficulty in any flow calculation with viscoplastic fluids such as Bingham fluids is the determination of possible plug zones in which no deformation occurs. This paper investigates the flow in a concentric annulus when there is both an axial and tangential flow, the tangent flow arising from ...
Exact two-dimensionalization of rapidly rotating large-Reynolds-number flows
Gallet, Basile
2015-01-01
We consider the flow of a Newtonian fluid in a three-dimensional domain, rotating about a vertical axis and driven by a vertically invariant horizontal body-force. This system admits vertically invariant solutions that satisfy the 2D Navier-Stokes equation. At high Reynolds number and without global rotation, such solutions are usually unstable to three-dimensional perturbations. By contrast, for strong enough global rotation, we prove rigorously that the 2D (and possibly turbulent) solutions are stable to vertically dependent perturbations: the flow becomes 2D in the long-time limit. These results shed some light on several fundamental questions of rotating turbulence: for arbitrary Reynolds number and small enough Rossby number, the system is attracted towards purely 2D flow solutions, which display no energy dissipation anomaly and no cyclone-anticyclone asymmetry. Finally, these results challenge the applicability of wave turbulence theory to describe stationary rotating turbulence in bounded domains.
Three-dimensional flow past rotating wing at low Reynolds number: a computational study
Energy Technology Data Exchange (ETDEWEB)
Ruifeng, Hu, E-mail: rfhu@xidian.edu.cn [School of Mechano-Electronic Engineering, Xidian University, Xi’an 710071 (China)
2015-08-15
In this work, we performed a computational study on the three-dimensional (3D) flow past a rotating wing at a low Reynolds number (Re = 200). The 3D vortical structures and aerodynamic performances of the rotating wing with different aspect ratios and rotating speeds are computed and analyzed. A quasi-steady model is adopted for prediction of aerodynamic performances of the wing, and its applicability is evaluated by the computation. It is found that there exists a periodic vortex shedding pattern at a low rotating speed, while vortices may cluster near the wing when rotating speed is high enough. The wake vortex topology is also affected by the aspect ratio. The current quasi-steady aerodynamic model could only be used for rotating wing aerodynamics at a low rotating speed when regularly periodic vortex shedding exists. (paper)
Thomas, S.; Faghri, A.; Hankey, W.
1990-01-01
The mean thickness of a thin liquid film of deionized water with a free surface on a stationary and rotating horizontal disk has been measured with a nonobtrusive capacitance technique. The measurements were taken when the rotational speed was 0-300 RPM and the flow rate was 7.0-15.0 LPM. A flow visualization study of the thin film was also performed to determine the characteristics of the waves on the free surface. When the disk was stationary, a circular hydraulic jump was present on the disk. Surface waves were found in the supercritical and subcritical regions at all flow rates studied. When the rotational speed of the disk is low, a standing wave at the edge of the disk was present. As the rotational speed increased, the surface waves changed from the wavy-laminar region to a region in which the waves ran nearly radially across the disk on top of a thin substrate of fluid.
Sinha, A.; Mondal, A.; Shit, G. C.; Kundu, P. K.
2016-08-01
This paper theoretically analyzes the heat transfer characteristics associated with electroosmotic flow of blood through a micro-vessel having permeable walls. The analysis is based on the Debye-Hückel approximation for charge distributions and the Navier-Stokes equations are assumed to represent the flow field in a rotating system. The velocity slip condition at the vessel walls is taken into account. The essential features of the rotating electroosmotic flow of blood and associated heat transfer characteristics through a micro-vessel are clearly highlighted by the variation in the non-dimensional flow velocity, volumetric flow rate and non-dimensional temperature profiles. Moreover, the effect of Joule heating parameter and Prandtl number on the thermal transport characteristics are discussed thoroughly. The study reveals that the flow of blood is appreciably influenced by the elctroosmotic parameter as well as rotating Reynolds number.
Rotating turbulent Rayleigh–Bénard convection subject to harmonically forced flow reversals
Geurts, Bernard J.; Kunnen, Rudie P.J.
2014-01-01
The characteristics of turbulent flow in a cylindrical Rayleigh–Bénard convection cell which can be modified considerably in case rotation is included in the dynamics. By incorporating the additional effects of an Euler force, i.e., effects induced by non-constant rotation rates, a remarkably strong
Performance and Internal Flow of Sirocco Fan Using Contra-Rotating Rotors
Institute of Scientific and Technical Information of China (English)
J. Fukutomi; T.Shigemitsu; T. Yasunobu
2008-01-01
A sirocco fan using contra-rotating rotors in which an inner rotor is settled inside the sirocco fan rotor end each rotor rotates in an opposite direction was proposed for the purpose of getting the higher pressure and making the structure of a sirocco fan more compact. If the high discharge pressure is obtained with the adoption of the contra-rotating rotors, it could be used for various purposes. Pressure coefficient of a sirocco fan with contra-rotating rotors is 2.5 times as high as the conventional sirocco fan and the maximum efficiency point of contra-rotating rotors shifts to larger flow rate than a conventional sirocco fan. On the other hand, it was clarified from the flow measurement results that circumferential velocity component at the outlet of the outer rotor of contra-rotating rotors becomes larger than a conventional one. In the present paper, the performance of a conventional sirocco fan and a sirocco fan with contra-rotating rotors are shown and the internal flow field at the outlet of outer rotor of both cases is clarified. Then, the effect of different kind of contra-rotating rotors on the performance and internal flow field is investigated and the rotor design with higher performanco would be discussed.
Pfeiffer, F.; Meyer-Koenig, W.
1949-01-01
By means of characteristics theory, formulas for the numerical treatment of stationary compressible supersonic flows for the two-dimensional and rotationally symmetrical cases have been obtained from their differential equations.
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.
Prediction of Heat Transfer For Turbulent Flow in Rotating Radial Duct
Directory of Open Access Journals (Sweden)
P. Tekriwal
1995-01-01
in the case of low-Re model, the computation time is relatively high and the convergence is rather slow, thus rendering the low-Re model as an unattractive choice for rotating flows at high Reynolds number.
岡本, 正芳; 永江, 聡美; Masayoshi, OKAMOTO; Satomi, NAGAE; 静岡大工; 東北大流体研; Dept. of Mech. Eng., Shizuoka Univ.; Institute of Fluid Science, Tohoku Univ.
2007-01-01
Transient phenomena in turbulent concentric annular pipe flow with sudden outer-wall rotation were investigated by means of the direct numerical simulation (DNS). Due to the sudden rotation, the wall friction becomes small and the flow is stabilized. In the transient state, the axial mean velocity profile changes drastically and the Reynolds stresses vanish near the outer wall. When the wall friction increases suddenly, the vortex structures are invigorated.
Haurissa, Jusuf; Wahyudi, Slamet; Irawan, Yudy Surya; Soenoko, Rudy
2012-01-01
page number: 448-453; International audience; The focus of this research is the turbine flow behavior toward the turbine rotation quality, the turbine efficiency and the turbine power generated. The turbine rotation quality is really needed for the high quality electricity power generated. The method used in this research is the experimental method. The fluid flow behavior was observed by using a Casio 1000 handy camera and a Canon 550D camera. The data obtained from this observation is in a ...
Haurissa, Jusuf; Wahyudi, Slamet; Irawan,Yudy Surya; Soenoko, Rudy
2012-01-01
page number: 448-453; International audience; The focus of this research is the turbine flow behavior toward the turbine rotation quality, the turbine efficiency and the turbine power generated. The turbine rotation quality is really needed for the high quality electricity power generated. The method used in this research is the experimental method. The fluid flow behavior was observed by using a Casio 1000 handy camera and a Canon 550D camera. The data obtained from this observation is in a ...
Convective and absolute instabilities in counter-rotating spiral Poiseuille flow
Energy Technology Data Exchange (ETDEWEB)
Langenberg, J.; Heise, M.; Pfister, G. [University of Kiel, Institute of Experimental and Applied Physics, Kiel (Germany); Abshagen, J. [University of Kiel, Leibniz-Institute of Marine Science, Kiel (Germany)
2004-11-01
We present results of an experimental study on the stability of Taylor-Couette flow in case of counter-rotating cylinders and an imposed axial through flow. We are able to confirm results form recent numerical investigations done by Pinter et al. [24] by measuring the absolute and convective stability boundaries of both propagating Taylor vortices (PTV) and spiral vortices (SPI). Thus our work shows that these theoretical concepts from hydrodynamic stability in open flows apply to experimental counter-rotating Taylor-Couette systems with an imposed axial through flow. (orig.)
Flow measurement in base cooling air passages of a rotating turbine blade
Liebert, C. H.; Pollack, F. G.
1974-01-01
The operational performance is decribed of a shaft-mounted system for measuring the air mass flow rate in the base cooling passages of a rotating turbine blade. Shaft speeds of 0 to 9000 rpm, air mass flow rates of 0.0035 to 0.039 kg/sec (0.0077 to 0.085 lbm/sec), and blade air temperatures of 300 to 385 K (80 to 233 F) were measured. Comparisons of individual rotating blade flows and corresponding stationary supply orifice flows agreed to within 10 percent.
Polymer solutions in co-rotating Taylor-Couette flow without vorticity
Zell, A.; Wagner, C.
2012-02-01
We present experimental results of the flow of dilute and semi-dilute polymer solutions in co-rotating Taylor-Couette cylinders. The experimental set-up consists of a modified Mars II rheometer (Thermo Scientific) with two drive units that are mounted opposite each other. The rotational velocities of the inner and outer cylinders are chosen in a way such that the angular velocity has a 1/r profile and the flow is free of vorticity, but the direction of elongation is not constant, but rotates with the flow. Our particle image velocimetry (PIV) measurements show that for polymer solutions without shear thinning the flow is indeed free of vorticity and is equal to a stagnation point flow at a given position and a given instant in time. In contrast, torque measurements reveal that the stresses are identical to the stresses that are present in a plane shear flow. Thus, we find that for polymer solutions a flow with vorticity and a constant direction of elongation is equal to a flow without vorticity in which the direction of elongation is rotating. Finally, we show that for shear thinning solutions the flow velocity becomes non-monotonic through the gap and resembles a pluglike profile which is known from the Poiseuille flow.
Lift of a rotating circular cylinder in unsteady flows
DEFF Research Database (Denmark)
Carstensen, Stefan; Mandviwalla, Xerxes; Vita, Luca
2012-01-01
A cylinder rotating in steady current experiences a lift known as the Magnus effect. In the present study the effect of waves on the Magnus effect has been investigated. This situation is experienced with the novel floating offshore vertical axis wind turbine (VAWT) concept called the DEEPWIND...... concept, which incorporates a rotating spar buoy and thereby utilizes seawater as a roller-bearing. The a priori assumption and the results suggest that the lift in waves, to a first approximation, may be represented by a formulation similar to the well-known Morison formulation. The force coefficients...
Rotating flow of a nanofluid due to an exponentially stretching surface with suction
Salleh, Siti Nur Alwani; Bachok, Norfifah; Arifin, Norihan Md
2017-08-01
An analysis of the rotating nanofluid flow past an exponentially stretched surface with the presence of suction is studied in this work. Three different types of nanoparticles, namely, copper, titania and alumina are considered. The system of ordinary differential equations is computed numerically using a shooting method in Maple software after being transformed from the partial differential equations. This transformation has considered the similarity transformations in exponential form. The physical effect of the rotation, suction and nanoparticle volume fraction parameters on the rotating flow and heat transfer phenomena is investigated and has been described in detail through graphs. The dual solutions are found to appear when the governing parameters reach a certain range.
Rotation induced flow suppression around two tandem circular cylinders at low Reynolds number
Chatterjee, Dipankar; Gupta, Krishan; Kumar, Virendra; Varghese, Sachin Abraham
2017-08-01
The rotation to a bluff object is known to have a stabilizing effect on the fluid dynamic transport around the body. An unsteady periodic flow can be degenerated into a steady flow pattern depending on the rate of rotation imparted to the body. On the other hand, multiple bodies placed in tandem arrangement with respect to an incoming flow can cause destabilization to the flow as a result of the complicated wake interaction between the bodies. Accordingly, the spacing between the bodies and the rate of rotation have significant impact on the overall fluid dynamic transport around them. The present work aims to understand how these two competing factors are actually influencing the fluidic transport across a pair of identical rotating circular cylinders kept in tandem arrangement in an unconfined medium. The cylinders are subjected to a uniform free stream flow and the gaps between the cylinders are varied as 0.2, 0.7, 1.5 and 3.0. Both the cylinders are made to rotate in the clockwise sense. The Reynolds number based on the free stream flow is taken as 100. A two-dimensional finite volume based transient computation is performed for a range of dimensionless rotational speeds of the cylinders (0 ≤ Ω ≤ 2.75). The results show that the shedding phenomena can be observed up to a critical rate of rotation (Ωcr) depending on the gap spacing. Beyond Ωcr, the flow becomes stabilized and finally completely steady as Ω increases further. Increasing the gap initially causes a slight decrease in the critical rotational speed, however, it increases at a rapid rate for larger gap spacing.
A Method of Three-Dimensional Micro-Rotational Flow Generation for Biological Applications
Directory of Open Access Journals (Sweden)
Yaxiaer Yalikun
2016-08-01
Full Text Available We report a convenient method to create a three-dimensional micro-rotational fluidic platform for biological applications in the direction of a vertical plane (out-of-plane without contact in an open space. Unlike our previous complex fluidic manipulation system, this method uses a micro-rotational flow generated near a single orifice when the solution is pushed from the orifice by using a single pump. The three-dimensional fluidic platform shows good potential for fluidic biological applications such as culturing, stimulating, sorting, and manipulating cells. The pattern and velocity of the micro-rotational flow can be controlled by tuning the parameters such as the flow rate and the liquid-air interface height. We found that bio-objects captured by the micro-rotational flow showed self-rotational motion and orbital motion. Furthermore, the path length and position, velocity, and pattern of the orbital motion of the bio-object could be controlled. To demonstrate our method, we used embryoid body cells. As a result, the orbital motion had a maximum length of 2.4 mm, a maximum acceleration of 0.63 m/s2, a frequency of approximately 0.45 Hz, a maximum velocity of 15.4 mm/s, and a maximum rotation speed of 600 rpm. The capability to have bio-objects rotate or move orbitally in three dimensions without contact opens up new research opportunities in three-dimensional microfluidic technology.
1976-06-01
Hz at -800 screen rpm (26.7 Hz). Inspection of thc inlet dyna- mic pressure, q, , records at rotating sta.l inception shows that as negative screen...of tma .’nes% of these 4iszu~ancrei. - - -_ ~ I- S. . . .. In the following analysis, we will consider the response of the blade row to a distortion
A study on heat-flow analysis of friction stir welding on a rotation affected zone
Energy Technology Data Exchange (ETDEWEB)
Kang, Sung Wook; Jang, Beom Seon [Seoul National University, Seoul (Korea, Republic of); Kim, Jae Woong [Daewoo Shipbuilding and Marine Engineering Co., Soeul (Korea, Republic of)
2014-09-15
In recent years, as interest in environmental protection and energy conservation rose, technological development for lightweight efficiency of transport equipment, such as aircrafts, railcars, automobiles and vessels, have been briskly proceeding. This has led to an expansion of the application of lightweight alloys such as aluminum and magnesium. For the welding of these lightweight alloys, friction stir welding has been in development by many researchers. Heat-flow analysis of friction stir welding is one such research. The flow and energy equation is solved using the computational fluid dynamic commercial program 'Fluent'. In this study, a rotation affected zone concept is imposed. The rotation affected zone is a constant volume. In this volume, flow is rotated the same as the tool rotation speed and so plastic dissipation occurs. Through this simulation, the temperature distribution results are calculated and the simulation results are compared with the experimental results.
Inception mechanism and suppression of rotating stall in an axial-flow fan
Nishioka, T.
2013-12-01
Inception patterns of rotating stall at two stagger-angle settings for the highly loaded rotor blades were experimentally investigated in a low-speed axial-flow fan. Rotor-tip flow fields were also numerically investigated to clarify the mechanism behind the rotating stall inception. The stall inception patterns depended on the rotor stagger-angle settings. The stall inception from a rotating instability was confirmed at the design stagger-angle settings. The stall inception from a short length-scale stall cell (spike) was also confirmed at the small stagger-angle setting. The spillage of tip-leakage flow and the tip-leakage vortex breakdown influence the rotating stall inception. An air-separator has been developed based on the clarified inception mechanism of rotating stall. The rotating stall was suppressed by the developed air-separator, and the operating range of fan was extended towards low flow rate. The effect of developed air-separator was also confirmed by application to a primary air fan used in a coal fired power plant. It is concluded from these results that the developed air-separator can provide a wide operating range for an axial-flow fan.
THE PERTURBATION SOLUTIONS OF THE FLOW IN A ROTATING CURVED ANNULAR PIPE
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
In this paper, the flow in a rotating curved annular pipe isexamined by a perturbation method. A second order perturbation solution is presented. The characteristics of the secondary flow and the axial flow are studied in detail.The study indicates that the loops of the secondary flow are more complex than those in a curved annular pipe without rotation and its numbers depend on the ratio of the Coriolis force to centrifugal force F. As F ≈- 1 , the secondary flow has eight loops and its intensity reaches the minimum value, and the distribution of the axial flow is like that of the Poiseuille flow. The position of the maximum axial velocity is pushed to either outer bend or inner bend, which is also determined by F.
Powerful Swirl Generation of Flow-driven Rotating Mixing Vane for Enhancing CHF
Energy Technology Data Exchange (ETDEWEB)
Seo, Han; Seo, Seok Bin; Heo, Hyo; Bang, In Cheol [Ulsan National Institute of Science and Technology, Ulsan (Korea, Republic of)
2014-05-15
Mixing vanes are utilized to improve CHF and heat transfer performance in the rod bundle during normal operation. Experimental measurement of the swirling flow from a split vane pair was conducted using particle image velocimetry (PIV) and boroscope. The lateral velocity fields show that the swirling flow was initially centered in the subchannel and the computational fluid dynamics (CFD) analysis was performed based on the experiment. To visualize flow patterns in the 5Χ5 subchannel using PIV, matching the refraction between the working fluid and the structure was considered and the experiment aimed to develop the experimental data for providing fundamental information of the CFD analysis. The fixed split vane is the main mixing inducer in the fuel assembly. In a heat exchanger research, propeller type swirl generates at several pitch ratios and different blades angles were used to enhance heat transfer rate. Significant improvements of the heat transfer rate using the propellers were confirmed due to creation of tangential flow. In the present study, the mixing effect of rotation vane which has a shape of propeller was studied using PIV. A split vane was considered in the experiment to show the effect of rotation vane. Vertical and horizontal flow analyses were conducted to show the possible use of rotation vane in a subchannel. In the present work, the study of flow visualization using three types of vanes is conducted to show the mixing effect. The vertical flow and the horizontal flow distributions were analyzed in the two experimental facilities. For the vertical flow facility, flow distributions, flow profiles, and the turbulence kinetic energy are analyzed at the centerline of the channel. The results show that the rotation vane has the highest flow and turbulence kinetic intensity at the centerline of the channel. For the horizontal flow facility, the results indicate that lateral flow of the rotation vane is generated and maintained along with the flow
Numerical Study of Flow Motion and Patterns Driven by a Rotating Permanent Helical Magnetic Field
Yang, Wenzhi; Wang, Xiaodong; Wang, Bo; Baltaretu, Florin; Etay, Jacqueline; Fautrelle, Yves
2016-10-01
Liquid metal magnetohydrodynamic flow driven by a rotating permanent helical magnetic field in a cylindrical container is numerically studied. A three-dimensional numerical simulation provides insight into the visualization of the physical fields, including the magnetic field, the Lorentz force density, and the flow structures, especially the flow patterns in the meridional plane. Because the screen parameter is sufficiently small, the model is decoupled into electromagnetic and hydrodynamic components. Two flow patterns in the meridional plane, i.e., the global flow and the secondary flow, are discovered and the impact of several system parameters on their transition is investigated. Finally, a verifying model is used for comparison with the previous experiment.
Numerical study for MHD peristaltic flow in a rotating frame.
Hayat, T; Zahir, Hina; Tanveer, Anum; Alsaedi, A
2016-12-01
The aim of present investigation is to model and analyze the magnetohydrodynamic (MHD) peristaltic transport of Prandtl fluid in a channel with flexible walls. The whole system consisting of fluid and channel are in a rotating frame of reference with uniform angular velocity. Viscous dissipation in thermal equation is not ignored. The channel boundaries satisfy the convective conditions in terms of temperature. The arising complicated problems are reduced in solvable form using large wavelength and small Reynolds number assumptions. Numerical solution for axial and secondary velocities, temperature and heat transfer coefficient are presented. Main emphasis is given to the outcome of rotation and material parameters of Prandtl fluid on the physical quantities of interest.
Experimental investigation of three-dimensional flow instabilities in a rotating lid-driven cavity
DEFF Research Database (Denmark)
Sørensen, Jens Nørkær; Naumov, I.; Mikkelsen, Robert Flemming
2006-01-01
The flow between a rotating lid and a stationary cylinder is studied experimentally. The flow is governed by two parameters: The ratio of container height to disk radius, h, and the Reynolds number, Re, based on the disk angular velocity, cylinder radius and kinematic viscosity of the working...
Flow characteristics of screws and special mixing enhancers in a co-rotating twin screw extruder
Brouwer, T.; Todd, D.B.; Janssen, L.P.B.M.
2002-01-01
The flow behavior of a Newtonian fluid through special mixing enhancers in a modular intermeshing co-rotating twin screw extruder has been examined. The mixing enhancers are slotted screws and gear mixing elements. Particular attention has been directed to drag and pressure flow characteristics and
Interaction of a decaying vortex ring with a rotational background flow bounded by a solid wall
Ishii, K.; Liu, C. H.
1987-01-01
The interaction between a vortex ring of finite strength and an axisymmetric rotational background flow bounded by a solid wall is studied by a singular perturbation method. The analysis is carried out by combining a composite solution of a vortex ring and an unsteady Navier-Stokes solution for the background rotational flow. Using the method of averaging, numerical scheme is developed to obtain a Navier-Stokes solution in which the grid and time-step sizes depend solely on the length and velocity scales of the background flow. Numerical results are presented to illustrate the separation of the boundary layer on a solid wall and its interaction with the vortex ring.
Bi-stability in turbulent, rotating spherical Couette flow
Zimmerman, Daniel S; Lathrop, Daniel P; 10.1063/1.3593465
2011-01-01
Flow between concentric spheres of radius ratio $\\eta = r_\\mathrm{i}/r_\\mathrm{o} = 0.35$ is studied in a 3 m outer diameter experiment. We have measured the torques required to maintain constant boundary speeds as well as localized wall shear stress, velocity, and pressure. At low Ekman number $E = 2.1\\times10^{-7}$ and modest Rossby number $0.07 < Ro < 3.4$, the resulting flow is highly turbulent, with a Reynolds number ($Re=Ro/E$) exceeding fifteen million. Several turbulent flow regimes are evident as $Ro$ is varied for fixed $E$. We focus our attention on one flow transition in particular, between $Ro = 1.8$ and $Ro = 2.6$, where the flow shows bistable behavior. For $Ro$ within this range, the flow undergoes intermittent transitions between the states observed alone at adjacent $Ro$ outside the switching range. The two states are clearly distinguished in all measured flow quantities, including a striking reduction in torque demanded from the inner sphere by the state lying at higher $Ro$. The redu...
The effect of particle rotation in multi-particle flow simulations
Sierakowski, Adam; Prosperetti, Andrea
2013-11-01
In multi-particle flow simulations, particle rotation is difficult to calculate and is often imprecisely accounted for or ignored altogether. We examine the effect of these procedures on the overall flow characteristics through large systems of particles when the particle center is fixed and either allowed or not to rotate. We use a newly developed GPU-centric implementation of the Physalis method for the solution of the Navier-Stokes equations in the presence of finite-size spheres. We investigate periodic systems of more than 100 randomly-distributed particles at Reynolds numbers up to 100. By considering flow characteristics such as mean velocity and pressure drop, we shed light on the importance of including particle rotation effects in large particle-flow simulations. Study supported by NSF grant CBET 1258398.
FLOW AND HEAT TRANSFER OF OLDROYD-B FLUIDS IN A ROTATING CURVED PIPE
Institute of Scientific and Technical Information of China (English)
SHEN Xin-rong; ZHANG Ming-kan; MA Jian-feng; ZHANG Ben-zhao
2008-01-01
The flow and convected heat transfer of the Oldroyd-B fluids in a rotating curved pipe with circular cross-section were investigated by employing a perturbation method. A perturbation solution up to the second order was obtained for a small curvature ratio, κ. The variations of axial velocity distribution and secondary flow structure with F, Re and We were discussed in detail in order to investigate the combined effects of the three parameters on flow structure. The combined effects of the Coriolis force, inertia force and elastic force on the temperature distribution were also analyzed, which are greater than the adding independent effects of the three forces. The variations of the flow rate and Nusselt number with the rotation, inertia and elasticity were examined as well. The results show the characteristics of the heat and mass transfer of the Oldroyd-B fluids in a rotating curved pipe.
Motion and decay of vortex rings submerged in a rotational flow
Ishii, K.; Liu, C. H.
1987-01-01
The interaction between vortex rings of finite strength and an axisymmetric rotational background flow is studied by a singular perturbation method, because it is difficult to use a finite-difference method to analyze the viscous decay in the small core of a vortex ring. The analysis is carried out by combining a composite solution of a vortex ring and an unsteady Euler solution for the background rotational flow. Using the method of averaging, a numerical scheme is developed to obtain an Euler solution in which the grid and time-step sizes depend solely on the length and velocity scales of the background flow. Numerical results are presented to illustrate the interaction between the trajectories and decay rates of the vortex rings and the background rotational flow.
Regimes of Axisymmetric Flow and Scaling Laws in a Rotating Annulus with Local Convective Forcing
Directory of Open Access Journals (Sweden)
Susie Wright
2017-07-01
Full Text Available We present a numerical study of axisymmetric flow in a rotating annulus in which local thermal forcing, via a heated annular ring on the outside of the base and a cooled circular disk in the centre of the top surface, drives convection. This new configuration is a variant of the classical thermally-driven annulus, where uniform heating and cooling are applied through the outer and inner sidewalls respectively. The annulus provides an analogue to a planetary circulation and the new configuration, with its more relaxed vertical thermal boundary conditions, is expected to better emulate vigorous convection in the tropics and polar regions as well as baroclinic instability in the mid-latitude baroclinic zone. Using the Met Office/Oxford Rotating Annulus Laboratory (MORALS code, we have investigated a series of equilibrated, two dimensional axisymmetric flows across a large region of parameter space. These are characterized in terms of their velocity and temperature fields. When rotation is applied several distinct flow regimes may be identified for different rotation rates and strengths of differential heating. These regimes are defined as a function of the ratio of the horizontal Ekman layer thickness to the non-rotating thermal boundary layer thickness and are found to be similar to those identified in previous annulus experiments. Convection without rotation is also considered and the scaling of the heat transport with Rayleigh number is calculated. This is then compared with existing work on the classical annulus as well as horizontal and Rayleigh-Bénard convection. As with previous studies on both rotating and non-rotating convection the system’s behaviour is found to be aspect ratio dependent. This dependence is seen in the scaling of the non-rotating Nusselt number and in transitions between regimes in the rotating case although further investigation is required to fully explain these observations.
Hybrid RANS/LES of turbulent flow in a rotating rib-roughened channel
Xun, Qian-Qiu; Wang, Bing-Chen
2016-07-01
In this paper, we investigate the effect of the Coriolis force on the flow field in a rib-roughened channel subjected to either clockwise or counter-clockwise system rotation using hybrid RANS/LES based on wall modelling. A simplified dynamic forcing scheme incorporating backscatter is proposed for the hybrid simulation approach. The flow is characterized by a Reynolds number of Re = 1.5 × 104 and a rotation number Ro ranging from -0.6 to 0.6. The mean flow speed and turbulence level near the roughened wall are enhanced under counter-clockwise rotation and suppressed under clockwise rotation. The Coriolis force significantly influences the stability of the wall shear layer and the free shear layers generated by the ribs. Consequently, it is interesting to observe that the classification of the roughness type relies not only on the pitch ratio, but also on the rotation number in the context of rotating rib-roughened flows. In order to validate the present hybrid approach, the first- and second-order statistical moments of the velocity field obtained from the simulations are thoroughly compared with the available laboratory measurement data.
DIRECT NUMERICAL SIMULATION OF TURBULENT HEAT TRANSFER IN A WALL-NORMAL ROTATING CHANNEL FLOW
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
Direct Nmerical Simulation (DNS) of turbulent heat transfer in a wall-normal rotating channel flow has been carried out for the rotation number Nτ from 0 to 0.1, the Reynolds number 194 based on the friction velocity of non-rotating case and the half-height of the channel, and the Prandtl number 1. The objective of this study is to reveal the effects of rotation on the characteristics of turbulent flow and heat transfer. Based on the present calculated results, two typical rotation regimes are identified. When 0＜Nτ＜0.06, turbulence and thermal statistics correlated with the spanwise velocity fluctuation are enhanced since the shear rate of spanwise mean flow induced by Coriolis force increases; however, the other statistics are suppressed. When Nτ＞0.06, turbulence and thermal statistics are suppressed significantly because the Coriolis force effect plays as a dominated role in the rotating flow. Remarkable change of the direction of near-wall streak structures based on the velocity and temperature fluctuations is identified.
The flow of a thin liquid film on a stationary and rotating disk. II - Theoretical prediction
Rahman, M. M.; Faghri, A.; Hankey, W. L.
1990-01-01
The existing theoretical models are improved and a systematic procedure to compute the free surface flow of a thin liquid film is suggested. The solutions for axisymmetric radial flow on a stationary horizontal disk and for the disk rotating around its axis are presented. The theoretical predictions are compared with the experimental data presented in Part I of this report. The analysis shows results for both supercritical and subcritical flows and the flow structure in the vicinity of a hydraulic jump which isolates these two flow types. The detailed flow structure in a hydraulic jump was computed and shown to contain regions of separation including a 'surface roller'. The effects of surface tension are found to be important near the outer edge of the disk where the fluid experiences a free fall. At other locations, the surface tension is negligible. For a rotating disk, the frictional resistance in the angular direction is found to be as important as that in the radial direction.
Bhatia, Tanayveer Singh
2016-01-01
The emergence of turbulence in shear flows is a well-investigated field. Yet, one of major issues is the apparent contradiction between linear stability analysis quoting a flow to be stable and results from experiments and simulations proving it to be otherwise. There is some success, in particular in astrophysical systems, based on Magneto-Rotational Instability (MRI). However, MRI requires the system to be weakly magnetized, which is not a feature of general magnetohydrodynamic (MHD) flows. Nevertheless, linear perturbations of such flows are nonnormal in nature which argues for an origin of nonlinearity therein. The idea is, nonnormal perturbations could produce huge transient energy growth (TEG), which may lead to non-linearity and further turbulence. However, so far, nonnormal effects in shear flows have not been explored much in the presence of magnetic fields. Here, we consider the perturbed visco-resistive incompressible MHD shear flows with rotation in general. Basically we consider the magnetized ve...
Two-equation modeling of turbulent rotating flows
Cazalbou, Jean-Bernard; Chassaing, Patrick; Dufour, Guillaume; CARBONNEAU, Xavier
2005-01-01
The possibility to take into account the effects of the Coriolis acceleration on turbulence is examined in the framework of two-equation eddy-viscosity models. General results on the physical consistency of such turbulence models are derived from a dynamical-system approach to situations of time-evolving homogeneous turbulence in a rotating frame. Application of this analysis to a (k,epsilon) model fitted with an existing Coriolis correction [J. H. G. Howard, S. V. Patankar, and R. M. Bordynu...
A semi-direct solver for compressible three-dimensional rotational flow
Chang, S.-C.; Adamczyk, J. J.
1983-01-01
An iterative procedure is presented for solving steady inviscid 3-D subsonic rotational flow problems. The procedure combines concepts from classical secondary flow theory with an extension to 3-D of a novel semi-direct Cauchy-Riemann solver. It is developed for generalized coordinates and can be exercised using standard finite difference procedures. The stability criterion of the iterative procedure is discussed along with its ability to capture the evolution of inviscid secondary flow in a turning channel.
A semi-direct solver for compressible 3-dimensional rotational flow
Chang, S. C.; Adamczyk, J. J.
1983-01-01
An iterative procedure is presented for solving steady inviscid 3-D subsonic rotational flow problems. The procedure combines concepts from classical secondary flow theory with an extension to 3-D of a novel semi-direct Cauchy-Riemann solver. It is developed for generalized coordinates and can be exercised using standard finite difference procedures. The stability criterion of the iterative procedure is discussed along with its ability to capture the evolution of inviscid secondary flow in a turning channel.
Calderer, Antoni; Neal, Douglas; Prevost, Richard; Mayrhofer, Arno; Lawrenz, Alan; Foss, John; Sotiropoulos, Fotis
2015-11-01
Secondary flows in a rotating flow in a cylinder, resulting in the so called ``tea leaf paradox'', are fundamental for understanding atmospheric pressure systems, developing techniques for separating red blood cells from the plasma, and even separating coagulated trub in the beer brewing process. We seek to gain deeper insights in this phenomenon by integrating numerical simulations and experiments. We employ the Curvilinear Immersed boundary method (CURVIB) of Calderer et al. (J. Comp. Physics 2014), which is a two-phase flow solver based on the level set method, to simulate rotating free-surface flow in a cylinder partially filled with water as in the tea leave paradox flow. We first demonstrate the validity of the numerical model by simulating a cylinder with a rotating base filled with a single fluid, obtaining results in excellent agreement with available experimental data. Then, we present results for the cylinder case with free surface, investigate the complex formation of secondary flow patterns, and show comparisons with new experimental data for this flow obtained by Lavision. Computational resources were provided by the Minnesota Supercomputing Institute.
Oscillatory and Steady Flows in the Annular Fluid Layer inside a Rotating Cylinder
Directory of Open Access Journals (Sweden)
Veronika Dyakova
2016-01-01
Full Text Available The dynamics of a low-viscosity fluid inside a rapidly rotating horizontal cylinder were experimentally studied. In the rotating frame, the force of gravity induces azimuthal fluid oscillations at a frequency equal to the velocity of the cylinder’s rotation. This flow is responsible for a series of phenomena, such as the onset of centrifugal instability in the Stokes layer and the growth of the relief at the interface between the fluid and the granular medium inside the rotating cylinder. The phase inhomogeneity of the oscillatory fluid flow in the viscous boundary layers near the rigid wall and the free surface generates the azimuthal steady streaming. We studied the relative contribution of the viscous boundary layers in the generation of the steady streaming. It is revealed that the velocity of the steady streaming can be calculated using the velocity of the oscillatory fluid motion.
Direct numerical simulation of rotating fluid flow in a closed cylinder
DEFF Research Database (Denmark)
Sørensen, Jens Nørkær; Christensen, Erik Adler
1995-01-01
, is validated against experimental visualizations of both transient and stable periodic flows. The complexity of the flow problem is illuminated numerically by injecting flow tracers into the flow domain and following their evolution in time. The vortex dynamics appears as stretching, folding and squeezing...... to three multiple solutions for the same Reynolds number, and to contain four discernible branches. The transition to strange attractor behavior was identified as a nontrivial Ruelle-Takens transition through a transient torus. The various solution branches of the rotating flow problem are illustrated...
Flow field investigation in rotating rib-roughened channel by means of particle image velocimetry
Energy Technology Data Exchange (ETDEWEB)
Coletti, Filippo [Karman Institute for Fluid Dynamics, Turbomachinery and Propulsion Department, Rhode-Saint-Genese (Belgium); Stanford University, Mechanical Engineering Department, Stanford, CA (United States); Maurer, Thomas [Karman Institute for Fluid Dynamics, Turbomachinery and Propulsion Department, Rhode-Saint-Genese (Belgium); Stuttgart University, Institute of Aerospace Thermodynamics, Stuttgart (Germany); Arts, Tony [Karman Institute for Fluid Dynamics, Turbomachinery and Propulsion Department, Rhode-Saint-Genese (Belgium); Di Sante, Alberto [Karman Institute for Fluid Dynamics, Turbomachinery and Propulsion Department, Rhode-Saint-Genese (Belgium); General Electric, Florence (Italy)
2012-04-15
The turbulent velocity field over the rib-roughened wall of an orthogonally rotating channel is investigated by means of two-dimensional particle image velocimetry (PIV). The flow direction is outward, with a bulk Reynolds number of 1.5 x 10{sup 4} and a rotation number ranging from 0.3 to 0.38. The measurements are obtained along the wall-normal/streamwise plane at mid-span. The PIV system rotates with the channel, allowing to measure directly the relative flow velocity with high spatial resolution. Coriolis forces affect the stability of the boundary layer and free shear layer. Due to the different levels of shear layer entrainment, the reattachment point is moved downstream (upstream) under stabilizing (destabilizing) rotation, with respect to the stationary case. Further increase in rotation number pushes further the reattachment point in stabilizing rotation, but does not change the recirculation length in destabilizing rotation. Turbulent activity is inhibited along the leading wall, both in the boundary layer and in the separated shear layer; the opposite is true along the trailing wall. Coriolis forces affect indirectly the production of turbulent kinetic energy via the Reynolds shear stresses and the mean shear. Two-point correlation is used to characterize the coherent motion of the separated shear layer. Destabilizing rotation is found to promote large-scale coherent motions and accordingly leads to larger integral length scales; on the other hand, the spanwise vortices created in the separating shear layer downstream of the rib are less organized and tend to be disrupted by the three-dimensional turbulence promoted by the rotation. The latter observation is consistent with the distributions of span-wise vortices detected in instantaneous flow realizations. (orig.)
An Approximate Solution for Flow between Two Disks Rotating about Distinct Axes at Different Speeds
Directory of Open Access Journals (Sweden)
H. Volkan Ersoy
2007-01-01
Full Text Available The flow of a linearly viscous fluid between two disks rotating about two distinct vertical axes is studied. An approximate analytical solution is obtained by taking into account the case of rotation with a small angular velocity difference. It is shown how the velocity components depend on the position, the Reynolds number, the eccentricity, the ratio of angular speeds of the disks, and the parameters satisfying the conditions u=0 and ν=0 in midplane.
Heat Transfer for Elastico-Viscous Flow Between Two Rotating Porous Discs
Directory of Open Access Journals (Sweden)
P. R. Sharma
1983-04-01
Full Text Available The problem of temperature distribution and heat transfer for elastico-viscous fluid flow between two rotating porous discs is studied. The equations of motion and energy are solved by a regular Perturbation method for small Reynolds number. The effects of the elasticity of the fluid, suction/injection parameter, rotation parameter, Prandt1 number and Eckert number on Nusselt numbers at the two discs have been discussed numerically and compared with Newtonian fluid case.
Steady hydromagnetic Couette flow in a rotating system with non ...
African Journals Online (AJOL)
user
energy equation and numerical values of rate of heat transfer at both plates are ... It may be noted that MHD Couette flow may be generated into two ways and .... Equations (5), (6), (10) and (11) with the use of (12), in non-dimensional form, ...
Free-surface grease flow on a rotating plate
Westerberg, L.G.; Li, Jianchang; Höglund, E.; Lugt, Pieter Martin; Baart, P.
2014-01-01
Grease lubrication is traditionally used in a great variety of mechanical systems such as rolling bearings, seals, and gears where it has been shown more advantageous than oil, mainly due to its consistency allowing the grease to stay inside the system and not leak out. Knowledge of the flow dynamic
Self-motion Perception from Optic Flow and Rotation Signals
J.A. Beintema (Jaap)
2000-01-01
textabstractThe value of optic flow for retrieving movement direction was recognised already two centuries ago by astronomers, searching the sky for meteorite showers. The point from which the shower appeared to emanate they termed the radiant, knowing it indicated the direction along which the mete
Self-motion Perception from Optic Flow and Rotation Signals
J.A. Beintema (Jaap)
2000-01-01
textabstractThe value of optic flow for retrieving movement direction was recognised already two centuries ago by astronomers, searching the sky for meteorite showers. The point from which the shower appeared to emanate they termed the radiant, knowing it indicated the direction along which the mete
Accelerated micropolar fluid-flow past an uniformly rotating circular cylinder
Siddiqui, Abuzar Abid
2016-10-01
In this paper, we formulated the non-steady flow due to the uniformly accelerated and rotating circular cylinder from rest in a stationary, viscous, incompressible and micropolar fluid. This flow problem is examined numerically by adopting a special scheme comprising the Adams-Bashforth Temporal Fourier Series method and the Runge-Kutta Temporal Special Finite-Difference method. This numerical scheme transforms the governing equation into a system of finite-difference equations. This system was further solved numerically by point successive-over-relaxation method. These results were also further extrapolated by the Richardson extrapolation method. This scheme is valid for all values of the flow and fluid-parameters and for all time. Moreover the boundary conditions of the vorticity and the spin at points far from the cylinder are being imposed and encountered too. The results are compared with existing results (for non-rotating circular cylinder in Newtonian fluids). The comparison is good. The enhancement of lift and reduction in drag is observed if the micropolarity effects are intensified. Same is happened if the rotation of a cylinder increases. Furthermore, the vortex-pair in the wake is delayed to successively higher times as rotation parameter increases. In addition, the rotation helps not only in dissolving vortices adjacent to the cylinder and adverse pressure region but also in dissolving the boundary layer separation. Furthermore, the rotation reduces the micropolar spin boundary layer.
Accelerated micropolar fluid–flow past an uniformly rotating circular cylinder
Directory of Open Access Journals (Sweden)
Abuzar Abid Siddiqui
2016-10-01
Full Text Available In this paper, we formulated the non-steady flow due to the uniformly accelerated and rotating circular cylinder from rest in a stationary, viscous, incompressible and micropolar fluid. This flow problem is examined numerically by adopting a special scheme comprising the Adams-Bashforth Temporal Fourier Series method and the Runge-Kutta Temporal Special Finite-Difference method. This numerical scheme transforms the governing equation into a system of finite-difference equations. This system was further solved numerically by point successive-over-relaxation method. These results were also further extrapolated by the Richardson extrapolation method. This scheme is valid for all values of the flow and fluid-parameters and for all time. Moreover the boundary conditions of the vorticity and the spin at points far from the cylinder are being imposed and encountered too. The results are compared with existing results (for non-rotating circular cylinder in Newtonian fluids. The comparison is good. The enhancement of lift and reduction in drag is observed if the micropolarity effects are intensified. Same is happened if the rotation of a cylinder increases. Furthermore, the vortex-pair in the wake is delayed to successively higher times as rotation parameter increases. In addition, the rotation helps not only in dissolving vortices adjacent to the cylinder and adverse pressure region but also in dissolving the boundary layer separation. Furthermore, the rotation reduces the micropolar spin boundary layer.
Directory of Open Access Journals (Sweden)
Hailong Xu
2016-01-01
Full Text Available Rotated blades are key mechanical components in turbomachinery and high cycle fatigues often induce blade cracks. Accurate detection of small cracks in rotated blades is very significant for safety, reliability, and availability. In nature, a breathing crack model is fit for a small crack in a rotated blade rather than other models. However, traditional vibration displacements-based methods are less sensitive to nonlinear characteristics due to small breathing cracks. In order to solve this problem, vibration power flow analysis (VPFA is proposed to analyze nonlinear dynamic behaviors of rotated blades with small breathing cracks in this paper. Firstly, local flexibility due to a crack is derived and then time-varying dynamic model of the rotated blade with a small breathing crack is built. Based on it, the corresponding vibration power flow model is presented. Finally, VPFA-based numerical simulations are done to validate nonlinear behaviors of the cracked blade. The results demonstrate that nonlinear behaviors of a crack can be enhanced by power flow analysis and VPFA is more sensitive to a small breathing crack than displacements-based vibration analysis. Bifurcations will occur due to breathing cracks and subharmonic resonance factors can be defined to identify breathing cracks. Thus the proposed method can provide a promising way for detecting and predicting small breathing cracks in rotated blades.
Institute of Scientific and Technical Information of China (English)
LIU; Nansheng; LU; Xiyun; ZHUANG; Lixian
2004-01-01
A new dynamic subgrid-scale (SGS) model, which is proved to satisfy the principle of asymptotic material frame indifference (AMFI) for rotating turbulence, is proposed based on physical and mathematical analysis. Comparison with direct numerical simulation (DNS) results verifies that the new SGS model is effective for large eddy simulation (LES) on rotating turbulent flow. The SGS model is then applied to the LES of the spanwise rotating turbulent channel flow to investigate the rotation effect on turbulence characteristics, budget terms in the transport equations of resolved Reynolds stresses, and flow structures near the wall regions of the rotating channel.
Sauret, Alban; Morize, Cyprien; Bars, Michael Le; 10.1017/S0022112010004052
2011-01-01
We study both experimentally and numerically the steady zonal flow generated by longitudinal librations of a spherical rotating container. This study follows the recent weakly nonlinear analysis of Busse (2010), developed in the limit of small libration frequency - rotation rate ratio, and large libration frequency - spin-up time product. Using PIV measurements as well as results from axisymmetric numerical simulations, we confirm quantitatively the main features of Busse's analytical solution: the zonal flow takes the form of a retrograde solid body rotation in the fluid interior, which does not depend on the libration frequency nor on the Ekman number, and which varies as the square of the amplitude of excitation. We also report the presence of an unpredicted prograde flow at the equator near the outer wall.
Effect of advanced and delayed rotation on the dominant flow pattern and its temporal evolution
Uksul, Esra; Krishna, Swathi; Mulleners, Karen
2015-11-01
During a flapping cycle of an insect, complex time dependent flows are produced as the wing reciprocates, producing a maximum lift at the stroke reversals. By flipping the wing rapidly at the end of each stroke, the insect modulates the flow around the wing and hence the aerodynamic forces necessary to hover. The duration and starting point of the flip play an important role in determining the amount of lift produced. To understand and tailor the effect of wing kinematics on the aerodynamic performance we focussed on the vortex dynamics of the flow field. Phase-averaged data from particle image velocimetry was used to evaluate the flow features inherent to changes in rotation during a stroke of a flat plate, which is modelled based on hoverfly characteristics. The period of rotation is one-third of the total time period. A +10% phase shift is used for delayed rotation, a -10% phase shift for advanced rotation. Vortex detection methods like the λ2 and Γ2 criteria are used to determine the effect of a delay or early rotation on the trajectories, size, shape and location of the prominent vortical structures. Proper orthogonal decomposition is used to study the influence of the phase-shifts on the dominant mode structure and the related time-scales.
Unsteady Axisymmetric Rotational Flow of Dusty Elastico Viscous Liquid
Directory of Open Access Journals (Sweden)
G. C. Mandal
1990-04-01
Full Text Available This paper reports the flow of elastico-viscous liquid embedded with particles in an oscillating cylinder. Explicit expressions are obtained for the velocities of liquid and dust particles by the technique of Laplace transforms. Numerical computations of the velocity fields are carried out for different values of mass concentration and relaxation time of the dust particles and varying elastic elements in the liquid.
Modeling the Material Flow and Heat Transfer in Reverse Dual-Rotation Friction Stir Welding
Shi, L.; Wu, C. S.; Liu, H. J.
2014-08-01
Reverse dual-rotation friction stir welding (RDR-FSW) is a novel modification of conventional friction stir welding (FSW) process. During the RDR-FSW process, the tool pin and the assisted shoulder are separated and rotate with opposite direction independently, so that there are two material flows with reverse direction. The material flow and heat transfer in RDR-FSW have significant effects on the microstructure and properties of the weld joint. A 3D model is developed to quantitatively analyze the effects of the separated tool pin and the assisted shoulder which rotate in reverse direction on the material flow and heat transfer during RDR-FSW process. Numerical simulation is conducted to predict the temperature profile, material flow field, streamlines, strain rate, and viscosity distributions near the tool. The calculated results show that as the rotation speed of the tool pin increases, the temperature near the tool gets higher, the zone with higher temperature expands, and approximately symmetric temperature distribution is obtained near the tool. Along the workpiece thickness direction, the calculated material flow velocity and its layer thickness near the tool get lowered because the effect of the shoulder is weakened as the distance away from the top surface increases. The model is validated by comparing the predicted values of peak temperature at some typical locations with the experimentally measured ones.
Pettigrew, M. J.; Zhang, C.; Mureithi, N. W.; Pamfil, D.
2005-05-01
Two-phase cross-flow exists in many shell-and-tube heat exchangers. A detailed knowledge of the characteristics of two-phase cross-flow in tube bundles is required to understand and formulate flow-induced vibration parameters such as damping, fluidelastic instability, and random excitation due to turbulence. An experimental program was undertaken with a rotated-triangular array of cylinders subjected to air/water flow to simulate two-phase mixtures. The array is made of relatively large diameter cylinders (38 mm) to allow for detailed two-phase flow measurements between cylinders. Fiber-optic probes were developed to measure local void fraction. Local flow velocities and bubble diameters or characteristic lengths of the two-phase mixture are obtained by using double probes. Both the dynamic lift and drag forces were measured with a strain gauge instrumented cylinder.
The effect of magnetic field on mean flow generation by rotating two-dimensional convection
Currie, Laura K
2016-01-01
Motivated by the significant interaction of convection, rotation and magnetic field in many astrophysical objects, we investigate the interplay between large-scale flows driven by rotating convection and an imposed magnetic field. We utilise a simple model in two dimensions comprised of a plane layer that is rotating about an axis inclined to gravity. It is known that this setup can result in strong mean flows; we numerically examine the effect of an imposed horizontal magnetic field on such flows. We show that increasing the field strength in general suppresses the time-dependent mean flows, but in some cases it organises them leading to stronger time-averaged flows. Further, we discuss the effect of the field on the correlations responsible for driving the flows and the competition between Reynolds and Maxwell stresses. A change in behaviour is observed when the (fluid and magnetic) Prandtl numbers are decreased. In the smaller Prandtl number regime, it is shown that significant mean flows can persist even ...
Hall Effects on Unsteady Hydromagnetic Flow Past an Accelerated Porous Plate in a Rotating System
Directory of Open Access Journals (Sweden)
Sanatan Das
2015-01-01
Full Text Available An unsteady hydromagnetic flow of a viscous incompressible electrically conducting fluid past an accelerated porous flat plate in the presence of a uniform transverse magnetic field in a rotating system taking the Hall effects into account have been presented. An analytical solution describing the flow at large and small times after the start is obtained by the use of Laplace transform technique. The influences of the physical parameters acting on the flow are discussed in detail with the help of several graphs. It is found that interplay of Coriolis force and hydromagnetic force in the presence of Hall currents plays an important role in characterizing the flow behavior.
Euler-like modelling of dense granular flows: application to a rotating drum
Bonamy, D.; Chavanis, P.-H.; Cortet, P.-P.; Daviaud, F.; Dubrulle, B.; Renouf, M.
2009-04-01
General conservation equations are derived for 2D dense granular flows from the Euler equation within the Boussinesq approximation. In steady flows, the 2D fields of granular temperature, vorticity and stream function are shown to be encoded in two scalar functions only. We checked such prediction on steady surface flows in a rotating drum simulated through the Non-Smooth Contact Dynamics method even though granular flows are dissipative and therefore not necessarily compatible with Euler equation. Finally, we briefly discuss some possible ways to predict theoretically these two functions using statistical mechanics.
Experimental and numerical investigation of the flow in rotating diverging channels
van den Braembussche, R. A.; Prinsier, J.; di Sante, A.
2010-04-01
This paper reports on an experimental and numerical study at low Reynolds number in order to evaluate the influence of the Coriolis forces on the flow in radial rotating channels. Operating conditions correspond to the flow in radial impellers for micro gasturbine applications. A comparison of detailed flow measurements with CFD results indicates that Navier Stokes solvers with standard k-ω and SST turbulence models predict the flow surprisingly well and that no extra corrections for Coriolis forces are required at these operating conditions
Stationary instability of an axiosymmetric fluid flow in a rotating magnetic field
Energy Technology Data Exchange (ETDEWEB)
Kapusta, A.B.; Zibol' d, A.F.
1977-07-01
A study is made in a noninduction approximation of the effect that the profile deformation of a primary velocity and the interactions between secondary flows and a primary magnetic field have on the stationary instability of an axiosymmetric fluid flow in a rotating magnetic field. The critical state was shown to be determined by two or three independent criteria. Two regions of absolute primary flow stability were identified, and the critical values for the Reynolds number for these regions were calculated. Profiles of velocity perturbances and secondary flow lines were constructed for various sets of values. 6 references, 3 figures, 2 tables.
Drag and Lift Force Acting on a Rotational Spherical Particle in a Logarithmic Boundary Flow
Institute of Scientific and Technical Information of China (English)
XU Wei-jiang; CHE De-fu; XU Tong-mo
2006-01-01
The drag and lift forces acting on a rotational spherical particle in a logarithmic boundary flow are numerically studied. The effects of the drag velocity and rotational speed of the sphere on the drag force are examined for the particle Reynolds number from 50 to 300 and for the dimensionless rotational angular speed of 0≤Ω≤1.0. The influence of dimensionless roughness height z0of the wall is also evaluated for z0≤10. The results show that the drag forces on a sphere both in a logarithmic flow and in a uniform unsheared flow increase with the increase of the drag velocity. For 50≤Rep≤300, the drag coefficient (-C)D increases with decreased roughness height z0. The time-averaged drag coefficient is also significantly affected by rotational speed of the sphere and roughness height z0 . The lift coefficient -CL increases with increased rotational speed and decreases with increased roughness height.
Zero absolute vorticity: insight from experiments in rotating laminar plane Couette flow.
Suryadi, Alexandre; Segalini, Antonio; Alfredsson, P Henrik
2014-03-01
For pressure-driven turbulent channel flows undergoing spanwise system rotation, it has been observed that the absolute vorticity, i.e., the sum of the averaged spanwise flow vorticity and system rotation, tends to zero in the central region of the channel. This observation has so far eluded a convincing theoretical explanation, despite experimental and numerical evidence reported in the literature. Here we show experimentally that three-dimensional laminar structures in plane Couette flow, which appear under anticyclonic system rotation, give the same effect, namely, that the absolute vorticity tends to zero if the rotation rate is high enough. It is shown that this is equivalent to a local Richardson number of approximately zero, which would indicate a stable condition. We also offer an explanation based on Kelvin's circulation theorem to demonstrate that the absolute vorticity should remain constant and approximately equal to zero in the central region of the channel when going from the nonrotating fully turbulent state to any state with sufficiently high rotation.
Turbulent Compressible Convection with Rotation. Part 1; Flow Structure and Evolution
Brummell, Nicholas H.; Hurlburt, Neal E.; Toomre, Juri
1996-01-01
The effects of Coriolis forces on compressible convection are studied using three-dimensional numerical simulations carried out within a local modified f-plane model. The physics is simplified by considering a perfect gas occupying a rectilinear domain placed tangentially to a rotating sphere at various latitudes, through which a destabilizing heat flux is driven. The resulting convection is considered for a range of Rayleigh, Taylor, and Prandtl (and thus Rossby) numbers, evaluating conditions where the influence of rotation is both weak and strong. Given the computational demands of these high-resolution simulations, the parameter space is explored sparsely to ascertain the differences between laminar and turbulent rotating convection. The first paper in this series examines the effects of rotation on the flow structure within the convection, its evolution, and some consequences for mixing. Subsequent papers consider the large-scale mean shear flows that are generated by the convection, and the effects of rotation on the convective energetics and transport properties. It is found here that the structure of rotating turbulent convection is similar to earlier nonrotating studies, with a laminar, cellular surface network disguising a fully turbulent interior punctuated by vertically coherent structures. However, the temporal signature of the surface flows is modified by inertial motions to yield new cellular evolution patterns and an overall increase in the mobility of the network. The turbulent convection contains vortex tubes of many scales, including large-scale coherent structures spanning the full vertical extent of the domain involving multiple density scale heights. Remarkably, such structures align with the rotation vector via the influence of Coriolis forces on turbulent motions, in contrast with the zonal tilting of streamlines found in laminar flows. Such novel turbulent mechanisms alter the correlations which drive mean shearing flows and affect the
Effects of Rotation and Relativistic Charge Flow on Pulsar Magnetospheric Structure
Muslimov, A G; Muslimov, Alex G.; Harding, Alice K.
2005-01-01
We propose an analytical 3-D model of the open field-line region of a neutron star (NS) magnetosphere. We construct an explicit analytic solution for arbitrary obliquity (angle between the rotation and magnetic axes) incorporating the effects of magnetospheric rotation, relativistic flow of charges (e.g. primary electron beam) along the open field lines, and E X B drift of these charges. Our solution employs the space-charge-limited longitudinal current calculated in the electrodynamic model of Muslimov & Tsygan (1992) and is valid up to very high altitudes nearly approaching the light cylinder. We assume that in the innermost magnetosphere, the NS magnetic field can be well represented by a static magnetic dipole configuration. At high altitudes the open magnetic field lines significantly deviate from those of a static dipole and tend to focus into a cylindrical bundle, swept back in the direction opposite to the rotation, and also bent towards the rotational equator. We briefly discuss some implications...
Heat Transfer and Flows of Thermal Convection in a Fluid-Saturated Rotating Porous Medium
Directory of Open Access Journals (Sweden)
Jianhong Kang
2015-01-01
Full Text Available Thermal convection at the steady state for high Rayleigh number in a rotating porous half space is investigated. Taking into account the effect of rotation, Darcy equation is extended to incorporate the Coriolis force term in a rotating reference frame. The velocity and temperature fields of thermal convection are obtained by using the homotopy analysis method. The influences of Taylor number and Rayleigh number on the Nusselt number, velocity profile, and temperature distribution are discussed in detail. It is found that the Nusselt number decreases rapidly with the increase of Taylor number but tends to have an asymptotic value. Besides, the rotation can give rise to downward flow in contrast with the upward thermal convection.
Forced convection of power-law fluids flow over a rotating nonisothermal body
Kim, H. W.; Essemyi, A. J.
1993-10-01
Presented is an analysis of steady laminar flow of power-law fluids past a rotating body with nonisothermal surfaces. A coordinate transformation combined with the Merk-type series expansion is employed to transform the governing momentum equations into a set of coupled ordinary differential equations. The equations are numerically integrated to obtain the axial and tangential velocity gradients for determining the friction coefficient. For forced convection, a generalized coordinate transformation is used to analyze the temperature field of the power-law flow. Solutions to the transformed energy equations are obtained in the form of universal functions. The heat transfer coefficients in terms of NuRe(sup 1/(n + 1)) are presented for a rotating sphere. The effects of power-law index, rotation sphere, Prandtl number, and the location of step discontinuity in surface temperature on the local Nusselt number are fully investigated and demonstrated.
Thermocapillary bubble flow and coalescence in a rotating cylinder: A 3D study
Alhendal, Yousuf; Turan, A.; Al-mazidi, M.
2015-12-01
The process of thermocapillary bubbles rising in a rotating 3D cylinder in zero gravity was analysed and presented numerically with the aid of computational fluid dynamics (CFD) by means of the volume of fluid (VOF) method. Calculations were carried out to investigate in detail the effect of the rotational speed of the hosted liquid on the trajectory of both single and group bubbles driven by the Marangoni force in zero-gravity conditions. For rotational speeds from 0.25 to 2 rad/s, bubble displacement with angular motion was found to be directed between the hotter surface and the rotational axis. This is contrary to the conventional bubble flow from areas of high pressure to low pressure, radial direction, or from cold to hot regions, axial direction. The results demonstrate that for the ratio of rotational speeds to the thermocapillary bubble velocity larger than unity, the surface tension gradient is the dominant force and the bubble motion towards the hotter. On the other hand, for ratio less than 1, the bubble motion is dominated and is significantly affected by centrifugal force. As rotation speed increases, the amount of deflection increases and the Marangoni effect vanishes. The current study is novel in the sense that single- and multi-bubble motion incorporating thermocapillary forces in a rotating liquid in a zero-gravity environment has never been numerically investigated.
Hydrodynamic instabilities in the developing region of an axially rotating pipe flow
Energy Technology Data Exchange (ETDEWEB)
Miranda-Barea, A; Fabrellas-García, C; Parras, L; Pino, C del, E-mail: cpino@uma.es [Universidad de Málaga, Escuela Técnica Superior de Ingeniería Industrial, Ampliación Campus de Teatinos, 29071, Málaga, España (Spain)
2015-06-15
We conduct experiments in a rotating Hagen–Poiseuille flow (RHPF) through flow visualizations when the flow becomes convectively and absolutely unstable at low-to-moderate Reynolds numbers, Re. We characterize periodic patterns at a very high swirl parameter, L, when the flow overcomes the absolutely unstable region. These non-steady helical filaments wrapped around the axis appear in the developing region of the pipe. Experimentally, we compute the onset of these oscillations in the (L, Re)-plane finding that the rotation rate decreases as the Reynolds number increases in the process of achieving the time-dependent state. Additionally, we report information regarding frequencies and wavelengths that appear downstream of the rotating pipe for convectively and absolutely unstable flows, even for very high swirl parameters at which the flow becomes time-dependent in the developing region. We do not observe variations in the trends of these parameters, so these hydrodynamic instabilities in the developing region do not affect the unstable travelling waves downstream of the pipe. (paper)
Torque scaling in turbulent Taylor–Couette flow between independently rotating cylinders
Eckhardt, Bruno; Grossmann, Siegfried; Lohse, Detlef
2007-01-01
Turbulent Taylor–Couette flow with arbitrary rotation frequencies ω1, ω2 of the two coaxial cylinders with radii r1 < r2 is analysed theoretically. The current Jω of the angular velocity ω(x,t) = u(r,,z,t)/r across the cylinder gap and and the excess energy dissipation rate w due to the turbulent, c
Numerical study of swirling flow in a cylinder with rotating top and bottom
DEFF Research Database (Denmark)
Shen, Wen Zhong; Sørensen, Jens Nørkær; Michelsen, Jess
2006-01-01
A numerical investigation of oscillatory instability is presented for axisymmetric swirling flow in a closed cylinder with rotating top and bottom. The critical Reynolds number and frequency of the oscillations are evaluated as function of the ratio of angular velocities of the bottom and the top...
Two-Phase Flow in Rotating Hele-Shaw Cells with Coriolis Effects
Escher, Joachim; Walker, Christoph
2011-01-01
The free boundary problem of a two phase flow in a rotating Hele-Shaw cell with Coriolis effects is studied. Existence and uniqueness of solutions near spheres is established, and the asymptotic stability and instability of the trivial solution is characterized in dependence on the fluid densities.
Torque scaling in turbulent Taylor-Couette flow between independentely rotating cylinders
Eckhardt, Bruno; Grossmann, Siegfried; Lohse, Detlef
2007-01-01
Turbulent Taylor–Couette flow with arbitrary rotation frequencies ω1, ω2 of the two coaxial cylinders with radii r1 < r2 is analysed theoretically. The current Jω of the angular velocity ω(x,t) = u(r,,z,t)/r across the cylinder gap and and the excess energy dissipation rate w due to the turbulent, c
An analogy of Taylor's instability criterion in Couette and rotating-magnetic-field-driven flows
Ungarish, Marius
2012-01-01
The classical stability solution of Taylor for the Couette flow between a rotating inner cylinder and a stationary outer cylinder is used to model the "critical magnetic Taylor number," Tacr, in a flow of a liquid metal driven by a rotating magnetic field (RMF) in a cylindrical cavity characterized by the parameter H = height/radius. (The magnetic Taylor number is defined as Ta =σωBo2Ro4/(2ρν2), where σ ,ν, and ρ are the electrical conductivity, kinematic viscosity, and density of the liquid; ω and Bo are the magnetic field frequency and induction; Ro is the radius of the cavity; the cr superscript means "critical") In typical conditions, the RMF flow develops a solid-body-rotating core analogous to the inner rotating cylinder, embedded in a layer in which the swirl decays to zero at the outer wall. Using small-Ekman-number approximations for the core and gap flow, the analogy yields an insightful expression for Tacr. In particular, the model indicates that Tacr depends strongly on the parameter H. Comparisons of the present theoretical results with available realistic data show a good qualitative agreement and plausible quantitative agreement. The model was improved by an empirical adjustment of a coefficient and can be used as simple approximate prediction tool for Tacr in a quite wide range of cylindrical cavity configurations.
Experimental study of monodisperse granular flow through an inclined rotating chute
Shirsath, S.S.; Padding, J.T.; Deen, N.G.; Clercx, H.J.H.; Kuipers, J.A.M.
2013-01-01
In blast furnaces, particles like coke, sinter and pellets enter from a hopper and are distributed on the burden surface by a rotating chute. Such particulate flows suffer occasionally from particle segregation during transportation caused by differences in density or size. To get a more fundamental
Numerical investigation of monodisperse granular flow through an inclined rotating chute
Shirsath, Sushil S.; Padding, Johan T.; Kuipers, J.A.M. (Hans); Peeters, Tim W.J.; Clercx, Herman J.H.
2014-01-01
A discrete element model of spherical glass particles flowing down a rotating chute is validated against high quality experimental data. The simulations are performed in a corotating frame of reference, taking into account Coriolis and centrifugal forces. In view of future extensions aimed at segreg
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.
Mondal, Rabindra Nath; Roy, Titob; Shaha, Poly Rani; Yanase, Shinichiro
2016-07-01
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.
Simulations of turbulent flow between a rotating and a stationary disk
Energy Technology Data Exchange (ETDEWEB)
Lygren, Magne
2001-07-01
The main focus of this thesis is turbulent flow between a rotating and a stationary disk. The extension of the disks is assumed to be large enough to prevent the outer boundary conditions to influence the flow at the region of interest. This flow is driven by the shear between the disks, but an imbalance between centrifugal and pressure forces in the radial direction induces a radial cross flow. The result is a complex three-dimensional flow where the direction of the mean flow varies with the axial position. Direct numerical simulations (DNS) and large eddy simulations (LES) have been used to investigate the flow. The simulations utilised a special set of quasi-periodic boundary conditions which allowed the use of a computational domain which captured only a section of the flow. Locally, the disk flow is characterised by a rotational Reynolds number and a local gap ratio of 0.02. Turbulence statistics were compared to results from the turbulent plane Couette flow and from an experimental investigation of an enclosed rotor-stator flow. The plane Couette flow is a two-dimensional equivalence to the flow between the disks. Although the turbulence statistics had many similarities in the two cases, there were differences caused by three-dimensionality of the mean-flow in the disk case. In the disk flow the direction of the Reynolds shear stress vector was not aligned with the mean-gradient vector and the ratio of the magnitude of the shear stress vector to the mean turbulent kinetic energy was reduce compared to the Couette flow. The flow between the disks statistically stationary. It is therefore a suitable case for studying effects of mean-flow three-dimentionality on the underlying coherent structures in the boundary layers. Ensemble averages, probability-density functions and a quadrant analysis of conditional averages in the regions near the disks were performed in order to study the coherent quasistreamwise vortices. By comparing with corresponding conditional
Oliveira, L. A.; Pecheux, J.; Restivo, A. O.
1991-06-01
The rotating flow between coaxial disks in a radially confined geometry is studied by numerical integration of the full Navier-Stokes equations. The results indicate that both Batchelor's and Stewartson's flow structures can be observed near the axis of rotation, depending on what conditions are set at the peripheral boundary.
Experimental investigation of three-dimensional flow instabilities in a rotating lid-driven cavity
DEFF Research Database (Denmark)
Sørensen, Jens Nørkær; Naumov, I.; Mikkelsen, Robert Flemming
2006-01-01
The flow between a rotating lid and a stationary cylinder is studied experimentally. The flow is governed by two parameters: The ratio of container height to disk radius, h, and the Reynolds number, Re, based on the disk angular velocity, cylinder radius and kinematic viscosity of the working...... liquid. For the first time the onset of three-dimensionality and transition are analysed by combining the high spatial resolution of Particle Image Velocimetry (PIV) and the temporal accuracy of Laser Doppler Anemometry (LDA). A detailed mapping of the transition from steady and axisymmetric flow...
On the inverse Magnus effect for flow past a rotating cylinder
John, Benzi; Gu, Xiao-Jun; Barber, Robert W.; Emerson, David R.
2016-11-01
Flow past a rotating cylinder has been investigated using the direct simulation Monte Carlo method. The study focuses on the occurrence of the inverse Magnus effect under subsonic flow conditions. In particular, the variations in the coefficients of lift and drag have been investigated as a function of the Knudsen and Reynolds numbers. Additionally, a temperature sensitivity study has been carried out to assess the influence of the wall temperature on the computed aerodynamic coefficients. It has been found that both the Reynolds number and the cylinder wall temperature significantly affect the drag as well as the onset of lift inversion in the transition flow regime.
Accelerated micropolar fluid--flow past an uniformly rotating circular cylinder
Siddiqui, Abuzar Abid
2016-01-01
In this paper, we formulated the non-steady flow due to the uniformly accelerated and rotating circular cylinder from rest in a stationary, viscous, incompressible and micropolar fluid. This flow problem is examined numerically by adopting a special scheme comprising the Adams-Bashforth Temporal Fourier Series method and the Runge-Kutta Temporal Special Finite-Difference method. This numerical scheme transforms the governing equation for micropolar fluids for this problem into system of finite-difference equations. This system was further solved numerically by point SOR-method. These results were also further extrapolated by the Richardson extrapolation method. This scheme is valid for all values of the flow and fluid-parameters and for all time. Moreover the boundary conditions of the vorticity and the spin at points far from the cylinder are being imposed and encountered too. The results are compared with existing results (for non-rotating circular cylinder in Newtonian fluids). The comparison is good. The ...
Laboratory Studies of the Stratified Rotating Flow Passing over an Isolated Obstacle
Institute of Scientific and Technical Information of China (English)
高守亭; 平凡
2003-01-01
We study the flow of a density-stratified fluid passing over an isolated obstacle, using towing-tank experiments.Our special concern is the response of the flow with different Froude numbers passing over a three-dimensional obstacle. A series of experiments of the stratified rotating flow passing over an isolated obstacle was carried out with the towering-tank controlled by the similarity laws and dynamic non-dimension parameters. These experiments show that the Froude number is a very important parameter, and the lee wave and the eddy structure appear simultaneously under an appropriate conditions. The effect of rotation on the lee wave is mainly to change wave amplitude, particularly to restrain the development of the lee wave and to promote the formation of an eddy.
Directory of Open Access Journals (Sweden)
Oluwole D. Makinde
2015-11-01
Full Text Available In this paper, we employed both first and second laws of thermodynamics to analyze the flow and thermal decomposition in a variable viscosity Couette flow of a conducting fluid in a rotating system under the combined influence of magnetic field and Hall current. The non-linear governing differential equations are obtained and solved numerically using shooting method coupled with fourth order Runge–Kutta–Fehlberg integration technique. Numerical results obtained for velocities and temperature profiles are utilized to determine the entropy generation rate, skin fictions, Nusselt number and the Bejan number. By plotting the graphs of various values of thermophysical parameters, the features of the flow characteristics are analyzed in detail. It is found that fluid rotation increases the dominant effect of heat transfer irreversibility at the upper moving plate region while the entropy production is more at the lower fixed plate region.
Wave-front propagation of rinsing flows on rotating semiconductor wafers
Frostad, John M.; Ylitalo, Andy; Walls, Daniel J.; Mui, David S. L.; Fuller, Gerald G.
2016-11-01
The semiconductor manufacturing industry is migrating to a cleaning technology that involves dispersing cleaning solutions onto a rotating wafer, similar to spin-coating. Advantages include a more continuous overall fabrication process, lower particle level, no cross contamination from the back side of a wafer, and less usage of harsh chemicals for a lower environmental impact. Rapid rotation of the wafer during rinsing can be more effective, but centrifugal forces can pull spiral-like ribbons of liquid radially outward from the advancing wave-front where particles can build up, causing higher instances of device failure at these locations. A better understanding of the rinsing flow is essential for reducing yield losses while taking advantage of the benefits of rotation. In the present work, high-speed video and image processing are used to study the dynamics of the advancing wave-front from an impinging jet on a rotating substrate. The flow-rate and rotation-speed are varied for substrates coated with a thin layer of a second liquid that has a different surface tension than the jet liquid. The difference in surface tension of the two fluids gives rise to Marangoni stresses at the interface that have a significant impact on the rinsing process, despite the extremely short time-scales involved.
Raju, C. S. K.; Sandeep, N.
2017-01-01
In this study, we investigated the momentum and heat transfer characteristics of Casson nanofluid flow over a rotating cone in a rotating frame filled with water based CoFe2O4 nano particles. Heat flux conditions and wall temperature conditions are very important in controlling of up and down heat transport phenomena's in industrial as well as engineering application. Resulting set of coupled nonlinear governing equations are solved numerically using Runge-Kutta based shooting technique. In graphical results we presented dual solutions for the prescribed wall temperature (PWT) and prescribed heat flux (PHF) cases. The effect of governing parameters on velocity and temperature fields along with the skin friction coefficient and the heat transfer rate are presented with the help of graphs and tables. Results indicate that the rising values of the volume fraction of ferro particles and buoyancy parameter have tendency to improve the skin friction coefficient as well as the heat transfer rate for both the prescribed wall temperature (PWT) and prescribed heat flux (PHF) cases.
Near-Wall Turbulence Modelling of Rotating and Curved Shear Flows
Energy Technology Data Exchange (ETDEWEB)
Pettersson, Bjoern Anders
1997-12-31
This thesis deals with verification and refinement of turbulence models within the framework of the Reynolds-averaged approach. It pays special attention to modelling the near-wall region, where the turbulence is strongly non-homogeneous and anisotropic. It also studies in detail the effects associated with an imposed rotation of the reference frame or streamline curvature. The objective with near-wall turbulence closure modelling is to formulate a set of equations governing single point turbulence statistics, which can be solved in the region of the flow which extends to the wall. This is in contrast to the commonly adopted wall-function approach in which the wall-boundary conditions are replaced by matching conditions in the logarithmic region. The near-wall models allow more flexibility by not requiring any such universal behaviour. Assessment of the novel elliptic relaxation approach to model the proximity of a solid boundary reveals an encouraging potential used in conjunction with second-moment and eddy-viscosity closures. The most natural level of closure modelling to predict flows affected by streamline curvatures or an imposed rotation of the reference frame is at the second-moment closure (SMC) level. Although SMCs naturally accounts for the effects of system rotation, the usual application of a scalar dissipation rate equation is shown to require ad hoc corrections in some cases in order to give good results. The elliptic relaxation approach is also used in conjunction with non-linear pressure-strain models and very encouraging results are obtained for rotating flows. Rotational induced secondary motions are vital to predicting the effects of system rotation. Some severe weaknesses of non-linear pressure-strain models are also indicated. Finally, a modelling methodology for anisotropic dissipation in nearly homogeneous turbulence are proposed. 84 refs., 56 figs., 16 tabs.
The Rolling Transition in a Granular Flow along a Rotating Wall
Directory of Open Access Journals (Sweden)
Aurélie Le Quiniou
2011-11-01
Full Text Available The flow of a dry granular material composed of spherical particles along a rotating boundary has been studied by the discrete element method (DEM. This type of flow is used, among others, as a process to spread particles. The flow consists of several phases. A compression phase along the rotating wall is followed by an elongation of the flow along the same boundary. Eventually, the particles slide or roll independently along the boundary. We show that the main motion of the flow can be characterized by a complex deformation rate of traction/compression and shear. We define numerically an effective friction coefficient of the flow on the scale of the continuum and show a strong decrease of this effective friction beyond a certain critical friction coefficient μ*. We correlate this phenomenon with the apparition of a new transition from a sliding regime to a rolling without sliding regime that we called the rolling transition; this dynamic transition is controlled by the value of the friction coefficient between the particle and the wall. We show that the spherical shape for the particles may represent an optimum for the flow in terms of energetic.
Numerical Study of Transonic Axial Flow Rotating Cascade Aerodynamics – Part 1: 2D Case
Directory of Open Access Journals (Sweden)
Irina Carmen ANDREI
2014-06-01
Full Text Available The purpose of this paper is to present a 2D study regarding the numerical simulation of flow within a transonic highly-loaded rotating cascade from an axial compressor. In order to describe an intricate flow pattern of a complex geometry and given specific conditions of cascade’s loading and operation, an appropriate accurate flow model is a must. For such purpose, the Navier-Stokes equations system was used as flow model; from the computational point of view, the mathematical support is completed by a turbulence model. A numerical comparison has been performed for different turbulence models (e.g. KE, KO, Reynolds Stress and Spallart-Allmaras models. The convergence history was monitored in order to focus on the numerical accuracy. The force vector has been reported in order to express the aerodynamics of flow within the rotating cascade at the running regime, in terms of Lift and Drag. The numerical results, expressed by plots of the most relevant flow parameters, have been compared. It comes out that the selecting of complex flow models and appropriate turbulence models, in conjunction with CFD techniques, allows to obtain the best computational accuracy of the numerical results. This paper aims to carry on a 2D study and a prospective 3D will be intended for the same architecture.
Flow between two stretchable rotating disks with Cattaneo-Christov heat flux model
Hayat, Tasawar; Qayyum, Sumaira; Imtiaz, Maria; Alsaedi, Ahmed
An analysis is performed to investigate flow between two stretchable rotating disks. Thermal equation is constructed by Cattaneo-Christov heat flux theory. Porous medium is also taken into account. The nonlinear partial differential equations are first converted to ordinary differential equations and then computed for the convergent series solutions. Discussion about impact of dimensionless parameters on velocities, temperature and skin friction coefficient is given. It is observed that the radial velocity at upper disk enhances for larger values of ratio of corresponding stretching rate to angular velocity. Velocity in y-direction decays with an increase in rotational parameter. Magnitude of temperature profile decays for larger Prandtl number and thermal relaxation parameter.
Tennakoon, S G K; Hegseth, J J; Riecke, H; Tennakoon, Sarath G. K.; Hegseth, John. J.; Riecke, Hermann
1996-01-01
The effect of temporal modulation on traveling waves in the flows in two distinct systems of rotating cylinders, both with broken azimuthal symmetry, has been investigated. It is shown that by modulating the control parameter at twice the critical frequency one can excite phase-locked standing waves and standing-wave-like states which are not allowed when the system is rotationally symmetric. We also show how previous theoretical results can be extended to handle patterns such as these, that are periodic in two spatial direction.
Wave Instabilities and Unidirectional Light Flow in a Cavity with Rotating Walls
Lannebère, Sylvain
2016-01-01
We investigate the conditions for the emergence of wave instabilities in a vacuum cavity delimited by cylindrical metallic walls in relative rotation. It is shown that for a small vacuum gap and for a rotation velocity exceeding a certain threshold, the interactions between the surface plasmon polaritons supported by each wall give rise to an unstable behavior of the electromagnetic field manifested in an exponential growth with time. The instabilities occur only for certain modes of oscillation and are due to the transformation of kinetic energy into electromagnetic energy. We also study the possibility of having asymmetric light flows and optical isolation relying on the relative motion of the cavity walls.
Combined effect of free and forced convection on MHD flow in a rotating porous channel
Directory of Open Access Journals (Sweden)
D. R. V. Prasada Rao
1982-01-01
Full Text Available This paper gives a steady linear theory of the combined effect of the free and forced convection in rotating hydromagnetic viscous fluid flows in a porous channel under the action of a uniform magnetic field. The flow is governed by the Grashof number G, the Hartmann number H, the Ekman number E, and the suction Reynolds number S. The solutions for the velocity field, temperature distribution, magnetic field, mass rate of flow and the shear stresses on the channel boundaries are obtained using a perturbation method with the small parameter S. The nature of the associated boundary layers is investigated for various values of the governing flow parameters. The velocity, the temperature, and the shear stresses are discussed numerically by drawing profiles with reference to the variations in the flow parameters.
Flow behavior inside a novel rotating fluidized bed for solar gasification of biomass
Lu, Zhao; Jafarian, Mehdi; Chinnici, Alfonso; Arjomandi, Maziar; Nathan, Graham J.
2017-06-01
The present paper reports a numerical investigation of the iso-thermal flow field and particle deposition onto the reactor window of a novel concept of Rotating Fluidized Bed Solar Reactor (RFBSR) and their sensitivity to reactor inner diameter. The RFBSR differs from conventional fluidized bed solar reactors in that it relies on the centrifugal force generated through rotation to counteract the drag force produced by the fluidizing gas on the particles. A three dimensional Computational Fluid Dynamics (CFD) model of the RFBSR was developed and combined with a Lagrangian particle tracking model to investigate the flow velocity components at various locations and particle concentration onto the window surface. The CFD model was partially verified by comparing its predictions with the published experimental measurements in a rotating porous cylindrical vessel with a radially injected flow. It was found that the Baseline Reynold Stress Model (RSM BSL) produces more agreeable predictions with the experimental measurements than Re-Normalization Group (RNG) k-ɛ and k-ω Shear Stress Transport (SST) models. Also, it was found that for the reactor configurations investigated here, reducing the reactor diameter has the effects of increasing the core axial flow velocity and particle deposition onto the window. The results presented assist in developing an understanding of the operation of the RFBSR.
Directory of Open Access Journals (Sweden)
Cha'o-Kuang Chen
2009-01-01
Full Text Available The main object of this paper is to study the weakly nonlinear hydrodynamic stability of the thin Newtonian fluid flowing on a rotating circular disk. A long-wave perturbation method is used to derive the nonlinear evolution equation for the film flow. The linear behaviors of the spreading wave are investigated by normal mode approach, and its weakly nonlinear behaviors are explored by the method of multiple scales. The Ginzburg-Landau equation is determined to discuss the necessary condition for the existence of such flow pattern. The results indicate that the superctitical instability region increases, and the subcritical stability region decreases with the increase of the rotation number or the radius of circular disk. It is found that the rotation number and the radius of circular disk not only play the significant roles in destabilizing the flow in the linear stability analysis but also shrink the area of supercritical stability region at high Reynolds number in the weakly nonlinear stability analysis.
Generation of rotational flows in toroidally confined visco-resistive magnetohydrodynamics
Morales, Jorge; Bos, Wouter; Schneider, Kai; Montgomery, David
2015-11-01
We investigate by numerical simulation the generation of rotational flows in a toroid confining a conducting magnetofluid. A current is driven by the application of externally supported electric and magnetic fields. We show how the properties and intensity of the rotations are regulated by dimensionless numbers (Lundquist and viscous Lundquist) that contain the resistivity and viscosity of the magnetofluid. At the magnetohydrodynamic level (uniform mass density and incompressible magnetofluids), rotational flows appear in toroidal, driven MHD. The evolution of these flows with the transport coefficients, geometry, and safety factor are described. Two different toroidal geometries are considered, one with an up-down symmetric and the other with an asymmetric cross section. We show that there exists a fundamental difference between both studied cases: the volume-averaged angular momentum is zero for the symmetric case, while for the asymmetric cross section a finite volume-averaged angular momentum appears. We observe a breaking in the up-down symmetry of the flow and a toroidal preferred direction emerges.
The competition of convective and absolute instabilities in rotating-disk flow transition
Imayama, Shintaro; Alfredsson, P. Henrik; Lingwood, R. J.
2014-11-01
The main objective of this experimental study is to investigate laminar-turbulent transition mechanisms in the rotating-disk boundary-layer flow. Lingwood (1995) found that the flow becomes locally absolutely unstable above a critical Reynolds number and suggested that absolutely unstable travelling waves triggered nonlinearity leading to transition. However, the growth of convectively unstable stationary vortices is also a possible alternative route if the surface roughness of the disk is sufficiently large. The convectively unstable stationary vortices are attributed to an inviscid crossflow mechanism. Flow-visualization studies and hot-wire measurements of the rotating-disk boundary layer typically capture 28-32 stationary vortices in the transition regime (e.g. Imayama et al. 2014). The hot-wire measurements presented here were performed on a smooth glass disk with a diameter of 474 mm. To excite stationary vortices disk-shaped roughness elements with a diameter of 2 mm and a height of 5 micron were put on the disk at a radial position of 110 mm. In the presentation, the details of the convectively unstable stationary vortices in the rotating-disk boundary layer are shown and compared with travelling waves and similarities/differences in the turbulent transition discussed. This work is supported by the Swedish Research Council (VR) and the Linné FLOW Centre.
Three-dimensional coating and rimming flow: a ring of fluid on a rotating horizontal cylinder
Leslie, G. A.
2013-01-29
The steady three-dimensional flow of a thin, slowly varying ring of Newtonian fluid on either the outside or the inside of a uniformly rotating large horizontal cylinder is investigated. Specifically, we study \\'full-ring\\' solutions, corresponding to a ring of continuous, finite and non-zero thickness that extends all of the way around the cylinder. In particular, it is found that there is a critical solution corresponding to either a critical load above which no full-ring solution exists (if the rotation speed is prescribed) or a critical rotation speed below which no full-ring solution exists (if the load is prescribed). We describe the behaviour of the critical solution and, in particular, show that the critical flux, the critical load, the critical semi-width and the critical ring profile are all increasing functions of the rotation speed. In the limit of small rotation speed, the critical flux is small and the critical ring is narrow and thin, leading to a small critical load. In the limit of large rotation speed, the critical flux is large and the critical ring is wide on the upper half of the cylinder and thick on the lower half of the cylinder, leading to a large critical load. We also describe the behaviour of the non-critical full-ring solution and, in particular, show that the semi-width and the ring profile are increasing functions of the load but, in general, non-monotonic functions of the rotation speed. In the limit of large rotation speed, the ring approaches a limiting non-uniform shape, whereas in the limit of small load, the ring is narrow and thin with a uniform parabolic profile. Finally, we show that, while for most values of the rotation speed and the load the azimuthal velocity is in the same direction as the rotation of the cylinder, there is a region of parameter space close to the critical solution for sufficiently small rotation speed in which backflow occurs in a small region on the upward-moving side of the cylinder. © 2013
Banerjee, Ayan Kumar; Bhattacharya, Amitabh; Balasubramanian, Sridhar
2016-11-01
Laboratory experiments, with a rotating cylindrical annulus and thermal gradient in both radial and vertical directions (so that radial temperature difference decreases with the elevation), were conducted to study the convection dynamics and heat transport. Temperature data captured using thermocouples, combined with ANSYS Fluent simulation hinted at the co-existence of thermal plume and baroclinicity (inclined isotherms). Presence of columnar plume structure parallel to the rotation axis was found, which had a phase velocity and aided in vertical heat transport. Nusselt number (Nu) plotted as a function of Taylor number (Ta) showed the effect of rotation on heat transport in such systems, where the interplay of plumes and baroclinic waves control the scalar transport. Laser based PIV imaging at a single vertical plane also showed evidence of such flow structures.
Bakar, Nor Ashikin Abu; Bachok, Norfifah; Arifin, Norihan Md.
2017-08-01
The boundary layer flow and heat transfer in rotating nanofluid over a stretching sheet using Buongiorno model and thermophysical properties of nanoliquids is studied. Four types of nanoparticles, namely silver (Ag), copper (Cu), alumina (Al2O3) and titania (TiO2) are used in our analysis with water as the base fluid (Prandtl number, Pr = 6.2). The nonlinear partial differential equations are transformed into ordinary differential equations by using the similarity transformation. The numerical solutions of these equation is obtained using shooting method in Maple software. The numerical results is concentrated on the effects of nanoparticle volume fraction φ, Brownian motion Nb, thermophoresis Nt, rotation Ω and suction S parameters on the skin friction coefficient and heat transfer rate. Dual solutions are observed in a certain range of the rotating parameter.
Magnetohydrodynamic instabilities in rotating and precessing sheared flows: an asymptotic analysis.
Salhi, A; Lehner, T; Cambon, C
2010-07-01
Linear magnetohydrodynamic instabilities are studied analytically in the case of unbounded inviscid and electrically conducting flows that are submitted to both rotation and precession with shear in an external magnetic field. For given rotation and precession the possible configurations of the shear and of the magnetic field and their interplay are imposed by the "admissibility" condition (i.e., the base flow must be a solution of the magnetohydrodynamic Euler equations): we show that an "admissible" basic magnetic field must align with the basic absolute vorticity. For these flows with elliptical streamlines due to precession we undertake an analytical stability analysis for the corresponding Floquet system, by using an asymptotic expansion into the small parameter ε (ratio of precession to rotation frequencies) by a method first developed in the magnetoelliptical instabilities study by Lebovitz and Zweibel [Astrophys. J. 609, 301 (2004)]10.1086/420972. The present stability analysis is performed into a suitable frame that is obtained by a systematic change of variables guided by symmetry and the existence of invariants of motion. The obtained Floquet system depends on three parameters: ε , η (ratio of the cyclotron frequency to the rotation frequency) and χ=cos α, with α being a characteristic angle which, for circular streamlines, ε=0, identifies with the angle between the wave vector and the axis of the solid body rotation. We look at the various (centrifugal or precessional) resonant couplings between the three present modes: hydrodynamical (inertial), magnetic (Alfvén), and mixed (magnetoinertial) modes by computing analytically to leading order in ε the instabilities by estimating their threshold, growth rate, and maximum growth rate and their bandwidths as functions of ε, η, and χ. We show that the subharmonic "magnetic" mode appears only for η>square root of 5/2 and at large η (>1) the maximal growth rate of both the "hydrodynamic" and
Institute of Scientific and Technical Information of China (English)
MIRZAEISEFAT Sina; FERNANDES Antonio Carlos
2013-01-01
This work describes investigations performed on the interaction of uniform current and freely rotating plate about a fixed vertical axis. Fluttering and autorotation are two different motions that may occur during the flow induced rotation. The dimensional analysis proves that the motion in flow induced rotation motion is governed essentially by the dimensionless moment of inertia and Reynolds number. Certain combinations define the stability boundaries between fluttering and autorotation. Fluttering is oscillation of body about a vertical axis and the autorotation is a name given to the case when the body turns continuously about the vertical axis. First, the loads and moment coefficients are calculated by experiments and streamline theory for different angles of attack for a fixed flat plate. Then for dynamic case, a bifurcation diagram is presented based on experiments to classify different motion states of flow induced rotation. Finally, a dynamical model is proposed for stability analysis of flow induced rotation of a flat plate.
Dubrulle, B; Daviaud, F; Longaretti, P-Y; Richard, D; Zahn, J-P
2011-01-01
This paper provides a prescription for the turbulent viscosity in rotating shear flows for use e.g. in geophysical and astrophysical contexts. This prescription is the result of the detailed analysis of the experimental data obtained in several studies of the transition to turbulence and turbulent transport in Taylor-Couette flow. We first introduce a new set of control parameters, based on dynamical rather than geometrical considerations, so that the analysis applies more naturally to rotating shear flows in general and not only to Taylor-Couette flow. We then investigate the transition thresholds in the supercritical and the subcritical regime in order to extract their general dependencies on the control parameters. The inspection of the mean profiles provides us with some general hints on the mean to laminar shear ratio. Then the examination of the torque data allows us to propose a decomposition of the torque dependence on the control parameters in two terms, one completely given by measurements in the ca...
Modeling dynamic stall on wind turbine blades under rotationally augmented flow fields
Energy Technology Data Exchange (ETDEWEB)
Guntur, S. [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Schreck, S. [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Sorensen, N. N. [Technical Univ. of Denmark, Lyngby (Denmark); Bergami, L. [Technical Univ. of Denmark, Lyngby (Denmark)
2015-04-22
It is well known that airfoils under unsteady flow conditions with a periodically varying angle of attack exhibit aerodynamic characteristics different from those under steady flow conditions, a phenomenon commonly known as dynamic stall. It is also well known that the steady aerodynamic characteristics of airfoils in the inboard region of a rotating blade differ from those under steady two-dimensional (2D) flow conditions, a phenomenon commonly known as rotational augmentation. This paper presents an investigation of these two phenomena together in the inboard parts of wind turbine blades. This analysis is carried out using data from three sources: (1) the National Renewable Energy Laboratory’s Unsteady Aerodynamics Experiment Phase VI experimental data, including constant as well as continuously pitching blade conditions during axial operation, (2) data from unsteady Delayed Detached Eddy Simulations (DDES) carried out using the Technical University of Denmark’s in-house flow solver Ellipsys3D, and (3) data from a simplified model based on the blade element momentum method with a dynamic stall subroutine that uses rotationally augmented steady-state polars obtained from steady Phase VI experimental sequences, instead of the traditional 2D nonrotating data. The aim of this work is twofold. First, the blade loads estimated by the DDES simulations are compared to three select cases of the N sequence experimental data, which serves as a validation of the DDES method. Results show reasonable agreement between the two data in two out of three cases studied. Second, the dynamic time series of the lift and the moment polars obtained from the experiments are compared to those from the dynamic stall subroutine that uses the rotationally augmented steady polars. This allowed the differences between the stall phenomenon on the inboard parts of harmonically pitching blades on a rotating wind turbine and the classic dynamic stall representation in 2D flow to be
Electro/Magnetically Induced Controllable Rotation In Small-scale Liquid Flow
Amjadi, A; Sobhani, S O; Shirsavar, R
2013-01-01
We study all the possibilities of producing rotating flow in an incompressible fluid by electric and magnetic fields. We start with a general theoretical basis and look for different configurations and set-ups which electric/magnetic field and an electric current affect the vorticity of fluid resulting in rotation on liquid flow. We assume steady-state conditions and time-independent electric and magnetic fields as the external body torque. Regarding the theoretical basis, we propose three experimental set-ups in which by applying fields on a fluid, rotational vortices are produced: (a) a uniform electric field and a uniform electric current, (b) a uniform electric current and a non-uniform magnetic field, and (c) a non-uniform electric current and a uniform magnetic field. The first case has been reported in detail named "Liquid Film Motor". The two other cases are experimentally investigated here for a cubic an cylindrical cells. The rotational velocity patterns are obtained by PIV technique, and the result...
Effect of Shear Stress in Flow on Cultured Cell: Using Rotating Disk at Microscope
Directory of Open Access Journals (Sweden)
Haruka Hino
2016-08-01
Full Text Available An experimental system of the Couette type flow with a rotating disk has been designed to apply wall shear stress quantitatively on the cell culture at the microscopic observation in vitro. The shear stress on the wall is calculated with an estimated Couette type of the velocity profile between the rotating disk and the culture plate. The constant rotational speed (lower than 400 rpm produces the wall shear stress lower than 2 Pa. The rotating disk system is mounted on the stage of an inverted phase contrast microscope to observe the behavior of cells adhered on the plate under the shear flow. Two kinds of cells were used in the test: C2C12 (mouse myoblast cell line, and MC3T3-E1 (mouse osteoblast precursor cell line. The experiments show that C2C12 tends to make orientation diagonal to the stream line, and that MC3T3-E1 tends to make orientation parallel to the stream line. Deformation and exfoliation of cells can be observed under controlled wall shear stress by the experimental system.
Turbulent Taylor-Couette flow over riblets: drag reduction and the effect of bulk fluid rotation
Greidanus, A. J.; Delfos, R.; Tokgoz, S.; Westerweel, J.
2015-05-01
A Taylor-Couette facility was used to measure the drag reduction of a riblet surface on the inner cylinder. The drag on the surfaces of the inner and outer cylinders is determined from the measured torque when the cylinders are in exact counter-rotation. The three velocity components in the instantaneous flow field were obtained by tomographic PIV and indicate that the friction coefficients are strongly influenced by the flow regimes and structures. The riblet surface changes the friction at the inner-cylinder wall, which generates an average bulk fluid rotation. A simple model is proposed to distinguish drag changes due to the rotation effect and the riblet effect, as a function of the measured drag change and shear Reynolds number . An uncorrected maximum drag reduction of 5.3 % was found at that corresponds to riblet spacing Reynolds number . For these conditions, the model predicts an azimuthal bulk velocity shift of 1.4 %, which is confirmed by PIV measurements. This shift indicates a drag change due to a rotation effect of -1.9 %, resulting in a net maximum drag reduction of 3.4 %. The results correspond well with earlier reported results and demonstrate that the Taylor-Couette facility is a suitable and accurate measurement tool to characterize the drag performance of surfaces.
A RANS/DES Numerical Procedure for Axisymmetric Flows with and without Strong Rotation
Energy Technology Data Exchange (ETDEWEB)
Andrade, Andrew Jacob [Univ. of California, Davis, CA (United States)
2007-01-01
A RANS/DES numerical procedure with an extended Lax-Wendroff control-volume scheme and turbulence model is described for the accurate simulation of internal/external axisymmetric flow with and without strong rotation. This new procedure is an extension, from Cartesian to cylindrical coordinates, of (1) a second order accurate multi-grid, control-volume integration scheme, and (2) a k-ω turbulence model. This paper outlines both the axisymmetric corrections to the mentioned numerical schemes and the developments of techniques pertaining to numerical dissipation, multi-block connectivity, parallelization, etc. Furthermore, analytical and experimental case studies are presented to demonstrate accuracy and computational efficiency. Notes are also made toward numerical stability of highly rotational flows.
Analysis of laminar flow between stationary and rotating disks with inflow
Rohatgi, U.; Reshotko, E.
1974-01-01
The laminar flow between a rotating and a stationary disk with inflow was analyzed. Solutions to the dimensionless governing equations are sought by expanding each of the velocity components in powers of inverse radius. The equations to leading order are those for the configuration with no inflow. The subsequent orders yield sets of linear ordinary differential equations. Solutions are obtained for the first two of these subsequent orders. The solutions indicate that inflow tends to increase the magnitude of the azimuthal velocity in the flow between the two disks and to decrease the torque on the rotating disk. For Prandtl number one, an energy integral is obtained which relates the temperature distribution to the velocity distribution for all Reynolds numbers and therefore eliminates the needs for separate solution of the energy equation.
Directory of Open Access Journals (Sweden)
Ram Paras
2016-01-01
Full Text Available An attempt has been made to describe the effects of geothermal viscosity with viscous dissipation on the three dimensional time dependent boundary layer flow of magnetic nanofluids due to a stretchable rotating plate in the presence of a porous medium. The modelled governing time dependent equations are transformed a from boundary value problem to an initial value problem, and thereafter solved by a fourth order Runge-Kutta method in MATLAB with a shooting technique for the initial guess. The influences of mixed temperature, depth dependent viscosity, and the rotation strength parameter on the flow field and temperature field generated on the plate surface are investigated. The derived results show direct impact in the problems of heat transfer in high speed computer disks (Herrero et al. [1] and turbine rotor systems (Owen and Rogers [2].
Measuring the orientation and rotation rate of 3D printed particles in turbulent flow
Voth, Greg; Kramel, Stefan; Cole, Brendan
2015-03-01
The orientation distribution and rotations of anisotropic particles plays a key role in many applications ranging from icy clouds to papermaking and drag reduction in pipe flow. Experimental access to time resolved orientations of anisotropic particles has not been easy to achieve. We have found that 3D printing technology can be used to fabricate a wide range of particle shapes with smallest dimension down to 300 ?m. So far we have studied rods, crosses, jacks, tetrads, and helical shapes. We extract the particle orientations from stereoscopic video images using a method of least squares optimization in Euler angle space. We find that in turbulence the orientation and rotation rate of many particles can be understood using a simple picture of alignment of both the vorticity and a long axis of the particle with the Lagrangian stretching direction of the flow.
Review of fluid flow and convective heat transfer within rotating disk cavities with impinging jet
Harmand, Souad; Poncet, Sébastien; Shevchuk, Igor V; 10.1016/j.ijthermalsci.2012.11.009
2013-01-01
Fluid flow and convective heat transfer in rotor-stator configurations, which are of great importance in different engineering applications, are treated in details in this review. The review focuses on convective heat transfer in predominantly outward air flow in the rotor-stator geometries with and without impinging jets and incorporates two main parts, namely, experimental/theoretical methodologies and geometries/results. Experimental methodologies include naphthalene sublimation techniques, steady state (thin layer) and transient (thermochromic liquid crystals) thermal measurements, thermocouples and infra-red cameras, hot-wire anemometry, laser Doppler and particle image velocimetry, laser plane and smoke generator. Theoretical approaches incorporate modern CFD computational tools (DNS, LES, RANS etc). Geometries and results part being mentioned starting from simple to complex elucidates cases of a free rotating disk, a single disk in the crossflow, single jets impinging onto stationary and rotating disk,...
Two-dimensional nonstationary flow of a conducting fluid, induced by a rotating magnetic field
Energy Technology Data Exchange (ETDEWEB)
Kapusta, A.B.
1977-07-01
An examination is made of a full induction problem on the planar movement of a conducting fluid in a rotating magnetic field. The solution to this problem is sought by the method of degradation into Fourier series by harmonics of the rotating field. The initial system of partial differential equations is reduced to the system 2+1 of normal differential equations that bind the amplitudes of function harmonics and electrical vector potential. A solution to the problem for small anti ..omega.. was found with an accuracy up to the second approximation. The unsteadiness of flow was found to be manifested in a form of induced cross-sectional waves, traveling along the stream tubes of this flow at a speed that is equal to the phase velocity of the magnetic field. The appearance of wave effects is explained by considerations of symmetry. 5 references, 1 figure.
Co-rotational Oldroyd Fluid B Model for Spinning Flow of Liquid Crystalline Polymer
Institute of Scientific and Technical Information of China (English)
付强
2003-01-01
The relationship between the extensional viscosity and material parameters was studied through the analytical formulas of stress and extensional viscosity. The differential equations were solved to obtain the relationship between extensional viscosity and strain rates. The results obtained qualitatively agree with the experimental results. The study makes it practicable to simulate the rheologic behaviors of spinning flow of liquid crystalline polymer using co-rotational Oldroyd fluid B model.
Heat Transfer on Steady MHD rotating flow through porous medium in a parallel plate channel
Directory of Open Access Journals (Sweden)
Dr. G. Prabhakara Rao,
2015-04-01
Full Text Available We discussed the combined effects of radiative heat transfer and a transverse magnetic field on steady rotating flow of an electrically conducting optically thin fluid through a porous medium in a parallel plate channel and non-uniform temperatures at the walls. The analytical solutions are obtained from coupled nonlinear partial differential equations for the problem. The computational results are discussed quantitatively with the aid of the dimensionless parameters entering in the solution.
Flow of a Second Order Fluid Between Two Infinite Porous Rotating Disks
Directory of Open Access Journals (Sweden)
H. G. Sharma
1983-07-01
Full Text Available The flow of an incompressible second-order fluid between two infinite porous rotating disks has been studied with the assumption that the rate of injuction of the fluid at one disc is equal to the rate of suction at the other. The velocity components have been expressed in terms of three dimensionless functions, which in turn are obtained in ascending powers of the Reynold number (taken to be small, defined in terms of the angular velocities of the disks.
Numerical Modelling of Non-Newtonian Fluid in a Rotational Cross-Flow MBR
DEFF Research Database (Denmark)
Bentzen, Thomas Ruby; Ratkovich, Nicolas Rios; Rasmussen, Michael R.
2011-01-01
Fouling is the main bottleneck of the widespread of MBR systems. One way to decrease and/or control fouling is by process hydrodynamics. This can be achieved by the increase of liquid crossflow velocity. In rotational cross-flow MBR systems, this is attained by the spinning of e.g. impellers. Val...... as function of the angular velocity and the total suspended solids concentration....
Off-centered stagnation point flow of a couple stress fluid towards a rotating disk.
Khan, Najeeb Alam; Riaz, Fatima
2014-01-01
An investigation has been made to study the off-centered stagnation flow of a couple stress fluid over a rotating disk. The model developed for the governing problem in the form of partial differential equations has been converted to ordinary differential equations with the use of suitable similarity transformation. The analytical approximation has been made with the most promising analytical approach, homotopy analysis method (HAM). The convergence region of the obtained solution is determined and plotted. The effects of couple stress and nondimensional parameters have been observed on the flows of couple stress fluid. Also comparison has been made with the Newtonian fluid as the special case of considered problem.
Slip flow by a variable thickness rotating disk subject to magnetohydrodynamics
Imtiaz, Maria; Hayat, Tasawar; Alsaedi, Ahmed; Asghar, Saleem
Objective of the present study is to determine the characteristics of magnetohydrodynamic flow by a rotating disk having variable thickness. At the fluid-solid interface we consider slip velocity. The governing nonlinear partial differential equations of the problem are converted into a system of nonlinear ordinary differential equations. Obtained series solutions of velocity are convergent. Impact of embedded parameters on fluid flow and skin friction coefficient is graphically presented. It is observed that axial and radial velocities have an opposite impact on the thickness coefficient of disk. Also surface drag force has a direct relationship with Hartman number.
Locally-rotationally-symmetric Bianchi type-V cosmology with heat flow
Indian Academy of Sciences (India)
C P Singh; A Beesham
2009-10-01
In this paper we present a spatially homogeneous locally-rotationally-symmetric (LRS) Bianchi type-V cosmological model with perfect fluid and heat flow. A general approach is introduced to solve Einstein’s field equations using a law of variation for the mean Hubble parameter, which is related to average scale factor of the model that yields a constant value for the deceleration parameter. Exact solutions that correspond to singular and non-singular models are found with heat flow. The physical constraints on the solution and, in particular, the thermodynamical laws that govern such solutions are discussed in some detail.
Unsteady hydromagnetic Couette flow through a porous medium in a rotating system
Institute of Scientific and Technical Information of China (English)
无
2011-01-01
This paper investigates the unsteady hydromagnetic Couette fluid flow through a porous medium between two infinite horizontal plates induced by the non-torsional oscillations of one of the plates in a rotating system using boundary layer approximation.The fluid is assumed to be Newtonian and incompressible.Laplace transform technique is adopted to obtain a unified solution of the velocity fields.Such a flow model is of great interest,not only for its theoretical significance,but also for its wide applicatio...
Self-Similar Hot Accretion Flow onto a Rotating Neutron Star Structure and Stability
Medvedev, M V; Medvedev, Mikhail; Narayan, Ramesh
2001-01-01
We present analytical and numerical solutions which describe a hot, viscous, two-temperature accretion flow onto a rotating neutron star or any other rotating compact star with a surface. We assume Coulomb coupling between the protons and electrons, and free-free cooling from the electrons. Outside a thin boundary layer, where the accretion flow meets the star, we show that there is an extended settling region which is well-described by two self-similar solutions: (i) a two-temperature solution which is valid in an inner zone $r\\le10^{2.5}$ ($r$ is in Schwarzchild units), and (ii) a one-temperature solution at larger radii. In both zones, $\\rho\\propto r^{-2}, \\Omega\\propto r^{-3/2}, v\\propto r^0, T_p\\propto r^{-1}$; in the two-temperature zone, $T_e\\propto r^{-1/2}$. The luminosity of the settling zone arises from the rotational energy of the star as the star is braked by viscosity. Hence the luminosity and the flow parameters (density, temperature, angular velocity) are independent of $\\dot M$. The settling ...
Energy Technology Data Exchange (ETDEWEB)
Wang, W. X.; Hahm, T. S.; Ethier, S.; Rewoldt, G.; Tang, W. M.; Lee, W. W.; Diamond, P. H.
2011-03-20
Toroidal plasma flow driven by turbulent torque associated with nonlinear residual stress generation is shown to recover the observed key features of intrinsic rotation in experiments. Specifically, the turbulence-driven intrinsic rotation scales close to linearly with plasma gradients and the inverse of the plasma current, qualitatively reproducing empirical scalings obtained from a large experimental data base. The effect of magnetic shear on the symmetry breaking in the parallel wavenumber spectrum is identified. The origin of the current scaling is found to be the enhanced kll symmetry breaking induced by increased radial variation of the safety factor as the current decreases. The physics origin for the linear dependence of intrinsic rotation on the pressure gradient comes from the fact that both turbulence intensity and the zonal flow shear, which are two key ingredients for driving the residual stress, are increased with the strength of the turbulence drives, which are R/LTe and R/Lne for the collisionless trapped electron mode (CTEM). Highlighted results also include robust radial pinches in toroidal flow, heat and particle transport driven by CTEM turbulence, which emerge "in phase", and are shown to play important roles in determining plasma profiles. Also discussed are experimental tests proposed to validate findings from these gyrokinetic simulations.
Subgrid-scale models for large-eddy simulation of rotating turbulent flows
Silvis, Maurits; Trias, Xavier; Abkar, Mahdi; Bae, Hyunji Jane; Lozano-Duran, Adrian; Verstappen, Roel
2016-11-01
This paper discusses subgrid models for large-eddy simulation of anisotropic flows using anisotropic grids. In particular, we are looking into ways to model not only the subgrid dissipation, but also transport processes, since these are expected to play an important role in rotating turbulent flows. We therefore consider subgrid-scale models of the form τ = - 2νt S +μt (SΩ - ΩS) , where the eddy-viscosity νt is given by the minimum-dissipation model, μt represents a transport coefficient; S is the symmetric part of the velocity gradient and Ω the skew-symmetric part. To incorporate the effect of mesh anisotropy the filter length is taken in such a way that it minimizes the difference between the turbulent stress in physical and computational space, where the physical space is covered by an anisotropic mesh and the computational space is isotropic. The resulting model is successfully tested for rotating homogeneous isotropic turbulence and rotating plane-channel flows. The research was largely carried out during the CTR SP 2016. M.S, and R.V. acknowledge the financial support to attend this Summer Program.
Subramanian, S. V.; Bozzola, R.; Povinelli, L. A.
1986-01-01
The performance of a three dimensional computer code developed for predicting the flowfield in stationary and rotating turbomachinery blade rows is described in this study. The four stage Runge-Kutta numerical integration scheme is used for solving the governing flow equations and yields solution to the full, three dimensional, unsteady Euler equations in cylindrical coordinates. This method is fully explicit and uses the finite volume, time marching procedure. In order to demonstrate the accuracy and efficiency of the code, steady solutions were obtained for several cascade geometries under widely varying flow conditions. Computed flowfield results are presented for a fully subsonic turbine stator and a low aspect ratio, transonic compressor rotor blade under maximum flow and peak efficiency design conditions. Comparisons with Laser Anemometer measurements and other numerical predictions are also provided to illustrate that the present method predicts important flow features with good accuracy and can be used for cost effective aerodynamic design studies.
Kinematic Morphology of Large-scale Structure: Evolution from Potential to Rotational Flow
Wang, Xin; Aragon-Calvo, Miguel A; Neyrinck, Mark C; Eyink, Gregory L
2013-01-01
As an alternative way of describing the cosmological velocity field, we discuss the evolution of rotational invariants constructed from the velocity gradient tensor. Compared with the traditional divergence-vorticity decomposition, these invariants, defined as coefficients of characteristic equation of the velocity gradient tensor, enable a complete classification of all possible flow patterns in the dark-matter comoving frame, including both potential and vortical flows. Before shell-crossing, different categories of potential flow are highly associated with cosmic web structure, because of the coherent evolution of density and velocity. This correspondence is even preserved at some level when vorticity is generated after shell-crossing. The evolution from the potential to vortical flow can be traced continuously by these invariants. With the help of this tool, we show that the vorticity is generated in a particular way that is highly correlated with the large-scale structure. This includes a distinct spatia...
Liquid flow on a rotating disk prior to centrifugal atomization and spray deposition
Zhao, Y. Y.; Jacobs, M. H.; Dowson, A. L.
1998-12-01
Video observations of the flow patterns that develop on a rotating disk during centrifugal atomization and spray deposition, and subsequent metallographic studies conducted on solid skulls removed from the disk after processing, have indicated a circular discontinuity or hydraulic jump, which is manifested by a rapid increase in the thickness of the liquid metal and by a corresponding decrease in the radial velocity. A mathematical model has been developed that is capable of predicting both the occurrence and location of the jump, and the associated changes in the thickness profile and in the radial and tangential velocities of the liquid metal. Good correlations have been observed between model predictions and the flow patterns observed on the skull after atomization, and the effects of changes in material and operational parameters such as kinematic viscosity, volume flow rate, metallostatic head, and disk rotation speed have been quantified. Liquid metal flow is controlled primarily by the volume flow rate and by the metallostatic head prior to the hydraulic jump and by the centrifugal forces after the jump. The implications of these observations in terms of the atomization process are discussed.
Technological study of laser cutting silicon steel controlled by rotating gas flow
Lei, Hong; Yi, Zhang; chenglong, Mi
2009-04-01
Using traditional laser cutting technology, it is easy to produce molten slag in laser cutting silicon steel sheet. The main reason is the inevitable oxidizing reaction in the process caused by the use of oxygen as the aided gas. As a common solution, high pressure and high purity N 2 or an inert gas is therefore used instead of oxygen. Although the cut quality is improved, the cutting efficiency is reduced because of the lack of energy generated from an exothermic oxidation reaction. The technology used in this paper is to employ a newly developed cyclone slag separator. The slag separator is located under the workpiece to form rotating gas flow for controlling the direction of the flowing slag gas. Adopting the new technology reported here, oxygen is still used as the aided gas. The experiments prove that, by controlling the technical parameters reasonably tightly, glossy and dross-free cutting kerfs are obtained for reduced laser power. The gas flow acting under the workpiece is simulated using the finite element method (FEM). The operating law of the rotating gas flow is verified by ANSYS, which provides an academic basis for controlling the flowing direction of the slag gas.
Numerical simulation of fluid flow and heat transfer in a thin liquid film over a rotating disk
Rahman, M. M.; Faghri, A.
1992-01-01
The results of a numerical simulation of the flow field and associated heat transfer coefficient are presented for the free surface flow of a thin liquid film adjacent to a horizontal rotating disk. The computation has been performed for different flow rates and rotational velocities using a three-dimensional boundary-fitted coordinate system. Since the geometry of the free surface is unknown and dependent on flow rate, rate of rotation, and other parameters, an interative procedure had to be used to ascertain its location. The computed film height agreed well with existing experimental measurements. The flow was dominated by inertia near the entrance and close to the free surface, and dominated by centrifugal force at larger radii and adjacent to the disk. The rotation enhanced the heat transfer coefficient by a significant amount.
Energy Technology Data Exchange (ETDEWEB)
Harlander, Uwe; Alexandrov, Kiril; Wang, Yongtai; Egbers, Christoph [Brandenburg University of Technology Cottbus, Department of Aerodynamics and Fluid Mechanics, Cottbus (Germany); Wenzel, Julia [University of Leipzig, Institute of Meteorology, Leipzig (Germany)
2012-04-15
A radial barrier has been mounted in a differentially heated rotating annulus that partially blocks the azimuthal flow component. The experiment can be seen as an analog to geophysical flows with constrictions, e.g., the Antarctic Circumpolar Current. However, the experiment has been carried out without a particular natural flow in mind. The main interest was to observe a baroclinic annulus flow that does not become saturated. Hence, in contrast to the annulus flow without a barrier, the partially blocked flow remains transient and surface heat fluxes associated with baroclinic life cycles can be studied. The annulus can be subdivided into the upstream half of the barrier, where waves amplify, and the downstream half of the barrier, where waves decay. In the upstream half, the azimuthal mean flow is moderate but with a significant positive eddy radial heat flux. In the downstream half, we find a strong jet in the mean azimuthal flow and furthermore an increased radial mean temperature gradient. The latter points to a weakened or even reversed radial eddy heat flux in the lee side of the barrier. Temperature anomalies appear as large bulges in the outer part of the annulus. Moreover, an outward shift of vortex centers can be observed with respect to centers of temperature anomalies. This phase shift between pressure and temperature anomalies differs from that of classical Eady modes of baroclinic instability. (orig.)
Singh Bhatia, Tanayveer; Mukhopadhyay, Banibrata
2016-10-01
The emergence of turbulence in shear flows is a well-investigated field. Yet, there are some lingering issues that have not been sufficiently resolved. One of them is the apparent contradiction between the results of linear stability analysis showing a flow to be stable and yet experiments and simulations proving it to be otherwise. There is some success, in particular in astrophysical systems, based on magnetorotational instability (MRI), revealing turbulence. However, MRI requires the system to be weakly magnetized. Such instability is neither a feature of general magnetohydrodynamic (MHD) flows nor revealed in purely hydrodynamic flows. Nevertheless, linear perturbations of such flows are non-normal in nature, which argues for a possible origin of nonlinearity therein. The concept behind this is that non-normal perturbations could produce huge transient energy growth (TEG), which may lead to nonlinearity and further turbulence. However, so far, non-normal effects in shear flows have not been explored much in the presence of magnetic fields. In this spirit, here we consider the perturbed viscoresistive MHD shear flows with rotation in general. Basically we recast the magnetized momentum balance and associated equations into the magnetized version of Orr-Sommerfeld and Squire equations and their magnetic analogs. We also assume the flow to be incompressible and in the presence of Coriolis effect solve the equations using a pseudospectral eigenvalue approach. We investigate the possible emergence of instability and large TEG in three different types of flows, namely, the Keplerian flow, the Taylor-Couette (or constant angular momentum) flow, and plane Couette flow. We show that, above a certain value of magnetic field, instability and TEG both stop occurring. We also show that TEG is maximum in the vicinity of regions of instability in the wave number space for a given magnetic field and Reynolds number, leading to nonlinearity and plausible turbulence. Rotating
Directory of Open Access Journals (Sweden)
Sharf Abdusalam M.
2014-03-01
Full Text Available In the oil and gas industries, understanding the behaviour of a flow through an annulus gap in a vertical position, whose outer wall is stationary whilst the inner wall rotates, is a significantly important issue in drilling wells. The main emphasis is placed on experimental (using an available rig and computational (employing CFD software investigations into the effects of the rotation speed of the inner pipe on the axial velocity profiles. The measured axial velocity profiles, in the cases of low axial flow, show that the axial velocity is influenced by the rotation speed of the inner pipe in the region of almost 33% of the annulus near the inner pipe, and influenced inversely in the rest of the annulus. The position of the maximum axial velocity is shifted from the centre to be nearer the inner pipe, by increasing the rotation speed. However, in the case of higher flow, as the rotation speed increases, the axial velocity is reduced and the position of the maximum axial velocity is skewed towards the centre of the annulus. There is a reduction of the swirl velocity corresponding to the rise of the volumetric flow rate.
Nalbach, H O
1992-01-01
Pigeons freely standing in the centre of a two-dimensionally textured cylinder not only rotate but also laterally translate their head in response to the pattern sinusoidally oscillating or unidirectionally rotating around their vertical axis. The translational head movement dominates the response at high oscillation frequencies, whereas in a unidirectionally rotating drum head translation declines at about the same rate as the rotational response increases. It is suggested that this is a consequence of charging the 'velocity storage' in the vestibulo-ocular system. Similar to the rotational head movement (opto-collic reflex), the translational head movement is elicited via a wide-field motion sensitive system. The underlying mechanism can be described as vector integration of movement vectors tangential to the pattern rotation. Stimulation of the frontal visual field elicits largest translational responses while rotational responses can be elicited equally well from any azimuthal position of a moving pattern. Experiments where most of the pattern is occluded by a screen and the pigeon is allowed to view the stimulus through one or two windows demonstrate a short-range inhibition and long-range excitation between movement detectors that feed into the rotational system. Furthermore, the results obtained from such types of experiments suggest that the rotational system inhibits the translational system. These mechanisms may help the pigeon to decompose image flow into its translational and rotational components. Because of their translational response to a rotational stimulus, it is concluded, however, that pigeons either generally cannot perfectly perform the task or they need further visual information, like differential image motion, that was not available to them in the paradigms.
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Nemati Hasan
2011-01-01
Full Text Available A numerical investigation of the two-dimensional laminar flow and heat transfer a rotating circular cylinder with uniform planar shear, where the free-stream velocity varies linearly across the cylinder using Multi-Relaxation-Time Lattice Boltzmann method is conducted. The effects of variation of Reynolds number, rotational speed ratio at shear rate 0.1, blockage ratio 0.1 and Prandtl number 0.71 are studied. The Reynolds number changing from 50 to 160 for three rotational speed ratios of 0, 0.5, 1 is investigated. Results show that flow and heat transfer depends significantly on the rotational speed ratio as well as the Reynolds number. The effect of Reynolds number on the vortex-shedding frequency and period-surface Nusselt numbers is overall very strong compared with rotational speed ratio. Flow and heat conditions characteristics such as lift and drag coefficients, Strouhal number and Nusselt numbers are studied.
Nemati, Hasan; Sedighi, Kurosh; Farhadi, Mousa; Pirouz, Mohammad Mohammadi; Fattahi, Ehsan
2010-03-01
A numerical investigation of the two-dimensional laminar flow around side-by-side rotating circular cylinders using Lattice Boltzmann method is conducted. The effects of variation of rotational speed ratio β and different gap spacings g* at Reynolds number of 100 are studied. A various range of rotational speed ratio 0 ≤ β ≤ 2 for four different gap spacings of 3, 1.5, 0.7 and 0.2 are investigated. Flow conditions and its characteristics, such as lift and drag coefficients and Strouhal number, is studied. The results indicated that as β increases, the flow changes its condition from periodic to steady after a critical rotational speed. Results also indicated that variation of the gap spacing and rotational speed has significant effect on wake pattern. Wake pattern in turn has significant effect on the Strouhal number. Finally, the result is compared with experimental and other numerical data.
Inertial modes and their transition to turbulence in a differentially rotating spherical gap flow
Hoff, Michael; Harlander, Uwe; Andrés Triana, Santiago; Egbers, Christoph
2016-04-01
We present a study of inertial modes in a spherical shell experiment. Inertial modes are Coriolis-restored linear wave modes, often arise in rapidly-rotating fluids (e.g. in the Earth's liquid outer core [1]). Recent experimental works showed that inertial modes exist in differentially rotating spherical shells. A set of particular inertial modes, characterized by (l,m,ˆω), where l, m is the polar and azimuthal wavenumber and ˆω = ω/Ωout the dimensionless frequency [2], has been found. It is known that they arise due to eruptions in the Ekman boundary layer of the outer shell. But it is an open issue why only a few modes develop and how they get enhanced. Kelley et al. 2010 [3] showed that some modes draw their energy from detached shear layers (e.g. Stewartson layers) via over-reflection. Additionally, Rieutord et al. (2012) [4] found critical layers within the shear layers below which most of the modes cannot exist. In contrast to other spherical shell experiments, we have a full optical access to the flow. Therefore, we present an experimental study of inertial modes, based on Particle-Image-Velocimetry (PIV) data, in a differentially rotating spherical gap flow where the inner sphere is subrotating or counter-rotating at Ωin with respect to the outer spherical shell at Ωout, characterized by the Rossby number Ro = (Ωin - Ωout)/Ωout. The radius ratio of η = 1/3, with rin = 40mm and rout = 120mm, is close to that of the Earth's core. Our apparatus is running at Ekman numbers (E ≈ 10-5, with E = ν/(Ωoutrout2), two orders of magnitude higher than most of the other experiments. Based on a frequency-Rossby number spectrogram, we can partly confirm previous considerations with respect to the onset of inertial modes. In contrast, the behavior of the modes in the counter-rotation regime is different. We found a triad interaction between three dominant inertial modes, where one is a slow axisymmetric Rossby mode [5]. We show that the amplitude of the most
Grid Sensitivity Analysis of Simulations of a Flow around a Single Rotating Wind Turbine Blade
Kaiser, Bryan E.; Snider, Michael A.; Poroseva, Svetlana V.; Hovsapian, Rob O.
2012-11-01
Design of a wind farm layout with the purpose of optimizing the power outcome requires accurate and reliable simulations of a flow around and behind wind turbines. Such computations are expensive even for a single turbine. To find an optimal set of simulation parameters that satisfies both requirements in simulation accuracy and cost in an acceptable degree, a sensitivity study on how the parameters' variation influences results of simulations should be conducted at the early stage of computations. In the current study, the impact of a grid refinement, grid stretching, and cell shape on simulation results is analyzed in a flow around a single rotating blade utilized in a mid-sized Rim Driven Wind Turbine design (U.S. Patent #7399162) developed by Keuka Energy LLC, and in its near wake. Simulation results obtained with structured and unstructured grids are compared. Industry relies on commercial software for conducting fluid flow simulations. Therefore, STAR-CCM+ software was used in our study. A choice of a turbulence model was made based on our previous sensitivity study of flow simulations over a rotating disk (see M. A. Snider, S. V. Poroseva, AIAA-2012-3146). Center for Advanced Power Systems, Florida State University.
Experiments on Heat Transfer in a Thin Liquid Film Flowing Over a Rotating Disk
Sankaran, Subramanian (Technical Monitor); Ozar, B.; Cetegen, B. M.; Faghri, A.
2004-01-01
An experimental study of heat transfer into a thin liquid film on a rotating heated disk is described. Deionized water was introduced at the center of a heated. horizontal disk with a constant film thickness and uniform radial velocity. Radial distribution of the disk surface temperatures was measured using a thermocouple/slip ring arrangement. Experiments were performed for a range of liquid flow rates between 3.01pm and 15.01pm. The angular speed of the disk was varied from 0 rpm to 500 rpm. The local heat transfer coefficient was determined based on the heat flux supplied to the disk and the temperature difference between the measured disk surface temperature and the liquid entrance temperature onto the disk. The local heat transfer coefficient was seen to increase with increasing flow rate as well as increasing angular velocity of the disk. Effect of rotation on heat transfer was largest for the lower liquid flow rates with the effect gradually decreasing with increasing liquid flow rates. Semi-empirical correlations are presented in this study for the local and average Nusselt numbers.
An experimental investigation on the tip leakage noise in axial-flow fans with rotating shroud
Canepa, Edward; Cattanei, Andrea; Mazzocut Zecchin, Fabio; Milanese, Gabriele; Parodi, Davide
2016-08-01
The tip leakage noise generated by a shrouded rotor of an axial-flow fan has been experimentally studied. The measurements have been taken at high flow rate and at the design point in a hemi-anechoic chamber, at constant rotational speed and during speed ramps. A test plenum designed according to ISO 10302 has been employed to modify the operating conditions and different inlet configurations, ducted and unducted with standard and reduced tip gap, have been considered. The basic features of the inflow have been studied by means of aerodynamic measurements taken upstream of the rotor. To separate the noise generating mechanisms from the acoustic propagation effects, the acoustic response function of the test configuration has been computed employing the spectral decomposition method, and then it has been compared with the velocity-scaled, constant-Strouhal number SPL. In this way, the noise components related to the tip leakage flow have been identified and their connection with geometry have been highlighted. The broadband part of the spectra and the peaks related to the tip leakage flow are affected by the same propagation effects, but show a different dependence on the rotational speed and on the operating point. The upstream geometry affects the radiated noise much more than the performance and even a strong reduction in the tip-gap cannot completely eliminate the related noise.
Krygier, Michael; Grigoriev, Roman
2015-11-01
A direct transition from laminar to turbulent flow has recently been discovered experimentally in the small-gap Taylor-Couette flow with counter-rotating cylinders. The subcritical nature of this transition is a result of relatively small aspect ratio, Γ = 5 . 26 for large Γ the transition is supercritical and involves an intermediate stable state (Coughlin & Marcus, 1996) - interpenetrating spirals (IPS). We investigate this transition numerically to probe the dynamics in regimes inaccessible to experiments for a fixed Reo = - 1000 by varying Rei . The numerics reproduce all the experimentally observed features and confirm the hysteretic nature of the transition. As Rei is increased, the laminar flow transitions to turbulence, with an unstable IPS state mediating the transition, similar to the Tollmien-Schlichting waves in plane Poiseuille flow. As Rei is decreased, turbulent flow transitions to a stable, temporally chaotic IPS state. This IPS state further transitions to either laminar or turbulent flow as Rei is decreased or increased. The stable IPS state is reminiscent of the pre-turbulent chaotic states found numerically in plane Poiseuille flow (Zammert & Eckhardt, 2015), but previously never observed experimentally.
Hydromagnetic oscillatory Couette flow in rotating system with induced magnetic field
Institute of Scientific and Technical Information of China (English)
G.S.SETH; S.M.HUSSAIN; S.SARKAR
2014-01-01
This paper presents a study of hydromagnetic Couette flow of an incompress-ible and electrically conducting fluid between two parallel rotating plates, one of which is oscillating in its own plane. A uniform transverse magnetic field is used, and the induced magnetic field is taken into account. The exact solution to the governing equations is obtained in a closed form. The solution to the problem in the case of vanishing and small finite magnetic Prandtl numbers is also derived from the general solution. The asymp-totic behavior of the solution for large values of the frequency parameter is analyzed to gain some physical insights into the flow pattern. Expressions for the shear stress at both the oscillatory and stationary plates due to primary and secondary flows and mass flow rate in the primary and secondary flow directions are also obtained. The results of the fluid velocity and the induced magnetic field are presented. The shear stresses on the plates due to the primary and secondary flows and the corresponding mass flow rates are presented in a tabular form.
Primate-inspired vehicle navigation using optic flow and mental rotations
Arkin, Ronald C.; Dellaert, Frank; Srinivasan, Natesh; Kerwin, Ryan
2013-05-01
Robot navigation already has many relatively efficient solutions: reactive control, simultaneous localization and mapping (SLAM), Rapidly-Exploring Random Trees (RRTs), etc. But many primates possess an additional inherent spatial reasoning capability: mental rotation. Our research addresses the question of what role, if any, mental rotations can play in enhancing existing robot navigational capabilities. To answer this question we explore the use of optical flow as a basis for extracting abstract representations of the world, comparing these representations with a goal state of similar format and then iteratively providing a control signal to a robot to allow it to move in a direction consistent with achieving that goal state. We study a range of transformation methods to implement the mental rotation component of the architecture, including correlation and matching based on cognitive studies. We also include a discussion of how mental rotations may play a key role in understanding spatial advice giving, particularly from other members of the species, whether in map-based format, gestures, or other means of communication. Results to date are presented on our robotic platform.
Banerjee, Ayan Kumar; Bhattacharya, Amitabh; Balasubramanian, Sridhar
2016-01-01
Laboratory experiments were conducted to study heat transport characteristics in a nonhomogeneously heated fluid annulus subjected to rotation along the vertical axis (z). The nonhomogeneous heating was obtained by imposing radial and vertical temperature gradient ({\\Delta}T). The parameter range for this study was Rayleigh number, Ra=2.43x10^8-3.66x10^8, and Taylor number, Ta=6.45x10^8-27x10^8. The working fluid was water with a Prandtl number, Pr=7. Heat transport was measured for varying rotation rates ({\\Omega}) for fixed values of {\\Delta}T. The Nusselt number, Nu, plotted as a function of Ta distinctly showed the effect of rotation on heat transport. In general, Nu was found to have a larger value for non-rotating convection. This could mean an interplay of columnar plumes and baroclinic wave in our system as also evident from temperature measurements. Laser based imaging at a single vertical plane also showed evidence of such flow structure.
Fowle, A. A.; Soto, L.; Strong, P. F.; Wang, C. A.
1980-01-01
A low Bond number simulation technique was used to establish the stability limits of cylindrical and conical floating liquid columns under conditions of isorotation, equal counter rotation, rotation of one end only, and parallel axis offset. The conditions for resonance in cylindrical liquid columns perturbed by axial, sinusoidal vibration of one end face are also reported. All tests were carried out under isothermal conditions with water and silicone fluids of various viscosities. A technique for the quantitative measurement of stream velocity within a floating, isothermal, liquid column confined between rotatable disks was developed. In the measurement, small, light scattering particles were used as streamline markers in common arrangement, but the capability of the measurement was extended by use of stereopair photography system to provide quantitative data. Results of velocity measurements made under a few selected conditions, which established the precision and accuracy of the technique, are given. The general qualitative features of the isothermal flow patterns under various conditions of end face rotation resulting from both still photography and motion pictures are presented.
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Wei Tong
2001-01-01
Full Text Available An important characteristic of wall rotating-driven flows is the tendency of fluid with high angular momentum to be flung radially outward. For a generator, the rotor rotating-driven flow, usually referred to as the rotating pumping flow, plays an important role in rotor winding cooling. In this study, three-dimensional numerical analyzes are presented for turbulent pumping flow in the inter-coil rotor cavity and short cooling grooves of a generator. Calculations of the flow field and the mass flux distribution through the grooves were carried out in a sequence of four related cases Under an isothermal condition: (a pumping flow, which is the self-generated flow resulted from the rotor pumping action; (b mixing flow, which is the combination of the ventilating flow and pumping flow, under a constant density condition; (c mixing flow, with density modeled by the ideal gas law; and (d mixing flow, with different pressure differentials applied on the system. The comparisons of the results from these cases can provide useful information regarding the impacts of the ventilating flow, gas density, and system pressure differential on the mass flux distribution in the short cooling grooves. Results show that the pumping effect is strong enough to generate the cooling flow for rotor winding cooling. Therefore, for small- or mid-size generators ventilation fans may be eliminated. It also suggests that increasing the chimney dimension can improve the distribution uniformity of mass flux through the cooling grooves.
Experimental analysis and flow visualization of a thin liquid film on a stationary and rotating disk
Thomas, S.; Faghri, A.; Hankey, W.
1991-01-01
The mean thickness of a thin liquid film of deionized water with a free surface on a stationary and rotating horizontal disk has been measured with a nonobtrusive capacitance technique. The measurements were taken when the rotational speed ranged from 0-300 rpm and the flow rate varied from 7.0-15.0 lpm. A flow visualization study of the thin film was also performed to determine the characteristics of the waves on the free surface. When the disk was stationary, a circular hydraulic jump was present on the disk. Upstream from the jump, the film thickness was determined by the inertial and frictional forces on the fluid, and the radial spreading of the film. The surface tension at the edge of the disk affected the film thickness downstream from the jump. For the rotating disk, the film thickness was dependent upon the inertial and frictional forces near the center of the disk and the centrifugal forces near the edge of the disk.
Experimental study of flow and heat transfer in a rotating chemical vapor deposition reactor
Wong, Sun
An experimental model was set up to study the rotating vertical impinging chemical vapor deposition reactor. Deposition occurs only when the system has enough thermal energy. Therefore, understanding the fluid characteristic and heat transfer of the system will provide a good basis to understand the full model. Growth rate and the uniformity of the film are the two most important factors in CVD process and it is depended on the flow and thermal characteristic within the system. Optimizing the operating parameters will result in better growth rate and uniformity. Operating parameters such as inflow velocity, inflow diameter and rotational speed are used to create different design simulations. Fluid velocities and various temperatures are recorded to see the effects of the different operating parameters. Velocities are recorded by using flow meter and hot wire anemometer. Temperatures are recorded by using various thermocouples and infrared thermometer. The result should provide a quantitative basis for the prediction, design and optimization of the system and process for design and fabrication of future CVD reactors. Further assessment of the system results will be discuss in detail such as effects of buoyancy and effects of rotation. The experimental study also coupled with a numerical study for further validation of both model. Comparisons between the two models are also presented.
Horn, S.; Schmid, P. J.; Aurnou, J. M.
2016-12-01
The Earth's metal core acts as a dynamo whose efficiency in generating and maintaining the magnetic field is essentially determined by the rotation rate and the convective motions occurring in its outer liquid part. For the description of the primary physics in the outer core the idealized system of rotating Rayleigh-Bénard convection is often invoked, with the majority of studies considering only working fluids with Prandtl numbers of Pr ≳ 1. However, liquid metals are characterized by distinctly smaller Prandtl numbers which in turn result in an inherently different type of convection. Here, we will present results from direct numerical simulations of rapidly rotating convection in a fluid with Pr ≈ 0.025 in cylindrical containers and Ekman numbers as low as 5 × 10-6. In this system, the Coriolis force is the source of two types of inertial modes, the so-called wall modes, that also exist at moderate Prandtl numbers, and cylinder-filling oscillatory modes, that are a unique feature of small Prandtl number convection. The obtained flow fields were analyzed using the Dynamic Mode Decomposition (DMD). This technique allows to extract and identify the structures that govern the dynamics of the system as well as their corresponding frequencies. We have investigated both the regime where the flow is purely oscillatory and the regime where wall modes and oscillatory modes co-exist. In the purely oscillatory regime, high and low frequency oscillatory modes characterize the flow. When both types of modes are present, the DMD reveals that the wall-attached modes dominate the flow dynamics. They precess with a relatively low frequency in retrograde direction. Nonetheless, also in this case, high frequency oscillations have a significant contribution.
Tang, Fei; Wang, Chunze; Shi, Yupeng; Wang, Xiaohao
2015-04-01
For a micro-gap rotational flow field with a large horizontal extent, tiny gap and fast flow velocity, the two-dimensional images shot by the micro-scale Particle ImageVelocimetry(Micro-PIV) technique are not sufficient for the study of local or whole flow characteristics. In this paper, by establishing a test bench of a rotational flow field with the functions of driving, positioning, adjustment and sensing, all the local states of the micro-gap rotational flow field can be obtained by horizontally moving the rotating axis to observe point by point. While measuring some local flow fields, two-dimensional pictures are taken by adjusting the focusing height of the objective lens, and then superposed and interpolated according to their shooting order to obtain a quasi-three-dimensional distribution image of the local flow fields, thus obtaining the flow condition of the vertical section of the flow field. The position of the focusing plane and mutual distance are adjusted to realize the measurement of wall shear force in the flow field, providing a feasible reference method for detecting the rheological property of the gap flow field and the effect of surface drag reduction.
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Fei Tang
2015-04-01
Full Text Available For a micro-gap rotational flow field with a large horizontal extent, tiny gap and fast flow velocity, the two-dimensional images shot by the micro-scale Particle ImageVelocimetry(Micro-PIV technique are not sufficient for the study of local or whole flow characteristics. In this paper, by establishing a test bench of a rotational flow field with the functions of driving, positioning, adjustment and sensing, all the local states of the micro-gap rotational flow field can be obtained by horizontally moving the rotating axis to observe point by point. While measuring some local flow fields, two-dimensional pictures are taken by adjusting the focusing height of the objective lens, and then superposed and interpolated according to their shooting order to obtain a quasi-three-dimensional distribution image of the local flow fields, thus obtaining the flow condition of the vertical section of the flow field. The position of the focusing plane and mutual distance are adjusted to realize the measurement of wall shear force in the flow field, providing a feasible reference method for detecting the rheological property of the gap flow field and the effect of surface drag reduction.
A rotating hot-wire technique for spatial sampling of disturbed and manipulated duct flows
Wark, C. E.; Nagib, H. M.; Jennings, M. J.
1990-01-01
A duct flow spatial sampling technique, in which an X-wire probe is rotated about the center of a cylindrical test section at a radius equal to one-half that of the test section in order to furnish nearly instantaneous multipoint measurements of the streamwise and azimuthal components, is presently evaluated in view of the control of flow disturbances downstream of various open inlet contractions. The effectiveness of a particular contraction in controlling ingested flow disturbances was ascertained by artificially introducing disturbances upstream of the contractions; control effectiveness if found to be strongly dependent on inlet contraction, with consequences for the reduction of passing-blade frequency noise during gas turbine engine ground testing.
A rotating hot-wire technique for spatial sampling of disturbed and manipulated duct flows
Wark, C. E.; Nagib, H. M.; Jennings, M. J.
1990-01-01
A duct flow spatial sampling technique, in which an X-wire probe is rotated about the center of a cylindrical test section at a radius equal to one-half that of the test section in order to furnish nearly instantaneous multipoint measurements of the streamwise and azimuthal components, is presently evaluated in view of the control of flow disturbances downstream of various open inlet contractions. The effectiveness of a particular contraction in controlling ingested flow disturbances was ascertained by artificially introducing disturbances upstream of the contractions; control effectiveness if found to be strongly dependent on inlet contraction, with consequences for the reduction of passing-blade frequency noise during gas turbine engine ground testing.
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.
Experimental researches on mass and heat transfer in new typical cross-flow rotating packed bed
Institute of Scientific and Technical Information of China (English)
CHEN Haihui; ZENG Yingying; GAO Wenshuai
2006-01-01
New typical cross-flow Rotating Packed Bed(RPB)called multi-pulverizing RPB was manufactured.There is enough void in multi-pulverizing RPB,where liquid easily flows and is repeatedly pulverized by light packing,which decreases the material consumed,lightens the weight,and compacts the structure.Mass and heat transfer property in the new type PRB were studied by two experimental models.In the mass transfer model,the axial fan pumping gas press is only 100 Pa,mass transfer coefficient and volumetric mass transfer coefficient are similar to countercurrent RPB,which are an order quantity lager than that in the conventional packed tower.In the heat transfer experiment,the axial fan pumping gas press is only 120 Pa;volumetric heatwhich especially suits the treatment of large gas flow and lower gas pressure drop.
Boundary layer development in the flow field between a rotating and a stationary disk
van Eeten, K. M. P.; van der Schaaf, J.; Schouten, J. C.; van Heijst, G. J. F.
2012-03-01
This paper discusses the development of boundary layers in the flow of a Newtonian fluid between two parallel, infinite disks. One of the disks is rotating at a constant angular velocity while the other remains stationary. An analytical series approximation and a numerical solution method are used to describe the velocity profiles of the flow. Both methods rely on the commonly used similarity transformation first proposed by Von Kármán [T. von Kármán, ZAMM 1, 233 (1921)], 10.1002/zamm.19210010401. For Reh Batchelor type of flow was observed for Reh > 300, with two boundary layers near the disks and a non-viscous core in the middle. A remarkable conclusion of the current work is the coincidence of the power series' radius of convergence, a somewhat abstract mathematical notion, with the physically tangible concept of the boundary layer thickness. The coincidence shows a small deviation of only 2% to 4%.
Reciprocal inhibitory connections within a neural network for rotational optic-flow processing
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Juergen Haag
2007-10-01
Full Text Available Neurons in the visual system of the blowfly have large receptive fields that are selective for specific optic flow fields. Here, we studied the neural mechanisms underlying flow-field selectivity in proximal Vertical System (VS-cells, a particular subset of tangential cells in the fly. These cells have local preferred directions that are distributed such as to match the flow field occurring during a rotation of the fly. However, the neural circuitry leading to this selectivity is not fully understood. Through dual intracellular recordings from proximal VS cells and other tangential cells, we characterized the specific wiring between VS cells themselves and between proximal VS cells and horizontal sensitive tangential cells. We discovered a spiking neuron (Vi involved in this circuitry that has not been described before. This neuron turned out to be connected to proximal VS cells via gap junctions and, in addition, it was found to be inhibitory onto VS1.
Wang, Chengduan; Chen, Wenmei; Li, Jianming; Jiang, Guangming
2002-07-01
A new type of polypropylene tubular membrane apparatus of rotating cross flow was designed to study experimentally the flow field characteristics of the tangential section of the membrane annular gap. The authors designed rotary linear tangential flow tubular membrane separator and its test system for the first time. Through the system, the flow field of rotary linear tangential flow with the advanced Particle Image Velocimetry (PIV) was tested for the first time. A lot of streamlines and vorticity maps of the tangential section of separator in different operation conditions were obtained. The velocity distribution characteristics were analyzed quantitatively: 1. At non-vortex area, no matter how the operation parameters change, the velocity near to rotary tangential flow entrance was higher than the velocity far from entrance at the same radial coordinates. At vortex area, generally the flow velocity of inner vortex was lower than the outer vortex. At the vortex center, the velocity was lowest, the tangential velocity were equal to zero generally. At the vortex center zone, the tangential velocity was less than the axial velocity. 2. Under test operations, the tangential velocity and axial velocity of vortices borders are 1-2 times of average axial velocity of membrane module annular gap. The maximum tangential velocity and axial velocity of ellipse vortices were 2-6 times of average axial velocity of membrane module annular gap. 3. The vortices that are formed on the tangential section, there existed mass transfer between inner and outer parts of fluid. Much fluid of outer vortices got into the inner ones, which was able to prevent membrane tube from particles blocking up very soon.
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Tasawar Hayat
Full Text Available This paper investigates the unsteady MHD flow of viscous fluid between two parallel rotating disks. Fluid fills the porous space. Energy equation has been constructed by taking Joule heating, thermal stratification and radiation effects into consideration. We convert system of partial differential equations into system of highly nonlinear ordinary differential equations after employing the suitable transformations. Convergent series solutions are obtained. Behavior of different involved parameters on velocity and temperature profiles is examined graphically. Numerical values of skin friction coefficient and Nusselt number are computed and inspected. It is found that tangential velocity profile is increasing function of rotational parameter. Fluid temperature reduces for increasing values of thermal stratification parameter. At upper disk heat transfer rate enhances for larger values of Eckert and Prandtl numbers.
Hayat, Tasawar; Qayyum, Sumaira; Imtiaz, Maria; Alsaedi, Ahmed
2016-01-01
This paper investigates the unsteady MHD flow of viscous fluid between two parallel rotating disks. Fluid fills the porous space. Energy equation has been constructed by taking Joule heating, thermal stratification and radiation effects into consideration. We convert system of partial differential equations into system of highly nonlinear ordinary differential equations after employing the suitable transformations. Convergent series solutions are obtained. Behavior of different involved parameters on velocity and temperature profiles is examined graphically. Numerical values of skin friction coefficient and Nusselt number are computed and inspected. It is found that tangential velocity profile is increasing function of rotational parameter. Fluid temperature reduces for increasing values of thermal stratification parameter. At upper disk heat transfer rate enhances for larger values of Eckert and Prandtl numbers.
Radiation Effects in Flow through Porous Medium over a Rotating Disk with Variable Fluid Properties
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Shalini Jain
2016-01-01
Full Text Available The present study investigates the radiation effects in flow through porous medium over a permeable rotating disk with velocity slip and temperature jump. Fluid properties density (ρ, viscosity (μ, and thermal conductivity (κ are taken to be dependent on temperature. Particular case considering these fluid properties’ constant is also discussed. The governing partial differential equations are converted into nonlinear normal differential equation using similarity alterations. Transformed system of equations is solved numerically by using Runge-Kutta method with shooting technique. Effects of various parameters such as porosity parameter K, suction parameter Ws, rotational Reynolds number Re, Knudsen number Kn, Prandtl number Pr, radiation parameter N, and relative temperature difference parameter ε on velocity profiles along radial, tangential, and axial direction and temperature distribution are investigated for both variable fluid properties and constant fluid properties. Results obtained are analyzed and depicted through graphs and table.
Families of subcritical spirals in highly counter-rotating Taylor-Couette flow.
Meseguer, Alvaro; Mellibovsky, Fernando; Avila, Marc; Marques, Francisco
2009-03-01
A comprehensive numerical exploration of secondary finite-amplitude solutions in small-gap Taylor-Couette flow for high counter-rotating Reynolds numbers is provided, using Newton-Krylov methods embedded within arclength continuation schemes. Two different families of rotating waves have been identified: short axial wavelength subcritical spirals ascribed to centrifugal mechanisms and large axial scale supercritical spirals and ribbons associated with shear dynamics in the outer linearly stable radial region. This study is a first step taken in order to provide the inner structure of the skeleton of equilibria that may be responsible for the intermittent regime usually termed as spiral turbulence that has been reported by many experimentalists in the past.
Dual E × B flow responses in the dayside ionosphere to a sudden IMF By rotation
Eriksson, S.; Maimaiti, M.; Baker, J. B. H.; Trattner, K. J.; Knipp, D. J.; Wilder, F. D.
2017-07-01
We report for the first time a dual transition state in the dayside ionosphere following a sudden rotation of the interplanetary magnetic field (IMF) in the upstream magnetosheath from IMF By By > 0 during Bz rotation of lower latitude E × B flow from dusk to dawn. We propose that this sequence of events is consistent with two separate X lines coexisting on the subsolar and lobe magnetopause. Time delays are proposed for merged flux of the draped preceding IMF to exit the subsolar region before the new IMF may be processed along a newly reconfigured component reconnection X line. Finally, a strong direct correlation is observed between magnetosheath plasma density and auroral zone E × B speeds.
Bulk flow coupled to a viscous interfacial film sheared by a rotating knife edge
Raghunandan, Aditya; Rasheed, Fayaz; Hirsa, Amir; Lopez, Juan
2015-11-01
The measurement of the interfacial properties of highly viscous biofilms, such as DPPC (the primary component of lung surfactant), present on the surface of liquids (bulk phase) continues to attract significant attention. Most measurement techniques rely on shearing the interfacial film and quantifying its viscous response in terms of a surface (excess) viscosity at the air-liquid interface. The knife edge viscometer offers a significant advantage over other approaches used to study highly viscous films as the film is directly sheared by a rotating knife edge in direct contact with the film. However, accurately quantifying the viscous response is non-trivial and involves accounting for the coupled interfacial and bulk phase flows. Here, we examine the nature of the viscous response of water insoluble DPPC films sheared in a knife edge viscometer over a range of surface packing, and its influence on the strength of the coupled bulk flow. Experimental results, obtained via Particle Image Velocimetry in the bulk and at the surface (via Brewster Angle Microscopy), are compared with numerical flow predictions to quantify the coupling across hydrodynamic flow regimes, from the Stokes flow limit to regimes where flow inertia is significant. Supported by NNX13AQ22G, National Aeronautics and Space Administration.
Experimental investigation of three-dimensional flow instabilities in a rotating lid-driven cavity
Energy Technology Data Exchange (ETDEWEB)
Soerensen, Jens Noerkaer; Mikkelsen, Robert [Technical University of Denmark, Department of Mechanical Engineering, Lyngby (Denmark); Naumov, Igor [Technical University of Denmark, Department of Mechanical Engineering, Lyngby (Denmark); SB RAS, Institute of Thermophysics, Novosibirsk (Russian Federation)
2006-09-15
The swirling flow between a rotating lid and a stationary cylinder is studied experimentally. The flow is governed by two parameters: the ratio of container height to disk radius, h, and the Reynolds number, Re, based on the disk angular velocity, cylinder radius and kinematic viscosity of the working liquid. For the first time, the onset of three-dimensional flow behavior is measured by combining the high spatial resolution of particle image velocimetry and the temporal accuracy of laser Doppler anemometry. A detailed mapping of the transition scenario from steady and axisymmetric flow to unsteady and three-dimensional flow is investigated for 1 {>=}h{>=} 3.5. The flow is characterized by the development of azimuthal modes of different wave numbers. A range of different modes is detected and critical Reynolds numbers and associated frequencies are identified. The results are compared to the numerical stability analysis of Gelfgat et al. (J Fluid Mech 438:363-377, 2001). In most cases, the measured onset of three-dimensionality is in good agreement with the numerical results and disagreements can be explained by bifurcations not accounted for by the numerical stability analysis. (orig.)
A numerical study of double-diffusive flow in a long rotating porous channel
Alhusseny, Ahmed; Turan, A.
2015-04-01
The problem of double-diffusive flow in a long rotating porous channel has been analysed numerically. The two opposite vertical walls of the channel are maintained at constant but different temperature and concentration, while both horizontal walls are kept insulated. The generalised model is used to mathematically simulate the momentum equations with employing the Boussinesq approximation for the density variation. Moreover, both the fluid and solid phases are assumed to be at a local thermal equilibrium. The Coriolis effect is considered to be the main effect of rotation, which is induced by means of the combined natural heat and mass transfer within the transverse plane. The governing equations are discretised according to the finite volume method with employing the hybrid differencing scheme to calculate the fluxes across the faces of each control volume. The problem of pressure-velocity coupling is sorted out by relying on PISO algorithm. Computations are performed for a wide range of dimensionless parameters such as Darcy-Rayleigh number (100 ≤ Ra* ≤ 10,000), Darcy number (10-6 ≤ Da ≤ 10-4), the buoyancy ratio (-10 ≤ N ≤ 8), and Ekman number (10-7 ≤ Ek ≤ 10-3), while the values of Prandtl and Schmidt numbers are maintained constant and equal to 1.0. The results reveal that the rotation seems to have a dominant role at high levels of porous medium permeability, where it reduces the strength of the secondary flow, and hence the rates of heat and mass transfer. However, this dominance decreases gradually with lessening the permeability for the same level of rotation, but does not completely vanish.
Film stability in a vertical rotating tube with a core-gas flow.
Sarma, G. S. R.; Lu, P. C.; Ostrach, S.
1971-01-01
The linear hydrodynamic stability of a thin-liquid layer flowing along the inside wall of a vertical tube rotating about its axis in the presence of a core-gas flow is examined. The stability problem is formulated under the conditions that the liquid film is thin, the density and viscosity ratios of gas to liquid are small and the relative (axial) pressure gradient in the gas is of the same order as gravity. The resulting eigenvalue problem is first solved by a perturbation method appropriate to axisymmetric long-wave disturbances. The damped nature (to within the thin-film and other approximations made) of the nonaxisymmetric and short-wave disturbances is noted. In view of the limitations on a truncated perturbation solution when the disturbance wavenumber is not small, an initial value method using digital computer is presented. Stability characteristics of neutral, growing, and damped modes are presented showing the influences of rotation, surface tension, and the core-gas flow. Energy balance in a neutral mode is also illustrated.
Hassanzadeh, Pedram
Large coherent vortices are abundant in geophysical and astrophysical flows. They play significant roles in the Earth's oceans and atmosphere, the atmosphere of gas giants, such as Jupiter, and the protoplanetary disks around forming stars. These vortices are essentially three-dimensional (3D) and baroclinic, and their dynamics are strongly influenced by the rotation and density stratification of their environments. This work focuses on improving our understanding of the physics of 3D baroclinic vortices in rotating and continuously stratified flows using 3D spectral simulations of the Boussinesq equations, as well as simplified mathematical models. The first chapter discusses the big picture and summarizes the results of this work. In Chapter 2, we derive a relationship for the aspect ratio (i.e., vertical half-thickness over horizontal length scale) of steady and slowly-evolving baroclinic vortices in rotating stratified fluids. We show that the aspect ratio is a function of the Brunt-Vaisala frequencies within the vortex and outside the vortex, the Coriolis parameter, and the Rossby number of the vortex. This equation is basically the gradient-wind equation integrated over the vortex, and is significantly different from the previously proposed scaling laws that find the aspect ratio to be only a function of the properties of the background flow, and independent of the dynamics of the vortex. Our relation is valid for cyclones and anticyclones in either the cyclostrophic or geostrophic regimes; it works with vortices in Boussinesq fluids or ideal gases, and non-uniform background density gradient. The relation for the aspect ratio has many consequences for quasi-equilibrium vortices in rotating stratified flows. For example, cyclones must have interiors more stratified than the background flow (i.e., super-stratified), and weak anticyclones must have interiors less stratified than the background (i.e., sub-stratified). In addition, this equation is useful to
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
We investigates the effect of Taylor-Grtler vortex on the Reynolds stress transport in the rotating turbulent channel flow by direct numerical simulation. The Taylor-Grtler vortex is detected by longitudinal average of velocity fluctuation in the channel and defined as TG fluctuation. It has been found that turbulent diffusion is significant in the Reynolds stress transportation at the suction side of rotating turbulent channel in contrast with the turbulent channel flow without rotation and Taylor-Grtler vortex plays an important role in the turbulent diffusion in Reynolds stress transport. The paper focuses on the low and moderate rotation number, but the effect of the rotation number on the Reynolds stress transport is also reported.
The neutral curve for stationary disturbances in rotating-disk flow
Malik, M. R.
1986-01-01
The neutral curve for stationary vortex disturbances in rotating-disk flow is computed up to a Reynolds number of 10 to the 7th using the sixth-order system of linear stability equations which includes the effects of streamline curvature and Coriolis force. It is found that the neutral curve has two minima: one at R = 285.36 (upper branch) and the other at R = 440.88 (lower branch). At large Reynolds numbers, the upper branch tends to Stuart's asymptotic solution while the lower branch tends to a solution that is associated with the wave angle corresponding to the direction of zero mean wall shear.
Unsteady Hydromagnetic Rotating Flow through an Oscillating Porous Plate Embedded in a Porous Medium
Directory of Open Access Journals (Sweden)
I. Khan
2013-01-01
Full Text Available This paper investigates unsteady hydromagnetic flow of a viscous fluid in a rotating frame. The fluid is bounded by an oscillating porous plate embedded in a porous medium. The Laplace transform and Fourier sine transform methods are employed to find the exact solutions. They satisfy all imposed initial and boundary conditions and as special cases are reduced to some published results from the literature. The graphical results are plotted for different values of pertinent parameters and some interesting conclusions are made.
Directory of Open Access Journals (Sweden)
Faiz G Awad
Full Text Available In this study, the Spectral Relaxation Method (SRM is used to solve the coupled highly nonlinear system of partial differential equations due to an unsteady flow over a stretching surface in an incompressible rotating viscous fluid in presence of binary chemical reaction and Arrhenius activation energy. The velocity, temperature and concentration distributions as well as the skin-friction, heat and mass transfer coefficients have been obtained and discussed for various physical parametric values. The numerical results obtained by (SRM are then presented graphically and discussed to highlight the physical implications of the simulations.
A "horizon adapted" approach to the study of relativistic accretion flows onto rotating black holes
Font, J A; Papadopoulos, P P; Font, José A.; Ibanez, José M.; Papadopoulos, Philippos
1998-01-01
We present a new geometrical approach to the study of accretion flows onto rotating (Kerr) black holes. Instead of Boyer-Lindquist coordinates, the standard choice in all existing numerical simulations in the literature, we employ the simplest example of a horizon adapted coordinate system, the Kerr-Schild coordinates. This choice eliminates boundary ambiguities and unphysical divergent behavior at the event horizon. Computations of Bondi-Hoyle accretion onto extreme Kerr black holes, performed here for the first time, demonstrate the key advantages of this procedure. We argue it offers the best approach to the numerical study of the, observationally, increasingly more accesible relativistic inner region around black holes.
Investigations of Reduced Equations for Rotating, Stratified and Non-hydrostatic Flows
Nieves, David J.
This thesis is a collection of studies concerning an asymptotically reduced equation set derived from the Boussinesq approximation describing rotationally constrained geophysical flow. The first investigation is concerned with a statistical identification of coherent and long-lived structures in rotationally constrained Rayleigh-Benard convection. Presently, physical laboratory limitations challenge experimentalists while spatio-temporal resolution requirements challenges numericists performing direct numerical simulations of the Boussinesq equations. These challenges prevent an exhaustive analysis of the flow morphology in the rapid rotating limit. In this study the flow morphologies obtained from simulations of the reduced equations are investigated from a statistical perspective. Auto- and cross-correlations are computed from temporal and spatial signals that synthesize experimental data that may be obtained in laboratory experiments via thermistor measurements or particle image velocimetry. The statistics used can be employed in laboratory experiments to identify regime transitions in flow morphology, capture radial profiles of coherent structures, and extract transport properties belonging to these structures. These results provide a foundation for comparison and a measure for understanding the extent to which rotationally constrained regime has been accessed by laboratory experiments and direct numerical simulations. A related study comparing the influence of fixed temperature and fixed heat flux thermal boundary conditions on rapidly rotating convection in the plane layer geometry is also investigated and briefly summarized for the case of stress-free mechanical boundary conditions. It is shown that the difference between these thermal boundary conditions on the interior geostrophically balanced convection is asymptotically weak. Through a simple rescaling of thermal variables, the leading order reduced system is shown to be equivalent for both thermal
Directory of Open Access Journals (Sweden)
Greg F. Naterer
2009-07-01
Full Text Available An experimental design is presented for an optical method of measuring spatial variations of flow irreversibilities in laminar viscous fluid motion. Pulsed laser measurements of fluid velocity with PIV (Particle Image Velocimetry are post-processed to determine the local flow irreversibilities. The experimental technique yields whole-field measurements of instantaneous entropy production with a non-intrusive, optical method. Unlike point-wise methods that give measured velocities at single points in space, the PIV method is used to measure spatial velocity gradients over the entire problem domain. When combined with local temperatures and thermal irreversibilities, these velocity gradients can be used to find local losses of energy availability and exergy destruction. This article focuses on the frictional portion of entropy production, which leads to irreversible dissipation of mechanical energy to internal energy through friction. Such effects are significant in various technological applications, ranging from power turbines to internal duct flows and turbomachinery. Specific problems of a rotational stirring tank and channel flow are examined in this paper. By tracking the local flow irreversibilities, designers can focus on problem areas of highest entropy production to make local component modifications, thereby improving the overall energy efficiency of the system.
On the lifetime of a pancake anticyclone in a rotating stratified flow
Facchini, Giulio; Le Bars, Michael
2016-11-01
We present an experimental study of the time evolution of an isolated anticyclonic pancake vortex in a laboratory rotating stratified flow. Motivations come from the variety of compact anticyclones observed to form and persist for a strikingly long lifetime in geophysical and astrophysical settings combining rotation and stratification. We generate anticyclones by injecting a small amount of isodense fluid at the center of a rotating tank filled with salty water linearly stratified in density. Our two control parameters are the Coriolis parameter f and the Brunt-Väisälä frequency N. We observe that anticyclones always slowly decay by viscous diffusion, spreading mainly in the horizontal direction irrespective of the initial aspect ratio. This behavior is correctly explained by a linear analytical model in the limit of small Rossby and Ekman numbers, where density and velocity equations reduce to a single equation for the pressure. Direct numerical simulations further confirm the theoretical predictions. Notably, they show that the azimuthal shear stress generates secondary circulations, which advect the density anomaly: this mechanism is responsible for the slow time evolution, rather than the classical viscous dissipation of the azimuthal kinetic energy.
Magnetohydrodynamic (MHD) flow of Cu-water nanofluid due to a rotating disk with partial slip
Energy Technology Data Exchange (ETDEWEB)
Hayat, Tasawar [Department of Mathematics, Quaid-I-Azam University 45320, Islamabad 44000 (Pakistan); Nonlinear Analysis and Applied Mathematics Research Group, Department of Mathematics, Faculty of Science, King Abdulaziz University, Jeddah 21589 (Saudi Arabia); Rashid, Madiha; Imtiaz, Maria, E-mail: mi-qau@yahoo.com [Department of Mathematics, Quaid-I-Azam University 45320, Islamabad 44000 (Pakistan); Alsaedi, Ahmed [Nonlinear Analysis and Applied Mathematics Research Group, Department of Mathematics, Faculty of Science, King Abdulaziz University, Jeddah 21589 (Saudi Arabia)
2015-06-15
This paper investigates MHD steady flow of viscous nanofluid due to a rotating disk. Water is treated as a base fluid and copper as nanoparticle. Nanofluid fills the porous medium. Effects of partial slip, viscous dissipation and thermal radiation are also considered. Similarity transformations reduce the nonlinear partial differential equations to ordinary differential equations. Flow and heat transfer characteristics are computed by HAM solutions. Also computations for skin friction coefficient and Nusselt number are presented and examined for pertinent parameters. It is noted that higher velocity slip parameter decreases the radial and azimuthal velocities while temperature decreases for larger values of the thermal slip parameter. Also the rate of heat transfer enhances when the nanoparticle volume fraction increases.
Transient hydromagnetic reactive Couette flow and heat transfer in a rotating frame of reference
Directory of Open Access Journals (Sweden)
S. Das
2016-03-01
Full Text Available This paper is concerned with the study of a transient hydromagnetic Couette flow and heat transfer of a reactive viscous incompressible electrically conducting fluid 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 transient momentum equations are solved analytically using the Laplace transform technique and the velocity field and shear stresses are obtained in a unified closed form. The energy equation is tackled numerically using MATLAB. The effects of the pertinent parameters on the fluid velocity, temperature, the shear stress and the rate of heat transfer at the plates are presented in graphical form and discussed in detail. Our results reveal that the combined effects of magnetic field, rotation, exothermic reaction and variable thermal conductivity have significant impact on the hydromagnetic flow and heat transfer.
Restricted Equilibrium and the Energy Cascade in Rotating and Stratified Flows
Herbert, Corentin; Marino, Raffaele
2014-01-01
Most of the turbulent flows appearing in nature (e.g. geophysical and astrophysical flows) are subjected to strong rotation and stratification. These effects break the symmetries of classical, homogenous isotropic turbulence. In doing so, they introduce a natural decomposition of phase space in terms of wave modes and potential vorticity modes. The appearance of a new time scale associated to the propagation of waves, in addition to the eddy turnover time, increases the complexity of the energy transfers between the various scales; nonlinearly interacting waves may dominate at some scales while balanced motion may prevail at others. In the end, it is difficult to predict \\emph{a priori} if the energy cascades downscale as in homogeneous isotropic turbulence, upscale as expected from balanced dynamics, or follows yet another phenomenology. In this paper, we suggest a theoretical approach based on equilibrium statistical mechanics for the ideal system, inspired from the restricted partition function formalism i...
Haber, S; Filipovic, N; Kojic, M; Tsuda, A
2006-10-01
The dissipative particle dynamics (DPD) method was used to simulate the flow in a system comprised of a fluid occupying the space between two cylinders rotating with equal angular velocities. The fluid, initially at rest, ultimately reaches a steady, linear velocity distribution (a rigid-body rotation). Since the induced flow field is solely associated with the no-slip boundary condition at the walls, we employed this system as a benchmark to examine the effect of bounce-back reflections, specular reflections, and Pivkin-Karniadakis no-slip boundary conditions, upon the steady-state velocity, density, and temperature distributions. An additional advantage of the foregoing system is that the fluid occupies inherently a finite bounded domain so that the results are affected by the prescribed no-slip boundary conditions only. Past benchmark systems such as Couette flow between two infinite parallel plates or Poiseuille flow in an infinitely long cylinder must employ artificial periodic boundary conditions at arbitrary upstream and downstream locations, a possible source of spurious effects. In addition, the effect of the foregoing boundary conditions on the time evolution of the simulated velocity profile was compared with that of the known, time-dependent analytical solution. It was shown that bounce-back reflection yields the best results for the velocity distributions with small fluctuations in density and temperature at the inner fluid domain and larger deviations near the walls. For the unsteady solutions a good fit is obtained if the DPD friction coefficient is proportional to the kinematic viscosity. Based on dimensional analysis and the numerical results a universal correlation is suggested between the friction coefficient and the kinematic viscosity.
Instability modes on a solid-body-rotation flow in a finite-length pipe
Feng, Chunjuan; Liu, Feng; Rusak, Zvi; Wang, Shixiao
2017-09-01
Numerical solutions of the incompressible Navier-Stokes equations are obtained to study the time evolution of both axisymmetric and three-dimensional perturbations to a base solid-body-rotation flow in a finite-length pipe with non-periodic boundary conditions imposed at the pipe inlet and outlet. It is found that for a given Reynolds number there exists a critical swirl number beyond which the initial perturbations grow, in contrast to the solid-body rotation flow in an infinitely-long pipe or a finite-length pipe with periodic inlet and exit boundary conditions for which the classical Kelvin analysis and Rayleigh stability criterion affirm neutrally stable for all levels of swirl. This paper uncovers for the first time the detailed evolution of the perturbations in both the axisymmetric and three-dimensional situations. The computations reveal a linear growth stage of the perturbations with a constant growth rate after a brief initial period of decay of the imposed initial perturbations. The fastest growing axisymmetric and three-dimensional instability modes and the associated growth rates are identified numerically for the first time. The computations show that the critical swirl number increases and the growth rate of instability decreases at the same swirl number with decreasing Reynolds number. The growth rate of the axisymmetric mode at high Reynolds number agrees well with previous stability theory for inviscid flow. More importantly, three-dimensional simulations uncover that the most unstable mode is the spiral type m = 1 mode, which appears at a lower critical swirl number than that for the onset of the axisymmetric mode. This spiral mode grows faster than the unstable axisymmetric mode at the same swirl. Moreover, the computations reveal that after the linear growing stage of the perturbation the flow continues to evolve nonlinearly to a saturated axisymmetric vortex breakdown state.
Experimental study of rotating Hagen-Poiseuille flow discharging into a 1:8 sudden expansion
Miranda-Barea, A.; Martínez-Arias, B.; Parras, L.; Burgos, M. A.; del Pino, C.
2015-03-01
In this paper, we present experimental evidence for the five different states that result from rotating Hagen-Poiseuille flow when it discharges into a 1:8 sudden expansion, namely: stable, convectively unstable, unstable shear layer, stable and unstable vortex breakdowns. Sanmiguel-Rojas et al. ["Three-dimensional structure of confined swirling jets at moderately large Reynolds numbers," Phys. Fluids 20, 044104 (2008)] numerically predicted four of these five states and mapped the transition from one state to another. Our main objective is to study the onset of instabilities and vortex breakdown in these states experimentally. For this purpose, we visualize the flow at the inlet of the expansion for several values of moderately large Reynolds numbers, Re, and of swirl parameters, S. We analyze the inner region of the state that corresponds to the unstable shear layer in the sudden expansion and find two different states that share the same character, although they have different non-dimensional frequencies. The first relates to an oscillating structure near the axis, which arises at a small value of the swirl parameter, as well as to a generation of vortices that move downstream. The second shows, for greater values of the swirl parameter, vortices interacting with the boundary layer located on the wall of the static container that is perpendicular to the flow direction. In addition, we find a transition from stable to unstable vortex breakdown when perturbations become absolutely unstable inside the rotating pipe flow. Therefore, the most remarkable experimental finding is a new state, namely, unstable or transient vortex breakdown that takes place for the same pair of values (Rea, Sa) at which the onset of the absolute instability curve appears and intersects the region of stable vortex breakdown.
Shirsath, Sushil S.; Padding, Johan T.; Kuipers, J.A.M. (Hans); Clercx, Herman J.H.
2015-01-01
A discrete element model (DEM) is used to investigate the behavior of spherical particles flowing down a semicylindrical rotating chute. The DEM simulations are validated by comparing with particle tracking velocimetry results of spherical glass particles flowing through a smooth semicylindrical chu
Stability analysis of the rimming flow inside a uniformly heated rotating horizontal cylinder
Kumawat, Tara Chand; Tiwari, Naveen
2017-03-01
The stability analysis is presented for a thin viscous liquid film flowing inside a uniformly heated horizontal cylinder that is rotating about its axis. The free surface evolution equation for the liquid-gas interface is obtained by simplifying the Navier-Stokes and energy equations within the lubrication approximation. Various dimensionless numbers are obtained that quantify the effect of gravity, viscous drag, inertia, surface tension, and thermocapillary stress. The film thickness evolution equation is solved numerically to obtain two-dimensional, steady state solutions neglecting axial variations. A liquid pool forms at the bottom of the cylinder when gravity dominates other forces. This liquid pool is shifted in the direction of rotation when inertia or viscous drag is increased. Small axial perturbations are then imposed to the steady solutions to study their stability behavior. It is found that the inertia and capillary pressure destabilize whereas the gravity and thermocapillary stress stabilize the rimming flow. The influence of Marangoni number is reported by computing the stable and unstable parametric regions. Thicker films are shown to be more susceptible to become unstable.
Wosnik, Martin
2015-11-01
Recently an analytical and experimental investigation of the turbulent axisymmetric wake with rotation found a new asymptotic scaling function for the mean swirl, Wmax ~Uo3/ 2 ~x-1 (Dufresne and Wosnik, Mar Technol Soc J, 47, no.4, 193-205, 2013). An equilibrium similarity theory derived scaling functions from the conditions for the existence of similarity directly from the equations of motion. Axial and azimuthal (swirl) velocities were measured in the wake of a single 3-bladed wind turbine in a free stream up to 20 diameters downstream, and the data were found to support the theoretical results. The scaling implies that the mean swirl decays faster, with x-1, than the mean velocity deficit, with x - 2 / 3. Real wind turbines, however, operate in the atmospheric boundary layer. They are subjected to mean shear and turbulence, both have been observed to improve wake recovery. Similarity considerations are extended to place a turbulent axisymmetric wake with rotation in a boundary layer flow, and the scaling implications are examined. Corresponding experiments were carried out in the UNH Flow Physics Facility, using model wind turbines of various sizes as swirling wake generators. Supported by NSF CBET grant 1150797.
The Universal Aspect Ratio of Vortices in Rotating Stratifi?ed Flows: Experiments and Observations
Aubert, Oriane; Gal, Patrice Le; Marcus, Philip S
2012-01-01
We validate a new law for the aspect ratio $\\alpha = H/L$ of vortices in a rotating, stratified flow, where $H$ and $L$ are the vertical half-height and horizontal length scale of the vortices. The aspect ratio depends not only on the Coriolis parameter f and buoyancy (or Brunt-Vaisala) frequency $\\bar{N}$ of the background flow, but also on the buoyancy frequency $N_c$ within the vortex and on the Rossby number $Ro$ of the vortex such that $\\alpha = f \\sqrt{[Ro (1 + Ro)/(N_c^2- \\bar{N}^2)]}$. This law for $\\alpha$ is obeyed precisely by the exact equilibrium solution of the inviscid Boussinesq equations that we show to be a useful model of our laboratory vortices. The law is valid for both cyclones and anticyclones. Our anticyclones are generated by injecting fluid into a rotating tank filled with linearly-stratified salt water. The vortices are far from the top and bottom boundaries of the tank, so there is no Ekman circulation. In one set of experiments, the vortices viscously decay, but as they do, they c...
DEFF Research Database (Denmark)
Nordkvist, Mikkel; Vognsen, Marie; Nienow, Alfred W.
2008-01-01
Mixing times were obtained by the iodine-thiosulphate decolorization technique using rotary jet heads (RJH) for mixing in a Perspex tank with an inner diameter of 0.75 m and an aspect ratio of 2.5 using both water (turbulent flow) and shear-thinning, carboxymethyl cellulose (CMC) solutions...... increases. Experiments in 0.75 wt% and 1.25 wt% CMC showed that the transition from transitional to turbulent flow occurs at a lower Reynolds number with head rotation than without. Furthermore, the decrease in mixing time caused by the rotation is much more pronounced when the flow is transitional than...
Chemical Kinetics in the expansion flow field of a rotating detonation-wave engine
Kailasanath, Kazhikathra; Schwer, Douglas
2014-11-01
Rotating detonation-wave engines (RDE) are a form of continuous detonation-wave engines. They potentially provide further gains in performance than an intermittent or pulsed detonation-wave engine (PDE). The overall flow field in an idealized RDE, primarily consisting of two concentric cylinders, has been discussed in previous meetings. Because of the high pressures involved and the lack of adequate reaction mechanisms for this regime, previous simulations have typically used simplified chemistry models. However, understanding the exhaust species concentrations in propulsion devices is important for both performance considerations as well as estimating pollutant emissions. A key step towards addressing this need will be discussed in this talk. In this approach, an induction parameter model is used for simulating the detonation but a more detailed finite-chemistry model is used in the expansion flow region, where the pressures are lower and the uncertainties in the chemistry model are greatly reduced. Results show that overall radical concentrations in the exhaust flow are substantially lower than from earlier predictions with simplified models. The performance of a baseline hydrogen/air RDE increased from 4940 s to 5000 s with the expansion flow chemistry, due to recombination of radicals and more production of H2O, resulting in additional heat release.
Paule, A; Lauga, B; Ten-Hage, L; Morchain, J; Duran, R; Paul, E; Rols, J L
2011-11-15
In their natural environment, the structure and functioning of microbial communities from river phototrophic biofilms are driven by biotic and abiotic factors. An understanding of the mechanisms that mediate the community structure, its dynamics and the biological succession processes during phototrophic biofilm development can be gained using laboratory-scale systems operating with controlled parameters. For this purpose, we present the design and description of a new prototype of a rotating annular bioreactor (RAB) (Taylor-Couette type flow, liquid working volume of 5.04 L) specifically adapted for the cultivation and investigation of phototrophic biofilms. The innovation lies in the presence of a modular source of light inside of the system, with the biofilm colonization and development taking place on the stationary outer cylinder (onto 32 removable polyethylene plates). The biofilm cultures were investigated under controlled turbulent flowing conditions and nutrients were provided using a synthetic medium (tap water supplemented with nitrate, phosphate and silica) to favour the biofilm growth. The hydrodynamic features of the water flow were characterized using a tracer method, showing behaviour corresponding to a completely mixed reactor. Shear stress forces on the surface of plates were also quantified by computer simulations and correlated with the rotational speed of the inner cylinder. Two phototrophic biofilm development experiments were performed for periods of 6.7 and 7 weeks with different inoculation procedures and illumination intensities. For both experiments, biofilm biomasses exhibited linear growth kinetics and produced 4.2 and 2.4 mg cm(-)² of ash-free dry matter. Algal and bacterial community structures were assessed by microscopy and T-RFLP, respectively, and the two experiments were different but revealed similar temporal dynamics. Our study confirmed the performance and multipurpose nature of such an innovative photosynthetic bioreactor
Anisotropic turbulence and zonal jets in rotating flows with a β-effect
Directory of Open Access Journals (Sweden)
B. Galperin
2006-01-01
Full Text Available Numerical studies of small-scale forced, two-dimensional turbulent flows on the surface of a rotating sphere have revealed strong large-scale anisotropization that culminates in the emergence of quasi-steady sets of alternating zonal jets, or zonation. The kinetic energy spectrum of such flows also becomes strongly anisotropic. For the zonal modes, a steep spectral distribution, E(n=CZ (Ω/R2 n-5, is established, where CZ=O(1 is a non-dimensional coefficient, Ω is the angular velocity, and R is the radius of the sphere, respectively. For other, non-zonal modes, the classical, Kolmogorov-Batchelor-Kraichnan, spectral law is preserved. This flow regime, referred to as a zonostrophic regime, appears to have wide applicability to large-scale planetary and terrestrial circulations as long as those are characterized by strong rotation, vertically stable stratification and small Burger numbers. The well-known manifestations of this regime are the banded disks of the outer planets of our Solar System. Relatively less known examples are systems of narrow, subsurface, alternating zonal jets throughout all major oceans discovered in state-of-the-art, eddy-permitting simulations of the general oceanic circulation. Furthermore, laboratory experiments recently conducted using the Coriolis turntable have basically confirmed that the lateral gradient of ''planetary vorticity'' (emulated via the topographic β-effect is the primary cause of the zonation and that the latter is entwined with the development of the strongly anisotropic kinetic energy spectrum that tends to attain the same zonal and non-zonal distributions, −5 and , respectively, in both the slope and the magnitude, as the corresponding spectra in other environmental conditions. The non-dimensional coefficient CZ in the −5 spectral law appears to be invariant, , in a variety of simulated and natural flows. This paper provides a brief review of the zonostrophic regime. The review includes the
Directory of Open Access Journals (Sweden)
Sahin Ahmed
2014-12-01
Full Text Available This study focuses analytically on the oscillatory hydromagnetic flow of a viscous, incompressible, electrically-conducting, non-Newtonian fluid in an inclined, rotating channel with non-conducting walls, incorporating couple stress effects. The model is then non-dimensionalized with appropriate variables and shown to be controlled by the inverse Ekman number (K2 = 1/Ek, the hydromagnetic body force parameter (M, channel inclination (α, Grashof number (Gr, Prandtl number (Pr, oscillation frequency (ω and time variable (ωT. Analytical solutions are derived using complex variables. Excellent agreement is obtained between both previous and present work. The influence of the governing parameters on the primary velocity, secondary velocity, temperature (θ, primary and secondary flow discharges per unit depth in the channel, and frictional shear stresses due to primary and secondary flow, is studied graphically and using tables. Applications of the study arise in the simulation of the manufacture of electrically-conducting polymeric liquids and hydromagnetic energy systems exploiting rheological working fluids.
Numerical analysis of 3-D unsteady flow in a vaneless counter-rotating turbine
Institute of Scientific and Technical Information of China (English)
ZHAO Qingjun; WANG Huishe; ZHAO Xiaolu; XU Jianzhong
2007-01-01
To reveal the unsteady flow characteristics of a vaneless counter-rotating turbine (VCRT),a threedimensional,viscous,unsteady computational fluid dynamics (CFD) analysis was performed.The results show that unsteady simulation is superior to steady simulation because more flow characteristics can be obtained.The unsteady effects in upstream airfoil rows are weaker than those in downstream airfoil rows in the VCRT.The static pressure distribution along the span in the pressure surface of a high pressure turbine stator is more uniform than that in the suction surface.The static pressure distributions along the span in the pressure surfaces and the suction surfaces of a high pressure turbine rotor and a low pressure turbine rotor are all uneven.The numerical results also indicate that the load of a high pressure turbine rotor will increase with the increase of the span.The deviation is very big between the direction of air flow at the outlet of a high pressure turbine rotor and the axial direction.A similar result can also be obtained in the outlet of a low pressure turbine rotor.This means that the specific work of a high pressure turbine rotor and a low pressure turbine rotor is big enough to reach the design objectives.
Flow of immiscible ferrofluids in a planar gap in a rotating magnetic field
Energy Technology Data Exchange (ETDEWEB)
Sule, Bhumika [Department of Chemical Engineering, University of Florida, Gainesville, Florida 32611 (United States); Torres-Díaz, Isaac [J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, Florida 32611 (United States); Rinaldi, Carlos [Department of Chemical Engineering, University of Florida, Gainesville, Florida 32611 (United States); J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, Florida 32611 (United States)
2015-07-15
Analytical solutions are obtained for the steady, fully developed flow of two layers of immiscible ferrofluids of different thicknesses between two parallel plates. Interfacial linear and internal angular momentum balance relations are derived for the case when there is a ferrofluid-ferrofluid interface to obtain the translational and spin velocity profiles in the gap. As expected for the limit of low applied field amplitude, the magnitude of the translational velocity is directly proportional to the frequency of the applied magnetic field and to the square of the magnetic field amplitude. Expressions for the velocity profiles are obtained for the zero spin viscosity and non-zero spin viscosity cases and the effect of applied pressure gradient on the flows is studied. The spin velocity in both ferrofluid phases is in the direction of the rotating magnetic field, except for cases of extreme applied pressure gradients for which the fluid vorticity opposes the spin. We find that for the case of non-zero spin viscosity, flow reversals are predicted using representative ferrofluid property values and field conditions. The unique predictions of the solution with non-zero spin viscosity could be used to experimentally test the existence of couple stresses in ferrofluids and the validity of previously reported values of the so-called spin viscosity.
Institute of Scientific and Technical Information of China (English)
M. Turkyilmazoglu
2012-01-01
The present paper is concerned with a class of exact solutions to the steady Navier-Stokes equations for the incompressible Newtonian viscous electrically conducting fluid flow due to a porous disk rotating with a constant angular speed.The three-dimensional hydromagnetic equations of motion are treated analytically to obtained exact solutions with the inclusion of suction and injection.The well-known thinning/thickening flow field effect of the suction/injection is better understood from the constructed closed form velocity equations.Making use of this solution,analytical formulas for the angular velocity components as well as for the permeable wall shear stresses are derived.Interaction of the resolved flow field with the surrounding temperature is further analyzed via the energy equation.The temperature field is shown to accord with the dissipation and the Joule heating.As a result,exact formulas are obtained for the temperature field which take different forms corresponding to the condition of suction or injection imposed on the wall.
Energy Technology Data Exchange (ETDEWEB)
Tanabe, S.; Kashiwada, Y.; Waka, R. (Tottori Univ., Tottori (Japan). Faculty of Engineering); Liu, Guobang (Okayama Univ., Okayama (Japan). Graduate School)
1994-04-25
In recent years, there are many cases of usage of the intake system aiming at formation of swirls because of the demand for improvement of combustion of internal combustion engines. This study has the objective to examine experimentally the effect of the rotating strength on the discharge coefficient of an intake valve in the stationary flow by changing the strength of intake rotation around the valve axis in case when the air is running into the cylinder while rotating around the intake valve axis. The information obtained as a result is as follows; at a part where the valve head is small, the effect of the rotation in the upper flow of the valve on the discharge coefficient is small, but as the valve head becomes bigger, the effect of rotation increases, and as the rotation is stronger, the flow coefficient becomes less. In case when the valve head angle is 0[degree], the discharge coefficient at the low valve head becomes bigger than the case when the valve head angle is 20[degree]. Concerning the discharge coefficient obtained from the difference between the pressure in the cylinder and the atmospheric pressure, in case when the valve head is small, the discharge coefficient becomes big since the theoretical air capacity is estimated less due to the pressure recovery. 7 refs., 13 figs.
Energy Technology Data Exchange (ETDEWEB)
Barbosa, Marcos Pinotti
1992-07-01
Flow study in the formatted channel for two disks in rotation is discussed including the following main issues: flow description between disks in rotation; computational model; and numerical results. The parametric studies accomplished of the spacing between disks, of the diameter, and of the rotor angular speed allowed the influence analysis of these variables in the flow inside the channel and in the generated pressure difference. The disks rotation, evaluated through Reynolds' rotational number, is the main parameter that influences the pressure difference between channel entrance and exit. It verified although how much larger the rotation larger the pressure difference.
Directory of Open Access Journals (Sweden)
Navid Freidoonimehr
2014-01-01
Full Text Available A coupled system of nonlinear ordinary differential equations that models the three-dimensional flow of a nanofluid in a rotating channel on a lower permeable stretching porous wall is derived. The mathematical equations are derived from the Navier-Stokes equations where the governing equations are normalized by suitable similarity transformations. The fluid in the rotating channel is water that contains different nanoparticles: silver, copper, copper oxide, titanium oxide, and aluminum oxide. The differential transform method (DTM is employed to solve the coupled system of nonlinear ordinary differential equations. The effects of the following physical parameters on the flow are investigated: characteristic parameter of the flow, rotation parameter, the magnetic parameter, nanoparticle volume fraction, the suction parameter, and different types of nanoparticles. Results are illustrated graphically and discussed in detail.
Effects of Taylor-Görtler vortices on turbulent flows in a spanwise-rotating channel
Dai, Yi-Jun; Huang, Wei-Xi; Xu, Chun-Xiao
2016-11-01
Fully developed turbulent channel flow with system rotation in the spanwise direction has been studied by direct numerical simulation at Rem = 2800 and 7000 with 0 ≤ Rom ≤ 0.5. The width of the computational domain is adjusted for each case to contain two pairs of Taylor-Görtler (TG) vortices. Under a relatively low rotation rate, the turbulent vortical structures are strongly influenced by the TG vortices. A conditional average method is employed to investigate the effects of these TG vortices on turbulence. In the upwash region where the fluid is pumped away from the pressure wall by the TG vortices, turbulence is found to be enhanced, while the opposite scenario occurs in the downwash region where the fluid is shifted toward the pressure wall. The statistics along the centerlines of the two regions of a TG vortex are presented in detail. Through the budget analysis of the transport equation of vorticity fluctuations, we found that the wall-normal stretching term caused by the TG vortices plays an important role in initiating the differences of turbulence intensities between the two regions, which are further augmented by the Coriolis force term in the streamwise direction. Meanwhile, the shear stress on the suction wall is observed to fluctuate in a quasi-periodic manner at Rem = 7000 and Rom = 0.3, which is also revealed to be induced by the TG vortices. Such quasi-periodicity is not found at Rem = 2800 and Rom = 0.3, where turbulence on the suction side is strongly suppressed by rotation.
Chen, K.; Shorthill, R. W.; Flandro, G. A.
1986-08-01
The development of a Laser Doppler Velocimeter (LDV) designed to measure two orthogonal velocity components in a complex rotating flow is described; this flow simulates the unsteady flows encountered in spinning rocket motor operations as well as such time-dependent phenomena as low frequency acoustic oscillations. The LDV is a three watt, two color, three beam system with a velocity measurement device that follows the flow continuously without any disturbance. The focusing optics, photo multipliers, amplifiers and test chamber are mounted on a precision Genisco C-181 rate-of-return table and spun to about 60 RPM. The silicon carbide particles used for seeding follow velocity fluctuations up to several hundred KHz. Two-dimensional unsteady velocity measurement systems for water flow rotating in the horizontal direction and tilting in the vertical direction are presented and discussed.
Theoretical Investigation of Creeping Viscoelastic Flow Transition Around a Rotating Curved Pipe
Hamza, S E E
2015-01-01
The study of creeping motion of viscoelastic fluid around a rotating rigid torus is investigated. The analysis of the problem is performed using a second-order viscoelastic model. The study is carried out in terms of the bipolar toroidal system of coordinates where the toroid is rotating about its axis of symmetry (z-axis). The problem is solved within the frame of slow flow approximation. Therefore, all variables in the governing equations are expanded in a power series of angular velocity. A set of successive partial differential equations is obtained. The equations of motion governing the first and second-order are formulated and solved for the first-order only in this paper. However, the solution of the second-order equations will be the subject of a part two of this series of papers. Analytically, Laplace's equation is solved via the usual method of separation of variables. This method shows that, the solution is given in a form of infinite sums over Legendre functions of the first and second kinds. From...
Counter-rotating type axial flow pump unit in turbine mode for micro grid system
Kasahara, R.; Takano, G.; Murakami, T.; Kanemoto, T.; Komaki, K.
2012-11-01
Traditional type pumped storage system contributes to adjust the electric power unbalance between day and night, in general. This serial research proposes the hybrid power system combined the wind power unit with the pump-turbine unit, to provide the constant output for the grid system, even at the suddenly fluctuating/turbulent wind. In the pumping mode, the pump should operate unsteadily at not only the normal but also the partial discharge. The operation may be unstable in the rising portion of the head characteristics at the lower discharge, and/or bring the cavitation at the low suction head. To simultaneously overcome both weak points, the authors have proposed a superior pump unit that is composed of counter-rotating type impellers and a peculiar motor with double rotational armatures. This paper discusses the operation at the turbine mode of the above unit. It is concluded with the numerical simulations that this type unit can be also operated acceptably at the turbine mode, because the unit works so as to coincide the angular momentum change through the front runners/impellers with that thorough the rear runners/impellers, namely to take the axial flow at not only the inlet but also the outlet without the guide vanes.
The Universal Aspect Ratio of Vortices in Rotating Stratified Flows: Theory and Simulation
Hassanzadeh, Pedram; Gal, Patrice Le
2012-01-01
We derive a relationship for the vortex aspect ratio $\\alpha$ (vertical half-thickness over horizontal length scale) for steady and slowly evolving vortices in rotating stratified fluids, as a function of the Brunt-Vaisala frequencies within the vortex $N_c$ and in the background fluid outside the vortex $\\bar{N}$, the Coriolis parameter $f$, and the Rossby number $Ro$ of the vortex: $\\alpha^2 = Ro(1+Ro) f^2/(N_c^2-\\bar{N}^2)$. This relation is valid for cyclones and anticyclones in either the cyclostrophic or geostrophic regimes; it works with vortices in Boussinesq fluids or ideal gases, and the background density gradient need not be uniform. Our relation for $\\alpha$ has many consequences for equilibrium vortices in rotating stratified flows. For example, cyclones must have $N_c^2 > \\bar{N}^2$; weak anticyclones (with $|Ro| \\bar{N}^2$. We verify our relation for $\\alpha$ with numerical simulations of the three-dimensional Boussinesq equations for a wide variety of vortices, including: vortices that are i...
Modelling of liquid flow after a hydraulic jump on a rotating disk prior to centrifugal atomization
Zhao, Y. Y.; Dowson, A. L.; Jacobs, M. H.
2000-01-01
This paper describes a simplified numerical model which is used to calculate the height distribution, and the radial and tangential velocities of a liquid on a rotating disk after a hydraulic jump and prior to centrifugal atomization. The results obtained from this numerical model are compared with predictions made using previously derived `hydraulic jump' and `analytical' models. Calculations, in conjunction with experimental measurements relating to the trajectory of liquid flow on the atomizing disk, have shown that the numerical model can not only give a reasonable prediction of the hydraulic jump location, but also yields more accurate information regarding the variations in liquid height, and radial and tangential velocities. The model is ideally suited for engineering applications.
Directory of Open Access Journals (Sweden)
Butrymowicz Dariusz
2016-09-01
Full Text Available The theoretical basis for the indirect measurement approach of mean heat transfer coefficient for the packed bed based on the modified single blow technique was presented and discussed in the paper. The methodology of this measurement approach dedicated to the matrix of the rotating regenerative gas heater was discussed in detail. The testing stand consisted of a dedicated experimental tunnel with auxiliary equipment and a measurement system are presented. Selected experimental results are presented and discussed for selected types of matrices of regenerative air preheaters for the wide range of Reynolds number of gas. The agreement between the theoretically predicted and measured temperature profiles was demonstrated. The exemplary dimensionless relationships between Colburn heat transfer factor, Darcy flow resistance factor and Reynolds number were presented for the investigated matrices of the regenerative gas heater.
Directory of Open Access Journals (Sweden)
R. S. Agarwal
1980-04-01
Full Text Available The Newton Raphson technique has been employed to solve the set of non-linear equations governing the problem of flow and heat transfer from an enclosed rotating disc. /The disc called rotor is subjected to uniform injection while the top of the housing called stator, to an equal suction. The results for small Reynold numbers are found in good agreement to that obtained earlier by series solution. The radial and transverse velocity profiles for large Reynolds have been plotted in the regions of no recirculation. The effect of net radial inflow and outflow on temperature in the no-recirculation region has also been studied. The method is significant in this respect that it yields satisfactory results for large Reynolds numbers.
Directory of Open Access Journals (Sweden)
Girishwar Nath
1970-10-01
Full Text Available A closed form solution of the Navier-Stokes equations has been obtained in the case of steady axisymmetric flow of an incompressible electrically conducting viscous fluid between two concentric rotating cylinders composed of an insulating material under the influence of radial magnetic field. It has been found that the velocity components are less than those of the classical hydrodynamic case. In the presence of the magnetic field, the tangential velocity becomes fully developed in a smaller axial distance than in the absence of the magnetic field. For small Reynolds number, the fully developed tangential velocity is achieved in a small axial distance, but it requires greater axial distance for large Reynolds number.
MHD flow of Burger's fluid over an off-centered rotating disk in a porous medium
Khan, Najeeb Alam; Khan, Sidra; Ullah, Saif
2015-08-01
In this study, off-centered stagnation flow of three dimensional Burger's fluid over an infinite rotating disk in a porous medium with a uniform magnetic field, which is applying normal to the disk, is investigated. A uniform suction/injection is applied through the surface of the porous disk. The structure has been modeled in the form of ordinary differential equations, which are reduced from partial differential equations by using the similarity transformation. Analytical solution is obtained by non-perturbation technique of homotopy analysis method (HAM). The influence of non-dimensional parameters on velocity profile is presented in graphical form and the numerical comparison is made with the viscous fluid as a special case.
Vertical rotation effect on turbulence characteristics in an open channel flow
Institute of Scientific and Technical Information of China (English)
Zou Li-Yong; Bai Jing-Song; Li Bu-Yang; Tan Duo-Wang; Li Ping; Liu Cang-Li
2008-01-01
This paper solves the three-dimensional Navier-Stokes equation by a fractional-step method with the Reynolds number Reγ=194 and the rotation number Nγ=0-0.12. When Nγ is less than 0.06, the turbulence statistics relevant to the spanwise velocity fluctuation are enhanced, but other statistics are suppressed. When Nγ is larger than 0.06,all the turbulence statistics decrease significantly. Reynolds stress budgets elucidate that turbulence kinetic energy in the vertical direction is transferred into the streamwise and spanwise directions. The flow structures exhibit that the bursting processes near the bottom wall are ejected toward the free surface.Evident change of near-surface streak structures of the velocity fluctuations are revealed.
Akimoto, Hiromichi; Hara, Yutaka; Kawamura, Takafumi; Nakamura, Takuju; Lee, Yeon-Seung
2013-12-01
In a vertical axis wind turbine (VAWT), turbine blades are subjected to the curved flow field caused by the revolution of turbine. However, performance prediction of VAWT is usually based on the fluid dynamic coefficients obtained in wind tunnel measurements of the two-dimensional static wing. The difference of fluid dynamic coefficients in the curved flow and straight flow deteriorates the accuracy of performance prediction. To find the correlation between the two conditions of curved and straight flow, the authors propose a conformal mapping method on complex plane. It provides bidirectional mapping between the two flow fields. For example, the flow around a symmetric wing in the curved flow is mapped to that around a curved (cambered) wing in the straight flow. Although the shape of mapped wing section is different from the original one, its aerodynamic coefficients show a good correlation to those of the original in the rotating condition. With the proposed method, we can reproduce the local flow field around a rotating blade from the flow data around the mapped static wing in the straight flow condition.
A study of the effect of BTA on flow electrification using rotating cylindrical electrodes
Energy Technology Data Exchange (ETDEWEB)
Washabaugh, A.P.; Zahn, M. [Massachusetts Institute of Technology, Cambridge, MA (United States)
1995-05-01
A rotating cylindrical electrode apparatus was used to simulate flow electrification in an electric power transformer and study the effects of the additive 1,2,3 benzotriazole (BTA). The experiments had Shell Diala A transformer oil filling the annulus between coaxial cylindrical (stainless steel) electrodes and EHV-Weidmann HiVal pressboard covering a thin copper sheet epoxied to the inner cylinder. Time transient and steady state measurements of the charge density in the core region of the fluid flow and the terminal current or voltage were performed over temperatures ranging from 15-70{degrees}C, inner cylinder rotation rates of 100-1400 rpm (Reynolds numbers of 5x10{sup 3}-5x10{sup 5}), and oil BTA concentrations of 0-60 ppm. The BTA appeared to cause competing effects: it reduced the volume charge density on the liquid side of the interface (by a factor of 10) which reduces the electrification but also decreased the oil conductivity (by a factor of 10), which increases the electrification. The BTA also had both long term and short term effects on the electrification. The steady state charge density, short-circuit current and open-circuit voltage had a minimum magnitude for a BTA concentration between 5 and 8 ppm. This paper also develops a physical model for the electrification which uses established representations for the interfacial charge transfer boundary condition. Based on the model, the steady state experimental data shows the largest magnitudes when the diffusion sublayer thickness is small compared to the Debye length. Interfacial volume charge densities ({rho}{sup w}`s) were estimated from the open-circuit data. From the short-circuit data, rate constants for the interfacial charge transfer appear to be large, but cannot always be taken as infinite.
Flow past a rotating cylinder at high Reynolds number using PANS method
Kumar, Rajesh
2016-11-01
In the present study, high-Reynolds number flow past a rotating cylinder has been simulated using Partially-Averaged Navier-Stokes (PANS) method. The simulations are performed at Re = 140000. The spin ratio of the cylinder, which is defined by the ratio of the circumferential speed of the cylinder to the free-stream speed, varies from a = 0 to a = 4. The resolved and the modeled physical scales have been compared with the corresponding LES data for better understanding of the efficacy of the PANS method. The comparison of PANS results with the LES results showed good agreement. It has been recognized that the PANS simulation is able to produce fairly acceptable results using even a coarse-mesh. It is recognized that the time-averaged flow statistics obtained using PANS and URANS simulations are approximately same. However the vortex structure is much better captured by the PANS method. With the increase in the spin ratio, decrease in the time-averaged drag and increase in the time-averaged lift force acting on the cylinder have been observed. The vortices in far wake region are displaced and deformed but those in the vicinity of the cylinder are stretched at the bottom and accumulated over the top of the cylinder.
Three-dimensional particle tracking velocimetry applied to granular flows down rotating chutes
Clercx, Herman; Shirsath, Sushil; Padding, Johan; Kuipers, Hans
2014-11-01
We report on the cross-validation of 3D particle tracking velocimetry (3D-PTV) with other measurement techniques, such as particle image velocimetry (PIV), electronic ultrasonic sensor measurements for bed height and the discrete element model (DEM), for gaining more insight into the behavior of granular flows down inclined rotating chutes. In particular we aim at gaining access to Lagrangian displacement data of surface particles in granular flows and to obtain independent measurements of both the surface velocity and the bed height in the chute. The 3D-PTV method is based on imaging and tracking colored tracer particles that are introduced in the granular material, which are viewed from three directions. The three cameras collect consecutive frames a known Δt apart and the PTV algorithm for locating and tracking particles is used to determine particle trajectories and velocities. The PTV and PIV results are in good mutual agreement with regard to the streamwise and spanwise surface velocity. The particle bed height obtained from 3D-PTV was compared with data from an ultrasonic bed-height sensor and it is found to be in good mutual agreement, as was the case for the comparison between the experimental findings from 3D-PTV and simulations by DEM.
Effects of Thermal Radiation on Hydromagnetic Flow due to a Porous Rotating Disk with Hall Effect
Directory of Open Access Journals (Sweden)
S.P Anjali Devi
2012-01-01
Full Text Available Radiation effect on steady laminar hydromagnetic flow of a viscous, Newtonian and electrically conducting fluid past a porous rotating infinite disk is studied taking Hall current into account. The system of axisymmetric nonlinear partial differential equations governing the MHD flow and heat transfer are reduced to nonlinear ordinary differential equations by introducing suitable similarity variables introduced by von Karman and the resulting nonlinear equations are solved numerically using Runge-Kutta based shooting method. A parametric study of all parameters involved was conducted and a representative set of results showing the effect of the magnetic field, the radiation parameter, the uniform suction/injection parameter and Hall parameter are illustrated graphically. The numerical values of the radial and tangential skin-friction coefficient and Nusselt number are calculated and displayed in the tables showing the effects of various parameters. Finally, a good comparison between the present numerical predictions and the previously published data are presented in the absence of magnetic field and radiation.
Institute of Scientific and Technical Information of China (English)
Jingxuan Zhang; Feng Lin; Jingyi Chen; Chaoqun Nie
2009-01-01
The stall behavior in a single-stage low-speed axial compressor under rotating inlet distortion (RID) is investi-gated in the first half of this paper. The tests demonstrate that the tip leakage flow (TLF) plays an important rolein triggering rotating stall. The tracking of the spike-like disturbances caused by the spillage of TLV indicates that most of such spike-like disturbances will be smeared by non-distorted sector and the growth of the spike-like dis-turbances actually relate closely to how and how often the path of the propagating disturbances come across the path of the rotating distorted sector. In the second half of this paper, micro air injections are applied to test the ef-fect behavior of TLF on stall inception. Contrasts to without micro air injections, the spike-like disturbances are much fewer, so the possibilities that spike-like disturbances may trigger rotating stall are fewer too. As a result, the compressor gets a lower mass flow rate at stall for both co-rotating inlet distortion and counter-rotating inlet distortion.
Huang, D.; Pan, Z. Y.
2015-01-01
In order to study the flow-head characteristic curve, the SST turbulence model, homogeneous multiphase model and Rayleigh-Plesset equation were applied to simulate the cavitation characteristics in contra-rotating axial flow waterjet pump under different conditions based on ANSYS CFX software. The distribution of cavity, pressure coefficient of the blade at the design point under different cavitation conditions were obtained. The analysis results of flow field show that the vapour volume distribution on the impeller indicates that the vapour first appears at the leading edge of blade and then extends to the outlet of impeller with the reduction of Net Positive Suction Head Allowance (NPSHA). The present study illustrates that the main reason for the decline of the pump performance is the development of cavitation, and the simulation can truly reflect the cavitation performance of the contra-rotating axial flow waterjet pump.
Klein, Simon; Bérut, Antoine; Bodenschatz, Eberhard
2012-01-01
We report a novel experimental technique that measures simultaneously in three dimensions the trajectories, the translation, and the rotation of finite size inertial particles together with the turbulent flow. The flow field is analyzed by tracking the temporal evolution of small fluorescent tracer particles. The inertial particles consist of a super-absorbent polymer that makes them index and density matched with water and thus invisible. The particles are marked by inserting at various locations tracer particles into the polymer. Translation and rotation, as well as the flow field around the particle are recovered dynamically from the analysis of the marker and tracer particle trajectories. We apply this technique to study the dynamics of inertial particles much larger in size (Rp/{\\eta} \\approx 100) than the Kolmogorov length scale {\\eta} in a von K\\'arm\\'an swirling water flow (R{\\lambda} \\approx 400). We show, using the mixed (particle/fluid) Eulerian second order velocity structure function, that the in...
Froessling, Nils
1958-01-01
The fundamental boundary layer equations for the flow, temperature and concentration fields are presented. Two dimensional symmetrical and unsymmetrical and rotationally symmetrical steady boundary layer flows are treated as well as the transfer boundary layer. Approximation methods for the calculation of the transfer layer are discussed and a brief survey of an investigation into the validity of the law that the Nusselt number is proportional to the cube root of the Prandtl number is presented.
Institute of Scientific and Technical Information of China (English)
YUAN Feng; ZHU Xiaocheng; DU Zhaohui
2007-01-01
An experimental investigation of three-dimensional flow field in a film-cooled turbine model is carried out by using particle image velocimeter (PIV) in a low-speed wind tunnel. The effects of different blowing ratios (M=1.5, 2) on the flow field are studied. The experimental results reveal the classical phenomena of the formation of kidney vortex pair and secondary flow in wake region behind the jet hole. And the changes of the kidney vortex pair and the wake at different locations away from the hole on the suction and pressure sides are also studied. Compared with the flow field in stationary cascade, there are centrifugal force and Coriolis force existing in the flow field of rotating turbine, and these forces bring the radial velocity in the jet flow. The effect of rotation on the flow field of the pressure side is more distinct than that on the suction side from the measured flow fields in Y-Z plane and radial velocity contours. The increase of blowing ratio makes the kidney vortex pair and the secondary flow in the wake region stronger and makes the range of the wake region enlarged.
Rosén, T; Do-Quang, M; Aidun, C K; Lundell, F
2015-05-01
This work describes the inertial effects on the rotational behavior of an oblate spheroidal particle confined between two parallel opposite moving walls, which generate a linear shear flow. Numerical results are obtained using the lattice Boltzmann method with an external boundary force. The rotation of the particle depends on the particle Reynolds number, Re(p)=Gd(2)ν(-1) (G is the shear rate, d is the particle diameter, ν is the kinematic viscosity), and the Stokes number, St=αRe(p) (α is the solid-to-fluid density ratio), which are dimensionless quantities connected to fluid and particle inertia, respectively. The results show that two inertial effects give rise to different stable rotational states. For a neutrally buoyant particle (St=Re(p)) at low Re(p), particle inertia was found to dominate, eventually leading to a rotation about the particle's symmetry axis. The symmetry axis is in this case parallel to the vorticity direction; a rotational state called log-rolling. At high Re(p), fluid inertia will dominate and the particle will remain in a steady state, where the particle symmetry axis is perpendicular to the vorticity direction and has a constant angle ϕ(c) to the flow direction. The sequence of transitions between these dynamical states were found to be dependent on density ratio α, particle aspect ratio r(p), and domain size. More specifically, the present study reveals that an inclined rolling state (particle rotates around its symmetry axis, which is not aligned in the vorticity direction) appears through a pitchfork bifurcation due to the influence of periodic boundary conditions when simulated in a small domain. Furthermore, it is also found that a tumbling motion, where the particle symmetry axis rotates in the flow-gradient plane, can be a stable motion for particles with high r(p) and low α.
DEFF Research Database (Denmark)
Sheikholeslami, R; Ashorynejad, H.R; Barari, Amin
2013-01-01
Purpose – The purpose of this paper is to analyze hydromagnetic flow between two horizontal plates in a rotating system. The bottom plate is a stretching sheet and the top one is a solid porous plate. Heat transfer in an electrically conducting fluid bounded by two parallel plates is also studied...
Institute of Scientific and Technical Information of China (English)
Shude JI; Aili ZOU; Yumei YUE; Guohong LUAN; Yanye JIN; Fu LI
2012-01-01
The rotational tool is put forward,which is composed of the one-spiral-flute shoulder and the rotational pin with screw.Using the turbulent model of the FLUENT software,material plastic flow behavior during the process of friction stir welding of Ti6Al4V alloy is researched by the numerical simulation method and then the effect of rotational tool geometry on material flow during the welding process is attained.The results show that the flow direction of the material near the rotational tool is mainly the same as the rotational direction of the tool while the material near tool flows more violently than the other regions.For the tapered rotational pin,the flow velocity of material inside the workpiece decreases with the increase of the distance away from the workpiece surface because of the change of pin diameter.For the rotational tool,the flute added to the shoulder and the screw added to the pin can greatly increase the flow velocity of material during the welding process while the peak value of the flow velocity of material appears on the flute or the screw.Moreover,the rotational tool with the one-spiral-flute shoulder is better than the tool with the concentriccircles-flute shoulder.Decreasing the width of pin screw and increasing the diameter of pin tip are both good for the increase of flow velocity.
National Research Council Canada - National Science Library
Brahim Berrabah Miloud Aminallah
.... The density ratios were 0.13, 0.23 and 0.50. The results show that at high buoyancy parameter and high rotation number with a low density ratio, the flow in the first passage is governed by the secondary flow induced by the rotation whereas...
Directory of Open Access Journals (Sweden)
Ashfaq Ahmed Pathan
2015-04-01
Full Text Available The performance of greywater treatment through RBC (Rotating Biological Contactor is related to many factors including rotational speed of disc, surface area of the media, thickness of biological film; quality and flow rate of influent. The plastic media provides surface for biological slime. The slime is rotated alternatively into the settled wastewater and then into atmosphere to provide aerobic conditions for the microorganisms. In this study the performance of RBC is investigated at different flow rates and disk areas of media by introducing additional discs on the shaft of RBC. Initially efficiency of the RBC was observed on six flow rates at the disc area of 9.78m2. Furthermore optimized three flow rates were used to augment the disk area. The efficiency of RBC system was improved significantly at disk area of 11.76m2 and flow rate of 20 L/h. Under these conditions the removal of BOD5 (Biochemical Oxygen Demand COD (Chemical Oxygen Demand and TSS (Total Suspended Solid was observed 83, 57 and 90% respectively
Hayat, Tasawar; Rafiq, Maimona; Ahmad, Bashir
2016-01-01
The objective of present paper is to examine the peristaltic flow of magnetohydrodynamic (MHD) Jeffrey fluid saturating porous space in a channel through rotating frame. Unlike the previous attempts, the flow formulation is based upon modified Darcy's law porous medium effect in Jeffrey fluid situation. In addition the impacts due to Soret and Dufour effects in the radiative peristaltic flow are accounted. Rosseland’s approximation has been utilized for the thermal radiative heat flux. Lubrication approach is implemented for the simplification. Resulting problems are solved for the stream function, temperature and concentration. Graphical results are prepared and analyzed for different parameters of interest entering into the problems. PMID:26808387
Directory of Open Access Journals (Sweden)
Tasawar Hayat
Full Text Available The objective of present paper is to examine the peristaltic flow of magnetohydrodynamic (MHD Jeffrey fluid saturating porous space in a channel through rotating frame. Unlike the previous attempts, the flow formulation is based upon modified Darcy's law porous medium effect in Jeffrey fluid situation. In addition the impacts due to Soret and Dufour effects in the radiative peristaltic flow are accounted. Rosseland's approximation has been utilized for the thermal radiative heat flux. Lubrication approach is implemented for the simplification. Resulting problems are solved for the stream function, temperature and concentration. Graphical results are prepared and analyzed for different parameters of interest entering into the problems.
MHD UNSTEADY FLOWS DUE TO NON-COAXIAL ROTATIONS OF A DISK AND A FLUID AT INFINITY
Institute of Scientific and Technical Information of China (English)
T.HAYAT; S.MUMTAZ; R.ELLAHI
2003-01-01
Exact analytical solution for flows of an electrically conducting fluid over an infinite oscillatory disk in the presence of a uniform transverse magnetic field is constructed.Both the disk and the fluid are in a state of non-coaxial rotation.Such a flow model has a great significance not only due to its own theoretical interest,but also due to applications to geophysics and engineering.The resulting initial value problem has been solved analytically by applying the Laplace transform technique and the explicit expressions for the velocity for steady and unsteady cases have been established.The analysis of the obtained results shows that the flow field is appreciably influenced by the applied magnetic field,the frequency and rotation parameters.
Cotrell, David L.; Pearlstein, Arne J.
2000-11-01
We report computations of the velocity field for flows driven by rotation of a screw in a circular cylinder with an applied opposing pressure gradient. Use of a helical coordinate system in a frame rotating with the screw reduces the flow calculation to a steady one, which is taken to be fully-developed in the helical direction. The full incompressible Navier-Stokes equations in primitive-variables form are solved numerically using a finite-element method employing quadrilateral elements with quadratic velocity and linear pressure interpolation. A consistent penalty method is used to satisfy incompressibility. The screw cross-section is rectangular. The effect of screw clearance and other geometric parameters on the velocity field will be discussed for low and intermediate Reynolds numbers and compared to the Stokes flow case.
MHD UNSTEADY FLOWS DUE TO NON—COAXIAL ROTATIONS OF A DISK AND A FLUID AT INFINITY
Institute of Scientific and Technical Information of China (English)
T.HAYAT
2003-01-01
Exact analytical solution for flows of an electrically conducting fluid over an infiniteoscillatory disk in the presence of a uniform transverse magnetic field is constructed. Both the disk andthe fluid are in a state of non-coaxial rotation. Such a flow model has a great significance not only clueto its own theoretical interest, but also clue to applications to geophysics and engineering. The resultinginitial value problem has been solved analytically by applying the Laplace transform technique and theexplicit expressions for the velocity for steady and unsteady cases have been established. The analysisof the obtained results shows that the flow field is appreciably influenced by the applied magnetic field,the frequency and rotation parameters.
Kahouadji, L.; Witkowski, L. Martin
2014-07-01
The flow driven by a rotating disk at the bottom of an open fixed cylindrical cavity is studied numerically and experimentally. The steady axisymmetric Navier-Stokes equations projected onto a curvilinear coordinate system are solved by a Newton-Raphson algorithm. The free surface shape is computed by an iterative process in order to satisfy a zero normal stress balance at the interface. In previous studies, regarding the free surface deflection, there is a significant disagreement between a first-order approximation [M. Piva and E. Meiburg, "Steady axisymmetric flow in an open cylindrical container with a partially rotating bottom wall," Phys. Fluids 17, 063603 (2005)] and a full numerical simulation [R. Bouffanais and D. Lo Jacono, "Unsteady transitional swirling flow in the presence of a moving free surface," Phys. Fluids 21, 064107 (2009)]. For a small deflection, the first-order approximation matches with our numerical simulation and for a large deflection a good agreement is found with experimental measurements.
Directory of Open Access Journals (Sweden)
G. Nath
2012-12-01
Full Text Available Self-similar solutions are obtained for unsteady, one-dimensional isothermal flow behind a shock wave in a rotational axisymmetric non-ideal gas in the presence of an azimuthal magnetic field. The shock wave is driven out by a piston moving with time according to power law. The fluid velocities and the azimuthal magnetic field in the ambient medium are assumed to be varying and obeying a power law. The density of the ambient medium is assumed to be constant. The gas is assumed to be non-ideal having infinite electrical conductivity and the angular velocity of the ambient medium is assumed to be decreasing as the distance from the axis increases. It is expected that such an angular velocity may occur in the atmospheres of rotating planets and stars. The effects of the non-idealness of the gas and the Alfven-Mach number on the flow-field are obtained. It is shown that the presence of azimuthal magnetic field and the rotation of the medium has decaying effect on the shock wave. Also, a comparison is made between rotating and non-rotating cases.
Counter-Rotatable Fan Gas Turbine Engine with Axial Flow Positive Displacement Worm Gas Generator
Giffin, Rollin George (Inventor); Murrow, Kurt David (Inventor); Fakunle, Oladapo (Inventor)
2014-01-01
A counter-rotatable fan turbine engine includes a counter-rotatable fan section, a worm gas generator, and a low pressure turbine to power the counter-rotatable fan section. The low pressure turbine maybe counter-rotatable or have a single direction of rotation in which case it powers the counter-rotatable fan section through a gearbox. The gas generator has inner and outer bodies having offset inner and outer axes extending through first, second, and third sections of a core assembly. At least one of the bodies is rotatable about its axis. The inner and outer bodies have intermeshed inner and outer helical blades wound about the inner and outer axes and extending radially outwardly and inwardly respectively. The helical blades have first, second, and third twist slopes in the first, second, and third sections respectively. A combustor section extends through at least a portion of the second section.
Directory of Open Access Journals (Sweden)
Matteo Pascotto
2013-01-01
Full Text Available The flow field inside a cooling channel for the trailing edge of gas turbine blades has been numerically investigated with the aim to highlight the effects of channel rotation and orientation. A commercial 3D RANS solver including a SST turbulence model has been used to compute the isothermal steady air flow inside both static and rotating passages. Simulations were performed at a Reynolds number equal to 20000, a rotation number (Ro of 0, 0.23, and 0.46, and channel orientations of γ=0∘, 22.5°, and 45°, extending previous results towards new engine-like working conditions. The numerical results have been carefully validated against experimental data obtained by the same authors for conditions γ=0∘ and Ro = 0, 0.23. Rotation effects are shown to alter significantly the flow field inside both inlet and trailing edge regions. These effects are attenuated by an increase of the channel orientation from γ=0∘ to 45°.
Stability of 3D Gaussian vortices in rotating stratified Boussinesq flows: Linear analysis
Mahdinia, Mani; Jiang, Chung-Hsiang
2016-01-01
The linear stability of three-dimensional (3D) vortices in rotating, stratified flows has been studied by analyzing the non-hydrostatic inviscid Boussinesq equations. We have focused on a widely-used model of geophysical and astrophysical vortices, which assumes an axisymmetric Gaussian structure for pressure anomalies in the horizontal and vertical directions. For a range of Rossby number ($-0.5 < Ro < 0.5$) and Burger number ($0.02 < Bu < 2.3$) relevant to observed long-lived vortices, the growth rate and spatial structure of the most unstable eigenmodes have been numerically calculated and presented as a function of $Ro-Bu$. We have found neutrally-stable vortices only over a small region of the $Ro-Bu$ parameter space: cyclones with $Ro \\sim 0.02-0.05$ and $Bu \\sim 0.85-0.95$. However, we have also found that anticyclones in general have slower growth rates compared to cyclones. In particular, growth rate of the most unstable eigenmode for anticyclones in a large region of the parameter space ...
Buoyancy effects on rotation and translation of large particles in turbulent flow
Byron, Margaret; Tao, Yiheng; Variano, Evan
2013-11-01
We use laboratory experiments to investigate the effects of homogeneous, isotropic turbulence on particles of varying buoyancy, size, and shape. The buoyancy is varied between a specific gravity of 1.001 and 1.05. All particles are roughly 1 cm, which in this flow is close to Taylor's turbulent microscale. We vary the shape to compare spherical particles to non-spherical particles while matching the settling velocity, volume, and/or surface area. Particles are fabricated in custom shapes using transparent hydrogels whose refractive index is close to water. We embed tracers within the particles and use PIV to image the interior of the particle simultaneously with the exterior flowfield of homogeneous isotropic turbulence, generated by two active-grid synthetic jet arrays. We find that the settling velocity of these particles, regardless of shape, is reduced relative to the quiescent settling velocity as predicted by the Clift-Gauvin model. We explore the distribution of rotation rates, as characterized by the variance of angular velocity. We find significant anisotropy in the angular velocities of negatively buoyant particles, which vanishes as particles approach neutral buoyancy. We also see differences in angular velocity distribution between particles of varying eccentricity.
Fully-resolved simulation of particle rotation in a turbulent flow
Wang, Yayun; Sierakowski, Adam J.; Prosperetti, Andrea
2016-11-01
Some results on the statistics of particle rotation induced by hydrodynamic stresses in a weakly turbulent flow, with a Taylor Reynolds number of about 32, are presented. Two particle Reynolds numbers, 80 and 150, and two different particle moments of inertia, are considered.The particle center is held fixed so that the particle statistics can be compared with those of the fluid vorticity in the absence of the particle. It is found that the particle essentially responds only to vortex structures with a scale comparable to, or larger than, its diameter, thus acting as a low-pass filter for the incident turbulent vorticity. An analysis of the flatness of the PDF's of the angular acceleration and angular velocity shows that the former is mildly non-Gaussian, while the latter is very close to Gaussian. The numerical method used, Physalis, is particularly suited for this problem due to the high accuracy with which the couple is calculated. Supported by NSF Grant CBET 1335965.
Directory of Open Access Journals (Sweden)
Hemant Poonia
2015-06-01
Full Text Available In this paper the effects of Hall current on MHD free convection flow in a vertical rotating channel filled with porous medium have been studied. A uniform magnetic field is applied in the direction normal to the plates. The entire system rotates about an axis normal to the planes of the plates with uniform angular velocity ' . The temperature of one of the plates varies periodically and the temperature difference of the plates is high enough to induce radiative heat transfer. The effects of various parameters on the velocity and temperature field are shown graphically. Also the results on Skin Frication and Nusselt Number are shown in tables.
Directory of Open Access Journals (Sweden)
Michael Hoff
2015-01-01
random noise. In that context, we also address the question of the appropriate filter technique to remove noise from the data prior to the empirical SV-analysis. We ask whether there is an objective mean to distinguish between noise and signal. Finally, we compare the results with earlier findings from a numerical low-order model of baroclinic waves for which the system matrix is known. The results from the low-order model suggested that irregular flows have in general larger SV growth rates. These findings have been used to explain the gradual increase of irregularity when the rotation rate of the annulus is increased while keeping the radial temperature contrast constant. This simple picture cannot be confirmed by the laboratory data. The singular value spectrum becomes rather broad for irregular flows similar to the SV spectrum of atmospheric models. Thus the irregularity might be related to the presence of a large number of SVs with similar growth rates and not to few SVs with exceptional large growth rates.
Nath, G.
2011-05-01
The propagation of a strong cylindrical shock wave in an ideal gas with azimuthal magnetic field, and with or without axisymmetric rotational effects, is investigated. The shock wave is driven out by a piston moving with time according to power law. The ambient medium is assumed to have radial, axial and azimuthal component of fluid velocities. The fluid velocities, the initial density and the initial magnetic field of the ambient medium are assumed to be varying and obey power laws. Solutions are obtained, when the flow between the shock and the piston is isothermal. The gas is assumed to have infinite electrical conductivity and the angular velocity of the ambient medium is assumed to be decreasing as the distance from the axis increases. It is expected that such an angular velocity may occur in the atmospheres of rotating planets and stars. The shock wave moves with variable velocity and the total energy of the wave is non-constant. The effects of variation of the initial density and the Alfven-Mach number on the flow-field are obtained. A comparison is also made between rotating and non-rotating cases.
An experimental study of the edge effect on transition of the rotating-disk boundary-layer flow
Imayama, Shintaro; Lingwood, R. J.; Alfredsson, P. Henrik
2011-11-01
Lingwood [J. Fluid Mech., 299, 17 (1995)] showed that the flow instability in the rotating-disk boundary layer is not only of convective nature but also that the flow becomes absolutely unstable. Furthermore, in the absence of bypass mechanisms, the absolute instability triggers nonlinearity and transition to turbulence at a fixed Reynolds number (Re). Healey [J. Fluid Mech., 663, 148 (2010)] suggested that the observed spread (albeit small) in transition Re in different experiments is an effect of the Re at the disk edge and provided a nonlinear model to take this effect into account. Here, we further investigate this problem experimentally with hot-wire measurements on a rotating polished glass disk with a diameter of 474 mm and a total imbalance and surface roughness less than 10 μm. To investigate the influence of the disk edge, we vary Re at the disk edge by changing the rotational speed and map the development of the disturbance velocity in the radial direction. Furthermore, the effect of a stationary annular plate around the edge of the rotating disk is also investigated. Our experiments show no effect of the disk edge Re on the stability and transition, however there was a shift of both the growth curve and the transition Re by about 10 units with and without the outer stationary plate, with the lower Re observed with the plate.
Zaleski, Daniel P.; Prozument, Kirill
2017-06-01
Chirped-pulsed (CP) Fourier transform rotational spectroscopy invented by Brooks Pate and coworkers a decade ago is an attractive tool for gas phase chemical dynamics and kinetics studies. A good reactor for such a purpose would have well-defined (and variable) temperature and pressure conditions to be amenable to accurate kinetic modeling. Furthermore, in low pressure samples with large enough number of molecular emitters, reaction dynamics can be observable directly, rather than mediated by supersonic expansion. In the present work, we are evaluating feasibility of in situ time-resolved CP spectroscopy in a room temperature flow tube reactor. Vinyl cyanide (CH_2CHCN), neat or mixed with inert gasses, flows through the reactor at pressures 1-50 μbar (0.76-38 mTorr) where it is photodissociated by a 193 nm laser. Millimeter-wave beam of the CP spectrometer co-propagates with the laser beam along the reactor tube and interacts with nascent photoproducts. Rotational transitions of HCN, HNC, and HCCCN are detected, with ≥10 μs time-steps for 500 ms following photolysis of CH_2CHCN. The post-photolysis evolution of the photoproducts' rotational line intensities is investigated for the effects of rotational and vibrational thermalization of energized photoproducts. Possible contributions from bimolecular and wall-mediated chemistry are evaluated as well.
Energy Technology Data Exchange (ETDEWEB)
Gwynllyw, D.Rh.; Phillips, T.N. [Univ. of Wales, Aberystwyth (United Kingdom)
1994-12-31
The journal bearing is an essential part of all internal combustion engines as a means of transferring the energy from the piston rods to the rotating crankshaft. It consists essentially of an inner cylinder (the journal), which is part of the crankshaft, and an outer cylinder (the bearing), which is at the end of the piston rod. In general, the two cylinders are eccentric and there is a lubricating film of oil separating the two surfaces. The addition of polymers to mineral (Newtonian) oils to minimize the variation of viscosity with temperature has the added effect of introducing strain-dependent viscosity and elasticity. The physical problem has many complicating features which need to be modelled. It is a fully three-dimensional problem which means that significant computational effort is required to solve the problem numerically. The system is subject to dynamic loading in which the journal is allowed to move under the forces the fluid imparts on it and also any other loads such as that imparted by the engine force. The centre of the journal traces out a nontrivial locus in space. In addition, there is significant deformation of the bearing and journal and extensive cavitation of the oil lubricant. In the present study the authors restrict themselves to the two-dimensional statically loaded problem. In previous work a single domain spectral method was used which employed a bipolar coordinate transformation to map the region between the journal and the bearing onto a rectangle. The flow variables were then approximated on this rectangle using Fourier-Chebyshev expansions. However, to allow for future possible deformation of the journal and bearing surfaces due to increased load in the dynamically loaded case they have decided to use a more versatile spectral element formulation.
Features of Rotating Stall Cell in a Diagonal Flow Fan(in Case of Mid-loading Rotor)
Institute of Scientific and Technical Information of China (English)
N. SHIOMI; K. KANEKO; Y. KINOUE; T. SETOGUCHI
2006-01-01
The structure and behavior of rotating stall cell were experimentally clarified in a diagonal flow fan. The specific-speed of the fan was 1140 (r/min, m3/min, m), and the total pressure-rise coefficient at design flow-rate was 0.345. The static pressure on outer casing wall and the total pressure at rotor inlet and outlet were measured using a high response pressure transducer. The measured data were processed by the use of DPLA technique, and the structure and behavior of rotating stall cell were obtained. As a result, the stall cell extent for circumferential and spanwise direction and the pressure distributions inside stall cell were clarified. The details of stall cell propagation were also shown.
Papaloizou, J C B
2004-01-01
We carry out a general study of the stability of astrophysical flows that appear steady in a uniformly rotating frame. Such a flow might correspond to a stellar pulsation mode or an accretion disk with a free global distortion giving it finite eccentricity. We consider perturbations arbitrarily localized in the neighbourhood of unperturbed fluid streamlines.When conditions do not vary around them, perturbations take the form of oscillatory inertial or gravity modes. However, when conditions do vary so that a circulating fluid element is subject to periodic variations, parametric instability may occur. For nearly circular streamlines, the dense spectra associated with inertial or gravity modes ensure that resonance conditions can always be satisfied when twice the period of circulation round a streamline falls within. We apply our formalism to a differentially rotating disk for which the streamlines are Keplerian ellipses, with free eccentricity up to 0.7, which do not precess in an inertial frame. We show tha...
Flow shear stabilization of rotating plasmas due to the Coriolis effect
Haverkort, J. W.; de Blank, H. J.
2012-01-01
A radially decreasing toroidal rotation frequency can have a stabilizing effect on nonaxisymmetric magnetohydrodynamic (MHD) instabilities. We show that this is a consequence of the Coriolis effect that induces a restoring pressure gradient force when plasma is perturbed radially. In a rotating cyli
Flow shear stabilization of rotating plasmas due to the Coriolis effect
Haverkort, J. W.; de Blank, H. J.
2012-01-01
A radially decreasing toroidal rotation frequency can have a stabilizing effect on nonaxisymmetric magnetohydrodynamic (MHD) instabilities. We show that this is a consequence of the Coriolis effect that induces a restoring pressure gradient force when plasma is perturbed radially. In a rotating cyli
Thomas, Lucy C; McLeod, Lucy R; Osmotherly, Peter G; Rivett, Darren A
2015-06-01
Cervical spine manual therapy has been associated with a small risk of serious adverse neurovascular events, particularly to the vertebral arteries. Sustained end-range rotation is recommended clinically as a pre-manipulative screening tool; however ultrasound studies have yielded conflicting results about the effect of rotation on blood flow in the vertebral arteries. There has been little research on internal carotid arterial flow or utilising the reference standard of angiography. To evaluate the mean effect of cervical rotation on blood flow in the craniocervical arteries and blood supply to the brain, as well as individual variation. This was an observational study. Magnetic resonance angiography was used to measure average blood flow volume in the vertebral arteries, internal carotid arteries, and total cerebral inflow, in three neck positions: neutral, end-range left rotation and end-range right rotation in healthy adults. Twenty participants were evaluated. There was a decrease in average blood flow volume in the vertebral and internal carotid arteries on contralateral rotation, compared to neutral. This was statistically significant on left rotation only. Ipsilateral rotation had no effect on average blood flow volume in any artery. Total cerebral inflow was not significantly affected by rotation in either direction. It appears that in healthy adults the cerebral vasculature can compensate for decreased flow in one or more arteries by increasing flow in other arteries, to maintain cerebral perfusion. Sustained end-range rotation may therefore reflect the compensatory capacity of the system as a whole rather than isolated vertebrobasilar function. Copyright © 2014 Elsevier Ltd. All rights reserved.
Directory of Open Access Journals (Sweden)
Eric Mucunguzi-Rugwebe
2013-09-01
Full Text Available In this study, the results of the effect of water-flow rate and air fraction component on intensity, I, are presented and discussed. The study which was carried out at Bergen University in Norway, presents the impact of monochromatic defects on polarization and measurements of small oil fractions of various crude oils are presented. When there was refraction, it was observed that in static sea-water &mustatic = 0.38 and in running water &muflow = 0.42 When refraction was eliminated by grafting windows in the pipe, &mustatic = 0, &muflow = 0.11 and in both cases &muflow was independent of the flow rate. Air fraction component, &alpha> = 0.12 reduced light intensity. With rate flow Q = 13.6m3/h and Q = 27.2 m3/h critical air fraction was found at &alphac = 0.18 and &alphac = 0.12 respectively. For &alphac = 0.18 up to &alpha 0.87 at Q = 13.6m3/h and &alphac = 0.12 up to &alpha = 0.78 at Q = 27.2 m3/h light intensity was found independent of &alpha. The highest rotation was found in Gullfaks crude oil, followed by Heidrun, the rotation is Statfjord crude oil was less than one in Heidrun and the least rotation was observed in 0A sg 0a rd crude oil. At 40ppm, the rotation was as follows: Gullfaks &empty = 27.0±0.20, Heidrun &empty = 23.9±0.20, Statfjord &empty = 20.0±0.20 and 0Asg 0ard &empty = 10.0±0.10. This method studys very well when small oil fractions from 5.0-70 ppm are in sea-water flow. This technique can be deployed to monitor the environment and to control the re-injected process water.
Institute of Scientific and Technical Information of China (English)
GONG Xiao-Long; WANG Ding-Xiong
2005-01-01
@@ We discuss jet production from an advection dominated accretion flow (ADAF) around a rotating black hole (BH) in an electromagnetic regime. An analytical expression for the jet power is derived by using an equivalent circuit in the BH magnetosphere. It turns out that a large fraction of jet powers is contributed from the inner region of the ADAF, and the jet power depends sensitively on the degree to which the flow is advection-dominated. In addition, we use our model to fit the strong jet powers of several BL Lac objects, which cannot be explained by virtue of the BZ process.
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Khan Ilyas
2015-01-01
Full Text Available The present paper is concerned with the magnetohydrodynamic unsteady rotating flows of generalized Burgers' fluid with a porous medium. The flows are created by the plate oscillations. Modified Darcy's law has been employed to model the governing problem. Closed-form solutions corresponding to cosine and sine oscillations are obtained by the Laplace transform method. The performed calculations disclose that Hartmann number, porosity of the medium, angular frequency, and oscillating frequency have strong influence on the velocity. The graphs are presented for such influence and examined carefully.
Augenbaum, J. M.
1985-01-01
A Lagrangian scheme using the Voronoi mesh is applied to study shallow water flow on a sphere. Discrete approximations to the shallow water equations are obtained for the surfaces of a nonrotating and a rotating sphere, and discrete differential operators are defined for the gradient and the divergence on the sphere. Dissipation is put into the model, when needed, by merging fluid points when they get too close to each other. The full numerical scheme is described and results of numerical computations on various test cases are given, including zonal flow and the Riemann problem.
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.
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
An eight-compartment model of the energy dynamics of an alpine meadow-sheep grazing ecosystem was proposed based on SHIYOMI's system approach. The compartments were the above-ground plant portion, the underground live portion including roots, the underground dead portion including roots, the above-ground litter Ⅰ (degradable portion), the above-ground litter Ⅱ (undegradable portion), the sheep intake, the sheep liveweight, and the faeces. Energy flows between the eight compartments were described by eight simultaneous differential equations. All parameters in the model were determined from paddock experiments.The model was designed to provide a practical method for estimating the effects of the number of rotational grazing subplots, grazing period, and grazing pressure on the performance of grazing systems for perennial alpine meadow pasture. The model provides at least 28 different attributes for characterizing the performance of the grazing system. Analyses of 270 simulated rotational grazing systems of summer-autumn meadow pasture (grazing from 1st June to 30 October each year) provided an inference base to support two recommendations concerning management variables. First, with a three-paddock, 29-day grazing period and 30.14kJ·m-2·day-1 grazing pressure scheme, the system has the highest total grazing intake, 4250.44 kJ·m-2, during the grazing season. Secondly, with a three-paddock, 7-day grazing period and 28.89kJ·m-2·day-1 grazing pressure scheme, the accumulated graze is 4073.34kJ*m-2.The potential productivity of the alpine meadow under grazing is defined in this paper as the maximal dry biomass of herbage grazed by the grazing animals over the whole growing season. It has been analysed by applying optimal control theory to the model. The productivity is regarded as the objective function to be maximized through optimization of the time course of the grazing pressure, the control variable. The results show that: (1) under constant grazing pressure
Experimental Studies of Flow Patterns of Different Fluids in a Partially Filled Rotating Cylinder
Directory of Open Access Journals (Sweden)
P.R. Mukunda
2009-01-01
Full Text Available An attempt has been made to investigate the various parameters affecting the fluid behaviour, partially filled in a rotating cylinder. When the cylinder is rotating at ‘high’ speed, a liquid forms a hollow cylinder. Different patterns are observed in the fluids for the rotatioal speeds below a critical speed. This study should give us some insight into molten metal behaviour during centrifugal casting. An extensive experimental investigation is required to obtain an appropriate functional relationship by knowing and understanding some dimensionless parameters. Here the effect of dimensionless parameters ε (which is 2 g/ω2d, where g, ω and d denotes gravitational acceleration, container rotation rate and inner diameter of liquid cylinder and G (number of times the gravity was studied as variation of rotation speed, viscosity and aspect ratio of the mould.
Thermo-fluid-dynamic analysis of the flow in a rotating channel with a sharp ‘‘U’’ turn
Gallo, M.; Astarita, T.; Carlomagno, G.M.
2012-01-01
Infrared thermography has been employed to carry out a detailed convective heat transfer measurements at Re = 20,000 in a two-pass square channel both for the static case (absence of channel rotation) and for the rotating case (Ro = 0.3). At the same time, the main and secondary flow fields have bee
Thermo-fluid-dynamic analysis of the flow in a rotating channel with a sharp ‘‘U’’ turn
Gallo, M.; Astarita, T.; Carlomagno, G.M.
2012-01-01
Infrared thermography has been employed to carry out a detailed convective heat transfer measurements at Re = 20,000 in a two-pass square channel both for the static case (absence of channel rotation) and for the rotating case (Ro = 0.3). At the same time, the main and secondary flow fields have bee
Kaladhar, K.; Srinivasacharya, D.
2016-12-01
The chemical reaction, Soret and Dufour effects on steady flow of a couple stress fluid between two rotating disks are studied. The lower disc is rotating with angular velocity Ω1 where as the upper disc is rotating with Ω2. The density variation in centrifugal and Coriolis force terms are taken into consideration by invoking a linear density-temperature relation and Boussinesq approximation to account the buoyancy effects. The non-linear governing partial differential equations are transformed into system of ordinary differential equations by using the similarity transformations. Homotopy Analysis Method (HAM) has been used to solve the resulting equations. Graphical illustrations of the dimensionless velocity, concentration and temperature profiles are presented at different values of the emerging parameter of the present study. It has been found that as an increase in couple stresses leads to the decrease in velocity, temperature and increase in concentration of the fluid. Flow velocities, temperature and concentration profiles are decreases with an increase in reaction parameter.
Energy Technology Data Exchange (ETDEWEB)
Hayat, Tasawar [Department of Mathematics, Quaid-I-Azam University 45320, Islamabad 44000 (Pakistan); Nonlinear Analysis and Applied Mathematics (NAAM) Research Group, Department of Mathematics, Faculty of Science, King Abdulaziz University, Jeddah 21589 (Saudi Arabia); Qayyum, Sumaira [Department of Mathematics, Quaid-I-Azam University 45320, Islamabad 44000 (Pakistan); Imtiaz, Maria, E-mail: mi_qau@yahoo.com [Department of Mathematics, Quaid-I-Azam University 45320, Islamabad 44000 (Pakistan); Alzahrani, Faris; Alsaedi, Ahmed [Nonlinear Analysis and Applied Mathematics (NAAM) Research Group, Department of Mathematics, Faculty of Science, King Abdulaziz University, Jeddah 21589 (Saudi Arabia)
2016-09-01
This paper addresses the flow of magnetic nanofluid (ferrofluid) between two parallel rotating stretchable disks with different rotating and stretching velocities. Water based fluid comprising magnetite-Fe{sub 3}O{sub 4} nanoparticles is addressed. Velocity slip and temperature jump at solid–fluid interface are also taken into account. Appropriate transformations reduce the nonlinear partial differential system to ordinary differential system. Convergent series solutions are obtained. Effects of various pertinent parameters on the velocity and temperature profiles are shown and evaluated. Computations for skin friction coefficient and Nusselt number are presented and examined for the influence of involved parameters. It is noted that tangential velocity of fluid decreases for larger velocity slip parameter. Fluid temperature also reduces for increasing value of thermal slip parameter. Surface drag force and heat transfer rate at lower disk are enhanced when magnetic field strength is increased. - Highlights: • Flow and heat transfer of ferrofluid induced by two stretchable rotating disks with velocity and thermal slips are explored. • Fluid temperature increases for larger solid volume fraction of nanofluid. • Heat transfer rate decreases for increasing values of thermal slip parameter.
Experiments on the Flow of a Thin Liquid Film Over a Horizontal Stationary and Rotating Disk Surface
Ozar, B.; Cetegen, B. M.; Faghri, A.
2003-01-01
Experiments on characterization of thin liquid films flowing over stationary and rotating disk surfaces are described. The thin liquid film was created by introducing deionized water from a flow collar at the center of an aluminum disk with a known initial film thickness and uniform radial velocity. Radial film thickness distribution was measured using a non-intrusive laser light interface reflection technique that enabled the measurement of the instantaneous film thickness over a finite segment of the disk. Experiments were performed for a range of flow rates between 3.01pm and 15.01pm, corresponding to Reynolds numbers based on the liquid inlet gap height and velocity between 238 and 1,188. The angular speed of the disk was varied from 0 rpm to 300 rpm. When the disk was stationary, a circular hydraulic jump was present in the liquid film. The liquid-film thickness in the subcritical region (down-stream of the hydraulic jump) was an order of magnitude greater than that in the supercritical region (upstream of the hydraulic jump) which was of the order of 0.3 mm. As the Reynolds number increased, the hydraulic jump migrated toward the edge of the disk. In the case of rotation, the liquid-film thickness exhibited a maximum on the disk surface. The liquid-film inertia and friction influenced the inner region where the film thickness progressively increased. The outer region where the film thickness decreased was primarily affected by the centrifugal forces. A flow visualization study of the thin film was also performed to determine the characteristics of the waves on the free surface. At high rotational speeds, spiral waves were observed on the liquid film. It was also determined that the angle of the waves which form on the liquid surface was a function of the ratio of local radial to tangential velocity.
DEFF Research Database (Denmark)
Sørensen, Jens Nørkær; Gelfgat, A. Yu; Naumov, I. V.;
2009-01-01
The three-dimensional axisymmetry-breaking instability of axisymmetric flow between a rotating lid and a stationary cylinder is analyzed both numerically and experimentally for the case of tall cylinders with the height/radius aspect ratio between 3.3 and 5.5. A complete stability diagram...... for each mode. The onset of three-dimensional flow behavior is measured by combining the high spatial resolution of particle image velocimetry and the temporal accuracy of laser Doppler anemometry. The results are compared to the numerical stability analysis. The measured onset of three dimensionality...... is in a good agreement with the numerical results. Disagreements observed in supercritical regimes can be explained by secondary bifurcations that are not accounted for by linear stability analysis of the primary base flow. ©2009 American Institute of Physics...
Khan, Najeeb Alam
2016-01-01
This study deals with the investigation of MHD flow of Williamson fluid over an infinite rotating disk with the effects of Soret, Dufour, and anisotropic slip. The anisotropic slip and the Soret and Dufour effects are the primary features of this study, which greatly influence the flow, heat and mass transport properties. In simultaneous appearance of heat and mass transfer in a moving fluid, the mass flux generated by temperature gradients is known as the thermal-diffusion or Soret effect and the energy flux created by a composition gradient is called the diffusion-thermo or Dufour effect, however, difference in slip lengths in streamwise and spanwise directions is named as anisotropic slip. The system of nonlinear partial differential equations (PDEs), which governs the flow, heat and mass transfer characteristics, is transformed into ordinary differential equations (ODEs) with the help of von K\\'arm\\'an similarity transformation. A numerical solution of the complicated ODEs is carried out by a MATLAB routi...
Directory of Open Access Journals (Sweden)
G.S. Seth
2014-06-01
Full Text Available An investigation of the effects of Hall current and rotation on unsteady hydromagnetic natural convection flow with heat and mass transfer of an electrically conducting, viscous, incompressible and optically thick radiating fluid past an impulsively moving vertical plate embedded in a fluid saturated porous medium, when temperature of the plate has a temporarily ramped profile, is carried out. Exact solution of the governing equations is obtained in closed form by Laplace transform technique. Exact solution is also obtained in case of unit Schmidt number. Expressions for skin friction due to primary and secondary flows and Nusselt number are derived for both ramped temperature and isothermal plates. Expression for Sherwood number is also derived. The numerical values of primary and secondary fluid velocities, fluid temperature and species concentration are displayed graphically whereas those of skin friction are presented in tabular form for various values of pertinent flow parameters.
Assessment of Geometry and In-Flow Effects on Contra-Rotating Open Rotor Broadband Noise Predictions
Zawodny, Nikolas S.; Nark, Douglas M.; Boyd, D. Douglas, Jr.
2015-01-01
Application of previously formulated semi-analytical models for the prediction of broadband noise due to turbulent rotor wake interactions and rotor blade trailing edges is performed on the historical baseline F31/A31 contra-rotating open rotor configuration. Simplified two-dimensional blade element analysis is performed on cambered NACA 4-digit airfoil profiles, which are meant to serve as substitutes for the actual rotor blade sectional geometries. Rotor in-flow effects such as induced axial and tangential velocities are incorporated into the noise prediction models based on supporting computational fluid dynamics (CFD) results and simplified in-flow velocity models. Emphasis is placed on the development of simplified rotor in-flow models for the purpose of performing accurate noise predictions independent of CFD information. The broadband predictions are found to compare favorably with experimental acoustic results.
Flow of a Dusty Gas with Suspended Particles in a Rotating Frame of Reference
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P. Mitra
1981-01-01
Full Text Available The solution is given for the problem on the motion of a dusty gas under a rotating system of co-ordinates. The gas containing a uniform distribution of dust particles, occupies the infinite space above a rigid plane boundary. The motion of the dusty gas is induced by the motion of the plate moving with a velocity which decreases exponentially with time in a rotating frame of reference such that the plate and the gas are in a state of rigid body rotation about an axis normal to the plate. The velocity fields for the dusty gas, and the dust particles along and normal to the direction of motion of the plate are obtained in closed forms. Finally, some velocity distributions are calculated with particular reference to the effect of rotation at different times, and it is found that with the increase of the value of the rotation parameter omega, the velocity of the dusty gas along the direction of motion of the plate gradually increases while the velocity of the dust particle along the same direction gradually decreases.
Ambrus, Victor E
2016-01-01
We consider rigidly rotating states in thermal equilibrium on static spherically symmetric spacetimes. Using the Maxwell-Juttner equilibrium distribution function, onstructed as a solution of the relativistic Boltzmann equation, the equilibrium particle flow four-vector, stress-energy tensor and the transport coefficients in the Marle model are computed. Their properties are discussed in view of the topology of the speed-of-light surface induced by the rotation for two classes of spacetimes: maximally symmetric (Minkowski, de Sitter and anti-de Sitter) and charged (Reissner-Nordstrom) black-hole spacetimes. To facilitate our analysis, we employ a non-holonomic comoving tetrad field, obtained unambiguously by applying a Lorentz boost on a fixed background tetrad.
Partial slip effect in flow of magnetite-Fe3O4 nanoparticles between rotating stretchable disks
Hayat, Tasawar; Qayyum, Sumaira; Imtiaz, Maria; Alzahrani, Faris; Alsaedi, Ahmed
2016-09-01
This paper addresses the flow of magnetic nanofluid (ferrofluid) between two parallel rotating stretchable disks with different rotating and stretching velocities. Water based fluid comprising magnetite-Fe3O4 nanoparticles is addressed. Velocity slip and temperature jump at solid-fluid interface are also taken into account. Appropriate transformations reduce the nonlinear partial differential system to ordinary differential system. Convergent series solutions are obtained. Effects of various pertinent parameters on the velocity and temperature profiles are shown and evaluated. Computations for skin friction coefficient and Nusselt number are presented and examined for the influence of involved parameters. It is noted that tangential velocity of fluid decreases for larger velocity slip parameter. Fluid temperature also reduces for increasing value of thermal slip parameter. Surface drag force and heat transfer rate at lower disk are enhanced when magnetic field strength is increased.
Energy Technology Data Exchange (ETDEWEB)
Kheradmand, Saeid; Esmailian, Mojtaba; Fatahy, A. [Malek-Ashtar University of Technology (MUT), Isfahan (Iran, Islamic Republic of)
2017-04-15
Finishing of a workpiece is a main process in the production. This affects the quality and lifetime. Finishing in order of nanometer, nowadays, is a main demand of the industries. Thus, some new finishing process, such as abrasive flow finishing, is introduced to respond this demand. This may be aided by rotating workpiece and imposing a magnetic field. Numerical simulation of this process can be beneficial to reduce the expense and predict the result in a minimum time. Accordingly, in this study, magnetorheological fluid finishing is numerically simulated. The working medium contains magnetic and abrasive particles, blended in a base fluid. Some hydrodynamic parameters and surface roughness variations are studied. It is found that combination of rotating a workpiece and imposing a magnetic field can improve the surface roughness up to 15 percent.
Frewer, Michael
2016-01-01
The study by Oberlack et al. (2006) consists of two main parts: a direct numerical simulation (DNS) of a turbulent plane channel flow with streamwise rotation and a preceding Lie-group symmetry analysis on the two-point correlation equation (TPC) to analytically predict the scaling of the mean velocity profiles for different rotation rates. We will only comment on the latter part, since the DNS result obtained in the former part has already been commented on by Recktenwald et al. (2009), stating that the observed mismatch between DNS and their performed experiment is possibly due to the prescription of periodic boundary conditions on a too small computational domain in the spanwise direction. By revisiting the group analysis part in Oberlack et al. (2006), we will generate more natural scaling laws describing better the mean velocity profiles than the ones proposed. However, due to the statistical closure problem of turbulence, this improvement is illusive. As we will demonstrate, any arbitrary invariant scal...
Flow between caoxial rotating disks: with and without externally applied magnetic field
Directory of Open Access Journals (Sweden)
R. K. Bhatnagar
1981-01-01
when such a fluid is confined between two infinite rotating coaxial disks. The governing system of a pair of non-linear ordinary differential equation is solved by treating Reynolds number to small. The three cases discussed are: (I one disks is held at rest while other rotates with a constant angular velocity, (ii one disk rorates faster than the other but in the same sense and (iii the disks rotate in opposite senses and with different angular velocities. The radial, tranverse and axial components of the velocity field are plotted for the above three cases for different values of the Reynolds number. The results obtained for a viscoelastic fluid are compared with those for a Newtonian fluid. The velocity field for case (i is also computed when a magnetic field is applied in a direction perpendicular to the discs and the results are compared with the case when magnetic field is absent. Some interesting features are observed for a viscoelastic fluid.
Flow shear stabilization of rotating plasmas due to the Coriolis effect.
Haverkort, J W; de Blank, H J
2012-07-01
A radially decreasing toroidal rotation frequency can have a stabilizing effect on nonaxisymmetric magnetohydrodynamic (MHD) instabilities. We show that this is a consequence of the Coriolis effect that induces a restoring pressure gradient force when plasma is perturbed radially. In a rotating cylindrical plasma, this Coriolis-pressure effect is canceled by the centrifugal effect responsible for the magnetorotational instability. In a magnetically confined toroidal plasma, a large aspect ratio expansion shows that only half of the effect is canceled. This analytical result is confirmed by numerical computations. When the plasma rotates faster toroidally in the core than near the edge, the effect can contribute to the formation of transport barriers by stabilizing MHD instabilities.
Cantillon-Murphy, P.; Wald, L. L.; Adalsteinsson, E.; Zahn, M.
2010-09-01
transverse rotating magnetic field in the presence of B0 are investigated to demonstrate the effect of Ω, the rotating field frequency, and the magnetic field amplitude on the fluid suspension magnetization. The transverse magnetization due to the rotating transverse field shows strong dependence on the characteristic time constant of the fluid suspension, τ. The analysis shows that as the rotating field frequency increases so that Ωτ approaches unity, the transverse fluid magnetization vector is significantly non-aligned with the applied rotating field and the magnetization's magnitude is a strong function of the field frequency. In this frequency range, the fluid's transverse magnetization is controlled by the applied field which is determined by the operator. The phenomenon, which is due to the physical rotation of the magnetic nanoparticles in the suspension, is demonstrated analytically when the nanoparticles are present in high concentrations (1-3% solid volume fractions) more typical of hyperthermia rather than in clinical imaging applications, and in low MRI field strengths (such as open MRI systems), where the magnetic nanoparticles are not magnetically saturated. The effect of imposed Poiseuille flow in a planar channel geometry and changing nanoparticle concentration is examined. The work represents the first known attempt to analyze the dynamic behavior of magnetic nanoparticles in the MRI environment including the effects of the magnetic nanoparticle spin-velocity. It is shown that the magnitude of the transverse magnetization is a strong function of the rotating transverse field frequency. Interactive fluid magnetization effects are predicted due to non-uniform fluid magnetization in planar Poiseuille flow with high nanoparticle concentrations.
Convective mass transfer from a horizontal rotating cylinder in a slot air jet flow
Institute of Scientific and Technical Information of China (English)
Hongting MA; Dandan MA; Na YANG
2009-01-01
The effects of air jet impinging on the mass transfer characteristics from a rotating spinning cylinder surface were experimentally investigated. The effects of rotational Reynolds numberRer, jet-exit Reynolds number Rej, the nozzle width-to-cylinder diameter ratio B/d, and the ratio of the distance between nozzle exit and the front of cylinder to nozzle width L/B on the mean Sh were determined. The phenomena of the first and second critical point was analyzed and validated. On the basis of experimental data, the correlation equation was obtained.
Ilin, Konstantin
2015-01-01
We study the stability of two-dimensional flows in an annulus between two permeable cylinders with respect to three-dimensional perturbations. The basic flow is irrotational, and both radial and azimuthal components of the velocity are non-zero. The direction of the radial flow can be from the inner cylinder to the outer one (the diverging flow) or from the outer cylinder to the inner one (the converging flow). It is shown that, independent of the direction of the radial flow, the basic flow is unstable to small two-dimensional perturbations provided that the ratio of the azimuthal component of the velocity to the radial one is sufficiently large. The instability is oscillatory, and the unstable modes represent travelling azimuthal waves. Neutral curves in the space of parameters of the problem are computed. It turns out that for any geometry of the problem, the most unstable modes (corresponding to the smallest ratio of the azimuthal velocity to the radial one) are two-dimensional ones studied earlier in \\ci...
Directory of Open Access Journals (Sweden)
Hao Ming Li
2016-12-01
Full Text Available Traditionally, the formation of the Counter-Rotating Vortex Pair (CRVP has been attributed to three main sources: the jet-mainstream shear layer where the jet meets with the mainstream flow right outside the pipe, the in-tube boundary layer developing along the pipe wall, and the in-tube vortices associated with the tube inlet vorticity; whereas the liftoff-reattachment phenomenon occurring in the main flow along the plate right downstream of the jet has been associated with the jet flow trajectory. The jet-mainstream shear layer has also been demonstrated to be the dominant source of CRVP formation, whereby the shear layer disintegrates into vortex rings that deform as the jet convects downstream, becoming a pair of CRVPs flowing within the jet and eventually turning into the main flow direction. These traditional findings are assessed qualitatively and quantitatively for film-cooling flow in gas turbines by simulating numerically the flow and evaluating the extent to which the traditional flow phenomena are taking place particularly for CRVP and for flow liftoff-reattachment. To this end, three flow simulation cases are used; they are referred to as 1—the baseline case; 2—the free-slip in-tube wall case (FSIT; and 3—the unsteady flow case. The baseline case is a typical film-cooling case. The FSIT case is used to assess the in-tube boundary layer. Cases 1 and 2 are simulated using the Reynolds-averaged Navier-Stokes equations (RANS, whereas Case 3 solves a Detached Eddy Simulation (DES model. It is concluded that decreasing the strength of the CRVP, which is the case for e.g., shaped holes, provides high cooling performance, and the liftoff-reattachment phenomenon was thus found to be strongly influenced by the entrainment caused by the CRVP, rather than the jet flow trajectory. These interpretations of the flow physics that are more relevant to gas turbine cooling flow are new and provide a physics-based guideline for designing new film
Munhoz, D. S.; Bityurin, V. A.; Klimov, A. I.; Moralev, I. A.
2016-11-01
An experimental study of the flow around a circular cylinder model with magnetohydrodynamic (MHD) actuator was carried out in subsonic wind tunnels (M high frequency and pulsed-periodic) electrical discharge was used in this MHD actuator. This intense pulsed-periodic discharge had the following characteristics: voltage amplitude up to 15 kV, current amplitude up to 16 A and frequency up to 1 kHz. Permanent magnets with an induction of B = 0.1 T on the model surface were placed inside the cylindrical model. Annular electrodes were situated on the surface of the cylindrical model. The Lorentz force causes the rotation of the electric arc on the model surface. In turn, the movement of the arc discharge induces the rotation of the gas near the surface of the model. In this experiment were carried out the measurement of the flow velocity profile near the surface of the model on the following operational modes: with plasma and without plasma. A parametric study of the aerodynamic performance of the model was fulfilled with respect to the discharge parameters and the flow velocity. To measure the velocity profile was used particle image velocimetry method.
Coriolis effects on rotating Hele-Shaw flows: a conformal-mapping approach.
Miranda, José A; Gadêlha, Hermes; Dorsey, Alan T
2010-12-01
The zero surface tension fluid-fluid interface dynamics in a radial Hele-Shaw cell driven by both injection and rotation is studied by a conformal-mapping approach. The situation in which one of the fluids is inviscid and has negligible density is analyzed. When Coriolis force effects are ignored, exact solutions of the zero surface tension rotating Hele-Shaw problem with injection reveal suppression of cusp singularities for sufficiently high rotation rates. We study how the Coriolis force affects the time-dependent solutions of the problem, and the development of finite time singularities. By employing Richardson's harmonic moments approach we obtain conformal maps which describe the time evolution of the fluid boundary. Our results demonstrate that the inertial Coriolis contribution plays an important role in determining the time for cusp formation. Moreover, it introduces a phase drift that makes the evolving patterns rotate. The Coriolis force acts against centrifugal effects, promoting (inhibiting) cusp breakdown if the more viscous and dense fluid lies outside (inside) the interface. Despite the presence of Coriolis effects, the occurrence of finger bending events has not been detected in the exact solutions.
Granular flow in a rotating cone partly submerged in a fluidized bed
Janse, Arthur M.C.; Biesheuvel, P. Maarten; Prins, Wolter; Swaaij, van Wim P.M.
2000-01-01
When a rotating cone with supply openings near the bottom is partly inserted into a fluidized bed, solid particles are taken up and conveyed spirally over the inner surface. This principle for particle transport was used in a novel reactor for the flash pyrolysis of biomass with several distinct adv
On the relative rotational motion between rigid fibers and fluid in turbulent channel flow
Energy Technology Data Exchange (ETDEWEB)
Marchioli, C. [Department of Electrical, Management and Mechanical Engineering, University of Udine, 33100 Udine (Italy); Zhao, L., E-mail: lihao.zhao@ntnu.no [Department of Energy and Process Engineering, Norwegian University of Science and Technology, 7491 Trondheim (Norway); Andersson, H. I. [Department of Electrical, Management and Mechanical Engineering, University of Udine, 33100 Udine (Italy); Department of Energy and Process Engineering, Norwegian University of Science and Technology, 7491 Trondheim (Norway)
2016-01-15
In this study, the rotation of small rigid fibers relative to the surrounding fluid in wall-bounded turbulence is examined by means of direct numerical simulations coupled with Lagrangian tracking. Statistics of the relative (fiber-to-fluid) angular velocity, referred to as slip spin in the present study, are evaluated by modelling fibers as prolate spheroidal particles with Stokes number, St, ranging from 1 to 100 and aspect ratio, λ, ranging from 3 to 50. Results are compared one-to-one with those obtained for spherical particles (λ = 1) to highlight effects due to fiber length. The statistical moments of the slip spin show that differences in the rotation rate of fibers and fluid are influenced by inertia, but depend strongly also on fiber length: Departures from the spherical shape, even when small, are associated with an increase of rotational inertia and prevent fibers from passively following the surrounding fluid. An increase of fiber length, in addition, decouples the rotational dynamics of a fiber from its translational dynamics suggesting that the two motions can be modelled independently only for long enough fibers (e.g., for aspect ratios of order ten or higher in the present simulations)
Energy Technology Data Exchange (ETDEWEB)
Yin, Chenguang; Zheng, Liancun [Univ. of Science and Technology Beijing (China). School of Mathematics and Physics; Zhang, Chaoli [Univ. of Science and Technology Beijing (China). School of Mathematics and Physics; Univ. of Science and Technology Beijing (China). School of Mechanical Engineering; Zhang, Xinxin [Univ. of Science and Technology Beijing (China). School of Mechanical Engineering
2015-09-01
In this article, we discuss the flow and heat transfer of nanofluids over a rotating porous disk with velocity slip and temperature jump. Three types of nanoparticles - Cu, Al{sub 2}O{sub 3}, and CuO - are considered with water as the base fluid. The nonlinear governing equations are reduced into ordinary differential equations by Von Karman transformations and solved using homotopy analysis method (HAM), which is verified in good agreement with numerical ones. The effects of involved parameters such as porous parameter, velocity slip, temperature jump, as well as the types of nanofluids on velocity and temperature fields are presented graphically and analysed.
G. Nath
2012-01-01
Self-similar solutions are obtained for unsteady, one-dimensional isothermal flow behind a shock wave in a rotational axisymmetric non-ideal gas in the presence of an azimuthal magnetic field. The shock wave is driven out by a piston moving with time according to power law. The fluid velocities and the azimuthal magnetic field in the ambient medium are assumed to be varying and obeying a power law. The density of the ambient medium is assumed to be constant. The gas is assumed to be non-ideal...
Institute of Scientific and Technical Information of China (English)
ALONZO-GARCA A; GUTIRREZ-TORRES C del C; JIMNEZ BERNAL J A; MOLLINEDO-PONCE de LEN H R; MARTINEZ-DELGADILLO S A; BARBOSA-SALDAA J G
2015-01-01
This paper presents a CFD study about the effect of the V and U grooves in the flow over four cylinders in diamond shape configuration at subcritical flow conditions(Re=41000). Thek-ε Realizable turbulence model was implemented to fully structured hexahedral grids with near-wall refinements. Results showed that the numerical model was able to reproduce the impinging flow pattern and the repulsive forces present in the lateral cylinders of the smooth cylinder array. As a consequence of the flow alignment induced by the grooves, a jet-flow is formed between the lateral cylinders, which could cause an important vortex induced vibration effect especially in the rear cylinder. The magnitudes of the shear stresses at the valleys and peaks for the V grooved cylinders were lower than those of the U grooved cylinders, but the separation points were delayed due the U grooves presence. It is discussed the presence of a blowing effect caused by counter-rotating eddies located near the grooves peaks that cause a decrease of the shear stresses in the valleys, and promote them at the peaks.
Energy Technology Data Exchange (ETDEWEB)
Ibragimov, Nail H. [Department of Mathematics and Science, Blekinge Institute of Technology, SE-371 79 Karlskrona (Sweden); Ibragimov, Ranis N., E-mail: Ranis.Ibragimov@utb.edu [Department of Mathematics, College of Science, Mathematics and Technology, University of Texas at Brownsville, TX 78520 (United States)
2011-10-24
We study the nonlinear incompressible non-viscous fluid flows within a thin rotating atmospheric shell that serve as a simple mathematical description of an atmospheric circulation caused by the temperature difference between the equator and the poles. The model is also superimposed by a particular stationary flow which, under the assumption of no friction and a distribution of temperature dependent only upon latitude, models the zonal west-to-east flows in the upper atmosphere between the Ferrel and Polar cells. Owing to the Coriolis effects, the resulting achievable meteorological flows correspond to the asymptotical stable flows that are being translated along the equatorial plane. The exact solutions in terms of elementary functions are found by using Lie group methods. -- Highlights: → This article provides new exact solutions of the Euler and Navier-Stokes equations. → The exact solutions are written in terms of elementary functions. → The exact solutions were obtained by Lie group analysis. → A wider class of exact solutions is contained in the obtained Lie algebra.
Institute of Scientific and Technical Information of China (English)
HONG Taehyup; KIM Chang Nyung
2011-01-01
The effects of implantation angles of Bileaflet Mechanical Heart Valves (BMHVs) on the blood flow and the leaflet motion are investigated in this paper.The physiological blood flow interacting with the moving leaflets ofa BMHV is simulated with a strongly coupled implicit Fluid-Structure Interaction (FSI) method based on the Arbitrary-Lagrangian-Eulerian (ALE) approach and the dynamic mesh method (remeshing) in Fluent.BMHVs are widely used to be implanted to replace the diseascd heart valves,but the patients would suffer from some complications such as hemolysis,platelet activation,tissue overgrowth and device failure.These complications are closely related to both the flow characteristics near the valves and the leaflet dynamics.The currentnumerical model is validated against a previous experimental study.The numerical results show that as the rotation angle of BMHV is increased the degree of asymmetry of the blood flow and the leaflet motion is increased,which may lead to an unbalanced force acting on the BMHVs.This study shows the applicability of the FSI model for the interaction between the blood flow and the leaflet motion in BMHVs.
Zhu, Yunzeng; Chen, Yiqi; Meng, Xiangrui; Wang, Jing; Lu, Ying; Xu, Youchun; Cheng, Jing
2017-09-05
Centrifugal microfluidics has been widely applied in the sample-in-answer-out systems for the analyses of nucleic acids, proteins, and small molecules. However, the inherent characteristic of unidirectional fluid propulsion limits the flexibility of these fluidic chips. Providing an extra degree of freedom to allow the unconstrained and reversible pumping of liquid is an effective strategy to address this limitation. In this study, a wirelessly charged centrifugal microfluidic platform with two rotation axes has been constructed and the flow control strategy in such platform with two degrees of freedom was comprehensively studied for the first time. Inductively coupled coils are installed on the platform to achieve wireless power transfer to the spinning stage. A micro servo motor is mounted on both sides of the stage to alter the orientation of the device around a secondary rotation axis on demand during stage rotation. The basic liquid operations on this platform, including directional transport of liquid, valving, metering, and mixing, are comprehensively studied and realized. Finally, a chip for the simultaneous determination of hexavalent chromium [Cr(VI)] and methanal in water samples is designed and tested based on the strategy presented in this paper, demonstrating the potential use of this platform for on-site environmental monitoring, food safety testing, and other life science applications.
Directory of Open Access Journals (Sweden)
Liou Tong-Miin
2005-01-01
Full Text Available The local turbulent fluid flow and heat transfer in a rotating two-pass square duct with 19 pairs of in-line 90 ∘ ribs have been investigated computationally. A Reynolds-averaged Navier-Stokes equation (RANS with a two-layer k − ϵ turbulence model was solved. The in-line 90 ∘ ribs were arranged on the leading and trailing walls with rib height-to-hydraulic diameter ratio and pitch-to-height ratio of 0.136 and 10, respectively. The Reynolds number, based on duct hydraulic diameter and bulk mean velocity, was fixed at 1.0 × 10 4 whereas the rotational number varied from 0 to 0.2 . Results are validated with previous measured velocity field and heat transfer coefficient distributions. The validation shows that the effect of rotation on the passage-averaged Nusselt number ratio can be predicted reasonably well; nevertheless, the transverse mean velocity and, in turn, the distribution of regional-averaged Nusselt number ratio are markedly underpredicted in the regions toward which the Coriolis force is directed. Further CFD studies are needed.
Li, Xing; Leonard, Drew; Jeska, Lauren
2012-01-01
During 2011/09/24, as observed by the Atmospheric Imaging Assembly (AIA) instrument of the Solar Dynamic Observatory (SDO) and ground-based \\Ha\\ telescopes, a prominence and associated cavity appeared above the southwest limb. On 2011/09/25 8:00UT material flows upwards from the prominence core along a narrow loop-like structure, accompanied by a rise ($\\geq$50,000km) of the prominence core and the loop. As the loop fades by 10:00, small blobs and streaks of varying brightness rotate around the top part of the prominence and cavity, mimicking a cyclone. The most intense and coherent rotation lasts for over three hours, with emission in both hot ($\\sim$1MK) and cold (hydrogen and helium) lines. We suggest that the cyclonic appearance and overall evolution of the structure can be interpreted in terms of the expansion of helical structures into the cavity, and the movement of plasma along helical structures which appears as a rotation when viewed along the helix axis. The coordinated movement of material between...
McDowell, L M; Burzio, L A; Waite, J H; Schaefer, J
1999-07-16
13C2H rotational echo double resonance NMR has been used to provide the first evidence for the formation of quinone-derived cross-links in mussel byssal plaques. Labeling of byssus was achieved by allowing mussels to filter feed from seawater containing L-[phenol-4-13C]tyrosine and L-[ring-d4]tyrosine for 2 days. Plaques and threads were harvested from two groups of mussels over a period of 28 days. One group was maintained in stationary water while the other was exposed to turbulent flow at 20 cm/s. The flow-stressed byssal plaques exhibited significantly enhanced levels of 5, 5'-di-dihydroxyphenylalanine cross-links. The average concentration of di-dihydroxyphenylalanine cross-links in byssal plaques is 1 per 1800 total protein amino acid residues.
Directory of Open Access Journals (Sweden)
Gauri Shanker Seth
2015-01-01
Full Text Available An investigation of unsteady hydromagnetic natural convection flow of a viscous, incompressible, electrically conducting and heat absorbing fluid past an impulsively moving vertical plate with Newtonian heating embedded in a porous medium in a rotating system is carried out. The governing partial differential equations are first subjected to Laplace transformation and then inverted numerically using INVLAP routine of Matlab. The governing partial differential equations are also solved numerically by Crank-Nicolson implicit finite difference scheme and a comparison has been provided between the two solutions. The numerical solution for fluid velocity and fluid temperature are depicted graphically whereas the numerical values of skin friction and Nusselt number are presented in tabular form for various values of pertinent flow parameters. Present solution in special case is compared with previously obtained solution and is found to be in excellent agreement.
A numerical simulation of the inviscid flow through a counter-rotating propeller
Celestina, M. L.; Mulac, R. A.; Adamczyk, J. H.
1986-01-01
The results of a numerical simulation of the time-averaged inviscid flow field through the blade rows of a multiblade row turboprop configuration are presented. The governing equations are outlined along with a discussion of the solution procedure and coding strategy. Numerical results obtained from a simulation of the flow field through a modern high-speed turboprop will be shown.
Institute of Scientific and Technical Information of China (English)
Haitao Qi; Hui Jin
2006-01-01
The fractional calculus is used in the constitutive relationship model of viscoelastic fluid.A generalized Maxwell model with fractional calculus is considered.Based on the flow conditions described,two flow cases are solved and the exact solutions are obtained by using the Weber transform and the Laplace transform for fractional calculus.
Multiscale Gyrokinetics for Rotating Tokamak Plasmas: Fluctuations, Transport and Energy Flows
Abel, I G; Wang, E; Barnes, M; Cowley, S C; Dorland, W; Schekochihin, A A
2012-01-01
This paper presents a complete theoretical framework for plasma turbulence and transport in tokamak plasmas. The fundamental scale separations present in plasma turbulence are codified as an asymptotic expansion in the ratio of the gyroradius to the equilibrium scale length. Proceeding order-by-order in this expansion, a framework for plasma turbulence is developed. It comprises an instantaneous equilibrium, the fluctuations driven by gradients in the equilibrium quantities, and the transport-timescale evolution of mean profiles of these quantities driven by the fluctuations. The equilibrium distribution functions are local Maxwellians with each flux surface rotating toroidally as a rigid body. The magnetic equillibrium is obtained from the Grad-Shafranov equation for a rotating plasma and the slow (resistive) evolution of the magnetic field is given by an evolution equation for the safety factor q. Large-scale deviations of the distribution function from a Maxwellian are given by neoclassical theory. The flu...
Energy Technology Data Exchange (ETDEWEB)
Torres-Diaz, I.; Cortes, A.; Rinaldi, C., E-mail: carlos.rinaldi@bme.ufl.edu [Department of Chemical Engineering, University of Puerto Rico, Mayagüez, Puerto Rico 00681-9000 (United States); Cedeño-Mattei, Y. [Department of Chemistry, University of Puerto Rico, Mayagüez, Puerto Rico 00681-9019 (United States); Perales-Perez, O. [Department of Engineering Science and Materials, University of Puerto Rico, Mayagüez, Puerto Rico 00681-9044 (United States)
2014-01-15
Ferrofluid flow in cylindrical and annular geometries under the influence of a uniform rotating magnetic field was studied experimentally using aqueous ferrofluids consisting of low concentrations (<0.01 v/v) of cobalt ferrite nanoparticles with Brownian relaxation to test the ferrohydrodynamic equations, elucidate the existence of couple stresses, and determine the value of the spin viscosity in these fluids. An ultrasound technique was used to measure bulk velocity profiles in the spin-up (cylindrical) and annular geometries, varying the intensity and frequency of the rotating magnetic field generated by a two pole stator winding. Additionally, torque measurements in the cylindrical geometry were made. Results show rigid-body like velocity profiles in the bulk, and no dependence on the axial direction. Experimental velocity profiles were in quantitative agreement with the predictions of the spin diffusion theory, with a value of the spin viscosity of ∼10{sup −8} kg m/s, two orders of magnitude larger than the value estimated earlier for iron oxide based ferrofluids, and 12 orders of magnitude larger than estimated using dimensional arguments valid in the infinite dilution limit. These results provide further evidence of the existence of couple stresses in ferrofluids and their role in driving the spin-up flow phenomenon.
Directory of Open Access Journals (Sweden)
A.M. Rashad
2014-04-01
Full Text Available This work is focused on the study of unsteady magnetohydrodynamics boundary-layer flow and heat transfer for a viscous laminar incompressible electrically conducting and rotating fluid due to a stretching surface embedded in a saturated porous medium with a temperature-dependent viscosity in the presence of a magnetic field and thermal radiation effects. The fluid viscosity is assumed to vary as an inverse linear function of temperature. The Rosseland diffusion approximation is used to describe the radiative heat flux in the energy equation. With appropriate transformations, the unsteady MHD boundary layer equations are reduced to local nonsimilarity equations. Numerical solutions of these equations are obtained by using the Runge–Kutta integration scheme as well as the local nonsimilarity method with second order truncation. Comparisons with previously published work have been conducted and the results are found to be in excellent agreement. A parametric study of the physical parameters is conducted and a representative set of numerical results for the velocity in primary and secondary flows as well as the local skin-friction coefficients and the local Nusselt number are illustrated graphically to show interesting features of Darcy number, viscosity-variation, magnetic field, rotation of the fluid, and conduction radiation parameters.
Directory of Open Access Journals (Sweden)
Garg B.P.
2015-02-01
Full Text Available An analysis of an oscillatory magnetohydrodynamic (MHD convective flow of a second order (viscoelastic, incompressible, and electrically conducting fluid through a porous medium bounded by two infinite vertical parallel porous plates is presented. The two porous plates with slip-flow condition and the no-slip condition are subjected respectively to a constant injection and suction velocity. The pressure gradient in the channel varies periodically with time. A magnetic field of uniform strength is applied in the direction perpendicular to the planes of the plates. The induced magnetic field is neglected due to the assumption of a small magnetic Reynolds number. The temperature of the plate with no-slip condition is non-uniform and oscillates periodically with time and the temperature difference of the two plates is assumed high enough to induce heat radiation. The entire system rotates in unison about the axis perpendicular to the planes of the plates. Adopting complex variable notations, a closed form solution of the problem is obtained. The analytical results are evaluated numerically and then presented graphically to discuss in detail the effects of different parameters of the problem. The velocity, temperature and the skin-friction in terms of its amplitude and phase angle have been shown graphically to observe the effects of the viscoelastic parameter γ, rotation parameter Ω, suction parameter λ , Grashof number Gr, Hartmann number M, the pressure A, Prandtl number Pr, radiation parameter N and the frequency of oscillation ω .
Directory of Open Access Journals (Sweden)
R. Mantovani
2002-01-01
Full Text Available This paper presents the analysis of symmetric circulations of a rotating baroclinic flow, forced by a steady thermal wind and dissipated by Laplacian friction. The analysis is performed with numerical time-integration. Symmetric flows, vertically bound by horizontal walls and subject to either periodic or vertical wall lateral boundary conditions, are investigated in the region of parameter-space where unstable small amplitude modes evolve into stable stationary nonlinear solutions. The distribution of solutions in parameter-space is analysed up to the threshold of chaotic behaviour and the physical nature of the nonlinear interaction operating on the finite amplitude unstable modes is investigated. In particular, analysis of time-dependent energy-conversions allows understanding of the physical mechanisms operating from the initial phase of linear instability to the finite amplitude stable state. Vertical shear of the basic flow is shown to play a direct role in injecting energy into symmetric flow since the stage of linear growth. Dissipation proves essential not only in limiting the energy of linearly unstable modes, but also in selecting their dominant space-scales in the finite amplitude stage.
Rotating Turbulent Flow Simulation with LES and Vreman Subgrid-Scale Models in Complex Geometries
Directory of Open Access Journals (Sweden)
Tao Guo
2014-07-01
Full Text Available The large eddy simulation (LES method based on Vreman subgrid-scale model and SIMPIEC algorithm were applied to accurately capture the flowing character in Francis turbine passage under the small opening condition. The methodology proposed is effective to understand the flow structure well. It overcomes the limitation of eddy-viscosity model which is excessive, dissipative. Distributions of pressure, velocity, and vorticity as well as some special flow structure in guide vane near-wall zones and blade passage were gained. The results show that the tangential velocity component of fluid has absolute superiority under small opening condition. This situation aggravates the impact between the wake vortices that shed from guide vanes. The critical influence on the balance of unit by spiral vortex in blade passage and the nonuniform flow around guide vane, combined with the transmitting of stress wave, has been confirmed.
Time-dependent rotating stratified shear flow: exact solution and stability analysis.
Salhi, A; Cambon, C
2007-01-01
A solution of the Euler equations with Boussinesq approximation is derived by considering unbounded flows subjected to spatially uniform density stratification and shear rate that are time dependent [S(t)= partial differentialU3/partial differentialx2]. In addition to vertical stratification with constant strength N(v)2, this base flow includes an additional, horizontal, density gradient characterized by N(h)2(t). The stability of this flow is then analyzed: When the vertical stratification is stabilizing, there is a simple harmonic motion of the horizontal stratification N(h)2(t) and of the shear rate S(t), but this flow is unstable to certain disturbances, which are amplified by a Floquet mechanism. This analysis may involve an additional Coriolis effect with Coriolis parameter f, so that governing dimensionless parameters are a modified Richardson number, R=[S(0)2+N(h)4(0)/N(v)2]1/2, and f(v)=f/N(v), as well as the initial phase of the periodic shear rate. Parametric resonance between the inertia-gravity waves and the oscillating shear is demonstrated from the dispersion relation in the limit R-->0. The parametric instability has connection with both baroclinic and elliptical flow instabilities, but can develop from a very different base flow.
Wu, Chung-Hua
1993-01-01
This report represents a general theory applicable to axial, radial, and mixed flow turbomachines operating at subsonic and supersonic speeds with a finite number of blades of finite thickness. References reflect the evolution of computational methods used, from the inception of the theory in the 50's to the high-speed computer era of the 90's. Two kinds of relative stream surfaces, S(sub 1) and S(sub 2), are introduced for the purpose of obtaining a three-dimensional flow solution through the combination of two-dimensional flow solutions. Nonorthogonal curvilinear coordinates are used for the governing equations. Methods of computing transonic flow along S(sub 1) and S(sub 2) stream surfaces are given for special cases as well as for fully three-dimensional transonic flows. Procedures pertaining to the direct solutions and inverse solutions are presented. Information on shock wave locations and shapes needed for computations are discussed. Experimental data from a Deutsche Forschungs- und Versuchsanstalt fur Luft- und Raumfahrt e.V. (DFVLR) rotor and from a Chinese Academy of Sciences (CAS) transonic compressor rotor are compared with the computed flow properties.
Three-dimensional instability of a multipolar vortex in a rotating flow
Le Dizès, Stéphane
2000-11-01
In this paper, the elliptic instability is generalized to account for Coriolis effects and higher order symmetries. We consider, in a frame rotating at the angular frequency Ω, a stationary vortex which is described near its center r=0 by the stream function written in polar coordinates Ψ=-(r2/2)+p(rn/n)cos(nθ), where the integer n is the order of the azimuthal symmetry, and p is a small positive parameter which measures the strength of the nonaxisymmetric field. Based on the Lifschitz and Hameiri [Phys. Fluids A 3, 2644-2651 (1991)] theory, the local stability analysis of the streamline Ψ=-1/2 is performed in the limit of small p. As for the elliptic instability [Bayly, Phys. Rev. Lett. 57, 2160-2163 (1986)], the instability is shown to be due to a parametric resonance of inertial waves when the inclination angle ξ of their wave vector with respect to the rotation axis takes a particular value given by cos ξ=±4/(n(1+Ω)). An explicit formula for the maximum growth rate of the inertial wave is obtained for arbitrary ξ, Ω, and n. As an immediate consequence, it is shown that a vortex core of relative vorticity Wr (assumed positive) is locally unstable if Ω(-1+n/4-p(n-1)/2)Wr/2. The predictive power of the local theory is demonstrated on several vortex examples by comparing the local stability predictions with global stability results. For both the Kirchhoff vortex and Moore and Saffman vortex, it is shown how global stability results can be derived from the local stability analysis using the dispersion relation of normal (Kelvin) modes. These results are compared to those obtained by global methods and a surprisingly good agreement is demonstrated. The local results are also applied to rotating Stuart vortices and compared to available numerical data.
Energy Technology Data Exchange (ETDEWEB)
Kwon, Kyung [Tuskegee Univ., Tuskegee, AL (United States); Fan, Liang-Shih [The Ohio State Univ., Columbus, OH (United States); Zhou, Qiang [The Ohio State Univ., Columbus, OH (United States); Yang, Hui [The Ohio State Univ., Columbus, OH (United States)
2014-09-30
A new and efficient direct numerical method with second-order convergence accuracy was developed for fully resolved simulations of incompressible viscous flows laden with rigid particles. The method combines the state-of-the-art immersed boundary method (IBM), the multi-direct forcing method, and the lattice Boltzmann method (LBM). First, the multi-direct forcing method is adopted in the improved IBM to better approximate the no-slip/no-penetration (ns/np) condition on the surface of particles. Second, a slight retraction of the Lagrangian grid from the surface towards the interior of particles with a fraction of the Eulerian grid spacing helps increase the convergence accuracy of the method. An over-relaxation technique in the procedure of multi-direct forcing method and the classical fourth order Runge-Kutta scheme in the coupled fluid-particle interaction were applied. The use of the classical fourth order Runge-Kutta scheme helps the overall IB-LBM achieve the second order accuracy and provides more accurate predictions of the translational and rotational motion of particles. The preexistent code with the first-order convergence rate is updated so that the updated new code can resolve the translational and rotational motion of particles with the second-order convergence rate. The updated code has been validated with several benchmark applications. The efficiency of IBM and thus the efficiency of IB-LBM were improved by reducing the number of the Lagragian markers on particles by using a new formula for the number of Lagrangian markers on particle surfaces. The immersed boundary-lattice Boltzmann method (IBLBM) has been shown to predict correctly the angular velocity of a particle. Prior to examining drag force exerted on a cluster of particles, the updated IB-LBM code along with the new formula for the number of Lagrangian markers has been further validated by solving several theoretical problems. Moreover, the unsteadiness of the drag force is examined when a
Navier-Stokes flow around a rotating obstacle mathematical analysis of its asymptotic behavior
Necasova, Sarka
2016-01-01
The book provides a comprehensive, detailed and self-contained treatment of the fundamental mathematical properties of problems arising from the motion of viscous incompressible fluids around rotating obstacles. It offers a new approach to this type of problems. We derive the fundamental solution of the steady case and we give pointwise estimates of velocity and its gradient (first and second one). Each chapter is preceded by a thorough discussion of the investigated problems, along with their motivation and the strategy used to solve them. The book will be useful to researchers and graduate students in mathematics, in particular mathematical fluid mechanics and differential equations.
Free-surface flow in horizontally rotating cylinder: experiment and simulation
Bohacek, J.; Kharicha, A.; Ludwig, A.; Wu, M.; Paar, A.; Brandner, M.; Elizondo, L.; Trickl, T.
2016-07-01
The horizontal centrifugal casting process targets on a liquid layer with a uniform thickness. To achieve this, the rotations of the mold have to be large enough so that the liquid can pick up the speed of the mold. In the present paper, an experiment was conducted using a laboratory plexi-glass mold with water as a working fluid. Starting with an initial volume fraction of liquid resting in the bottom of the mold, the mold rotations were gradually increased from 0 rpm to max rpm and a new position of the contact line was recorded. In addition, first critical rpm was recorded, at which the transition from the liquid pool to a uniform liquid layer occurred. While gradually going back from max rpm to 0 rpm, second critical rpm was recorded, at which the uniform liquid layer collapsed. The experiment was compared with the numerical simulation solving the modified shallow water equations using the Newton-Raphson method with the Wallington filter.
Characterization of Flow and Ohm's Law in the Rotating Wall Machine
Hannum, David; Brookhart, M.; Forest, C. B.; Kendrick, R.; Mengin, G.; Paz-Soldan, C.
2010-11-01
The rotating wall machine is a linear screw-pinch built to study the role of different electromagnetic boundary conditions on the Resistive Wall Mode (RWM). Its plasma is created by an array of electrostatic washer guns which can be biased to discharge up to 1 kA of current each. Individual flux ropes from the guns shear, merge, and expand into a 20 cm diameter, ˜1 m long plasma column. Langmuir (singletip) and tri-axial B-dot probes move throughout the column to measure radial and axial profiles of key plasma parameters. As the plasma current increases, more H2 fuel is ionized, raising ne to 5 x10^20 m-3 while Te stays at a constant 3 eV. The electron density expands to the wall while the current density (Jz) stays pinched to the central axis. E xB and diamagnetic drifts create radially and axially sheared plasma rotation. Plasma resistivity follows the Spitzer model in the core while exceeding it at the edge. These measurements improve the model used to predict the RWM growth rate.
Kovalenko, V. M.; Byehkov, N. M.; Kisel, G. A.; Dikovskaia, N. D.
1984-03-01
Measurements have been made of pressure distributions and pulsations in a cross flow past a circular cylinder placed near a plane screen of finite length. The experiments reported here have been carried out under low turbulence conditions over a range of Reynolds numbers that includes the critical values. The boundary layer separation points and the evolution of the front critical point and other characteristic zones with the distance to the screen are determined. The components of the aerodynamic force acting on the cylinder and the Strouhal number are calculated on the basis of the predominant pulsation frequencies on the cylinder.
Modelling thermal development of liquid metal flow on rotating disc in centrifugal atomisation
Energy Technology Data Exchange (ETDEWEB)
Ho, K.H.; Zhao, Y.Y
2004-01-25
In centrifugal atomisation the formation of a solid skull on the atomising disc is a major problem, which has adverse effects on the quality and quantity of the as-produced powder and also on the balance of the disc during atomisation. It is costly and difficult to study the flow behaviour because of the complex interaction between the liquid metal and the atomising disc. A computational fluid dynamics model has been developed using Flow-3D to simulate the thermal development of the liquid metal on the atomising disc. Under a fixed process condition, the liquid metal has a nearly constant solidification rate before the steady state is achieved and a solid skull is formed gradually. The volume of the skull decreases with increasing liquid metal flow rate, initial disc temperature and initial liquid temperature.
Dif-Pradalier, G.; Grandgirard, V.; Sarazin, Y.; Garbet, X.; Ghendrih, Ph.
2009-08-01
The impact of ion-ion collisions on confinement is investigated with the full-f and global gyrokinetic Gysela code through a series of nonlinear turbulence simulations for tokamak parameters. A twofold scan in the turbulence drive and in collisionality is performed, highlighting (i) a heat transport expressed in terms of critical quantities—threshold and exponent, (ii) a first evidence of turbulent generation of poloidal momentum, and (iii) the dominance of mean flow shear, mediated through the turbulent corrugation of the mean profiles, with regard to the oft-invoked zonal flow shear.
Faghri, Amir; Swanson, Theodore D.
1990-01-01
In the first section, improvements in the theoretical model and computational procedure for the prediction of film height and heat-transfer coefficient of the free surface flow of a radially-spreading thin liquid film adjacent to a flat horizontal surface of finite extent are presented. Flows in the presence and absence of gravity are considered. Theoretical results are compared to available experimental data with good agreement. In the presence of gravity, a hydraulic jump is present, isolating the flow into two regimes: supercritical upstream from the jump and subcritical downstream of it. In this situation, the effects of surface tension are important near the outer edge of the disk where the fluid experiences a free fall. A region of flow separation is present just downstream of the jump. In the absence of gravity, no hydraulic jump or separated flow region is present. The variation of the heat-transfer coefficient for flows in the presence and absence of gravity are also presented. In the second section, the results of a numerical simulation of the flow field and associated heat transfer coefficients are presented for the free surface flow of a thin liquid film adjacent to a horizontal rotating disk. The computation was performed for different flow rates and rotational velocities using a 3-D boundary-fitted coordinate system. Since the geometry of the free surface is unknown and dependent on flow rate, rate of rotation, and other parameters, an iterative procedure had to be used to ascertain its location. The computed film height agreed well with existing experimental measurements. The flow is found to be dominated by inertia near the entrance and close to the free surface and dominated by centrifugal force at larger radii and adjacent to the disk. The rotation enhances the heat transfer coefficient by a significant amount.
DEFF Research Database (Denmark)
Santos, M. B. L.; Sørensen, Jens Nørkær
1996-01-01
. This one is a coaxial disk in contact with the fluid surface but without covering it entirely. The study focuses on the occurrence of time-dependent flow, more specifically, the first transition to unsteadiness, by considering cavity cases with different amounts of free surface, for a fixed aspect ratio...
Institute of Scientific and Technical Information of China (English)
沈远胜; 刘高联; 刘永杰
2004-01-01
The variational analysis of the Pseudo-potential function-vortex-potential function model, a new mathematical model, was developed and by which the flow field with transonic speed and curl was decided, and different sorts of the variational principle for vortexpotential function were established by transforming the original equation for vortex-function, the boundary conditions for vortex-potential function was raised.
A Rotational Pressure-Correction Scheme for Incompressible Two-Phase Flows with Open Boundaries.
Dong, S; Wang, X
2016-01-01
Two-phase outflows refer to situations where the interface formed between two immiscible incompressible fluids passes through open portions of the domain boundary. We present several new forms of open boundary conditions for two-phase outflow simulations within the phase field framework, as well as a rotational pressure correction based algorithm for numerically treating these open boundary conditions. Our algorithm gives rise to linear algebraic systems for the velocity and the pressure that involve only constant and time-independent coefficient matrices after discretization, despite the variable density and variable viscosity of the two-phase mixture. By comparing simulation results with theory and the experimental data, we show that the method produces physically accurate results. We also present numerical experiments to demonstrate the long-term stability of the method in situations where large density contrast, large viscosity contrast, and backflows occur at the two-phase open boundaries.
Energy Technology Data Exchange (ETDEWEB)
Kishibe, T. [Hitachi, Ltd., Tokyo (Japan); Kaji, S. [The University of Tokyo, Tokyo (Japan). Faculty of Engineering
2000-02-25
In the previous papers, the swirling flow field in a rotating hollow turbine shaft was solved using computational fluid dynamics. It was observed that a large-scale spiral vortex existed at a place where the swirling flow turned radially outward. In this report, the pressure fluctuations in the swirling flow field are measured. The main part of the internal cooling air system of a gas turbine is used as the experimental apparatus. A specially devised liner in inserted inside the hollow turbine shaft and ten pressure sensors are embedded axially and circumferentially in the liner to measure the unsteady wall pressures. The pressure fluctuations which have the same characteristics as the rotating spiral vortex predicted in the numerical results are captured. The amplitude is great at the sensors near the place where the vortex was predicted in the numerical results and the precession frequency of the rotating spiral vortex is in close agreement with the calculated frequency. (author)
Directory of Open Access Journals (Sweden)
Xiaojun Zhang
2013-01-01
particle contaminant, moisture and gas simultaneously. As the major unit of HIGEE, the RPB uses centrifugal force to intensify mass transfer. Because of the special structure of RPB, the hydraulic characteristics of the RPB are very important. In this study, the multiphase flow model in porous media of the RPB is presented, and the dynamical oil-water separation in the RPB is simulated using a commercial computational fluid dynamics code. The operating conditions and configuration on the hydraulic performance of the RPB are investigated. The results have indicated that the separation efficiency of HIGEE rotating oil purifier is predominantly affected by operating conditions and the configurations. The best inlet pressure is 0.002 MPa. When the liquid inlet is placed in the outside of the lower surface of RPB; oil outlet is placed in the upper surface, where it is near the rotation axis; and water outlet is placed in the middle of the RPB, where it is far away from the oil outlet, the separating efficiency is the best.
Energy Technology Data Exchange (ETDEWEB)
Derks, Didi; Wisman, Hans; Blaaderen, Alfons van; Imhof, Arnout [Soft Condensed Matter, Debye Institute, Utrecht University, Princetonplein 5, 3584 CC Utrecht, The (Netherlands)
2004-09-29
We report on novel possibilities for studying colloidal suspensions in a steady shear field in real space. Fluorescence confocal microscopy is combined with the use of a counter-rotating cone-plate shear cell. This allows imaging of individual particles in the bulk of a sheared suspension in a stationary plane. Moreover, this plane of zero velocity can be moved in the velocity gradient direction while keeping the shear rate constant. The colloidal system under study consists of rhodamine labelled PMMA spheres in a nearly density and refractive index matched mixture of cyclohexylbromide and cis-decalin. We show measured flow profiles in both the fluid and the crystalline phase and find indications for shear banding in the case of a sheared crystal. Furthermore, we show that, thanks to the counter-rotating principle of the cone-plate shear cell, a layer of particles in the bulk of a sheared crystalline suspension can be imaged for a prolonged time, with the result that their positions can be tracked.
MHD flow of Burger’s fluid over an off-centered rotating disk in a porous medium
Directory of Open Access Journals (Sweden)
Najeeb Alam Khan
2015-08-01
Full Text Available In this study, off-centered stagnation flow of three dimensional Burger’s fluid over an infinite rotating disk in a porous medium with a uniform magnetic field, which is applying normal to the disk, is investigated. A uniform suction/injection is applied through the surface of the porous disk. The structure has been modeled in the form of ordinary differential equations, which are reduced from partial differential equations by using the similarity transformation. Analytical solution is obtained by non-perturbation technique of homotopy analysis method (HAM. The influence of non-dimensional parameters on velocity profile is presented in graphical form and the numerical comparison is made with the viscous fluid as a special case.
FINITE ELEMENT ANALYSIS OF THE FLOW INDUCED BY ROTATING BLADES IN AN INCOMPRESSIBLE VISCOUS FLUID
Institute of Scientific and Technical Information of China (English)
无
2002-01-01
Aerodynamic loads on a multi-bladed helicopter rotor in hovering flight were calculated by solving the three-dimensional incompressible Navier-Stokes equations. The rotor wake effects were accounted by the correction of local geometric angle of attack according to a free-wake modeling in addition to an empirical modification for the tip flow effect. The validity and efficiency of the present method were verified by the comparisons between numerical results and experimental data.
Research of products of high temperature synthesis flowing in the rotation conditions
Ksandopulo, G.; Baideldinova, A.; Riabikin, Y.; Mukhina, L.; Ponomareva, E.; Vasilieva, N.
2017-02-01
The method of production of materials by out-furnace process of self-propagating high temperature synthesis (SHS), flowing in the conditions of action of centrifugal force, is developed presently. The primary purpose of working is achievement high level of generating of energy and use of it for forming of steady meta-stable crystalline phases with an uncommon set of physical and chemical properties.
Investigations of non-hydrostatic, stably stratified and rapidly rotating flows
Nieves, David; Juilen, Keith; Weiss, Jeffrey B
2016-01-01
We present an investigation of rapidly rotating (small Rossby number $Ro\\ll 1$) and stratified turbulence where the stratification strength is varied from weak (large Froude number $Fr\\gg1$) to strong ($Fr\\ll1$). The investigation is set in the context of a reduced model derived from the Boussinesq equations that efficiently retains anisotropic inertia-gravity waves with order-one frequencies and highlights a regime of wave-eddy interactions. Numerical simulations of the reduced model are performed where energy is injected by a stochastic forcing of vertical velocity, which forces wave modes only. The simulations reveal two regimes characterized by the presence of well-formed, persistent and thin turbulent layers of locally-weakened stratification at small Froude numbers, and by the absence of layers at large Froude numbers. Both regimes are characterized by a large-scale barotropic dipole enclosed by small-scale turbulence. When the Reynolds number is not too large a direct cascade of barotropic kinetic ener...
Relativistic thermodynamics, a Lagrangian field theory for general flows including rotation
Frønsdal, Christian
Any theory that is based on an action principle has a much greater predictive power than one that does not have such a formulation. The formulation of a dynamical theory of General Relativity, including matter, is here viewed as a problem of coupling Einstein’s theory of pure gravity to an independently chosen and well-defined field theory of matter. It is well known that this is accomplished in a most natural way when both theories are formulated as relativistic, Lagrangian field theories, as is the case with Einstein-Maxwell theory. Special matter models of this type have been available; here a more general thermodynamical model that allows for vortex flows is presented. In a wider context, the problem of subjecting hydrodynamics and thermodynamics to an action principle is one that has been pursued for at least 150 years. A solution to this problem has been known for some time, but only under the strong restriction to potential flows. A variational principle for general flows has become available. It represents a development of the Navier-Stokes-Fourier approach to fluid dynamics. The principal innovation is the recognition that two kinds of flow velocity fields are needed, one the gradient of a scalar field and the other the time derivative of a vector field, the latter closely associated with vorticity. In the relativistic theory that is presented here, the latter is the Hodge dual of an exact 3-form, well known as the notoph field of Ogievetskij and Palubarinov, the B-field of Kalb and Ramond and the vorticity field of Lund and Regge. The total number of degrees of freedom of a unary system, including the density and the two velocity fields is 4, as expected — as in classical hydrodynamics. In this paper, we do not reduce Einstein’s dynamical equation for the metric to phenomenology, which would have denied the relevance of any intrinsic dynamics for the matter sector, nor do we abandon the equation of continuity - the very soul of hydrodynamics.
Modeling dynamic stall on wind turbine blades under rotationally augmented flow fields
DEFF Research Database (Denmark)
Guntur, Srinivas; Sørensen, Niels N.; Schreck, Scott
2016-01-01
Experiment Phase VI experimental data, including constant as well as continuously pitching blade conditions during axial operation; (2) data from unsteady delayed detached eddy simulations (DDES) carried out using the Technical University of Denmark’s in-house flow solver Ellipsys3D; and (3) data from...... agreement between the model and the experimental data in many cases, which suggests that the current two-dimensional dynamic stall model as used in blade element momentum-based aeroelastic codes may provide a reasonably accurate representation of three-dimensional rotor aerodynamics when used in combination...
Erdos, J. I.; Alzner, E.
1977-01-01
A numerical method of solution of the inviscid, compressible, two-dimensional unsteady flow on a blade-to-blade stream surface through a stage (rotor and stator) or a single blade row of an axial flow compressor or fan is described. A cyclic procedure has been developed for representation of adjacent blade-to-blade passages which asymptotically achieves the correct phase between all passages of a stage. A shock-capturing finite difference method is employed in the interior of the passage, and a method of characteristics technique is used at the boundaries. The blade slipstreams form two of the passage boundaries and are treated as moving contact surfaces capable of supporting jumps in entropy and tangential velocity. The Kutta condition is imposed by requiring the slipstreams to originate at the trailing edges, which are assumed to be sharp. Results are presented for several transonic fan rotors and compared with available experimental data, consisting of holographic observations of shock structure and pressure contour maps. A subcritical stator solution is also compared with results from a relaxation method. Finally, a periodic solution for a stage consisting of 44 rotor blades and 46 stator blades is discussed.
Fingering instability in the flow of a power-law fluid on a rotating disc
Arora, Akash; Doshi, Pankaj
2016-01-01
A computational study of the flow of a non-Newtonian power law fluid on a spinning disc is considered here. The main goal of this work is to examine the effect of non-Newtonian nature of the fluid on the flow development and associated contact line instability. The governing mass and momentum balance equations are simplified using the lubrication theory. The resulting model equation is a fourth order non-linear PDE which describes the spatial and temporal evolutions of film thickness. The movement of the contact line is modeled using a constant angle slip model. To solve this moving boundary problem, a numerical method is developed using a Galerkin/finite element method based approach. The numerical results show that the spreading rate of the fluid strongly depends on power law exponent n. It increases with the increase in the shear thinning character of the fluid (n 1). It is also observed that the capillary ridge becomes sharper with the value of n. In order to examine the stability of these ridges, a linear stability theory is also developed for these power law fluids. The dispersion relationship depicting the growth rate for a given wave number has been reported and compared for different power-law fluids. It is found that the growth rate of the instability decreases as the fluid becomes more shear thinning in nature, whereas it increases for more shear thickening fluids.
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.
Directory of Open Access Journals (Sweden)
Hayat Tasawar
2003-01-01
Full Text Available The governing equations for the unsteady flow of a uniformly conducting incompressible fourth-grade fluid due to noncoaxial rotations of a porous disk and the fluid at infinity are constructed. The steady flow of the fourth-grade fluid subjected to a magnetic field with suction/blowing through the disk is studied. The nonlinear ordinary differential equations resulting from the balance of momentum and mass are discretised by a finite-difference method and numerically solved by means of an iteration method in which, by a coordinate transformation, the semi-infinite physical domain is converted to a finite calculation domain. In order to solve the fourth-order nonlinear differential equations, asymptotic boundary conditions at infinity are augmented. The manner in which various material parameters affect the structure of the boundary layer is delineated. It is found that the suction through the disk and the magnetic field tend to thin the boundary layer near the disk for both the Newtonian fluid and the fourth-grade fluid, while the blowing causes a thickening of the boundary layer with the exception of the fourth-grade fluid under strong blowing. With the increase of the higher-order viscosities, the boundary layer has the tendency of thickening.
Savonina, Elena Yu; Fedotov, Petr S; Wennrich, Rainer
2012-01-15
Dynamic fractionation is considered to be an attractive alternative to conventional batch sequential extraction procedures for partitioning of trace metals and metalloids in environmental solid samples. This paper reports the first results on the continuous-flow dynamic fractionation of selenium using two different extraction systems, a microcolumn (MC) packed with the solid sample and a rotating coiled column (RCC) in which the particulate matter is retained under the action of centrifugal forces. The eluents (leachants) were applied in correspondence with a four-step sequential extraction scheme for selenium addressing "soluble", "adsorbed", "organically bound", and "elemental" Se fractions extractable by distilled water, phosphate buffer, tetramethylammonium hydroxide, and sodium sulphite solutions, respectively. Selenium was determined in the effluent by using an inductively coupled plasma atomic emission spectrometer. Contaminated creek sediment and dumped waste (soil) samples from the abandoned mining area were used to evaluate resemblances and discrepancies of two continuous-flow methods for Se fractionation. In general, similar trends were found for Se distribution between extractable and residual fractions. However, for the dumped waste sample which is rich in organic matter, the extraction in RCC provided more effective recovery of environmentally relevant Se forms (the first three leachable fractions). The most evident deviation was observed for "adsorbed" Se (recoveries by RCC and MC are 43 and 7 mg kg(-1), respectively). The data obtained were correlated with peculiarities of samples under investigation and operational principles of RCC and MC.
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.
Suresh, M; Manglik, A
2014-01-01
This paper proposes the exact solution for unsteady flow of a viscous incompressible electrically conducting fluid past a impulsively started infinite horizontal surface which is rotating with an angular velocity embedded in a saturated porous medium under the influence of strong magnetic field with hall effect. Our study focuses on the change of direction of the external magnetic field on the flow system which leads to change in the flow behavior and skin frictional forces at the boundary. Systems of flow equations are solved using Laplace transform technique. The impacts of control parameters Hartman number, rotation of the system, hall effect, inclination of the magnetic field, and Darcy number on primary and secondary velocities are shown graphically, skin friction at horizontal boundary in tabular form. For validating our results, in the absence of permeability of the porous medium and inclination of the magnetic field the results are in good agreement with the published results.
Timokhin, A. N.; Arons, J.
2013-01-01
We report the results of an investigation of particle acceleration and electron-positron plasma generation at low altitude in the polar magnetic flux tubes of rotation-powered pulsars, when the stellar surface is free to emit whatever charges and currents are demanded by the force-free magnetosphere. We apply a new 1D hybrid plasma simulation code to the dynamical problem, using Particle-in-Cell methods for the dynamics of the charged particles, including a determination of the collective electrostatic fluctuations in the plasma, combined with a Monte Carlo treatment of the high-energy gamma-rays that mediate the formation of the electron-positron pairs.We assume the electric current flowing through the pair creation zone is fixed by the much higher inductance magnetosphere, and adopt the results of force-free magnetosphere models to provide the currents which must be carried by the accelerator. The models are spatially one dimensional, and designed to explore the physics, although of practical relevance to young, high-voltage pulsars. We observe novel behaviour (a) When the current density j is less than the Goldreich-Julian value (0 1), the system develops high voltage drops (TV or greater), causing emission of curvature gamma-rays and intense bursts of pair creation. The bursts exhibit limit cycle behaviour, with characteristic time-scales somewhat longer than the relativistic fly-by time over distances comparable to the polar cap diameter (microseconds). (c) In return current regions, where j/j(sub GJ) rotating frame), finding that such steady flows can occupy only a small fraction of the current density parameter space exhibited by the force-free magnetospheric model. The generic polar flow dynamics and pair creation are strongly time dependent. The model has an essential difference from almost all previous quantitative studies, in that we sought the accelerating voltage (with pair creation, when the voltage drops are sufficiently large; without, when they are
Unsteady rotating laminar flow: analytical solution of relevant Navier-Stokes equations
Bocci, Alessio; Ritelli, Daniele
2016-01-01
We provide a integration of Navier-Stokes equations concerning the unsteady-state laminar flow of an incompressible, isothermal (newtonian) fluid in a cylindrical vessel spinning about its symmetry axis, say $z$, and inside which the liquid velocity starts with a non-zero axial component as well. Basic physical assumptions are that the pressure axial gradient keeps itself on its hydrostatic value and that no radial velocity exists. In such a way the PDEs become uncoupled and can be faced separately from each other. We succeed in computing both the unsteady velocities, i.e. the axial $v_z$ and the circumferential $v_\\theta$ as well, by means of infinite series expansions of Fourier-Bessel type under time exponential damping. Following this, we also find the unsteady surfaces of dynamical equilibrium, the wall shear stress and the Stokesian streamlines
Energy Technology Data Exchange (ETDEWEB)
Debacq, M.; Patisson, F.; Ablitzer, D. [Ecoles des Mines de Nancy, Lab. de Science et Genie des Materiaux Metalliques, UMR 7584, 54 - Nancy (France); Houzelot, J.L. [Ecole Nationale Superieure des Industries Chimiques (ENSIC), Lab. des Sciences du Genie Chimique, UPR 6811, 54 - Villers-les-Nancy (France); Feugier, A. [Societe Franco-Belge de Fabrication Combustibles, F.B.F.C., Dir. Technique, 26 - Romans (France); Hartmann, D. [Cogema, 26 - Pierrelatte (France)
2001-07-01
The transverse flow of cohesive powders of uranium in a rotating kiln equipped with raising levers has been studied experimentally at ambient temperature and at the temperatures of the process. The simple laws obtained have permitted to calculate the average distribution of the powder in a straight section of the kiln. (J.S.)
Duran-Matute, M.; Di Nitto, G.; Trieling, R.R.; Kamp, L.P.J.; van Heijst, G.J.F.
2012-01-01
We present an experimental/numerical study of a dipolar flow structure in a shallow layer of electrolyte driven by electromagnetic forcing and subjected to background rotation. The aim of this study is to determine the influence of a non-conservative body force on the range of applicability of the
Duran-Matute, M.; Di Nitto, G.; Trieling, R.R.; Kamp, L.P.J.; van Heijst, G.J.F.
2012-01-01
We present an experimental/numerical study of a dipolar flow structure in a shallow layer of electrolyte driven by electromagnetic forcing and subjected to background rotation. The aim of this study is to determine the influence of a non-conservative body force on the range of applicability of the c
Scale dependence of the alignment between strain rate and rotation in turbulent shear flow
Fiscaletti, D.
2016-10-24
The scale dependence of the statistical alignment tendencies of the eigenvectors of the strain-rate tensor e(i), with the vorticity vector omega, is examined in the self-preserving region of a planar turbulent mixing layer. Data from a direct numerical simulation are filtered at various length scales and the probability density functions of the magnitude of the alignment cosines between the two unit vectors vertical bar e(i) . (omega) over cap vertical bar are examined. It is observed that the alignment tendencies are insensitive to the concurrent large-scale velocity fluctuations, but are quantitatively affected by the nature of the concurrent large-scale velocity-gradient fluctuations. It is confirmed that the small-scale (local) vorticity vector is preferentially aligned in parallel with the large-scale (background) extensive strain-rate eigenvector e(1), in contrast to the global tendency for omega to be aligned in parallelwith the intermediate strain-rate eigenvector [Hamlington et al., Phys. Fluids 20, 111703 (2008)]. When only data from regions of the flow that exhibit strong swirling are included, the so-called high-enstrophy worms, the alignment tendencies are exaggerated with respect to the global picture. These findings support the notion that the production of enstrophy, responsible for a net cascade of turbulent kinetic energy from large scales to small scales, is driven by vorticity stretching due to the preferential parallel alignment between omega and nonlocal e(1) and that the strongly swirling worms are kinematically significant to this process.
Energy Technology Data Exchange (ETDEWEB)
Kishibe, T. [Hitachi, Ltd, Tokyo (Japan); Kaji, S. [The University of Tokyo, Tokyo (Japan)
2000-01-25
In the 1st report, numerical results were presented for the swirling flow field in a rotating hollow turbine shaft. The existence of a rotating spiral vortex at the place where the swirling flow turns radially outward was shown. The first non-axisymmetric mode of a single spiral vortex was transformed into the second mode of a double spiral vortex at a specific rotating speed of the shaft. In this report, the downstream region of the computational domain is extended to the wheel space, the cavity between the corotating turbine disks, to solve the swirling flow field in the internal cooling air system of a gas turbine. The data on precessing frequencies of the rotating spiral vortex in this numerical analysis are compared with experimental results in a companion paper (3rd report). In addition, attention is paid to the three-dimensional swirling flow field in the rotating cavity with the rotating spiral vortex in the straight tube. (author)
Directory of Open Access Journals (Sweden)
S. Srinivas
2016-01-01
Full Text Available The present work investigates the effects of thermal-diffusion and diffusion-thermo on MHD flow of viscous fluid between expanding or contracting rotating porous disks with viscous dissipation. The partial differential equations governing the flow problem under consideration have been transformed by a similarity transformation into a system of coupled nonlinear ordinary differential equations. An analytical approach, namely the homotopy analysis method is employed in order to obtain the solutions of the ordinary differential equations. The effects of various emerging parameters on flow variables have been discussed numerically and explained graphically. Comparison of the HAM solutions with the numerical solutions is performed.
Directory of Open Access Journals (Sweden)
José Antonio Alves Cutrim Junior
2013-02-01
Full Text Available Biomass flow characteristics and forage accumulation were evaluated in Bermudagrass (Tifton 85 pasture managed under intermittent stocking with different management strategies. The management levels utilized were conventional (10 cm residual height and unfertilized, light (20 cm residual height and unfertilized, moderate (20 cm residual height with fertilization of 300 kg N/ha.year and intensive (10 cm residual height with fertilization of 600 kg N/ha.year. A randomized design was used with repeated measurements over time, in two periods of the year, with four replicates. There was significant effect of management × period of the year on the leaf elongation rate (LER. The management levels under fertilization (0.59 and 0.60 cm/tiller.day for the intensive and moderate management, respectively and the rainy season (0.49 cm/tiller.day showed the greatest stem elongation rate. Leaf senescence rate (LSR before and after and total LSR were modified by the management × period of the year interaction. The intensive management, with 0.38 leaves/tiller.day, as well as the dry period, with 0.27 leaves/tiller.day, showed higher leaf appearance rate. The lowest phyllochron was observed in intensive management and dry periods, as well as an interaction with the management of the same periods of the year. There was management × period of year interaction effect on leaf lifespan; the highest value was found under conventional management and dry period. Both production and forage accumulation rates were higher in the intensive and moderate management levels and dry season, and there was interaction of the intensive management system with the seasons. Managing pastures under moderate and intensive rotational stocking, which occurred mainly in the rainy and dry seasons, respectively, maximizes the flow of tissues and consequently production and accumulation of forage.
Gorton, C. A.; Lakshminarayana, B.
1975-01-01
A method of measuring the three-dimensional components of mean velocity and turbulence quantities within a rotating turbomachinery passage is developed through the use of hot wire anemometry techniques. Equations are derived which, when solved simultaneously and in conjunction with the data obtained from the hot wire anemometer measurements, will provide values for the radial, axial and tangential components of mean velocity, turbulence intensity and turbulence stress within the rotating turbomachinery passage. A three-bladed rocket pump inducer model, operating in air, was used in the experimentation. The method is very accurate and provides very useful information on the characteristics of the flow inside rotor passages hitherto unexplored.
Escamilla-Ruíz, I. A.; Sierra-Espinosa, F. Z.; García, J. C.; Valera-Medina, A.; Carrillo, F.
2017-09-01
Single-phase flows in stirred tank reactors have useful characteristics for a wide number of industrial applications. Usually, reactors are cylindrical vessels and complex impeller designs, which are often highly energy consuming and produce complicated flow patterns. Therefore, a novel configuration consisting of a square stirred tank reactor is proposed in this study with potential advantages over conventional reactors. In the present work hydrodynamics and turbulence have been studied for a single-phase flow in steady state operating in batch condition. The flow was induced by drag from a rotating cylinder with two diameters. The effects of drag from the stirrer as well as geometrical parameters of the system on the hydrodynamic behavior were investigated using Computational Fluids Dynamics (CFD) and non-intrusive Laser Doppler Anemometry, (LDA). Data obtained from LDA measurements were used for the validation of the CFD simulations, and to detecting the macro-instabilities inside the tank, based on the time series analysis for three rotational speeds N = 180, 1000 and 2000 rpm. The numerical results revealed the formation of flow patterns and macro-vortex structures in the upper part of the tank as consequence of the Reynolds number and the stream discharge emanated from the cylindrical stirrer. Moreover, increasing the cylinder diameter has an impact on the number of recirculation loops as well as the energy consumption of the entire system showing better performance in the presence of turbulent flows.
Escamilla-Ruíz, I. A.; Sierra-Espinosa, F. Z.; García, J. C.; Valera-Medina, A.; Carrillo, F.
2017-04-01
Single-phase flows in stirred tank reactors have useful characteristics for a wide number of industrial applications. Usually, reactors are cylindrical vessels and complex impeller designs, which are often highly energy consuming and produce complicated flow patterns. Therefore, a novel configuration consisting of a square stirred tank reactor is proposed in this study with potential advantages over conventional reactors. In the present work hydrodynamics and turbulence have been studied for a single-phase flow in steady state operating in batch condition. The flow was induced by drag from a rotating cylinder with two diameters. The effects of drag from the stirrer as well as geometrical parameters of the system on the hydrodynamic behavior were investigated using Computational Fluids Dynamics (CFD) and non-intrusive Laser Doppler Anemometry, (LDA). Data obtained from LDA measurements were used for the validation of the CFD simulations, and to detecting the macro-instabilities inside the tank, based on the time series analysis for three rotational speeds N = 180, 1000 and 2000 rpm. The numerical results revealed the formation of flow patterns and macro-vortex structures in the upper part of the tank as consequence of the Reynolds number and the stream discharge emanated from the cylindrical stirrer. Moreover, increasing the cylinder diameter has an impact on the number of recirculation loops as well as the energy consumption of the entire system showing better performance in the presence of turbulent flows.
Institute of Scientific and Technical Information of China (English)
A.M.Abd-Alla; S.M.Abo-Dahab; H.D.El-Shahrany
2013-01-01
In this paper,the effects of both rotation and magnetic field of the peristaltic transport of a second-order fluid through a porous medium in a channel are studied analytically and computed numerically.The material is represented by the constitutive equations for a second-order fluid.Closed-form solutions under the consideration of long wavelength and low Reynolds number is presented.The analytical expressions for the pressure gradient,pressure rise,friction force,stream function,shear stress,and velocity are obtained in the physical domain.The effects of the non-dimensional wave amplitude,porosity,magnetic field,rotation,and the dimensionless time-mean flow in the wave frame are analyzed theoretically and computed numerically.Numerical results are given and illustrated graphically in each case considered.Comparison was made with the results obtained in the presence and absence of rotation,magnetic field,and porosity.The results indicate that the effects of the non-dimensional wave amplitude,porosity,magnetic field,rotation,and the dimensionless time-mean flow are very pronounced in the phenomena.
Gils, Dennis P.M.; Bruggert, Gert-Wim; Lathrop, Daniel P.; Sun, Chao; Lohse, Detlef
2011-01-01
A new turbulent Taylor–Couette system consisting of two independently rotating cylinders has been constructed. The gap between the cylinders has a height of 0.927 m, an inner radius of 0.200 m, and a variable outer radius (from 0.279 to 0.220 m). The maximum angular rotation rates of the inner and o
Xia, Qixiao; Zhang, Jianhui; Lei, Hong; Cheng, Wei
2012-05-01
Typically, liquid pump and liquids mixer are two separate devices. The invention of piezoelectric pump makes it possible to integrate the two devices. Hower, the existing piezoelectric mixing-pumps are larger because the need the space outside the chamber, and another shortcome of them is that they cannot adjust the mixing ratio of two liquids. In this paper, a new piezoelectric pump being capable of integrating mixer and pump is presented, based on the theory of the piezoelectric pump with the unsymmetrical slopes element (USE). Besides the features of two inlets and one outlet, the piezoelectric pump has a rotatable unsymmetrical slopes element(RUSE). When the pump works, two fluids flow into the inlet channels respectively. Then the RUSE controls the ratio of the two flows by adjusting the flow resistances of the two inlet channels. The fluids form a net flow due to the USE principle, while they are mixed into a homogeneous solution due to strong turbulence flow field and complex vortices generated by RUSE in the chamber. And then the solution flows through the outlet. Firstly, the theoretical analysis on this pump is performed. Meanwhile, the flow field in the chamber is calculated and simulated. And then, the relationship between the flows of the two channels and the rotating angle of the RUSE is set up and analyzed. Finally, experiment with the proposed pump is carried out to verify the numerical results. A RUSE with 20° slope angle is used in the experiment. Four sets of data are tested with the RUSE at the rotating angles of 0°, 6°, 11°, and 16°, respectively, corresponding to the numerical models. The experimental results show that the empirical data and the theoretical data share the same trend. The maximum error between the theoretical flow and the experimental flow is 11.14%, and the maximum error between the theoretical flow ratio of the two inlets and the experimental one is 2.5%. The experiment verified the theoretical analysis. The proposed
DEFF Research Database (Denmark)
De Luca, Sergio; Todd, Billy; Hansen, Jesper Schmidt;
2014-01-01
by an external spatially uniform rotating electric field and confined between two planar surfaces exposing different degrees of hydrophobicity. The permanent dipole moment of water follows the rotating field, thus inducing the molecules to spin, and the torque exerted by the field is continuously injected...... into the fluid, enabling a steady conversion of spin angular momentum into linear momentum. The translational–rotational coupling is a sensitive function of the rotating electric field parameters. In this work, we have found that there exists a small energy dissipation region attainable when the frequency...... of the rotating electric field matches the inverse of the dielectric relaxation time of water and when its amplitude lies in a range just before dielectric saturation effects take place. In this region, that is, when the frequency lies in a small window of the microwave region around ∼20 GHz and amplitude ∼0.03 V...
Sakata, Yuu; Ohta, Yutaka
2017-02-01
The interaction between surge and rotating stall in an axial flow compressor was investigated from the viewpoint of an unsteady inner flow structure. The aim of this study was to identify the key factor that determines the switching phenomenon of a surge cycle. The main feature of the tested compressor is a shock tube connected in series to the compressor outlet through a diaphragm, slits, and a concentric duplex pipe: this system allows surge and rotating stall to be generated by connecting the shock tube with the compressor, or enables the compression plane wave injection. The unsteady characteristics and the internal flow velocity fluctuations were measured in detail, and the stall cell structure was averaged and visualized along the movement of the operation point under a coexisting state of surge. A coefficient of the cell scale fluctuation was calculated using the result of the averaging, and it confirmed that the processes of inner flow structure change differed from each other according to the next cycle of the surge. The result suggests that the key factor that determines the next cycle is the transformation of the internal flow structure, particularly between the stall cell and the entire circumferential stall, in both the recovering and stalling processes.
Usui, Yuta; Kanemoto, Toshiaki; Hiraki, Koju
2013-12-01
The authors have invented the unique counter-rotating type tidal stream power unit composed of the tandem propellers and the double rotational armature type peculiar generator without the traditional stator. The front and the rear propellers counter-drive the inner and the outer armatures of the peculiar generator, respectively. The unit has the fruitful advantages that not only the output is sufficiently higher without supplementary equipment such as a gearbox, but also the rotational moment hardly act on the pillar because the rotational torque of both propellers/armatures are counter-balanced in the unit. This paper discusses experimentally the performances of the power unit and the effects of the propeller rotation on the sea surface. The axial force acting on the pillar increases naturally with the increase of not only the stream velocity but also the drag of the tandem propellers. Besides, the force vertical to the stream also acts on the pillar, which is induced from the Karman vortex street and the dominant frequencies appear owing to the front and the rear propeller rotations. The propeller rotating in close to the sea surface brings the abnormal wave and the amplitude increases as the stream velocity is faster and/or the drag is stronger.
Energy Technology Data Exchange (ETDEWEB)
Kishibe, T. [Hitachi, Ltd., Tokyo (Japan); Kaji, S. [The University of Tokyo, Tokyo (Japan). Faculty of Engineering
1999-04-25
The swirling flow field including non-axisymmetric phenomena in a rotating hollow turbine shaft is solved using computational fluid dynamics. The three-dimensional compressible Navier-Stokes equations are adopted and discretized by an implicit TVD scheme. No axisymmetric assumption is applied in order to find non-axisymmetric phenomena. The computational domain, therefore, is extended circumferentially to 360 degree and axisymmetric boundary conditions along the center axis are avoided. The existence of a rotating spiral vortex at the place where the swirling flow turns radially outward is shown. The spiral vortex rotates about the shaft center axis in the same direction as the circumferential velocity of the main flow. Conversely, the vortex has a spiral form opposite to the rotational direction of the fluid. The first non-axisymmetric mode of a single spiral vortex is transformed into the second mode of a double spiral vortex at a specific rotating speed of the shaft. (author)
Maqbool, Khadija; Anwar Bég, O.; Sohail, Ayesha; Idreesa, Shafaq
2016-05-01
The theoretical analysis of magnetohydrodynamic (MHD) incompressible flows of a Burgers fluid through a porous medium in a rotating frame of reference is presented. The constitutive model of a Burgers fluid is used based on a fractional calculus formulation. Hydrodynamic slip at the wall (plate) is incorporated and the fractional generalized Darcy model deployed to simulate porous medium drag force effects. Three different cases are considered: namely, the flow induced by a general periodic oscillation at a rigid plate, the periodic flow in a parallel plate channel and, finally, the Poiseuille flow. In all cases the plate(s) boundary(ies) are electrically non-conducting and a small magnetic Reynolds number is assumed, negating magnetic induction effects. The well-posed boundary value problems associated with each case are solved via Fourier transforms. Comparisons are made between the results derived with and without slip conditions. Four special cases are retrieved from the general fractional Burgers model, viz. Newtonian fluid, general Maxwell viscoelastic fluid, generalized Oldroyd-B fluid and the conventional Burgers viscoelastic model. Extensive interpretation of graphical plots is included. We study explicitly the influence of the wall slip on primary and secondary velocity evolution. The model is relevant to MHD rotating energy generators employing rheological working fluids.
Institute of Scientific and Technical Information of China (English)
LIN Shang-jing; WEI Gang; LIU Li-long; LIU Yu-di
2005-01-01
Beta effects on surface flows in a rotating annulus with a radial temperature gradient and a sloping bottom were studied experimentally. An azimuthal jet was produced by the action of the Coriolis force in the convective region between the two side walls of the annulus. Propagating velocity and patterns of the baroclinic wave on the surface were obtained by using a frequency-meter and a streak photograph respectively. It is shown that there exists the nonlinear interaction between the baroclinic and beta effects. The beta effect exerts little influence on the stratification flows and constrains the baroclinic instability, and it prompts the instability of the weak stratification flows and results in the surface pattern of waves with higher frequency. It is also indicated that the beta effect can reduce the propagating speed of the surface waves in the jet, and increase the thermal Rossby number for those same surface patterns under a given Taylor number.
Swadling, G F; Lebedev, S V; Hall, G N; Patankar, S; Stewart, N H; Smith, R A; Harvey-Thompson, A J; Burdiak, G C; de Grouchy, P; Skidmore, J; Suttle, L; Suzuki-Vidal, F; Bland, S N; Kwek, K H; Pickworth, L; Bennett, M; Hare, J D; Rozmus, W; Yuan, J
2014-11-01
A suite of laser based diagnostics is used to study interactions of magnetised, supersonic, radiatively cooled plasma flows produced using the Magpie pulse power generator (1.4 MA, 240 ns rise time). Collective optical Thomson scattering measures the time-resolved local flow velocity and temperature across 7-14 spatial positions. The scattering spectrum is recorded from multiple directions, allowing more accurate reconstruction of the flow velocity vectors. The areal electron density is measured using 2D interferometry; optimisation and analysis are discussed. The Faraday rotation diagnostic, operating at 1053 nm, measures the magnetic field distribution in the plasma. Measurements obtained simultaneously by these diagnostics are used to constrain analysis, increasing the accuracy of interpretation.
Energy Technology Data Exchange (ETDEWEB)
Swadling, G. F., E-mail: swadling@imperial.ac.uk; Lebedev, S. V.; Hall, G. N.; Patankar, S.; Stewart, N. H.; Smith, R. A.; Burdiak, G. C.; Grouchy, P. de; Skidmore, J.; Suttle, L.; Suzuki-Vidal, F.; Bland, S. N.; Kwek, K. H.; Pickworth, L.; Bennett, M.; Hare, J. D. [Plasma Physics Group, Imperial College, London SW6 7LZ (United Kingdom); Harvey-Thompson, A. J. [Sandia National Laboratory, Albuquerque, New Mexico 87185-1193 (United States); Rozmus, W. [Department of Physics, University of Alberta, Edmonton, Alberta T6G 2J1 (Canada); Yuan, J. [Key Laboratory of Pulsed Power, Institute of Fluid Physics, CAE, Mianyang 621900 (China)
2014-11-15
A suite of laser based diagnostics is used to study interactions of magnetised, supersonic, radiatively cooled plasma flows produced using the Magpie pulse power generator (1.4 MA, 240 ns rise time). Collective optical Thomson scattering measures the time-resolved local flow velocity and temperature across 7–14 spatial positions. The scattering spectrum is recorded from multiple directions, allowing more accurate reconstruction of the flow velocity vectors. The areal electron density is measured using 2D interferometry; optimisation and analysis are discussed. The Faraday rotation diagnostic, operating at 1053 nm, measures the magnetic field distribution in the plasma. Measurements obtained simultaneously by these diagnostics are used to constrain analysis, increasing the accuracy of interpretation.
Energy Technology Data Exchange (ETDEWEB)
Abd-Alla, A.M., E-mail: mohmrr@yahoo.com [Maths Department, Faculty of Science, Taif University (Saudi Arabia); Abo-Dahab, S.M., E-mail: sdahb@yahoo.com [Maths Department, Faculty of Science, Taif University (Saudi Arabia); Maths Department, Faculty of Science, SVU, Qena 83523 (Egypt); Al-Simery, R.D. [Maths Department, Faculty of Science, Taif University (Saudi Arabia)
2013-12-15
In this paper, the effects of both rotation and magnetic field of a micropolar fluid through a porous medium induced by sinusoidal peristaltic waves traveling down the channel walls are studied analytically and computed numerically. Closed-form solutions under the consideration of long wavelength and low-Reynolds number is presented. The analytical expressions for axial velocity, pressure rise per wavelength, mechanical efficiency, spin velocity, stream function and pressure gradient are obtained in the physical domain. The effect of the rotation, density, Hartmann number, permeability, coupling number, micropolar parameter and the non-dimensional wave amplitude in the wave frame is analyzed theoretically and computed numerically. Numerical results are given and illustrated graphically in each case considered. Comparison was made with the results obtained in the presence and absence of rotation and magnetic field. The results indicate that the effect of rotation, density, Hartmann number, permeability, coupling number, micropolar parameter and the non-dimensional wave amplitude are very pronounced in the phenomena. - Highlights: • The effects of induced magnetic field and rotation in peristaltic motion of a two dimensional of a micropolar fluid through a porous medium • The exact and closed form solutions are presented • Different wave shapes are considered to observe the behavior of the axial velocity, pressure rise, mechanical efficiency, spin velocity, stream function and pressure gradient.
Institute of Scientific and Technical Information of China (English)
王贺元
2012-01-01
To discuss the dynamical behavior of the flow between two concentric rotating spheres we study the dynamical behavior and the numerical simulation of the model system similar to the Lorenz equations of the Navier-Stokes equations for the flow between two concentric rotating spheres. Its stationary points and the stability are presented, the existence of attractor is proved, and the global stability of the system is discussed. Chaos behavior is simulated numerically by computer with the changing of Reynolds number.
Directory of Open Access Journals (Sweden)
Gauri Shanker Seth
2015-01-01
Full Text Available An investigation of unsteady hydromagnetic natural convection heat and mass trans fer flow with Hall current of a viscous, incompressible, electrically conducting, heat absorbing and optically thin radiating fluid past an accelerated moving vertical plate through fluid saturated porous medium in a rotating environment is carried out when temperature of the plate has a temporarily ramped profile. The exact solutions of momentum, energy and concentration equations are obtained in closed form by Laplace transform technique. The expressions of skin friction, Nusselt number and Sherwood number are also derived. For both ramped temperature and isothermal plates, Hall current tends to accelerate primary and secondary fluid velocities whereas heat absorption and radiation have reverse effect on it. Rotation tends to retard primary fluid velocity whereas it has a reverse effect on secondary fluid velocity. Heat absorption and radiation have tendency to enhance rate of heat transfer at the plate.
Doblhoff-Dier, Veronika; Werkmeister, René M.; Gröschl, Martin; Schmetterer, Leopold
2014-03-01
We present a method capable of measuring the total retinal blood flow in arteries and veins based on dual beam Fourierdomain Doppler optical coherence tomography (OCT) in combination with a fundus camera based Dynamic Vessel Analyzer. Incorporating a Dynamic vessel analyzer into the system not only gives a live image of the fundus - it also allows determining the vessels' diameter precisely during the OCT measurement, which is necessary for the determination of the blood flow. While dual beam systems with fixed detection plane allow only vessels with certain orientations to be measured, the detection plane of our system can be rotated by 90°. This ensures that the blood's velocity can be measured in all vessels around the optic nerve head. The results of the total blood flow measurements are in the same range as previously published data. Additionally, the high degree of conformity between the measured venous and arterial flow corroborated the system's validity. For larger vessels, the logarithmic values of vessel diameter and blood flow were found to be related linearly with a regression coefficient of around 3, which is in accordance with Murray's law. For smaller vessels (diameter below 60 μm), the values diverge from the linear dependence. The high sensitivity and the good agreement with published data suggest a high potential for examining the retinal blood flow in patients with ocular diseases.
Verscharen, Daniel; Bourouaine, Sofiane; Hollweg, Joseph V
2014-01-01
Protons and alpha particles in the fast solar wind are only weakly collisional and exhibit a number of non-equilibrium features, including relative drifts between particle species. Two non-collisional mechanisms have been proposed for limiting differential flow between alpha particles and protons: plasma instabilities and the rotational force. Both mechanisms decelerate the alpha particles. In this paper, we derive an analytic expression for the rate $Q_{\\mathrm{flow}}$ at which energy is released by alpha-particle deceleration, accounting for azimuthal flow and conservation of total momentum. We find that $Q_{\\mathrm{flow}} > 0 $ at $r r_{\\mathrm{crit}}$. We compare the value of $Q_{\\mathrm{flow}}$ at $r< r_{\\mathrm{crit}}$ with empirical heating rates for protons and alpha particles, denoted $Q_{\\mathrm{p}}$ and $Q_{\\alpha}$, deduced from in-situ measurements of fast-wind streams from the Helios and Ulysses spacecraft. We find that $Q_{\\mathrm{flow}}$ exceeds $Q_{\\alpha}$ at $r < 1\\,\\mathrm{AU}$, $Q_{...
Exact solution of the problem of steady-state MHD flow for the case of slow sphere rotation
Energy Technology Data Exchange (ETDEWEB)
Antimirov, M.Ya.
1979-01-01
A nonconducting sphere rotates in a conducting liquid at a constant angular velocity about a specified axis in a homogeneous external magnetic field, directed along the axis of rotation. Spherical coordinates are used in the derivation of the system of equations in a Stokes approximation. The solution of the linear system of equations for the velocity field and the induced magnetic field is obtained in the form of series containing Bessel functions and Legendre polynomials. The expression which is derived relating the moment of rotation, L, to the moment of rotation in the absence of the field, L/sub O/, and the Hartmann number Ha is L/sub O/(5/63)Ha, which is less than half the value (L/sub O/Ha/6) from earlier literature, where Ha tends to infinity. At small values of Ha, the same approximate formulas are obtained as in the earlier literature and the qualitative agreement is the same (L increases linearly with Ha). An exact solution could not be derived for the case of finite conductivity, and the previous approximate solution when Ha tends to infinity yields results which are only qualitatively true. Quantitatively accurate results for this case can apparently be obtained by employing a Wenzel-Kramers-Brillouin approximation for the system of equations derived in this paper. 3 references.
Hossain, Delowar; Samad, Abdus; Alam, Mahmud
2017-06-01
The ion-slip effects on unsteady MHD free convection flow past an infinite vertical porous plate with the effect of temperature stratified porous medium in a rotating system with viscous dissipation and Joule heating has been studied numerically. Introducing a time dependent suction to the plate, a similarity procedure has been adopted by taking a time dependent similarity parameter. The governing differential equations are transformed by introducing usual similarity variables. The resultant equations are solved numerically using Runge-Kutta method along with shooting technique. Resulting non-dimensional velocity and temperature profiles are then presented graphically for different values of the parameters entering into the problem.
Directory of Open Access Journals (Sweden)
P. D. Williams
2004-01-01
Full Text Available We report on a numerical study of the impact of short, fast inertia-gravity waves on the large-scale, slowly-evolving flow with which they co-exist. A nonlinear quasi-geostrophic numerical model of a stratified shear flow is used to simulate, at reasonably high resolution, the evolution of a large-scale mode which grows due to baroclinic instability and equilibrates at finite amplitude. Ageostrophic inertia-gravity modes are filtered out of the model by construction, but their effects on the balanced flow are incorporated using a simple stochastic parameterization of the potential vorticity anomalies which they induce. The model simulates a rotating, two-layer annulus laboratory experiment, in which we recently observed systematic inertia-gravity wave generation by an evolving, large-scale flow. We find that the impact of the small-amplitude stochastic contribution to the potential vorticity tendency, on the model balanced flow, is generally small, as expected. In certain circumstances, however, the parameterized fast waves can exert a dominant influence. In a flow which is baroclinically-unstable to a range of zonal wavenumbers, and in which there is a close match between the growth rates of the multiple modes, the stochastic waves can strongly affect wavenumber selection. This is illustrated by a flow in which the parameterized fast modes dramatically re-partition the probability-density function for equilibrated large-scale zonal wavenumber. In a second case study, the stochastic perturbations are shown to force spontaneous wavenumber transitions in the large-scale flow, which do not occur in their absence. These phenomena are due to a stochastic resonance effect. They add to the evidence that deterministic parameterizations in general circulation models, of subgrid-scale processes such as gravity wave drag, cannot always adequately capture the full details of the nonlinear interaction.
DEFF Research Database (Denmark)
Angelsky, O. V.; Bekshaev, A. Ya; Maksimyak, P. P.
2012-01-01
The internal energy flow in a light beam can be divided into the "orbital" and "spin" parts, associated with the spatial and polarization degrees of freedom of light. In contrast to the orbital one, experimental observation of the spin flow seems problematic because it is converted into an orbital...... particles within a field where the transverse energy circulation is associated exclusively with the spin flow. This result can be treated as the first demonstration of mechanical action of the spin flow of a light field....
Indian Academy of Sciences (India)
H VOLKAN ERSOY
2017-03-01
This paper is concerned with the unsteady flow of a disk performing non-torsional oscillation in its own plane and a Newtonian fluid at infinity while they are initially rotating with the same angular velocity about non-coaxial axes. For a more general study, it is considered that the disk executes non-torsional oscillation along any desired direction in its own plane. An exact solution obtained for the velocity field is compared with aperiodic solution presented in order to find the time when the periodic flow starts. A very good agreement is found between the two solutions in the periodic state. It is an interesting result that the x- and y-components of the force per unit area exerted by the fluid on the disk vary in almost opposite direction when the non-torsional oscillation takes place along the eccentricity direction. Further, the change in the y-component of the translational velocity becomes noticeable in this case.
Institute of Scientific and Technical Information of China (English)
邵雄飞; 吴忠标
2004-01-01
The flow field of gas and liquid in a φ150mm rotating-stream-tray (RST) scrubber is simulated by using computational fluid dynamic (CFD) method. The simulation is based on the two-equation RNG κ-ε turbulence model, Eulerian multiphase model, mad a real-shape 3D model with a huge number of meshes. The simulation results include detailed information about velocity, pressure, volume fraction and so on. Some features of the flow field are obtained: liquid is atomized in a thin annular zone; a high velocity air zone prevents water drops at the bottom from flying towards the wall;the pressure varies sharply at the end of blades and so on. The results will be helpful for structure optimization and engineering design.
Riblet drag reduction and the effect of bulk fluid rotation in a fully turbulent Taylor-Couette flow
Greidanus, A.J.; Delfos, R.; Tokgoez, S.; Westerweel, J.
2015-01-01
Low drag surfaces are often desired in many industries with applications in open and closed channel flows, such as ship hulls and pipe flows. Drag reduction is a phenomenon that can have substantial energy savings, resulting in ecological and economical benefits. We use a Taylor-Couette facility as
Huisman, Sander G; Bruggert, Gert-Wim H; Lohse, Detlef; Sun, Chao
2016-01-01
A new Taylor-Couette system has been designed and constructed with precise temperature control. Two concentric independently rotating cylinders are able to rotate at maximum rates of $f_i = \\pm20$ Hz for the inner cylinder and $f_o = \\pm10$ Hz for the outer cylinder. The inner cylinder has an outside radius of $r_i = 75$ mm, and the outer cylinder has an inside radius of $r_o = 105$ mm, resulting in a gap of $d=30$ mm. The height of the gap $L =549$ mm, giving a volume of $V=9.3$l. The geometric parameters are $\\eta = r_i/r_o = 0.714$ and $\\Gamma = L/d = 18.3$. With water as working fluid at room temperature the Reynolds numbers that can be achieved are $\\text{Re}_i = \\omega_i r_i (r_o-r_i)/\
Directory of Open Access Journals (Sweden)
Linga Raju T.
2016-05-01
Full Text Available An unsteady MHD two-layered fluid flow of electrically conducting fluids in a horizontal channel bounded by two parallel porous plates under the influence of a transversely applied uniform strong magnetic field in a rotating system is analyzed. The flow is driven by a common constant pressure gradient in a channel bounded by two parallel porous plates, one being stationary and the other oscillatory. The two fluids are assumed to be incompressible, electrically conducting with different viscosities and electrical conductivities. The governing partial differential equations are reduced to the linear ordinary differential equations using two-term series. The resulting equations are solved analytically to obtain exact solutions for the velocity distributions (primary and secondary in the two regions respectively, by assuming their solutions as a combination of both the steady state and time dependent components of the solutions. Numerical values of the velocity distributions are computed for different sets of values of the governing parameters involved in the study and their corresponding profiles are also plotted. The details of the flow characteristics and their dependence on the governing parameters involved, such as the Hartmann number, Taylor number, porous parameter, ratio of the viscosities, electrical conductivities and heights are discussed. Also an observation is made how the velocity distributions vary with the rotating hydromagnetic interaction in the case of steady and unsteady flow motions. The primary velocity distributions in the two regions are seen to decrease with an increase in the Taylor number, but an increase in the Taylor number causes a rise in secondary velocity distributions. It is found that an increase in the porous parameter decreases both the primary and secondary velocity distributions in the two regions.
Ramachandra, S. M.; Bober, L. J.
1986-01-01
An unsteady lifting service theory for the counter-rotating propeller is presented using the linearized governing equations for the acceleration potential and representing the blades by a surface distribution of pulsating acoustic dipoles distributed according to a modified Birnbaum series. The Birnbaum series coefficients are determined by satisfying the surface tangency boundary conditions on the front and rear propeller blades. Expressions for the combined acoustic resonance modes of the front prop, the rear prop and the combination are also given.
Energy Technology Data Exchange (ETDEWEB)
Galvan-Martinez, R. [Grupo Anticorrosion-Instituto de Ingenieria, Universidad Veracruzana SS. Juan Pablo II, Veracruz (Mexico); Mendoza-Flores, J.; Duran-Romero, R. [Instituto Mexicano del Petroleo, Direccion Ejecutiva de Exploracion y Produccion, Mexico (Mexico); Genesca, J. [Universidad Nacional Autonoma Mexico, UNAM Ciudad Universitaria, Mexico (Mexico). Dept. Ingenieria Metalurgica, Facultad Quimica
2007-07-15
This work presents the electrochemical kinetics results measured during the corrosion of API X52 pipeline steel immersed in aqueous environments, containing dissolved hydrogen sulfide (H{sub 2}S) under turbulent flow conditions. In order to control the turbulent flow conditions, a rotating cylinder electrode (RCE) was used. Five different rotation rates were studied: 0 (or static conditions), 1000, 3000, 5000 and 7000 rpm. It was found that the turbulent flow increases the corrosion rate and the corrosion mechanism for X52 steel exhibits a significant dependence on mass transfer on the cathodic kinetics. (Abstract Copyright [2007], Wiley Periodicals, Inc.)
Energy Technology Data Exchange (ETDEWEB)
Jeng, Tzer-Ming [Air Force Institute of Technology, Gangshan (Taiwan). Department of Mechanical Engineering; Tzeng, Sheng-Chung; Lin, Chao-Hsien [ChienKuo Technology University, Changhua (Taiwan). Department of Mechanical Engineering
2007-01-15
This work experimentally investigates the heat transfer characteristics of Taylor-Couette-Poiseuille flow in an annular channel by mounting longitudinal ribs on the rotating inner cylinder. The ranges of the axial Reynolds number (Re) and the rotational Reynolds number (Re{sub {omega}}) are Re=30-1200 and Re{sub {omega}}=0-2922, respectively. Three modes of the inner cylinder without/with longitudinal ribs are considered. A special entry and exit design for the axial coolant flow reveals some interesting findings. The value of Nusselt number (Nu) is almost minimal at the inlet of the annular channel, and then sharply rises in the axial direction. The average Nusselt number (Nu|) increases with Re. Nu increases rapidly with Re{sub {omega}} at low Re (such as at Re=30 and 60) but that the effect of Re{sub {omega}} decreases as the value increases (such as at Re=300-1200). The ratio Nu|/Nu|{sub 0} increases with Re{sub {omega}} and exceed two at all Re and in the test modes. The heat transfer is typically promoted by mounting longitudinal ribs on the rotating inner cylinder, especially at Re=300 and 600. When Re=300 or 600 and Re{sub {omega}}>2000, the Nu| of the system with ribs reaches around 1.4 times that of Nu|{sub A} (Nu| in mode A). Under a given pumping power constraint (PRe{sup 3}), the Nu| of the system with ribs (modes B and C) generally exceeds that without ribs (mode A), while the difference between the values of Nu| in modes B and A slowly falls as PRe{sup 3} increases. Additionally, mode B (with ribs) is preferred for high heat transfer when PRe{sup 3}<4.5x10{sup 13} but mode C (with cavities on ribs) is optimal for high heat transfer when PRe{sup 3}>4.5x10{sup 13}. (author)
Cambonie, T; Aider, J -L
2013-01-01
Circular flush Jets In Cross-Flow were experimentally studied in a water tunnel using Volumetric Particle Tracking Velocimetry, for a range of jet to cross-flow velocity ratios, r, from 0.5 to 3, jet exit diameters $d$ from 0.8 cm to 1 cm and cross-flow boundary layer thickness delta from 1 to 2.5 cm. The analysis of the 3D mean velocity fields allows for the definition, computation and study of Counter-rotating Vortex Pair trajectories. The influences of r, d and delta were investigated. A new scaling based on momentum ratio r_m taking into account jet and cross-flow momentum distributions is introduced based on the analysis of jet trajectories published in the literature. Using a rigorous scaling quality factor Q to quantify how well a given scaling successfully collapses trajectories, we show that the proposed scaling also improves the collapse of CVP trajectories, leading to a final scaling law for these trajectories.
Directory of Open Access Journals (Sweden)
Khan Najeeb Alam
2017-03-01
Full Text Available An investigation is performed for an alyzing the effect of entropy generation on the steady, laminar, axisymmetric flow of an incompressible Powell-Eyring fluid. The flow is considered in the presence of vertically applied magnetic field between radially stretching rotating disks. The Energy and concentration equation is taking into account to investigate the heat dissipation, Soret, Dufour and Joule heating effects. To describe the considered flow non-dimensionalized equations, an exact similarity function is used to reduce a set of the partial differential equation into a system of non-linear coupled ordinary differential equation with the associated boundary conditions. Using homotopy analysis method (HAM, an analytic solution for velocity, temperature and concentration profiles are obtained over the entire range of the imperative parameters. The velocity components, concentration and temperature field are used to determine the entropy generation. Plots illustrate important results on the effect of physical flow parameters. Results obtained by means of HAM are then compared with the results obtained by using optimized homotopy analysis method (OHAM. They are in very good agreement.
Weihang, Kong; Lingfu, Kong; Lei, Li; Xingbin, Liu; Tao, Cui
2017-06-01
Water volume fraction is an important parameter of two-phase flow measurement, and it is an urgent task for accurate measurement in horizontal oil field development and optimization of oil production. The previous ring-shaped conductance water-cut meter cannot obtain the response values corresponding to the oil field water conductivity for oil-water two-phase flow in horizontal oil-producing wells characterized by low yield liquid, low velocity and high water cut. Hence, an inserted axisymmetric array structure sensor, i.e. a six-group local-conductance probe (SGLCP), is proposed in this paper. Firstly, the electric field distributions generated by the exciting electrodes of SGLCP are investigated by the finite element method (FEM), and the spatial sensitivity distributions of SGLCP are analyzed from the aspect of different separations between two electrodes and different axial rotation angles respectively. Secondly, the numerical simulation responses of SGLCP in horizontal segregated flow are calculated from the aspect of different water cut and heights of the water layer, respectively. Lastly, an SGLCP-based well logging instrument was developed, and experiments were carried out in a horizontal pipe with an inner diameter of 125 mm on the industrial-scale experimental multiphase flow setup in the Daqing Oilfield, China. In the experiments, the different oil-water two-phase flow, mineralization degree, temperature and pressure were tested. The results obtained from the simulation experiments and simulation well experiments demonstrate that the designed and developed SGLCP-based instrument still has a good response characteristic for measuring water conductivity under the different conditions mentioned above. The validity and reliability of obtaining the response values corresponding to the water conductivity through the designed and developed SGLCP-based instrument are verified by the experimental results. The significance of this work can provide an effective
Kan, Chung-Dann; Roan, Jun-Neng; Wu, Jing-Ming; Yang, Yu-Jen
2006-02-01
A 1.9-kg premature boy with transposition of the great arteries, ventricular septal defect, and patent ductus arteriosus received a Jatene procedure at 16 days of age. His coronary artery pattern was type A. His arteries were harvested and translocated to appropriate holes in the sinus portion of his neoaorta. Partial obstruction due to torsion of the translocated right coronary artery was suspected, because the right ventricle turned pink in color to blue and bradycardia developed when cardiopulmonary bypass support was weaned. This was relieved by clockwise rotation of the heart, and the patient recovered well. Follow-up echocardiography 6 months later revealed good biventricular function.
DEFF Research Database (Denmark)
Bentzen, Thomas Ruby; Ratkovich, Nicolas Rios; Madsen, S.;
2012-01-01
Fouling is the main bottleneck of the widespread use of MBR systems. One way to decrease and/or control fouling is by process hydrodynamics. This can be achieved by the increase of liquid cross- ﬂow velocity. In rotational cross-ﬂow MBR systems, this is attained by the spinning of, for example, i......-weighted average shear stress was developed for water and AS as a function of the angular velocity and the total suspended solids concentration. These relationships can be linked to the energy consumption of this type of systems.......Fouling is the main bottleneck of the widespread use of MBR systems. One way to decrease and/or control fouling is by process hydrodynamics. This can be achieved by the increase of liquid cross- ﬂow velocity. In rotational cross-ﬂow MBR systems, this is attained by the spinning of, for example......, impellers. Validation of the CFD (computational ﬂuid dynamics) model was made against laser Doppler anemometry (LDA) tangential velocity measurements (error less than 8%) using water as a ﬂuid. The shear stress over the membrane surface was inferred from the CFD simulations for water. However, activated...
Linga Raju, T.; Neela Rao, B.
2016-08-01
The paper aims to analyze the heat transfer aspects of a two-layered fluid flow in a horizontal channel under the action of an applied magnetic and electric fields, when the whole system is rotated about an axis perpendicular to the flow. The flow is driven by a common constant pressure gradient in the channel bounded by two parallel porous insulating plates, one being stationary and the other one oscillatory. The fluids in the two regions are considered electrically conducting, and are assumed to be incompressible with variable properties, namely, different densities, viscosities, thermal and electrical conductivities. The transport properties of the two fluids are taken to be constant and the bounding plates are maintained at constant and equal temperature. The governing partial differential equations are then reduced to the ordinary linear differential equations by using a two-term series. The temperature distributions in both fluid regions of the channel are derived analytically. The results are presented graphically to discuss the effect on the heat transfer characteristics and their dependence on the governing parameters, i.e., the Hartmann number, Taylor number, porous parameter, and ratios of the viscosities, heights, electrical and thermal conductivities. It is observed that, as the Coriolis forces become stronger, i.e., as the Taylor number increases, the temperature decreases in the two fluid regions. It is also seen that an increase in porous parameter diminishes the temperature distribution in both the regions.
Nath, G.
2012-01-01
A self-similar solution is obtained for one dimensional adiabatic flow behind a cylindrical shock wave propagating in a rotating dusty gas in presence of heat conduction and radiation heat flux with increasing energy. The dusty gas is assumed to be a mixture of non-ideal (or perfect) gas and small solid particles, in which solid particles are continuously distributed. It is assumed that the equilibrium flow-condition is maintained and variable energy input is continuously supplied by the piston (or inner expanding surface). The heat conduction is expressed in terms of Fourier's law and the radiation is considered to be of the diffusion type for an optically thick grey gas model. The thermal conductivity K and the absorption coefficient αR are assumed to vary with temperature only. In order to obtain the similarity solutions the initial density of the ambient medium is assumed to be constant and the angular velocity of the ambient medium is assumed to be decreasing as the distance from the axis increases. The effects of the variation of the heat transfer parameters and non-idealness of the gas in the mixture are investigated. The effects of an increase in (i) the mass concentration of solid particles in the mixture and (ii) the ratio of the density of solid particles to the initial density of the gas on the flow variables are also investigated.
Alzner, E.; Kalben, P. P.
1977-01-01
Documentation for the FORTRAN program B2DATL is provided. The program input, output, and operational procedures are described; a dictionary of the principal FORTRAN variables is provided; the function of all subroutines; is outlined and flow charts of the principal subroutines and the main program are presented.
DEFF Research Database (Denmark)
Meyer, Knud Erik; Sørensen, Jens Nørkær; Naumov, Igor
2009-01-01
Time-resolved Particle Image Velocimetry (PIV) measurements in two perpendicular planes are used to reconstruct a flow in an axisymmetric facility in both time and space. The reconstruction is based on Proper Orthogonal Decomposition (POD) and is used to distinguish between spatial and temporal...
DEFF Research Database (Denmark)
Guntur, Srinivas; Sørensen, Niels N.
2015-01-01
This work presents an analysis of data from existing as well as new full-rotor computational fluid dynamics computations on the MEXICO rotor, with focus on the flow around the inboard parts of the blades. The boundary layer separation characteristics on the airfoil sections in the inboard parts...
Shirsath, S.S.; Padding, J.T.; Clercx, H.J.H.; Kuipers, J.A.M.
2015-01-01
Three-dimensional particle tracking velocimetry (3D-PTV) is a promising technique to study the behavior of granular flows. The aim of this paper is to cross-validate 3D-PTV against independent or more established techniques, such as particle image velocimetry (PIV), electronic ultrasonic sensor meas
Energy Technology Data Exchange (ETDEWEB)
Filipovic, N [Faculty of Mechanical Engineering, University of Kragujevac (Serbia); Haber, S [Technion-Israel Institute of Technology, Haifa (Israel); Kojic, M [Faculty of Mechanical Engineering, University of Kragujevac (Serbia); Tsuda, A [Harvard School of Public Health, Harvard University, Boston, MA (United States)
2008-02-07
Traditional DPD methods address dissipative and random forces exerted along the line connecting neighbouring particles. Espanol (1998 Phys. Rev. E 57 2930-48) suggested adding dissipative and random force components in a direction perpendicular to this line. This paper focuses on the advantages and disadvantages of such an addition as compared with the traditional DPD method. Our benchmark system comprises fluid initially at rest occupying the space between two concentric cylinders rotating with various angular velocities. The effect of the lateral force components on the time evolution of the simulated velocity profile was also compared with that of the known analytical solution. The results show that (i) the solution accuracy at steady state has improved and the error has been reduced by at least 30% (in one case by 75%), (ii) the DPD time to reach steady state has been halved, (iii) the CPU time has increased by only 30%, and (iv) no significant differences exist in density and temperature distributions.
Filipovic, N.; Haber, S.; Kojic, M.; Tsuda, A.
2008-02-01
Traditional DPD methods address dissipative and random forces exerted along the line connecting neighbouring particles. Espanol (1998 Phys. Rev. E 57 2930-48) suggested adding dissipative and random force components in a direction perpendicular to this line. This paper focuses on the advantages and disadvantages of such an addition as compared with the traditional DPD method. Our benchmark system comprises fluid initially at rest occupying the space between two concentric cylinders rotating with various angular velocities. The effect of the lateral force components on the time evolution of the simulated velocity profile was also compared with that of the known analytical solution. The results show that (i) the solution accuracy at steady state has improved and the error has been reduced by at least 30% (in one case by 75%), (ii) the DPD time to reach steady state has been halved, (iii) the CPU time has increased by only 30%, and (iv) no significant differences exist in density and temperature distributions.
Bano, Kiran; Kennedy, Gareth F; Zhang, Jie; Bond, Alan M
2012-04-14
The theory for large amplitude Fourier transformed ac voltammetry at a rotating disc electrode is described. Resolution of time domain data into dc and ac harmonic components reveals that the mass transport for the dc component is controlled by convective-diffusion, while the background free higher order harmonic components are flow rate insensitive and mainly governed by linear diffusion. Thus, remarkable versatility is available; Levich behaviour of the dc component limiting current provides diffusion coefficient values and access to higher harmonics allows fast electrode kinetics to be probed. Two series of experiments (dc and ac voltammetry) have been required to extract these parameters; here large amplitude ac voltammetry with RDE methodology is used to demonstrate that kinetics and diffusion coefficient information can be extracted from a single experiment. To demonstrate the power of this approach, theoretical and experimental comparisons of data obtained for the reversible [Ru(NH(3))(6)](3+/2+) and quasi-reversible [Fe(CN)(6)](3-/4-) electron transfer processes are presented over a wide range of electrode rotation rates and with different concentrations and electrode materials. Excellent agreement of experimental and simulated data is achieved, which allows parameters such as electron transfer rate, diffusion coefficient, uncompensated resistance and others to be determined using a strategically applied approach that takes into account the different levels of sensitivity of each parameter to the dc or the ac harmonic.
Abdel-Wahed, Mohamed; Akl, Mohamed
2016-09-01
Analysis of the MHD Nanofluid boundary layer flow over a rotating disk with a constant velocity in the presence of hall current and non-linear thermal radiation has been covered in this work. The variation of viscosity and thermal conductivity of the fluid due to temperature and nanoparticles concentration and size is considered. The problem described by a system of P.D.E that converted to a system of ordinary differential equations by the similarity transformation technique, the obtained system solved analytically using Optimal Homotopy Asymptotic Method (OHAM) with association of mathematica program. The velocity profiles and temperature profiles of the boundary layer over the disk are plotted and investigated in details. Moreover, the surface shear stress, rate of heat transfer explained in details.
Roşca, Natalia C.; Pop, Ioan
2017-01-01
In this paper, the problem of normal impingement rotational stagnation-point flow on a radially permeable stretching sheet in a viscous fluid, recently studied in a very interesting paper, is extended to a water-based nanofluid. A similarity transformation is used to reduce the system of governing nonlinear partial differential equations to a system of ordinary differential equations, which is then solved numerically using the function bvp4c from Matlab. It is found that dual (upper and lower branch) solutions exist for some values of the governing parameters. From the stability analysis, it is found that the upper branch solution is stable, while the lower branch solution is unstable. Sample velocity and temperature profiles along both solution branches are graphically presented.
Roşca, Natalia C.; Pop, Ioan
2017-01-01
In this paper, the problem of normal impingement rotational stagnation-point flow on a radially permeable stretching sheet in a viscous fluid, recently studied in a very interesting paper, is extended to a water-based nanofluid. A similarity transformation is used to reduce the system of governing nonlinear partial differential equations to a system of ordinary differential equations, which is then solved numerically using the function bvp4c from Matlab. It is found that dual (upper and lower branch) solutions exist for some values of the governing parameters. From the stability analysis, it is found that the upper branch solution is stable, while the lower branch solution is unstable. Sample velocity and temperature profiles along both solution branches are graphically presented. PMID:28079124
Reddy, G. J.; Raju, R. S.; Rao, J. A.; Gorla, R. S. R.
2017-02-01
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.
Directory of Open Access Journals (Sweden)
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.
Feng, Biao; Levitas, Valery I.
2016-01-01
Combined plastic flow and strain-induced phase transformations (PTs) under high pressure in a sample within a gasket subjected to three dimensional compression and torsion in a rotational diamond anvil cell (RDAC) are studied using a finite element approach. The results are obtained for the weaker, equal-strength, and stronger high-pressure phases in comparison with low-pressure phases. It is found that, due to the strong gasket, the pressure in the sample is relatively homogenous and the geometry of the transformed zones is mostly determined by heterogeneity in plastic flow. For the equal-strength phases, the PT rate is higher than for the weaker and stronger high-pressure phases. For the weaker high-pressure phase, transformation softening induces material instability and leads to strain and PT localization. For the stronger high-pressure phase, the PT is suppressed by strain hardening during PT. The effect of the kinetic parameter k that scales the PT rate in the strain-controlled kinetic equation is also examined. In comparison with a traditional diamond anvil cell without torsion, the PT progress is much faster in RDAC under the same maximum pressure in the sample. Finally, the gasket size and strength effects are discussed. For a shorter and weaker gasket, faster plastic flow in radial and thickness directions leads to faster PT kinetics in comparison with a longer and stronger gasket. The rates of PT and plastic flows are not very sensitive to the modest change in a gasket thickness. Multiple experimental results are reproduced and interpreted. Obtained results allow one to design the desired pressure-plastic strain loading program in the experiments for searching new phases, reducing PT pressure by plastic shear, extracting kinetic properties from experiments with heterogeneous fields, and controlling homogeneity of all fields and kinetics of PTs.
Energy Technology Data Exchange (ETDEWEB)
Forest, Cary B. [Univ. of Wisconsin, Madison, WI (United States). Dept. of Physics
2016-11-10
This report covers the UW-Madison activities that took place within a larger DoE Center Administered and directed by Professor George Tynan at the University of California, San Diego. The work at Wisconsin will also be covered in the final reporting for the entire center, which will be submitted by UCSD. There were two main activities, one experimental and one that was theoretical in nature, as part of the Center activities at the University of Wisconsin, Madison. First, the Center supported an experimentally focused postdoc (Chris Cooper) to carry out fundamental studies of momentum transport in rotating and weakly magnetized plasma. His experimental work was done on the Plasma Couette Experiment, a cylindrical plasma confinement device, with a plasma flow created through electromagnetically stirring plasma at the plasma edge facilitated by arrays of permanent magnets. Cooper's work involved developing optical techniques to measure the ion temperature and plasma flow through Doppler-shifted line radiation from the plasma argon ions. This included passive emission measurements and development of a novel ring summing Fabry-Perot spectroscopy system, and the active system involved using a diode laser to induce fluorescence. On the theoretical side, CMTFO supported a postdoc (Johannes Pueschel) to carry out a gyrokinetic extension of residual zonal flow theory to the case with magnetic fluctuations, showing that magnetic stochasticity disrupts zonal flows. The work included a successful comparison with gyrokinetic simulations. This work and its connection to the broader CMTFO will be covered more thoroughly in the final CMTFO report from Professor Tynan.
Directory of Open Access Journals (Sweden)
Nicholas Mansel Wilkinson
2014-02-01
Full Text Available Visual scan paths exhibit complex, stochastic dynamics. Even during visual fixation, the eye is in constant motion. Fixational drift and tremor are thought to reflect fluctuations in the persistent neural activity of neural integrators in the oculomotor brainstem, which integrate sequences of transient saccadic velocity signals into a short term memory of eye position. Despite intensive research and much progress, the precise mechanisms by which oculomotor posture is maintained remain elusive. Drift exhibits a stochastic statistical profile which has been modelled using random walk formalisms. Tremor is widely dismissed as noise. Here we focus on the dynamical profile of fixational tremor, and argue that tremor may be a signal which usefully reflects the workings of the oculomotor postural control. We identify signatures reminiscent of a certain flavour of transient neurodynamics; toric travelling waves which rotate around a central phase singularity. Spiral waves play an organisational role in dynamical systems at many scales throughout nature, though their potential functional role in brain activity remains a matter of educated speculation. Spiral waves have a repertoire of functionally interesting dynamical properties, including persistence, which suggest that they could in theory contribute to persistent neural activity in the oculomotor postural control system. Whilst speculative, the singularity hypothesis of oculomotor postural control implies testable predictions, and could provide the beginnings of an integrated dynamical framework for eye movements across scales.
Jou, W.-H.
1982-01-01
An attempt is made to develop a three-dimensional, finite volume computational code for highly swept, twisted, small aspect ratio propeller blades with supersonic tip speeds, in a way that accounts for cascade effects, hub-induced flow, and nonlinear transonic effects. Attention is presently given to the generation of a computational mesh for such a complex propeller configuration, with the aim of sharing developmental process experience. The problem treated is unique, in that blade chord, blade length, hub length and blade-to-blade distance represent several characteristic length scales among which there is considerable disparity. An ad hoc mesh-generation scheme is accordingly developed.
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.