Nonlinear, unsteady aerodynamic loads on rectangular and delta wings
Atta, E. H.; Kandil, O. A.; Mook, D. T.; Nayfeh, A. H.
1977-01-01
Nonlinear unsteady aerodynamic loads on rectangular and delta wings in an incompressible flow are calculated by using an unsteady vortex-lattice model. Examples include flows past fixed wings in unsteady uniform streams and flows past wings undergoing unsteady motions. The unsteadiness may be due to gusty winds or pitching oscillations. The present technique establishes a reliable approach which can be utilized in the analysis of problems associated with the dynamics and aeroelasticity of wings within a wide range of angles of attack.
Nonlinear programming extensions to rational function approximations of unsteady aerodynamics
Tiffany, Sherwood H.; Adams, William M., Jr.
1987-01-01
This paper deals with approximating unsteady generalized aerodynamic forces in the equations of motion of a flexible aircraft. Two methods of formulating these approximations are extended to include both the same flexibility in constraining them and the same methodology in optimizing nonlinear parameters as another currently used 'extended least-squares' method. Optimal selection of 'nonlinear' parameters is made in each of the three methods by use of the same nonlinear (nongradient) optimizer. The objective of the nonlinear optimization is to obtain rational approximations to the unsteady aerodynamics whose state-space realization is of lower order than that required when no optimization of the nonlinear terms is performed. The free 'linear' parameters are determined using least-squares matrix techniques on a Lagrange multiplier formulation of an objective function which incorporates selected linear equality constraints. State-space mathematical models resulting from the different approaches are described, and results are presented which show comparative evaluations from application of each of the extended methods to a numerical example. The results obtained for the example problem show a significant (up to 63 percent) reduction in the number of differential equations used to represent the unsteady aerodynamic forces in linear time-invariant equations of motion as compared to a conventional method in which nonlinear terms are not optimized.
Bayesian inference of nonlinear unsteady aerodynamics from aeroelastic limit cycle oscillations
Sandhu, Rimple; Poirel, Dominique; Pettit, Chris; Khalil, Mohammad; Sarkar, Abhijit
2016-07-01
A Bayesian model selection and parameter estimation algorithm is applied to investigate the influence of nonlinear and unsteady aerodynamic loads on the limit cycle oscillation (LCO) of a pitching airfoil in the transitional Reynolds number regime. At small angles of attack, laminar boundary layer trailing edge separation causes negative aerodynamic damping leading to the LCO. The fluid-structure interaction of the rigid, but elastically mounted, airfoil and nonlinear unsteady aerodynamics is represented by two coupled nonlinear stochastic ordinary differential equations containing uncertain parameters and model approximation errors. Several plausible aerodynamic models with increasing complexity are proposed to describe the aeroelastic system leading to LCO. The likelihood in the posterior parameter probability density function (pdf) is available semi-analytically using the extended Kalman filter for the state estimation of the coupled nonlinear structural and unsteady aerodynamic model. The posterior parameter pdf is sampled using a parallel and adaptive Markov Chain Monte Carlo (MCMC) algorithm. The posterior probability of each model is estimated using the Chib-Jeliazkov method that directly uses the posterior MCMC samples for evidence (marginal likelihood) computation. The Bayesian algorithm is validated through a numerical study and then applied to model the nonlinear unsteady aerodynamic loads using wind-tunnel test data at various Reynolds numbers.
Bayesian inference of nonlinear unsteady aerodynamics from aeroelastic limit cycle oscillations
Energy Technology Data Exchange (ETDEWEB)
Sandhu, Rimple [Department of Civil and Environmental Engineering, Carleton University, Ottawa, Ontario (Canada); Poirel, Dominique [Department of Mechanical and Aerospace Engineering, Royal Military College of Canada, Kingston, Ontario (Canada); Pettit, Chris [Department of Aerospace Engineering, United States Naval Academy, Annapolis, MD (United States); Khalil, Mohammad [Department of Civil and Environmental Engineering, Carleton University, Ottawa, Ontario (Canada); Sarkar, Abhijit, E-mail: abhijit.sarkar@carleton.ca [Department of Civil and Environmental Engineering, Carleton University, Ottawa, Ontario (Canada)
2016-07-01
A Bayesian model selection and parameter estimation algorithm is applied to investigate the influence of nonlinear and unsteady aerodynamic loads on the limit cycle oscillation (LCO) of a pitching airfoil in the transitional Reynolds number regime. At small angles of attack, laminar boundary layer trailing edge separation causes negative aerodynamic damping leading to the LCO. The fluid–structure interaction of the rigid, but elastically mounted, airfoil and nonlinear unsteady aerodynamics is represented by two coupled nonlinear stochastic ordinary differential equations containing uncertain parameters and model approximation errors. Several plausible aerodynamic models with increasing complexity are proposed to describe the aeroelastic system leading to LCO. The likelihood in the posterior parameter probability density function (pdf) is available semi-analytically using the extended Kalman filter for the state estimation of the coupled nonlinear structural and unsteady aerodynamic model. The posterior parameter pdf is sampled using a parallel and adaptive Markov Chain Monte Carlo (MCMC) algorithm. The posterior probability of each model is estimated using the Chib–Jeliazkov method that directly uses the posterior MCMC samples for evidence (marginal likelihood) computation. The Bayesian algorithm is validated through a numerical study and then applied to model the nonlinear unsteady aerodynamic loads using wind-tunnel test data at various Reynolds numbers.
Tiffany, Sherwood H.; Adams, William M., Jr.
1988-01-01
The approximation of unsteady generalized aerodynamic forces in the equations of motion of a flexible aircraft are discussed. Two methods of formulating these approximations are extended to include the same flexibility in constraining the approximations and the same methodology in optimizing nonlinear parameters as another currently used extended least-squares method. Optimal selection of nonlinear parameters is made in each of the three methods by use of the same nonlinear, nongradient optimizer. The objective of the nonlinear optimization is to obtain rational approximations to the unsteady aerodynamics whose state-space realization is lower order than that required when no optimization of the nonlinear terms is performed. The free linear parameters are determined using the least-squares matrix techniques of a Lagrange multiplier formulation of an objective function which incorporates selected linear equality constraints. State-space mathematical models resulting from different approaches are described and results are presented that show comparative evaluations from application of each of the extended methods to a numerical example.
Fundamentals of modern unsteady aerodynamics
Gülçat, Ülgen
2010-01-01
This introduction to the principles of unsteady aerodynamics covers all the core concepts, provides readers with a review of the fundamental physics, terminology and basic equations, and covers hot new topics such as the use of flapping wings for propulsion.
Fundamentals of modern unsteady aerodynamics
Gülçat, Ülgen
2016-01-01
In this book, the author introduces the concept of unsteady aerodynamics and its underlying principles. He provides the readers with a comprehensive review of the fundamental physics of free and forced unsteadiness, the terminology and basic equations of aerodynamics ranging from incompressible flow to hypersonics. The book also covers modern topics related to the developments made in recent years, especially in relation to wing flapping for propulsion. The book is written for graduate and senior year undergraduate students in aerodynamics and also serves as a reference for experienced researchers. Each chapter includes ample examples, questions, problems and relevant references. The treatment of these modern topics has been completely revised end expanded for the new edition. It now includes new numerical examples, a section on the ground effect, and state-space representation.
Unsteady aerodynamics modeling for flight dynamics application
Wang, Qing; He, Kai-Feng; Qian, Wei-Qi; Zhang, Tian-Jiao; Cheng, Yan-Qing; Wu, Kai-Yuan
2012-02-01
In view of engineering application, it is practicable to decompose the aerodynamics into three components: the static aerodynamics, the aerodynamic increment due to steady rotations, and the aerodynamic increment due to unsteady separated and vortical flow. The first and the second components can be presented in conventional forms, while the third is described using a one-order differential equation and a radial-basis-function (RBF) network. For an aircraft configuration, the mathematical models of 6-component aerodynamic coefficients are set up from the wind tunnel test data of pitch, yaw, roll, and coupled yawroll large-amplitude oscillations. The flight dynamics of an aircraft is studied by the bifurcation analysis technique in the case of quasi-steady aerodynamics and unsteady aerodynamics, respectively. The results show that: (1) unsteady aerodynamics has no effect upon the existence of trim points, but affects their stability; (2) unsteady aerodynamics has great effects upon the existence, stability, and amplitudes of periodic solutions; and (3) unsteady aerodynamics changes the stable regions of trim points obviously. Furthermore, the dynamic responses of the aircraft to elevator deflections are inspected. It is shown that the unsteady aerodynamics is beneficial to dynamic stability for the present aircraft. Finally, the effects of unsteady aerodynamics on the post-stall maneuverability are analyzed by numerical simulation.
Unsteady aerodynamics modeling for flight dynamics application
Institute of Scientific and Technical Information of China (English)
Qing Wang; Kai-Feng He; Wei-Qi Qian; Tian-Jiao Zhang; Yan-Qing Cheng; Kai-Yuan Wu
2012-01-01
In view of engineering application,it is practicable to decompose the aerodynamics into three components:the static aerodynamics,the aerodynamic increment due to steady rotations,and the aerodynamic increment due to unsteady separated and vortical flow.The first and the second components can be presented in conventional forms,while the third is described using a one-order differential equation and a radial-basis-function (RBF) network. For an aircraft configuration,the mathematical models of 6-component aerodynamic coefficients are set up from the wind tunnel test data of pitch,yaw,roll,and coupled yawroll large-amplitude oscillations.The flight dynamics of an aircraft is studied by the bifurcation analysis technique in the case of quasi-steady aerodynamics and unsteady aerodynamics,respectively.The results show that:(1) unsteady aerodynamics has no effect upon the existence of trim points,but affects their stability; (2) unsteady aerodynamics has great effects upon the existence,stability,and amplitudes of periodic solutions; and (3) unsteady aerodynamics changes the stable regions of trim points obviously.Furthermore,the dynamic responses of the aircraft to elevator deflections are inspected.It is shown that the unsteady aerodynamics is beneficial to dynamic stability for the present aircraft.Finally,the effects of unsteady aerodynamics on the post-stall maneuverability are analyzed by numerical simulation.
Prediction of Unsteady Transonic Aerodynamics Project
National Aeronautics and Space Administration — An accurate prediction of aero-elastic effects depends on an accurate prediction of the unsteady aerodynamic forces. Perhaps the most difficult speed regime is...
Unsteady Aerodynamic Force Sensing from Strain Data
Pak, Chan-Gi
2017-01-01
A simple approach for computing unsteady aerodynamic forces from simulated measured strain data is proposed in this study. First, the deflection and slope of the structure are computed from the unsteady strain using the two-step approach. Velocities and accelerations of the structure are computed using the autoregressive moving average model, on-line parameter estimator, low-pass filter, and a least-squares curve fitting method together with analytical derivatives with respect to time. Finally, aerodynamic forces over the wing are computed using modal aerodynamic influence coefficient matrices, a rational function approximation, and a time-marching algorithm.
Calculated Unsteady Aerodynamics of Wings.
1987-12-15
test-and- evaluation turnaround time of only a few minutes per case. The following sections outline the derivation and implementation of this...computer program. Inputs degrees at the higher end, and is purely a numerical to the prgram include the threshold vortex offset dis- error. The present...precise + - (4.2) aumerical evaluation . U . P U. The (non-linear) expressions for lift and moment includ- I R cidt"() eC ca 1 rig the appropriate wake
Wind turbines. Unsteady aerodynamics and inflow noise
Energy Technology Data Exchange (ETDEWEB)
Riget Broe, B.
2009-12-15
Aerodynamical noise from wind turbines due to atmospheric turbulence has the highest emphasis in semi-empirical models. However it is an open question whether inflow noise has a high emphasis. This illustrates the need to investigate and improve the semi-empirical model for noise due to atmospheric turbulence. Three different aerodynamical models are investigated in order to estimate the lift fluctuations due to unsteady aerodynamics. Two of these models are investigated to find the unsteady lift distribution or pressure difference as function of chordwise position on the aerofoil. An acoustic model is investigated using a model for the lift distribution as input. The two models for lift distribution are used in the acoustic model. One of the models for lift distribution is for completely anisotropic turbulence and the other for perfectly isotropic turbulence, and so is also the corresponding models for the lift fluctuations derived from the models for lift distribution. The models for lift distribution and lift are compared with pressure data which are obtained by microphones placed flush with the surface of an aerofoil. The pressure data are from two experiments in a wind tunnel, one experiment with a NACA0015 profile and a second with a NACA63415 profile. The turbulence is measured by a triple wired hotwire instrument in the experiment with a NACA0015 profile. Comparison of the aerodynamical models with data shows that the models capture the general characteristics of the measurements, but the data are hampered by background noise from the fan propellers in the wind tunnel. The measurements are in between the completely anisotropic turbulent model and the perfectly isotropic turbulent model. This indicates that the models capture the aerodynamics well. Thus the measurements suggest that the noise due to atmospheric turbulence can be described and modeled by the two models for lift distribution. It was not possible to test the acoustical model by the measurements
Unsteady aerodynamics and flow control for flapping wing flyers
Ho, Steven; Nassef, Hany; Pornsinsirirak, Nick; Tai, Yu-Chong; Ho, Chih-Ming
2003-11-01
The creation of micro air vehicles (MAVs) of the same general sizes and weight as natural fliers has spawned renewed interest in flapping wing flight. With a wingspan of approximately 15 cm and a flight speed of a few meters per second, MAVs experience the same low Reynolds number (10 4-10 5) flight conditions as their biological counterparts. In this flow regime, rigid fixed wings drop dramatically in aerodynamic performance while flexible flapping wings gain efficacy and are the preferred propulsion method for small natural fliers. Researchers have long realized that steady-state aerodynamics does not properly capture the physical phenomena or forces present in flapping flight at this scale. Hence, unsteady flow mechanisms must dominate this regime. Furthermore, due to the low flight speeds, any disturbance such as gusts or wind will dramatically change the aerodynamic conditions around the MAV. In response, a suitable feedback control system and actuation technology must be developed so that the wing can maintain its aerodynamic efficiency in this extremely dynamic situation; one where the unsteady separated flow field and wing structure are tightly coupled and interact nonlinearly. For instance, birds and bats control their flexible wings with muscle tissue to successfully deal with rapid changes in the flow environment. Drawing from their example, perhaps MAVs can use lightweight actuators in conjunction with adaptive feedback control to shape the wing and achieve active flow control. This article first reviews the scaling laws and unsteady flow regime constraining both biological and man-made fliers. Then a summary of vortex dominated unsteady aerodynamics follows. Next, aeroelastic coupling and its effect on lift and thrust are discussed. Afterwards, flow control strategies found in nature and devised by man to deal with separated flows are examined. Recent work is also presented in using microelectromechanical systems (MEMS) actuators and angular speed
Wind Turbines: Unsteady Aerodynamics and Inflow Noise
DEFF Research Database (Denmark)
Broe, Brian Riget
; and Graham, J. M. R.: 1970, Lifting surface theory for the problem of an arbitrarily yawed sinusoidal gust incident on a thin aerofoil in incompressible flow). Two of these models are investigated to find the unsteady lift distribution or pressure difference as function of chordwise position on the aerofoil...... (Sears, W. R.: 1941; and Graham, J. M. R.: 1970). An acoustic model is investigated using a model for the lift distribution as input (Amiet, R. K.: 1975, Acoustic radiation from an airfoil in a turbulent stream). The two models for lift distribution are used in the acoustic model. One of the models...... and the perfectly isotropic turbulent model. This indicates that the models capture the aerodynamics well. Thus the measurements suggest that the noise due to atmospheric turbulence can be described and modeled by the two models for lift distribution. It was not possible to test the acoustical model...
Application of neural networks to unsteady aerodynamic control
Faller, William E.; Schreck, Scott J.; Luttges, Marvin W.
1994-01-01
The problem under consideration in this viewgraph presentation is to understand, predict, and control the fluid mechanics of dynamic maneuvers, unsteady boundary layers, and vortex dominated flows. One solution is the application of neural networks demonstrating closed-loop control. Neural networks offer unique opportunities: simplify modeling of three dimensional, vortex dominated, unsteady separated flow fields; are effective means for controlling unsteady aerodynamics; and address integration of sensors, controllers, and time lags into adaptive control systems.
Unsteady aerodynamic modelling of wind turbines
Energy Technology Data Exchange (ETDEWEB)
Coton, F.N.; Galbraith, R.A. [Univ. og Glasgow, Dept. of Aerospace Engineering, Glasgow (United Kingdom)
1997-08-01
The following current and future work is discussed: Collaborative wind tunnel based PIV project to study wind turbine wake structures in head-on and yawed flow. Prescribed wake model has been embedded in a source panel representation of the wind tunnel walls to allow comparison with experiment; Modelling of tower shadow using high resolution but efficient vortex model in tower shadow domain; Extension of model to yawing flow; Upgrading and tuning of unsteady aerodynamic model for low speed, thick airfoil flows. Glasgow has a considerable collection of low speed dynamic stall data. Currently, the Leishman - Beddoes model is not ideally suited to such flows. For example: Range of stall onset criteria used for dynamic stall prediction including Beddoes. Wide variation of stall onset prediction. Beddoes representation was developed primarily with reference to compressible flows. Analyses of low speed data from Glasgow indicate deficiencies in the current model; Predicted versus measured response during ramp down motion. Modification of the Beddoes representation is required to obtain a fit with the measured data. (EG)
Influence of unsteady aerodynamics on driving dynamics of passenger cars
Huemer, Jakob; Stickel, Thomas; Sagan, Erich; Schwarz, Martin; Wall, Wolfgang A.
2014-11-01
Recent approaches towards numerical investigations with computational fluid dynamics methods on unsteady aerodynamic loads of passenger cars identified major differences compared with steady-state aerodynamic excitations. Furthermore, innovative vehicle concepts such as electric-vehicles or hybrid drives further challenge the basic layout of passenger cars. Therefore, the relevance of unsteady aerodynamic loads on cross-wind stability of changing basic vehicle architectures should be analysed. In order to assure and improve handling and ride characteristics at high velocity of the actual range of vehicle layouts, the influence of unsteady excitations on the vehicle response was investigated. For this purpose, a simulation of the vehicle dynamics through multi-body simulation was used. The impact of certain unsteady aerodynamic load characteristics on the vehicle response was quantified and key factors were identified. Through a series of driving simulator tests, the identified differences in the vehicle response were evaluated regarding their significance on the subjective driver perception of cross-wind stability. Relevant criteria for the subjective driver assessment of the vehicle response were identified. As a consequence, a design method for the basic layout of passenger cars and chassis towards unsteady aerodynamic excitations was defined.
Algorithmic Enhancements for Unsteady Aerodynamics and Combustion Applications
Venkateswaran, Sankaran; Olsen, Michael (Technical Monitor)
2001-01-01
Research in the FY01 focused on the analysis and development of enhanced algorithms for unsteady aerodynamics and chemically reacting flowfields. The research was performed in support of NASA Ames' efforts to improve the capabilities of the in-house computational fluid dynamics code, OVERFLOW. Specifically, the research was focused on the four areas: (1) investigation of stagnation region effects; (2) unsteady preconditioning dual-time procedures; (3) dissipation formulation for combustion; and (4) time-stepping methods for combustion.
Unsteady Aerodynamics of Flapping Wing of a Bird
Directory of Open Access Journals (Sweden)
M. Agoes Moelyadi
2013-04-01
Full Text Available The unsteady flow behavior and time-dependent aerodynamic characteristics of the flapping motion of a bird’s wing were investigated using a computational method. During flapping, aerodynamic interactions between bird wing surfaces and surrounding flow may occur, generating local time-dependent flow changes in the flow field and aerodynamic load of birds. To study the effect of flapping speed on unsteady aerodynamic load, two kinds of computational simulations were carried out, namely a quasi-steady and an unsteady simulation. To mimic the movement of the down-stroke and the upstroke of a bird, the flapping path accorded to a sinus function, with the wing attitude changing in dihedral angle and time. The computations of time-dependent viscous flow were based on the solution of the Reynolds Averaged Navier-Stokes equations by applying the k-e turbulence model. In addition, the discretization for the computational domain around the model used multi-block structured grid to provide more accuracy in capturing viscous flow, especially in the vicinity of the wing and body surfaces, to obtain a proper wing-body geometry model. For this research, the seagull bird was chosen, which has high aspect ratio wings with pointed wing-tips and a high camber wing section. The results include mesh movement, velocity contours as well as aerodynamic coefficients of the flapping motion of the bird at various flapping frequencies.
Linear Unsteady Aerodynamic Forces on Vibrating Annular Cascade Blades
Institute of Scientific and Technical Information of China (English)
Taketo Nagasaki; Nobuhiko Yamasaki
2003-01-01
The paper presents the formulation to compute numerically the unsteady aerodynamic forces on the vibrating annular cascade blades. The formulation is based on the finite volume method. By applying the TVD scheme to the linear unsteady calculations, the precise calculation of the peak of unsteady aerodynamic forces at the shock wave location like the delta function singularity becomes possible without empirical constants. As a further feature of the present paper, results of the present numerical calculation are compared with those of the double lineaxization theory (DLT), which assumes small unsteady and steady disturbances but the unsteady disturbances are much smaller than the steady disturbances. Since DLT requires fax less computational resources than the present numerical calculation, the validation of DLT is quite important from the engineering point of view. Under the conditions of small steady disturbances, a good agreement between these two results is observed, so that the two codes axe cross-validated.The comparison also reveals the limitation on the applicability of DLT.
Survey of research on unsteady aerodynamic loading of delta wings
Ashley, H.; Vaneck, T.; Katz, J.; Jarrah, M. A.
1991-01-01
For aeronautical applications, there has been recent interest in accurately determining the aerodynamic forces and moments experienced by low-aspect-ratio wings performing transient maneuvers which go to angles of attack as high as 90 deg. Focusing on the delta planform with sharp leading edges, the paper surveys experimental and theoretical investigations dealing with the associated unsteady flow phenomena. For maximum angles above a value between 30 and 40 deg, flow details and airloads are dominated by hysteresis in the 'bursting' instability of intense vortices which emanate from the leading edge. As examples of relevant test results, force and moment histories are presented for a model series with aspect ratios 1, 1.5 and 2. Influences of key parameters are discussed, notably those which measure unsteadiness. Comparisons are given with two theories: a paneling approximation that cannot capture bursting but clarifies other unsteady influences, and a simplified estimation scheme which uses measured bursting data.
Survey of research on unsteady aerodynamic loading of delta wings
Ashley, H.; Vaneck, T.; Katz, J.; Jarrah, M. A.
1991-01-01
For aeronautical applications, there has been recent interest in accurately determining the aerodynamic forces and moments experienced by low-aspect-ratio wings performing transient maneuvers which go to angles of attack as high as 90 deg. Focusing on the delta planform with sharp leading edges, the paper surveys experimental and theoretical investigations dealing with the associated unsteady flow phenomena. For maximum angles above a value between 30 and 40 deg, flow details and airloads are dominated by hysteresis in the 'bursting' instability of intense vortices which emanate from the leading edge. As examples of relevant test results, force and moment histories are presented for a model series with aspect ratios 1, 1.5 and 2. Influences of key parameters are discussed, notably those which measure unsteadiness. Comparisons are given with two theories: a paneling approximation that cannot capture bursting but clarifies other unsteady influences, and a simplified estimation scheme which uses measured bursting data.
Estimation of unsteady aerodynamic forces using pointwise velocity data
Gómez, F; Blackburn, H M
2016-01-01
A novel method to estimate unsteady aerodynamic force coefficients from pointwise velocity measurements is presented. The methodology is based on a resolvent-based reduced-order model which requires the mean flow to obtain physical flow structures and pointwise measurement to calibrate their amplitudes. A computationally-affordable time-stepping methodology to obtain resolvent modes in non-trivial flow domains is introduced and compared to previous existing matrix-free and matrix-forming strategies. The technique is applied to the unsteady flow around an inclined square cylinder at low Reynolds number. The potential of the methodology is demonstrated through good agreement between the fluctuating pressure distribution on the cylinder and the temporal evolution of the unsteady lift and drag coefficients predicted by the model and those computed by direct numerical simulation.
System Identification and POD Method Applied to Unsteady Aerodynamics
Tang, Deman; Kholodar, Denis; Juang, Jer-Nan; Dowell, Earl H.
2001-01-01
The representation of unsteady aerodynamic flow fields in terms of global aerodynamic modes has proven to be a useful method for reducing the size of the aerodynamic model over those representations that use local variables at discrete grid points in the flow field. Eigenmodes and Proper Orthogonal Decomposition (POD) modes have been used for this purpose with good effect. This suggests that system identification models may also be used to represent the aerodynamic flow field. Implicit in the use of a systems identification technique is the notion that a relative small state space model can be useful in describing a dynamical system. The POD model is first used to show that indeed a reduced order model can be obtained from a much larger numerical aerodynamical model (the vortex lattice method is used for illustrative purposes) and the results from the POD and the system identification methods are then compared. For the example considered, the two methods are shown to give comparable results in terms of accuracy and reduced model size. The advantages and limitations of each approach are briefly discussed. Both appear promising and complementary in their characteristics.
Some applications of the quasi vortex-lattice method in steady and unsteady aerodynamics
Lan, C. E.
1976-01-01
The quasi vortex-lattice method is reviewed and applied to the evaluation of backwash, with applications to ground effect analysis. It is also extended to unsteady aerodynamics, with particular interest in the calculation of unsteady leading-edge suction. Some applications in ornithopter aerodynamics are given.
Unsteady Thick Airfoil Aerodynamics: Experiments, Computation, and Theory
Strangfeld, C.; Rumsey, C. L.; Mueller-Vahl, H.; Greenblatt, D.; Nayeri, C. N.; Paschereit, C. O.
2015-01-01
An experimental, computational and theoretical investigation was carried out to study the aerodynamic loads acting on a relatively thick NACA 0018 airfoil when subjected to pitching and surging, individually and synchronously. Both pre-stall and post-stall angles of attack were considered. Experiments were carried out in a dedicated unsteady wind tunnel, with large surge amplitudes, and airfoil loads were estimated by means of unsteady surface mounted pressure measurements. Theoretical predictions were based on Theodorsen's and Isaacs' results as well as on the relatively recent generalizations of van der Wall. Both two- and three-dimensional computations were performed on structured grids employing unsteady Reynolds-averaged Navier-Stokes (URANS). For pure surging at pre-stall angles of attack, the correspondence between experiments and theory was satisfactory; this served as a validation of Isaacs theory. Discrepancies were traced to dynamic trailing-edge separation, even at low angles of attack. Excellent correspondence was found between experiments and theory for airfoil pitching as well as combined pitching and surging; the latter appears to be the first clear validation of van der Wall's theoretical results. Although qualitatively similar to experiment at low angles of attack, two-dimensional URANS computations yielded notable errors in the unsteady load effects of pitching, surging and their synchronous combination. The main reason is believed to be that the URANS equations do not resolve wake vorticity (explicitly modeled in the theory) or the resulting rolled-up un- steady flow structures because high values of eddy viscosity tend to \\smear" the wake. At post-stall angles, three-dimensional computations illustrated the importance of modeling the tunnel side walls.
A SIMPLIFIED THEORY FOR UNSTEADY AERODYNAMIC FORCES ACTING ON AN AIRFOIL FLYING ABOVE SEA-WAVES
Institute of Scientific and Technical Information of China (English)
SHENG Qi-hu; WU De-ming; ZHANG Liang
2004-01-01
A simplified theoretical method based on the quasi-steady wing theory was proposed to study the unsteady aerodynamic forces acting on an airfoil flying in non-uniform flow. Comparison between the theoretical results and the numerical results based on nonlinear theory was made. It shows that the simplified theory is a good approximation for the investigation of the aerodynamic characteristics of an airfoil flying above sea-waves. From on the simplified theory it is also found that an airfoil can get thrust from a wave-disturbed airflow and thus the total drag is reduced. And the relationship among the thrust, the flying altitude, the flying speed and the wave parameters was worked out and discussed.
Simultaneous Excitation of Multiple-Input Multiple-Output CFD-Based Unsteady Aerodynamic Systems
Silva, Walter A.
2008-01-01
A significant improvement to the development of CFD-based unsteady aerodynamic reduced-order models (ROMs) is presented. This improvement involves the simultaneous excitation of the structural modes of the CFD-based unsteady aerodynamic system that enables the computation of the unsteady aerodynamic state-space model using a single CFD execution, independent of the number of structural modes. Four different types of inputs are presented that can be used for the simultaneous excitation of the structural modes. Results are presented for a flexible, supersonic semi-span configuration using the CFL3Dv6.4 code.
Vega Coso, Almudena
2017-01-01
This thesis studies the unsteady aerodynamics of oscillating airfoils in the low reduced frequency regime, with special emphasis on its impact on the scaling of the work per cycle curves, using an asymptotic approach and numerical experiments. The unsteady aerodynamics associated with the vibration of turbine and compressor bladed-discs and stator vanes is nowadays routinely analysed within the design loop of the aeroengine companies, and it has also been the subject of dedicated experiments....
Unsteady aerodynamic modeling based on POD-observer method
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
A new hybrid approach to constructing reduced-order models(ROM)of unsteady aerodynamics applicable to aeroelastic analysis is presented by using proper orthogonal decomposition(POD)in combination with observer techniques.Fluid modes are generated through POD by sampling observations of solutions derived from the full-order model.The response in the POD training is projected onto the fluid modes to determine the time history of the modal amplitudes.The resulting data are used to extract the Markov parameters of the low-dimensional model for modal amplitudes using a related deadbeat observer.The state-space realization is synthesized from the system’s Markov parameters that are processed with the eigensystem realization algorithm.The POD-observer method is applied to a two-dimensional airfoil system in subsonic flow field.The results predicted by the ROM are in general agreement with those from the full-order system.The ROM obtained by the hybrid approach captures the essence of a fluid system and produces vast reduction in both degrees of freedom and computational time relative to the full-order model.
Petot, D.; Loiseau, H.
1982-01-01
Unsteady aerodynamic methods adopted for the study of aeroelasticity in helicopters are considered with focus on the development of a semiempirical model of unsteady aerodynamic forces acting on an oscillating profile at high incidence. The successive smoothing algorithm described leads to the model's coefficients in a very satisfactory manner.
Dynamic importance of unsteady effects in glottal flow aerodynamics
Krane, Michael; Peltier, Joel; Medvitz, Richard
2008-11-01
Finite element computations of flow through a constriction are used to illuminate the role of unsteady flow dynamics in glottal flow and voice production. Unsteady computations were performed for a series of prescribed idealized vocal fold wall motions over reduced frequencies f*=0, 0.04 and 0.08, which correspond to quasi-steady, adult male and adult female speaking voices, respectively. Glottal resistance and estimates of the relative magnitudes of the various terms of the integral momentum equation are presented. Results suggest that glottal flow is inherently unsteady.
Energy Technology Data Exchange (ETDEWEB)
Afungchui, David [University of Buea, Faculty of Science, Department of Physics, UB Street, PO Box 63, Molyko, Buea, South West (Cameroon); Kamoun, Baddreddinne; Helali, Ali; Ben Djemaa, Abdellatif [Faculte des Sciences de Sfax, Departement de Physique, Laboratoire de Physique, Appliquee (L.P.A.), Sfax (Tunisia)
2010-01-15
The aim of this paper is to numerically explore the non-linear two-dimensional unsteady potential flow over a Savonius rotor and to develop a code for predicting its aerodynamics performances. In the model developed, the rotor is represented in a median plane by two semicircles, displaced along their common diameter. The two semicircles can be considered to produce lifting effects. As a result, they are modelled by a collection of discrete vortices on their contours. The flow field is then governed by the Laplace equation. The versatile Neumann boundary condition, applied over the contour of the semicircles and the Kutta Joukowsky condition applied at the four extremities of the semicircles have been used in the modelling. The torque distribution of the stationary rotor and the unsteady pressure field on the blades of the rotating rotor, predicted by the code developed, have been compared and validated by some experimental data. (author)
Estimation of Aircraft Nonlinear Unsteady Parameters From Wind Tunnel Data
Klein, Vladislav; Murphy, Patrick C.
1998-01-01
Aerodynamic equations were formulated for an aircraft in one-degree-of-freedom large amplitude motion about each of its body axes. The model formulation based on indicial functions separated the resulting aerodynamic forces and moments into static terms, purely rotary terms and unsteady terms. Model identification from experimental data combined stepwise regression and maximum likelihood estimation in a two-stage optimization algorithm that can identify the unsteady term and rotary term if necessary. The identification scheme was applied to oscillatory data in two examples. The model identified from experimental data fit the data well, however, some parameters were estimated with limited accuracy. The resulting model was a good predictor for oscillatory and ramp input data.
Continuous-time state-space unsteady aerodynamic modelling for efficient aeroelastic load analysis
Werter, N.P.M.; De Breuker, R.; Abdalla, M.M.
2015-01-01
Over the years, wings have become lighter and more flexible, making them more prone to aeroelastic effects. Thus, aeroelasticity in design becomes more important. In order to determine the response of an aircraft to, for example, a gust, an unsteady aerodynamic model is required to determine the dyn
Effect of chordwise deformation on unsteady aerodynamic mechanisms in hovering flapping flight
Noyon, T.A.; Tay, W.B.; Van Oudheusden, B.W.; Bijl, H.
2014-01-01
A three-dimensional simulation of hovering flapping wings was performed using an immersed boundary method. This was done to investigate the effects of chordwise wing deformation on three important unsteady aerodynamic mechanisms found in flapping flight, namely Leading Edge Vortex (LEV) shedding, wa
Unsteady Aerodynamic Models for Flight Control of Agile Micro Air Vehicles
2010-08-13
AUG 2010 2. REPORT TYPE Final 3. DATES COVERED 01-02-2007 to 30-11-2009 4. TITLE AND SUBTITLE Unsteady Aerodynamic Models for Flight Control...non-physical. First, it is impossible to command in experiments or simulations, because it would correspond to a body instanta- neously dematerializing
Yao, Weigang; Liou, Meng-Sing
2016-08-01
To preserve nonlinearity of a full-order system over a range of parameters of interest, we propose an accurate and robust nonlinear modeling approach by assembling a set of piecewise linear local solutions expanded about some sampling states. The work by Rewienski and White [1] on micromachined devices inspired our use of piecewise linear local solutions to study nonlinear unsteady aerodynamics. These local approximations are assembled via nonlinear weights of radial basis functions. The efficacy of the proposed procedure is validated for a two-dimensional airfoil moving with different pitching motions, specifically AGARD's CT2 and CT5 problems [27], in which the flows exhibit different nonlinear behaviors. Furthermore, application of the developed aerodynamic model to a two-dimensional aero-elastic system proves the approach is capable of predicting limit cycle oscillations (LCOs) by using AGARD's CT6 [28] as a benchmark test. All results, based on inviscid solutions, confirm that our nonlinear model is stable and accurate, against the full model solutions and measurements, and for predicting not only aerodynamic forces but also detailed flowfields. Moreover, the model is robust for inputs that considerably depart from the base trajectory in form and magnitude. This modeling provides a very efficient way for predicting unsteady flowfields with varying parameters because it needs only a tiny fraction of the cost of a full-order modeling for each new condition-the more cases studied, the more savings rendered. Hence, the present approach is especially useful for parametric studies, such as in the case of design optimization and exploration of flow phenomena.
Unsteady aerodynamic interaction effects on turbomachinery blade life and performance
Adamczyk, John J.
1992-01-01
This paper is an attempt to address the impact of a class of unsteady flows on the life and performance of turbomachinery blading. These class of flows to be investigated are those whose characteristic frequency is an integral multiple of rotor shaft speed. Analysis of data recorded downstream of a compressor and turbine rotor will reveal that this class of flows can be highly three-dimensional and may lead to the generation of secondary flows within downstream blading. By explicitly accounting for these unsteady flows in the design of turbomachinery blading for multistage applications, it may be possible to bring about gains in performance and blade life.
Directory of Open Access Journals (Sweden)
Hadar Ben-Gida
Full Text Available Wing flapping is one of the most widespread propulsion methods found in nature; however, the current understanding of the aerodynamics in bird wakes is incomplete. The role of the unsteady motion in the flow and its contribution to the aerodynamics is still an open question. In the current study, the wake of a freely flying European starling has been investigated using long-duration high-speed Particle Image Velocimetry (PIV in the near wake. Kinematic analysis of the wings and body of the bird has been performed using additional high-speed cameras that recorded the bird movement simultaneously with the PIV measurements. The wake evolution of four complete wingbeats has been characterized through reconstruction of the time-resolved data, and the aerodynamics in the wake have been analyzed in terms of the streamwise forces acting on the bird. The profile drag from classical aerodynamics was found to be positive during most of the wingbeat cycle, yet kinematic images show that the bird does not decelerate. It is shown that unsteady aerodynamics are necessary to satisfy the drag/thrust balance by approximating the unsteady drag term. These findings may shed light on the flight efficiency of birds by providing a partial answer to how they minimize drag during flapping flight.
Unsteady Low Reynolds Number Aerodynamics for Micro Air Vehicles (MAVs)
2010-05-01
horizontal model. The first has advantages of placing t he force balance above the water line and thus solving the balance waterproofing i ssues , an d h...ABSTRACT This work introduces the Micro Air Vehicle (MAV) problem from the viewpoint of aerodynamics. Water tunnels are assessed as tools for MAV...aerodynamics. The design, construction and instrumentation of RB’s “Horizontal Free-surface Water Tunnel” is documented. Experiments in steady
Panel/full-span free-wake coupled method for unsteady aerodynamics of helicopter rotor blade
Institute of Scientific and Technical Information of China (English)
Tan Jianfeng; Wang Haowen
2013-01-01
A full-span free-wake method is coupled with an unsteady panel method to accurately predict the unsteady aerodynamics of helicopter rotor blades in hover and forward flight.The unsteady potential-based panel method is used to consider aerodynamics of finite thickness multi-bladed rotors,and the full-span free-wake method is applied to simulating dynamics of rotor wake.These methods are tightly coupled through trailing-edge Kutta condition and by converting doublet-wake panels to full-span vortex filaments.A velocity-field integration technique is also adopted to overcome singularity problem during the interaction between the rotor wake and blades.Helicopter rotors including Caradonna-Tung,UH-60A,and AH-1G rotors,are simulated in hover and forward flight to validate the accuracy of this approach.The predicted aerodynamic loads of rotor blades agree well with available measured data and computational fluid dynamics (CFD) results,and the unsteady dynamics of rotor wake is also well simulated.Compared to CFD,the present method obtains accurate results more efficiently and is suitable to rotorcraft aeroelastic analysis.
Unsteady Aerodynamic Interaction in a Closely Coupled Turbine Consistent with Contra-Rotation
2014-08-01
30320. [4] Puterbaugh, S. L. and Copenhaver , W. W., 1994, "Flow Field Unsteadiness in the Tip Region of a Transonic Compressor Rotor," in...8] Kemp, N. H. and Sears, W. R., “Aerodynamic Interference Between Moving Blade Rows,” Journal of Aero. Science , Vol. 20, No. 9, September 1953, pp...585-597 [9] Kemp, N. H. and Sears, W. R., “The Unsteady Forces Due to Viscous Wakes in Turbomachines,” Journal of Aero. Science , Vol. 22, No. 7
Aerodynamic Experiments on DelFly II: Unsteady Lift Enhancement
De Clercq, K.M.E.; De Kat, R.; Remes, B.; Van Oudheusden, B.W.; Bijl, H.
2009-01-01
Particle image velocimetry measurements and simultaneous force measurements have been performed on the DelFly II flapping-wing MAV, to investigate the flow-field behavior and the aerodynamic forces generated. For flapping wing motion it is expected that both the clap and peel mechanism and the occur
National Aeronautics and Space Administration — CFD-based design-oriented (DO) steady/unsteady aerodynamic analysis tools for Aeroelastic / Aeroservoelastic (AE/ASE) evaluation lag significantly behind other...
Wing flutter boundary prediction using unsteady Euler aerodynamic method
Lee-Rausch, Elizabeth M.; Batina, John T.
1993-01-01
Modifications to an existing 3D implicit upwind Euler/Navier-Stokes code for the aeroelastic analysis of wings are described. These modifications include the incorporation of a deforming mesh algorithm and the addition of the structural equations of motion for their simultaneous time-integration with the governing flow equations. The paper gives a brief description of these modifications and presents unsteady calculations which check the modifications to the code. Euler flutter results for an isolated 45 deg swept-back wing are compared with experimental data for seven freestream Mach numbers which define the flutter boundary over a range of Mach number from 0.499 to 1.14. These comparisons show good agreement in flutter characteristics for freestream Mach numbers below unity. For freestream Mach numbers above unity, the computed aeroelastic results predict a premature rise in the flutter boundary as compared with the experimental boundary. Steady and unsteady contours of surface Mach number and pressure are included to illustrate the basic flow characteristics of the time-marching flutter calculations and to aid in identifying possible causes for the premature rise in the computational flutter boundary.
Development of Unsteady Aerodynamic State-Space Models from CFD-Based Pulse Responses
Silva, Walter A.; Raveh, Daniella E.
2001-01-01
A method for computing discrete-time state-space models of linearized unsteady aerodynamic behavior directly from aeroelastic CFD codes is presented. The method involves the treatment of CFD-based pulse responses as Markov parameters for use in a system identification /realization algorithm. Results are presented for the AGARD 445.6 Aeroelastic Wing with four aeroelastic modes at a Mach number of 0.96 using the EZNSS Euler/Navier-Stokes flow solver with aeroelastic capability. The System/Observer/Controller Identification Toolbox (SOCIT) algorithm, based on the Ho-Kalman realization algorithm, is used to generate 15th- and 32nd-order discrete-time state-space models of the unsteady aerodynamic response of the wing over the entire frequency range of interest.
State-space model identification and feedback control of unsteady aerodynamic forces
Brunton, Steven L; Rowley, Clarence W
2014-01-01
Unsteady aerodynamic models are necessary to accurately simulate forces and develop feedback controllers for wings in agile motion; however, these models are often high dimensional or incompatible with modern control techniques. Recently, reduced-order unsteady aerodynamic models have been developed for a pitching and plunging airfoil by linearizing the discretized Navier-Stokes equation with lift-force output. In this work, we extend these reduced-order models to include multiple inputs (pitch, plunge, and surge) and explicit parameterization by the pitch-axis location, inspired by Theodorsen's model. Next, we investigate the na\\"{\\i}ve application of system identification techniques to input--output data and the resulting pitfalls, such as unstable or inaccurate models. Finally, robust feedback controllers are constructed based on these low-dimensional state-space models for simulations of a rigid flat plate at Reynolds number 100. Various controllers are implemented for models linearized at base angles of ...
The Theoretical Research for the Rotor/Fuselage Unsteady Aerodynamic Interaction Problem
Directory of Open Access Journals (Sweden)
Liu Dawei
2016-07-01
Full Text Available Based on coupled unsteady panel/free-wake method, a universal analysis model was established, which provides a good prediction for the rotor/fuselage unsteady aerodynamic interaction. Considering the deficiencies of the traditional time-marching rotor free-wake algorithms, notably on stability and efficiency, the CB3D algorithm with 3rd-order accuracy is proposed. For solving the problem that part of the wake vortices may penetrate the fuselage, a “material line” rectification method with 3rd-order accuracy is proposed. An analysis for the model accuracy was then conducted to validate the accuracy of the new model, and a comparison against the available experimental data is performed. The simulated results show a good agreement with these experimental data. With the new model, several simulations are conducted for the typical rotor/fuselage aerodynamic interaction, and the results are analyzed.
Peele, E. L.; Adams, W. M., Jr.
1979-01-01
A computer program, ISAC, is described which calculates the stability and response of a flexible airplane equipped with active controls. The equations of motion relative to a fixed inertial coordinate system are formulated in terms of the airplane's rigid body motion and its unrestrained normal vibration modes. Unsteady aerodynamic forces are derived from a doublet lattice lifting surface theory. The theoretical basis for the program is briefly explained together with a description of input data and output results.
Unsteady aerodynamics of membrane wings with adaptive compliance
Kiser, Jillian; Breuer, Kenneth
2016-11-01
Membrane wings are known to provide superior aerodynamic performance at low Reynolds numbers (Re =104 -105), primarily due to passive shape adaptation to flow conditions. In addition to this passive deformation, active control of the fluid-structure interaction and resultant aerodynamic properties can be achieved through the use of dielectric elastomer actuators as the wing membrane material. When actuated, membrane pretension is decreased and wing camber increases. Additionally, actuation at resonance frequencies allows additional control over wing camber. We present results using synchronized (i) time-resolved particle image velocimetry (PIV) to resolve the flow field, (ii) 3D direct linear transformation (DLT) to recover membrane shape, (iii) lift/drag/torque measurements and (iv) near-wake hot wire anemometry measurements to characterize the fluid-structure interactions. Particular attention is paid to cases in which the vortex shedding frequency, the membrane resonance, and the actuation frequency coincide. In quantitatively examining both flow field and membrane shape at a range of actuation frequencies and vortex shedding frequencies, this work seeks to find actuation parameters that allow for active control of boundary layer separation over a range of flow conditions. Also at Naval Undersea Warfare Center, Division Newport.
APPROXIMATE FUNCTION FOR UNSTEADY AERODYNAMIC KERNEL FUNCTION OF AEROELASTIC LIFTING SURFACES
Directory of Open Access Journals (Sweden)
Erwin Sulaeman
2014-05-01
Full Text Available Normal 0 false false false EN-US X-NONE X-NONE ABSTRACT: Prediction of unsteady aerodynamic loads is still the most challenging task in flutter aeroelastic analysis. Generally the numerical estimation of steady and unsteady aerodynamic of thin lifting surface is conducted based on an integral equation relating aerodynamic pressure and normal wash velocity. The present work attempts to increase the accuracy of the prediction by using an approximate approach to evaluate kernel function occurring in the integral equation in the form of cylindrical function. Following previous approximation approach by other researchers to solve the cylindrical function for planar lifting surfaces, in the present work such approach is extended to non planar lifting surfaces. To increase the accuracy of the method, the integration region of the kernel function is divided into two parts namely near and far regions, where a nonlinear regression curve fitting technique is adapted to approximate the denominator part of the cylindrical function of each region.ABSTRAK: Penelahan daya aerodinamik tidak stabil merupakan satu tugas yang mencabar dalam menganalisis getaran aeroanjalan. Umumnya, anggaran berangka untuk daya aerodinamik stabil dan tidak stabil pada permukaan mengangkat yang nipis, adalah berdasarkan kepada persamaan kamiran di antara tekanan aerodinamik dan halaju aliran udara pada garis normal yang terhasil di bawah sayap pesawat. Kajian ini adalah bertujuan untuk menghasilkan penelahan daya aerodinamik yang lebih tepat dengan menggunakan pendekatan kira hampir untuk menilai fungsi Kernel yang terdapat dalam persamaan kamiran dalam bentuk fungsi silinder. Dengan menggunakan pendekatan kira hampir yang digunakan oleh penyelidik sebelumnya untuk menyelesaikan fungsi silinder pada permukaan mengangkat satah, kajian ini mengembangkan pendekatan tersebut kepada permukaan mengangkat tak sesatah. Untuk meningkatkan lagi ketepatan penelahan, kawasan pengamiran
Unsteady Aerodynamics on a Pitching Plunging Flat Plate
Hart, Adam; Ukeiley, Lawrence
2010-11-01
Biology has shown that natural fliers utilize unsteady flow mechanisms to enhance their lift characteristics in low Reynolds number flight regimes. This study will investigate the interaction between the leading edge vortices (LEVs) and tip vortices over a low aspect ratio flat plate being subjected to a pitch-plunge kinematic motion. Previous studies have shown the creation of stable vortices off the leading edge at the three quarter span location between times 0.25 and 0.50 in the kinematic motion. This study furthers previous knowledge by mapping the flow field around these vortex cores. This will allow for an understanding into the interaction of the LEV with tip vortices and how the LEVs convect downstream. Specifically we look to validate the interactions between these vortex systems leading to enhanced lift as has been demonstrated in very low Reynolds number numerical simulations. A combination of two dimensional and stereo Particle Image Velocimetery (PIV) is used to measure the flow field around the flat plate at various spanwise and chordwise locations. The PIV measurements are triggered by the dynamic motion rig allowing for phase averaging at key locations throughout the motion cycle.
CFD calculations on the unsteady aerodynamic characteristics of a tilt-rotor in a conversion mode
Institute of Scientific and Technical Information of China (English)
Li Peng; Zhao Qijun; Zhu Qiuxian
2015-01-01
In order to calculate the unsteady aerodynamic characteristics of a tilt-rotor in a conver-sion mode, a virtual blade model (VBM) and an real blade model (RBM) are established respec-tively. A new multi-layer moving-embedded grid technique is proposed to reduce the numerical dissipation of the tilt-rotor wake in a conversion mode. In this method, a grid system generated abound the rotor accounts for rigid blade motions, and a new searching scheme named adaptive inverse map (AIM) is established to search corresponding donor elements in the present moving-embedded grid system to translate information among the different computational zones. A dual-time method is employed to fulfill unsteady calculations on the flowfield of the tilt-rotor, and a second-order centered difference scheme considering artificial viscosity is used to calculate the flux. In order to improve the computing efficiency, the single program multiple data (SPMD) model parallel acceleration technology is adopted, according to the characteristic of the current grid system. The lift and drag coefficients of an NACA0012 airfoil, the dynamic pressure distributions below a typical rotor plane, and the sectional pressure distributions on a three-bladed Branum–Tung tilt-rotor in hover flight are calculated respectively, and the present VBM and RBM are val-idated by comparing the calculated results with available experimental data. Then, unsteady aero-dynamic forces and flowfields of an XV-15 tilt-rotor in different modes, such as a fixed conversion mode at different tilt angles (15?, 30?, 60?) and a whole conversion mode which converses from 0? to 90?, are numerically simulated by the VBM and RBM respectively. By analyses and comparisons on the simulated results of unsteady aerodynamic forces of the tilt-rotor in different modes, some meaningful conclusions about distorted blade-tip vortex distribution and unsteady aerodynamic force variation in a conversion mode are obtained, and these investigation
CFD calculations on the unsteady aerodynamic characteristics of a tilt-rotor in a conversion mode
Directory of Open Access Journals (Sweden)
Li Peng
2015-12-01
Full Text Available In order to calculate the unsteady aerodynamic characteristics of a tilt-rotor in a conversion mode, a virtual blade model (VBM and an real blade model (RBM are established respectively. A new multi-layer moving-embedded grid technique is proposed to reduce the numerical dissipation of the tilt-rotor wake in a conversion mode. In this method, a grid system generated abound the rotor accounts for rigid blade motions, and a new searching scheme named adaptive inverse map (AIM is established to search corresponding donor elements in the present moving-embedded grid system to translate information among the different computational zones. A dual-time method is employed to fulfill unsteady calculations on the flowfield of the tilt-rotor, and a second-order centered difference scheme considering artificial viscosity is used to calculate the flux. In order to improve the computing efficiency, the single program multiple data (SPMD model parallel acceleration technology is adopted, according to the characteristic of the current grid system. The lift and drag coefficients of an NACA0012 airfoil, the dynamic pressure distributions below a typical rotor plane, and the sectional pressure distributions on a three-bladed Branum–Tung tilt-rotor in hover flight are calculated respectively, and the present VBM and RBM are validated by comparing the calculated results with available experimental data. Then, unsteady aerodynamic forces and flowfields of an XV-15 tilt-rotor in different modes, such as a fixed conversion mode at different tilt angles (15°, 30°, 60° and a whole conversion mode which converses from 0° to 90°, are numerically simulated by the VBM and RBM respectively. By analyses and comparisons on the simulated results of unsteady aerodynamic forces of the tilt-rotor in different modes, some meaningful conclusions about distorted blade-tip vortex distribution and unsteady aerodynamic force variation in a conversion mode are obtained, and these
Pototzky, Anthony S.
2008-01-01
A simple matrix polynomial approach is introduced for approximating unsteady aerodynamics in the s-plane and ultimately, after combining matrix polynomial coefficients with matrices defining the structure, a matrix polynomial of the flutter equations of motion (EOM) is formed. A technique of recasting the matrix-polynomial form of the flutter EOM into a first order form is also presented that can be used to determine the eigenvalues near the origin and everywhere on the complex plane. An aeroservoelastic (ASE) EOM have been generalized to include the gust terms on the right-hand side. The reasons for developing the new matrix polynomial approach are also presented, which are the following: first, the "workhorse" methods such as the NASTRAN flutter analysis lack the capability to consistently find roots near the origin, along the real axis or accurately find roots farther away from the imaginary axis of the complex plane; and, second, the existing s-plane methods, such as the Roger s s-plane approximation method as implemented in ISAC, do not always give suitable fits of some tabular data of the unsteady aerodynamics. A method available in MATLAB is introduced that will accurately fit generalized aerodynamic force (GAF) coefficients in a tabular data form into the coefficients of a matrix polynomial form. The root-locus results from the NASTRAN pknl flutter analysis, the ISAC-Roger's s-plane method and the present matrix polynomial method are presented and compared for accuracy and for the number and locations of roots.
Bird Flight as a Model for a Course in Unsteady Aerodynamics
Jacob, Jamey; Mitchell, Jonathan; Puopolo, Michael
2014-11-01
Traditional unsteady aerodynamics courses at the graduate level focus on theoretical formulations of oscillating airfoil behavior. Aerodynamics students with a vision for understanding bird-flight and small unmanned aircraft dynamics desire to move beyond traditional flow models towards new and creative ways of appreciating the motion of agile flight systems. High-speed videos are used to record kinematics of bird flight, particularly barred owls and red-shouldered hawks during perching maneuvers, and compared with model aircraft performing similar maneuvers. Development of a perching glider and associated control laws to model the dynamics are used as a class project. Observations are used to determine what different species and sizes of birds share in their methods to approach a perch under similar conditions. Using fundamental flight dynamics, simplified models capable of predicting position, attitude, and velocity of the flier are developed and compared with the observations. By comparing the measured data from the videos and predicted and measured motions from the glider models, it is hoped that the students gain a better understanding of the complexity of unsteady aerodynamics and aeronautics and an appreciation for the beauty of avian flight.
Directory of Open Access Journals (Sweden)
T. M. Huang
2017-01-01
Full Text Available High-speed passenger car requires a lighter weight for improving power performance and reducing fuel consumption; a car with higher-speed and lighter weight will lead to the passenger car more sensitive to the crosswind, which will affect the stability and drivability of the passenger car. This study employs the fully-coupled method to investigate a passenger car subjected “1-cos” crosswind with consideration of the vehicle motion. Large eddy simulation (LES and dynamic mesh is adopted to investigate the unsteady aerodynamic, and the vehicle is treated as a three-freedom-system and driver’s control is considered to investigate the vehicle dynamic. The one-way simulation and quasi-steady simulation are also conducted to compare with the fully-coupled simulation. The results of the three simulation methods show large difference. The peak value of the lateral displacement in fully-coupled simulation is the smallest between the three simulation approaches. While the change of aerodynamic loads and vehicle motion in fully-coupled simulation is more complicated than in one-way and quasi-steady simulation. These results clearly indicate the significance of including of the unsteady aerodynamic loads in passenger car moving analysis.
Linearized Unsteady Aerodynamic Analysis of the Acoustic Response to Wake/Blade-Row Interaction
Verdon, Joseph M.; Huff, Dennis L. (Technical Monitor)
2001-01-01
The three-dimensional, linearized Euler analysis, LINFLUX, is being developed to provide a comprehensive and efficient unsteady aerodynamic scheme for predicting the aeroacoustic and aeroelastic responses of axial-flow turbomachinery blading. LINFLUX couples a near-field, implicit, wave-split, finite-volume solution to far-field acoustic eigensolutions, to predict the aerodynamic responses of a blade row to prescribed structural and aerodynamic excitations. It is applied herein to predict the acoustic responses of a fan exit guide vane (FEGV) to rotor wake excitations. The intent is to demonstrate and assess the LINFLUX analysis via application to realistic wake/blade-row interactions. Numerical results are given for the unsteady pressure responses of the FEGV, including the modal pressure responses at inlet and exit. In addition, predictions for the modal and total acoustic power levels at the FEGV exit are compared with measurements. The present results indicate that the LINFLUX analysis should be useful in the aeroacoustic design process, and for understanding the three-dimensional flow physics relevant to blade-row noise generation and propagation.
Unsteady aerodynamics of reverse flow dynamic stall on an oscillating blade section
Lind, Andrew H.; Jones, Anya R.
2016-07-01
Wind tunnel experiments were performed on a sinusoidally oscillating NACA 0012 blade section in reverse flow. Time-resolved particle image velocimetry and unsteady surface pressure measurements were used to characterize the evolution of reverse flow dynamic stall and its sensitivity to pitch and flow parameters. The effects of a sharp aerodynamic leading edge on the fundamental flow physics of reverse flow dynamic stall are explored in depth. Reynolds number was varied up to Re = 5 × 105, reduced frequency was varied up to k = 0.511, mean pitch angle was varied up to 15∘, and two pitch amplitudes of 5∘ and 10∘ were studied. It was found that reverse flow dynamic stall of the NACA 0012 airfoil is weakly sensitive to the Reynolds numbers tested due to flow separation at the sharp aerodynamic leading edge. Reduced frequency strongly affects the onset and persistence of dynamic stall vortices. The type of dynamic stall observed (i.e., number of vortex structures) increases with a decrease in reduced frequency and increase in maximum pitch angle. The characterization and parameter sensitivity of reverse flow dynamic stall given in the present work will enable the development of a physics-based analytical model of this unsteady aerodynamic phenomenon.
8th International Symposium on Unsteady Aerodynamics and Aeroelasticity of Turbomachines
1998-01-01
Twenty-one years have passed since the first symposium in this series was held in Paris (1976). Since then there have been meetings in Lausanne (1980), Cambridge (1984), Aachen (1987), Beijing (1989), Notre Dame (1991) and Fukuoka (1994). During this period a tremendous development in the field of unsteady aerodynamics and aeroelasticity in turbomachines has taken place. As steady-state flow conditions become better known, and as blades in the turbomachine are constantly pushed towards lower weight, and higher load and efficiency, the importance of unsteady phenomena appear more clearly. th The 8 Symposium was, as the previous ones, of high quality. Furthermore, it presented the audience with the latest developments in experimental, numerical and theoretical research. More papers than ever before were submitted to the conference. As the organising committee wanted to preserve the uniqueness of the symposium by having single sessions, and thus mingle speakers and audience with different backgrounds in this int...
Institute of Scientific and Technical Information of China (English)
Toshiaki KANEMOTO; Seita SEKI; Kazunori IDENO; Ahmed Mohamed GALAL
2005-01-01
It is desired to increase the rotational speed of the core engine of the turbofan so as to get the best efficiency for the next leap of engine technology. The conventional mechanism in which the front fan is directly connected to the output shaft of a core engine, have a limit of increasing the spool speed, because the fan diameter is very large. The authors have proposed a new driving system in which the front fan is driven through the aerodynamic torque converter. The front fan can work at the best performance at slower speed while the core engine runs more efficiently at higher speed. Continuously, this paper discusses the response of the front fan in the unsteady operation of the core engine, accompanying with the internal flow. The system has the acceptable responsibility in the unsteady operation which is very important for the aircrafts.
The Torsional Vibration of Turbo Axis Induced by Unsteady Aerodynamic Force on Rotor blade
Institute of Scientific and Technical Information of China (English)
ChenZuoyi; WuXiaofeng
1998-01-01
An algorithm for computing the 3-D oscillating flow field of the balde passage under the torsional vibration of the rotor is applied to analyze the stability in turbomachines.The induced flow field responding to blade vibration is computed by Oscillating Fluid Mechanics Method and parametric Polynomial Method.After getting the solution of the unsteady flow field,the work done by the unsteay aerodynamic force acting on the blade can be obtained.The negative or positive work is the criterion of the aeroelastic stability.Numerical results indicate that there are instabilities of the torsional vibration in some frequency bands.
Gangwani, S. T.
1985-01-01
A reliable rotor aeroelastic analysis operational that correctly predicts the vibration levels for a helicopter is utilized to test various unsteady aerodynamics models with the objective of improving the correlation between test and theory. This analysis called Rotor Aeroelastic Vibration (RAVIB) computer program is based on a frequency domain forced response analysis which utilizes the transfer matrix techniques to model helicopter/rotor dynamic systems of varying degrees of complexity. The results for the AH-1G helicopter rotor were compared with the flight test data during high speed operation and they indicated a reasonably good correlation for the beamwise and chordwise blade bending moments, but for torsional moments the correlation was poor. As a result, a new aerodynamics model based on unstalled synthesized data derived from the large amplitude oscillating airfoil experiments was developed and tested.
Stochastic model for aerodynamic force dynamics on wind turbine blades in unsteady wind inflow
Luhur, Muhammad Ramzan; Kühn, Martin; Wächter, Matthias
2015-01-01
The paper presents a stochastic approach to estimate the aerodynamic forces with local dynamics on wind turbine blades in unsteady wind inflow. This is done by integrating a stochastic model of lift and drag dynamics for an airfoil into the aerodynamic simulation software AeroDyn. The model is added as an alternative to the static table lookup approach in blade element momentum (BEM) wake model used by AeroDyn. The stochastic forces are obtained for a rotor blade element using full field turbulence simulated wind data input and compared with the classical BEM and dynamic stall models for identical conditions. The comparison shows that the stochastic model generates additional extended dynamic response in terms of local force fluctuations. Further, the comparison of statistics between the classical BEM, dynamic stall and stochastic models' results in terms of their increment probability density functions gives consistent results.
Barlas, Thanasis; Jost, Eva; Pirrung, Georg; Tsiantas, Theofanis; Riziotis, Vasilis; Navalkar, Sachin T.; Lutz, Thorsten; van Wingerden, Jan-Willem
2016-09-01
Simulations of a stiff rotor configuration of the DTU 10MW Reference Wind Turbine are performed in order to assess the impact of prescribed flap motion on the aerodynamic loads on a blade sectional and rotor integral level. Results of the engineering models used by DTU (HAWC2), TUDelft (Bladed) and NTUA (hGAST) are compared to the CFD predictions of USTUTT-IAG (FLOWer). Results show fairly good comparison in terms of axial loading, while alignment of tangential and drag-related forces across the numerical codes needs to be improved, together with unsteady corrections associated with rotor wake dynamics. The use of a new wake model in HAWC2 shows considerable accuracy improvements.
Shimada, Kenji; Ishihara, Takeshi
2012-01-01
It is well known that a bluff body cross-section exhibits various kinds of aerodynamic instabilities such as vortex-induced vibration, galloping and torsional flutter. Since these cross-sections are used in long-span bridges and tall buildings, it is important to predict their occurrence in wind resistant structural design. In this paper, the authors make a series of comparisons of unsteady wind forces, unsteady pressure distributions and free vibration responses between previously conducted studies and an unsteady two-dimensional k-ɛ model for rectangular cross-sections with cross-sectional ratios of 2 and 4 in a smooth uniform flow in order to verify computational predictability of aerodynamic instabilities. As a result, the computation successfully predicted the onset velocities and responses of these aerodynamic instabilities for these cross-sectional ratios, which are common to tall buildings and long bridges.
Estimation of unsteady aerodynamics in the wake of a freely flying European starling
Ben-Gida, Hadar; Taylor, Zachary J; Bezner-Kerr, Wayne; Guglielmo, Christopher G; Kopp, Gregory A; Gurka, Roi
2013-01-01
Wing flapping is one of the most widespread propulsion methods found in nature; however, the current understanding of the aerodynamics in bird wakes is incomplete. The role of the unsteady motion in the flow and its contribution to the aerodynamics is still an open question. In the current study, the wake of a freely flying European starling has been investigated using long-duration high-speed Particle Image Velocimetry (PIV) in the near wake. Kinematic analysis of the wings and body of the bird has been performed using additional high-speed cameras that recorded the bird movement simultaneously with the PIV measurements. The wake evolution of four complete wingbeats has been characterized through reconstruction of the time resolved data, and the aerodynamics in the wake have been analyzed in terms of the streamwise forces acting on the bird. The profile drag from classical aerodynamics was found to be positive during most of the wingbeat cycle, yet kinematic images show that the bird does not decelerate. It ...
Unsteady Aerodynamics and Vortex-sheet Formation of A Two-dimensional Airfoil
Xia, Xi
2016-01-01
Unsteady inviscid flow models of wings and airfoils have been developed to study the aerodynamics of natural and man-made flyers. Vortex methods have been extensively applied to reduce the dimensionality of these aerodynamic models, based on the proper estimation of the strength and distribution of the vortices in the wake. In such modeling approaches, one of the most fundamental questions is how the vortex sheets are generated and released from sharp edges. To determine the formation of the trailing-edge vortex sheet, the classical Kutta condition can be extended to unsteady situations by realizing that a flow cannot turn abruptly around a sharp edge. This condition can be readily applied to a flat plate or an airfoil with cusped trailing edge since the direction of the forming vortex sheet is known to be tangential to the trailing edge. However, for a finite-angle trailing edge, or in the case of flow separation away from a sharp corner, the direction of the forming vortex sheet is ambiguous. To remove any ...
Unsteady transonic aerodynamics and aeroelastic calculations at low-supersonic freestreams
Guruswamy, Guru P.; Goorjian, Peter M.
1988-01-01
A computational procedure is presented to simulate transonic unsteady flows and corresponding aeroelasticity of wings at low-supersonic freestreams. The flow is modeled by using the transonic small-perturbation theory. The structural equations of motions are modeled using modal equations of motion directly coupled with aerodynamics. Supersonic freestreams are simulated by properly accounting for the boundary conditions based on pressure waves along the flow characteristics in streamwise planes. The flow equations are solved using the time-accurate, alternating-direction implicit finite-difference scheme. The coupled aeroelastic equations of motion are solved by an integration procedure based on the time-accurate, linear-acceleration method. The flow modeling is verified by comparing calculations with experiments for both steady and unsteady flows at supersonic freestreams. The unsteady computations are made for oscillating wings. Comparisons of computed results with experiments show good agreement. Aeroelastic responses are computed for a rectangular wing at Mach numbers ranging from subtransonic to upper-transonic (supersonic) freestreams. The extension of the transonic dip into the upper transonic regime is illustrated.
Unsteady aerodynamic analysis for offshore floating wind turbines under different wind conditions.
Xu, B F; Wang, T G; Yuan, Y; Cao, J F
2015-02-28
A free-vortex wake (FVW) model is developed in this paper to analyse the unsteady aerodynamic performance of offshore floating wind turbines. A time-marching algorithm of third-order accuracy is applied in the FVW model. Owing to the complex floating platform motions, the blade inflow conditions and the positions of initial points of vortex filaments, which are different from the fixed wind turbine, are modified in the implemented model. A three-dimensional rotational effect model and a dynamic stall model are coupled into the FVW model to improve the aerodynamic performance prediction in the unsteady conditions. The effects of floating platform motions in the simulation model are validated by comparison between calculation and experiment for a small-scale rigid test wind turbine coupled with a floating tension leg platform (TLP). The dynamic inflow effect carried by the FVW method itself is confirmed and the results agree well with the experimental data of a pitching transient on another test turbine. Also, the flapping moment at the blade root in yaw on the same test turbine is calculated and compares well with the experimental data. Then, the aerodynamic performance is simulated in a yawed condition of steady wind and in an unyawed condition of turbulent wind, respectively, for a large-scale wind turbine coupled with the floating TLP motions, demonstrating obvious differences in rotor performance and blade loading from the fixed wind turbine. The non-dimensional magnitudes of loading changes due to the floating platform motions decrease from the blade root to the blade tip.
Effects of unsteady deformation of flapping wing on its aerodynamic forces
Institute of Scientific and Technical Information of China (English)
DU Gang; SUN Mao
2008-01-01
Effects of unsteady deformation of a flapping model insect wing on its aerodynamic force production are studied by solving the Navier-Stokes equations on a dynamically deforming grid.Aerodynamic forces on the flapping wing are not much affected by considerable twist,but affected by camber deformation.The effect of combined camber and twist deformation is similar to that of camber deformation.With a deformation of 6% camber and 20°twist(typical values observed for wings of many insects),lift is increased bv 10%～20%and lift-to-drag ratio by around 10%compared with the case of a rigid flat-plate wing.As a result.the deformation can increase the maximum lift coefficient of an insect.and reduce its power requirement for flight.For example,for a hovering bumblebee with dynamically deforming wings(6%camber and 20°twist),aerodynamic power required is reduced by about 16%compared with the case of rigid wings.
Subsonic Indicial Aerodynamics for Aerofoil's Unsteady Loads via Numerical and Analytical Methods
Berci, Marco
2016-01-01
This study deals with generating aerodynamic indicial-admittance functions for predicting the unsteady lift of two-dimensional aerofoils in subsonic flow, using approximate numerical and analytical formulations. Both a step-change in the angle of attack and a sharp-edge gust are suitably considered as small perturbations. Novel contributions concern both a systematic analysis of the computational simulations process and an effective theoretical synthesis of its outcome, providing with sound cross-validation. Good practice for generating the indicial-admittance functions via computational fluid dynamics is first investigated for several Mach numbers, angles of attack and aerofoil profiles. Convenient analytical approximations of such indicial functions are then obtained by generalising those available for incompressible flow, taking advantage of acoustic wave theory for the non-circulatory airload and Prandtl-Glauert's scalability rule for the circulatory airload. An explicit parametric formula is newly propos...
Directory of Open Access Journals (Sweden)
Xu Liu
2015-01-01
Full Text Available Unsteady aerodynamic system modeling is widely used to solve the dynamic stability problems encountering aircraft design. In this paper, single degree-of-freedom (SDF vibration model and forced simple harmonic motion (SHM model for dynamic derivative prediction are developed on the basis of modified Etkin model. In the light of the characteristics of SDF time domain solution, the free vibration identification methods for dynamic stability parameters are extended and applied to the time domain numerical simulation of blunted cone calibration model examples. The dynamic stability parameters by numerical identification are no more than 0.15% deviated from those by experimental simulation, confirming the correctness of SDF vibration model. The acceleration derivatives, rotary derivatives, and combination derivatives of Army-Navy Spinner Rocket are numerically identified by using unsteady N-S equation and solving different SHV patterns. Comparison with the experimental result of Army Ballistic Research Laboratories confirmed the correctness of the SHV model and dynamic derivative identification. The calculation result of forced SHM is better than that by the slender body theory of engineering approximation. SDF vibration model and SHM model for dynamic stability parameters provide a solution to the dynamic stability problem encountering aircraft design.
Tiffany, S. H.; Adams, W. M., Jr.
1984-01-01
A technique which employs both linear and nonlinear methods in a multilevel optimization structure to best approximate generalized unsteady aerodynamic forces for arbitrary motion is described. Optimum selection of free parameters is made in a rational function approximation of the aerodynamic forces in the Laplace domain such that a best fit is obtained, in a least squares sense, to tabular data for purely oscillatory motion. The multilevel structure and the corresponding formulation of the objective models are presented which separate the reduction of the fit error into linear and nonlinear problems, thus enabling the use of linear methods where practical. Certain equality and inequality constraints that may be imposed are identified; a brief description of the nongradient, nonlinear optimizer which is used is given; and results which illustrate application of the method are presented.
Directory of Open Access Journals (Sweden)
Somashekar V
2014-01-01
Full Text Available A Micro air vehicle (MAV is defined as class of unmanned air vehicle (UAV having a linear dimension of less than 15 centimeters and a mass of less than 100 grams with flight speeds of 6 to 12 meters per second. MAVs fall within a Reynolds number (Re range of 50,000 and 120,000, in which many causes of unsteady aerodynamic effects are not fully understood. The research field of low Reynolds number aerodynamics is currently an active one, with many defence organizations, universities, and corporations working towards a better understanding of the physical processes of this aerodynamic regime. In the present work, it is proposed to study the unsteady aerodynamic analysis of 2D airfoil using CFD software and Xfoil panel code method. The various steps involved in this work are geometric modelling using CATIA V5R17, meshing using ICEM CFD, and solution and postprocessing through FLUENT. The finite control volume analysis and Xfoil panel code method has been carried out to predict aerodynamic characteristics such as lift coefficients, drag coefficients, moment coefficients, pressure coefficients, and flow visualization. The lift and drag coefficients were compared for all the simulations with experimental results. It was observed that for the 2D airfoil, lift and drag both compared well for the midrange angle of attack from −10 to 15 degree AOA.
National Aeronautics and Space Administration — ZONA Technology proposes to develop an innovative nonlinear structural reduced order model (ROM) - nonlinear aerodynamic ROM methodology for the inflatable...
Friedmann, P. P.; Robinson, L. H.
1988-01-01
This paper describes the incorporation of finite-state, time-domain aerodynamics in a flag-lag-torsional aeroelastic stability and response analysis in forward flight. Improvements to a previous formulation are introduced which eliminate spurious singularities. The methodology for solving the aeroelastic stability and response problems with augmented states, in the time domain, is presented using an implicit formulation. Results describing the aeroelastic behavior of soft and stiff in-plane hingeless rotor blades, in forward flight, are presented to illustrate the sensitivity of both the stability and response problems to time domain unsteady aerodynamics.
Friedmann, P. P.; Robinson, L. H.
1988-01-01
This paper describes the incorporation of finite-state, time-domain aerodynamics in a flag-lag-torsional aeroelastic stability and response analysis in forward flight. Improvements to a previous formulation are introduced which eliminate spurious singularities. The methodology for solving the aeroelastic stability and response problems with augmented states, in the time domain, is presented using an implicit formulation. Results describing the aeroelastic behavior of soft and stiff in-plane hingeless rotor blades, in forward flight, are presented to illustrate the sensitivity of both the stability and response problems to time domain unsteady aerodynamics.
Computationally efficient simulation of unsteady aerodynamics using POD on the fly
Moreno-Ramos, Ruben; Vega, José M.; Varas, Fernando
2016-12-01
Modern industrial aircraft design requires a large amount of sufficiently accurate aerodynamic and aeroelastic simulations. Current computational fluid dynamics (CFD) solvers with aeroelastic capabilities, such as the NASA URANS unstructured solver FUN3D, require very large computational resources. Since a very large amount of simulation is necessary, the CFD cost is just unaffordable in an industrial production environment and must be significantly reduced. Thus, a more inexpensive, yet sufficiently precise solver is strongly needed. An opportunity to approach this goal could follow some recent results (Terragni and Vega 2014 SIAM J. Appl. Dyn. Syst. 13 330-65 Rapun et al 2015 Int. J. Numer. Meth. Eng. 104 844-68) on an adaptive reduced order model that combines ‘on the fly’ a standard numerical solver (to compute some representative snapshots), proper orthogonal decomposition (POD) (to extract modes from the snapshots), Galerkin projection (onto the set of POD modes), and several additional ingredients such as projecting the equations using a limited amount of points and fairly generic mode libraries. When applied to the complex Ginzburg-Landau equation, the method produces acceleration factors (comparing with standard numerical solvers) of the order of 20 and 300 in one and two space dimensions, respectively. Unfortunately, the extension of the method to unsteady, compressible flows around deformable geometries requires new approaches to deal with deformable meshes, high-Reynolds numbers, and compressibility. A first step in this direction is presented considering the unsteady compressible, two-dimensional flow around an oscillating airfoil using a CFD solver in a rigidly moving mesh. POD on the Fly gives results whose accuracy is comparable to that of the CFD solver used to compute the snapshots.
Rowe, W. S.; Sebastian, J. D.; Petrarca, J. R.
1979-01-01
Results of theoretical and numerical investigations conducted to develop economical computing procedures were applied to an existing computer program that predicts unsteady aerodynamic loadings caused by leading and trailing edge control surface motions in subsonic compressible flow. Large reductions in computing costs were achieved by removing the spanwise singularity of the downwash integrand and evaluating its effect separately in closed form. Additional reductions were obtained by modifying the incremental pressure term that account for downwash singularities at control surface edges. Accuracy of theoretical predictions of unsteady loading at high reduced frequencies was increased by applying new pressure expressions that exactly satisified the high frequency boundary conditions of an oscillating control surface. Comparative computer result indicated that the revised procedures provide more accurate predictions of unsteady loadings as well as providing reduction of 50 to 80 percent in computer usage costs.
Nonlinear switched models for control of unsteady forces on a rapidly pitching airfoil
Dawson, Scott; Brunton, Steven; Rowley, Clarence
2013-11-01
The unsteady aerodynamic forces incident on a pitching flat plate airfoil at a Reynolds number of 100 are investigated through direct numerical simulation. Linear state-space models, identified from impulse response data via the eigensystem realization algorithm, are used to accurately track rapid changes in lift coefficient through either feedback or feedforward control, even in the presence of gust disturbances. We develop a technique to project between states of linear models obtained at different angles of attack using primal and pseudo-adjoint balanced POD modes. This allows for the formation of a nonlinear switched model that is accurate over a wide range of angles of attack, in both pre- and post-stall regimes. We additionally investigate phenomena that are not captured by linear models, such as an increase in mean lift that occurs when vortex shedding frequencies are excited. The effect of changing the pitch axis is also investigated, where it is found that pitching aft of the mid-chord results in right half plane zeros that increase the difficulty of the control problem. This work was supported by AFOSR grant FA9550-12-1-0075.
Srivastava, R.; Reddy, T. S. R.
1996-01-01
This guide describes the input data required, for steady or unsteady aerodynamic and aeroelastic analysis of propellers and the output files generated, in using PROP3D. The aerodynamic forces are obtained by solving three dimensional unsteady, compressible Euler equations. A normal mode structural analysis is used to obtain the aeroelastic equations, which are solved using either time domain or frequency domain solution method. Sample input and output files are included in this guide for steady aerodynamic analysis of single and counter-rotation propellers, and aeroelastic analysis of single-rotation propeller.
Nonlinear prediction of the aerodynamic loads on lifting surfaces
Kandil, O. A.; Mook, D. T.; Nayfeh, A. H.
1974-01-01
A numerical procedure is used to predict the nonlinear aerodynamic characteristics of lifting surfaces of low aspect ratio at high angles of attack for low subsonic Mach numbers. The procedure utilizes a vortex-lattice method and accounts for separation at sharp tips and leading edges. The shapes of the wakes emanating from the edges are predicted, and hence the nonlinear characteristics are calculated. Parallelogram and delta wings are presented as numerical examples. The numerical results are in good agreement with the experimental data.
Non-linear dynamics of inlet film thickness during unsteady rolling process
Fu, Kuo; Zang, Yong; Gao, Zhiying; Qin, Qin; Wu, Diping
2016-05-01
The inlet film thickness directly affects film and stress distribution of rolling interfaces. Unsteady factors, such as unsteady back tension, may disturb the inlet film thickness. However, the current models of unsteady inlet film thickness lack unsteady disturbance factors and do not take surface topography into consideration. In this paper, based on the hydrodynamic analysis of inlet zone an unsteady rolling film model which concerns the direction of surface topography is built up. Considering the small fluctuation of inlet angle, absolute reduction, reduction ratio, inlet strip thickness and roll radius as the input variables and the fluctuation of inlet film thickness as the output variable, the non-linear relationship between the input and output is discussed. The discussion results show that there is 180° phase difference between the inlet film thickness and the input variables, such as the fluctuant absolute reduction, the fluctuant reduction ratio and non-uniform inlet strip thickness, but there is no phase difference between unsteady roll radius and the output. The inlet angle, the steady roll radius and the direction of surface topography have significant influence on the fluctuant amplitude of unsteady inlet film thickness. This study proposes an analysis method for unsteady inlet film thickness which takes surface topography and new disturbance factors into consideration.
National Aeronautics and Space Administration — ZONA proposes a phase II effort to fully develop a comprehensive methodology for aeroelastic predictions of the nonlinear aerodynamic/aerothermodynamic - structure...
Petrarca, J. R.; Harrison, B. A.; Redman, M. C.; Rowe, W. S.
1979-01-01
A digital computer program was developed to calculate unsteady loadings caused by motions of lifting surfaces with leading edge and trailing edge controls based on the subsonic kernel function approach. The pressure singularities at hinge line and side edges were extracted analytically as a preliminary step to solving the integral equation of collocation. The program calculates generalized aerodynamic forces for user supplied deflection modes. Optional intermediate output includes pressure at an array of points, and sectional generalized forces. From one to six controls on the half span can be accomodated.
Energy Technology Data Exchange (ETDEWEB)
Yamada, H.; Miyata, T. [Yokohama National Univ. (Japan). Faculty of Engineering; Nakajima, S. [Yokohama National Univ., Yokohama (Japan). Graduate School
1996-04-21
In wind resistance design of long span bridge, as the vibration found in long span bridges is very complicated, the estimation with high precision of the unsteady aerodynamic force acting on structures in complicated motion becomes more and more important. In this paper, as a problem to directly identify the parameter by using the observation hysteresis response obtained from wind tunnel test, the problems existing in combining the system identification into unsteady aerodynamic force estimation were indicated. Then, newly developed flexible method in extension relating to two dimensional aerodynamic force measurement concerning composite flutter was proposed. Using the wind tunnel test response observation data obtained from two dimensional rigid model, and from the estimated results of unsteady aerodynamic force, it is possible to obtain stable results in the relationship among the plural eigenvalues displaying identified vibration frequency and attenuation rate with the reduced wind velocity. As a new unsteady aerodynamic force measuring method, the method proposed by this study is considered to be very useful. 6 refs., 5 figs., 1 tab.
Ferreira, C.; Gonzalez, A.; Baldacchino, D.; Aparicio, M.; Gómez, S.; Munduate, X.; Garcia, N. R.; Sørensen, J. N.; Jost, E.; Knecht, S.; Lutz, T.; Chassapogiannis, P.; Diakakis, K.; Papadakis, G.; Voutsinas, S.; Prospathopoulos, J.; Gillebaart, T.; van Zuijlen, A.
2016-09-01
The FP7 AdVanced Aerodynamic Tools for lArge Rotors - Avatar project aims to develop and validate advanced aerodynamic models, to be used in integral design codes for the next generation of large scale wind turbines (10-20MW). One of the approaches towards reaching rotors for 10-20MW size is the application of flow control devices, such as flaps. In Task 3.2: Development of aerodynamic codes for modelling of flow devices on aerofoils and, rotors of the Avatar project, aerodynamic codes are benchmarked and validated against the experimental data of a DU95W180 airfoil in steady and unsteady flow, for different angle of attack and flap settings, including unsteady oscillatory trailing-edge-flap motion, carried out within the framework of WP3: Models for Flow Devices and Flow Control, Task 3.1: CFD and Experimental Database. The aerodynamics codes are: AdaptFoil2D, Foil2W, FLOWer, MaPFlow, OpenFOAM, Q3UIC, ATEFlap. The codes include unsteady Eulerian CFD simulations with grid deformation, panel models and indicial engineering models. The validation cases correspond to 18 steady flow cases, and 42 unsteady flow cases, for varying angle of attack, flap deflection and reduced frequency, with free and forced transition. The validation of the models show varying degrees of agreement, varying between models and flow cases.
Directory of Open Access Journals (Sweden)
M. T. Schobeiri
2000-01-01
Full Text Available Aerodynamic and heat transfer investigations were done on a constant curvature curved plate in a subsonic wind tunnel facility for various wake passing frequencies and zero pressure gradient conditions. Steady and unsteady boundary layer transition measurements were taken on the concave surface of the curved plate at different wake passing frequencies where a rotating squirrel-cage generated the unsteady wake flow. The data were analyzed using timeaveraged and ensemble-averaged techniques to provide insight into the growth of the boundary layer and transition. Ensemble-averaged turbulence intensity contours in the temporal spatial domain showed that transition was induced for increasing wake passing frequency and structure. The local heat transfer coefficient distribution for the concave and convex surface was determined at those wake passing frequencies using a liquid crystal heat transfer measurement technique. Detailed aerodynamic and heat transfer investigations showed that higher wake passing frequency caused transition to occur earlier on the concave surface. Local Stanton numbers were also calculated on the concave surface and compared with Stanton numbers predicted using a differential boundary layer and heat transfer calculation method. On the convex side, no effect of wake passing frequency on heat transfer was observed due to a separation bubble that induced transition.
A versatile low-dimensional vortex model for investigating unsteady aerodynamics
Darakananda, Darwin; Eldredge, Jeff D.
2016-11-01
In previous work, we demonstrated a hybrid vortex sheet/point vortex model that captures the non-linear aerodynamics of a plate translating at a high angle of attack. We used vortex sheets to model the shear layers emerging from the plate, and point vortices to capture the effect of the coherent vortex structures. In this work, we introduce modifications that allow the model to work for a larger range of plate kinematics over longer periods of time. First, following the example of Ramesh et al., we relax the Kutta condition at the leading edge and determine vorticity flux based on a suction parameter instead. To prevent the vortex sheet from becoming unstable near the resulting singular edge, we explicitly filter out short-wave disturbances along the sheet while redistributing the sheet's control points. Second, by looking for intersections between the vortex sheets and any repelling Lagrangian coherent structures, the model can detect the formation of new coherent vortices. Trailing portions of the sheets that become dynamically distinct from the shear layers are rolled up into point vortices. We test these modifications on a variety of problems, including pitch-up, impulsive translation at low angles of attack, as well as flow response to pulse actuation near the leading edge. This work has been supported by AFOSR, under award FA9550-14-1-0328.
Nonlinear Aerodynamics-Structure Time Simulation for HALE Aircraft Design/Analysis Project
National Aeronautics and Space Administration — Time simulation of a nonlinear aerodynamics model (NA) developed at Virginia Tech coupled with a nonlinear structure model (NS) is proposed as a design/analysis...
DEFF Research Database (Denmark)
Skrzypinski, Witold Robert
Wind turbine blade vibrations at standstill conditions were investigated in the present work. These included vortex-induced and stall-induced vibrations. Thus, it was investigated whether the stand still vibrations are vortex-induced, stall-induced or a combination of both types. The work comprised...... limits. The motivation for it was that the standard aerodynamics existing in state-of-the-art aeroelastic codes is effectively quasi-steady in deep stall. If such an assumption was incorrect, these codes could predict stall-induced vibrations inaccurately. The main conclusion drawn from these analyzes...... was that even a relatively low amount of temporal lag in the aerodynamic response may significantly increase the aerodynamic damping and therefore influence the aeroelastic stability limits, relative to quasisteady aerodynamic response. Two- and three-dimensional CFD computations included non-moving, prescribed...
Unsteady Aerodynamic Simulations of a Finned Projectile at a Supersonic Speed With Jet Interaction
2014-06-01
The conical nose is 2.84 cal. long and is followed by a 7.16-cal cylindrical section. Four rectangular planform fins are located on the back end of...Turbulence Modeling for Unsteady Flow With Acoustic Resonance ; AIAA Paper 00-0473. Presented at 38th AIAA Aerospace Sciences Conference, Reno, NV
Panda, Jayatana; Martin, Fred W.; Sutliff, Daniel L.
2008-01-01
At the wake of the Columbia (STS-107) accident it was decided to remove the Protuberance Aerodynamic Load (PAL) Ramp that was originally intended to protect various protuberances outside of the Space Shuttle External Tank from high buffet load induced by cross-flows at transonic speed. In order to establish the buffet load without the PAL ramp, a wind tunnel test was conducted where segments of the protuberances were instrumented with dynamic pressure transducers; and power-spectra of sectional lift and drag forces at various span-wise locations between two adjacent support brackets were measured under different cross flow angles, Mach number and other conditions. Additionally, frequency-dependent spatial correlations between the sectional forces were also established. The sectional forces were then adjusted by the correlation length to establish span-averaged spectra of normal and lateral forces that can be suitably "added" to various other unsteady forces encountered by the protuberance. This paper describes the methodology used for calculating the correlation-adjusted power spectrum of the buffet load. A second part of the paper describes wind-tunnel results on the difference in the buffet load on the protuberances with and without the PAL ramp. In general when the ramp height is the same as that of the protuberance height, such as that found on the liquid Oxygen part of the tank, the ramp is found to cause significant reduction of the unsteady aerodynamic load. However, on the liquid Hydrogen part of the tank, where the Oxygen feed-line is far larger in diameter than the height of the PAL ramp, little protection is found to be available to all but the Cable Tray.
Viscous-Inviscid Methods in Unsteady Aerodynamic Analysis of Bio-Inspired Morphing Wings
Dhruv, Akash V.
Flight has been one of the greatest realizations of human imagination, revolutionizing communication and transportation over the years. This has greatly influenced the growth of technology itself, enabling researchers to communicate and share their ideas more effectively, extending the human potential to create more sophisticated systems. While the end product of a sophisticated technology makes our lives easier, its development process presents an array of challenges in itself. In last decade, scientists and engineers have turned towards bio-inspiration to design more efficient and robust aerodynamic systems to enhance the ability of Unmanned Aerial Vehicles (UAVs) to be operated in cluttered environments, where tight maneuverability and controllability are necessary. Effective use of UAVs in domestic airspace will mark the beginning of a new age in communication and transportation. The design of such complex systems necessitates the need for faster and more effective tools to perform preliminary investigations in design, thereby streamlining the design process. This thesis explores the implementation of numerical panel methods for aerodynamic analysis of bio-inspired morphing wings. Numerical panel methods have been one of the earliest forms of computational methods for aerodynamic analysis to be developed. Although the early editions of this method performed only inviscid analysis, the algorithm has matured over the years as a result of contributions made by prominent aerodynamicists. The method discussed in this thesis is influenced by recent advancements in panel methods and incorporates both viscous and inviscid analysis of multi-flap wings. The surface calculation of aerodynamic coefficients makes this method less computationally expensive than traditional Computational Fluid Dynamics (CFD) solvers available, and thus is effective when both speed and accuracy are desired. The morphing wing design, which consists of sequential feather-like flaps installed
DEFF Research Database (Denmark)
Ferreira, C.; Gonzalez, A.; Baldacchino, D.;
2016-01-01
The FP7 AdVanced Aerodynamic Tools for lArge Rotors - Avatar project aims to develop and validate advanced aerodynamic models, to be used in integral design codes for the next generation of large scale wind turbines (10-20MW). One of the approaches towards reaching rotors for 10-20MW size...... is the application of flow control devices, such as flaps. In Task 3.2: Development of aerodynamic codes for modelling of flow devices on aerofoils and, rotors of the Avatar project, aerodynamic codes are benchmarked and validated against the experimental data of a DU95W180 airfoil in steady and unsteady flow......, for different angle of attack and flap settings, including unsteady oscillatory trailing-edge-flap motion, carried out within the framework of WP3: Models for Flow Devices and Flow Control, Task 3.1: CFD and Experimental Database. The aerodynamics codes are: AdaptFoil2D, Foil2W, FLOWer, MaPFlow, OpenFOAM, Q3UIC...
Prediction of Ship Unsteady Maneuvering in Calm Water by a Fully Nonlinear Ship Motion Model
Directory of Open Access Journals (Sweden)
Ray-Qing Lin
2012-01-01
Full Text Available This is the continuation of our research on development of a fully nonlinear, dynamically consistent, numerical ship motion model (DiSSEL. In this study we will report our results in predicting ship motions in unsteady maneuvering in calm water. During the unsteady maneuvering, both the rudder angle, and ship forward speed vary with time. Therefore, not only surge, sway, and yaw motions occur, but roll, pitch and heave motions will also occur even in calm water as heel, trim, and sinkage, respectively. When the rudder angles and ship forward speed vary rapidly with time, the six degrees-of-freedom ship motions and their interactions become strong. To accurately predict the six degrees-of-freedom ship motions in unsteady maneuvering, a universal method for arbitrary ship hull requires physics-based fully-nonlinear models for ship motion and for rudder forces and moments. The numerical simulations will be benchmarked by experimental data of the Pre-Contract DDG51 design and an Experimental Hull Form. The benchmarking shows a good agreement between numerical simulations by the enhancement DiSSEL and experimental data. No empirical parameterization is used, except for the influence of the propeller slipstream on the rudder, which is included using a flow acceleration factor.
NUMERICAL SIMULATIONS OF HIGHLY NONLINEAR STEADY AND UNSTEADY FREE SURFACE FLOWS
Institute of Scientific and Technical Information of China (English)
YANG Chi; HUANG Fuxin; WANG Lijue; WAN De-cheng
2011-01-01
A numerical simulation model based on an open source Computational Fluid Dynamics (CFD) package-Open Field Operation and Manipulation (OpenFOAM) has been developed to study highly nonlinear steady and unsteady free surface flows.A two-fluid formulation is used in this model and the free surface is captured using the classical Volume Of Fluid (VOF) method.The incompressible Euler/Navier-Stokes equations are solved using a finite volume method on unstructured polyhedral cells.Both steady and unsteady free surface flows are simulated,which include:(1) a submerged NACA0012 2-D hydrofoil moving at a constant speed,(2) the Wigley hull moving at a constant speed,(3) numerical wave tank,(4) green water overtopping a fixed 2-D deck,(5) green water impact on a fixed 3-D body without or with a vertical wall on the deck.The numerical results obtained have been compared with the experimental measurements and other CFD results,and the agreements are satisfactory.The present numerical model can thus be used to simulate highly nonlinear steady and unsteady free surface flows.
Reddy, T. S. R.
1995-01-01
This guide describes the input data required for using ECAP2D (Euler Cascade Aeroelastic Program-Two Dimensional). ECAP2D can be used for steady or unsteady aerodynamic and aeroelastic analysis of two dimensional cascades. Euler equations are used to obtain aerodynamic forces. The structural dynamic equations are written for a rigid typical section undergoing pitching (torsion) and plunging (bending) motion. The solution methods include harmonic oscillation method, influence coefficient method, pulse response method, and time integration method. For harmonic oscillation method, example inputs and outputs are provided for pitching motion and plunging motion. For the rest of the methods, input and output for pitching motion only are given.
Unsteady aerodynamic force mechanisms of a hoverfly hovering with a short stroke-amplitude
Zhu, Hao Jie; Sun, Mao
2017-08-01
Hovering insects require a rather large lift coefficient. Many insects hover with a large stroke amplitude (120°-170°), and it has been found that the high lift is mainly produced by the delayed-stall mechanism. However, some insects hover with a small stroke amplitude (e.g., 65°). The delayed-stall mechanism might not work for these insects because the wings travel only a very short distance in a stroke, and other aerodynamic mechanisms must be operating. Here we explore the aerodynamic mechanisms of a hoverfly hovering with an inclined stroke plane and a small stroke amplitude (65.6°). The Navier-Stokes equations are numerically solved to give the flows and forces and the theory of vorticity dynamics used to reveal the aerodynamic mechanisms. The majority of the weight-supporting vertical force is produced in the mid portion of the downstroke, a short period (about 26% of the stroke cycle) in which the vertical force coefficient is larger than 4. The force is produced using a new mechanism, the "paddling mechanism." During the short period, the wing moves rapidly downward and forward at a large angle of attack (about 48°), and strong counter clockwise vorticity is produced continuously at the trailing edge and clockwise vorticity at the leading edge, resulting in a large time rate of change in the first moment of vorticity, hence the large aerodynamic force. It is interesting to note that with the well known delayed stall mechanism, the force is produced by the relative motion of two vortices of opposite sign, while in the "paddling mechanism," it is produced by generating new vortices of opposite sign at different locations.
Unsteady aerodynamic forces and power requirements of a bumblebee in forward flight
Institute of Scientific and Technical Information of China (English)
Jianghao Wu; Mao Sun
2005-01-01
Aerodynamic forces and power requirements in forward flight in a bumblebee (Bombus terrestris) were studied using the method of computational fluid dynamics. Actual wing kinematic data of free flight were used in the study (the speed ranges from 0 m/s to 4.5 m/s; advance ratio ranges from 0-0.66). The bumblebee employs the delayed stall mechanism and the fast pitching-up rotation mechanism to produce vertical force and thrust. The leading-edge vortex does not shed in the translatory phase of the half-strokes and is much more concentrated than that of the fruit fly in a previous study. At hovering and low-speed flight, the vertical force is produced by both the half-strokes and is contributed by wing lift; at medium and high speeds, the vertical force is mainly produced during the downstroke and is contributed by both wing lift and wing drag. At all speeds the thrust is mainly produced in the upstroke and is contributed by wing drag.The power requirement at low to medium speeds is not very different from that of hovering and is relatively large at the highest speed (advance ratio 0.66), i.e. the power curve is Jshaped. Except at the highest flight speed, storing energy elastically can save power up to 20%-30%. At the highest speed,because of the large increase of aerodynamic torque and the slight decrease of inertial torque (due to the smaller stroke amplitude and stroke frequency used), the power requirement is dominated by aerodynamic power and the effect of elastic storage of energy on power requirement is limited.
Directory of Open Access Journals (Sweden)
G. Q. Zhang
2013-01-01
Full Text Available The aerodynamic characteristics of propeller-wing interaction for the rocket launched UAV have been investigated numerically by means of sliding mesh technology. The corresponding forces and moments have been collected for axial wing placements ranging from 0.056 to 0.5D and varied rotating speeds. The slipstream generated by the rotating propeller has little effects on the lift characteristics of the whole UAV. The drag can be seen to remain unchanged as the wing's location moves progressively closer to the propeller until 0.056D away from the propeller, where a nearly 20% increase occurred sharply. The propeller position has a negligible effect on the overall thrust and torque of the propeller. The efficiency affected by the installation angle of the propeller blade has also been analyzed. Based on the pressure cloud and streamlines, the vortices generated by propeller, propeller-wing interaction, and wing tip have also been captured and analyzed.
Real-Time Onboard Global Nonlinear Aerodynamic Modeling from Flight Data
Brandon, Jay M.; Morelli, Eugene A.
2014-01-01
Flight test and modeling techniques were developed to accurately identify global nonlinear aerodynamic models onboard an aircraft. The techniques were developed and demonstrated during piloted flight testing of an Aermacchi MB-326M Impala jet aircraft. Advanced piloting techniques and nonlinear modeling techniques based on fuzzy logic and multivariate orthogonal function methods were implemented with efficient onboard calculations and flight operations to achieve real-time maneuver monitoring and analysis, and near-real-time global nonlinear aerodynamic modeling and prediction validation testing in flight. Results demonstrated that global nonlinear aerodynamic models for a large portion of the flight envelope were identified rapidly and accurately using piloted flight test maneuvers during a single flight, with the final identified and validated models available before the aircraft landed.
Nonlinear unsteady supersonic flow analysis for slender bodies of revolution: Theory
Directory of Open Access Journals (Sweden)
D. E. Panayotounakos
1997-01-01
Full Text Available We construct analytical solutions for the problem of nonlinear supersonic flow past slender bodies of revolution due to small amplitude oscillations. The method employed is based on the splitting of the time dependent small perturbation equation to a nonlinear time independent partial differential equation (P.D.E. concerning the steady flow, and a linear time dependent one, concerning the unsteady flow. Solutions in the form of three parameters family of surfaces for the first equation are constructed, while solutions including one arbitrary function for the second equation are extracted. As an application the evaluation of the small perturbation velocity resultants for a flow past a right circular cone is obtained making use of convenient boundary and initial conditions in accordance with the physical problem.
Modelling of nonlinear bridge aerodynamics and aeroelasticity: a convolution based approach
Directory of Open Access Journals (Sweden)
Wu T.
2012-07-01
Full Text Available Innovative bridge decks exhibit nonlinear behaviour in wind tunnel studies which has placed increasing importance on the nonlinear bridge aerodynamics/aeroelasticity considerations for long-span bridges. The convolution scheme concerning the first-order kernels for linear analysis is reviewed, which is followed by an introduction to higher-order kernels for nonlinear analysis. A numerical example of a longspan suspension bridge is presented that demonstrates the efficacy of the proposed scheme.
Parametric Reduced-Order Models for Probabilistic Analysis of Unsteady Aerodynamic Applications
2007-01-01
method is to discretize the domain under consideration, Ω, into elements Ωe. Next, a space of polynomials of degree at most p, Uph (Ωe), is defined on...approximate solution wh can be found by enforcing the nonlinear conservation law (1) locally, for all test functions vh ∈ Uph (Ωe): ∫ Ωe vTh ∂wh ∂t dΩe...computed using the inner state and boundary condition data. The final form of the DG discretization is constructed by selecting a basis for Uph (Ωe
Nonlinear Aerodynamic Modeling From Flight Data Using Advanced Piloted Maneuvers and Fuzzy Logic
Brandon, Jay M.; Morelli, Eugene A.
2012-01-01
Results of the Aeronautics Research Mission Directorate Seedling Project Phase I research project entitled "Nonlinear Aerodynamics Modeling using Fuzzy Logic" are presented. Efficient and rapid flight test capabilities were developed for estimating highly nonlinear models of airplane aerodynamics over a large flight envelope. Results showed that the flight maneuvers developed, used in conjunction with the fuzzy-logic system identification algorithms, produced very good model fits of the data, with no model structure inputs required, for flight conditions ranging from cruise to departure and spin conditions.
LINEAR AND NONLINEAR AERODYNAMIC THEORY OF INTERACTION BETWEEN FLEXIBLE LONG STRUCTURE AND WIND
Institute of Scientific and Technical Information of China (English)
徐旭; 曹志远
2001-01-01
In light of the characteristics of the interactions between flexible structure and wind in three directions, and based on the rational mechanical section-model of structure, a new aerodynamic force model is accepted, i. e. the coefficients of three component forces are the functions of the instantaneous attack angle and rotational speed Ci = Ci(β(t),θ),(i = D, L, M). So, a new method to formulate the linear and nonlinear aerodynamic items of wind and structure interacting has been put forward in accordance with "strip theory"and modified "quasi-static theory ", and then the linear and nonlinear coupled theory of super-slender structure for civil engineering analyzing are converged in one model. For the linear aerodynamic-force parts, the semi-analytical expressions of the items so-called "flutter derivatives" corresponding to the one in the classic equations have been given here,and so have the nonlinear parts. The study of the stability of nonlinear aerodynamic-coupled torsional vibration of the old Tacoma bridge shows that the form and results of the nonlinear control equation in rotational direction are in agreement with that of V. F. Bohm's.
Directory of Open Access Journals (Sweden)
Muhammad Ramzan Luhur
2014-01-01
Full Text Available This contribution provides the development of a stochastic lift and drag model for an airfoil FX 79-W-151A under unsteady wind inflow based on wind tunnel measurements. Here we present the integration of the stochastic model into a well-known standard BEM (Blade Element Momentum model to obtain the corresponding aerodynamic forces on a rotating blade element. The stochastic model is integrated as an alternative to static tabulated data used by classical BEM. The results show that in comparison to classical BEM, the BEM with stochastic approach additionally reflects the local force dynamics and therefore provides more information on aerodynamic forces that can be used by wind turbine simulation codes
Ramachandran, S.; Wells, W. R.
1974-01-01
This paper is concerned with the estimation of stability and control parameters of a high performance fighter aircraft from data obtained from high angle of attack flight. The estimation process utilizes a maximum likelihood algorithm derived for the case of a nonlinear aerodynamic force and moment model. The aircraft used was a high speed variable sweep heavy weight fighter with twin vertical tails. Comparisons of results from the nonlinear analysis are made with linear theory and wind tunnel results when available.
Directory of Open Access Journals (Sweden)
A. I. Khlupnov
2015-01-01
Full Text Available Ecology and security clearance of cargo into Earth orbit space considered in unsteadyaerodynamics of the separated parts of of launch vehicles for space applications, which directly involves the definition of the shape and size of fields separated by falling parts, fragmentation issues and software problems aeroballistic reusable space systems (such as "Baikal" (Russian Federation, Falcon - Task 1 (USA and others..To resolve the methodological issues determining the value of the aerodynamic damping (and / or anti-damping separable parts as the object of study was chosen cylindrical model as a bluff body for which there are no systematic dependence of unsteady aerodynamic coefficients pitch moment of defining the parameters of the problem (the Mach number, angle of attack, Reynolds number, etc..The value of the derivative of pitching moment coefficient of the angular velocitydetermined numerically for the most intense stress of supersonic flight mode as the method of curved bodies, and direct numerical simulation of unsteady motion of the body in the air flow within the full Navier-Stokes equations.Comparison of these two approaches implemented as a tool for scientific research in theform of a software package FineOpen (products of the Company Numeca and programs for solving the Navier-Stokes equations (the author's version helped establish the limits of applicability of the curved bodies in the implementation of the marked change in the form of slots defining parameters of the problem.
Directory of Open Access Journals (Sweden)
Moutaz Elgammi
2016-06-01
Full Text Available Prediction of the unsteady aerodynamic flow phenomenon on wind turbines is challenging and still subject to considerable uncertainty. Under yawed rotor conditions, the wind turbine blades are subjected to unsteady flow conditions as a result of the blade advancing and retreating effect and the development of a skewed vortical wake created downstream of the rotor plane. Blade surface pressure measurements conducted on the NREL Phase VI rotor in yawed conditions have shown that dynamic stall causes the wind turbine blades to experience significant cycle-to-cycle variations in aerodynamic loading. These effects were observed even though the rotor was subjected to a fixed speed and a uniform and steady wind flow. This phenomenon is not normally predicted by existing dynamic stall models integrated in wind turbine design codes. This paper couples blade pressure measurements from the NREL Phase VI rotor to a free-wake vortex model to derive the angle of attack time series at the different blade sections over multiple rotor rotations and three different yaw angles. Through the adopted approach it was possible to investigate how the rotor self-induced aerodynamic load fluctuations influence the unsteady variations in the blade angles of attack and induced velocities. The hysteresis loops for the normal and tangential load coefficients plotted against the angle of attack were plotted over multiple rotor revolutions. Although cycle-to-cycle variations in the angles of attack at the different blade radial locations and azimuth positions are found to be relatively small, the corresponding variations in the normal and tangential load coefficients may be significant. Following a statistical analysis, it was concluded that the load coefficients follow a normal distribution at the majority of blade azimuth angles and radial locations. The results of this study provide further insight on how existing engineering models for dynamic stall may be improved through
Rowe, W. S.; Petrarca, J. R.
1980-01-01
Changes to be made that provide increased accuracy and increased user flexibility in prediction of unsteady loadings caused by control surface motions are described. Analysis flexibility is increased by reducing the restrictions on the location of the downwash stations relative to the leading edge and the edges of the control surface boundaries. Analysis accuracy is increased in predicting unsteady loading for high Mach number analysis conditions through use of additional chordwise downwash stations. User guideline are presented to enlarge analysis capabilities of unusual wing control surface configurations. Comparative results indicate that the revised procedures provide accurate predictions of unsteady loadings as well as providing reductions of 40 to 75 percent in computer usage cost required by previous versions of this program.
Sampling Strategies for Reduced-Order Modeling of Nonlinear and Unsteady Aerodynamics
2014-01-13
topologies using a cell-centered finite volume method. Second-order accuracy in space is achieved using the exact Riemann solver of Gottlieb and Groth,18...attack zero during the rotation, the grid moves right and upward. III. Test Case The X-31 aircraft is considered in this paper. The aircraft geometry ...Department of Defense Engineering Research Development Center (ERDC). The X-31 geometry was provided by NATO RTO Task Group AVT-161 on Assessment of
高速列车受电弓非定常气动特性研究%Unsteady Aerodynamic Characteristics of High-speed Pantograph
Institute of Scientific and Technical Information of China (English)
郭迪龙; 姚拴宝; 刘晨辉; 杨国伟
2012-01-01
The current collection performance of pantograph is critical to safe operation of high-speed trains. The unsteady aerodynamic characteristics of pantograph influence the stitus of current collection of the pantograph system severely. In this paper, unsteady aerodynamic characteristics of high-speed train pantograph were studied with detached eddy simulation (DES). The research results indicates as follows: The aerodynamic lift coefficient of pantograph was strongly affected by the strength and shedding frequency of the detached eddy; when without the cross wind,the lift of pantograph is negative, and when the train runs at the speed of 350 km/h, the fluctuating amplitude of the lift is 110%, and the fluctuating implitude and frequency of pantograph increases with further speed raising and the side force applied on the pantograph remains very small; when with the cross wind, the vibration frequency of the pantograph lift differs from that in absence of the cross wind greatly whereas the lift coefficient changes little, and the side force applied on the pantograph increases as the cross wind speed increases. The results are helpful to optimized design of high-speed pantographs.%受电弓系统的受流特性对高速列车的安全运行至关重要,受电弓的非定常气动特性严重影响受电弓系统的受流状态.本文采用脱体涡模拟(DES),对高速列车受电弓的非定常气动特性进行深入研究.研究表明:受电弓脱体涡的强度、脱落频率对受电弓气动升力系数影响很大.无横风条件下,受电弓受到的升力为负升力,列车运行速度为350 km/h时,其升力的波动幅度达110％,速度增加,其波动幅度增大,频率增大,受电弓的横向受力很小；横风条件下,受电弓的升力振动频率与无横风时有很大不同,升力系数变比不大,侧向力随横风速度的增大而增大.研究结果为高速受电弓的优化设计提供了依据.
Analysis on nonlinear wind-induced dynamic response of membrane roofs with aerodynamic effects
Institute of Scientific and Technical Information of China (English)
LI Qing-xiang; SUN Bing-nan
2008-01-01
Based on the characteristics of membrane structures and the air influence factors, this paper presen-ted a method to simulate the air aerodynamic force effects including the added air mass, the acoustic radiation damping and the pneumatic stiffness. The infinite air was modeled using the acoustic fluid element of commer-cial FE software and the finite element membrane roof models were coupled with fluid models. A comparison be-tween the results obtained by IrE computation and those obtained by the vibration experiment for a cable-mem-brane verified the validity of the method. Furthermore, applying the method to a flat membrane roof structure and using its wind tunnel test results, the analysis of nonlinear wind-induced dynamic responses for such geo-metrically nonlinear roofs, including the roof-air coupled model was performed. The result shows that the air has large influence on vibrating membrane roofs according to results of comparing the nodal time-history displace-ments, accelerations and stress of the two different cases. Meantime, numerical studies show that the method developed can successfully solve the nonlinear wind-induced dynamic response of the membrane roof with aero-dynamic effects.
Welch, Gerard E.
2012-01-01
The design-point and off-design performance of an embedded 1.5-stage portion of a variable-speed power turbine (VSPT) was assessed using Reynolds-Averaged Navier-Stokes (RANS) analyses with mixing-planes and sector-periodic, unsteady RANS analyses. The VSPT provides one means by which to effect the nearly 50 percent main-rotor speed change required for the NASA Large Civil Tilt-Rotor (LCTR) application. The change in VSPT shaft-speed during the LCTR mission results in blade-row incidence angle changes of as high as 55 . Negative incidence levels of this magnitude at takeoff operation give rise to a vortical flow structure in the pressure-side cove of a high-turn rotor that transports low-momentum flow toward the casing endwall. The intent of the effort was to assess the impact of unsteadiness of blade-row interaction on the time-mean flow and, specifically, to identify potential departure from the predicted trend of efficiency with shaft-speed change of meanline and 3-D RANS/mixing-plane analyses used for design.
Shao, Xuefei; Fu, Yiming; Chen, Yang
2015-05-01
Based on the higher order shear deformation theory and the geometric nonlinear theory, the nonlinear motion equations, to which the effects of the positive and negative piezoelectric and the thermal are introduced by piezoelectric fiber metal laminated (FML) plates in an unsteady temperature, are established by Hamilton’s variational principle. Then, the control algorithm of negative-velocity feedback is applied to realize the vibration control of the piezoelectric FML plates. During the solving process, firstly, the formal functions of the displacements that fulfilled the boundary conditions are proposed. Then, heat conduction equations and nonlinear differential equations are dealt with using the differential quadrature (DQ) and Galerkin methods, respectively. On the basis of the previous processing, the time domain is dispersed by the Newmark-β method. Finally, the whole problem can be investigated by the iterative method. In the numerical examples, the influence of the applied voltage, the temperature loading and geometric parameters on the nonlinear dynamic response of the piezoelectric FML plates is analyzed. Meanwhile, the effect of feedback control gain and the position of the piezoelectric layer, the initial deflection and the external temperature on the active control effect of the piezoelectric layers has been studied. The model development and the research results can serve as a basis for nonlinear vibration analysis of the FML structures.
模型昆虫翼作非定常i运动时的气动力特性%AERODYNAMIC PROPERTIES OF A WING PERFORMING UNSTEADY ROTATIONAL MOTIONS
Institute of Scientific and Technical Information of China (English)
兰世隆; 孙茂
2001-01-01
The aerodynamic forces and flow structures of a wing of relatively small, aspect ratio in some unsteady rotational motions at low Reynolds number (Re = 100) are studied by numerically solving the Navier-Stokes equations. These motions include wing in constant-speed rotation after a fast start, wing accelerating and decelerating from one rotational speed to another,and wing rapidly pitching-up in constant-speed rotation. When a wing performing constant-speed rotation at small Reynolds number after started from rest at large angle of attack (α = 35°), a large lift coefficient can be maintained. The mechanism for the large lift coefficient is that for a rotating wing, the variation of the relative velocity along the wing-span causes a pressure gradient,centrifugal force also exists and hence a spanwise flow which can prevent the dynamic stall vortex from shedding. When a wing rapidly accelerating or decelerating from one rotational speed to another, or rapidly pitching-up during constant-speed rotation, even if the aspect ratio of the wing is small and the flow Reynolds number is low, large aerodynamic force can be obtained. During these rapid unsteady motions, new layers of strong vorticity are formed near the wing surfaces in very short time, resulting large time rate of change of the fluid impulse which is responsible for the generation of large aerodynamic force.%基于Navier-Stokes方程的数值解，研究了一模型昆虫翼在小雷诺数(Re=100)下作非定常运动时的气动力特性.这些运动包括：翼启动后的常速转动，快速加、减速转动，常速转动中快速上仰(模拟昆虫翼的上挥或下拍、翻转等运动).有如下结果：在小雷诺数下，模型昆虫翼以大攻角(α=35°)作常速转动运动时，由于失速涡不脱落，可产生较大的升力系数.其机理是：翼转动时，翼尖附近(该处线速度大)上翼面压强比翼根附近(该处线速度小)的小得多，因而存在展向压强梯度
Numerical simulations of the aerodynamic behavior of large horizontal-axis wind turbines
Energy Technology Data Exchange (ETDEWEB)
Gebhardt, C.G. [Departamento de Estructuras, Facultad de Ciencias Exactas Fisicas y Naturales, Universidad Nacional de Cordoba, Av. Velez Sarsfield N 1611, CP 5000, Cordoba (Argentina); Consejo Nacional de Investigaciones Cientificas y Tecnicas, Avenida Rivadavia 1917, CP C1033AAJ, Ciudad de Buenos Aires (Argentina); Preidikman, S. [Departamento de Estructuras, Facultad de Ciencias Exactas Fisicas y Naturales, Universidad Nacional de Cordoba, Av. Velez Sarsfield N 1611, CP 5000, Cordoba (Argentina); Departamento de Mecanica, Facultad de Ingenieria, Universidad Nacional de Rio, Cuarto, Ruta Nacional 36, Km 601, CP 5800, Rio Cuarto (Argentina); Consejo Nacional de Investigaciones Cientificas y Tecnicas, Avenida Rivadavia 1917, CP C1033AAJ, Ciudad de Buenos Aires (Argentina); Massa, J.C. [Departamento de Estructuras, Facultad de Ciencias Exactas Fisicas y Naturales, Universidad Nacional de Cordoba, Av. Velez Sarsfield N 1611, CP 5000, Cordoba (Argentina); Departamento de Mecanica, Facultad de Ingenieria, Universidad Nacional de Rio, Cuarto, Ruta Nacional 36, Km 601, CP 5800, Rio Cuarto (Argentina)
2010-06-15
In the present work, the non-linear and unsteady aerodynamic behavior of large horizontal-axis wind turbines is analyzed. The flowfield around the wind turbine is simulated with the general non-linear unsteady vortex-lattice method, widely used in aerodynamics. By using this technique, it is possible to compute the aerodynamic loads and their evolution in the time domain. The results presented in this paper help to understand how the existence of the land-surface boundary layer and the presence of the turbine support tower, affect its aerodynamic efficiency. The capability to capture these phenomena is a novel aspect of the computational tool developed in the present effort. (author)
Su, Xiaohui; Cao, Yuanwei; Zhao, Yong
2016-06-01
In this paper, an unstructured mesh Arbitrary Lagrangian-Eulerian (ALE) incompressible flow solver is developed to investigate the aerodynamics of insect hovering flight. The proposed finite-volume ALE Navier-Stokes solver is based on the artificial compressibility method (ACM) with a high-resolution method of characteristics-based scheme on unstructured grids. The present ALE model is validated and assessed through flow passing over an oscillating cylinder. Good agreements with experimental results and other numerical solutions are obtained, which demonstrates the accuracy and the capability of the present model. The lift generation mechanisms of 2D wing in hovering motion, including wake capture, delayed stall, rapid pitch, as well as clap and fling are then studied and illustrated using the current ALE model. Moreover, the optimized angular amplitude in symmetry model, 45°, is firstly reported in details using averaged lift and the energy power method. Besides, the lift generation of complete cyclic clap and fling motion, which is simulated by few researchers using the ALE method due to large deformation, is studied and clarified for the first time. The present ALE model is found to be a useful tool to investigate lift force generation mechanism for insect wing flight.
Energy Technology Data Exchange (ETDEWEB)
D' Alessandro, V.; Montelpare, S.; Ricci, R.; Secchiaroli, A. [Universita Politecnica delle Marche, Dipartimento di Energetica, Via Brecce Bianche 1, 60131 Ancona (Italy)
2010-08-15
When compared with of other wind turbine the Savonius wind rotor offers lower performance in terms of power coefficient, on the other hand it offers a number of advantages as it is extremely simple to built, it is self-starting and it has no need to be oriented in the wind direction. Although it is well suited to be integrated in urban environment as mini or micro wind turbine it is inappropriate when high power is requested. For this reason several studies have been carried-out in recent years in order to improve its aerodynamic performance. The aim of this research is to gain an insight into the complex flow field developing around a Savonius wind rotor and to evaluate its performance. A mathematical model of the interaction between the flow field and the rotor blades was developed and validated by comparing its results with data obtained at Environmental Wind Tunnel (EWT) laboratory of the ''Polytechnic University of Marche''. (author)
A new non-linear vortex lattice method:Applications to wing aerodynamic optimizations
Institute of Scientific and Technical Information of China (English)
Oliviu S? ugar Gabor; Andreea Koreanschi; Ruxandra Mihaela Botez
2016-01-01
This paper presents a new non-linear formulation of the classical Vortex Lattice Method (VLM) approach for calculating the aerodynamic properties of lifting surfaces. The method accounts for the effects of viscosity, and due to its low computational cost, it represents a very good tool to perform rapid and accurate wing design and optimization procedures. The mathematical model is constructed by using two-dimensional viscous analyses of the wing span-wise sections, according to strip theory, and then coupling the strip viscous forces with the forces generated by the vortex rings distributed on the wing camber surface, calculated with a fully three-dimensional vortex lifting law. The numerical results obtained with the proposed method are validated with experimental data and show good agreement in predicting both the lift and pitching moment, as well as in predicting the wing drag. The method is applied to modifying the wing of an Unmanned Aerial System to increase its aerodynamic efficiency and to calculate the drag reductions obtained by an upper surface morphing technique for an adaptable regional aircraft wing.
A new non-linear vortex lattice method: Applications to wing aerodynamic optimizations
Directory of Open Access Journals (Sweden)
Oliviu Şugar Gabor
2016-10-01
Full Text Available This paper presents a new non-linear formulation of the classical Vortex Lattice Method (VLM approach for calculating the aerodynamic properties of lifting surfaces. The method accounts for the effects of viscosity, and due to its low computational cost, it represents a very good tool to perform rapid and accurate wing design and optimization procedures. The mathematical model is constructed by using two-dimensional viscous analyses of the wing span-wise sections, according to strip theory, and then coupling the strip viscous forces with the forces generated by the vortex rings distributed on the wing camber surface, calculated with a fully three-dimensional vortex lifting law. The numerical results obtained with the proposed method are validated with experimental data and show good agreement in predicting both the lift and pitching moment, as well as in predicting the wing drag. The method is applied to modifying the wing of an Unmanned Aerial System to increase its aerodynamic efficiency and to calculate the drag reductions obtained by an upper surface morphing technique for an adaptable regional aircraft wing.
Kamel, Ouari; Mohand, Ouhrouche; Toufik, Rekioua; Taib, Nabil
2015-01-01
In order to improvement of the performances for wind energy conversions systems (WECS), an advanced control techniques must be used. In this paper, as an alternative to conventional PI-type control methods, a nonlinear predictive control (NPC) approach is developed for DFIG-based wind turbine. To enhance the robustness of the controller, a disturbance observer is designed to estimate the aerodynamic torque which is considered as an unknown perturbation. An explicitly analytical form of the optimal predictive controller is given consequently on-line optimization is not necessary The DFIG is fed through the rotor windings by a back-to-back converter controlled by Pulse Width Modulation (PWM), where the stator winding is directly connected to the grid. The presented simulation results show a good performance in trajectory tracking of the proposed strategy and rejection of disturbances is successfully achieved.
Barthelemy, X; Peirson, W L; Dias, F; Allis, M
2015-01-01
The kinematic properties of unsteady highly non-linear 3D wave groups have been investigated using a numerical wave tank. Although carrier wave speeds based on zero-crossing analysis remain within +-7% of linear theory predictions, crests and troughs locally undertake a systematic cyclical leaning from forward to backward as the crests/troughs transition through their maximum amplitude. Consequently, both crests and troughs slow down by approximately 15% of the linear velocity, in sharp contrast to the predictions of finite amplitude Stokes steady wavetrain theory. Velocity profiles under the crest maximum have been investigated and surface values in excess of 1.8 times the equivalent Stokes velocity can be observed. Equipartitioning between depth-integrated kinetic and potential energy holds globally on the scale of the wave group. However, equipartitioning does not occur at crests and troughs (even for low amplitude Stokes waves), where the local ratio of potential to total energy varies systemically as a f...
A Three-Dimensional Linearized Unsteady Euler Analysis for Turbomachinery Blade Rows
Montgomery, Matthew D.; Verdon, Joseph M.
1997-01-01
A three-dimensional, linearized, Euler analysis is being developed to provide an efficient unsteady aerodynamic analysis that can be used to predict the aeroelastic and aeroacoustic responses of axial-flow turbo-machinery blading.The field equations and boundary conditions needed to describe nonlinear and linearized inviscid unsteady flows through a blade row operating within a cylindrical annular duct are presented. A numerical model for linearized inviscid unsteady flows, which couples a near-field, implicit, wave-split, finite volume analysis to a far-field eigenanalysis, is also described. The linearized aerodynamic and numerical models have been implemented into a three-dimensional linearized unsteady flow code, called LINFLUX. This code has been applied to selected, benchmark, unsteady, subsonic flows to establish its accuracy and to demonstrate its current capabilities. The unsteady flows considered, have been chosen to allow convenient comparisons between the LINFLUX results and those of well-known, two-dimensional, unsteady flow codes. Detailed numerical results for a helical fan and a three-dimensional version of the 10th Standard Cascade indicate that important progress has been made towards the development of a reliable and useful, three-dimensional, prediction capability that can be used in aeroelastic and aeroacoustic design studies.
Study of unsteady cavitation on NACA66 hydrofoil using dynamic cubic nonlinear subgrid-scale model
Directory of Open Access Journals (Sweden)
Xianbei Huang
2015-11-01
Full Text Available In this article, we describe the use of a new dynamic cubic nonlinear model, a new nonlinear subgrid-scale model, for simulating the cavitating flow around an NACA66 series hydrofoil. For comparison, the dynamic Smagorinsky model is also used. It is found that the dynamic cubic nonlinear model can capture the turbulence spectrum, while the dynamic Smagorinsky model fails. Both models reproduce the cavity growth/destabilization cycle, but the results of the dynamic cubic nonlinear model are much smoother. The re-entrant jet is clearly captured by the models, and it is shown that the re-entrant jet cuts the cavity into two parts. In general, the dynamic cubic nonlinear model provides improvement over the dynamic Smagorinsky model for the calculation of cavitating flow.
Haviland, J. K.
1974-01-01
The results are reported of two unrelated studies. The first was an investigation of the formulation of the equations for non-uniform unsteady flows, by perturbation of an irrotational flow to obtain the linear Green's equation. The resulting integral equation was found to contain a kernel which could be expressed as the solution of the adjoint flow equation, a linear equation for small perturbations, but with non-constant coefficients determined by the steady flow conditions. It is believed that the non-uniform flow effects may prove important in transonic flutter, and that in such cases, the use of doublet type solutions of the wave equation would then prove to be erroneous. The second task covered an initial investigation into the use of the Monte Carlo method for solution of acoustical field problems. Computed results are given for a rectangular room problem, and for a problem involving a circular duct with a source located at the closed end.
Cunningham, A. M., Jr.
1976-01-01
The feasibility of calculating steady mean flow solutions for nonlinear transonic flow over finite wings with a linear theory aerodynamic computer program is studied. The methodology is based on independent solutions for upper and lower surface pressures that are coupled through the external flow fields. Two approaches for coupling the solutions are investigated which include the diaphragm and the edge singularity method. The final method is a combination of both where a line source along the wing leading edge is used to account for blunt nose airfoil effects; and the upper and lower surface flow fields are coupled through a diaphragm in the plane of the wing. An iterative solution is used to arrive at the nonuniform flow solution for both nonlifting and lifting cases. Final results for a swept tapered wing in subcritical flow show that the method converges in three iterations and gives excellent agreement with experiment at alpha = 0 deg and 2 deg. Recommendations are made for development of a procedure for routine application.
Compendium of Unsteady Aerodynamic Measurements
1982-08-01
Scientific esearch, EUropean Office of JAeropace Research and Develonment. /E 0-2 have required much labour and incurred the risk of introducing errors... influences the oscillatory atnd derivative pressures. Components p’/#0 and p"/#0 are, in goneral,-depende’it on the frequency of oscillation, and their...reference ooordinate * oad to provide a tim-varying vlectrical signal which is used as a phase reference for hormonic analyals. Wben the model cannot
Unsteady Aerodynamic Phenomena in Turbomachines
1990-02-01
ss crc ahlead of the cxpertrn’’" it evaluatlin of unfsteady acrodenramics in ii b~ achncr, n hcc sin incc i ac .crIdstames c rs ndtcsts arc on the same...caiculidn 0 0. 2 0.(. 0.6 0.8 7.0x Fig. 9: Dynamic presure for the~ compressor cascade in 1M sitaneous t x sgpitcin . -30 .1. a. 0. 2 3 - c omparisaon...naissance stir l’ar~t mame du bard d’altaque. En fail, physiquement, Ie calcul du d~collement dc bard d’ataque ndcessiterait sin calcul visqueux
Theoretical and applied aerodynamics and related numerical methods
Chattot, J J
2015-01-01
This book covers classical and modern aerodynamics, theories and related numerical methods, for senior and first-year graduate engineering students, including: -The classical potential (incompressible) flow theories for low speed aerodynamics of thin airfoils and high and low aspect ratio wings. - The linearized theories for compressible subsonic and supersonic aerodynamics. - The nonlinear transonic small disturbance potential flow theory, including supercritical wing sections, the extended transonic area rule with lift effect, transonic lifting line and swept or oblique wings to minimize wave drag. Unsteady flow is also briefly discussed. Numerical simulations based on relaxation mixed-finite difference methods are presented and explained. - Boundary layer theory for all Mach number regimes and viscous/inviscid interaction procedures used in practical aerodynamics calculations. There are also four chapters covering special topics, including wind turbines and propellers, airplane design, flow analogies and h...
Energy Technology Data Exchange (ETDEWEB)
Jakobi, A.
2007-07-01
Air flow around airship configurations is highly complex and is governed by 3D aerodynamic effects. Detailed knowledge of this nonlinear aerodynamics is important especially in airship design. The author describes the relevant physical effects governing flow and shows how they are taken account of in the method of calculation he presents. A panel boundary layer method is described in detail which calculates frictionless external flow in a 3D panel method coupled with a 3D integral method for laminar or turbulent boundary layers. The method calculates the tensor of the virtual mass of any given airship takes account of desplacement by the boundary layer, and simulates the effects of propellers. The modelling of free vortex layers in the context of potential theory is described in detail, and the results are discussed. A new panel with two-dimensional vortex distribution is derived. (orig.)
Mahabaleshwar, U. S.; Nagaraju, K. R.; Vinay Kumar, P. N.; Baleanu, Dumitru; Lorenzini, Giulio
2017-03-01
In this paper, we investigate the theoretical analysis for the unsteady magnetohydrodynamic laminar boundary layer flow due to impulsively stretching sheet. The third-order highly nonlinear partial differential equation modeling the unsteady boundary layer flow brought on by an impulsively stretching flat sheet was solved by applying Adomian decomposition method and Pade approximants. The exact analytical solution so obtained is in terms of rapidly converging power series and each of the variants are easily computable. Variations in parameters such as mass transfer (suction/injection) and Chandrasekhar number on the velocity are observed by plotting the graphs. This particular problem is technically sound and has got applications in expulsion process and related process in fluid dynamics problems.
Mahabaleshwar, U. S.; Nagaraju, K. R.; Vinay Kumar, P. N.; Baleanu, Dumitru; Lorenzini, Giulio
2016-12-01
In this paper, we investigate the theoretical analysis for the unsteady magnetohydrodynamic laminar boundary layer flow due to impulsively stretching sheet. The third-order highly nonlinear partial differential equation modeling the unsteady boundary layer flow brought on by an impulsively stretching flat sheet was solved by applying Adomian decomposition method and Pade approximants. The exact analytical solution so obtained is in terms of rapidly converging power series and each of the variants are easily computable. Variations in parameters such as mass transfer (suction/injection) and Chandrasekhar number on the velocity are observed by plotting the graphs. This particular problem is technically sound and has got applications in expulsion process and related process in fluid dynamics problems.
van der Male, Pim; van Dalen, Karel N.; Metrikine, Andrei V.
2016-11-01
Existing models for the analysis of offshore wind turbines account for the aerodynamic action on the turbine rotor in detail, requiring a high computational price. When considering the foundation of an offshore wind turbine, however, a reduced rotor model may be sufficient. To define such a model, the significance of the nonlinear velocity and history dependency of the aerodynamic force on a rotating blade should be known. Aerodynamic interaction renders the dynamics of a rotating blade in an ambient wind field nonlinear in terms of the dependency on the wind velocity relative to the structural motion. Moreover, the development in time of the aerodynamic force does not follow the flow velocity instantaneously, implying a history dependency. In addition, both the non-uniform blade geometry and the aerodynamic interaction couple the blade motions in and out of the rotational plane. Therefore, this study presents the Euler-Bernoulli formulation of a twisted rotating blade connected to a rigid hub, excited by either instantaneous or history-dependent aerodynamic forces. On this basis, the importance of the history dependency is determined. Moreover, to assess the nonlinear contributions, both models are linearized. The structural response is computed for a stand-still and a rotating blade, based on the NREL 5-MW turbine. To this end, the model is reduced on the basis of its first three free-vibration mode shapes. Blade tip response predictions, computed from turbulent excitation, correctly account for both modal and directional couplings, and the added damping resulting from the dependency of the aerodynamic force on the structural motion. Considering the deflection of the blade tip, the history-dependent and the instantaneous force models perform equally well, providing a basis for the potential use of the instantaneous model for the rotor reduction. The linearized instantaneous model provides similar results for the rotating blade, indicating its potential
Effect of compressibility on the nonlinear prediction of the aerodynamic loads on lifting surfaces
Kandil, O. A.; Mook, D. T.; Nayfeh, A. H.
1975-01-01
The vortex-lattice technique for incompressible flow which accounts for separation at sharp edges is modified to account for compressibility. This is accomplished by extending the Prandtl-Glauert transformation to moderate angles of attack. Thus, the aerodynamic characteristics for the compressible case are obtained from the solution of an equivalent incompressible problem. Numerical results are presented for parallelogram and delta wings to assess the effects of compressibility. The results are in good agreement with available experimental data.
Directory of Open Access Journals (Sweden)
Mohammed Almakki
2017-07-01
Full Text Available The entropy generation in unsteady three-dimensional axisymmetric magnetohydrodynamics (MHD nanofluid flow over a non-linearly stretching sheet is investigated. The flow is subject to thermal radiation and a chemical reaction. The conservation equations are solved using the spectral quasi-linearization method. The novelty of the work is in the study of entropy generation in three-dimensional axisymmetric MHD nanofluid and the choice of the spectral quasi-linearization method as the solution method. The effects of Brownian motion and thermophoresis are also taken into account. The nanofluid particle volume fraction on the boundary is passively controlled. The results show that as the Hartmann number increases, both the Nusselt number and the Sherwood number decrease, whereas the skin friction increases. It is further shown that an increase in the thermal radiation parameter corresponds to a decrease in the Nusselt number. Moreover, entropy generation increases with respect to some physical parameters.
Energy Technology Data Exchange (ETDEWEB)
Hau, Jan-Niklas, E-mail: hau@fdy.tu-darmstadt.de; Oberlack, Martin [Chair of Fluid Dynamics, Department of Mechanical Engineering, Technische Universität Darmstadt, Otto-Berndt-Strasse 2, 64287 Darmstadt (Germany); GSC CE, Technische Universität Darmstadt, Dolivostraße 15, 64293 Darmstadt (Germany); Chagelishvili, George [Chair of Fluid Dynamics, Department of Mechanical Engineering, Technische Universität Darmstadt, Otto-Berndt-Strasse 2, 64287 Darmstadt (Germany); Abastumani Astrophysical Observatory, Ilia State University, Tbilisi 0160, Georgia (United States); M. Nodia Institute of Geophysics, Tbilisi State University, Tbilisi 0128, Georgia (United States); Khujadze, George [Chair of Fluid Mechanics, Universität Siegen, Paul-Bonatz-Str. 9-11, 57068 Siegen (Germany); Tevzadze, Alexander [Faculty of Exact and Natural Sciences, Tbilisi State University, Tbilisi 0128, Georgia (United States)
2015-12-15
Aerodynamic sound generation in shear flows is investigated in the light of the breakthrough in hydrodynamics stability theory in the 1990s, where generic phenomena of non-normal shear flow systems were understood. By applying the thereby emerged short-time/non-modal approach, the sole linear mechanism of wave generation by vortices in shear flows was captured [G. D. Chagelishvili, A. Tevzadze, G. Bodo, and S. S. Moiseev, “Linear mechanism of wave emergence from vortices in smooth shear flows,” Phys. Rev. Lett. 79, 3178-3181 (1997); B. F. Farrell and P. J. Ioannou, “Transient and asymptotic growth of two-dimensional perturbations in viscous compressible shear flow,” Phys. Fluids 12, 3021-3028 (2000); N. A. Bakas, “Mechanism underlying transient growth of planar perturbations in unbounded compressible shear flow,” J. Fluid Mech. 639, 479-507 (2009); and G. Favraud and V. Pagneux, “Superadiabatic evolution of acoustic and vorticity perturbations in Couette flow,” Phys. Rev. E 89, 033012 (2014)]. Its source is the non-normality induced linear mode-coupling, which becomes efficient at moderate Mach numbers that is defined for each perturbation harmonic as the ratio of the shear rate to its characteristic frequency. Based on the results by the non-modal approach, we investigate a two-dimensional homentropic constant shear flow and focus on the dynamical characteristics in the wavenumber plane. This allows to separate from each other the participants of the dynamical processes — vortex and wave modes — and to estimate the efficacy of the process of linear wave-generation. This process is analyzed and visualized on the example of a packet of vortex modes, localized in both, spectral and physical, planes. Further, by employing direct numerical simulations, the wave generation by chaotically distributed vortex modes is analyzed and the involved linear and nonlinear processes are identified. The generated acoustic field is anisotropic in the wavenumber
Hau, Jan-Niklas; Chagelishvili, George; Khujadze, George; Oberlack, Martin; Tevzadze, Alexander
2015-12-01
Aerodynamic sound generation in shear flows is investigated in the light of the breakthrough in hydrodynamics stability theory in the 1990s, where generic phenomena of non-normal shear flow systems were understood. By applying the thereby emerged short-time/non-modal approach, the sole linear mechanism of wave generation by vortices in shear flows was captured [G. D. Chagelishvili, A. Tevzadze, G. Bodo, and S. S. Moiseev, "Linear mechanism of wave emergence from vortices in smooth shear flows," Phys. Rev. Lett. 79, 3178-3181 (1997); B. F. Farrell and P. J. Ioannou, "Transient and asymptotic growth of two-dimensional perturbations in viscous compressible shear flow," Phys. Fluids 12, 3021-3028 (2000); N. A. Bakas, "Mechanism underlying transient growth of planar perturbations in unbounded compressible shear flow," J. Fluid Mech. 639, 479-507 (2009); and G. Favraud and V. Pagneux, "Superadiabatic evolution of acoustic and vorticity perturbations in Couette flow," Phys. Rev. E 89, 033012 (2014)]. Its source is the non-normality induced linear mode-coupling, which becomes efficient at moderate Mach numbers that is defined for each perturbation harmonic as the ratio of the shear rate to its characteristic frequency. Based on the results by the non-modal approach, we investigate a two-dimensional homentropic constant shear flow and focus on the dynamical characteristics in the wavenumber plane. This allows to separate from each other the participants of the dynamical processes — vortex and wave modes — and to estimate the efficacy of the process of linear wave-generation. This process is analyzed and visualized on the example of a packet of vortex modes, localized in both, spectral and physical, planes. Further, by employing direct numerical simulations, the wave generation by chaotically distributed vortex modes is analyzed and the involved linear and nonlinear processes are identified. The generated acoustic field is anisotropic in the wavenumber plane, which
Tkachova, P.; Krot, A.; Minervina, H.
It is well known that there is chaos in convective process in atmosphere and ocean. In particular,dynamic model of Lorenz [1] describes the Rayleigh-Benard convection phenomenon. Phase trajectories of Lorenz equation system are characterized by strange alternative properties: on the one hand, they diverge (because of positive Lyapunov exponents), on the second hand, they attract to the limited domain of phase space called an attractor [1]. The Lorenz attractor has specific geometrical structure and can be characterized by means of fractal dimension. In this connection the aim of this work is development of analysis of Lorenz attractor based on the proposed nonlinear decomposition into matrix series [2]. This analysis permits to estimate the values of characteristic parameters (including control one) of Lorenz attractors and predict their evolution in time. Using results of matrix decomposition [2], it is not difficult to see that the change of vector function (describing the Lorenz attractor) can be approximated by only linear and quadratic terms [3]. Because values of the first and second order derivatives can be calculated by means of numerical methods we can estimate the change of the vector function from computational experiment. In result, the values of parameters of the Lorenz's attractor can be estimated. This permits us to solve the identification task of the current dynamical state of a convective aerodynamic flows. Moreover, using the results of matrix decomposition we can estimate the minimal embedding dimension [4] for the Lorenz attractor based on experimental data. References: [1] P.Berge,Y.Pomeau and C.Vidal. L'ordre dans le chaos: Vers une approche deterministe de la turbulence. Hermann:Paris,1988. [2] A.M.Krot, "Matrix decompositions of vector functions and shift operators on the trajectories of a nonlinear dynamical system", Nonlinear Phenomena in Complex Systems,vol.4, N2, pp.106- 115, 2001. [3] A.M.Krot and P
Hanson, D. B.
1991-01-01
A unified theory for the aerodynamics and noise of advanced turboprops are presented. Aerodynamic topics include calculation of performance, blade load distribution, and non-uniform wake flow fields. Blade loading can be steady or unsteady due to fixed distortion, counter-rotating wakes, or blade vibration. The aerodynamic theory is based on the pressure potential method and is therefore basically linear. However, nonlinear effects associated with finite axial induction and blade vortex flow are included via approximate methods. Acoustic topics include radiation of noise caused by blade thickness, steady loading (including vortex lift), and unsteady loading. Shielding of the fuselage by its boundary layer and the wing are treated in separate analyses that are compatible but not integrated with the aeroacoustic theory for rotating blades.
Goldman, Benjamin D.; Dowell, Earl H.; Scott, Robert C.
2015-01-01
Conical shell theory and a supersonic potential flow aerodynamic theory are used to study the nonlinear pressure buckling and aeroelastic limit cycle behavior of the thermal protection system for NASA's Hypersonic Inflatable Aerodynamic Decelerator. The structural model of the thermal protection system consists of an orthotropic conical shell of the Donnell type, resting on several circumferential elastic supports. Classical Piston Theory is used initially for the aerodynamic pressure, but was found to be insufficient at low supersonic Mach numbers. Transform methods are applied to the convected wave equation for potential flow, and a time-dependent aerodynamic pressure correction factor is obtained. The Lagrangian of the shell system is formulated in terms of the generalized coordinates for all displacements and the Rayleigh-Ritz method is used to derive the governing differential-algebraic equations of motion. Aeroelastic limit cycle oscillations and buckling deformations are calculated in the time domain using a Runge-Kutta method in MATLAB. Three conical shell geometries were considered in the present analysis: a 3-meter diameter 70 deg. cone, a 3.7-meter 70 deg. cone, and a 6-meter diameter 70 deg. cone. The 6-meter configuration was loaded statically and the results were compared with an experimental load test of a 6-meter HIAD. Though agreement between theoretical and experimental strains was poor, the circumferential wrinkling phenomena observed during the experiments was captured by the theory and axial deformations were qualitatively similar in shape. With Piston Theory aerodynamics, the nonlinear flutter dynamic pressures of the 3-meter configuration were in agreement with the values calculated using linear theory, and the limit cycle amplitudes were generally on the order of the shell thickness. The effect of axial tension was studied for this configuration, and increasing tension was found to decrease the limit cycle amplitudes when the circumferential
Unger, Eric R.; Hager, James O.; Agrawal, Shreekant
1999-01-01
This paper is a discussion of the supersonic nonlinear point design optimization efforts at McDonnell Douglas Aerospace under the High-Speed Research (HSR) program. The baseline for these optimization efforts has been the M2.4-7A configuration which represents an arrow-wing technology for the High-Speed Civil Transport (HSCT). Optimization work on this configuration began in early 1994 and continued into 1996. Initial work focused on optimization of the wing camber and twist on a wing/body configuration and reductions of 3.5 drag counts (Euler) were realized. The next phase of the optimization effort included fuselage camber along with the wing and a drag reduction of 5.0 counts was achieved. Including the effects of the nacelles and diverters into the optimization problem became the next focus where a reduction of 6.6 counts (Euler W/B/N/D) was eventually realized. The final two phases of the effort included a large set of constraints designed to make the final optimized configuration more realistic and they were successful albeit with a loss of performance.
Unsteady transonic flow in cascades
Surampudi, S. P.; Adamczyk, J. J.
1984-01-01
There is a need for methods to predict the unsteady air loads associated with flutter of turbomachinery blading at transonic speeds. The results of such an analysis in which the steady relative flow approaching a cascade of thin airfoils is assumed to be transonic, irrotational, and isentropic is presented. The blades in the cascade are allowed to undergo a small amplitude harmonic oscillation which generates a small unsteady flow superimposed on the existing steady flow. The blades are assumed to oscillate with a prescribed motion of constant amplitude and interblade phase angle. The equations of motion are obtained by linearizing about a uniform flow the inviscid nonheat conducting continuity and momentum equations. The resulting equations are solved by employing the Weiner Hopf technique. The solution yields the unsteady aerodynamic forces acting on the cascade at Mach number equal to 1. Making use of an unsteady transonic similarity law, these results are compared with the results obtained from linear unsteady subsonic and supersonic cascade theories. A parametric study is conducted to find the effects of reduced frequency, solidity, stagger angle, and position of pitching axis on the flutter.
Blackwell, Mark W.; Tutty, Owen R.; Rogers, Eric; Sandberg, Richard D.
2016-01-01
The inclusion of smart devices in wind turbine rotor blades could, in conjunction with collective and individual pitch control, improve the aerodynamic performance of the rotors. This is currently an active area of research with the primary objective of reducing the fatigue loads but mitigating the effects of extreme loads is also of interest. The aerodynamic loads on a wind turbine blade contain periodic and non-periodic components and one approach is to consider the application of iterative learning control algorithms. In this paper, the control design is based on a simple, in relative terms, computational fluid dynamics model that uses non-linear wake effects to represent flow past an airfoil. A representation for the actuator dynamics is included to undertake a detailed investigation into the level of control possible and on how performance can be effectively measured.
Validation and comparison of aerodynamic modelling approaches for wind turbines
Blondel, F.; Boisard, R.; Milekovic, M.; Ferrer, G.; Lienard, C.; Teixeira, D.
2016-09-01
The development of large capacity Floating Offshore Wind Turbines (FOWT) is an interdisciplinary challenge for the design solvers, requiring accurate modelling of both hydrodynamics, elasticity, servodynamics and aerodynamics all together. Floating platforms will induce low-frequency unsteadiness, and for large capacity turbines, the blade induced vibrations will lead to high-frequency unsteadiness. While yawed inflow conditions are still a challenge for commonly used aerodynamic methods such as the Blade Element Momentum method (BEM), the new sources of unsteadiness involved by large turbine scales and floater motions have to be tackled accurately, keeping the computational cost small enough to be compatible with design and certification purposes. In the light of this, this paper will focus on the comparison of three aerodynamic solvers based on BEM and vortex methods, on standard, yawed and unsteady inflow conditions. We will focus here on up-to-date wind tunnel experiments, such as the Unsteady Aerodynamics Experiment (UAE) database and the MexNext international project.
Unsteady flow about a circulation control airfoil
Institute of Scientific and Technical Information of China (English)
刘晶昌; 孙茂; 吴礼义
1996-01-01
The unsteady flow around a circulation control (CC) airfoil was investigated with Navier-Stokes method,which includes the flow around CC airfoil with pulsating jet,the flow around oscillating CC airfoil,and the flow around oscillating CC airfoil with pulsating jet.Dynamic properties of the flow and the aerodynamic forces were rewaled.
Flexible Launch Vehicle Stability Analysis Using Steady and Unsteady Computational Fluid Dynamics
Bartels, Robert E.
2012-01-01
Launch vehicles frequently experience a reduced stability margin through the transonic Mach number range. This reduced stability margin can be caused by the aerodynamic undamping one of the lower-frequency flexible or rigid body modes. Analysis of the behavior of a flexible vehicle is routinely performed with quasi-steady aerodynamic line loads derived from steady rigid aerodynamics. However, a quasi-steady aeroelastic stability analysis can be unconservative at the critical Mach numbers, where experiment or unsteady computational aeroelastic analysis show a reduced or even negative aerodynamic damping.Amethod of enhancing the quasi-steady aeroelastic stability analysis of a launch vehicle with unsteady aerodynamics is developed that uses unsteady computational fluid dynamics to compute the response of selected lower-frequency modes. The response is contained in a time history of the vehicle line loads. A proper orthogonal decomposition of the unsteady aerodynamic line-load response is used to reduce the scale of data volume and system identification is used to derive the aerodynamic stiffness, damping, and mass matrices. The results are compared with the damping and frequency computed from unsteady computational aeroelasticity and from a quasi-steady analysis. The results show that incorporating unsteady aerodynamics in this way brings the enhanced quasi-steady aeroelastic stability analysis into close agreement with the unsteady computational aeroelastic results.
Unsteady Aerodynamic Flow Control of Moving Platforms
2014-05-29
Hsiao et al. 1990, Neuberger and Wygnanski 1987, Williams et al. 1991, Chang et al. 1992, Seifert et al. 1993). An alternative approach uses actuation...34, Mechanics of Materials, Vol. 38, 2006, pp. 463-474. Neuberger D. and Wygnanski I., “The Use of a Vibrating Ribbon to Delay Separation on Two
Unsteady cooperative flow type in the axial compressor
Institute of Scientific and Technical Information of China (English)
ZHENG Xinqian; ZHOU Sheng; HOU Anping; XIONG Jinsong
2005-01-01
For increasing the performance of the axial compressor, a method for realizing unsteady cooperative flow type is proposed in this paper as a critical objective in the new generation of the axial compressor design system. Unsteady excitations were utilized to trigger the transformation from the unsteady natural flow pattern into the unsteady cooperative flow pattern, resulting in increment of aerodynamic performances of axial compressor. Numerical simulations show that distinct positive effect can be obtained for the 2D cascade in a wide range of subsonic working conditions. No positive effect can be observed under the 2D supersonic working conditions and unsteady excitations have little influence on the flow field space-time structure. However, positive effect can be obtained under the 3D transsonic working conditions. In addition, engineering applications of unsteady cooperative flow type are discussed.
Nonlinear aeroelastic analysis of airfoils: bifurcation and chaos
Lee, B. H. K.; Price, S. J.; Wong, Y. S.
1999-04-01
Different types of structural and aerodynamic nonlinearities commonly encountered in aeronautical engineering are discussed. The equations of motion of a two-dimensional airfoil oscillating in pitch and plunge are derived for a structural nonlinearity using subsonic aerodynamics theory. Three classical nonlinearities, namely, cubic, freeplay and hysteresis are investigated in some detail. The governing equations are reduced to a set of ordinary differential equations suitable for numerical simulations and analytical investigation of the system stability. The onset of Hopf-bifurcation, and amplitudes and frequencies of limit cycle oscillations are investigated, with examples given for a cubic hardening spring. For various geometries of the freeplay, bifurcations and chaos are discussed via the phase plane, Poincaré maps, and Lyapunov spectrum. The route to chaos is investigated from bifurcation diagrams, and for the freeplay nonlinearity it is shown that frequency doubling is the most commonly observed route. Examples of aerodynamic nonlinearities arising from transonic flow and dynamic stall are discussed, and special attention is paid to numerical simulation results for dynamic stall using a time-synthesized method for the unsteady aerodynamics. The assumption of uniform flow is usually not met in practice since perturbations in velocities are encountered in flight. Longitudinal atmospheric turbulence is introduced to show its effect on both the flutter boundary and the onset of Hopf-bifurcation for a cubic restoring force.
Aerodynamics profile not in stationary flow
Directory of Open Access Journals (Sweden)
А.А. Загорулько
2006-02-01
Full Text Available Consider the question about influence of unsteady flight on the size of drag and lift coefficients of theaerodynamic profile. Distinctive features of this investigation are obtaining data about aerodynamic drag chancing in process unsteady on high angle at attack and oscillation profile in subsonic and transonic flight. Given analysis of oscillation profile show, that dynamic loops accompany change of lift and dray force. The researches show that it is necessary to clarity the mathematic model of the airplane flight dynamics by introducing numbers, with take into account unsteady effects.
A High Order Accuracy Computational Tool for Unsteady Turbulent Flows and Acoustics Project
National Aeronautics and Space Administration — Accurate simulations of unsteady turbulent flows for aerodynamics applications, such as accurate computation of heat loads on space vehicles as well the interactions...
Unsteady computational fluid dynamics in aeronautics
Tucker, P G
2014-01-01
The field of Large Eddy Simulation (LES) and hybrids is a vibrant research area. This book runs through all the potential unsteady modelling fidelity ranges, from low-order to LES. The latter is probably the highest fidelity for practical aerospace systems modelling. Cutting edge new frontiers are defined. One example of a pressing environmental concern is noise. For the accurate prediction of this, unsteady modelling is needed. Hence computational aeroacoustics is explored. It is also emerging that there is a critical need for coupled simulations. Hence, this area is also considered and the tensions of utilizing such simulations with the already expensive LES. This work has relevance to the general field of CFD and LES and to a wide variety of non-aerospace aerodynamic systems (e.g. cars, submarines, ships, electronics, buildings). Topics treated include unsteady flow techniques; LES and hybrids; general numerical methods; computational aeroacoustics; computational aeroelasticity; coupled simulations and...
Nonlinear Aerodynamic Modeling and Research in Static Aeroelasticity%静气弹中非线性气动力建模方法与分析
Institute of Scientific and Technical Information of China (English)
吴欣龙; 王正平
2012-01-01
大展弦比低雷诺数气动布局容易较早出现气流分离,会带来明显的非线性气动力问题.针对此类布局提出了一种建立基于Kriging插值的非线性压力系数分布模型的方法.从Navier - Stokes方程计算的不同状态下飞机的压力系数中提取不同坐标的系数.利用Kriging插值函数建立CFD压力系数对迎角导数的响应面,将插值结果代入偶极子网格法(Double- Lattice Method,DLM)修正其线性方法.利用无限板样条(IPS)方法进行气动结构耦合,实现了有限元结构的非线性气弹响应分析.算例结果验证了方法对于静气弹分析的有效性,同时能准确地反映弹性带来的气动效率的降低和非线性力矩特征.%For the problem that large aspect ratio of the low reynold number aerodynamic layout appeared earlier in the laminar separation,and bring obvious nonlinear aerodynamic. The model of a distributed non - linear pressure coefficient based on the Kriging interpolation method is proposed for this layout. The pressure coefficient of the plane in different coordinate is extracted from the result calculated by the Navi-er- Stokes equations in different flight status, use of Kriging interpolation function to create the response surface which is derivative of CFD pressure coefficient on the angle of attack,put the interpolation results into the Double- of Lattice Method to amend its linear methods, use the infinite plate spline(IPS) method to couple the fluid- structure and realize finite element of nonlinear aeroelastic response analysis. Example is given in the text,the results demonstrate the validity of the method for the analysis of the static aeroelastic same time be able to accurately reflect the reduction of aerodynamic efficiency brought by flexibility and non- linear moment characteristics.
Fluidic Actuation and Control of Munition Aerodynamics
2009-08-31
RESULTS II. TECHNICAL BACKGOUND II.1 Aerodynamic Flow Control Active aerodynamic flow control techniques in recent years have primarily focused on... techniques used in previous studies have steady and unsteady blowing (Hsaio et. al., 1990), vibrating ribbons or flaps (Huang et. al., 1987), and usage...with 4 cables, and increased the tunnel speed until the lift produced by the wings balanced the model weight. Kiya et. al. (1990) used four piano
Directory of Open Access Journals (Sweden)
ARIF A. EBRAHEEM AL-QASSAR
2008-12-01
Full Text Available The design of the re-entry space vehicles and high-speed aircrafts requires special attention to the nonlinear thermoelastic and aerodynamic instabilities of their structural components. The thermal effects are important since temperature environment influences significantly the static and dynamic behaviors of flight structures in supersonic/hypersonic regimes. To contribute to the understanding of dynamic behavior of these “hot” structures, a double-wedge lifting surface with combined freeplay and cubic stiffening structural nonlinearities in both plunging and pitching degrees-of-freedom operating in supersonic/hypersonic flight speed regimes has been analyzed. A third order Piston Theory Aerodynamics is used to evaluate the applied nonlinear unsteady aerodynamic loads. The loss of torsional stiffness that may be incurred by lifting surfaces subjected to axial stresses induced by aerodynamic heating is also considered. The aerodynamic heating effect is estimated based on the adiabatic wall temperature due to high speed airstreams. Modelling issues as well as simulation results have been presented and pertinent conclusions outlined. It is highlighted that a serious loss of torsional stiffness may induce the dynamic instability of the lifting surfaces. The influence of various parameters such as flight condition, thickness ratio, freeplays and pitching stiffness nonlinearity are also discussed.
A theoretical study on the unsteady aerothermodynamics for attached flow models
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
The principle of the unsteady aerothermodynamics was theoretically investigated for the attached flow. Firstly, two simplified models with analytic solutions to the N-S equations were selected for the research, namely the compressible unsteady flows on the infinite flat plate with both time-varying wall velocity and time-varying wall temperature boundary conditions. The unsteady temperature field and the unsteady wall heat flux (heat flow) were analytically solved for the second model. Then, the interaction characteristic of the unsteady temperature field and the unsteady velocity field in the simplified models and the effects of the interaction on the transient wall heat transfer were studied by these two analytic solutions. The unsteady heat flux, which is governed by the energy equation, is directly related to the unsteady compression work and viscous dissipation which originates from the velocity field governed by the momentum equation. The main parameters and their roles in how the unsteady velocity field affects the unsteady heat flux were discussed for the simplified models. Lastly, the similarity criteria of the unsteady aerothermodynamics were derived based on the compressible boundary layer equations. Along with the Strouhal number Stu, the unsteadiness criterion of the velocity field, StT number, the unsteadiness criterion of the temperature field was proposed for the first time. Different from the traditional method used in unsteady aerodynamics which measures the flow unsteadiness only by the Stu number, present results show that the flow unsteadiness in unsteady aerothermodynamics should be comprehensively estimated by comparing the relative magnitudes of the temperature field unsteadiness criterion StT number with the coefficients of other terms in the dimensionless energy equation.
Ullah, Imran; Bhattacharyya, Krishnendu; Shafie, Sharidan; Khan, Ilyas
2016-01-01
Numerical results are presented for the effect of first order chemical reaction and thermal radiation on mixed convection flow of Casson fluid in the presence of magnetic field. The flow is generated due to unsteady nonlinearly stretching sheet placed inside a porous medium. Convective conditions on wall temperature and wall concentration are also employed in the investigation. The governing partial differential equations are converted to ordinary differential equations using suitable transformations and then solved numerically via Keller-box method. It is noticed that fluid velocity rises with increase in radiation parameter in the case of assisting flow and is opposite in the case of opposing fluid while radiation parameter has no effect on fluid velocity in the forced convection. It is also seen that fluid velocity and concentration enhances in the case of generative chemical reaction whereas both profiles reduces in the case of destructive chemical reaction. Further, increase in local unsteadiness parameter reduces fluid velocity, temperature and concentration. Over all the effects of physical parameters on fluid velocity, temperature and concentration distribution as well as on the wall shear stress, heat and mass transfer rates are discussed in detail.
Directory of Open Access Journals (Sweden)
Pedro A. Galvani
2016-08-01
Full Text Available The work presented in this paper has two major aspects: (i investigation of a simple, yet efficient model of the NREL (National Renewable Energy Laboratory 5-MW reference wind turbine; (ii nonlinear control system development through a real-time nonlinear receding horizon control methodology with application to wind turbine control dynamics. In this paper, the results of our simple wind turbine model and a real-time nonlinear control system implementation are shown in comparison with conventional control methods. For this purpose, the wind turbine control problem is converted into an optimization problem and is directly solved by the nonlinear backwards sweep Riccati method to generate the control protocol, which results in a non-iterative algorithm. One main contribution of this paper is that we provide evidence through simulations, that such an advanced control strategy can be used for real-time control of wind turbine dynamics. Examples are provided to validate and demonstrate the effectiveness of the presented scheme.
Fluid mechanics of dynamic stall. I - Unsteady flow concepts
Ericsson, L. E.; Reding, J. P.
1988-01-01
Advanced military aircraft 'supermaneuverability' requirements entail the sustained operation of airfoils at stalled flow conditions. The present work addresses the effects of separated flow on vehicle dynamics; an analytic method is presented which employs static experimental data to predict the separated flow effect on incompressible unsteady aerodynamics. The key parameters in the analytic relationship between steady and nonsteady aerodynamics are the time-lag before a change of flow conditions can affect the separation-induced aerodynamic loads, the accelerated flow effect, and the moving wall effect.
Basic numerical methods. [of unsteady and transonic flow
Steger, Joseph L.; Van Dalsem, William R.
1989-01-01
Some of the basic finite-difference schemes that can be used to solve the nonlinear equations that describe unsteady inviscid and viscous transonic flow are reviewed. Numerical schemes for solving the unsteady Euler and Navier-Stokes, boundary-layer, and nonlinear potential equations are described. Emphasis is given to the elementary ideas used in constructing various numerical procedures, not specific details of any one procedure.
Numerical simulations of unsteady flows in turbomachines
Dorney, Daniel Joseph
The performance of axial and centrifugal turbomachines is significantly affected by the presence of unsteady and viscous flow mechanisms. Most contemporary design systems, however, use steady or linearized unsteady inviscid flow analyses to generate new blade shapes. In an effort to increase the understanding of unsteady viscous flows in turbomachinery blade rows, and to determine the limitations of linearized inviscid flow analyses, a two-part investigation was conducted. In the first portion of this investigation, a nonlinear viscous flow analysis was developed for the prediction of unsteady flows in two dimensional axial turbomachinery blade rows. The boundary conditions were formulated to allow the specification of vortical, entropic and acoustic excitations at the inlet, and acoustic excitations at exit, of a cascade. Numerical simulations were performed for flat plate and compressor exit guide vane cascades, and the predicted results were compared with solutions from classical linearized theory and linearized inviscid flow analysis. The unsteady pressure fields predicted with the current analysis showed close agreement with the linearized solutions for low to moderate temporal frequency vortical and acoustic excitations. As the temporal frequency of the excitations was increased, nonlinear effects caused discrepancies to develop between the linearized and Navier-Stokes solution sets. The inclusion of viscosity had a significant impact on the unsteady vorticity field, but only a minimal effect on the unsteady pressure field. In the second part of this investigation, a quasi-three-dimensional Navier-Stokes analysis was modified and applied to flows in centrifugal turbomachinery blade rows. Inviscid and viscous flow simulations were performed for a centrifugal impeller at three operating conditions. By comparing the predicted and experimental circumferential distributions of the relative frame velocity and flow angle downstream of the impeller, it was
Nonlinear analysis and enhancement of wing-based piezoaeroelastic energy harvesters
Abdelkefi, Abdessattar
2014-01-01
We investigate the level of harvested power from aeroelastic vibrations for an elastically mounted wing supported by nonlinear springs. The energy is harvested by attaching a piezoelectric transducer to the plunge degree of freedom. The considered wing has a low-aspect ratio and hence three dimensional aerodynamic effects cannot be neglected. To this end, the three dimensional unsteady vortex lattice method for the prediction of the unsteady aerodynamic loads is developed. A strong coupling scheme that is based on Hamming\\'s fourth-order predictor-corrector method and accounts for the interaction between the aerodynamic loads and the motion of the wing is employed. The effects of the electrical load resistance, nonlinear torsional spring and eccentricity between the elastic axis and the gravity axis on the level of the harvested power, pitch and plunge amplitudes are investigated for a range of operating wind speeds. The results show that there is a specific wind speed beyond which the pitch motion does not pick any further energy from the incident flow. As such, the displacement in the plunge direction grows significantly and causes enhanced energy harvesting. The results also show that the nonlinear torsional spring plays an important role in enhancing the level of the harvested power. Furthermore, the harvested power can be increased by an order of magnitude by properly choosing the eccentricity and the load resistance. This analysis is helpful in designing piezoaeroelastic energy harvesters that can operate optimally at specific wind speeds. © 2013 Elsevier Ltd.
Katz, Joseph
2006-01-01
Race car performance depends on elements such as the engine, tires, suspension, road, aerodynamics, and of course the driver. In recent years, however, vehicle aerodynamics gained increased attention, mainly due to the utilization of the negative lift (downforce) principle, yielding several important performance improvements. This review briefly explains the significance of the aerodynamic downforce and how it improves race car performance. After this short introduction various methods to generate downforce such as inverted wings, diffusers, and vortex generators are discussed. Due to the complex geometry of these vehicles, the aerodynamic interaction between the various body components is significant, resulting in vortex flows and lifting surface shapes unlike traditional airplane wings. Typical design tools such as wind tunnel testing, computational fluid dynamics, and track testing, and their relevance to race car development, are discussed as well. In spite of the tremendous progress of these design tools (due to better instrumentation, communication, and computational power), the fluid dynamic phenomenon is still highly nonlinear, and predicting the effect of a particular modification is not always trouble free. Several examples covering a wide range of vehicle shapes (e.g., from stock cars to open-wheel race cars) are presented to demonstrate this nonlinear nature of the flow field.
Energy Technology Data Exchange (ETDEWEB)
Becker, B.G.; Lane, D.A.; Max, N.L.
1995-03-01
Flow volumes are extended for use in unsteady (time-dependent) flows. The resulting unsteady flow volumes are the 3 dimensional analog of streamlines. There are few examples where methods other than particle tracing have been used to visualize time varying flows. Since particle paths can become convoluted in time there are additional considerations to be made when extending any visualization technique to unsteady flows. We will present some solutions to the problems which occur in subdivision, rendering, and system design. We will apply the unsteady flow volumes to a variety of field types including moving multi-zoned curvilinear grids.
Aerodynamic stability of cable-stayed bridges under erection
Institute of Scientific and Technical Information of China (English)
ZHANG Xin-jun; SUN Bing-nan; XIANG Hai-fan
2005-01-01
In this work, nonlinear multimode aerodynamic analysis of the Jingsha Bridge under erection over the Yangtze River is conducted, and the evolutions of structural dynamic characteristics and the aerodynamic stability with erection are numerically generated. Instead of the simplified method, nonlinear multimode aerodynamic analysis is suggested to predict the aerodynamic stability of cable-stayed bridges under erection. The analysis showed that the aerodynamic stability maximizes at the relatively early stages, and decreases as the erection proceeds. The removal of the temporary piers in side spans and linking of the main girder to the anchor piers have important influence on the dynamic characteristics and aerodynamic stability of cable-stayed bridges under erection.
Aerodynamics of Small Vehicles
Mueller, Thomas J.
In this review we describe the aerodynamic problems that must be addressed in order to design a successful small aerial vehicle. The effects of Reynolds number and aspect ratio (AR) on the design and performance of fixed-wing vehicles are described. The boundary-layer behavior on airfoils is especially important in the design of vehicles in this flight regime. The results of a number of experimental boundary-layer studies, including the influence of laminar separation bubbles, are discussed. Several examples of small unmanned aerial vehicles (UAVs) in this regime are described. Also, a brief survey of analytical models for oscillating and flapping-wing propulsion is presented. These range from the earliest examples where quasi-steady, attached flow is assumed, to those that account for the unsteady shed vortex wake as well as flow separation and aeroelastic behavior of a flapping wing. Experiments that complemented the analysis and led to the design of a successful ornithopter are also described.
Raeesi, Arash; Cheng, Shaohong; Ting, David S.-K.
2016-08-01
The possibility of bridge stay cables experiencing violent dry inclined cable galloping raises great concern in the engineering community. Numerous experimental and analytical studies have been conducted to investigate this phenomenon, most of which were in the context of steady wind past a rigid cylindrical body. Real stay cables however, are generally long and flexible. They are exposed to more "broad" range of atmospheric boundary layer type of wind velocity profile which is also unsteady and turbulent by nature. To better understand the physics underlying this type of wind-induced cable vibration and to elucidate various contributing factors, a more realistic analytical model which is capable of addressing the above elements is imperative. In the current paper, a three-dimensional aeroelastic model is proposed to study the aerodynamic response of an inclined and/or yawed slender flexible cylindrical body subjected to unsteady mean wind, with practical application to wind-induced vibrations of bridge stay cables under no precipitation condition. The non-linear aerodynamic forces derived in the present study are combined with the cable free vibration equations available in literature to obtain the equations of motion for the wind-induced vibration of stay cables, which are solved numerically by an explicit finite difference scheme. The proposed three-dimensional aeroelastic model and numerical solution technique are validated by comparing the predicted cable free vibration responses with existing data in the literature. The mechanism which triggers dry inclined cable galloping and the required conditions for its growth are explored. In addition, the impact of different initial conditions and various unsteady mean wind scenarios on this violent cable motion are investigated. Results show that the occurrence of dry inclined cable galloping is associated with an opposite-phase relation between the relative wind speed and the aerodynamic force along the direction of
Unsteady Pressures on a Generic Capsule Shape
Burnside, Nathan; Ross, James C.
2015-01-01
While developing the aerodynamic database for the Orion spacecraft, the low-speed flight regime (transonic and below) proved to be the most difficult to predict and measure accurately. The flow over the capsule heat shield in descent flight was particularly troublesome for both computational and experimental efforts due to its unsteady nature and uncertainty about the boundary layer state. The data described here were acquired as part of a study to improve the understanding of the overall flow around a generic capsule. The unsteady pressure measurements acquired on a generic capsule shape are presented along with a discussion about the effects of various flight conditions and heat-shield surface roughness on the resulting pressure fluctuations.
Librescu, Liviu
2001-01-01
Within this NASA Grant, the following points should be emphasized: 1) All the objectives stated in the proposal of the grant have been accomplished. Moreover. the activity within the project has addressed additional issues, of the linear and nonlinear aeroelasticity, not included in the objectives of the grant. 2) During the activities within the grant, we have been in a permanent contact with Dr. Walter A. Silva, the monitor of the NASA Project, to whom we have reported continuously our achievements. 3) As a result of the activities within the grant a number of papers: a. have been submitted for publication to the AIAA Journals, namely the AIAA Journal and the Journal of Guidance, Control, and Dynamics, and b. have been presented at the specialized National Conferences and an International Congress, and have appeared in the proceedings of these Conferences. 4) A list of papers submitted for publication and presented at Conferences is appended herewith. 5) In all these papers, an acknowledgment to NASA Langley Research Center was included.
Unsteady transonic flow over cascade blades
Surampudi, S. P.; Adamczyk, J. J.
1986-01-01
An attempt is made to develop an efficient staggered cascade blade unsteady aerodynamics model for the neighborhood of March 1, representing the blade row by a rectilinear two-dimensional cascade of thin, flat plate airfoils. The equations of motion are derived on the basis of linearized transonic small perturbation theory, and an analytical solution is obtained by means of the Wiener-Hopf procedure. Making use of the transonic similarity law, the results obtained are compared with those of other linearized cascade analyses. A parametric study is conducted to find the effects of reduced frequency, stagger angle, solidity, and the location of the pitching axis on cascade stability.
Mehta, R. D.
1985-01-01
Research data on the aerodynamic behavior of baseballs and cricket and golf balls are summarized. Cricket balls and baseballs are roughly the same size and mass but have different stitch patterns. Both are thrown to follow paths that avoid a batter's swing, paths that can curve if aerodynamic forces on the balls' surfaces are asymmetric. Smoke tracer wind tunnel tests and pressure taps have revealed that the unbalanced side forces are induced by tripping the boundary layer on the seam side and producing turbulence. More particularly, the greater pressures are perpendicular to the seam plane and only appear when the balls travel at velocities high enough so that the roughness length matches the seam heigh. The side forces, once tripped, will increase with spin velocity up to a cut-off point. The enhanced lift coefficient is produced by the Magnus effect. The more complex stitching on a baseball permits greater variations in the flight path curve and, in the case of a knuckleball, the unsteady flow effects. For golf balls, the dimples trip the boundary layer and the high spin rate produces a lift coefficient maximum of 0.5, compared to a baseball's maximum of 0.3. Thus, a golf ball travels far enough for gravitational forces to become important.
Applications of URANS on predicting unsteady turbulent separated flows
Institute of Scientific and Technical Information of China (English)
Jinglei Xu; Huiyang Ma
2009-01-01
Accurate prediction of unsteady separated turbu-lent flows remains one of the toughest tasks and a practi-cal challenge for turbulence modeling. In this paper, a 2D flow past a circular cylinder at Reynolds number 3,900 is numerically investigated by using the technique of unsteady RANS (URANS). Some typical linear and nonlinear eddy viscosity turbulence models (LEVM and NLEVM) and a quadratic explicit algebraic stress model (EASM) are evalu-ated. Numerical results have shown that a high-performance cubic NLEVM, such as CLS, are superior to the others in simulating turbulent separated flows with unsteady vortex shedding.
Applications of URANS on predicting unsteady turbulent separated flows
Xu, Jinglei; Ma, Huiyang
2009-06-01
Accurate prediction of unsteady separated turbulent flows remains one of the toughest tasks and a practical challenge for turbulence modeling. In this paper, a 2D flow past a circular cylinder at Reynolds number 3,900 is numerically investigated by using the technique of unsteady RANS (URANS). Some typical linear and nonlinear eddy viscosity turbulence models (LEVM and NLEVM) and a quadratic explicit algebraic stress model (EASM) are evaluated. Numerical results have shown that a high-performance cubic NLEVM, such as CLS, are superior to the others in simulating turbulent separated flows with unsteady vortex shedding.
Dissipation in unsteady turbulence
Bos, Wouter
2016-01-01
Recent experiments and simulations have shown that unsteady turbulent flows, before reaching a dynamic equilibrium state, display a universal behaviour. We show that the observed universal non-equilibrium scaling can be explained using a non-equilibrium correction of Kolmogorov's energy spectrum. Given the universality of the experimental and numerical observations, the ideas presented here lay the foundation for the modeling of a wide class of unsteady turbulent flows.
The Mechanism of Aerodynamic Hysteresis for Sinusoidally Oscillating Delta Wings
Institute of Scientific and Technical Information of China (English)
黄国创; 王玉明; 曹桂兴
1994-01-01
An unsteady model of vortex system is developed to simulate the phenomena of aerodynamic hysteresis of sinusoidally oscillating delta wings.The dynamic behavior of leading-edge separation vortices simulated by the present method is in qualitative agreement with that of flow visualization by Gad-el-Hak and Ho.The calculated lift hysteresis loops are in quantitative agreement with the force measurements in the tunnel.The aerodynamic mechanism of the hysteresis phenomena is further investigated by the present method.
Active Control of Unsteady Gasdynamics for Shock Compression and Turbulence Generation
2012-09-13
see Fig. 1). This study will address the first: unsteady shock wave motion in ducts. II . Background Unsteady shock wave motion through ducts has...simulations were run using the General Aerodynamic Simulation Program ( GASP ) 100 . GASP is a 3D CFD flow solver that was used to compute these...Part II three-dimensional problems. J. Fluid Mech. 1959, 5, 369-386. SHOCK WAVES IN ALL OF THE BELOW: 42Schardin, H. and Reichenbach, H. The
A New Procedure for Simulating Unsteady Flows Through Turbomachinery Blade Passages
Chen, Jen Ping; Celestina, M. L.; Adamczyk, John J.
1996-01-01
The development of two new unsteady wake-blade row aerodynamic interaction models and of a rotor-stator unsteady aerodynamic interaction model are outlined. The solutions of Adamczyk's average-passage flow model were used. The responses to the potential disturbances through a blade row were calculated using the MSUTC code. This code can run with and without the use of wall functions. The solver is an implicit finite volume method with flux Jacobians which are evaluated by the flux-vector splitting and the residual fluxes by the Roe's flux-difference splitting.
Hanson, D. B.; Mccolgan, C. J.; Ladden, R. M.; Klatte, R. J.
1991-01-01
Results of the program for the generation of a computer prediction code for noise of advanced single rotation, turboprops (prop-fans) such as the SR3 model are presented. The code is based on a linearized theory developed at Hamilton Standard in which aerodynamics and acoustics are treated as a unified process. Both steady and unsteady blade loading are treated. Capabilities include prediction of steady airload distributions and associated aerodynamic performance, unsteady blade pressure response to gust interaction or blade vibration, noise fields associated with thickness and steady and unsteady loading, and wake velocity fields associated with steady loading. The code was developed on the Hamilton Standard IBM computer and has now been installed on the Cray XMP at NASA-Lewis. The work had its genesis in the frequency domain acoustic theory developed at Hamilton Standard in the late 1970s. It was found that the method used for near field noise predictions could be adapted as a lifting surface theory for aerodynamic work via the pressure potential technique that was used for both wings and ducted turbomachinery. In the first realization of the theory for propellers, the blade loading was represented in a quasi-vortex lattice form. This was upgraded to true lifting surface loading. Originally, it was believed that a purely linear approach for both aerodynamics and noise would be adequate. However, two sources of nonlinearity in the steady aerodynamics became apparent and were found to be a significant factor at takeoff conditions. The first is related to the fact that the steady axial induced velocity may be of the same order of magnitude as the flight speed and the second is the formation of leading edge vortices which increases lift and redistribute loading. Discovery and properties of prop-fan leading edge vortices were reported in two papers. The Unified AeroAcoustic Program (UAAP) capabilites are demonstrated and the theory verified by comparison with the
KIM, DONG-HYUN; LEE, IN
2000-07-01
A two-degree-of-freedom airfoil with a freeplay non-linearity in the pitch and plunge directions has been analyzed in the transonic and low-supersonic flow region, where aerodynamic non-linearities also exist. The primary purpose of this study is to show aeroelastic characteristics due to freeplay structural non-linearity in the transonic and low-supersonic regions. The unsteady aerodynamic forces on the airfoil were evaluated using two-dimensional unsteady Euler code, and the resulting aeroelastic equations are numerically integrated to obtain the aeroelastic time responses of the airfoil motions and to investigate the dynamic instability. The present model has been considered as a simple aeroelastic model, which is equivalent to the folding fin of an advanced generic missile. From the results of the present study, characteristics of important vibration responses and aeroelastic instabilities can be observed in the transonic and supersonic regions, especially considering the effect of structural non-linearity in the pitch and plunge directions. The regions of limit-cycle oscillation are shown at much lower velocities, especially in the supersonic flow region, than the divergent flutter velocities of the linear structure model. It is also shown that even small freeplay angles can lead to severe dynamic instabilities and dangerous fatigue conditions for the flight vehicle wings and control fins.
Mathematical modeling of the aerodynamic characteristics in flight dynamics
Tobak, M.; Chapman, G. T.; Schiff, L. B.
1984-01-01
Basic concepts involved in the mathematical modeling of the aerodynamic response of an aircraft to arbitrary maneuvers are reviewed. The original formulation of an aerodynamic response in terms of nonlinear functionals is shown to be compatible with a derivation based on the use of nonlinear functional expansions. Extensions of the analysis through its natural connection with ideas from bifurcation theory are indicated.
Prediction of Hyper-X Stage Separation Aerodynamics Using CFD
Buning, Pieter G.; Wong, Tin-Chee; Dilley, Arthur D.; Pao, Jenn L.
2000-01-01
The NASA X-43 "Hyper-X" hypersonic research vehicle will be boosted to a Mach 7 flight test condition mounted on the nose of an Orbital Sciences Pegasus launch vehicle. The separation of the research vehicle from the Pegasus presents some unique aerodynamic problems, for which computational fluid dynamics has played a role in the analysis. This paper describes the use of several CFD methods for investigating the aerodynamics of the research and launch vehicles in close proximity. Specifically addressed are unsteady effects, aerodynamic database extrapolation, and differences between wind tunnel and flight environments.
Whitehead, Allen H., Jr.
1989-01-01
This paper discusses the critical aerodynamic technologies needed to support the development of a class of aircraft represented by the National Aero-Space Plane (NASP). The air-breathing, single-stage-to-orbit mission presents a severe challenge to all of the aeronautical disciplines and demands an extension of the state-of-the-art in each technology area. While the largest risk areas are probably advanced materials and the development of the scramjet engine, there remains a host of design issues and technology problems in aerodynamics, aerothermodynamics, and propulsion integration. The paper presents an overview of the most significant propulsion integration problems, and defines the most critical fluid flow phenomena that must be evaluated, defined, and predicted for the class of aircraft represented by the Aero-Space Plane.
Unsteady bio-fluid dynamics in flying and swimming
Liu, Hao; Kolomenskiy, Dmitry; Nakata, Toshiyuki; Li, Gen
2017-08-01
Flying and swimming in nature present sophisticated and exciting ventures in biomimetics, which seeks sustainable solutions and solves practical problems by emulating nature's time-tested patterns, functions, and strategies. Bio-fluids in insect and bird flight, as well as in fish swimming are highly dynamic and unsteady; however, they have been studied mostly with a focus on the phenomena associated with a body or wings moving in a steady flow. Characterized by unsteady wing flapping and body undulation, fluid-structure interactions, flexible wings and bodies, turbulent environments, and complex maneuver, bio-fluid dynamics normally have challenges associated with low Reynolds number regime and high unsteadiness in modeling and analysis of flow physics. In this article, we review and highlight recent advances in unsteady bio-fluid dynamics in terms of leading-edge vortices, passive mechanisms in flexible wings and hinges, flapping flight in unsteady environments, and micro-structured aerodynamics in flapping flight, as well as undulatory swimming, flapping-fin hydrodynamics, body-fin interaction, C-start and maneuvering, swimming in turbulence, collective swimming, and micro-structured hydrodynamics in swimming. We further give a perspective outlook on future challenges and tasks of several key issues of the field.
Introduction. Computational aerodynamics.
Tucker, Paul G
2007-10-15
The wide range of uses of computational fluid dynamics (CFD) for aircraft design is discussed along with its role in dealing with the environmental impact of flight. Enabling technologies, such as grid generation and turbulence models, are also considered along with flow/turbulence control. The large eddy simulation, Reynolds-averaged Navier-Stokes and hybrid turbulence modelling approaches are contrasted. The CFD prediction of numerous jet configurations occurring in aerospace are discussed along with aeroelasticity for aeroengine and external aerodynamics, design optimization, unsteady flow modelling and aeroengine internal and external flows. It is concluded that there is a lack of detailed measurements (for both canonical and complex geometry flows) to provide validation and even, in some cases, basic understanding of flow physics. Not surprisingly, turbulence modelling is still the weak link along with, as ever, a pressing need for improved (in terms of robustness, speed and accuracy) solver technology, grid generation and geometry handling. Hence, CFD, as a truly predictive and creative design tool, seems a long way off. Meanwhile, extreme practitioner expertise is still required and the triad of computation, measurement and analytic solution must be judiciously used.
Development of a fast-response multi-hole probe for unsteady and turbulent flowfields
Johansen, Espen Sten
The development of a fast-response aerodynamic probe calibration routine has been completed. This work includes the development of a theoretical probe and application and adaptation of potential flow theory to a fast-response 5-hole probe. Based on the theoretical probe, a procedure to determine the flow angles in flowfields with significant inertial effects was devised. It was further shown that this definition can be used to accurately predict the angles in flowfields with very high frequency oscillations (large inertial effects) over a wide range of flow incidence angles. The velocity magnitude was solved from the governing equation. This equation is a first-order, non-linear, ordinary differential equation, and a predictor-corrector method was formulated to calculate the velocity based on the measured port pressures. An experimental procedure to determine the steady and unsteady pressure coefficients was presented. The steady pressure coefficient is readily calculated from steady calibration data, but the determination of the unsteady coefficient requires a selective averaging procedure based on the rate-of-change parameter. A spherical probe with a fast-response pressure transducer was designed. The spherical probe was oscillated in water flow, and the coefficient determination procedure was experimentally verified. A facility was designed for the unsteady calibration of fast-response probes in air. This facility generates a repeatable velocity oscillation that is sinusoidal in nature with mean velocity up to Mach 0.5 and frequency up to 1.5 kHz. A fast-response 5-hole probe was developed that can resolve frequency content up to 20 kHz, and was used to verify the unsteady calibration routine. Several test cases were presented and excellent prediction capabilities were demonstrated. Acoustic pressure attenuation in the tubing systems for miniature multi-hole probes is discussed, and theoretical models are presented that determine the transfer function of such
A Computational Model for Rotor-Fuselage Interactional Aerodynamics
Boyd, D. Douglas, Jr.; Barnwell, Richard W.; Gorton, Susan Althoff
2000-01-01
A novel unsteady rotor-fuselage interactional aerodynamics model has been developed. This model loosely couples a Generalized Dynamic Wake Theory (GDWT) to a thin-layer Navier-Stokes solution procedure. This coupling is achieved using an unsteady pressure jump boundary condition in the Navier-Stokes model. The new unsteady pressure jump boundary condition models each rotor blade as a moving pressure jump which travels around the rotor azimuth and is applied between two adjacent planes in a cylindrical, non-rotating grid. Comparisons are made between measured and predicted time-averaged and time-accurate rotor inflow ratios. Additional comparisons are made between measured and predicted unsteady surface pressures on the top centerline and sides of the fuselage.
Scorer, R S
1958-01-01
Natural Aerodynamics focuses on the mathematics of any problem in air motion.This book discusses the general form of the law of fluid motion, relationship between pressure and wind, production of vortex filaments, and conduction of vorticity by viscosity. The flow at moderate Reynolds numbers, turbulence in a stably stratified fluid, natural exploitation of atmospheric thermals, and plumes in turbulent crosswinds are also elaborated. This text likewise considers the waves produced by thermals, transformation of thin layer clouds, method of small perturbations, and dangers of extra-polation.Thi
Nonpotential aerodynamics for windmills in shear wind, semi-annual report
Energy Technology Data Exchange (ETDEWEB)
Morino, L.
1975-01-01
A theoretical formulation is completed and extended to unsteady flows for analysis of lifting-surface Wind Energy Conversion Systems (WECS) aerodynamics. Its formulation is underway. A numerical formulation of Windmill Incompressible Lifting Surface Aerodynamics (WIlSA) is completed. This program is a modification of the program for Incompressible Lifting Surface aerodynamics. WILSA is completed, debugged, and exercised, and the results are detailed in an attachment. The power coefficient is presented as a function of angular speed. The theoretical formulation for the complex-configuration aerodynamic analysis of WECS includes the unsteadiness of the vorticity in the wake. A numerical formulation of the complex program, Windmill Incompressible Complex Configuration Aerodynamics (WICCA), is completed, debugged, and exercised and the results are presented in an attachment. Modification of WICCA for inclusion of the hub is completed and debugged. A completed preliminary simple formulation for inclusion of the boundary layer effects is provided.
Geometrical Nonlinear Aeroelastic Stability Analysis of a Composite High-Aspect-Ratio Wing
Directory of Open Access Journals (Sweden)
Chang Chuan Xie
2008-01-01
Full Text Available A composite high-aspect-ratio wing of a high-altitude long-endurance (HALE aircraft was modeled with FEM by MSC/NASTRAN, and the nonlinear static equilibrium state is calculated under design load with follower force effect, but without load redistribution. Assuming the little vibration amplitude of the wing around the static equilibrium state, the system is linearized and the natural frequencies and mode shapes of the deformed structure are obtained. Planar doublet lattice method is used to calculate unsteady aerodynamics in frequency domain ignoring the bending effect of the deflected wing. And then, the aeroelastic stability analysis of the system under a given load condition is successively carried out. Comparing with the linear results, the nonlinear displacement of the wing tip is higher. The results indicate that the critical nonlinear flutter is of the flap/chordwise bending type because of the chordwise bending having quite a large torsion component, with low critical speed and slowly growing damping, which dose not appear in the linear analysis. Furthermore, it is shown that the variation of the nonlinear flutter speed depends on the scale of the load and on the chordwise bending frequency. The research work indicates that, for the very flexible HALE aircraft, the nonlinear aeroelastic stability is very important, and should be considered in the design progress. Using present FEM software as the structure solver (e.g. MSC/NASTRAN, and the unsteady aerodynamic code, the nonlinear aeroelastic stability margin of a complex system other than a simple beam model can be determined.
Unsteady turbulent buoyant plumes
Woodhouse, Mark J; Hogg, Andrew J
2015-01-01
We model the unsteady evolution of turbulent buoyant plumes following temporal changes to the source conditions. The integral model is derived from radial integration of the governing equations expressing the conservation of mass, axial momentum and buoyancy. The non-uniform radial profiles of the axial velocity and density deficit in the plume are explicitly described by shape factors in the integral equations; the commonly-assumed top-hat profiles lead to shape factors equal to unity. The resultant model is hyperbolic when the momentum shape factor, determined from the radial profile of the mean axial velocity, differs from unity. The solutions of the model when source conditions are maintained at constant values retain the form of the well-established steady plume solutions. We demonstrate that the inclusion of a momentum shape factor that differs from unity leads to a well-posed integral model. Therefore, our model does not exhibit the mathematical pathologies that appear in previously proposed unsteady i...
El-Asrag, Hossam A.
2011-01-01
Direct simulation of all the length and time scales relevant to practical combustion processes is computationally prohibitive. When combustion processes are driven by reaction and transport phenomena occurring at the unresolved scales of a numerical simulation, one must introduce a dynamic subgrid model that accounts for the multiscale nature of the problem using information available on a resolvable grid. Here, we discuss a model that captures unsteady flow-flame interactions- including extinction, re-ignition, and history effects-via embedded simulations at the subgrid level. The model efficiently accounts for subgrid flame structure and incorporates detailed chemistry and transport, allowing more accurate prediction of the stretch effect and the heat release. In this chapter we first review the work done in the past thirty years to develop the flame embedding concept. Next we present a formulation for the same concept that is compatible with Large Eddy Simulation in the flamelet regimes. The unsteady flame embedding approach (UFE) treats the flame as an ensemble of locally one-dimensional flames, similar to the flamelet approach. However, a set of elemental one-dimensional flames is used to describe the turbulent flame structure directly at the subgrid level. The calculations employ a one-dimensional unsteady flame model that incorporates unsteady strain rate, curvature, and mixture boundary conditions imposed by the resolved scales. The model is used for closure of the subgrid terms in the context of large eddy simulation. Direct numerical simulation (DNS) data from a flame-vortex interaction problem is used for comparison. © Springer Science+Business Media B.V. 2011.
Unsteady Aerodynamics of ``Roll-Tacking'' in Olympic Class Sailboats
Schutt, Riley; Williamson, Chk
2015-11-01
When tacking a sailboat (turning a boat through the wind during upwind sailing), racers employ a ``roll-tacking'' technique. During a roll-tack, sailors use body weight movements to roll the boat through extreme angles of heel. This contrasts with a flat-tack, where the boat remains upright throughout the turn. The dynamic heeling motion of a roll-tack causes the sail to vigorously sweep through the air, resulting in large-scale vortex shedding and increased propulsion. In this research, we use a characteristic roll-tack motion derived from on-the-water data. On-the-water data is collected from a full-scale Olympic racing boat sailed by a national champion in the Laser sailboat class. Using this data, we run a series of representative experiments in the laboratory. Two dimensional flexible sail extrusions are built using rapid-prototyping and are tested in a three degree-of-freedom (X, Y, and theta) towing tank. Particle Image Velocimetry and force measurements are used to compare vortex dynamics and propulsive forces generated by roll-tacks versus flat-tacks. An increase in thrust observed during roll-tack tests agrees with on-the-water experiments, which show a racing advantage greater than one boatlength when a roll-tack is performed relative to a flat tack.
Into Turbulent Air: Hummingbird Aerodynamic Control in Unsteady Circumstances
2016-06-24
of this study, we also completed analysis of hummingbird kinematic responses to transient vertical gusts and to flight in sheared flows , and have...Distribution A - Approved for Public Release 13. SUPPLEMENTARY NOTES 14. ABSTRACT We have completed and published experimental results and analysis pertaining...enough to interact with both wings elicited the greatest changes in roll, pitch, and yaw fluctuations, and also induced major increases in metabolic
Efficient parallel implicit methods for rotary-wing aerodynamics calculations
Wissink, Andrew M.
Euler/Navier-Stokes Computational Fluid Dynamics (CFD) methods are commonly used for prediction of the aerodynamics and aeroacoustics of modern rotary-wing aircraft. However, their widespread application to large complex problems is limited lack of adequate computing power. Parallel processing offers the potential for dramatic increases in computing power, but most conventional implicit solution methods are inefficient in parallel and new techniques must be adopted to realize its potential. This work proposes alternative implicit schemes for Euler/Navier-Stokes rotary-wing calculations which are robust and efficient in parallel. The first part of this work proposes an efficient parallelizable modification of the Lower Upper-Symmetric Gauss Seidel (LU-SGS) implicit operator used in the well-known Transonic Unsteady Rotor Navier Stokes (TURNS) code. The new hybrid LU-SGS scheme couples a point-relaxation approach of the Data Parallel-Lower Upper Relaxation (DP-LUR) algorithm for inter-processor communication with the Symmetric Gauss Seidel algorithm of LU-SGS for on-processor computations. With the modified operator, TURNS is implemented in parallel using Message Passing Interface (MPI) for communication. Numerical performance and parallel efficiency are evaluated on the IBM SP2 and Thinking Machines CM-5 multi-processors for a variety of steady-state and unsteady test cases. The hybrid LU-SGS scheme maintains the numerical performance of the original LU-SGS algorithm in all cases and shows a good degree of parallel efficiency. It experiences a higher degree of robustness than DP-LUR for third-order upwind solutions. The second part of this work examines use of Krylov subspace iterative solvers for the nonlinear CFD solutions. The hybrid LU-SGS scheme is used as a parallelizable preconditioner. Two iterative methods are tested, Generalized Minimum Residual (GMRES) and Orthogonal s-Step Generalized Conjugate Residual (OSGCR). The Newton method demonstrates good
In vivo recording of aerodynamic force with an aerodynamic force platform: from drones to birds.
Lentink, David; Haselsteiner, Andreas F; Ingersoll, Rivers
2015-03-06
Flapping wings enable flying animals and biomimetic robots to generate elevated aerodynamic forces. Measurements that demonstrate this capability are based on experiments with tethered robots and animals, and indirect force calculations based on measured kinematics or airflow during free flight. Remarkably, there exists no method to measure these forces directly during free flight. Such in vivo recordings in freely behaving animals are essential to better understand the precise aerodynamic function of their flapping wings, in particular during the downstroke versus upstroke. Here, we demonstrate a new aerodynamic force platform (AFP) for non-intrusive aerodynamic force measurement in freely flying animals and robots. The platform encloses the animal or object that generates fluid force with a physical control surface, which mechanically integrates the net aerodynamic force that is transferred to the earth. Using a straightforward analytical solution of the Navier-Stokes equation, we verified that the method is accurate. We subsequently validated the method with a quadcopter that is suspended in the AFP and generates unsteady thrust profiles. These independent measurements confirm that the AFP is indeed accurate. We demonstrate the effectiveness of the AFP by studying aerodynamic weight support of a freely flying bird in vivo. These measurements confirm earlier findings based on kinematics and flow measurements, which suggest that the avian downstroke, not the upstroke, is primarily responsible for body weight support during take-off and landing.
Flow field analysis of a pentagonal-shaped bridge deck by unsteady RANS
Directory of Open Access Journals (Sweden)
Md. Naimul Haque
2016-01-01
Full Text Available Long-span cable-stayed bridges are susceptible to dynamic wind effects due to their inherent flexibility. The fluid flow around the bridge deck should be well understood for the efficient design of an aerodynamically stable long-span bridge system. In this work, the aerodynamic features of a pentagonal-shaped bridge deck are explored numerically. The analytical results are compared with past experimental work to assess the capability of two-dimensional unsteady RANS simulation for predicting the aerodynamic features of this type of deck. The influence of the bottom plate slope on aerodynamic response and flow features was investigated. By varying the Reynolds number (2 × 104 to 20 × 104 the aerodynamic behavior at high wind speeds is clarified.
Mechanism of unconventional aerodynamic characteristics of an elliptic airfoil
Directory of Open Access Journals (Sweden)
Sun Wei
2015-06-01
Full Text Available The aerodynamic characteristics of elliptic airfoil are quite different from the case of conventional airfoil for Reynolds number varying from about 104 to 106. In order to reveal the fundamental mechanism, the unsteady flow around a stationary two-dimensional elliptic airfoil with 16% relative thickness has been simulated using unsteady Reynolds-averaged Navier–Stokes equations and the γ-Reθt‾ transition turbulence model at different angles of attack for flow Reynolds number of 5 × 105. The aerodynamic coefficients and the pressure distribution obtained by computation are in good agreement with experimental data, which indicates that the numerical method works well. Through this study, the mechanism of the unconventional aerodynamic characteristics of airfoil is analyzed and discussed based on the computational predictions coupled with the wind tunnel results. It is considered that the boundary layer transition at the leading edge and the unsteady flow separation vortices at the trailing edge are the causes of the case. Furthermore, a valuable insight into the physics of how the flow behavior affects the elliptic airfoil’s aerodynamics is provided.
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.
Adamczyk, J. L.
1974-01-01
An approximate solution is reported for the unsteady aerodynamic response of an infinite swept wing encountering a vertical oblique gust in a compressible stream. The approximate expressions are of closed form and do not require excessive computer storage or computation time, and further, they are in good agreement with the results of exact theory. This analysis is used to predict the unsteady aerodynamic response of a helicopter rotor blade encountering the trailing vortex from a previous blade. Significant effects of three dimensionality and compressibility are evident in the results obtained. In addition, an approximate solution for the unsteady aerodynamic forces associated with the pitching or plunging motion of a two dimensional airfoil in a subsonic stream is presented. The mathematical form of this solution approaches the incompressible solution as the Mach number vanishes, the linear transonic solution as the Mach number approaches one, and the solution predicted by piston theory as the reduced frequency becomes large.
Directory of Open Access Journals (Sweden)
Gang Chen
2012-01-01
Full Text Available It is not easy for the system identification-based reduced-order model (ROM and even eigenmode based reduced-order model to predict the limit cycle oscillation generated by the nonlinear unsteady aerodynamics. Most of these traditional ROMs are sensitive to the flow parameter variation. In order to deal with this problem, a support vector machine- (SVM- based ROM was investigated and the general construction framework was proposed. The two-DOF aeroelastic system for the NACA 64A010 airfoil in transonic flow was then demonstrated for the new SVM-based ROM. The simulation results show that the new ROM can capture the LCO behavior of the nonlinear aeroelastic system with good accuracy and high efficiency. The robustness and computational efficiency of the SVM-based ROM would provide a promising tool for real-time flight simulation including nonlinear aeroelastic effects.
Flutter and forced response of turbomachinery with frequency mistuning and aerodynamic asymmetry
Miyakozawa, Tomokazu
This dissertation provides numerical studies to improve bladed disk assembly design for preventing blade high cycle fatigue failures. The analyses are divided into two major subjects. For the first subject presented in Chapter 2, the mechanisms of transonic fan flutter for tuned systems are studied to improve the shortcoming of traditional method for modern fans using a 3D time-linearized Navier-Stokes solver. Steady and unsteady flow parameters including local work on the blade surfaces are investigated. It was found that global local work monotonically became more unstable on the pressure side due to the flow rollback effect. The local work on the suction side significantly varied due to nodal diameter and flow rollback effect. Thus, the total local work for the least stable mode is dominant by the suction side. Local work on the pressure side appears to be affected by the shock on the suction side. For the second subject presented in Chapter 3, sensitivity studies are conducted on flutter and forced response due to frequency mistuning and aerodynamic asymmetry using the single family of modes approach by assuming manufacturing tolerance. The unsteady aerodynamic forces are computed using CFD methods assuming aerodynamic symmetry. The aerodynamic asymmetry is applied by perturbing the influence coefficient matrix. These aerodynamic perturbations influence both stiffness and damping while traditional frequency mistuning analysis only perturbs the stiffness. Flutter results from random aerodynamic perturbations of all blades showed that manufacturing variations that effect blade unsteady aerodynamics may cause a stable, perfectly symmetric engine to flutter. For forced response, maximum blade amplitudes are significantly influenced by the aerodynamic perturbation of the imaginary part (damping) of unsteady aerodynamic modal forces. This is contrary to blade frequency mistuning where the stiffness perturbation dominates.
Smolyak-Grid-Based Flutter Analysis with the Stochastic Aerodynamic Uncertainty
Directory of Open Access Journals (Sweden)
Yuting Dai
2014-01-01
Full Text Available How to estimate the stochastic aerodynamic parametric uncertainty on aeroelastic stability is studied in this current work. The aerodynamic uncertainty is more complicated than the structural one, and it takes more significant effect on the flutter boundary. First, the nominal unsteady aerodynamic influence coefficients were calculated with the doublet lattice method. Based on this nominal model, the stochastic uncertainty model for unsteady aerodynamic pressure coefficients was constructed with physical meaning. Afterwards, the methodology for flutter uncertainty quantification due to aerodynamic perturbation was developed, based on the nonintrusive polynomial chaos expansion theory. In order to enhance the computational efficiency, the integration algorithm, namely, Smolyak sparse grids, was employed to calculate the coefficients of the stochastic polynomial basis. Finally, the flutter uncertainty analysis methodology was applied to an aircraft's wing model. The influence of uncertainty with uniform distribution for aerodynamic pressure coefficients on flutter boundary was quantified. The numerical results indicate that, the influence of unsteady aerodynamic pressure due to the motion of coupling modes takes significant effect on flutter boundary. It is validated that the flutter uncertainty analysis based on Smolyak sparse grids integration is efficient and accurate for quantifying input uncertainty with high dimensions.
ERCOFTAC Symposium on Unsteady Separation in Fluid-Structure Interaction
Bottaro, Alessandro; Thompson, Mark
2016-01-01
This book addresses flow separation within the context of fluid-structure interaction phenomena. Here, new findings from two research communities focusing on fluids and structures are brought together, emphasizing the importance of a unified multidisciplinary approach. The book covers the theory, experimental findings, numerical simulations, and modeling in fluid dynamics and structural mechanics for both incompressible and compressible separated unsteady flows. There is a focus on the morphing of lifting structures in order to increase their aerodynamic and/or hydrodynamic performances, to control separation and to reduce noise, as well as to inspire the design of novel structures. The different chapters are based on contributions presented at the ERCOFTAC Symposium on Unsteady Separation in Fluid-Structure Interaction held in Mykonos, Greece, 17-21 June, 2013 and include extended discussions and new highlights. The book is intended for students, researchers and practitioners in the broad field of computatio...
Ricketts, R. H.; Watson, J. J.; Sandford, M. C.; Seidel, D. A.
1983-01-01
Wind-tunnel tests to measure unsteady aerodynamic data in the transonic region have been completed on an aspect ratio 2.0 rectangular wing with a supercritical airfoil. The geometric and structural properties of the wing are presented. (Other references contain the measured aerodynamic data.) Both measured and design airfoil coordinates are presented and compared. In addition, measured wing bending and torsional stiffness distributions and some trailing-edge flexibility influence coefficients are presented.
A wake bending unsteady dynamic inflow model of tiltrotor in conversion flight of tiltrotor aircraft
Institute of Scientific and Technical Information of China (English)
YUE HaiLong; XIA PinQi
2009-01-01
The aerodynamics, dynamic responses and aeroelasticity of tiltrotor aircraft in the tilting of rotor i.e.In conversion flight are extraordinarily complicated.The traditional quasi-steady assumption model can not reflect the unsteady aerodynamic problems in the tilting of rotor.The CFD method based on the vortex theory can get better results, but it consumes a lot of computing resources.In this paper, a wake bending dynamic inflow model of tilting rotor was established firstly based on the Peters-He dynamic inflow model used in helicopter.Then combining with the ONERA unsteady aerodynamic model, a wake bending unsteady dynamic inflow model of tilting rotor in conversion flight of tiltrotor aircraft was es-tablished.The wake bending unsteady dynamic inflow model of tilting rotor was verified by using the experimental data of an isolated rotor model in large angle pitching up maneuver and was used to calculate the dynamic responses of tilting rotor in conversion flight of a tiltrotor aircraft model.The calculated results were analyzed to be physically reasonable.
A wake bending unsteady dynamic inflow model of tiltrotor in conversion flight of tiltrotor aircraft
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
The aerodynamics, dynamic responses and aeroelasticity of tiltrotor aircraft in the tilting of rotor i.e. in conversion flight are extraordinarily complicated. The traditional quasi-steady assumption model can not reflect the unsteady aerodynamic problems in the tilting of rotor. The CFD method based on the vortex theory can get better results, but it consumes a lot of computing resources. In this paper, a wake bending dynamic inflow model of tilting rotor was established firstly based on the Peters-He dynamic inflow model used in helicopter. Then combining with the ONERA unsteady aerodynamic model, a wake bending unsteady dynamic inflow model of tilting rotor in conversion flight of tiltrotor aircraft was established. The wake bending unsteady dynamic inflow model of tilting rotor was verified by using the experimental data of an isolated rotor model in large angle pitching up maneuver and was used to calculate the dynamic responses of tilting rotor in conversion flight of a tiltrotor aircraft model. The calculated results were analyzed to be physically reasonable.
Nonpotential aerodynamics for windmills in shear wind. Quarterly report No. 3
Energy Technology Data Exchange (ETDEWEB)
Morino, L.
1975-01-01
The theoretical formulation of the lifting-surface aerodynamic analysis of Wind Energy Conversion Systems (WECS) is extended to unsteady flow and the formulation is included. The completed corresponding numerical formulation for the Windmill Incompressible Lifting Surface Aerodynamics (WILSA) program is listed in an attachment. The power coefficient is presented as a function of angular speed. The improved theoretical formulation for the complex-configuration aerodynamic analysis of WECS is being written. This formulation includes the unsteadiness of vorticity in the wake. The numerical formulation of the computer program, Windmill Incompressible Complex Configuration Aerodynamics (WICCA) is completed, and WICCA is debugged and exercised. The WICCA results are included in an attachment. Modification of WICCA for inclusion of the hub is being debugged. The projected inclusion of viscous effects through vorticity dynamics is replaced with a preliminary simple formulation for inclusion of boundary layer effects, numerical implementation of which is underway.
Research on Aerodynamic Noise Reduction for High-Speed Trains
Yadong Zhang; Jiye Zhang; Tian Li; Liang Zhang; Weihua Zhang
2016-01-01
A broadband noise source model based on Lighthill’s acoustic theory was used to perform numerical simulations of the aerodynamic noise sources for a high-speed train. The near-field unsteady flow around a high-speed train was analysed based on a delayed detached-eddy simulation (DDES) using the finite volume method with high-order difference schemes. The far-field aerodynamic noise from a high-speed train was predicted using a computational fluid dynamics (CFD)/Ffowcs Williams-Hawkings (FW-H)...
Research on Aerodynamic Noise Reduction for High-Speed Trains
Yadong Zhang; Jiye Zhang; Tian Li; Liang Zhang; Weihua Zhang
2016-01-01
A broadband noise source model based on Lighthill’s acoustic theory was used to perform numerical simulations of the aerodynamic noise sources for a high-speed train. The near-field unsteady flow around a high-speed train was analysed based on a delayed detached-eddy simulation (DDES) using the finite volume method with high-order difference schemes. The far-field aerodynamic noise from a high-speed train was predicted using a computational fluid dynamics (CFD)/Ffowcs Williams-Hawkings (FW-H)...
Rottmeier, Fabrice; Bölcs, Albin
2005-01-01
An experimental investigation has been conducted in the non-rotating annular test facility of the "Laboratoire de Thermique Appliquée et de Turbomachines" (LTT), "École Polytechnique Fédérale de Lausanne" (EPFL). During this investigation, the unsteady aerodynamic response of a turbine cascade was investigated for three different cases: (1) the clamped blades subjected to periodic, upstream generated aerodynamic gusts, (2) the cascade forced to vibrate in the travelling wave mode in a uniform...
Rottmeier, Fabrice
2003-01-01
An experimental investigation has been conducted in the non-rotating annular test facility of the "Laboratoire de Thermique Appliquée et de Turbomachines" (LTT), "École Polytechnique Fédérale de Lausanne" (EPFL). During this investigation, the unsteady aerodynamic response of a turbine cascade was investigated for three different cases: (1) the clamped blades subjected to periodic, upstream generated aerodynamic gusts, (2) the cascade forced to vibrate in the travelling wave mode in a uniform...
Jones, R. T. (Compiler)
1979-01-01
A collection of papers on modern theoretical aerodynamics is presented. Included are theories of incompressible potential flow and research on the aerodynamic forces on wing and wing sections of aircraft and on airship hulls.
Advanced Topics in Aerodynamics
DEFF Research Database (Denmark)
Filippone, Antonino
1999-01-01
"Advanced Topics in Aerodynamics" is a comprehensive electronic guide to aerodynamics,computational fluid dynamics, aeronautics, aerospace propulsion systems, design and relatedtechnology. We report data, tables, graphics, sketches,examples, results, photos, technical andscientific literature...
Advanced Topics in Aerodynamics
DEFF Research Database (Denmark)
Filippone, Antonino
1999-01-01
"Advanced Topics in Aerodynamics" is a comprehensive electronic guide to aerodynamics,computational fluid dynamics, aeronautics, aerospace propulsion systems, design and relatedtechnology. We report data, tables, graphics, sketches,examples, results, photos, technical andscientific literature...
Aerodynamic stability of cable-stayed-suspension hybrid bridges
Institute of Scientific and Technical Information of China (English)
ZHANG Xin-jun; SUN Bing-nan
2005-01-01
Three-dimensional nonlinear aerodynamic stability analysis was applied to study the aerodynamic stability of a cable-stayed-suspension (CSS) hybrid bridge with main span of 1400 meters, and the effects of some design parameters (such as the cable sag, length of suspension portion, cable plane arrangement, subsidiary piers in side spans, the deck form, etc.) on the aerodynamic stability of the bridge are analytically investigated. The key design parameters, which significantly influence the aerodynamic stability of CSS hybrid bridges, are pointed out, and based on the wind stability the favorable structural system of CSS hybrid bridges is discussed.
Incremental Aerodynamic Coefficient Database for the USA2
Richardson, Annie Catherine
2016-01-01
In March through May of 2016, a wind tunnel test was conducted by the Aerosciences Branch (EV33) to visually study the unsteady aerodynamic behavior over multiple transition geometries for the Universal Stage Adapter 2 (USA2) in the MSFC Aerodynamic Research Facility's Trisonic Wind Tunnel (TWT). The purpose of the test was to make a qualitative comparison of the transonic flow field in order to provide a recommended minimum transition radius for manufacturing. Additionally, 6 Degree of Freedom force and moment data for each configuration tested was acquired in order to determine the geometric effects on the longitudinal aerodynamic coefficients (Normal Force, Axial Force, and Pitching Moment). In order to make a quantitative comparison of the aerodynamic effects of the USA2 transition geometry, the aerodynamic coefficient data collected during the test was parsed and incorporated into a database for each USA2 configuration tested. An incremental aerodynamic coefficient database was then developed using the generated databases for each USA2 geometry as a function of Mach number and angle of attack. The final USA2 coefficient increments will be applied to the aerodynamic coefficients of the baseline geometry to adjust the Space Launch System (SLS) integrated launch vehicle force and moment database based on the transition geometry of the USA2.
Goto, Susumu; Vassilicos, J. C.
2016-11-01
We have run a total of 311 direct numerical simulations (DNSs) of decaying three-dimensional Navier-Stokes turbulence in a periodic box with values of the Taylor length-based Reynolds number up to about 300 and an energy spectrum with a wide wave-number range of close to -5 /3 power-law dependence at the higher Reynolds numbers. On the basis of these runs, we have found a critical time when (i) the rate of change of the square of the integral length scale turns from increasing to decreasing, (ii) the ratio of interscale energy flux to high-pass filtered turbulence dissipation changes from decreasing to very slowly increasing in the inertial range, (iii) the signature of large-scale coherent structures disappears in the energy spectrum, and (iv) the scaling of the turbulence dissipation changes from the one recently discovered in DNSs of forced unsteady turbulence and in wind tunnel experiments of turbulent wakes and grid-generated turbulence to the classical scaling proposed by G. I. Taylor [Proc. R. Soc. London, Ser. A 151, 421 (1935), 10.1098/rspa.1935.0158] and A. N. Kolmogorov [Dokl. Akad. Nauk SSSR 31, 538 (1941)]. Even though the customary theoretical basis for this Taylor-Kolmogorov scaling is a statistically stationary cascade where large-scale energy flux balances dissipation, this is not the case throughout the entire time range of integration in all our DNS runs. The recently discovered dissipation scaling can be reformulated physically as a situation in which the dissipation rates of the small and large scales evolve together. We advance two hypotheses that may form the basis of a theoretical approach to unsteady turbulence cascades in the presence of large-scale coherent structures.
The interference aerodynamics caused by the wing elasticity during store separation
Lei, Yang; Zheng-yin, Ye
2016-04-01
Air-launch-to-orbit is the technology that has stores carried aloft and launched the store from the plane to the orbit. The separation between the aircraft and store is one of the most important and difficult phases in air-launch-to-orbit technology. There exists strong aerodynamic interference between the aircraft and the store in store separation. When the aspect ratio of the aircraft is large, the elastic deformations of the wing must be considered. The main purpose of this article is to study the influence of the interference aerodynamics caused by the elastic deformations of the wing to the unsteady aerodynamics of the store. By solving the coupled functions of unsteady Navier-Stokes equations, six degrees of freedom dynamic equations and structural dynamic equations simultaneously, the store separation with the elastic deformation of the aircraft considered is simulated numerically. And the interactive aerodynamic forces are analyzed. The study shows that the interference aerodynamics is obvious at earlier time during the separation, and the dominant frequency of the elastic wing determines the aerodynamic forces frequencies of the store. Because of the effect of the interference aerodynamics, the roll angle response and pitch angle response increase. When the store is mounted under the wingtip, the additional aerodynamics caused by the wingtip vortex is obvious, which accelerate the divergence of the lateral force and the lateral-directional attitude angle of the store. This study supports some beneficial conclusions to the engineering application of the air-launch-to-orbit.
Advanced multistage turbine blade aerodynamics, performance, cooling, and heat transfer
Energy Technology Data Exchange (ETDEWEB)
Fleeter, S.; Lawless, P.B. [Purdue Univ., West Lafayette, IN (United States)
1995-10-01
The gas turbine has the potential for power production at the highest possible efficiency. The challenge is to ensure that gas turbines operate at the optimum efficiency so as to use the least fuel and produce minimum emissions. A key component to meeting this challenge is the turbine. Turbine performance, both aerodynamics and heat transfer, is one of the barrier advanced gas turbine development technologies. This is a result of the complex, highly three-dimensional and unsteady flow phenomena in the turbine. Improved turbine aerodynamic performance has been achieved with three-dimensional highly-loaded airfoil designs, accomplished utilizing Euler or Navier-Stokes Computational Fluid Dynamics (CFD) codes. These design codes consider steady flow through isolated blade rows. Thus they do not account for unsteady flow effects. However, unsteady flow effects have a significant impact on performance. Also, CFD codes predict the complete flow field. The experimental verification of these codes has traditionally been accomplished with point data - not corresponding plane field measurements. Thus, although advanced CFD predictions of the highly complex and three-dimensional turbine flow fields are available, corresponding data are not. To improve the design capability for high temperature turbines, a detailed understanding of the highly unsteady and three-dimensional flow through multi-stage turbines is necessary. Thus, unique data are required which quantify the unsteady three-dimensional flow through multi-stage turbine blade rows, including the effect of the film coolant flow. This requires experiments in appropriate research facilities in which complete flow field data, not only point measurements, are obtained and analyzed. Also, as design CFD codes do not account for unsteady flow effects, the next logical challenge and the current thrust in CFD code development is multiple-stage analyses that account for the interactions between neighboring blade rows.
Perching aerodynamics and trajectory optimization
Wickenheiser, Adam; Garcia, Ephrahim
2007-04-01
Advances in smart materials, actuators, and control architecture have enabled new flight capabilities for aircraft. Perching is one such capability, described as a vertical landing maneuver using in-flight shape reconfiguration in lieu of high thrust generation. A morphing, perching aircraft design is presented that is capable of post stall flight and very slow landing on a vertical platform. A comprehensive model of the aircraft's aerodynamics, with special regard to nonlinear affects such as flow separation and dynamic stall, is discussed. Trajectory optimization using nonlinear programming techniques is employed to show the effects that morphing and nonlinear aerodynamics have on the maneuver. These effects are shown to decrease the initial height and distance required to initiate the maneuver, reduce the bounds on the trajectory, and decrease the required thrust for the maneuver. Perching trajectories comparing morphing versus fixed-configuration and stalled versus un-stalled aircraft are presented. It is demonstrated that a vertical landing is possible in the absence of high thrust if post-stall flight capabilities and vehicle reconfiguration are utilized.
Development of the Unsteady Coanda Effect in Human Phonation
Erath, Byron D.; Plesniak, Michael W.
2003-11-01
Human speech is initiated as air passing through the glottis triggers self-sustained oscillations of the vocal folds. These oscillations, caused by aerodynamic air pressures, glottal geometry and tissue properties, result in the glottis cyclically forming into a converging, straight, then diverging passage and finally closing. The varying shape of the glottis throughout the cycle causes different coherent structures to form. One such phenomenon evident in quasi-steady flow experiments is the skewing of the glottal jet towards one wall and attachment, i.e. the Coanda effect. It is not understood if the high frequency oscillations inherent in human phonation allow sufficient time for this oscillating jet to attach to the glottal wall, and thereby influence sound production. Unsteady flow through a high aspect ratio slot with an adjacent plate angled at 30 degrees to the streamwise direction was investigated. The driven, unsteady flow oscillation through the slot was chosen to represent known in-vivo velocity wave forms. Particle Image Velocimetry (PIV) was used to measure the phase-averaged development of the Coanda effect. The evolution of the unsteady Coanda effect over a range of frequencies typical of human phonation will be discussed.
Directory of Open Access Journals (Sweden)
Changchuan Xie
2016-01-01
Full Text Available VFAs (very flexible aircraft have begun to attract significant attention because of their good flight performances and significant application potentials; however, they also bring some challenges to researchers due to their unusual lightweight designs and large elastic deformations. A framework for the geometrically nonlinear aeroelastic stability analysis of very flexible wings is constructed in this paper to illustrate the unique aeroelastic characteristics and convenient use of these designs in engineering analysis. The nonlinear aeroelastic analysis model includes the geometrically nonlinear structure finite elements and steady and unsteady nonplanar aerodynamic computations (i.e., the nonplanar vortex lattice method and nonplanar doublet-lattice method. Fully nonlinear methods are used to analyse static aeroelastic features, and linearized structural dynamic equations are established at the structural nonlinear equilibrium state to estimate the stability of the system through the quasimode of the stressed and deformed structure. The exact flutter boundary is searched via an iterative procedure. A wind tunnel test is conducted to validate this theoretical analysis framework, and reasonable agreement is obtained. Both the analysis and test results indicate that the geometric nonlinearity of very flexible wings presents significantly different aeroelastic characteristics under different load cases with large deformations.
A fully unsteady prescribed wake model for HAWT performance prediction in yawed flow
Energy Technology Data Exchange (ETDEWEB)
Coton, F.N.; Tongguang, Wang; Galbraith, R.A.M.; Lee, D. [Univ. of Glasgow (United Kingdom)
1997-12-31
This paper describes the development of a fast, accurate, aerodynamic prediction scheme for yawed flow on horizontal axis wind turbines (HAWTs). The method is a fully unsteady three-dimensional model which has been developed over several years and is still being enhanced in a number of key areas. The paper illustrates the current ability of the method by comparison with field data from the NREL combined experiment and also describes the developmental work in progress. In particular, an experimental test programme designed to yield quantitative wake convection information is summarised together with modifications to the numerical model which are necessary for meaningful comparison with the experiments. Finally, current and future work on aspects such as tower-shadow and improved unsteady aerodynamic modelling are discussed.
Efficient Global Aerodynamic Modeling from Flight Data
Morelli, Eugene A.
2012-01-01
A method for identifying global aerodynamic models from flight data in an efficient manner is explained and demonstrated. A novel experiment design technique was used to obtain dynamic flight data over a range of flight conditions with a single flight maneuver. Multivariate polynomials and polynomial splines were used with orthogonalization techniques and statistical modeling metrics to synthesize global nonlinear aerodynamic models directly and completely from flight data alone. Simulation data and flight data from a subscale twin-engine jet transport aircraft were used to demonstrate the techniques. Results showed that global multivariate nonlinear aerodynamic dependencies could be accurately identified using flight data from a single maneuver. Flight-derived global aerodynamic model structures, model parameter estimates, and associated uncertainties were provided for all six nondimensional force and moment coefficients for the test aircraft. These models were combined with a propulsion model identified from engine ground test data to produce a high-fidelity nonlinear flight simulation very efficiently. Prediction testing using a multi-axis maneuver showed that the identified global model accurately predicted aircraft responses.
Unsteady adjoint of pressure loss for a fundamental transonic turbine vane
Talnikar, Chaitanya; Laskowski, Gregory M
2015-01-01
High fidelity simulations, e.g., large eddy simulation are often needed for accurately predicting pressure losses due to wake mixing in turbomachinery applications. An unsteady adjoint of such high fidelity simulations is useful for design optimization in these aerodynamic applications. In this paper we present unsteady adjoint solutions using a large eddy simulation model for a vane from VKI using aerothermal objectives. The unsteady adjoint method is effective in capturing the gradient for a short time interval aerothermal objective, whereas the method provides diverging gradients for long time-averaged thermal objectives. As the boundary layer on the suction side near the trailing edge of the vane is turbulent, it poses a challenge for the adjoint solver. The chaotic dynamics cause the adjoint solution to diverge exponentially from the trailing edge region when solved backwards in time. This results in the corruption of the sensitivities obtained from the adjoint solutions. An energy analysis of the unstea...
Unsteady fluid-structure interactions with a heaving compliant membrane wing
Alon Tzezana, Gali; Breuer, Kenneth
2016-11-01
Membrane wings have been shown to provide some benefits over rigid wings at the low Reynolds number regime (Re 103 to 105), specifically improved thrust in flapping flight. Here we present results from a theoretical framework used to characterize the unsteady aeroelastic behavior of compliant membrane wings executing a heaving motion. An analytical model is developed using 2D unsteady thin airfoil theory, coupled with an unsteady membrane equation. Chebyshev collocation methods are used to solve the coupled system efficiently. The model is used to explore the effects of wing compliance, inertia (including added mass effect) and flapping kinematics on the aerodynamic performance, identifying optimal conditions for maximum thrust and propulsive efficiency. A resonant frequency of the coupled system is identified and characterized for different fluid-structure interaction regimes. Extensions to pitching kinematics are also discussed.
Added costs of insect-scale flapping flight in unsteady airflows
Kolomenskiy, Dmitry; Takabayashi, Taku; Ikeda, Teruaki; Ueyama, Kohei; Engels, Thomas; Fisher, Alex; Tanaka, Hiroto; Schneider, Kai; Sesterhenn, Jörn; Liu, Hao
2016-01-01
The aerial environment in the operating domain of small-scale natural and artificial flapping wing fliers is highly complex, unsteady and generally turbulent. Considering flapping flight in an unsteady wind environment with a periodically varying lateral velocity component, we show that body rotations experienced by flapping wing fliers result in the reorientation of the aerodynamic force vector that can render a substantial cumulative deficit in the vertical force. We derive quantitative estimates of the body roll amplitude and the related energetic requirements to maintain the weight support in free flight under such conditions. We conduct force measurements of a miniature hummingbird-inspired robotic flapper and numerical simulations of a bumblebee. In both cases, we demonstrate the loss of weight support due to body roll rotations. Using semi-restrained flight measurements, we demonstrate the increased power requirements to maintain altitude in unsteady winds, achieved by increasing the flapping frequency...
DEFF Research Database (Denmark)
Bergami, Leonardo; Riziotis, Vasilis A.; Gaunaa, Mac
2015-01-01
–inviscid interaction method and an engineering dynamic stall model suitable for implementation in aeroelastic codes based on blade element momentum theory. The aerodynamic integral forces and pitching moment coefficients are first determined in steady conditions, at angles of attack spanning from attached flow...... generated by the airfoil undergoing harmonic pitching motions and harmonic flap deflections. The unsteady aerodynamic coefficients exhibit significant variations over the corresponding steady-state values. The dynamic characteristics of the unsteady response are predicted with an excellent agreement among...
A Synthesis of Hybrid RANS/LES CFD Results for F-16XL Aircraft Aerodynamics
Luckring, James M.; Park, Michael A.; Hitzel, Stephan M.; Jirasek, Adam; Lofthouse, Andrew J.; Morton, Scott A.; McDaniel, David R.; Rizzi, Arthur M.
2015-01-01
A synthesis is presented of recent numerical predictions for the F-16XL aircraft flow fields and aerodynamics. The computational results were all performed with hybrid RANS/LES formulations, with an emphasis on unsteady flows and subsequent aerodynamics, and results from five computational methods are included. The work was focused on one particular low-speed, high angle-of-attack flight test condition, and comparisons against flight-test data are included. This work represents the third coordinated effort using the F-16XL aircraft, and a unique flight-test data set, to advance our knowledge of slender airframe aerodynamics as well as our capability for predicting these aerodynamics with advanced CFD formulations. The prior efforts were identified as Cranked Arrow Wing Aerodynamics Project International, with the acronyms CAWAPI and CAWAPI-2. All information in this paper is in the public domain.
Computational aerodynamics and aeroacoustics for wind turbines
Energy Technology Data Exchange (ETDEWEB)
Shen, W.Z.
2009-10-15
was developed in [11], and in [12] tunnel wall corrections for wind tunnels with closed or open test sections were developed. The second part of the thesis deals with Computational Aero-Acoustics (CAA). With the spread of wind turbines near urban areas, there is an increasing need for accurate predictions of aerodynamically generated noise. Indeed, noise has become one of the most important issues for further development of wind power, and the iv Wen Zhong Shen ability of controlling and minimising noise emission may be advantageous when competing on the world energy market. To predict generation and propagation of aerodynamic noise, it is required to solve the compressible Navier-Stokes equations. As the scales of the flow and the acoustic waves are quite different (about 1/M, M=Mach number=Uinfinity/c), it is difficult to resolve them together at the same time. Hardin and Pope proposed a non-linear two-step (viscous incompressible flow and inviscid acoustic perturbation) splitting procedure for computational aero-acoustics that is suitable for both generation and propagation. The advantage of the splitting approach, as compared to the acoustic analogies, is that the source strength is obtained directly and that it accounts for sound radiation as well as scattering. In [13] and [14] an inconsistency in the original formulation of Hardin and Pope 1994 was analysed and a consistent formulation was proposed and applied to laminar flows. An aero-acoustic formulation for turbulent flows was in [15] developed for Large Eddy Simulation (LES), Unsteady Reynolds Averaged Navier-Stokes Simulation (URANS) and Detached Eddy Simulation (DES). In [16] a collocated grid / finite volume method for aero-acoustic computations was developed and implemented in the EllipSys2D/3D code. In [17] and [18] three dimensional flowacoustic computations were carried out. Finally, the aero-acoustic formulation using high order Finite Difference schemes (Dispersion Relation Preserving (DRP
INTEGRATED AERODYNAMIC MEASUREMENTS
SCHUTTE, HK
1992-01-01
The myoelastic-aerodynamic model of phonation implies that aerodynamic factors are crucial to the evaluation of voice function, Subglottal pressure and mean flow rate represent the vocal power source. If they can be related to the magnitude of the radiated sound power, they may provide an index of v
Reinforced aerodynamic profile
DEFF Research Database (Denmark)
2010-01-01
The present invention relates to the prevention of deformations in an aerodynamic profile caused by lack of resistance to the bending moment forces that are created when such a profile is loaded in operation. More specifically, the invention relates to a reinforcing element inside an aerodynamic...
Energy Technology Data Exchange (ETDEWEB)
1992-01-01
Consideration is given to vortex physics and aerodynamics; supersonic/hypersonic aerodynamics; STOL/VSTOL/rotors; missile and reentry vehicle aerodynamics; CFD as applied to aircraft; unsteady aerodynamics; supersonic/hypersonic aerodynamics; low-speed/high-lift aerodynamics; airfoil/wing aerodynamics; measurement techniques; CFD-solvers/unstructured grid; airfoil/drag prediction; high angle-of-attack aerodynamics; and CFD grid methods. Particular attention is given to transonic-numerical investigation into high-angle-of-attack leading-edge vortex flow, prediction of rotor unsteady airloads using vortex filament theory, rapid synthesis for evaluating the missile maneuverability parameters, transonic calculations of wing/bodies with deflected control surfaces; the static and dynamic flow field development about a porous suction surface wing; the aircraft spoiler effects under wind shear; multipoint inverse design of an infinite cascade of airfoils, turbulence modeling for impinging jet flows; numerical investigation of tail buffet on the F-18 aircraft; the surface grid generation in a parameter space; and the flip flop nozzle extended to supersonic flows.
Unsteady simulation for a high-speed train entering a tunnel
Institute of Scientific and Technical Information of China (English)
Xin-hua LI; Jian DENG; Da-wei CHEN; Fang-fang XIE; Yao ZHENG
2011-01-01
In order to study the unsteady aerodynamics effects in railway turmels,the 3D Reynolds average Navier-Stokes equations of a viscous compressible fluid are solved,and the two-equation k-ε model is used in the simulation of turbulence,while the dynamic grid technique is employed for moving bodies.We focus on obtaining the changing tendencies of the aerodynamic force of the train and the aerodynamic pressures on the tunnel wall and train surface,and discovering the relationship between the velocity of the train and the intensity of the micro pressure wave at the tunnel exit.It is shown that the amplitudes of the pressure changes in the tunnel and on the train surface are both approximately proportional to the square of the train speed,so are the microwave and the drag of the train.
Aerodynamics of advanced axial-flow turbomachinery
Serovy, G. K.; Kavanagh, P.; Kiishi, T. H.
1980-01-01
A multi-task research program on aerodynamic problems in advanced axial-flow turbomachine configurations was carried out at Iowa State University. The elements of this program were intended to contribute directly to the improvement of compressor, fan, and turbine design methods. Experimental efforts in intra-passage flow pattern measurements, unsteady blade row interaction, and control of secondary flow are included, along with computational work on inviscid-viscous interaction blade passage flow techniques. This final report summarizes the results of this program and indicates directions which might be taken in following up these results in future work. In a separate task a study was made of existing turbomachinery research programs and facilities in universities located in the United States. Some potentially significant research topics are discussed which might be successfully attacked in the university atmosphere.
Nonlinear airship aeroelasticity
Bessert, N.; Frederich, O.
2005-12-01
The aeroelastic derivatives for today's aircraft are calculated in the concept phase using a standard procedure. This scheme has to be extended for large airships, due to various nonlinearities in structural and aerodynamic behaviour. In general, the structural model of an airship is physically as well as geometrically nonlinear. The main sources of nonlinearity are large deformations and the nonlinear material behaviour of membranes. The aerodynamic solution is also included in the nonlinear problem, because the deformed airship influences the surrounding flow. Due to these nonlinearities, the aeroelastic problem for airships can only be solved by an iterative procedure. As one possibility, the coupled aerodynamic and structural dynamic problem was handled using linked standard solvers. On the structural side, the Finite-Element program package ABAQUS was extended with an interface to the aerodynamic solver VSAERO. VSAERO is based on the aerodynamic panel method using potential flow theory. The equilibrium of the internal structural and the external aerodynamic forces leads to the structural response and a trimmed flight state for the specified flight conditions (e.g. speed, altitude). The application of small perturbations around a trimmed state produces reaction forces and moments. These constraint forces are then transferred into translational and rotational acceleration fields by performing an inertia relief analysis of the disturbed structural model. The change between the trimmed flight state and the disturbed one yields the respective aeroelastic derivatives. By including the calculated derivatives in the linearised equation of motion system, it is possible to judge the stability and controllability of the investigated airship.
Berrino, M.; Satta, F.; Simoni, D.; Ubaldi, M.; Zunino, P.; Bertini, F.
2014-02-01
The present paper reports the results of an experimental investigation aimed at comparing aerodynamic performance of three low-pressure turbine cascades for several Reynolds numbers under steady and unsteady inflows. This study is focused on finding design criteria useful to reduce both profile and secondary losses in the aero-engine LP turbine for the different flight conditions. The baseline blade cascade, characterized by a standard aerodynamic loading (Zw=1.03), has been compared with two Ultra-High-Lift profiles with the same Zweifel number (Zw=1.3 for both cascades), but different velocity peak positions, leading to front and mid-loaded blade cascade configurations. The aerodynamic flow fields downstream of the cascades have been experimentally investigated for Reynolds numbers in the range 70000plane downstream of the cascade for both inflow conditions. The analysis of the results allows the evaluation of the aerodynamic performance of the blade cascades in terms of profile and secondary losses and the understanding of the effects of loading distribution and Zweifel number on secondary flows. When operating under unsteady inflow, contrarily to the steady case, the mid-loaded cascade has been found to be characterized by the lowest profile and secondary losses, making it the most attractive solution for the design of blades working in real conditions where unsteady inflow effects are present.
Dynamic control of aerodynamic forces on a moving platform using active flow control
Brzozowski, Daniel P.
The unsteady interaction between trailing edge aerodynamic flow control and airfoil motion in pitch and plunge is investigated in wind tunnel experiments using a two degree-of-freedom traverse which enables application of time-dependent external torque and forces by servo motors. The global aerodynamic forces and moments are regulated by controlling vorticity generation and accumulation near the trailing edge of the airfoil using hybrid synthetic jet actuators. The dynamic coupling between the actuation and the time-dependent flow field is characterized using simultaneous force and particle image velocimetry (PIV) measurements that are taken phase-locked to the commanded actuation waveform. The effect of the unsteady motion on the model-embedded flow control is assessed in both trajectory tracking and disturbance rejection maneuvers. The time-varying aerodynamic lift and pitching moment are estimated from a PIV wake survey using a reduced order model based on classical unsteady aerodynamic theory. These measurements suggest that the entire flow over the airfoil readjusts within 2--3 convective time scales, which is about two orders of magnitude shorter than the characteristic time associated with the controlled maneuver of the wind tunnel model. This illustrates that flow-control actuation can be typically effected on time scales that are commensurate with the flow's convective time scale, and that the maneuver response is primarily limited by the inertia of the platform.
Directory of Open Access Journals (Sweden)
A. Ishak
2012-08-01
Full Text Available An analysis is carried out to study the unsteady two dimensional stagnation point flow and heat transfer over a stretching/shrinking sheet with prescribed surface heat flux. The governing partial differential equations are converted into nonlinear ordinary differential equations using similarity variables, and solved numerically. The effects of the unsteadiness parameter A, stretching/shrinking parameter ε and Prandtl number Pr on the flow and heat transfer characteristics are studied. It is found that the skin friction f′′(0 and the local Nusselt number 1θ(0 increase as the the unsteadiness parameter A increases. Moreover, the velocity and temperature increase as ε and Pr increase.
Numerical modeling of wind turbine aerodynamic noise in the time domain.
Lee, Seunghoon; Lee, Seungmin; Lee, Soogab
2013-02-01
Aerodynamic noise from a wind turbine is numerically modeled in the time domain. An analytic trailing edge noise model is used to determine the unsteady pressure on the blade surface. The far-field noise due to the unsteady pressure is calculated using the acoustic analogy theory. By using a strip theory approach, the two-dimensional noise model is applied to rotating wind turbine blades. The numerical results indicate that, although the operating and atmospheric conditions are identical, the acoustical characteristics of wind turbine noise can be quite different with respect to the distance and direction from the wind turbine.
Energy Technology Data Exchange (ETDEWEB)
Rusanov, A.V.; Yershov, S.V. [Institute of Mechanical Engineering Problems of National Academy of Sciences of Ukraine Kharkov (Ukraine)
1997-12-31
The numerical method is suggested for the calculation of the 3D periodically unsteady viscous cascade flow evoked by the aerodynamics interaction of blade rows. Such flow is described by the thin-layer Reynolds-averaged unsteady Navier-Stokes equations. The turbulent effects are simulated with the modified Baldwin-Lomax turbulence model. The problem statement allows to consider an unsteady flow through either a single turbo-machine stage or a multi stage turbomachine. The sliding mesh techniques and the time-space non-oscillatory square interpolation are used in axial spacings to calculate the flow in a computational domain that contains the reciprocally moving elements. The gasdynamical equations are integrated numerically with the implicit quasi-monotonous Godunov`s type ENO scheme of the second or third order of accuracy. The suggested numerical method is incorporated in the FlowER code developed by authors for calculations of the 3D viscous compressible flows through multi stage turbomachines. The numerical results are presented for unsteady turbine stage throughflows. The method suggested is shown to simulate qualitatively properly the main unsteady cascade effects in particular the periodically blade loadings, the propagation of stator wakes through rotor blade passage and the unsteady temperature flowfields for stages with cooled stator blades. (author) 21 refs.
Horstman, Raymond H.
1992-01-01
Aerodynamic flow achieved by adding fixed fairings to butterfly valve. When valve fully open, fairings align with butterfly and reduce wake. Butterfly free to turn, so valve can be closed, while fairings remain fixed. Design reduces turbulence in flow of air in internal suction system. Valve aids in development of improved porous-surface boundary-layer control system to reduce aerodynamic drag. Applications primarily aerospace. System adapted to boundary-layer control on high-speed land vehicles.
Numerical study of unsteady starting characteristics of a hypersonic inlet
Institute of Scientific and Technical Information of China (English)
Wang Weixing; Guo Rongwei
2013-01-01
The impulse and self starting characteristics of a mixed-compression hypersonic inlet designed at Mach number of 6.5 are studied by applying the unsteady computational fluid dynamics (CFD) method.The full Navier-Stokes equations are solved with the assumption of viscous perfect gas model,and the shear-stress transport (SST) k-ω two-equation Reynolds averaged NavierStokes (RANS) model is used for turbulence modeling.Results indicate that during impulse starting,the flow field is divided into three zones with different aerodynamic parameters by primary shock and upstream-facing shock.The separation bubble on the shoulder of ramp undergoes a generating,growing,swallowing and disappearing process in sequence.But a separation bubble at the entrance of inlet exists until the freestream velocity is accelerated to the starting Mach number during self starting.The mass flux distribution of flow field is non-uniform because of the interaction between shock and boundary layer,so that the mass flow rate at throat is unsteady during impulse starting.The duration of impulse starting process increases almost linearly with the decrease of fleestream Mach number but rises abruptly when the freestream Mach number approaches the starting Mach number.The accelerating performance of booster almost has no influence on the self starting ability of hypersonic inlet.
Unsteady unidirectional micropolar fluid flow
Institute of Scientific and Technical Information of China (English)
无
2011-01-01
This paper considers the unsteady unidirectional flow of a micropolar fluid, produced by the sudden application of an arbitrary time dependent pressure gradient, between two parallel plates. The no-slip and the no-spin boundary conditions are used. Exact solutions for the velocity and microrotation distributions are obtained based on the use of the complex inversion formula of Laplace transform. The solution of the problem is also considered if the upper boundary of the flow is a free surface. The particula...
Mechanics and aerodynamics of insect flight control.
Taylor, G K
2001-11-01
Insects have evolved sophisticated fight control mechanisms permitting a remarkable range of manoeuvres. Here, I present a qualitative analysis of insect flight control from the perspective of flight mechanics, drawing upon both the neurophysiology and biomechanics literatures. The current literature does not permit a formal, quantitative analysis of flight control, because the aerodynamic force systems that biologists have measured have rarely been complete and the position of the centre of gravity has only been recorded in a few studies. Treating the two best-known insect orders (Diptera and Orthoptera) separately from other insects, I discuss the control mechanisms of different insects in detail. Recent experimental studies suggest that the helicopter model of flight control proposed for Drosophila spp. may be better thought of as a facultative strategy for flight control, rather than the fixed (albeit selected) constraint that it is usually interpreted to be. On the other hand, the so-called 'constant-lift reaction' of locusts appears not to be a reflex for maintaining constant lift at varying angles of attack, as is usually assumed, but rather a mechanism to restore the insect to pitch equilibrium following a disturbance. Differences in the kinematic control mechanisms used by the various insect orders are related to differences in the arrangement of the wings, the construction of the flight motor and the unsteady mechanisms of lift production that are used. Since the evolution of insect flight control is likely to have paralleled the evolutionary refinement of these unsteady aerodynamic mechanisms, taxonomic differences in the kinematics of control could provide an assay of the relative importance of different unsteady mechanisms. Although the control kinematics vary widely between orders, the number of degrees of freedom that different insects can control will always be limited by the number of independent control inputs that they use. Control of the moments
WECS Incompressible Complex Configuration Aerodynamics (WICCA)
Energy Technology Data Exchange (ETDEWEB)
Preuss, R.; Morino, L.
1976-05-01
A finite-element method for determining the aerodynamic loading on rotors is presented. The report describes the development of the formulation for the steady state and numerical results for horizontal axis windmills. It is based on a general theory for uncompressible potential aerodynamics for complex configurations in a rotating frame of reference. If a rotor is rotating at constant angular velocity and is directed along a uniform wind distribution, the problem may be solved in the steady state for a frame of reference rotating with the rotor. A computer program (WICCA) has been designed to incorporate the method, and results compare favorably with an existing lifting surface formation. The program has been modified to include the hub for analysis. Further modifications are planned to study the effect of the coning angle, chord length distribution, blade pitch angle distribution, and airfoil section. The method may also be applied to unsteady flow problems such as non-uniform wind distributions (windmills in shear winds). The appendices contain graphs, the verification of expressions for the indefinite doublet and source integrals, proof of far wake, and hub geometry.
Yang, Lei; Ye, Zheng-Yin; Wu, Jie
2016-11-01
The separation between the carrier and store is one of the most important and difficult phases in Air-launch-to-orbit technology. Based on the previous researches, the interference aerodynamic forces of the store caused by the carrier are obvious in the earlier time during the separation. And the interference aerodynamics will be more complex when considering the elastic deformation of the carrier. Focusing on the conditions that in the earlier time during the separation, the steady and unsteady interference aerodynamic forces of the store are calculated at different angle of attacks and relative distances between the carrier and store. During the calculation, the elastic vibrations of the carrier are considered. According to the cause of formations of the interference aerodynamics, the interference aerodynamic forces of the store are divided into several components. The relative magnitude, change rule, sphere of influence and mechanism of interference aerodynamic forces components of the store are analyzed quantitatively. When the relative distance between the carrier and store is small, the interference aerodynamic forces caused by the elastic vibration of the carrier is about half of the total aerodynamic forces of the store. And as the relative distance increases, the value of interference aerodynamic forces decrease. When the relative distance is larger than twice the mean aerodynamic chord of the carrier, the values of interference aerodynamic forces of the store can be ignored. Besides, under the influence of the steady interference aerodynamic forces, the lift characteristics of the store are worse and the static stability margin is poorer.
Institute of Scientific and Technical Information of China (English)
Lei Shi; Chengchun Zhang; Jing Wang; Luquan Ren
2012-01-01
Flow control can effectively reduce the aerodynamic noise radiated from a circular cylinder.As one of the flow control methods,a bionic method,inspired by the serrations at the leading edge of owls' wing,was proposed in this paper.The effects of bionic serrated structures arranged on the upper and lower sides of a cylinder on the aerodynamic and aeroacoustic performance of the cylinder were numerically investigated.At a free stream speed of 24.5 m·s-1,corresponding to Reynolds number of 1.58 × 104,the simulation results indicate that the bionic serrated structures can decrease the frequency of the vortex shedding and control the fluctuating aerodynamic force acting on the cylinder,thus reduce the aerodynamic noise.A qualitative-view of the vorticity in the wake of the cylinder suggest that the serrated structures reduce aerodynamic sound by suppressing the unsteady motion of vortices.
Energy Technology Data Exchange (ETDEWEB)
Bergami, L.; Gaunaa, M.
2012-02-15
The report presents the ATEFlap aerodynamic model, which computes the unsteady lift, drag and moment on a 2D airfoil section equipped with Adaptive Trailing Edge Flap. The model captures the unsteady response related to the effects of the vorticity shed into the wake, and the dynamics of flow separation a thin-airfoil potential flow model is merged with a dynamic stall model of the Beddoes-Leishmann type. The inputs required by the model are steady data for lift, drag, and moment coefficients as function of angle of attack and flap deflection. Further steady data used by the Beddoes- Leishmann dynamic stall model are computed in an external preprocessor application, which gives the user the possibility to verify, and eventually correct, the steady data passed to the aerodynamic model. The ATEFlap aerodynamic model is integrated in the aeroelastic simulation tool HAWC2, thus al- lowing to simulate the response of a wind turbine with trailing edge flaps on the rotor. The algorithms used by the preprocessor, and by aerodynamic model are presented, and modifications to previous implementations of the aerodynamic model are briefly discussed. The performance and the validity of the model are verified by comparing the dynamic response computed by the ATEFlap with solutions from CFD simulations. (Author)
Effects of fluid-structure interaction on the aerodynamics of an insect wing
Nguyen, Anh Tuan; Han, Jae-Hung
2016-04-01
In this paper, an insect wing structure is modeled based on data obtained from measurements on real hawkmoth (Manduca Sexta) wings. The aerodynamics of insect wings is simulated by an extended unsteady vortex-lattice method. The finite-element model of a flexible hawkmoth wing is built and validated. A computer program, which couples the finite-element model with the aerodynamic model, is used to study the effects of fluid-structure interaction. Some important features due to the fluid-structure interaction in hovering and forward flight are observed in the present study.
CONDITIONS OF PHYSICAL MODELING AERODYNAMIC CHARACTERISTICS OF AIRCRAFT WITH CHASSIS HOVERCRAFT
Directory of Open Access Journals (Sweden)
Yu. Yu. Merzlikin
2015-01-01
Full Text Available The features of the physical modeling in the experimental determination of aerodynamics-cal tubes (WT of low-velocity steady and unsteady aerodynamic characteristics at takeoff and landing of aircraft (LA with the chassis air-cushion (ball screw and in studies to determine the stability of equilibrium regimes of movement and shock-absorbing properties of ball screws. Are conscdered the requirements for the experimental facilities, model aircraft with ball screws and re-test of the latest zhimam on the free stream velocity, flow and pressure blowers VР, the frequencies and amplitudes of the oscillations are formulated.
Wind energy conversion. Volume II. Aerodynamics of horizontal axis wind turbines
Energy Technology Data Exchange (ETDEWEB)
Miller, R.H.; Dugundji, J.; Martinez-Sanchez, M.; Gohard, J.; Chung, S.; Humes, T.
1978-09-01
The basic aerodynamic theory of the wind turbine is presented, starting with the simple momentum theory based on uniform inflow and an infinite number of blades. The basic vortex theory is then developed. Following these basics, the more complete momentum theory, including swirl, non-uniform inflow, the effect of a finite number of blades, and empirical correction for the vortex ring condition is presented. The more complete vortex theory is presented which includes unsteady aerodynamic effects but based on a semi-rigid wake. Methods of applying this theory for performance estimation are discussed as well as for the purpose of computing time varying airloads due to windshear and tower interference.
Numerical simulation of the transient aerodynamic phenomena induced by passing manoeuvres
Uystepruyst, David
2015-01-01
Several three-dimensional Unsteady Reynolds-Averaged Navier-Stokes (URANS) simulations of the passing generic vehicles (Ahmed bodies) are presented. The relative motion of vehicles was obtained using a combination of deforming and sliding computational grids. The vehicle studied is an Ahmed body with an angle of the rear end slanted surface of $30^{\\circ}$. Several different relative velocities and transversal distances between vehicles were studied. The aerodynamic influence of the passage on the overtaken vehicle was studied. The results of the simulations were found to agree well with the existing experimental data. Numerical results were used to explain effects of the overtaking manoeuvre on the main aerodynamic coefficients.
An asymptotic model of unsteady airway reopening.
Naire, S; Jensen, O E
2003-12-01
We consider a simple physical model for the reopening of a collapsed lung airway involving the unsteady propagation of a long bubble of air, driven at a prescribed flow-rate, into a liquid-filled channel formed by two flexible membranes that are held under large longitudinal tension and are confined between two parallel rigid plates. This system is described theoretically using an asymptotic approximation, valid for uniformly small membrane slopes, which reduces to a fourth-order nonlinear evolution equation for the channel width ahead of the bubble tip, from which the time-evolution of the bubble pressure pb* and bubble speed may be determined. The model shows that there can be a substantial delay between the time at which the bubble starts to grow in volume and the time at which its tip starts to move. Under certain conditions, the start of the bubble's motion is accompanied by a transient overshoot in pb*, as seen previously in experiment; the model predicts that the overshoot is greatest in narrow channels when the bubble is driven with a large volume flux. It is also shown how the threshold pressure for steady bubble propagation in wide channels has distinct contributions from the capillary pressure drop across the bubble tip and viscous dissipation in the channel ahead of the bubble.
Unsteady axisymmetric flow and heat transfer over time-dependent radially stretching sheet
Directory of Open Access Journals (Sweden)
Azeem Shahzad
2017-03-01
Full Text Available This article address the boundary layer flow and heat transfer of unsteady and incompressible viscous fluid over an unsteady stretching permeable surface. First of all modeled nonlinear partial differential equations are transformed to a system of ordinary differential equations by using similarity transformations. Analytic solution of the reduced problem is constructed by using homotopy analysis method (HAM. To validate the constructed series solution a numerical counterpart is developed using shooting algorithm based on Runge-Kutta method. Both schemes are in an excellent agreement. The effects of the pertinent parameters on the velocity and energy profile are shown graphically and examined in detail.
Predicting wind-induced vibrations of high-rise buildings using unsteady CFD and modal analysis
Zhang, Yue
2015-01-01
This paper investigates the wind-induced vibration of the CAARC standard tall building model, via unsteady Computational Fluid Dynamics (CFD) and a structural modal analysis. In this numerical procedure, the natural unsteady wind in the atmospheric boundary layer is modeled with an artificial inflow turbulence generation method. Then, the turbulent flow is simulated by the second mode of a Zonal Detached-Eddy Simulation, and a conservative quadrature-projection scheme is adopted to transfer unsteady loads from fluid to structural nodes. The aerodynamic damping that represents the fluid-structure interaction mechanism is determined by empirical functions extracted from wind tunnel experiments. Eventually, the flow solutions and the structural responses in terms of mean and root mean square quantities are compared with experimental measurements, over a wide range of reduced velocities. The significance of turbulent inflow conditions and aeroelastic effects is highlighted. The current methodology provides predictions of good accuracy and can be considered as a preliminary design tool to evaluate the unsteady wind effects on tall buildings.
Aeroacoustic Study of a High-Fidelity Aircraft Model. Part 2; Unsteady Surface Pressures
Khorrami, Mehdi R.; Neuhart, Danny H.
2012-01-01
In this paper, we present unsteady surface pressure measurements for an 18%-scale, semi-span Gulfstream aircraft model. This high-fidelity model is being used to perform detailed studies of airframe noise associated with main landing gear, flap components, and gear-flap interaction noise, as well as to evaluate novel noise reduction concepts. The aerodynamic segment of the tests, conducted in the NASA Langley Research Center 14- by 22-Foot Subsonic Tunnel, was completed in November 2010. To discern the characteristics of the surface pressure fluctuations in the vicinity of the prominent noise sources, unsteady sensors were installed on the inboard and outboard flap edges, and on the main gear wheels, struts, and door. Various configurations were tested, including flap deflections of 0?, 20?, and 39?, with and without the main landing gear. The majority of unsteady surface pressure measurements were acquired for the nominal landing configuration where the main gear was deployed and the flap was deflected 39?. To assess the Mach number variation of the surface pressure amplitudes, measurements were obtained at Mach numbers of 0.16, 0.20, and 0.24. Comparison of the unsteady surface pressures with the main gear on and off shows significant interaction between the gear wake and the inboard flap edge, resulting in higher amplitude fluctuations when the gear is present.
Unsteady airfoil flows with application to aeroelastic stability
Energy Technology Data Exchange (ETDEWEB)
Johansen, Jeppe
1999-09-01
The present report describes numerical investigation of two-dimensional unsteady airfoil flows with application to aeroelastic stability. The report is divided in two parts. Part A describes the purely aerodynamic part, while Part B includes the aeroelastic part. In Part A a transition prediction algorithm based on a simplified version of the e{sup n} method is proposed. Laminar Boundary Layer instability data are stored in a database from which stability characteristics can be extracted by interpolation. Input to the database are laminar integral boundary layer parameters. These are computed from an integral boundary layer formulation coupled to a Navier-Stokes flow solver. Five different airfoils are considered at fixed angle of attack, and the flow is computed assuming both fully turbulent and transitional flow and compared with experimental data. Results indicate that using a transition model the drag prediction is improved considerably. Also the lift is slightly improved. At high angles of attack transition will affect leading edge separation which again will affect the overall vortex shedding. If the transition point is not properly predicted this will affect the whole hysteresis curve. The transition model developed in the present work showed more stable predictions compared to the empirical transition model. In Part B a simple three degrees-of-freedom (DOF) structural dynamics model is developed and coupled to the aerodynamics models from Part A. A 2nd order accurate time integration scheme is used to solve the equations of motion. Two airfoils are investigated. The aeroelastic models predict stable conditions well at low angle of attack. But at high angles of attack, and where unstable behaviour is expected, only the Navier-Stokes solver predict correct aeroelastic response. The semi-empirical dynamic stall model does not predict vortex shedding and moment correctly leading to an erroneous aerodynamic damping. (au) 5 tabs.; 55 ills., 52 refs.
Vortex Interaction and Roll-Up in Unsteady Flow past Tandem Airfoils
Directory of Open Access Journals (Sweden)
H. Aziz
2016-01-01
Full Text Available A discrete vortex model coupled with a vortex dissipation and vortex core criteria is used to study the unsteady ﬂow past two airfoils in conﬁguration. The unsteady wakes of the airfoils are modeled by discrete vortices and time-stepping is used to predict the individual wake shapes. The coupled ﬂow is solved using a combined zero-normal ﬂow boundary condition and Kelvin condition which result in (2N + 2X(2N + 2 equations. Results are presented showing the eﬀect of airfoil-airfoil and airfoil-wake interaction on the aerodynamic characteristics of the conﬁguration. The eﬀect of relative velocity, rate of pitching and phase-lag are studied on airfoil performance and wake shape is predicted.
Evaluation of the constant pressure panel method (CPM) for unsteady air loads prediction
Appa, Kari; Smith, Michael J. C.
1988-01-01
This paper evaluates the capability of the constant pressure panel method (CPM) code to predict unsteady aerodynamic pressures, lift and moment distributions, and generalized forces for general wing-body configurations in supersonic flow. Stability derivatives are computed and correlated for the X-29 and an Oblique Wing Research Aircraft, and a flutter analysis is carried out for a wing wind tunnel test example. Most results are shown to correlate well with test or published data. Although the emphasis of this paper is on evaluation, an improvement in the CPM code's handling of intersecting lifting surfaces is briefly discussed. An attractive feature of the CPM code is that it shares the basic data requirements and computational arrangements of the doublet lattice method. A unified code to predict unsteady subsonic or supersonic airloads is therefore possible.
Aerodynamic Analysis of Multistage Turbomachinery Flows in Support of Aerodynamic Design
Adamczyk, John J.
1999-01-01
This paper summarizes the state of 3D CFD based models of the time average flow field within axial flow multistage turbomachines. Emphasis is placed on models which are compatible with the industrial design environment and those models which offer the potential of providing credible results at both design and off-design operating conditions. The need to develop models which are free of aerodynamic input from semi-empirical design systems is stressed. The accuracy of such models is shown to be dependent upon their ability to account for the unsteady flow environment in multistage turbomachinery. The relevant flow physics associated with some of the unsteady flow processes present in axial flow multistage machinery are presented along with procedures which can be used to account for them in 3D CFD simulations. Sample results are presented for both axial flow compressors and axial flow turbines which help to illustrate the enhanced predictive capabilities afforded by including these procedures in 3D CFD simulations. Finally, suggestions are given for future work on the development of time average flow models.
Aerodynamic analysis of a supersonic cascade vibrating in a complex mode
Caruthers, J. E.; Riffel, R. E.
1980-01-01
An analysis is presented which has been used to predict the unsteady aerodynamic behavior of a finite supersonic cascade of airfoils forced in harmonic oscillation with airfoil-to-airfoil variations in amplitude. Theoretical predictions are compared with some recent experimental results at a reduced frequency representative of actual fan or compressor flutter cases. The similarity of the experimental situation in the finite cascade to the flutter of a severely mistuned rotor is noted.
Soda, Ante; Voß, Ralph
2005-01-01
This paper presents results of a numerical investigation dealing with steady and unsteady aerodynamic wing-nacelle-pylon (WNP) interference effects. In the first part of the paper the design process of the generic WIONA (Wing with Oscillating Nacelle) geometry is described. It is shown that development of major interference effects in the channel between wing and nacelle strongly depends on geometrical parameters of the configuration. After the geometry definition, the steady viscous interfer...
Aerodynamic shape optimization using control theory
Reuther, James
1996-01-01
Aerodynamic shape design has long persisted as a difficult scientific challenge due its highly nonlinear flow physics and daunting geometric complexity. However, with the emergence of Computational Fluid Dynamics (CFD) it has become possible to make accurate predictions of flows which are not dominated by viscous effects. It is thus worthwhile to explore the extension of CFD methods for flow analysis to the treatment of aerodynamic shape design. Two new aerodynamic shape design methods are developed which combine existing CFD technology, optimal control theory, and numerical optimization techniques. Flow analysis methods for the potential flow equation and the Euler equations form the basis of the two respective design methods. In each case, optimal control theory is used to derive the adjoint differential equations, the solution of which provides the necessary gradient information to a numerical optimization method much more efficiently then by conventional finite differencing. Each technique uses a quasi-Newton numerical optimization algorithm to drive an aerodynamic objective function toward a minimum. An analytic grid perturbation method is developed to modify body fitted meshes to accommodate shape changes during the design process. Both Hicks-Henne perturbation functions and B-spline control points are explored as suitable design variables. The new methods prove to be computationally efficient and robust, and can be used for practical airfoil design including geometric and aerodynamic constraints. Objective functions are chosen to allow both inverse design to a target pressure distribution and wave drag minimization. Several design cases are presented for each method illustrating its practicality and efficiency. These include non-lifting and lifting airfoils operating at both subsonic and transonic conditions.
Unsteady Stokes Equations: Some Complete General Solutions
Indian Academy of Sciences (India)
A Venkatlaxmi; B S Padmavathi; T Amaranath
2004-05-01
The completeness of solutions of homogeneous as well as non-homogeneous unsteady Stokes equations are examined. A necessary and sufficient condition for a divergence-free vector to represent the velocity field of a possible unsteady Stokes flow in the absence of body forces is derived.
Reduced order modeling of steady flows subject to aerodynamic constraints
DEFF Research Database (Denmark)
Zimmermann, Ralf; Vendl, Alexander; Goertz, Stefan
2014-01-01
A novel reduced-order modeling method based on proper orthogonal decomposition for predicting steady, turbulent flows subject to aerodynamic constraints is introduced. Model-order reduction is achieved by replacing the governing equations of computational fluid dynamics with a nonlinear weighted ...
Qasim, M.; Khan, Z. H.; Lopez, R. J.; Khan, W. A.
2016-01-01
The heat and mass transport of a nanofluid thin film over an unsteady stretching sheet has been investigated. This is the first paper on nanofluid thin film flow caused by unsteady stretching sheet using Buongiorno's model. The model used for the nanofluid film incorporates the effects of Brownian motion and thermophoresis. The self-similar non-linear ordinary differential equations are solved using Maple's built-in BVP solver. The results for pure fluid are found to be in good agreement with the literature. Present analysis shows that free surface temperature and nanoparticle volume fraction increase with both unsteadiness and magnetic parameters. The results reveal that effect of both nanofluid parameters and viscous dissipation is to reduce the heat transfer rate.
Dual Solutions in Unsteady Stagnation-Point Flow over a Shrinking Sheet
Institute of Scientific and Technical Information of China (English)
Krishnendu Bhattacharyya
2011-01-01
@@ An analysis is made to study the dual nature of solution of unsteady stagnation-point Sow due to a shrinking sheet.Using similarity transformations, the governing boundary layer equations are transformed into the self-similar nonlinear ordinary differential equations.The transformed equations are solved numerically using a very efficient shooting method.The study reveals the conditions of existence, uniqueness and non-existence of unsteady similarity solution.The dual solutions for velocity distribution exist for certain values of velocity ratio parameter (c/a), and the increment in the unsteadiness parameter A increases the range of cla where solution exists.Also,with increasing A, the skin friction coefficient increases for the first solution and decreases for the second.
DEFF Research Database (Denmark)
Kleissl, Kenneth
to a categorization of the different control technics together with an identification of two key mechanisms for reduction of the design drag force. During this project extensive experimental work examining the aerodynamics of the currently used cable surface modifications together with new innovative proposals have...
Aerodynamically shaped vortex generators
DEFF Research Database (Denmark)
Hansen, Martin Otto Laver; Velte, Clara Marika; Øye, Stig;
2016-01-01
An aerodynamically shaped vortex generator has been proposed, manufactured and tested in a wind tunnel. The effect on the overall performance when applied on a thick airfoil is an increased lift to drag ratio compared with standard vortex generators. Copyright © 2015 John Wiley & Sons, Ltd....
Generic Wing-Body Aerodynamics Data Base
Holst, Terry L.; Olsen, Thomas H.; Kwak, Dochan (Technical Monitor)
2001-01-01
The wing-body aerodynamics data base consists of a series of CFD (Computational Fluid Dynamics) simulations about a generic wing body configuration consisting of a ogive-circular-cylinder fuselage and a simple symmetric wing mid-mounted on the fuselage. Solutions have been obtained for Nonlinear Potential (P), Euler (E) and Navier-Stokes (N) solvers over a range of subsonic and transonic Mach numbers and angles of attack. In addition, each solution has been computed on a series of grids, coarse, medium and fine to permit an assessment of grid refinement errors.
Steady and unsteady transonic flow
Seegmiller, H. L.; Marvin, J. G.; Levy, L. L., Jr.
1978-01-01
An investigation of the transonic flow over a circular arc airfoil was conducted to obtain basic information for turbulence modeling of shock-induced separated flows and to verify numerical computer codes which are being developed to simulate such flows. The investigation included the employment of a laser velocimeter to obtain data concerning the mean velocity, the shear stress, and the turbulent kinetic energy profiles in the flowfield downstream of the airfoil midchord where the flow features are more complex. Depending on the free-stream Mach number, the flowfield developed was either steady with shock-wave-induced separation extending from the foot of the shock wave to beyond the trailing edge or unsteady with a periodic motion also undergoing shock-induced separation. The experimental data were compared with the results of numerical simulations in which a computer code was employed that solved the time-dependent Reynolds' averaged compressible Navier-Stokes equations.
Unsteady Flows in Axial Turbomachines
Marble, F. E.; Rannie, W. D.
1957-01-01
Of the various unsteady flows that occur in axial turbomachines certain asymmetric disturbances, of wave length large in comparison with blade spacing, have become understood to a certain extent. These disturbances divide themselves into two categories: self-induced oscillations and force disturbances. A special type of propagating stall appears as a self-induced disturbance; an asymmetric velocity profile introduced at the compressor inlet constitutes a forced disturbance. Both phenomena have been treated from a unified theoretical point of view in which the asymmetric disturbances are linearized and the blade characteristics are assumed quasi-steady. Experimental results are in essential agreement with this theory wherever the limitations of the theory are satisfied. For the self-induced disturbances and the more interesting examples of the forced disturbances, the dominant blade characteristic is the dependence of total pressure loss, rather than the turning angle, upon the local blade inlet angle.
SEDIMENT TRANSPORT EXPERIMENTSIN UNSTEADY FLOWS
Institute of Scientific and Technical Information of China (English)
DE SUTTER R.; HUYGENS M.; VERHOEVEN R.
2001-01-01
By means of a test flume with semi-circular cross-section, bedload and suspended-sediment transport of non-cohesive material have been studied in transient flow. The experimental facility enables us to investigate the time evolution of friction and transport parameters. Preliminary measurements with a fixed bottom instead of a sediment bed yield a reliable assessment of flow and friction characteristics. Time sequence in unsteady flow of the relevant parameters is revealed. The influence of turbulence variation and shear stress variation on the transport is investigated. As existing transport equations are found to be in poor agreement with experimental data, a new "engineering" concept is constructed which relates friction velocity to transport.
Nonstandard Gaits in Unsteady Hydrodynamics
Fairchild, Michael; Rowley, Clarence
2016-11-01
Marine biology has long inspired the design and engineering of underwater vehicles. The literature examining the kinematics and dynamics of fishes, ranging from undulatory anguilliform swimmers to oscillatory ostraciiform ones, is vast. Past numerical studies of these organisms have principally focused on gaits characterized by sinusoidal pitching and heaving motions. It is conceivable that more sophisticated gaits could perform better in some respects, for example as measured by thrust generation or by cost of transport. This work uses an unsteady boundary-element method to numerically investigate the hydrodynamics and propulsive efficiency of high-Reynolds-number swimmers whose gaits are encoded by Fourier series or by Jacobi elliptic functions. Numerical results are presented with an emphasis on identifying particular wake structures and modes of motion that are associated with optimal swimming. This work was supported by the Office of Naval Research through MURI Grant N00014-14-1-0533.
Unsteady processes in catalytic reactors
Energy Technology Data Exchange (ETDEWEB)
Matros, Yu.Sh.
1985-01-01
In recent years a realization has occurred that reaction and reactor dynamics must be considered when designing and operating catalytic reactors. In this book, the author has focussed on both the processes occurring on individual porous-catalyst particles as well as the phenomena displayed by collections of these particles in fixed-bed reactors. The major topics discussed include the effects of unsteady-state heat and mass transfer, the influence of inhomogeneities and stagnant regions in fixed beds, and reactor operation during forced cycling of operating conditions. Despite the title of the book, attention is also paid to the determination of the number and stability of fixed-bed steady states, with the aim of describing the possibility of controlling reactors at unstable steady states. However, this development is somewhat dated, given the recent literature on multiplicity phenomena and process control.
Unsteady Tip Clearance Flow in an Isolated Axial Compressor Rotor
Institute of Scientific and Technical Information of China (English)
Hongwu ZHANG; Xiangyang DENG; Jingyi CHEN; Weiguang HUANG
2005-01-01
The paper investigates effects of operating conditions, tip clearance sizes and external unsteady excitations on the unsteady tip clearance flow in an isolated axial compressor rotor by unsteady 3D Navier-Stokes simulations. The results show that the unsteady tip clearance vortex takes a periodic flow behavior in the rotor tip region. With the decrease of the flow coefficient, the unsteady tip clearance vortex is enhanced and its frequency becomes lower. A larger tip clearance size can cause bigger unsteady fluctuation amplitude and a lower fluctuation frequency of the tip clearance vortex at the near stall operating condition. The unsteady excitation with the natural frequency of the tip clearance vortex can enhance the unsteadiness of the tip clearance vortex and improve the overall rotor performance. The frequency of the unsteady tip clearance vortex is independent of external unsteady excitations with different frequencies.
Aerodynamic Leidenfrost effect
Gauthier, Anaïs; Bird, James C.; Clanet, Christophe; Quéré, David
2016-12-01
When deposited on a plate moving quickly enough, any liquid can levitate as it does when it is volatile on a very hot solid (Leidenfrost effect). In the aerodynamic Leidenfrost situation, air gets inserted between the liquid and the moving solid, a situation that we analyze. We observe two types of entrainment. (i) The thickness of the air gap is found to increase with the plate speed, which is interpreted in the Landau-Levich-Derjaguin frame: Air is dynamically dragged along the surface and its thickness results from a balance between capillary and viscous effects. (ii) Air set in motion by the plate exerts a force on the levitating liquid. We discuss the magnitude of this aerodynamic force and show that it can be exploited to control the liquid and even to drive it against gravity.
Computational electromagnetic-aerodynamics
Shang, Joseph J S
2016-01-01
Presents numerical algorithms, procedures, and techniques required to solve engineering problems relating to the interactions between electromagnetic fields, fluid flow, and interdisciplinary technology for aerodynamics, electromagnetics, chemical-physics kinetics, and plasmadynamics This book addresses modeling and simulation science and technology for studying ionized gas phenomena in engineering applications. Computational Electromagnetic-Aerodynamics is organized into ten chapters. Chapter one to three introduce the fundamental concepts of plasmadynamics, chemical-physics of ionization, classical magnetohydrodynamics, and their extensions to plasma-based flow control actuators, high-speed flows of interplanetary re-entry, and ion thrusters in space exploration. Chapter four to six explain numerical algorithms and procedures for solving Maxwell’s equation in the time domain for computational electromagnetics, plasma wave propagation, and the time-dependent c mpressible Navier-Stokes equation for aerodyn...
Singh, Kamakhya Prasad
1995-01-01
A new methodology is developed to simulate unsteady flows about prescribed and aerodynamically determined moving boundary problems. The method couples the fluid dynamics and rigid-body dynamics equations to capture the time-dependent interference between stationary and moving boundaries. The unsteady, compressible, inviscid (Euler) equations are solved on dynamic, unstructured grids by an explicit, finite-volume, upwind method. For efficiency, the grid adaptation is performed within a window around the moving object. The Eulerian equations of the rigid-body dynamics are solved by a Runge-Kutta method in a non-inertial frame of reference. The two-dimensional flow solver is validated by computing the flow past a sinusoidally-pitching airfoil and comparing these results with the experimental data. The overall methodology is used for two two-dimensional examples: the flow past an airfoil which is performing a three-degrees-of-freedom motion in a transonic freestream, and the free-fall of a store after separation from a wing-section. Then the unstructured mesh methodology is extended to three-dimensions to simulate unsteady flow past bodies in relative motion, where the trajectory is determined from the instantaneous aerodynamics. The flow solver and the adaptation scheme in three dimensions are validated by simulating the transonic, unsteady flow around a wing undergoing a forced, periodic, pitching motion, and comparing the results with the experimental data. To validate the trajectory code, the six-degrees-of-freedom motion of a store separating from a wing was computed using the experimentally determined force and moment fields, then comparing with an independently generated trajectory. Finally, the overall methodology was demonstrated by simulating the unsteady flowfield and the trajectory of a store dropped from a wing. The methodology, its computational cost notwithstanding, has proven to be accurate, automated, easy for dynamic gridding, and relatively efficient
Hypervelocity Aerodynamics and Control
1990-06-06
Report: Hypervelocity Aerodynamics and Control 12. PERSONAL AUTHOR(S) T. C. Adamson, Jr. and R. IA. Howe 13a. TYPE OF REPORT 13b. TIME COVERED 14. DATE...6] pulse applied. If the Mxyz system as shown is Fig. 3 r 3. , is used, then we have R21= k costo -t4 ksin yot 1 6r= ro 1 (4) -- (6k 2 - 5 -30k 2 sin
WECS incompressible Lifting Surface Aerodynamics (WILSA)
Energy Technology Data Exchange (ETDEWEB)
Suciu, E.; Morino, L.
1976-05-01
A method is described for computing the distribution for a zero-thickness horizontal axis windmill, as well as for obtaining the power coefficient. The problem is formulated in terms of velocity potential, and the study deals with a nonlinear finite-element lifting-surface analysis of horizontal-axis windmills in a steady incompressible, inviscid, irrotational flow, with a prescribed helicoidal wake. A zero-order-finite-element analysis is used with a straight-vortex line wake. The correct wake geometry is obtained and the pressure coefficient calculated using both linearized and nonlinear forms of the Bernoulli Theorem. The numerical results compare well with those obtained with Windmill Incompressible Complex Configuration Aerodynamics (WICCA), a computer program for solving the same problem which uses a completely different integral equation. A number of suggestions are offered to improve the model presented.
Spectral Homotopy Analysis Method for PDEs That Model the Unsteady Von Kàrmàn Swirling Flow
Directory of Open Access Journals (Sweden)
Zodwa Makukula
2014-01-01
Full Text Available A spectral homotopy analysis method (SHAM is used to find numerical solutions for the unsteady viscous flow problem due to an infinite rotating disk. The problem is governed by a set of two fully coupled nonlinear partial differential equations. The method was originally introduced for solutions of nonlinear ordinary differential equations. In this study, its application is extended to a system of nonlinear partial differential equations (PDEs that model the unsteady von Kàrmàn swirling flow. Numerical values of the pertinent flow properties were generated and validated against results obtained using the Keller-box numerical scheme. The results indicate that the present method is very accurate and can be used as an efficient tool for solving nonlinear PDEs of the type discussed in this paper.
Experimental Verification of Buffet Calculation Procedure Using Unsteady PSP
Panda, Jayanta
2016-01-01
Typically a limited number of dynamic pressure sensors are employed to determine the unsteady aerodynamic forces on large, slender aerospace structures. The estimated forces are known to be very sensitive to the number of the dynamic pressure sensors and the details of the integration scheme. This report describes a robust calculation procedure, based on frequency-specific correlation lengths, that is found to produce good estimation of fluctuating forces from a few dynamic pressure sensors. The validation test was conducted on a flat panel, placed on the floor of a wind tunnel, and was subjected to vortex shedding from a rectangular bluff-body. The panel was coated with fast response Pressure Sensitive Paint (PSP), which allowed time-resolved measurements of unsteady pressure fluctuations on a dense grid of spatial points. The first part of the report describes the detail procedure used to analyze the high-speed, PSP camera images. The procedure includes steps to reduce contamination by electronic shot noise, correction for spatial non-uniformities, and lamp brightness variation, and finally conversion of fluctuating light intensity to fluctuating pressure. The latter involved applying calibration constants from a few dynamic pressure sensors placed at selective points on the plate. Excellent comparison in the spectra, coherence and phase, calculated via PSP and dynamic pressure sensors validated the PSP processing steps. The second part of the report describes the buffet validation process, for which the first step was to use pressure histories from all PSP points to determine the "true" force fluctuations. In the next step only a selected number of pixels were chosen as "virtual sensors" and a correlation-length based buffet calculation procedure was applied to determine "modeled" force fluctuations. By progressively decreasing the number of virtual sensors it was observed that the present calculation procedure was able to make a close estimate of the "true
National Research Council Canada - National Science Library
M A Hye; M M Rahman; L Nowsher Ali; S Afrin
2013-01-01
... steady solutions with two- and four-vortex solutions are obtained by the Newton-Raphson iteration method. Then, in order to investigate the non-linear behavior of the unsteady solutions, time evolution calculations as well as power spectrum of the solutions are obtained, and it is found that the steady-state flow turns into periodic flow through ...
Analysis of Aerodynamic Noise Generated from Inclined Circular Cylinder
Institute of Scientific and Technical Information of China (English)
YasutakeHaramoto; ShoujiYasuda; 等
2000-01-01
Making clear the generation mechanism of fluid dynamic noise is essential to reduce noise deriving from turbomachinery.The analysis of the aerodynamic noise generated from circular cylinder is carried out numerically and experimentally in a low noise wind tunnel.in this study,aerodynamic sound radiated from a circular cylinder in uniform flow is predicted numericaslly by the following two step method,First,the three-dimensional unsteady incompressible Navier-Stokes equation is solved using the high order accurate upwind scheme.Next.the sound pressure level at the observed point is calculated from the fluctuating surface pressure on the cylinder.based on modified Lighthill-Curl's equation.It is worth to note that the noise generated from the model is reduced rapidly when it is inclined against the mean flow.In other works,the Peak level of the radiated noise decreases apidly with inclination of the circular cylinder.The simulated SPL for the inclined circular cylinder is compared with the measured value .and good agreement is obtained for the peak spectrum fequency of the sound pressue level and tendency of noise reduction,So we expect that the change of flow structures makes reduction of the aerodynamic noise from the inclined models.
Size effects on insect hovering aerodynamics: an integrated computational study
Energy Technology Data Exchange (ETDEWEB)
Liu, H [Graduate School of Engineering, Chiba University, Chiba, 263-8522 (Japan); Aono, H [Department of Aerospace Engineering, University of Michigan, Ann Arbor, MI48109 (United States)], E-mail: hliu@faculty.chiba-u.jp, E-mail: aonoh@umich.edu
2009-03-01
Hovering is a miracle of insects that is observed for all sizes of flying insects. Sizing effect in insect hovering on flapping-wing aerodynamics is of interest to both the micro-air-vehicle (MAV) community and also of importance to comparative morphologists. In this study, we present an integrated computational study of such size effects on insect hovering aerodynamics, which is performed using a biology-inspired dynamic flight simulator that integrates the modelling of realistic wing-body morphology, the modelling of flapping-wing and body kinematics and an in-house Navier-Stokes solver. Results of four typical insect hovering flights including a hawkmoth, a honeybee, a fruit fly and a thrips, over a wide range of Reynolds numbers from O(10{sup 4}) to O(10{sup 1}) are presented, which demonstrate the feasibility of the present integrated computational methods in quantitatively modelling and evaluating the unsteady aerodynamics in insect flapping flight. Our results based on realistically modelling of insect hovering therefore offer an integrated understanding of the near-field vortex dynamics, the far-field wake and downwash structures, and their correlation with the force production in terms of sizing and Reynolds number as well as wing kinematics. Our results not only give an integrated interpretation on the similarity and discrepancy of the near- and far-field vortex structures in insect hovering but also demonstrate that our methods can be an effective tool in the MAVs design.
Analysis of aerodynamic noise generated from inclined circular cylinder
Haramoto, Yasutake; Yasuda, Shouji; Matsuzaki, Kazuyoshi; Munekata, Mizue; Ohba, Hideki
2000-06-01
Making clear the generation mechanism of fluid dynamic noise is essential to reduce noise deriving from turbomachinery. The analysis of the aerodynamic noise generated from circular cylinder is carried out numerically and experimentally in a low noise wind tunnel. In this study, aerodynamic sound radiated from a circular cylinder in uniform flow is predicted numerically by the following two step method. First, the three-dimensional unsteady incompressible Navier-Stokes equation is solved using the high order accurate upwind scheme. Next, the sound pressure level at the observed point is calculated from the fluctuating surface pressure on the cylinder, based on modified Lighthill-Curl’s equation. It is worth to note that the noise generated from the model is reduced rapidly when it is inclined against the mean flow. In other words, the peak level of the radiated noise decreases rapidly with inclination of the circular cylinder. The simulated SPL for the inclined circular cylinder is compared with the measured value, and good agreement is obtained for the peak spectrum frequency of the sound pressure level and tendency of noise reduction. So we expect that the change of flow structures makes reduction of the aerodynamic noise from the inclined models.
Aerodynamic data of space vehicles
Weiland, Claus
2014-01-01
The capacity and quality of the atmospheric flight performance of space flight vehicles is characterized by their aerodynamic data bases. A complete aerodynamic data base would encompass the coefficients of the static longitudinal and lateral motions and the related dynamic coefficients. In this book the aerodynamics of 27 vehicles are considered. Only a few of them did really fly. Therefore the aerodynamic data bases are often not complete, in particular when the projects or programs were more or less abruptly stopped, often due to political decisions. Configurational design studies or the development of demonstrators usually happen with reduced or incomplete aerodynamic data sets. Therefore some data sets base just on the application of one of the following tools: semi-empirical design methods, wind tunnel tests, numerical simulations. In so far a high percentage of the data presented is incomplete and would have to be verified. Flight mechanics needs the aerodynamic coefficients as function of a lot of var...
Nonlinear acoustic propagation in rectangular ducts
Nayfeh, A. H.; Tsai, M.-S.
1974-01-01
The method of multiple scales is used to obtain a second-order uniformly valid expansion for nonlinear acoustic wave propagation in a rectangular duct whose walls are treated with a nonlinear acoustic material. The wave propagation in the duct is characterized by the unsteady nonlinear Euler equations. The results show that nonlinear materials attenuate sound more than linear materials except at high acoustic frequencies. The nonlinear materials produce higher and combination tones which have higher attenuation rates than the fundamentals. Moreover, the attenuation rates of the fundamentals increase with increasing amplitude.
Directory of Open Access Journals (Sweden)
Mohammad Mehdi Rashidi
2010-01-01
Full Text Available We investigated an axisymmetric unsteady two-dimensional flow of nonconducting, incompressible second grade fluid between two circular plates. The similarity transformation is applied to reduce governing partial differential equation (PDE to a nonlinear ordinary differential equation (ODE in dimensionless form. The resulting nonlinear boundary value problem is solved using homotopy analysis method and numerical method. The effects of appropriate dimensionless parameters on the velocity profiles are studied. The total resistance to the upper plate has been calculated.
Chinyoka, T.; Makinde, O. D.
2013-01-01
The thermodynamic second law analysis is utilized to investigate the inherent irreversibility in an unsteady hydromagnetic generalized Couette flow with variable electrical conductivity in the presence of induced electric field. Based on some simplified assumption, the model nonlinear governing equations are obtained and solved numerically using semidiscretization finite difference techniques. Effects of various thermophysical parameters on the fluid velocity, temperature, current density, skin friction, the Nusselt number, entropy generation number, and the Bejan number are presented graphically and discussed quantitatively. PMID:23956691
Unsteady Boundary-Layer Flow over Jerked Plate Moving in a Free Stream of Viscoelastic Fluid
Directory of Open Access Journals (Sweden)
Sufian Munawar
2014-01-01
Full Text Available This study aims to investigate the unsteady boundary-layer flow of a viscoelastic non-Newtonian fluid over a flat surface. The plate is suddenly jerked to move with uniform velocity in a uniform stream of non-Newtonian fluid. Purely analytic solution to governing nonlinear equation is obtained. The solution is highly accurate and valid for all values of the dimensionless time 0≤τ<∞. Flow properties of the viscoelastic fluid are discussed through graphs.
Zhou, Di; Lu, Zhiliang; Guo, Tongqing; Shen, Ennan
2016-06-01
In this paper, the research on two types of unsteady flow problems in turbomachinery including blade flutter and rotor-stator interaction is made by means of numerical simulation. For the former, the energy method is often used to predict the aeroelastic stability by calculating the aerodynamic work per vibration cycle. The inter-blade phase angle (IBPA) is an important parameter in computation and may have significant effects on aeroelastic behavior. For the latter, the numbers of blades in each row are usually not equal and the unsteady rotor-stator interactions could be strong. An effective way to perform multi-row calculations is the domain scaling method (DSM). These two cases share a common point that the computational domain has to be extended to multi passages (MP) considering their respective features. The present work is aimed at modeling these two issues with the developed MP model. Computational fluid dynamics (CFD) technique is applied to resolve the unsteady Reynolds-averaged Navier-Stokes (RANS) equations and simulate the flow fields. With the parallel technique, the additional time cost due to modeling more passages can be largely decreased. Results are presented on two test cases including a vibrating rotor blade and a turbine stage.
Impact of Periodic Unsteadiness on Performance and Heat Load in Axial Flow Turbomachines
Sharma, Om P.; Stetson, Gary M.; Daniels, William A,; Greitzer, Edward M.; Blair, Michael F.; Dring, Robert P.
1997-01-01
Results of an analytical and experimental investigation, directed at the understanding of the impact of periodic unsteadiness on the time-averaged flows in axial flow turbomachines, are presented. Analysis of available experimental data, from a large-scale rotating rig (LSRR) (low speed rig), shows that in the time-averaged axisymmetric equations the magnitude of the terms representing the effect of periodic unsteadiness (deterministic stresses) are as large or larger than those due to random unsteadiness (turbulence). Numerical experiments, conducted to highlight physical mechanisms associated with the migration of combustor generated hot-streaks in turbine rotors, indicated that the effect can be simulated by accounting for deterministic stress like terms in the time-averaged mass and energy conservation equations. The experimental portion of this program shows that the aerodynamic loss for the second stator in a 1-1/2 stage turbine are influenced by the axial spacing between the second stator leading edge and the rotor trailing edge. However, the axial spacing has little impact on the heat transfer coefficient. These performance changes are believed to be associated with the change in deterministic stress at the inlet to the second stator. Data were also acquired to quantify the impact of indexing the first stator relative to the second stator. For the range of parameters examined, this effect was found to be of the same order as the effect of axial spacing.
Single-shot temperature- and pressure-sensitive paint measurements on an unsteady helicopter blade
Disotell, Kevin J.; Peng, Di; Juliano, Thomas J.; Gregory, James W.; Crafton, Jim W.; Komerath, Narayanan M.
2014-02-01
Unsteady pressure-sensitive paint (PSP) measurements were acquired on an articulated model helicopter rotor of 0.26 m diameter in edgewise flow to simulate forward flight conditions. The rotor was operated at advance ratios (free stream velocity normalized by hover tip speed) of 0.15 and 0.30 at a cycle-averaged tip chord Reynolds number of 1.1 × 105, with collective and longitudinal cyclic pitch inputs of 10° and 2.5°, respectively. A single-shot data acquisition technique allowed a camera to record the paint luminescence after a single pulse of high-energy laser excitation, yielding sufficient signal-to-noise ratio to avoid image averaging. Platinum tetra(pentafluorophenyl) porphyrin (PtTFPP) in a porous polymer/ceramic binder served as the PSP. To address errors caused by image blurring and temperature sensitivity, a previously reported motion deblurring algorithm was implemented and the temperature correction was made using temperature-sensitive paint measurements on a second rotor blade. Instantaneous, unsteady surface pressure maps at a rotation rate of 82 Hz captured different aerodynamic responses between the two sides of the rotor disk and were compared to the nominally steady hover case. Cycle-to-cycle variations in tip unsteadiness on the retreating blade were also observed, causing oblique pressure features which may be linked to three-dimensional stall.
Unsteady Capillary Filling By Electrocapillarity
Kang, In Seok; Lee, Jung A.
2016-11-01
Unsteady filling of electrolyte solution inside a nanochannel by the electrocapillarity effect is studied. The filling rate is predicted as a function of the bulk concentration of the electrolyte, the surface potential (or surface charge density), and the cross sectional shape of the channel. Since the driving force of the flow is the electrocapillarity, it is first analyzed by using the solution of the Poisson-Boltzmann equation. From the analysis, it is found that the results for many different cross sectional shapes can be unified with good accuracy if the hydraulic radius is adopted as the characteristic length scale of the problem. Especially in the case of constant surface potential, for both limits of κh -> 0 and κh -> ∞ , it can be shown theoretically that the electrocapillarity is independent of the cross sectional shape if the hydraulic radius is the same. In order to analyze the geometric effects more systematically, we consider the regular N-polygons with the same hydraulic radius and the rectangles of different aspect ratios. Washburn's approach is then adopted to predict the filling rate of electrolyte solution inside a nanaochannel. It is found that the average filling velocity decreases as N increases in the case of regular N-polygons with the same hydraulic radius. This is because of that the regular N-polygons of the same hydraulic radius share the same inscribing circle. This work has been supported by BK21+ program.
Hansen, Martin O L
2015-01-01
Aerodynamics of Wind Turbines is the established essential text for the fundamental solutions to efficient wind turbine design. Now in its third edition, it has been substantially updated with respect to structural dynamics and control. The new control chapter now includes details on how to design a classical pitch and torque regulator to control rotational speed and power, while the section on structural dynamics has been extended with a simplified mechanical system explaining the phenomena of forward and backward whirling modes. Readers will also benefit from a new chapter on Vertical Axis W
Evolution of Unsteady Groundwater Flow Systems
Liang, Xing; Jin, Menggui; Niu, Hong
2016-04-01
Natural groundwater flow is usually transient, especially in long time scale. A theoretical approach on unsteady groundwater flow systems was adopted to highlight some of the knowledge gaps in the evolution of groundwater flow systems. The specific consideration was focused on evolution of groundwater flow systems from unsteady to steady under natural and mining conditions. Two analytical solutions were developed, using segregation variable method to calculate the hydraulic head under steady and unsteady flow conditions. The impact of anisotropy ratio, hydraulic conductivity (K) and specific yield (μs) on the flow patterns were analyzed. The results showed that the area of the equal velocity region increased and the penetrating depth of the flow system decreased while the anisotropy ratio (ɛ = °Kx-/Kz--) increased. Stagnant zones were found in the flow field where the directions of streamlines were opposite. These stagnant zones moved up when the horizontal hydraulic conductivity increased. The results of the study on transient flow indicated a positive impact on hydraulic head with an increase of hydraulic conductivity, while a negative effect on hydraulic head was observed when the specific yield was enhanced. An unsteady numerical model of groundwater flow systems with annual periodic recharge was developed using MODFLOW. It was observed that the transient groundwater flow patterns were different from that developed in the steady flow under the same recharge intensity. The water table fluctuated when the recharge intensity altered. The monitoring of hydraulic head and concentration migration revealed that the unsteady recharge affected the shallow local flow system more than the deep regional flow system. The groundwater flow systems fluctuated with the action of one or more pumping wells. The comparison of steady and unsteady groundwater flow observation indicated that the unsteady flow patterns cannot be simulated by the steady model when the condition
Unsteady jet in designing innovative drug delivery system
Wang, Cong; Mazur, Paul; Cosse, Julia; Rider, Stephanie; Gharib, Morteza
2014-11-01
Micro-needle injections, a promising pain-free drug delivery method, is constrained by its limited penetration depth. This deficiency can be overcome by implementing fast unsteady jet that can penetrate sub-dermally. The development of a faster liquid jet would increase the penetration depth and delivery volume of micro-needles. In this preliminary work, the nonlinear transient behavior of an elastic tube balloon in providing fast discharge is analyzed. A physical model that combines the Mooney Rivlin Material model and Young-Lapalce's Law was developed and used to investigate the fast discharging dynamic phenomenon. A proof of concept prototype was constructed to demonstrate the feasibility of a simple thumb-sized delivery system to generate liquid jet with desired speed in the range of 5-10 m/s. This work is supported by ZCUBE Corporation.
Viscous Flow over an Unsteady Shrinking Sheet with Mass Transfer
Institute of Scientific and Technical Information of China (English)
FANG Tie-Gang; ZHANG Ji; YAO Shan-Shan
2009-01-01
The unsteady viscous flow over a continuously shrinking surface with mass suction is studied. The solution is fortunately an exact solution of the unsteady Navier-Stokes equations. Similarity equations are obtained through the application of similarity transformation techniques. Numerical techniques are used to solve the similarity equations for different values of the mass suction parameters" and the unsteadiness parameters. Results show that multiple solutions exist for a certain range of mass suction and unsteadiness parameters. Quite different flow behaviour is observed for an unsteady shrinking sheet from an unsteady stretching sheet.
Unsteady transverse injection of kerosene into a supersonic flow
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
A shadowgraph and a new fuel injection system were used to study kerosene transversely injected into a supersonic flow. High pressure and velocity of injection can be attained. The pressure time histories were detected in oil-line and the shadowgraphs of the flow field were obtained at different time-delays. The inflow stagnation pressure was varied to change the local flow speed in test section. The results indicate that kerosene jet exhibits deep penetration and four regimes appear clearly during the fuel jet atomization in a high-speed flow. The jet disintegration is caused by surface waves propagating along the jet surface, and the breakup point is located at the wave trough. The surface waves are dominantly generated by aerodynamic force. The jet shock is close to windward surface of the jet. The shock reflects on and transmits in duct boundary layers. In the case of unsteady injection, the shock structure is very complicated and different from that of hydrogen injection. The results of kerosene injected into a quiescent gas and a subsonic flow are also provided for comparison.
Unsteady transverse injection of kerosene into a supersonic flow
Institute of Scientific and Technical Information of China (English)
徐胜利; R.D.Archer; B.E.Milton; 岳朋涛
2000-01-01
A shadowgraph and a new fuel injection system were used to study kerosene transversely injected into a supersonic flow. High pressure and velocity of injection can be attained. The pressure time histories were detected in oil-line and the shadowgraphs of the flow field were obtained at different time-delays. The inflow stagnation pressure was varied to change the local flow speed in test section. The results indicate that kerosene jet exhibits deep penetration and four regimes appear clearly during the fuel jet atomization in a high-speed flow. The jet disintegration is caused by surface waves propagating along the jet surface, and the breakup point is located at the wave trough. The surface waves are dominantly generated by aerodynamic force. The jet shock is close to windward surface of the jet. The shock reflects on and transmits in duct boundary layers. In the case of unsteady injection, the shock structure is very complicated and different from that of hydrogen injection. The results of kerosene inj
Numerical estimation of aircrafts' unsteady lateral-directional stability derivatives
Directory of Open Access Journals (Sweden)
Maričić N.L.
2006-01-01
Full Text Available A technique for predicting steady and oscillatory aerodynamic loads on general configuration has been developed. The prediction is based on the Doublet-Lattice Method, Slender Body Theory and Method of Images. The chord and span wise loading on lifting surfaces and longitudinal bodies (in horizontal and vertical plane load distributions are determined. The configuration may be composed of an assemblage of lifting surfaces (with control surfaces and bodies (with circular cross sections and a longitudinal variation of radius. Loadings predicted by this method are used to calculate (estimate steady and unsteady (dynamic lateral-directional stability derivatives. The short outline of the used methods is given in [1], [2], [3], [4] and [5]. Applying the described methodology software DERIV is developed. The obtained results from DERIV are compared to NASTRAN examples HA21B and HA21D from [4]. In the first example (HA21B, the jet transport wing (BAH wing is steady rolling and lateral stability derivatives are determined. In the second example (HA21D, lateral-directional stability derivatives are calculated for forward- swept-wing (FSW airplane in antisymmetric quasi-steady maneuvers. Acceptable agreement is achieved comparing the results from [4] and DERIV.
Load-estimation techniques for unsteady incompressible flows
Rival, David E.; Oudheusden, Bas van
2017-03-01
In a large variety of fluid-dynamic problems, it is often impossible to directly measure the instantaneous aerodynamic or hydrodynamic forces on a moving body. Examples include studies of propulsion in nature, either with mechanical models or living animals, wings, and blades subjected to significant surface contamination, such as icing, sting blockage effects, etc. In these circumstances, load estimation from flow-field data provides an attractive alternative method, while at the same time providing insight into the relationship between unsteady loadings and their associated vortex-wake dynamics. Historically, classical control-volume techniques based on time-averaged measurements have been used to extract the mean forces. With the advent of high-speed imaging, and the rapid progress in time-resolved volumetric measurements, such as Tomo-PIV and 4D-PTV, it is becoming feasible to estimate the instantaneous forces on bodies of complex geometry and/or motion. For effective application under these conditions, a number of challenges still exist, including the near-body treatment of the acceleration field as well as the estimation of pressure on the outer surfaces of the control volume. Additional limitations in temporal and spatial resolutions, and their associated impact on the feasibility of the various approaches, are also discussed. Finally, as an outlook towards the development of future methodologies, the potential application of Lagrangian techniques is explored.
Directory of Open Access Journals (Sweden)
Mohammad Mehdi Rashidi
2008-01-01
Full Text Available The flow of a viscous incompressible fluid between two parallel plates due to the normal motion of the plates is investigated. The unsteady Navier-Stokes equations are reduced to a nonlinear fourth-order differential equation by using similarity solutions. Homotopy analysis method (HAM is used to solve this nonlinear equation analytically. The convergence of the obtained series solution is carefully analyzed. The validity of our solutions is verified by the numerical results obtained by fourth-order Runge-Kutta.
Smith, Natalie Rochelle
2015-01-01
While the gas turbine engine has existed for nearly 80 years, much of the complex aerodynamics which governs compressor performance is still not well understood. The unsteady flow field consists of periodic blade row interactions from the wakes and potential fields of each blade and vane. Vane clocking is the relative circumferential indexing of adjacent vane rows with the same vane count, and it is one method to change blade row interactions. Though the potential of performance benefits with...
Zahm, A F
1924-01-01
This report gives the description and the use of a specially designed aerodynamic plane table. For the accurate and expeditious geometrical measurement of models in an aerodynamic laboratory, and for miscellaneous truing operations, there is frequent need for a specially equipped plan table. For example, one may have to measure truly to 0.001 inch the offsets of an airfoil at many parts of its surface. Or the offsets of a strut, airship hull, or other carefully formed figure may require exact calipering. Again, a complete airplane model may have to be adjusted for correct incidence at all parts of its surfaces or verified in those parts for conformance to specifications. Such work, if but occasional, may be done on a planing or milling machine; but if frequent, justifies the provision of a special table. For this reason it was found desirable in 1918 to make the table described in this report and to equip it with such gauges and measures as the work should require.
Research on Aerodynamic Noise Reduction for High-Speed Trains
Directory of Open Access Journals (Sweden)
Yadong Zhang
2016-01-01
Full Text Available A broadband noise source model based on Lighthill’s acoustic theory was used to perform numerical simulations of the aerodynamic noise sources for a high-speed train. The near-field unsteady flow around a high-speed train was analysed based on a delayed detached-eddy simulation (DDES using the finite volume method with high-order difference schemes. The far-field aerodynamic noise from a high-speed train was predicted using a computational fluid dynamics (CFD/Ffowcs Williams-Hawkings (FW-H acoustic analogy. An analysis of noise reduction methods based on the main noise sources was performed. An aerodynamic noise model for a full-scale high-speed train, including three coaches with six bogies, two inter-coach spacings, two windscreen wipers, and two pantographs, was established. Several low-noise design improvements for the high-speed train were identified, based primarily on the main noise sources; these improvements included the choice of the knuckle-downstream or knuckle-upstream pantograph orientation as well as different pantograph fairing structures, pantograph fairing installation positions, pantograph lifting configurations, inter-coach spacings, and bogie skirt boards. Based on the analysis, we designed a low-noise structure for a full-scale high-speed train with an average sound pressure level (SPL 3.2 dB(A lower than that of the original train. Thus, the noise reduction design goal was achieved. In addition, the accuracy of the aerodynamic noise calculation method was demonstrated via experimental wind tunnel tests.
COUETTE FLOW PROBLEM FOR AN UNSTEADY MHD THIRD-GRADE FLUID WITH HALL CURRENTS
Directory of Open Access Journals (Sweden)
Muhammad Azram
2014-12-01
Full Text Available ABSTRACT: In this work, we analyze Coutte flow problem for an unsteady mangneto-hydrodynamic (MHD third-grade fluid in the presence of a pressure gradient and Hall currnts. Existing literature on the topic shows that the effecs of Hall current on Coutte flow of an unsteady MHD third-grade fluid with a prssure gradient has not yet been investigated. The arising non-linear problem is solved by the homotopy analysis method (HAM and the convergence of the obtained complex series solution is carefully analyzed. The effects of pressure number, Hartmann number and Hall parameter on unsteady velocity are discussed via analysis of plots. ABSTRAK: Kajian dijalan untuk menganalisa masalah aliran Coutte bagi bendalir MHD gred ketiga dan arus Hall. Bagi topik ini kesan arus Hall terhadap aliran Couette dalam bendalir MHD gred ketiga tak mantap dengan kecerunan tekanan, belum pernah dikaji selidik. Masalah tak linear berbangkit diselesaikan dengan kaedah analisis homotopi (HAM dan ketumpuan solusi rangkaian kompleks dianalisa dengan teliti. Kesan nilai tekanan, nombor Hartmann dan parameter Hall terhadap halaju tak mantap diperbincangkan melalui plot yang dianalisis.KEYWORDS: Cuette; flow; hall currents; unsteady; third-grade fluid; HAM
Aerodynamics of a single-degree-of-freedom toy ornithopter
Chavez Alarcon, Ramiro; Balakumar, B. J.; Allen, James J.
2009-11-01
The flow field around a flight-worthy toy ornithopter is investigated using PIV diagnostics in combination with load cells to understand the aerodynamics during nominally steady flight and turning. Phase-locked measurements of the wake and inflow are performed using an automated PIV system around the flapping wings of the ornithopter with the ornithopter fixed to a load-cell inside a 1.3m x 1.2m wind tunnel test section. The mildly oscillating free flight of the ornithopter is compared to the wake measurements to understand the causes of the unsteadiness. Further, the modulation of the wake that causes the turning motion of the ornithopter is explained using the wake structure measurements.
Discrete vortex method simulations of aerodynamic admittance in bridge aerodynamics
DEFF Research Database (Denmark)
Rasmussen, Johannes Tophøj; Hejlesen, Mads Mølholm; Larsen, Allan;
, and to determine aerodynamic forces and the corresponding ﬂutter limit. A simulation of the three-dimensional bridge responseto turbulent wind is carried out by quasi steady theory by modelling the bridge girder as a line like structure [2], applying the aerodynamic load coefﬁcients found from the current version...... of DVMFLOW in a strip wise fashion. Neglecting the aerodynamic admittance, i.e. the correlation of the instantaneous lift force to the turbulent ﬂuctuations in the vertical velocities, leads to higher response to high frequency atmospheric turbulence than would be obtained from wind tunnel tests....
Convective heat transfer under unsteady impinging jets: the effect of the shape of the unsteadiness
Middelberg, G.; Herwig, H.
2009-10-01
Unsteady impinging jets are systematically controlled with respect to their time dependence in order to investigate the influence of unsteadiness on the heat transfer performance. This is achieved by a special mass flow control device, which allows almost arbitrary shapes of unsteadiness to be imposed onto the impinging jet. Three different standard signals (sinusoidal, triangular, rectangular) and two specially designed signals are applied and their influence on heat transfer is determined in terms of an enhancement factor. Heat transfer augmentation up to 30% was found and could be physically explained with the help of PIV and hot-wire measurements of the flow field.
Unsteady Airloads on Airfoils in Reverse Flow
Lind, Andrew; Jones, Anya
2014-11-01
This work gives insight into the influence of airfoil characteristics on unsteady airloads for rotor applications where local airfoil sections may operate at high and/or reverse flow angles of attack. Two-dimensional wind tunnel experiments have been performed on four airfoil sections to investigate the effects of thickness, camber, and trailing edge shape on unsteady airloads (lift, pressure drag, and pitching moment). These model rotor blades were tested through 360 deg of incidence for 104 vibrations for applications where airfoil sections are subjected to reverse flow, such as high-speed helicopters and tidal turbines.
Wind Turbines Wake Aerodynamics
DEFF Research Database (Denmark)
Vermeer, L.; Sørensen, Jens Nørkær; Crespo, A.
2003-01-01
The aerodynamics of horizontal axis wind turbine wakes is studied. The contents is directed towards the physics of power extraction by wind turbines and reviews both the near and the far wake region. For the near wake, the survey is restricted to uniform, steady and parallel flow conditions......, thereby excluding wind shear, wind speed and rotor setting changes and yawed conditions. The emphasis is put on measurements in controlled conditions.For the far wake, the survey focusses on both single turbines and wind farm effects, and the experimental and numerical work are reviewed; the main interest...... is to study how the far wake decays downstream, in order to estimate the effect produced in downstream turbines.The article is further restricted to horizontal axis wind turbines and excludes all other types of turbines....
DEFF Research Database (Denmark)
Hansen, Martin Otto Laver
Aerodynamics of Wind Turbines is the established essential text for the fundamental solutions to efficient wind turbine design. Now in its third edition, it has been substantially updated with respect to structural dynamics and control. The new control chapter now includes details on how to design...... a classical pitch and torque regulator to control rotational speed and power, while the section on structural dynamics has been extended with a simplified mechanical system explaining the phenomena of forward and backward whirling modes. Readers will also benefit from a new chapter on Vertical Axis Wind...... Turbines (VAWT). Topics covered include increasing mass flow through the turbine, performance at low and high wind speeds, assessment of the extreme conditions under which the turbine will perform and the theory for calculating the lifetime of the turbine. The classical Blade Element Momentum method...
Wind Turbines Wake Aerodynamics
DEFF Research Database (Denmark)
Vermeer, L.; Sørensen, Jens Nørkær; Crespo, A.
2003-01-01
The aerodynamics of horizontal axis wind turbine wakes is studied. The contents is directed towards the physics of power extraction by wind turbines and reviews both the near and the far wake region. For the near wake, the survey is restricted to uniform, steady and parallel flow conditions......, thereby excluding wind shear, wind speed and rotor setting changes and yawed conditions. The emphasis is put on measurements in controlled conditions.For the far wake, the survey focusses on both single turbines and wind farm effects, and the experimental and numerical work are reviewed; the main interest...... is to study how the far wake decays downstream, in order to estimate the effect produced in downstream turbines.The article is further restricted to horizontal axis wind turbines and excludes all other types of turbines....
Introduction to transonic aerodynamics
Vos, Roelof
2015-01-01
Written to teach students the nature of transonic flow and its mathematical foundation, this book offers a much-needed introduction to transonic aerodynamics. The authors present a quantitative and qualitative assessment of subsonic, supersonic, and transonic flow around bodies in two and three dimensions. The book reviews the governing equations and explores their applications and limitations as employed in modeling and computational fluid dynamics. Some concepts, such as shock and expansion theory, are examined from a numerical perspective. Others, including shock-boundary-layer interaction, are discussed from a qualitative point of view. The book includes 60 examples and more than 200 practice problems. The authors also offer analytical methods such as Method of Characteristics (MOC) that allow readers to practice with the subject matter. The result is a wealth of insight into transonic flow phenomena and their impact on aircraft design, including compressibility effects, shock and expansion waves, sho...
Reduction of aerodynamic load fluctuation on wind turbine blades through active flow control
Velarde, John-Michael; Coleman, Thomas; Magstadt, Andrew; Aggarwal, Somil; Glauser, Mark
2015-11-01
The current set of experiments deals with implementing active flow control on a Bergey Excel 1, 1kW turbine. The previous work in our group demonstrated successfully that implementation of a simple closed-loop controller could reduce unsteady aerodynamic load fluctuation by 18% on a vertically mounted wing. Here we describe a similar flow control method adapted to work in the rotating frame of a 2.5m diameter wind turbine. Strain gages at the base of each blade measure the unsteady fluctuation in the blades and pressure taps distributed along the span of the blades feed information to the closed-loop control scheme. A realistic, unsteady flow field has been generated by placing a cylinder upstream of the turbine to induce shedding vortices at frequencies in the bandwidth of the first structural bending mode of the turbine blades. The goal of these experiments is to demonstrate closed-loop flow control as a means to reduce the unsteady fluctuation in the blades and increase the overall lifespan of the wind turbine.
Directory of Open Access Journals (Sweden)
Dulal Pal
2016-01-01
Full Text Available In the present study an unsteady mixed convection boundary layer flow of an electrically conduct- ing fluid over an stretching permeable sheet in the presence of transverse magnetic field, thermal radiation and non-uniform heat source/sink effects is investigated. The unsteadiness in the flow and temperature fields is due to the time-dependent nature of the stretching velocity and the surface temperature. Both opposing and assisting flows are considered. The dimensionless governing or- dinary non-linear differential equations are solved numerically by applying shooting method using Runge-Kutta-Fehlberg method. The effects of unsteadiness parameter, buoyancy parameter, thermal radiation, Eckert number, Prandtl number and non-uniform heat source/sink parameter on the flow and heat transfer characteristics are thoroughly examined. Comparisons of the present results with previously published results for the steady case are found to be excellent.
Large eddy simulation for aerodynamics: status and perspectives.
Sagaut, Pierre; Deck, Sébastien
2009-07-28
The present paper provides an up-to-date survey of the use of large eddy simulation (LES) and sequels for engineering applications related to aerodynamics. Most recent landmark achievements are presented. Two categories of problem may be distinguished whether the location of separation is triggered by the geometry or not. In the first case, LES can be considered as a mature technique and recent hybrid Reynolds-averaged Navier-Stokes (RANS)-LES methods do not allow for a significant increase in terms of geometrical complexity and/or Reynolds number with respect to classical LES. When attached boundary layers have a significant impact on the global flow dynamics, the use of hybrid RANS-LES remains the principal strategy to reduce computational cost compared to LES. Another striking observation is that the level of validation is most of the time restricted to time-averaged global quantities, a detailed analysis of the flow unsteadiness being missing. Therefore, a clear need for detailed validation in the near future is identified. To this end, new issues, such as uncertainty and error quantification and modelling, will be of major importance. First results dealing with uncertainty modelling in unsteady turbulent flow simulation are presented.
Cricket Ball Aerodynamics: Myth Versus Science
Mehta, Rabindra D.; Koga, Demmis J. (Technical Monitor)
2000-01-01
Aerodynamics plays a prominent role in the flight of a cricket ball released by a bowler. The main interest is in the fact that the ball can follow a curved flight path that is not always under the control of the bowler. ne basic aerodynamic principles responsible for the nonlinear flight or "swing" of a cricket ball were identified several years ago and many papers have been published on the subject. In the last 20 years or so, several experimental investigations have been conducted on cricket ball swing, which revealed the amount of attainable swing, and the parameters that affect it. A general overview of these findings is presented with emphasis on the concept of late swing and the effects of meteorological conditions on swing. In addition, the relatively new concept of "reverse" swing, how it can be achieved in practice and the role in it of ball "tampering", are discussed in detail. A discussion of the "white" cricket ball used in last year's World Cup, which supposedly possesses different swing properties compared to a conventional red ball, is also presented.
Aerodynamics of flapping insect wing in inclined stroke plane hovering with ground effect
Gowda v, Krishne; Vengadesan, S.
2014-11-01
This work presents the time-varying aerodynamic forces and the unsteady flow structures of flapping insect wing in inclined stroke plane hovering with ground effect. Two-dimensional dragonfly model wing is chosen and the incompressible Navier-Stokes equations are solved numerically by using immersed boundary method. The main objective of the present work is to analyze the ground effect on the unsteady forces and vortical structures for the inclined stroke plane motions. We also investigate the influences of kinematics parameters such as Reynolds number (Re), stroke amplitude, wing rotational timing, for various distances between the airfoil and the ground. The effects of aforementioned parameters together with ground effect, on the stroke averaged force coefficients and regimes of force behavior are similar in both normal (horizontal) and inclined stroke plane motions. However, the evolution of the vortex structures which produces the effects are entirely different.
Modeling the Aerodynamic Lift Produced by Oscillating Airfoils at Low Reynolds Number
Khalid, Muhammad Saif Ullah
2015-01-01
For present study, setting Strouhal Number (St) as control parameter, numerical simulations for flow past oscillating NACA-0012 airfoil at 1,000 Reynolds Numbers (Re) are performed. Temporal profiles of unsteady forces; lift and thrust, and their spectral analysis clearly indicate the solution to be a period-1 attractor for low Strouhal numbers. This study reveals that aerodynamic forces produced by plunging airfoil are independent of initial kinematic conditions of airfoil that proves the existence of limit cycle. Frequencies present in the oscillating lift force are composed of fundamental (fs), even and odd harmonics (3fs) at higher Strouhal numbers. Using numerical simulations, shedding frequencies (f_s) were observed to be nearly equal to the excitation frequencies in all the cases. Unsteady lift force generated due to the plunging airfoil is modeled by modified van der Pol oscillator. Using method of multiple scales and spectral analysis of steady-state CFD solutions, frequencies and damping terms in th...
Structural dynamics and aerodynamics measurements of biologically inspired flexible flapping wings
Energy Technology Data Exchange (ETDEWEB)
Wu, P; Stanford, B K; Ifju, P G [Department of Mechanical and Aerospace Engineering, MAE-A 231, University of Florida, Gainesville, FL 32611 (United States); Saellstroem, E; Ukeiley, L, E-mail: diccidwp@ufl.edu [Department of Mechanical and Aerospace Engineering, University of Florida, Shalimar, FL 32579 (United States)
2011-03-15
Flapping wing flight as seen in hummingbirds and insects poses an interesting unsteady aerodynamic problem: coupling of wing kinematics, structural dynamics and aerodynamics. There have been numerous studies on the kinematics and aerodynamics in both experimental and computational cases with both natural and artificial wings. These studies tend to ignore wing flexibility; however, observation in nature affirms that passive wing deformation is predominant and may be crucial to the aerodynamic performance. This paper presents a multidisciplinary experimental endeavor in correlating a flapping micro air vehicle wing's aeroelasticity and thrust production, by quantifying and comparing overall thrust, structural deformation and airflow of six pairs of hummingbird-shaped membrane wings of different properties. The results show that for a specific spatial distribution of flexibility, there is an effective frequency range in thrust production. The wing deformation at the thrust-productive frequencies indicates the importance of flexibility: both bending and twisting motion can interact with aerodynamic loads to enhance wing performance under certain conditions, such as the deformation phase and amplitude. By measuring structural deformations under the same aerodynamic conditions, beneficial effects of passive wing deformation can be observed from the visualized airflow and averaged thrust. The measurements and their presentation enable observation and understanding of the required structural properties for a thrust effective flapping wing. The intended passive responses of the different wings follow a particular pattern in correlation to their aerodynamic performance. Consequently, both the experimental technique and data analysis method can lead to further studies to determine the design principles for micro air vehicle flapping wings.
Aerodynamic Modelling and Optimization of Axial Fans
DEFF Research Database (Denmark)
Sørensen, Dan Nørtoft
A numerically efficient mathematical model for the aerodynamics oflow speed axial fans of the arbitrary vortex flow type has been developed.The model is based on a blade-element principle, whereby therotor is divided into a number of annular streamtubes.For each of these streamtubes relations...... for velocity, pressure andradial position are derived from the conservationlaws for mass, tangential momentum and energy.The resulting system of equations is non-linear and, dueto mass conservation and pressure equilibrium far downstream of the rotor,strongly coupled.The equations are solved using the Newton...... distributionsof pitch angle and chord length have been chosen as independent variablesin the optimizations.Besides restricting the geometry of the rotor,constraints have been added to ensure a required pressure rise as well asnon-stalled flow conditions.Optimizations have been performed tomaximize the mean value...
Computational Aerodynamics and Aeroacoustics for Wind Turbines
DEFF Research Database (Denmark)
Shen, Wen Zhong
or actuator/Navier-Stokes computations. A simple and efficient technique for determining the angle of attack for flow past a wind turbine rotor was developed in [11], and in [12] tunnel wall corrections for wind tunnels with closed or open test sections were developed. The second part of the thesis deals...... with Computational Aero-Acoustics (CAA). With the spread of wind turbines near urban areas, there is an increasing need for accurate predictions of aerodynamically generated noise. Indeed, noise has become one of the most important issues for further development of wind power, and the ability of controlling......=U/c), it is difficult to resolve them together at the same time. Hardin and Pope proposed a non-linear two-step (viscous incompressible flow and inviscid acoustic perturbation) splitting procedure for computational aero-acoustics that is suitable for both generation and propagation. The advantage of the splitting...
Mazaheri, K.; Ebrahimi, A.
2010-05-01
Ornithopters or mechanical birds produce aerodynamic lift and thrust through the flapping motion of their wings. Here, we use an experimental apparatus to investigate the effects of a wing's twisting stiffness on the generated thrust force and the power required at different flapping frequencies. A flapping wing system and an experimental set-up were designed to measure the unsteady aerodynamic and inertial forces, power usage and angular speed of the flapping wing motion. A data acquisition system was set-up to record important data with the appropriate sampling frequency. The aerodynamic performance of the vehicle under hovering (i.e., no wind) conditions was investigated. The lift and thrust that were produced were measured for different flapping frequencies and for various wings with different chordwise flexibilities. The results show the manner in which the elastic deformation and inertial flapping forces affect the dynamical behavior of the wing. It is shown that the generalization of the actuator disk theory is, at most, only valid for rigid wings, and for flexible wings, the power P varies by a power of about 1.0 of the thrust T. This aerodynamic information can also be used as benchmark data for unsteady flow solvers.
A System for Unsteady Pressure Measurements Revisited
Tijdeman, H.; Spiering, R.M.E.J.
2003-01-01
An overview is presented of some recent developments in the field of the design of effective sound absorbers. The first part deals with the application of socalled coupled tubes. For this purpose use is made of a system originally applied for unsteady pressure measurements on oscillating wind tunnel
On the unsteady Reynolds thermal transpiration law
Ziółkowski, P.; Badur, J.
2016-10-01
This paper presents the phenomenon of unsteady Reynolds thermal transpiration flow. The possible constitutive equations in the transpiration shell-like layer were studied analytically and numerically. There has been also examined experimental case of helium flow from cold to hot reservoir in nanopipe.
Theory and Applications of Unsteady Flows
1979-07-05
unsteady boundary-layer solutions with flow reversal, Dr. Wang, a post- doctoral research associate for two years, produced further examples in the...Donnelen, L. L., "Transient Response of Thick Airfoil with inite Trailing Edge Anigle in a Compressible Fluid," Ph.D. ’ Tesis , Cornell University, 1 979
Naval Aerodynamics Test Facility (NATF)
Federal Laboratory Consortium — The NATF specializes in Aerodynamics testing of scaled and fullsized Naval models, research into flow physics found on US Navy planes and ships, aerosol testing and...
Computational aerodynamics and artificial intelligence
Mehta, U. B.; Kutler, P.
1984-01-01
The general principles of artificial intelligence are reviewed and speculations are made concerning how knowledge based systems can accelerate the process of acquiring new knowledge in aerodynamics, how computational fluid dynamics may use expert systems, and how expert systems may speed the design and development process. In addition, the anatomy of an idealized expert system called AERODYNAMICIST is discussed. Resource requirements for using artificial intelligence in computational fluid dynamics and aerodynamics are examined. Three main conclusions are presented. First, there are two related aspects of computational aerodynamics: reasoning and calculating. Second, a substantial portion of reasoning can be achieved with artificial intelligence. It offers the opportunity of using computers as reasoning machines to set the stage for efficient calculating. Third, expert systems are likely to be new assets of institutions involved in aeronautics for various tasks of computational aerodynamics.
Nonlinear acoustic propagation in two-dimensional ducts
Nayfeh, A. H.; Tsai, M.-S.
1974-01-01
The method of multiple scales is used to obtain a second-order uniformly valid expansion for the nonlinear acoustic wave propagation in a two-dimensional duct whose walls are treated with a nonlinear acoustic material. The wave propagation in the duct is characterized by the unsteady nonlinear Euler equations. The results show that nonlinear effects tend to flatten and broaden the absorption versus frequency curve, in qualitative agreement with the experimental observations. Moreover, the effect of the gas nonlinearity increases with increasing sound frequency, whereas the effect of the material nonlinearity decreases with increasing sound frequency.
Chlorine decay under steady and unsteady-state hydraulic conditions
DEFF Research Database (Denmark)
Stoianov, Ivan; Aisopou, Angeliki
2014-01-01
This paper describes a simulation framework for the scale-adaptive hydraulic and chlorine decay modelling under steady and unsteady-state flows. Bulk flow and pipe wall reaction coefficients are replaced with steady and unsteady-state reaction coefficients. An unsteady decay coefficient is defined...... which depends upon the absolute value of shear stress and the rate of change of shear stress for quasi-unsteady and unsteady-state flows. A preliminary experimental and analytical investigation was carried out in a water transmission main. The results were used to model monochloramine decay...
Unsteady heat transfer in non-axisymmetric Homann stagnation-point flows
Mahapatra, T. R.; Sidui, S.
2017-04-01
An analysis is carried out to study the unsteady non-axisymmetric Homann's stagnation-point flow and heat transfer of an incompressible viscous fluid over a rigid plate in the presence of time-dependent free stream. The temperature of the plate is assumed to be higher than the ambient fluid temperature. Using similarity variables, the governing partial differential equations are transformed into nonlinear ordinary differential equations. These equations are then solved numerically using fourth-order Runge-Kutta method with shooting technique. The effects of the shear-to-strain rate ratio parameter γ (γ =b/a where a and b are the strain rate and shear rate of the stagnation-point flow, respectively) and the unsteadiness parameter λ on wall shear stress parameters, dimensionless velocities, rate of heat transfer at the wall and dimensionless temperature are analysed. It is found that the large-γ asymptotes do not depend on the parameter λ.
Aerodynamic Measurements of a Gulfstream Aircraft Model With and Without Noise Reduction Concepts
Neuhart, Dan H.; Hannon, Judith A.; Khorrami, Mehdi R.
2014-01-01
Steady and unsteady aerodynamic measurements of a high-fidelity, semi-span 18% scale Gulfstream aircraft model are presented. The aerodynamic data were collected concurrently with acoustic measurements as part of a larger aeroacoustic study targeting airframe noise associated with main landing gear/flap components, gear-flap interaction noise, and the viability of related noise mitigation technologies. The aeroacoustic tests were conducted in the NASA Langley Research Center 14- by 22-Foot Subsonic Wind Tunnel with the facility in the acoustically treated open-wall (jet) mode. Most of the measurements were obtained with the model in landing configuration with the flap deflected at 39º and the main landing gear on and off. Data were acquired at Mach numbers of 0.16, 0.20, and 0.24. Global forces (lift and drag) and extensive steady and unsteady surface pressure measurements were obtained. Comparison of the present results with those acquired during a previous test shows a significant reduction in the lift experienced by the model. The underlying cause was traced to the likely presence of a much thicker boundary layer on the tunnel floor, which was acoustically treated for the present test. The steady and unsteady pressure fields on the flap, particularly in the regions of predominant noise sources such as the inboard and outboard tips, remained unaffected. It is shown that the changes in lift and drag coefficients for model configurations fitted with gear/flap noise abatement technologies fall within the repeatability of the baseline configuration. Therefore, the noise abatement technologies evaluated in this experiment have no detrimental impact on the aerodynamic performance of the aircraft model.
Vasconcellos, Rui; Abdelkefi, Abdessattar
2015-01-01
The effects of a multi-segmented nonlinearity in the pitch degree of freedom on the behavior of a two-degree of freedom aeroelastic system are investigated. The aeroelastic system is free to plunge and pitch and is supported by linear translational and nonlinear torsional springs and is subjected to an incoming flow. The unsteady representation based on the Duhamel formulation is used to model the aerodynamic loads. Using modern method of nonlinear dynamics, a nonlinear characterization is performed to identify the system's response when increasing the wind speed. It is demonstrated that four sudden transitions take place with a change in the system's response. It is shown that, in the first transition, the system's response changes from simply periodic (only main oscillating frequency) to two periods (having the main oscillating frequency and its superharmonic of order 2). In the second transition, the response of the system changes from two periods (having the main oscillating frequency and its superharmonic of order 2) to a period-1. The results also show that the third transition is accompanied by a change in the system's response from simply periodic to two periods (having the main oscillating frequency and its superharmonic of order 3). After this transition, chaotic responses take place and then the fourth transition is accompanied by a sudden change in the system's response from chaotic to two periods (having the main oscillating frequency and its superharmonic of order 3). The results show that these transitions are caused by the tangential contact between the trajectory and the multi-segmented nonlinearity boundaries and with a zero-pitch speed incidence. This observation is associated with the definition of grazing bifurcation.
Introduction to wind turbine aerodynamics
Schaffarczyk, Alois Peter
2014-01-01
Wind-Turbine Aerodynamics is a self-contained textbook which shows how to come from the basics of fluid mechanics to modern wind turbine blade design. It presents a fundamentals of fluid dynamics and inflow conditions, and gives a extensive introduction into theories describing the aerodynamics of wind turbines. After introducing experiments the book applies the knowledge to explore the impact on blade design.The book is an introduction for professionals and students of very varying levels.
A numerical study on parasitic capillary waves using unsteady conformal mapping
Murashige, Sunao; Choi, Wooyoung
2017-01-01
This paper describes fully nonlinear computation of unsteady motion of parasitic capillary waves that appear on the front face of steep gravity waves progressing on water of infinite depth, within the framework of irrotational plane flow. As an alternative to the widely-used boundary integral method with mixed-Eulerian-Lagrangian (MEL) time updating, we focus on a numerical method based on unsteady conformal mapping, which will be hereafter referred to as the unsteady hodograph transformation (UHT) method. In this method, we solve the nonlinear evolution equations to find an unsteady conformal map in a complex plane with which the flow domain is mapped onto the unit disk while the free surface is fixed on the unit circle. The aim of this work is to compare the UHT method with the MEL method and find a more efficient method to compute parasitic capillary waves. From linear stability analysis, it is found that a critical difference between these two methods arises from the kernel of cotangent function in singular integrals, and the UHT method can avoid some numerical instability due to it. Numerical examples demonstrate that the UHT method is more suitable than the MEL method for not only parasitic capillary waves, but also capillary dominated waves. In particular, the UHT method requires no artificial techniques, such as filtering, to control numerical errors, in these examples. In addition, another major difference between the two methods is observed in terms of the clustering property of sample points on the free surface, depending on the restoring force of waves (gravity or surface tension).
Three-dimensional nonlinear flutter analysis of long-span suspension bridges during erection.
Zhang, Xin-jun; Sun, Bing-nan; Xiang, Hai-fan
2003-01-01
In this work, the aerodynamic stability of the Yichang Suspension Bridge over Yangtze River during erection was determined by three-dimensional nonlinear flutter analysis, in which the nonlinearities of structural dynamic characteristics and aeroelastic forces caused by large deformation are fully considered. An interesting result obtained was that the bridge was more stable when the stiffening girders were erected in a non-symmetrical manner as opposed to the traditional symmetrical erection schedule. It was also found that the severe decrease in the aerodynamic stability was due to the nonlinear effects. Therefore, the nonlinear factors should be considered accurately in aerodynamic stability analysis of long-span suspension bridges during erection.
Three-dimensional nonlinear flutter analysis of long-span suspension bridges during erection
Institute of Scientific and Technical Information of China (English)
张新军; 孙炳楠; 项海帆
2003-01-01
In this work, the aerodynamic stability of the Yichang Suspension Bridge over Yangtze River during erection was determined by three-dimensional nonlinear flutter analysis, in which the nonlinearities of structural dynamic characteristics and aeroelastic forces caused by large deformation are fully considered. An interesting result obtained was that the bridge was more stable when the stiffening girders were erected in a non-symmetrical manner as opposed to the traditional symmetrical erection schedule. It was also found that the severe decrease in the aerodynamic stability was due to the nonlinear effects. Therefore, the nonlinear factors should be considered accurately in aerodynamic stability analysis of long-span suspension bridges during erection.
Three-dimensional nonlinear flutter analysis of long-span suspension bridges during erection
Institute of Scientific and Technical Information of China (English)
张新军; 孙炳楠; 项海帆
2003-01-01
In this work, the aerodynamic stability of the Yichang Suspension Bridge over Yangtze River during erection was determined by three-dimensional nonlinear flutter analysis, in which the nonlinearities of structural dynamic characteristics and aeroelastic forces caused by large deformation are fully considered. An interesting resuh obtained was that the bridge was more stable when the stiffening girders were erected in a non-symmetrical manner as opposed to the traditional symmetrical erection schedule. It was also found that the severe decrease in the aerodynamic stability was due to the nonlinear effects. Therefore, the nonlinear factors should be considered accurately in aerodynamic stability analysis of long-span suspension bridges during erection.
Aerodynamics of badminton shuttlecocks
Verma, Aekaansh; Desai, Ajinkya; Mittal, Sanjay
2013-08-01
A computational study is carried out to understand the aerodynamics of shuttlecocks used in the sport of badminton. The speed of the shuttlecock considered is in the range of 25-50 m/s. The relative contribution of various parts of the shuttlecock to the overall drag is studied. It is found that the feathers, and the net in the case of a synthetic shuttlecock, contribute the maximum. The gaps, in the lower section of the skirt, play a major role in entraining the surrounding fluid and causing a difference between the pressure inside and outside the skirt. This pressure difference leads to drag. This is confirmed via computations for a shuttlecock with no gaps. The synthetic shuttle experiences more drag than the feather model. Unlike the synthetic model, the feather shuttlecock is associated with a swirling flow towards the end of the skirt. The effect of the twist angle of the feathers on the drag as well as the flow has also been studied.
Modelling of unsteady airfoil aerodynamics for the prediction of blade standstill vibrations
DEFF Research Database (Denmark)
Skrzypinski, Witold Robert; Gaunaa, Mac; Sørensen, Niels N.;
2012-01-01
In the present work, CFD simulations of the DU96-W-180 airfoil at 26 and 24 deg. angles of attack were performed. 2D RANS and 3D DES computations with non-moving and prescribed motion airfoil suspensions were carried out. The openings of the lift coefficient loops predicted by CFD were different...
DEFF Research Database (Denmark)
Kim, Taeseong; Shin, SangJoon; Kim, Do-Hyung
2012-01-01
A further improvement is attempted of an existing analytical model for an accurate prediction of the aeroelastic stability of a tiltrotor aircraft. A rigid-bladed rotor structural model with the natural frequencies selected appropriately in both the flapping and lagging motions is used. The geome......A further improvement is attempted of an existing analytical model for an accurate prediction of the aeroelastic stability of a tiltrotor aircraft. A rigid-bladed rotor structural model with the natural frequencies selected appropriately in both the flapping and lagging motions is used...
Unsteady Aerodynamics for Micro Air Vehicles (Aerodynamique instable pour micro-vehicules aeriens)
2010-09-01
Braunschweig Wind Tunnel The TUBS facility is an atmospheric Eiffel -type wind tunnel with a closed test section (Figure 2-5). The settling chamber...Wind Tunnel The TU Darmstadt experimental setup consists of a pair of pitch-plunge motion rigs and an Eiffel -type wind tunnel with test section of...A schematic of the tandem configuration integrated into the Eiffel -type wind tunnel test section at the Institute of Fluid Mechanics and
Owen, A. Karl
1996-01-01
Extensive testing done on a T55-L-712 turboshaft engine compressor in a compressor test rig is being followed by engine tests in progress as part of the Army Non-Recoverable Stall Program. Goals include a greater understanding of the gas turbine engine start cycle and compressor/engine operation in the regions 'beyond' the normal compressor stall line (rotating stall/surge). Rig steady state instrumentation consisted of 497 steady state pressure sensors and 153 temperature sensors. Engine instrumentation was placed in similar radial/axial locations and consists of 122 steady state pressure sensors and 65 temperature sensors. High response rig instrumentation consisted of 34 wall static pressure transducers. Rig and engine high response pressure transducers were located in the same axial/radial/circumferential locations in front of the first three stages. Additional engine high response instrumentation was placed in mach probes in front of the engine and on the compressor hub. This instrumentation allows for the generation of detailed stage characteristics, overall compressor mapping, and detailed analysis of dynamic compressor events.
Integrated Experimental and Numerical Research on the Aerodynamics of Unsteady Moving Aircraft
2007-06-01
NWB were manufactured by the plastics workshop of DLR in Braunschweig from carbon fibre composits in moulds. Fig. 11 shows a schematic view of the...cross section wing. In order to evaluate the influence of individual components of the tested airplane configuration, such as winglets , vertical or
1982-02-01
18) is defined by Yd(t) - C xd(t). (19) The system defined by (18)-(19) is parameterized by y - (p,r, BC T). We define a to be the set of all...for which values have not been specified are the matrices B and C.and the matriz -valued function G(s;p). These quantities describe the dynamic model
1987-03-01
1979), Jutras and bow shock wave which spans the passage Stallone (1980) and Lubomski (1981). The to the suction surface of the adjacent mode is usually...rotor performance map wasBankhead i1978) and Jutras , Stallone, and demonstrated using a transonic rotorBankhead (1980). This flutter annular...Instability Results with Engine Data ( Jutras , Stallone, and nankhead, 1980) ll.lm.l.,.ir l .l
The Unsteady Aerodynamics of a Delta Wing Undergoing Large Amplitude Pitching Motions
1992-04-01
sequentially rather than simultaneously. The software used to control the data acquisition was written in part using National Instruments LabView 2.0. Im...0.50] n-- -Ross Pll EAMMENE. * 0.46 . 50 - 0-40 o 30 20 10 0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 t/At * k = 0.03 (f = 0. 19 -H) * k = 0.09 (f
Taneja, Jayant Kumar
Electricity is an indispensable commodity to modern society, yet it is delivered via a grid architecture that remains largely unchanged over the past century. A host of factors are conspiring to topple this dated yet venerated design: developments in renewable electricity generation technology, policies to reduce greenhouse gas emissions, and advances in information technology for managing energy systems. Modern electric grids are emerging as complex distributed systems in which a portfolio of power generation resources, often incorporating fluctuating renewable resources such as wind and solar, must be managed dynamically to meet uncontrolled, time-varying demand. Uncertainty in both supply and demand makes control of modern electric grids fundamentally more challenging, and growing portfolios of renewables exacerbate the challenge. We study three electricity grids: the state of California, the province of Ontario, and the country of Germany. To understand the effects of increasing renewables, we develop a methodology to scale renewables penetration. Analyzing these grids yields key insights about rigid limits to renewables penetration and their implications in meeting long-term emissions targets. We argue that to achieve deep penetration of renewables, the operational model of the grid must be inverted, changing the paradigm from load-following supplies to supply-following loads. To alleviate the challenge of supply-demand matching on deeply renewable grids, we first examine well-known techniques, including altering management of existing supply resources, employing utility-scale energy storage, targeting energy efficiency improvements, and exercising basic demand-side management. Then, we create several instantiations of supply-following loads -- including refrigerators, heating and cooling systems, and laptop computers -- by employing a combination of sensor networks, advanced control techniques, and enhanced energy storage. We examine the capacity of each load for supply-following and study the behaviors of populations of these loads, assessing their potential at various levels of deployment throughout the California electricity grid. Using combinations of supply-following strategies, we can reduce peak natural gas generation by 19% on a model of the California grid with 60% renewables. We then assess remaining variability on this deeply renewable grid incorporating supply-following loads, characterizing additional capabilities needed to ensure supply-demand matching in future sustainable electricity grids.
Metri, Prashant G; Abel, M Subhash
2016-01-01
In this paper we present a mathematical analysis of thin film flow and heat transfer to a laminar liquid film from a horizontal stretching sheet. The flow of thin liquid film and subsequent heat transfer from the stretching surface is investigated with the aid of similarity transformations. Similarity transformations are used to convert unsteady boundary layer equations to a system of non-linear ordinary differential equations. The resulting non-linear differential equations are solved numerically using Runge-kutta-Fehlberg and Newton-Raphson schemes. A relationship between film thickness $\\beta$ and the unsteadiness parameter $S$ is found, the effect of unsteadiness parameter $S$, and the Prandtl number $Pr$, Magnetic field parameter $Mn$, Radiation parameter $Nr$ and viscous dissipation parameter $Ec$ and heat source parameter $\\gamma$ on the temperature distributions are presented and discussed in detail. Present analysis shows that the combined effect of magnetic field, thermal radiation, heat source and ...
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
A two-dimensional model of unsteady turbulent flow induced by high-speed elevator system was established in the present study. The research was focused on the instantaneous variation of the aerodynamic force on the car structure during traversing motion of the counter weight in the hoistway. A dynamic meshing method was employed to treat the multi-body motion system to avoid poor distortion of meshes. A comprehensive understanding of this significant aspect was obtained by varying the horizontal gap (δ=0.1m, 0.2m, and 0.3m) between the elevator car and the counter weight, and the moving speed (U0=2m/s, 6m/s, and 10m/s) of the elevator system. A pulsed intensification of the aerodynamic force on the elevator car and subsequent appearance of large valley with negative aerodynamic force were clearly observed in the numerical results. In parameters studied (δ=0.1m, U0=2m/s, 6m/s, 10m/s), the peaked horizontal and vertical forces are respectively 7-11 and 4.3-5.65 times of that when the counter weight is far from the car. These results demonstrated the prominent influence of the traversing counter weight on aerodynamic force on the elevator car, which is of great significance to designers of high-speed elevator system.
Supersonic unstalled flutter. [aerodynamic loading of thin airfoils induced by cascade motion
Adamczyk, J. J.; Goldstein, M. E.; Hartmann, M. J.
1978-01-01
Flutter analyses were developed to predict the onset of supersonic unstalled flutter of a cascade of two-dimensional airfoils. The first of these analyzes the onset of supersonic flutter at low levels of aerodynamic loading (i.e., backpressure), while the second examines the occurrence of supersonic flutter at moderate levels of aerodynamic loading. Both of these analyses are based on the linearized unsteady inviscid equations of gas dynamics to model the flow field surrounding the cascade. These analyses are utilized in a parametric study to show the effects of cascade geometry, inlet Mach number, and backpressure on the onset of single and multi degree of freedom unstalled supersonic flutter. Several of the results are correlated against experimental qualitative observation to validate the models.
Experimental Identification of Concentrated Nonlinearity in Aeroelastic System
Directory of Open Access Journals (Sweden)
Nayfeh Ali H
2012-07-01
Full Text Available Identification of concentrated nonlinearity in the torsional spring of an aeroelastic system is performed. This system consists of a rigid airfoil that is supported by a linear spring in the plunge motion and a nonlinear spring in the pitch motion. Quadratic and cubic nonlinearities in the pitch moment are introduced to model the concentrated nonlinearity. The representation of the aerodynamic loads by the Duhamel formulation yielded accurate values for the flutter speed and frequency. The results show that the use of the Duhamel formulation to represent the aerodynamic loads yields excellent agreement between the experimental data and the numerical predictions.
Aerodynamic Ground Effect in Fruitfly Sized Insect Takeoff.
Directory of Open Access Journals (Sweden)
Dmitry Kolomenskiy
Full Text Available Aerodynamic ground effect in flapping-wing insect flight is of importance to comparative morphologies and of interest to the micro-air-vehicle (MAV community. Recent studies, however, show apparently contradictory results of either some significant extra lift or power savings, or zero ground effect. Here we present a numerical study of fruitfly sized insect takeoff with a specific focus on the significance of leg thrust and wing kinematics. Flapping-wing takeoff is studied using numerical modelling and high performance computing. The aerodynamic forces are calculated using a three-dimensional Navier-Stokes solver based on a pseudo-spectral method with volume penalization. It is coupled with a flight dynamics solver that accounts for the body weight, inertia and the leg thrust, while only having two degrees of freedom: the vertical and the longitudinal horizontal displacement. The natural voluntary takeoff of a fruitfly is considered as reference. The parameters of the model are then varied to explore possible effects of interaction between the flapping-wing model and the ground plane. These modified takeoffs include cases with decreased leg thrust parameter, and/or with periodic wing kinematics, constant body pitch angle. The results show that the ground effect during natural voluntary takeoff is negligible. In the modified takeoffs, when the rate of climb is slow, the difference in the aerodynamic forces due to the interaction with the ground is up to 6%. Surprisingly, depending on the kinematics, the difference is either positive or negative, in contrast to the intuition based on the helicopter theory, which suggests positive excess lift. This effect is attributed to unsteady wing-wake interactions. A similar effect is found during hovering.
CFD investigations of the aerodynamics of vehicle overtaking maneuvers
Uddin, Mesbah; Chellaram, Arune Dhiren; Robinson, Austin Clay
2017-06-01
When two vehicle bodies are involved in a passing maneuver, interesting and intricate aerodynamic interactions occur between them. Such passing maneuvers are very important in racing and have been an area of active interest in motorsports for quite some time. The existing literature shows only a few studies in this area, and, as such, very little is known about the complex aerodynamics of racing in proximity. This paper presents a Computational Fluid Dynamics (CFD) methodology capable of describing the transient effects that occur in this scenario. This is achieved by simulating two tandem simplified vehicle bodies, the Ahmed body, which were placed in a virtual wind tunnel. One Ahmed body was kept stationary, while the other was allowed to move in the longitudinal direction with a relatively low velocity. In order to achieve reliable CFD results when one of the solid objects is moving, a new meshing methodology, called the overset mesh model, was implemented in the CFD process. The simulations were run using Star CCM+, a commercial finite-volume CFD program, in which the unsteady Reynolds Averaged Navier-Stokes (URANS) solver was applied. The CFD results are compared against fully transient and quasi-steady-state experimental results where encouraging correlations between the CFD and experiments are observed. The veracity of the CFD work presented in this paper provides significant insight into the complex aerodynamics of a passing maneuver, and lays the foundation for further analysis in this area using more complex vehicle shapes and more complex tandem racing or passing maneuvers at a yaw angle.
Aerodynamic stability of cable-supported bridges using CFRP cables
Institute of Scientific and Technical Information of China (English)
ZHANG Xin-jun; YING Lei-dong
2007-01-01
To gain understanding of the applicability of carbon fiber reinforced polymer (CFRP) cable in cable-supported bridges, based on the Runyang Bridge and Jinsha Bridge, a suspension bridge using CFRP cables and a cable-stayed bridge using CFRP stay cables are designed, in which the cable's cross-sectional area is determined by the principle of equivalent axial stiffness.Numerical investigations on the aerodynamic stability of the two bridges are conducted by 3D nonlinear aerodynamic stability analysis. The results showed that as CFRP cables are used in cable-supported bridges, for suspension bridge, its aerodynamic stability is superior to that of the case using steel cables due to the great increase of the torsional frequency; for cable-stayed bridge,its aerodynamic stability is basically the same as that of the case using steel stay cables. Therefore as far as the wind stability is considered, the use of CFRP cables in cable-supported bridges is feasible, and the cable's cross-sectional area should be determined by the principle of equivalent axial stiffness.
Bradney, D. R.; Evans, S. P.; Salles Pereira Da Costa, M.; Clausen, P. D.
2016-09-01
Small horizontal-axis wind turbines are likely to operate in a broad range of operating flow conditions, often in highly turbulent flow, due, in part, to their varied site placements. This paper compares the computational simulations of the performance of a 5 kW horizontal-axis wind turbine to detailed field measurements, with a particular focus on the impact of unsteady operating conditions on the drivetrain performance and generator output. Results indicate that the current Blade Element Momentum Theory based aerodynamic models under-predict the effect of high turbine yaw on the rotor torque, leading to a difference between predicted and measured shaft speed and power production. Furthermore, the results show discrepancies between the predicted instantaneous turbine yaw performance and measurements.
Numerical Investigation of the Unsteady Flow in a Transonic Compressor with Curved Rotors
Institute of Scientific and Technical Information of China (English)
Mao Mingming; Song Yanping; Wang Zhongqi
2008-01-01
The unsteady 3D flow fields in a single-stage transonic compressor under designed conditions are simulated numerically to inves- tigate the effects of the curved rotors on the stage performance and the aerodynamic interaction between the blade rows. The results show that, compared to the compressor with un-curved rotors, the compressor under scrutiny acquires remarkable increases in efficiency with significantly reduced amplitudes of the time-dependent fluctuation. The amplitude of the pressure fluctuation around the stator leading edge decreases at both endwalls, but increases at the mid-span in the curved rotors. The pressure fluctuation near the stator lead- ing edge, therefore, becomes more uniform in the radial direction of this compressor. Except for the leading edge area, the pressure fluc- tuation amplitude declines remarkably in the tip region of stator surface downstream of the curved rotor, but hardly changes in the mid- dle and at the hub.
Discrete vortex method simulations of aerodynamic admittance in bridge aerodynamics
DEFF Research Database (Denmark)
Rasmussen, Johannes Tophøj; Hejlesen, Mads Mølholm; Larsen, Allan
, and to determine aerodynamic forces and the corresponding ﬂutter limit. A simulation of the three-dimensional bridge responseto turbulent wind is carried out by quasi steady theory by modelling the bridge girder as a line like structure [2], applying the aerodynamic load coefﬁcients found from the current version...... of DVMFLOW in a strip wise fashion. Neglecting the aerodynamic admittance, i.e. the correlation of the instantaneous lift force to the turbulent ﬂuctuations in the vertical velocities, leads to higher response to high frequency atmospheric turbulence than would be obtained from wind tunnel tests....... In the present work we have extended the laminar oncoming ﬂow in DVMFLOW to a turbulent one, modelled by seeding the upstream ﬂow with vortex particles synthesized from prescribed atmospheric turbulence velocity spectra [3] . The discrete spectrum is sampled from the continuous spectrum subject to a lower cutoff...
Unsteady near-critical flows in microgravity.
Polezhaev, V I; Gorbunov, A A; Soboleva, E B
2004-11-01
This paper presents analysis of the different time scales associated with unsteady fluid flow phenomena near the thermodynamical critical point and that are typical for experiments carried out in microgravity. A focus of the paper is modeling the initial stage of convection under low and zero gravity on the basis of the two-dimensional Navier-Stokes equations for a compressible gas with the Van der Waals state equation. We also consider a thermoacoustic problem on the basis of three-dimensional linearized equations for an isentropic inviscid gas near the critical point in zero gravity. We compare the heat transfer due to unsteady convection and the piston effect in an enclosure with side heating in zero and low gravity with pure conductivity.
Coupled nonlinear aeroelasticity and flight dynamics of fully flexible aircraft
Su, Weihua
This dissertation introduces an approach to effectively model and analyze the coupled nonlinear aeroelasticity and flight dynamics of highly flexible aircraft. A reduced-order, nonlinear, strain-based finite element framework is used, which is capable of assessing the fundamental impact of structural nonlinear effects in preliminary vehicle design and control synthesis. The cross-sectional stiffness and inertia properties of the wings are calculated along the wing span, and then incorporated into the one-dimensional nonlinear beam formulation. Finite-state unsteady subsonic aerodynamics is used to compute airloads along lifting surfaces. Flight dynamic equations are then introduced to complete the aeroelastic/flight dynamic system equations of motion. Instead of merely considering the flexibility of the wings, the current work allows all members of the vehicle to be flexible. Due to their characteristics of being slender structures, the wings, tail, and fuselage of highly flexible aircraft can be modeled as beams undergoing three dimensional displacements and rotations. New kinematic relationships are developed to handle the split beam systems, such that fully flexible vehicles can be effectively modeled within the existing framework. Different aircraft configurations are modeled and studied, including Single-Wing, Joined-Wing, Blended-Wing-Body, and Flying-Wing configurations. The Lagrange Multiplier Method is applied to model the nodal displacement constraints at the joint locations. Based on the proposed models, roll response and stability studies are conducted on fully flexible and rigidized models. The impacts of the flexibility of different vehicle members on flutter with rigid body motion constraints, flutter in free flight condition, and roll maneuver performance are presented. Also, the static stability of the compressive member of the Joined-Wing configuration is studied. A spatially-distributed discrete gust model is incorporated into the time simulation
Numerical simulation of aerodynamic interaction for a tilt rotor aircraft in helicopter mode
Institute of Scientific and Technical Information of China (English)
Ye Liang; Zhang Ying; Yang Shuo; Zhu Xinglin; Dong Jun
2016-01-01
A rotor CFD solver is developed for simulating the aerodynamic interaction phe-nomenon among rotor, wing and fuselage of a tilt rotor aircraft in its helicopter mode. The unsteady Navier–Stokes equations are discretized in inertial frame and embedded grid system is adopted for describing the relative motion among blades and nacelle/wing/fuselage. A combination of multi-layer embedded grid and‘‘extended hole fringe”technique is complemented in original grid system to tackle grid assembly difficulties arising from the narrow space among different aerody-namic components, and to improve the interpolation precision by decreasing the cell volume dis-crepancy among different grid blocks. An overall donor cell searching and automatic hole cutting technique is used for grid assembly, and the solution processes are speeded up by introduc-tion of OpenMP parallel method. Based on this solver, flow fields and aerodynamics of a tilt rotor aircraft in hover are simulated with several rotor collective angles, and the corresponding states of an isolated rotor and rotor/wing/fuselage model are also computed to obtain reference solution. Aerodynamic interference influences among the rotor and wing/fuselage/nacelle are analyzed, and some meaningful conclusions are drawn.
Numerical Investigation of Aerodynamic Performance and Loads of a Novel Dual Rotor Wind Turbine
Directory of Open Access Journals (Sweden)
Behnam Moghadassian
2016-07-01
Full Text Available The objective of this paper is to numerically investigate the effects of the atmospheric boundary layer on the aerodynamic performance and loads of a novel dual-rotor wind turbine (DRWT. Large eddy simulations are carried out with the turbines operating in the atmospheric boundary layer (ABL and in a uniform inflow. Two stability conditions corresponding to neutral and slightly stable atmospheres are investigated. The turbines are modeled using the actuator line method where the rotor blades are modeled as body forces. Comparisons are drawn between the DRWT and a comparable conventional single-rotor wind turbine (SRWT to assess changes in aerodynamic efficiency and loads, as well as wake mixing and momentum and kinetic energy entrainment into the turbine wake layer. The results show that the DRWT improves isolated turbine aerodynamic performance by about 5%–6%. The DRWT also enhances turbulent axial momentum entrainment by about 3.3 %. The highest entrainment is observed in the neutral stability case when the turbulence in the ABL is moderately high. Aerodynamic loads for the DRWT, measured as out-of-plane blade root bending moment, are marginally reduced. Spectral analyses of ABL cases show peaks in unsteady loads at the rotor passing frequency and its harmonics for both rotors of the DRWT.
Numerical Simulation of Unsteady Flow Around Forward Flight Helicopter with Coaxial Rotors
Institute of Scientific and Technical Information of China (English)
XU Heyong; YE Zhengyin
2011-01-01
Three-dimensional unsteady Euler equations are numerically solved to simulate the unsteady flows around forward flight helicopter with coaxial rotors based on unstructured dynamic overset grids. The performances of the two coaxial rotors both become worse because of the aerodynamic interaction between them, and the influence of the top rotor on the bottom rotor is greater than that of the bottom rotor on the top rotor. The downwash velocity at the bottom rotor plane is much larger than that at the top rotor plane, and the downwash velocity at the top rotor plane is a little larger than that at an individual rotor plane. The downwash velocity and thrust coefficient both become larger when the collective angle of blades is added. When the spacing between the two coaxial rotors increases, the thrust coefficient of the top rotor increases, but the total thrust coefficient reduces a little,because the decrease of the bottom rotor thrust coefficient is larger than the increase of the top rotor thrust coefficient.
Characterization of Unsteady Flow Structures Near Leading-Edge Slat. Part 1; PIV Measurements
Jenkins, Luther N.; Khorrami, Mehdi R.; Choudhari, Meelan
2004-01-01
A comprehensive computational and experimental study has been performed at the NASA Langley Research Center as part of the Quiet Aircraft Technology (QAT) Program to investigate the unsteady flow near a leading-edge slat of a two-dimensional, high-lift system. This paper focuses on the experimental effort conducted in the NASA Langley Basic Aerodynamics Research Tunnel (BART) where Particle Image Velocimetry (PIV) data was acquired in the slat cove and at the slat trailing edge of a three-element, high-lift model at 4, 6, and 8 degrees angle of attack and a freestream Mach Number of 0.17. Instantaneous velocities obtained from PIV images are used to obtain mean and fluctuating components of velocity and vorticity. The data show the recirculation in the cove, reattachment of the shear layer on the slat lower surface, and discrete vortical structures within the shear layer emanating from the slat cusp and slat trailing edge. Detailed measurements are used to examine the shear layer formation at the slat cusp, vortex shedding at the slat trailing edge, and convection of vortical structures through the slat gap. Selected results are discussed and compared with unsteady, Reynolds-Averaged Navier-Stokes (URANS) computations for the same configuration in a companion paper by Khorrami, Choudhari, and Jenkins (2004). The experimental dataset provides essential flow-field information for the validation of near-field inputs to noise prediction tools.
Unsteady 2D potential-flow forces and a thin variable geometry airfoil undergoing arbitrary motion
Energy Technology Data Exchange (ETDEWEB)
Gaunaa, M.
2006-07-15
In this report analytical expressions for the unsteady 2D force distribution on a variable geometry airfoil undergoing arbitrary motion are derived under the assumption of incompressible, irrotational, inviscid flow. The airfoil is represented by its camberline as in classic thin-airfoil theory, and the deflection of the airfoil is given by superposition of chordwise deflection mode shapes. It is shown from the expressions for the forces, that the influence from the shed vorticity in the wake is described by the same time-lag for all chordwise positions on the airfoil. This time-lag term can be approximated using an indicial function approach, making the practical calculation of the aerodynamic response numerically very efficient by use of Duhamel superposition. Furthermore, the indicial function expressions for the time-lag terms are formulated in their equivalent state-space form, allowing for use of the present theory in problems employing the eigenvalue approach, such as stability analysis. The analytical expressions for the forces simplify to all previously known steady and unsteady thin-airfoil solutions. Apart from the obvious applications within active load control/reduction, the current theory can be used for various applications which up to now have been possible only using much more computational costly methods. The propulsive performance of a soft heaving propulsor, and the influence of airfoil camberline elasticity on the flutter limit are two computational examples given in the report that highlight this feature. (au)
Courant number and unsteady flow computation
Lai, Chintu; ,
1993-01-01
The Courant number C, the key to unsteady flow computation, is a ratio of physical wave velocity, ??, to computational signal-transmission velocity, ??, i.e., C = ??/??. In this way, it uniquely relates a physical quantity to a mathematical quantity. Because most unsteady open-channel flows are describable by a set of n characteristic equations along n characteristic paths, each represented by velocity ??i, i = 1,2,....,n, there exist as many as n components for the numerator of C. To develop a numerical model, a numerical integration must be made on each characteristic curve from an earlier point to a later point on the curve. Different numerical methods are available in unsteady flow computation due to the different paths along which the numerical integration is actually performed. For the denominator of C, the ?? defined as ?? = ?? 0 = ??x/??t has been customarily used; thus, the Courant number has the familiar form of C?? = ??/??0. This form will be referred to as ???common Courant number??? in this paper. The commonly used numerical criteria C?? for stability, neutral stability and instability, are imprecise or not universal in the sense that r0 does not always reflect the true maximum computational data-transmission speed of the scheme at hand, i.e., Ctau is no indication for the Courant constraint. In view of this , a new Courant number, called the ???natural Courant number???, Cn, that truly reflects the Courant constraint, has been defined. However, considering the numerous advantages inherent in the traditional C??, a useful and meaningful composite Courant number, denoted by C??* has been formulated from C??. It is hoped that the new aspects of the Courant number discussed herein afford the hydraulician a broader perspective, consistent criteria, and unified guidelines, with which to model various unsteady flows.
Unsteady Processes in Solid Propellant Combustion,
1977-05-01
0—AflO ~5a INSTITUTO NACIONAL DE TECNICA AEROESPACIAL MADRID (SPAIN) F/S 21/9.2UNSTEADY PROCESSES IN SOLID PROPELLANT COMBUSTION . (U) MAY...PRO C E SS E S IN SOLID P R O P E L L A N T C O M B U S T I O N H A. Crespo and M. Kindelán Instituto Nacional de Técnica Aeroespacial Madrid , Spain j
Turbulence dynamics in unsteady atmospheric flows
Momen, Mostafa; Bou-Zeid, Elie
2016-11-01
Unsteady pressure-gradient forcing in geophysical flows challenges the quasi-steady state assumption, and can strongly impact the mean wind and higher-order turbulence statistics. Under such conditions, it is essential to understand when turbulence is in quasi-equilibrium, and what are the implications of unsteadiness on flow characteristics. The present study focuses on the unsteady atmospheric boundary layer (ABL) where pressure gradient, Coriolis, buoyancy, and friction forces interact. We perform a suite of LES with variable pressure-gradient. The results indicate that the dynamics are mainly controlled by the relative magnitudes of three time scales: Tinertial, Tturbulence, and Tforcing. It is shown that when Tf Tt , the turbulence is no longer in a quasi-equilibrium state due to highly complex mean-turbulence interactions; consequently, the log-law and turbulence closures are no longer valid in these conditions. However, for longer and, surprisingly, for shorter forcing times, quasi-equilibrium is maintained. Varying the pressure gradient in the presence of surface buoyancy fluxes primarily influences the buoyant destruction in the stable ABLs, while under unstable conditions it mainly influences the transport terms. NSF-PDM under AGS-10266362. Cooperative Institute for Climate Science, NOAA-Princeton University under NA08OAR4320752. Simulations performed at NCAR, and Della server at Princeton University.
BTT autopilot design for agile missiles with aerodynamic uncer tainty
Institute of Scientific and Technical Information of China (English)
Yueyue Ma; Jie Guo; Shengjing Tang
2015-01-01
The approach to the synthesis of autopilot with aerody-namic uncertainty is investigated in order to achieve large maneu-verability of agile missiles. The dynamics of the agile missile with reaction-jet control system (RCS) are presented. Subsequently, the cascade control scheme based on the bank-to-turn (BTT) steering technique is described. To address the aerodynamic un-certainties encountered by the control system, the active distur-bance rejection control (ADRC) method is introduced in the autopi-lot design. Furthermore, a compound control er, using extended state observer (ESO) to online estimate system uncertainties and calculate derivative of command signals, is designed based on dynamic surface control (DSC). Nonlinear simulation results show the feasibility of the proposed approach and validate the robust-ness of the control er with severe unmodeled dynamics.
Vibratory motion of fourth order fluid film over a unsteady heated flat
Mohmand, Muhammad Ismail; Mamat, Mustafa Bin; Shah, Qayyum; Gul, Taza
2017-03-01
Analysis of heat transfer is studied in magnetohydrodynamic (MHD) thin layer flow of an unsteady fourth grade fluid past a moving and oscillating vertical plate for lift and drainage problem. The governing equations are modelled in terms of nonlinear partial differential equations with some physical boundary conditions. Two different analytical methods, namely Adomian Decomposition Method (ADM) and the Optimal Homotopy Asymptotic Method (OHAM) are used for finding the series solution of the problem. The solutions obtained through two different techniques are compared using graphs and tables and found an excellent agreement. The variants of embedded flow parameters in the solution are analyzed through graphical illustrations.
Metri, Prashant G.; Narayana, Mahesha; Silvestrov, Sergei
2017-01-01
In this paper, we examine the hydromagnetic boundary layer flow and heat transfer characteristics of a laminar nanoliquid film over an unsteady stretching sheet is presented. The highly nonlinear partial differential equations governing flow and heat transport are simplified using similarity transformation. The analytical solutions of the resulting ODEs are obtained for some special case of nano liquid film using hypergeometric power series functions, and from which the analytical solutions of the original problem are presented. The influence of pertinent parameters such as the magnetic parameter, the solid volume fraction of nanoparticles and the type of nanofluid on the flow, heat transfer, Nusselt number and skin friction coefficient is discussed analytically.
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.
Hall Effects on Unsteady Magnetohydrodynamic Flow of a Third Grade Fluid
Institute of Scientific and Technical Information of China (English)
K.Fakhar; XU Zhen-Li; CHENG Yi
2007-01-01
The unsteady magnetohydrodynamic Bow of an electrically conducting viscous incompressible third grade fluid bounded by an infinite porous plate is studied with the Hall effect. An external uniform magnetic field is applied perpendicular to the plate and the fluid motion is subjected to a uniform suction and injection. Similarity transformations are employed to reduce the non-linear equations governing the Bow under discussion to two ordinary differential equations (with and without dispersion terms). Using the finite difference scheme, numerical solutions represented by graphs with reference to the various involved parameters of interest are discussed and appropriate conclusions are drawn.
Institute of Scientific and Technical Information of China (English)
MUKHOPADHYAY Swati; VAJRAVELU Kuppalapalle
2013-01-01
In this paper we investigate the two-dimensional flow of a non-Newtonian fluid over an unsteady stretching permeable surface.The Casson fluid model is used to characterize the non-Newtonian fluid behavior.First-order constructive/destructive chemical reaction is considered.With the help of a shooting method,numerical solutions for a class of nonlinear coupled differential equations subject to appropriate boundary conditions are obtained.For the steady flow,the exact solution is obtained.The flow features and the mass transfer characteristics for different values of the governing parameters are analyzed and discussed in detail.
Directory of Open Access Journals (Sweden)
Ahmada Omar Ali
2015-01-01
Full Text Available This paper investigates numerically the effects of variable viscosity on unsteady generalized Couette flow of a water base nanofluid with convective cooling at the moving surface. The Buongiorno model utilized for the nanofluid incorporates the effects of Brownian motion and thermophoresis. The nonlinear governing equations of continuity, momentum, energy and nanoparticles concentration are tackled numerically using a semi discretization finite difference method together with Runge-Kutta Fehlberg integration scheme. Numerical results for velocity, temperature, and nanoparticles concentration profiles together with skin friction and Nusselt number are obtained graphically and discussed quantitatively.
Aerodynamics Research Revolutionizes Truck Design
2008-01-01
During the 1970s and 1980s, researchers at Dryden Flight Research Center conducted numerous tests to refine the shape of trucks to reduce aerodynamic drag and improved efficiency. During the 1980s and 1990s, a team based at Langley Research Center explored controlling drag and the flow of air around a moving body. Aeroserve Technologies Ltd., of Ottawa, Canada, with its subsidiary, Airtab LLC, in Loveland, Colorado, applied the research from Dryden and Langley to the development of the Airtab vortex generator. Airtabs create two counter-rotating vortices to reduce wind resistance and aerodynamic drag of trucks, trailers, recreational vehicles, and many other vehicles.
The aerodynamics of wind turbines
DEFF Research Database (Denmark)
Sørensen, Jens Nørkær; Mikkelsen, Robert Flemming; Troldborg, Niels
2013-01-01
In the paper we present state-of-the-art of research in wind turbine aerodynamics. We start be giving a brief historical review and a survey over aerodynamic research in wind energy. Next, we focus on some recent research results obtained by our wind energy group at Department of Mechanical...... Engineering at DTU. In particular, we show some new results on the classical problem of the ideal rotor and present a series of new results from an on-going research project dealing with the modelling and simulation of turbulent flow structures in the wake behind wind turbines....
Rotor/body aerodynamic interactions
Betzina, M. D.; Smith, C. A.; Shinoda, P.
1985-01-01
A wind tunnel investigation was conducted in which independent, steady state aerodynamic forces and moments were measured on a 2.24 m diam. two bladed helicopter rotor and on several different bodies. The mutual interaction effects for variations in velocity, thrust, tip-path-plane angle of attack, body angle of attack, rotor/body position, and body geometry were determined. The results show that the body longitudinal aerodynamic characteristics are significantly affected by the presence of a rotor and hub, and that the hub interference may be a major part of such interaction. The effects of the body on the rotor performance are presented.
Schepers, J.G.
2012-01-01
The subject of aerodynamics is of major importance for the successful deployment of wind energy. As a matter of fact there are two aerodynamic areas in the wind energy technology: Rotor aerodynamics and wind farm aerodynamics. The first subject considers the flow around the rotor and the second
Schepers, J.G.
2012-01-01
The subject of aerodynamics is of major importance for the successful deployment of wind energy. As a matter of fact there are two aerodynamic areas in the wind energy technology: Rotor aerodynamics and wind farm aerodynamics. The first subject considers the flow around the rotor and the second subj
Directory of Open Access Journals (Sweden)
Diksha Gupta
2014-01-01
Full Text Available The objective of this investigation is to analyze the effect of unsteadiness on the mixed convection boundary layer flow of micropolar fluid over a permeable shrinking sheet in the presence of viscous dissipation. At the sheet a variable distribution of suction is assumed. The unsteadiness in the flow and temperature fields is caused by the time dependence of the shrinking velocity and surface temperature. With the aid of similarity transformations, the governing partial differential equations are transformed into a set of nonlinear ordinary differential equations, which are solved numerically, using variational finite element method. The influence of important physical parameters, namely, suction parameter, unsteadiness parameter, buoyancy parameter and Eckert number on the velocity, microrotation, and temperature functions is investigated and analyzed with the help of their graphical representations. Additionally skin friction and the rate of heat transfer have also been computed. Under special conditions, an exact solution for the flow velocity is compared with the numerical results obtained by finite element method. An excellent agreement is observed for the two sets of solutions. Furthermore, to verify the convergence of numerical results, calculations are conducted with increasing number of elements.
Dickinson, B. T.; Singler, J. R.; Batten, B. A.
2012-02-01
Bats possess arrays of distributed flow-sensitive hair-like mechanoreceptors on their dorsal and ventral wing surfaces. Bat wing hair receptors are known to play a significant role in flight maneuverability and are directionally most sensitive to reversed flow over the wing. In this work, we consider the mechanics of flexible hair-like structures for the time accurate detection and visualization of hydrodynamic images associated with unsteady near surface flow phenomena. A nonlinear viscoelastic model of a hair-like structure coupled to an unsteady nonuniform flow is proposed. Writing the hair model in nondimensional form, we identify five dimensionless groups that govern hair behavior. An order of magnitude analysis of the physical forces involved in the fluid-structure hair response is performed. Through the choice of hair material properties, we show how a local measure of near surface flow velocity may be obtained from hair tip displacement and resultant moment. When hair structures are placed into an array, time and space accurate hydrodynamic images may be obtained. We illustrate the imaging of reversed flow that occurs during a laminar unsteady flow separation with an array of hair-like structures.
Gupta, Diksha; Kumar, Lokendra; Singh, Bani
2014-01-01
The objective of this investigation is to analyze the effect of unsteadiness on the mixed convection boundary layer flow of micropolar fluid over a permeable shrinking sheet in the presence of viscous dissipation. At the sheet a variable distribution of suction is assumed. The unsteadiness in the flow and temperature fields is caused by the time dependence of the shrinking velocity and surface temperature. With the aid of similarity transformations, the governing partial differential equations are transformed into a set of nonlinear ordinary differential equations, which are solved numerically, using variational finite element method. The influence of important physical parameters, namely, suction parameter, unsteadiness parameter, buoyancy parameter and Eckert number on the velocity, microrotation, and temperature functions is investigated and analyzed with the help of their graphical representations. Additionally skin friction and the rate of heat transfer have also been computed. Under special conditions, an exact solution for the flow velocity is compared with the numerical results obtained by finite element method. An excellent agreement is observed for the two sets of solutions. Furthermore, to verify the convergence of numerical results, calculations are conducted with increasing number of elements.
Institute of Scientific and Technical Information of China (English)
余永亮; 童秉纲; 马晖扬
2003-01-01
Numerous studies on the aerodynamics of insect wing flapping were carried out on different approaches of flight investigations, model experiments, and numerical simulations, but the theoretical modeling remains to be explored. In the present paper, an analytic approach is presented to model the flow interactions of wing flapping in air for small insects with the surrounding flow fields being highly unsteady and highly viscous. The model of wing flapping is a 2-D flat plate, which makes plunging and pitching oscillations as well as quick rotations reversing its positions of leading and trailing edges, respectively, during stroke reversals. It contains three simplified aerodynamic assumptions:(i) unsteady potential flow; (ii) discrete vortices shed from both leading and trailing edges of the wing; (iii) Kutta conditions applied at both edges. Then the problem is reduced to the solution of the unsteady Laplace equation, by using distributed singularities, i.e., sources/sinks, and vortices in the field. To validate the present physical model and analytic method proposed via benchmark examples, two elemental motions in wing flapping and a case of whole flapping cycles are analyzed,and the predicted results agree well with available experimental and numerical data. This verifies that the present analytical approach may give qualitatively correct and quantitatively reasonable results.Furthermore, the total fluid-dynamic force in the present method can be decomposed into three parts:one due to the added inertial (or mass) effect, the other and the third due to the induction of vortices shed from the leading- and the trailing-edge and their images respectively, and this helps to reveal the flow control mechanisms in insect wing flapping.
Borazjani, Iman
2015-10-01
Unsteady aquatic locomotion is not an exception, but rather how animals often swim. It includes fast-starts (C-start or S-start), escape maneuvers, turns, acceleration/deceleration, and even during steady locomotion the swimming speed fluctuates, i.e., there is unsteadiness. Here, a review of the recent work on unsteady aquatic locomotion with emphasis on numerical simulations is presented. The review is started by an overview of different theoretical and numerical methods that have been used for unsteady swimming, and then the insights provided by these methods on (1) unsteadiness in straight-line swimming and (2) unsteady fast-starts and turns are discussed. The swimming speed's unsteady fluctuations during straight-line swimming are typically less than 3% of the average swimming speed, but recent simulations show that body shape affects fluctuations more than does body kinematics, i.e., changing the shape of the body generates larger fluctuations than does changing its kinematics. For fast-starts, recent simulations show that the best motion to maximize the distance traveled from rest are similar to the experimentally observed C-start maneuvers. Furthermore, another set of simulations, which are validated against measurements of flow in experiments with live fish, investigate the role of fins during the C-start. The simulations showed that most of the force is generated by the body of the fish (not by fins) during the first stage of the C-start when the fish bends itself into the C-shape. However, in the second stage, when it rapidly bends out of the C-shape, more than 70% of the instantaneous hydrodynamic force is produced by the tail. The effect of dorsal and anal fins was less than 5% of the instantaneous force in both stages, except for a short period of time (2 ms) just before the second stage. Therefore, the active control and the erection of the anal/dorsal fins might be related to retaining the stability of the sunfish against roll and pitch during the C
Energy Technology Data Exchange (ETDEWEB)
Oliveira, P.H.I.A. de; Bortolus, M.V.; Pinto, R.L.U. de F. [Minas Gerais Univ., Belo Horizonte, MG (Brazil). Dept. de Engenharia Mecanica
1998-07-01
This paper presents a numerical procedure to determine the optimal turbine blades geometry. It consists of the application of a non-linear algorithm on aerodynamic analysis model, developed from the Blade Element Method. Results are obtained for several tip speed ratios to determine the optimal operation condition. (author)
2016-02-01
control, turbulence, fluid mechanics, nonlinear coupling, planar jet experiment, Director’s Research Initiative (DRI) 16. SECURITY CLASSIFICATION OF...Successful development of active aerodynamic flow control technologies that delay or prevent separation could lead to substantial performance...improvements, including increased speed, maneuverability, payload capacity, and/or range. However, instances in which active flow control technologies have
Unsteady Velocity Measurements Taken Behind a Model Helicopter Rotor Hub in Forward Flight
Berry, John D.
1997-01-01
Drag caused by separated flow behind the hub of a helicopter has an adverse effect on aerodynamic performance of the aircraft. To determine the effect of separated flow on a configuration used extensively for helicopter aerodynamic investigations, an experiment was conducted using a laser velocimeter to measure velocities in the wake of a model helicopter hub operating at Mach-scaled conditions in forward flight. Velocity measurements were taken using a laser velocimeter with components in the vertical and downstream directions. Measurements were taken at 13 stations downstream from the rotor hub. At each station, measurements were taken in both a horizontal and vertical row of locations. These measurements were analyzed for harmonic content based on the rotor period of revolution. After accounting for these periodic velocities, the remaining unsteady velocities were treated as turbulence. Turbulence intensity distributions are presented. Average turbulent intensities ranged from approximately 2 percent of free stream to over 15 percent of free stream at specific locations and azimuths. The maximum average value of turbulence was located near the rear-facing region of the fuselage.
Institute of Scientific and Technical Information of China (English)
Mulugeta Biadgo Asress; Jelena Svorcan
2014-01-01
Increasing velocity combined with decreasing mass of modern high-speed trains poses a question about the influence of strong crosswinds on its aerodynamics. Strong crosswinds may affect the running stability of high-speed trains via the amplified aerodynamic forces and moments. In this study, a simulation of turbulent crosswind flows over the leading and end cars of ICE-2 high-speed train was performed at different yaw angles in static and moving ground case scenarios. Since the train aerodynamic problems are closely associated with the flows occurring around train, the flow around the train was considered as incompressible and was obtained by solving the incom-pressible form of the unsteady Reynolds-averaged Navier–Stokes (RANS) equations combined with the realizable k-epsilon turbulence model. Important aerodynamic coef-ficients such as the side force and rolling moment coeffi-cients were calculated for yaw angles ranging from-30? to 60? and compared with the results obtained from wind tunnel test. The dependence of the flow structure on yaw angle was also presented. The nature of the flow field and its structure depicted by contours of velocity magnitude and streamline patterns along the train’s cross-section were presented for different yaw angles. In addition, the pressure coefficient around the circumference of the train at dif-ferent locations along its length was computed for yaw angles of 30? and 60?. The computed aerodynamic coef-ficient outcomes using the realizable k-epsilon turbulence model were in good agreement with the wind tunnel data. Both the side force coefficient and rolling moment coeffi-cients increase steadily with yaw angle till about 50? before starting to exhibit an asymptotic behavior. Contours of velocity magnitude were also computed at different cross-sections of the train along its length for different yaw angles. The result showed that magnitude of rotating vortex in the lee ward side increased with increasing yaw angle, which
Hall, Edward J.; Delaney, Robert A.; Adamczyk, John J.; Miller, Christopher J.; Arnone, Andrea; Swanson, Charles
1993-01-01
The primary objective of this study was the development of a time-marching three-dimensional Euler/Navier-Stokes aerodynamic analysis to predict steady and unsteady compressible transonic flows about ducted and unducted propfan propulsion systems employing multiple blade rows. The computer codes resulting from this study are referred to as ADPAC-AOACR (Advanced Ducted Propfan Analysis Codes-Angle of Attack Coupled Row). This report is intended to serve as a computer program user's manual for the ADPAC-AOACR codes developed under Task 5 of NASA Contract NAS3-25270, Unsteady Counterrotating Ducted Propfan Analysis. The ADPAC-AOACR program is based on a flexible multiple blocked grid discretization scheme permitting coupled 2-D/3-D mesh block solutions with application to a wide variety of geometries. For convenience, several standard mesh block structures are described for turbomachinery applications. Aerodynamic calculations are based on a four-stage Runge-Kutta time-marching finite volume solution technique with added numerical dissipation. Steady flow predictions are accelerated by a multigrid procedure. Numerical calculations are compared with experimental data for several test cases to demonstrate the utility of this approach for predicting the aerodynamics of modern turbomachinery configurations employing multiple blade rows.
Energy Technology Data Exchange (ETDEWEB)
Isa, Sharena Mohamad; Ali, Anati [Department of Mathematical Sciences, Faculty of Science Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia sharena-ina@yahoo.com, anati@utm.my (Malaysia)
2015-10-22
In this paper, the hydromagnetic flow of dusty fluid over a vertical stretching sheet with thermal radiation is investigated. The governing partial differential equations are reduced to nonlinear ordinary differential equations using similarity transformation. These nonlinear ordinary differential equations are solved numerically using Runge-Kutta Fehlberg fourth-fifth order method (RKF45 Method). The behavior of velocity and temperature profiles of hydromagnetic fluid flow of dusty fluid is analyzed and discussed for different parameters of interest such as unsteady parameter, fluid-particle interaction parameter, the magnetic parameter, radiation parameter and Prandtl number on the flow.
Aerodynamic design via control theory
Jameson, Antony
1988-01-01
The question of how to modify aerodynamic design in order to improve performance is addressed. Representative examples are given to demonstrate the computational feasibility of using control theory for such a purpose. An introduction and historical survey of the subject is included.
POEMS in Newton's Aerodynamic Frustum
Sampedro, Jaime Cruz; Tetlalmatzi-Montiel, Margarita
2010-01-01
The golden mean is often naively seen as a sign of optimal beauty but rarely does it arise as the solution of a true optimization problem. In this article we present such a problem, demonstrating a close relationship between the golden mean and a special case of Newton's aerodynamical problem for the frustum of a cone. Then, we exhibit a parallel…
POEMS in Newton's Aerodynamic Frustum
Sampedro, Jaime Cruz; Tetlalmatzi-Montiel, Margarita
2010-01-01
The golden mean is often naively seen as a sign of optimal beauty but rarely does it arise as the solution of a true optimization problem. In this article we present such a problem, demonstrating a close relationship between the golden mean and a special case of Newton's aerodynamical problem for the frustum of a cone. Then, we exhibit a parallel…
Analysis of Porosity Effects on Unsteady Stretching Permeable Sheet
Directory of Open Access Journals (Sweden)
Phool SINGH
2014-07-01
Full Text Available The aim of this paper is to analyze two-dimensional unsteady flow of a viscous incompressible fluid about a stagnation point on a permeable stretching sheet in presence of a time dependent free stream velocity. Fluid is considered in the porous media with radiation effect. The Rosseland approximation is used to model the radiative heat transfer. Using a time-dependent stream function, partial differential equations corresponding to the momentum and energy equations are converted into non-linear ordinary differential equations. The numerical solutions of these equations are obtained by using the Runge-Kutta Fehlberg method with the help of shooting technique. In the present work, the effect of porosity parameter, radiation parameter and suction parameter on flow and heat transfer characteristics are discussed. The skin-friction coefficient and the Nusselt number at the sheet are computed and discussed. The results reported in the paper are in good agreement with published work in literature by other researchers.doi:10.14456/WJST.2014.13
Institute of Scientific and Technical Information of China (English)
孙茂; Hossein Hamdani
2001-01-01
The aerodynamic force and flow structure of NACA 0012 airfoil performing an unsteady motion at low Reynolds number (Re = 100) are calculated by solving Navier-Stokes equations. The motion consists of three parts: the first translation, rotation and the second translation in the direction opposite to the first.The rotation and the second translation in this motion are expected to represent the rotation and translation of the wing-section of a hovering insect. The flow structure is used in combination with the theory of vorticity dynamics to explain the generation of unsteady aerodynamic force in the motion. During the rotation, due to the creation of strong vortices in short time, large aerodynamic force is produced and the force is almost normal to the airfoil chord. During the second translation, large lift coefficient can be maintained for certain time period and CL1, the lift coefficient averaged over four chord lengths of travel, is larger than 2 (the corresponding steady-state lift coefficient is only 0.9). The large lift coefficient is due to two effects. The first is the delayed shedding of the stall vortex. The second is that the vortices created during the airfoil rotation and in the near wake left by previous translation form a short "vortex street" in front of the airfoil and the "vortex street" induces a "wind";against this "wind" the airfoil translates, increasing its relative speed. The above results provide insights to the understanding of the mechanism of high-lift generation by a hovering insect.
Unsteady Sail Dynamics in Olympic Class Sailboats
Williamson, Charles; Schutt, Riley
2016-11-01
Unsteady sailing techniques have evolved in competitive sailboat fleets, in cases where the relative weight of the sailor is sufficient to impart unsteady motions to the boat and sails. We will discuss three types of motion that are used by athletes to propel their boats on an Olympic race course faster than using the wind alone. In all of our cases, body weight movements induce unsteady sail motion, increasing driving force and speed through the water. In this research, we explore the dynamics of an Olympic class Laser sailboat equipped with a GPS, IMU, wind sensor, and a 6-GoPro camera array. We shall briefly discuss "sail flicking", whereby the helmsman periodically rolls the sail into the apparent wind, at an angle which is distinct from classical heave (in our case, the oscillations are not normal to the apparent flow). We also demonstrate "roll tacking", where there are considerable advantages to rolling the boat during such a maneuver, especially in light wind. In both of the above examples from on-the-water studies, corresponding experiments using a towing tank exhibit increases in the driving force, associated with the formation of strong vortex pairs into the flow. Finally, we focus on a technique known as "S-curving" in the case where the boat sails downwind. In contrast to the previous cases, it is drag force rather than lift force that the sailor is trying to maximise as the boat follows a zig-zag trajectory. The augmented apparent wind strength due to the oscillatory sail motion, and the growth of strong synchronised low-pressure wake vortices on the low-pressure side of the sail, contribute to the increase in driving force, and velocity-made-good downwind.
Unsteady natural convection in micropolar nanofluids
Directory of Open Access Journals (Sweden)
Rup Kazimierz
2014-09-01
Full Text Available This paper presents the analysis of momentum, angular momentum and heat transfer during unsteady natural convection in micropolar nanofluids. Selected nanofluids treated as single phase fluids contain small particles with diameter size 10-38.4 nm. In particular three water-based nanofluids were analyzed. Volume fraction of these solutions was 6%. The first of the analyzed nanofluids contained TiO2 nanoparticles, the second one contained Al2O3 nanoparticles, and the third one the Cu nanoparticles.
High-order implicit time-marching methods for unsteady fluid flow simulation
Boom, Pieter David
Unsteady computational fluid dynamics (CFD) is increasingly becoming a critical tool in the development of emerging technologies and modern aircraft. In spite of rapid mathematical and technological advancement, these simulations remain computationally intensive and time consuming. More efficient temporal integration will promote a wider use of unsteady analysis and extend its range of applicability. This thesis presents an investigation of efficient high-order implicit time-marching methods for application in unsteady compressible CFD. A generalisation of time-marching methods based on summation-by-parts (SBP) operators is described which reduces the number of stages required to obtain a prescribed order of accuracy, thus improving their efficiency. The classical accuracy and stability theory is formally extended for these generalised SBP (GSBP) methods, including superconvergence and nonlinear stability. Dual-consistent SBP and GSBP time-marching methods are shown to form a subclass of implicit Runge-Kutta methods, which enables extensions of nonlinear accuracy and stability results. A novel family of fully-implicit GSBP Runge-Kutta schemes based on Gauss quadrature are derived which are both algebraically stable and L-stable with order 2s - 1, where s is the number of stages. In addition, a numerical tool is developed for the construction and optimisation of general linear time-marching methods. The tool is applied to the development of several low-stage-order L-stable diagonally-implicit methods, including a diagonally-implicit GSBP Runge-Kutta scheme. The most notable and efficient method developed is a six-stage fifth-order L-stable stiffly-accurate explicit-first-stage singly-diagonally-implicit Runge-Kutta (ESDIRK5) method with stage order two. The theoretical results developed in this thesis are supported by numerical simulations, and the predicted relative efficiency of the schemes is realised.
A Coordinate Transformation for Unsteady Boundary Layer Equations
Directory of Open Access Journals (Sweden)
Paul G. A. CIZMAS
2011-12-01
Full Text Available This paper presents a new coordinate transformation for unsteady, incompressible boundary layer equations that applies to both laminar and turbulent flows. A generalization of this coordinate transformation is also proposed. The unsteady boundary layer equations are subsequently derived. In addition, the boundary layer equations are derived using a time linearization approach and assuming harmonically varying small disturbances.
Flutter and Forced Response Analyses of Cascades using a Two-Dimensional Linearized Euler Solver
Reddy, T. S. R.; Srivastava, R.; Mehmed, O.
1999-01-01
Flutter and forced response analyses for a cascade of blades in subsonic and transonic flow is presented. The structural model for each blade is a typical section with bending and torsion degrees of freedom. The unsteady aerodynamic forces due to bending and torsion motions. and due to a vortical gust disturbance are obtained by solving unsteady linearized Euler equations. The unsteady linearized equations are obtained by linearizing the unsteady nonlinear equations about the steady flow. The predicted unsteady aerodynamic forces include the effect of steady aerodynamic loading due to airfoil shape, thickness and angle of attack. The aeroelastic equations are solved in the frequency domain by coupling the un- steady aerodynamic forces to the aeroelastic solver MISER. The present unsteady aerodynamic solver showed good correlation with published results for both flutter and forced response predictions. Further improvements are required to use the unsteady aerodynamic solver in a design cycle.
The Aerodynamics of Deforming Wings at Low Reynolds Number
Medina, Albert
Flapping flight has gained much attention in the past decade driven by the desire to understand capabilities observed in nature and the desire to develop agile small-scale aerial vehicles. Advancing our current understanding of unsteady aerodynamics is an essential component in the development of micro-air vehicles (MAV) intended to utilize flight mechanics akin to insect flight. Thus the efforts undertaken that of bio-mimicry. The complexities of insect wing motion are dissected and simplified to more tractable problems to elucidate the fundamentals of unsteady aerodynamics in biologically inspired kinematics. The MAV's fruition would satisfy long established needs in both the military and civilian sectors. Although recent studies have provided great insight into the lift generating mechanisms of flapping wings the deflection response of such wings remains poorly understood. This dissertation numerically and experimentally investigates the aerodynamic performance of passively and actively deflected wings in hover and rotary kinematics. Flexibility is distilled to discrete lines of flexion which acknowledging major flexion lines in insect wings to be the primary avenue for deformation. Of primary concern is the development of the leading-edge vortex (LEV), a high circulation region of low pressure above the wing to which much of the wing's lift generation is attributed. Two-dimensional simulations of wings with chord-wise flexibility in a freestream reveal a lift generating mechanism unavailable to rigid wings with origins in vortical symmetry breaking. The inclusion of flexibility in translating wings accelerated from rest revealed the formation time of the initial LEV was very weakly dependent on the flexible stiffness of the wing, maintaining a universal time scale of four to five chords of travel before shedding. The frequency of oscillatory shedding of the leading and trailing-edge vortices that develops after the initial vortex shedding was shown to be
Three dimensional steady and unsteady asymmetric flow past wings of arbitrary planforms
Kandil, O. A.; Atta, E. H.; Nayfeh, A. H.
1978-01-01
The nonlinear discrete vortex method is extended to treat the problem of asymmetric flows past a wing with leading edge separation, including steady and unsteady flows. The problem is formulated in terms of a body fixed frame of reference and the nonlinear-discrete vortex method is modified accordingly. Although the method is general, only examples of flows past delta wings are presented due to the availability of experimental data as well as approximate theories. Comparison of results with experimental results for a delta wing undergoing a steady rolling motion at zero angle of attack demonstrate the superiority of the present method over existing approximate theories in obtaining highly accurate loads. Numerical results for yawed wings at large angles of attack are also presented. In all cases, total load coefficients, pressure distributions, and shapes of the free vortex sheets are shown.
Imaging unsteady three-dimensional transport phenomena
Indian Academy of Sciences (India)
K Muralidhar
2014-01-01
Careful and continuous measurements of flow, heat and mass transfer are required in quite a few contexts. Using appropriate light sources, it is possible to map velocity, temperature, and species concentration over a cross-section and as a function of time. Image formation in optical measurements may rely on scattering of radiation from particles. Alternatively, if the region of interest is transparent, refractive index would be a field variable and beam bending effects can be used to extract information about temperature and concentration of solutes dissolved in liquids. Time-lapsed images of light intensity can be used to determine fluid velocity. Though used originally for flow visualization, optical imaging has now emerged as a powerful tool for quantitative measurements. Optical methods that utilize the dependence of refractive index on concentration and temperature can be configured in many different ways. Three available routes considered are interferometry, schlieren imaging, and shadowgraph. Images recorded in these configurations can be analysed to yield time sequences of three-dimensional distributions of the transported variables. Optical methods are non-intrusive, inertia-free and can image cross-sections of the experimental apparatus. The image data can be jointly analysed with the physical laws governing transport and principles of image formation. Hence, with the experiment suitably carried out, three-dimensional physical domains with unsteady processes can be accommodated. Optical methods promise to breach the holy grail of measurements by extracting unsteady three-dimensional data in applications related to transport phenomena.
Unsteady measurement techniques for turbomachinery flows
Jaffa, Nicholas Andrew
Accurate unsteady measurements are required for studying the flows in high speed turbomachines, which rely on the interaction between rotating and stationary components. Using statistics of phase locked ensembles simplifies the problem, but accurate frequency response in the 10-100 kHz range significantly limits the applicable techniques. This research advances the state of the art for phase resolved measurement techniques using for high speed turbomachinery flows focusing on the following areas: development, validation, and uncertainty quantification. Four methods were developed and implemented: an unsteady total pressure probe, the multiple overheat hot-wire method, the slanted hot-wire method, and the phase peak yaw hot-wire method. These methods allow for the entire phase locked average flow field to be measured (temperature, pressure, and velocity components, swirl angle, etc.). No trusted reference measurement or representative canonical flow exists for comparison of the phase resolved quantities, making validation challenging. Five different validation exercises were performed to increase the confidence and explore the range of applicability. These exercises relied on checking for consistency with expected flow features, comparing independent measurements, and cross validation with CFD. The combined uncertainties for the measurements were quantified using uncertainty estimates from investigations into the elemental error sources. The frequency response uncertainty of constant temperature hot-wire system was investigated using a novel method of illuminating the wire with a laser pulse. The uncertainty analysis provided estimates for the uncertainty in the measurements as well as showing the sensitivity to various sources of error.
Rolling with the flow: bumblebees flying in unsteady wakes.
Ravi, Sridhar; Crall, James D; Fisher, Alex; Combes, Stacey A
2013-11-15
Our understanding of how variable wind in natural environments affects flying insects is limited because most studies of insect flight are conducted in either smooth flow or still air conditions. Here, we investigate the effects of structured, unsteady flow (the von Karman vortex street behind a cylinder) on the flight performance of bumblebees (Bombus impatiens). Bumblebees are 'all-weather' foragers and thus frequently experience variable aerial conditions, ranging from fully mixed, turbulent flow to unsteady, structured vortices near objects such as branches and stems. We examined how bumblebee flight performance differs in unsteady versus smooth flow, as well as how the orientation of unsteady flow structures affects their flight performance, by filming bumblebees flying in a wind tunnel under various flow conditions. The three-dimensional flight trajectories and orientations of bumblebees were quantified in each of three flow conditions: (1) smooth flow, (2) the unsteady wake of a vertical cylinder (inducing strong lateral disturbances) and (3) the unsteady wake of a horizontal cylinder (inducing strong vertical disturbances). In both unsteady conditions, bumblebees attenuated the disturbances induced by the wind quite effectively, but still experienced significant translational and rotational fluctuations as compared with flight in smooth flow. Bees appeared to be most sensitive to disturbance along the lateral axis, displaying large lateral accelerations, translations and rolling motions in response to both unsteady flow conditions, regardless of orientation. Bees also displayed the greatest agility around the roll axis, initiating voluntary casting maneuvers and correcting for lateral disturbances mainly through roll in all flow conditions. Both unsteady flow conditions reduced the upstream flight speed of bees, suggesting an increased cost of flight in unsteady flow, with potential implications for foraging patterns and colony energetics in natural
Dinarvand, S.; Hosseini, R.; Tamim, H.; Damangir, E.; Pop, I.
2015-07-01
An unsteady three-dimensional stagnation-point flow of a nanofluid past a circular cylinder with sinusoidal radius variation is investigated numerically. By introducing new similarity transformations for the velocity, temperature, and nanoparticle volume fraction, the basic equations governing the flow and heat and mass transfer are reduced to highly nonlinear ordinary differential equations. The resulting nonlinear system is solved numerically by the fourth-order Runge-Kutta method with the shooting technique. The thermophoresis and Brownian motion effects occur in the transport equations. The velocity, temperature, and nanoparticle concentration profiles are analyzed with respect to the involved parameters of interest, namely, unsteadiness parameter, Brownian motion parameter, thermophoresis parameter, Prandtl number, and Lewis number. Numerical values of the friction coefficient, diffusion mass flux, and heat flux are computed. It is found that the friction coefficient and heat transfer rate increase with increasing unsteadiness parameter (the highest heat transfer rate at the surface occurs if the thermophoresis and Brownian motion effects are absent) and decrease with increasing both thermophoresis and Brownian motion parameters. The present results are found to be in good agreement with previously published results.
Simulating Magneto-Aerodynamic Actuator
2007-12-20
2005. 19. Boeuf, J.P., Lagmich, Y., Callegari, Th., and Pitchford , L.C., Electro- hydrodynamic Force and Acceleration in Surface Discharge, AIAA 2006...Plasmadynamics and Laser Award, 2004 AFRL Point of Contact Dr. Donald B. Paul , AFRL/VA WPAFB, OH 937-255-7329, met weekly. Dr. Alan Garscadden, AFRL/PR...validating database for numerical simulation of magneto-aerodynamic actuator for hypersonic flow control. Points of contact at the AFRL/VA are Dr. D. Paul
Phonatory aerodynamics in connected speech.
Gartner-Schmidt, Jackie L; Hirai, Ryoji; Dastolfo, Christina; Rosen, Clark A; Yu, Lan; Gillespie, Amanda I
2015-12-01
1) Present phonatory aerodynamic data for healthy controls (HCs) in connected speech; 2) contrast these findings between HCs and patients with nontreated unilateral vocal fold paralysis (UVFP); 3) present pre- and post-vocal fold augmentation outcomes for patients with UVFP; 4) contrast data from patients with post-operative laryngeal augmentation to HCs. Retrospective, single-blinded. For phase I, 20 HC participants were recruited. For phase II, 20 patients with UVFP were age- and gender-matched to the 20 HC participants used in phase I. For phase III, 20 patients with UVFP represented a pre- and posttreatment cohort. For phase IV, 20 of the HC participants from phase I and 20 of the postoperative UVFP patients from phase III were used for direct comparison. Aerodynamic measures captured from a sample of the Rainbow Passage included: number of breaths, mean phonatory airflow rate, total duration of passage, inspiratory airflow duration, and expiratory airflow duration. The VHI-10 was also obtained pre- and postoperative laryngeal augmentation. All phonatory aerodynamic measures were significantly increased in patients with preoperative UVFP than the HC group. Patients with laryngeal augmentation took significantly less breaths, had less mean phonatory airflow rate during voicing, and had shorter inspiratory airflow duration than the preoperative UVFP group. None of the postoperative measures returned to HC values. Significant improvement in the Voice Handicap Index-10 scores postlaryngeal augmentation was also found. Methodology described in this study improves upon existing aerodynamic voice assessment by capturing characteristics germane to UVFP patient complaints and measuring change before and after laryngeal augmentation in connected speech. 4. © 2015 The American Laryngological, Rhinological and Otological Society, Inc.
Directory of Open Access Journals (Sweden)
Pierre Tchakoua
2016-10-01
Full Text Available The complex and unsteady aerodynamics of vertical axis wind turbines (VAWTs pose significant challenges for simulation tools. Recently, significant research efforts have focused on the development of new methods for analysing and optimising the aerodynamic performance of VAWTs. This paper presents an electric circuit model for Darrieus-type vertical axis wind turbine (DT-VAWT rotors. The novel Tchakoua model is based on the mechanical description given by the Paraschivoiu double-multiple streamtube model using a mechanical‑electrical analogy. Model simulations were conducted using MATLAB for a three-bladed rotor architecture, characterized by a NACA0012 profile, an average Reynolds number of 40,000 for the blade and a tip speed ratio of 5. The results obtained show strong agreement with findings from both aerodynamic and computational fluid dynamics (CFD models in the literature.
Aerodynamically generated noise by lightning arrester
Directory of Open Access Journals (Sweden)
Váchová J.
2007-10-01
Full Text Available This paper presents the general solution of aerodynamically generated noise by lightning arrester. Governing equations are presented in form of Lighthill acoustic analogy, as embodied in the Ffowcs Williams-Hawkings (FW-H equation. This equation is based on conservation laws of fluid mechanics rather than on the wave equation. Thus, the FW-H equation is valid even if the integration surface is in nonlinear region. That’s why the FWH method is superior in aeroacoustics. The FW-H method is implemented in program Fluent and the numerical solution is acquired by Fluent code.The general solution of acoustic signal generated by lightning arrester is shown and the results in form of acoustic pressure and frequency spectrum are presented. The verification of accuracy was made by evaluation of Strouhal number. A comparison of Strouhal number for circumfluence of a cylinder and the lightning arrester was done, because the experimental data for cylinder case are known and these solids are supposed to be respectively in shape relation.
Alternative Forms of Enhanced Boussinesq Equations with Improved Nonlinearity
Directory of Open Access Journals (Sweden)
Kezhao Fang
2013-01-01
Full Text Available We propose alternative forms of the Boussinesq equations which extend the equations of Madsen and Schäffer by introducing extra nonlinear terms during enhancement. Theoretical analysis shows that nonlinear characteristics are considerably improved. A numerical implementation of one-dimensional equations is described. Three tests involving strongly nonlinear evolution, namely, regular waves propagating over an elevated bar feature in a tank with an otherwise constant depth, wave group transformation over constant water depth, and nonlinear shoaling of unsteady waves over a sloping beach, are simulated by the model. The model is found to be effective.
DEFF Research Database (Denmark)
de Vaal, Jacobus B.; Hansen, Martin Otto Laver; Moan, Torgeir
2014-01-01
This paper discusses the influence of rigid body motions on rotor induced velocities and aerodynamic loads of a floating horizontal axis wind turbine. Analyses are performed with a simplified free wake vortex model specifically aimed at capturing the unsteady and non-uniform inflow typically...... experienced by a floating wind turbine. After discussing the simplified model in detail, comparisons are made to a state of the art free wake vortex code, using test cases with prescribed platform motion. It is found that the simplified model compares favourably with a more advanced numerical model......, and captures the essential influences of rigid body motions on the rotor loads, induced velocities and wake influence....
Non-linear aeroelastic prediction for aircraft applications
de C. Henshaw, M. J.; Badcock, K. J.; Vio, G. A.; Allen, C. B.; Chamberlain, J.; Kaynes, I.; Dimitriadis, G.; Cooper, J. E.; Woodgate, M. A.; Rampurawala, A. M.; Jones, D.; Fenwick, C.; Gaitonde, A. L.; Taylor, N. V.; Amor, D. S.; Eccles, T. A.; Denley, C. J.
2007-05-01
Current industrial practice for the prediction and analysis of flutter relies heavily on linear methods and this has led to overly conservative design and envelope restrictions for aircraft. Although the methods have served the industry well, it is clear that for a number of reasons the inclusion of non-linearity in the mathematical and computational aeroelastic prediction tools is highly desirable. The increase in available and affordable computational resources, together with major advances in algorithms, mean that non-linear aeroelastic tools are now viable within the aircraft design and qualification environment. The Partnership for Unsteady Methods in Aerodynamics (PUMA) Defence and Aerospace Research Partnership (DARP) was sponsored in 2002 to conduct research into non-linear aeroelastic prediction methods and an academic, industry, and government consortium collaborated to address the following objectives: To develop useable methodologies to model and predict non-linear aeroelastic behaviour of complete aircraft. To evaluate the methodologies on real aircraft problems. To investigate the effect of non-linearities on aeroelastic behaviour and to determine which have the greatest effect on the flutter qualification process. These aims have been very effectively met during the course of the programme and the research outputs include: New methods available to industry for use in the flutter prediction process, together with the appropriate coaching of industry engineers. Interesting results in both linear and non-linear aeroelastics, with comprehensive comparison of methods and approaches for challenging problems. Additional embryonic techniques that, with further research, will further improve aeroelastics capability. This paper describes the methods that have been developed and how they are deployable within the industrial environment. We present a thorough review of the PUMA aeroelastics programme together with a comprehensive review of the relevant research
Lakshminarayana, B.; Ho, Y.; Basson, A.
1993-01-01
The objective of this research is to simulate steady and unsteady viscous flows, including rotor/stator interaction and tip clearance effects in turbomachinery. The numerical formulation for steady flow developed here includes an efficient grid generation scheme, particularly suited to computational grids for the analysis of turbulent turbomachinery flows and tip clearance flows, and a semi-implicit, pressure-based computational fluid dynamics scheme that directly includes artificial dissipation, and is applicable to both viscous and inviscid flows. The values of these artificial dissipation is optimized to achieve accuracy and convergency in the solution. The numerical model is used to investigate the structure of tip clearance flows in a turbine nozzle. The structure of leakage flow is captured accurately, including blade-to-blade variation of all three velocity components, pitch and yaw angles, losses and blade static pressures in the tip clearance region. The simulation also includes evaluation of such quantities of leakage mass flow, vortex strength, losses, dominant leakage flow regions and the spanwise extent affected by the leakage flow. It is demonstrated, through optimization of grid size and artificial dissipation, that the tip clearance flow field can be captured accurately. The above numerical formulation was modified to incorporate time accurate solutions. An inner loop iteration scheme is used at each time step to account for the non-linear effects. The computation of unsteady flow through a flat plate cascade subjected to a transverse gust reveals that the choice of grid spacing and the amount of artificial dissipation is critical for accurate prediction of unsteady phenomena. The rotor-stator interaction problem is simulated by starting the computation upstream of the stator, and the upstream rotor wake is specified from the experimental data. The results show that the stator potential effects have appreciable influence on the upstream rotor wake
Hu, Hui; Ning, Zhe
2016-11-01
Due to the auto-rotating trait of maple seeds during falling down process, flow characteristics of rotating maple seeds have been studied by many researchers in recent years. In the present study, an experimental investigation was performed to explore maple-seed-inspired UAV propellers for improved aerodynamic and aeroacoustic performances. Inspired by the auto-rotating trait of maple seeds, the shape of a maple seed is leveraged for the planform design of UAV propellers. The aerodynamic and aeroacoustic performances of the maple-seed-inspired propellers are examined in great details, in comparison with a commercially available UAV propeller purchased on the market (i.e., a baseline propeller). During the experiments, in addition to measuring the aerodynamic forces generated by the maple-seed-inspired propellers and the baseline propeller, a high-resolution Particle Image Velocimetry (PIV) system was used to quantify the unsteady flow structures in the wakes of the propellers. The aeroacoustic characteristics of the propellers are also evaluated by leveraging an anechoic chamber available at the Aerospace Engineering Department of Iowa State University. The research work is supported by National Science Foundation under Award Numbers of OSIE-1064235.
Computation of Aerodynamic Noise Radiated from Ducted Tail Rotor Using Boundary Element Method
Directory of Open Access Journals (Sweden)
Yunpeng Ma
2017-01-01
Full Text Available A detailed aerodynamic performance of a ducted tail rotor in hover has been numerically studied using CFD technique. The general governing equations of turbulent flow around ducted tail rotor are given and directly solved by using finite volume discretization and Runge-Kutta time integration. The calculations of the lift characteristics of the ducted tail rotor can be obtained. In order to predict the aerodynamic noise, a hybrid method combining computational aeroacoustic with boundary element method (BEM has been proposed. The computational steps include the following: firstly, the unsteady flow around rotor is calculated using the CFD method to get the noise source information; secondly, the radiate sound pressure is calculated using the acoustic analogy Curle equation in the frequency domain; lastly, the scattering effect of the duct wall on the propagation of the sound wave is presented using an acoustic thin-body BEM. The aerodynamic results and the calculated sound pressure levels are compared with the known technique for validation. The sound pressure directivity and scattering effect are shown to demonstrate the validity and applicability of the method.
Stability-Constrained Aerodynamic Shape Optimization with Applications to Flying Wings
Mader, Charles Alexander
A set of techniques is developed that allows the incorporation of flight dynamics metrics as an additional discipline in a high-fidelity aerodynamic optimization. Specifically, techniques for including static stability constraints and handling qualities constraints in a high-fidelity aerodynamic optimization are demonstrated. These constraints are developed from stability derivative information calculated using high-fidelity computational fluid dynamics (CFD). Two techniques are explored for computing the stability derivatives from CFD. One technique uses an automatic differentiation adjoint technique (ADjoint) to efficiently and accurately compute a full set of static and dynamic stability derivatives from a single steady solution. The other technique uses a linear regression method to compute the stability derivatives from a quasi-unsteady time-spectral CFD solution, allowing for the computation of static, dynamic and transient stability derivatives. Based on the characteristics of the two methods, the time-spectral technique is selected for further development, incorporated into an optimization framework, and used to conduct stability-constrained aerodynamic optimization. This stability-constrained optimization framework is then used to conduct an optimization study of a flying wing configuration. This study shows that stability constraints have a significant impact on the optimal design of flying wings and that, while static stability constraints can often be satisfied by modifying the airfoil profiles of the wing, dynamic stability constraints can require a significant change in the planform of the aircraft in order for the constraints to be satisfied.
Zhu, Lifu; Jin, Yingzi; Li, Yi; Jin, Yuzhen; Wang, Yanping; Zhang, Li
2013-08-01
To improve the aerodynamic performance of small axial flow fan, in this paper the design of a small axial flow fan with splitter blades is studied. The RNG k-ɛ turbulence model and SIMPLE algorithm were applied to the steady simulation calculation of the flow field, and its result was used as the initial field of the large eddy simulation to calculate the unsteady pressure field. The FW-H noise model was adopted to predict aerodynamic noise in the six monitoring points. Fast Fourier transform algorithm was applied to process the pressure signal. Experiment of noise testing was done to further investigate the aerodynamic noise of fans. And then the results obtained from the numerical simulation and experiment were described and analyzed. The results show that the static characteristics of small axial fan with splitter blades are similar with the prototype fan, and the static characteristics are improved within a certain range of flux. The power spectral density at the six monitoring points of small axial flow fan with splitter blades have decreased to some extent. The experimental results show sound pressure level of new fan has reduced in most frequency bands by comparing with prototype fan. The research results will provide a proof for parameter optimization and noise prediction of small axial flow fans with high performance.
Numerical Investigation on Aerodynamic Force of Streamlined Box Girder with Uniform Air Suction
Directory of Open Access Journals (Sweden)
Tang Ke
2014-06-01
Full Text Available In the present study, the flow around a streamlined box girder with uniform air suction has been investigated numerically. Two-dimensional incompressible unsteady Reynolds averaged Navier-Stokes (URANS equations are solved in conjunction with the SST k −ω turbulence model in simulations. Taking the Great Belt Bridge girder as an example, cases of different suction positions on the girder section were discussed. The effect of the suction ratio and the angle of attack (AOA of wind also were investigated. The result showed that the aerodynamic drag force was influenced by the uniform suction through either upper surface or lower surface of the box girder. The larger the suction ratio was, the more the drag-reducing could be. The suction position and AOA had a comprehensive effect on the drag force. The vortex shedding frequency was also affected by air suction. For the aerodynamic lift force and moment, air suction showed no obvious influence. If necessary, using a combined suction scheme to reduce the aerodynamic drag force or to control the flow wake would be more efficient in engineering design.
Aerodynamic mechanism of forces generated by twisting model-wing in bat flapping flight
Institute of Scientific and Technical Information of China (English)
管子武; 余永亮
2014-01-01
The aerodynamic mechanism of the bat wing membrane along the lateral border of its body is studied. The twist-morphing that alters the angle of attack (AOA) along the span-wise direction is observed widely during bat flapping flight. An assumption is made that the linearly distributed AOA is along the span-wise direction. The plate with the aspect ratio of 3 is used to model a bat wing. A three-dimensional (3D) unsteady panel method is used to predict the aerodynamic forces generated by the flapping plate with leading edge separation. It is found that, relative to the rigid wing flapping, twisting motion can increase the averaged lift by as much as 25% and produce thrust instead of drag. Furthermore, the aerodynamic forces (lift/drag) generated by a twisting plate-wing are similar to those of a pitching rigid-wing, meaning that the twisting in bat flight has the same function as the supination/pronation motion in insect flight.
Wing kinematics measurement and aerodynamics of a dragonfly in turning flight.
Li, Chengyu; Dong, Haibo
2017-02-03
This study integrates high-speed photogrammetry, 3D surface reconstruction, and computational fluid dynamics to explore a dragonfly (Erythemis Simplicicollis) in free flight. Asymmetric wing kinematics and the associated aerodynamic characteristics of a turning dragonfly are analyzed in detail. Quantitative measurements of wing kinematics show that compared to the outer wings, the inner wings sweep more slowly with a higher angle of attack during the downstroke, whereas they flap faster with a lower angle of attack during the upstroke. The inner-outer asymmetries of wing deviations result in an oval wingtip trajectory for the inner wings and a figure-eight wingtip trajectory for the outer wings. Unsteady aerodynamics calculations indicate significantly asymmetrical force production between the inner and outer wings, especially for the forewings. Specifically, the magnitude of the drag force on the inner forewing is approximately 2.8 times greater than that on the outer forewing during the downstroke. In the upstroke, the outer forewing generates approximately 1.9 times greater peak thrust than the inner forewing. To keep the body aloft, the forewings contribute approximately 64% of the total lift, whereas the hindwings provide 36%. The effect of forewing-hindwing interaction on the aerodynamic performance is also examined. It is found that the hindwings can benefit from this interaction by decreasing power consumption by 13% without sacrificing force generation.
Directory of Open Access Journals (Sweden)
Srinivas Maripala
2015-06-01
Full Text Available An analysis is presented to study the forced convection in unsteady magnatohydrodynamic boundary layer flow of a nanofluid over a permeable shrinking sheet in the presence of thermal radiation and chemical reaction. A variable magnetic field is applied normal to the sheet. The nanofluid model includes Brownian motion and thermophoresis effects are also considered. The boundary layer equations governed by the partial differential equations are transformed into a set of ordinary differential equations the help of local similarity transformations. The coupled and nonlinear differential equations are solved by the implicit finite difference method along with the Thamous algorithm. We have explained the effect of various controlling flow parameters namely unsteadiness parameter A, magnetic parameter M, thermal radiation parameter R, Prandtl number Pr, Brownian motion parameter Nb, thermophoresis parameter Nt and Lewis number Le on the dimensionless velocity, temperature and nanoparticle volume fraction profiles are analyzed.
Directory of Open Access Journals (Sweden)
Lin Yanhai
2016-01-01
Full Text Available This paper presents an investigation on the MHD thin film flow and heat transfer of a power law fluid over an unsteady stretching sheet. The effects of power law viscosity on a temperature field are taken into account with a modified Fourier’s law Proposed by Zheng by assuming that the temperature field is similar to the velocity field. The governing equations are reduced to a system of nonlinear ordinary differential equations. The numerical solutions are obtained by using the shooting method coupled with the Runge-Kutta method. The influence of the Hartmann number, the power law exponent, the unsteadiness parameter, the thickness parameter and the generalized Prandtl number on the velocity and temperature fields are presented graphically and analyzed. Moreover, the critical formula for parameters are derived which indicated that the magnetic field has no effect on the critical value.
Directory of Open Access Journals (Sweden)
Motsa SS
2010-01-01
Full Text Available The problem of magnetohydrodynamic flow and heat transfer of a viscous, incompressible, and electrically conducting fluid past a semi-infinite unsteady stretching sheet is analyzed numerically. The problem was studied under the effects of Hall currents, variable viscosity, and variable thermal diffusivity. Using a similarity transformation, the governing fundamental equations are approximated by a system of nonlinear ordinary differential equations. The resultant system of ordinary differential equations is then solved numerically by the successive linearization method together with the Chebyshev pseudospectral method. Details of the velocity and temperature fields as well as the local skin friction and the local Nusselt number for various values of the parameters of the problem are presented. It is noted that the axial velocity decreases with increasing the values of the unsteadiness parameter, variable viscosity parameter, or the Hartmann number, while the transverse velocity increases as the Hartmann number increases. Due to increases in thermal diffusivity parameter, temperature is found to increase.
Accurate measurement of streamwise vortices in low speed aerodynamic flows
Waldman, Rye M.; Kudo, Jun; Breuer, Kenneth S.
2010-11-01
Low Reynolds number experiments with flapping animals (such as bats and small birds) are of current interest in understanding biological flight mechanics, and due to their application to Micro Air Vehicles (MAVs) which operate in a similar parameter space. Previous PIV wake measurements have described the structures left by bats and birds, and provided insight to the time history of their aerodynamic force generation; however, these studies have faced difficulty drawing quantitative conclusions due to significant experimental challenges associated with the highly three-dimensional and unsteady nature of the flows, and the low wake velocities associated with lifting bodies that only weigh a few grams. This requires the high-speed resolution of small flow features in a large field of view using limited laser energy and finite camera resolution. Cross-stream measurements are further complicated by the high out-of-plane flow which requires thick laser sheets and short interframe times. To quantify and address these challenges we present data from a model study on the wake behind a fixed wing at conditions comparable to those found in biological flight. We present a detailed analysis of the PIV wake measurements, discuss the criteria necessary for accurate measurements, and present a new dual-plane PIV configuration to resolve these issues.
Dispersion of Suspensions in Unsteady Microchannel Flows
Maxey, Martin; Howard, Amanda; Winklerprins, Lukas; Tripathi, Anubhuv; Yeo, Kyongmin
2013-11-01
We explore the dispersion of non-Brownian (Pe >> 1) suspensions in unsteady, low Reynolds number shear flows in a microchannel. Prior experimental work on oscillating Couette flows and Poiseuille flows has shown the importance of strain amplitude in determining the long term distribution of particles across the channel. We will present results from numerical simulations for the early development of these flows and the motion of finite length suspension plugs. The distortion of a plug by the shear flow results in inhomogeneous particle fluxes across the channel. This is largely reversible over the course of a full cycle, giving reversibility in the bulk. Self-diffusion gives irreversibility though at the microscale. As the strain amplitude increases or the initial volume fraction increases irreversibility in the bulk is seen. The dynamics behind these processes and the role of particle pressure will be noted, together with related experimental observations.
Acceleration feature points of unsteady shear flows
Kasten, Jens; Hotz, Ingrid; Hege, Hans-Christian; Noack, Bernd R; Daviller, Guillaume; Morzynski, Marek
2014-01-01
In this paper, we propose a novel framework to extract features such as vortex cores and saddle points in two-dimensional unsteady flows. This feature extraction strategy generalizes critical points of snapshot topology in a Galilean-invariant manner, allows to prioritize features according to their strength and longevity, enables to track the temporal evolution of features, is robust against noise and has no subjective parameters. These characteristics are realized via several constitutive elements. First, acceleration is employed as a feature identifier following Goto and Vassilicos (2006), thus ensuring Galilean invariance. Second, the acceleration magnitude is used as basis for a mathematically well-developed scalar field topology. The minima of this field are called acceleration feature points, a superset of the acceleration zeros. These points are discriminated into vortices and saddle points depending the spectral properties of the velocity Jacobian. Third, all operations are based on discrete topology...
Unsteady growth of ammonium chloride dendrites
Martyushev, L. M.; Terentiev, P. S.; Soboleva, A. S.
2016-02-01
Growth of ammonium chloride dendrites from aqueous solution is experimentally investigated. The growth rate υ and the radius ρ of curvature of branches are measured as a function of the relative supersaturation Δ for steady and unsteady growth conditions. It is shown that the experimental results are quantitatively described by the dependences ρ=a/Δ+b, υ=cΔ2, where the factors for primary branches are a=(1.3±0.2)·10-7 m, b=(2.5±0.4)·10-7 m, and c=(2.2±0.3)·10-4 m/s. The factor c is found to be approximately 7 times smaller for the side branches than that for the primary branches.
The Unsteady Incomes Distribution in Ukraine
Directory of Open Access Journals (Sweden)
Farion Mychailina M.
2017-06-01
Full Text Available The unsteady distribution of resources among the population of Ukraine is connected with the influence of both political and economic reasons and factors. Differentiation of incomes is reinforced by the economy over-shadowing. The article considers the main approaches to the distribution of household incomes of Ukrainian population by the decile groups, taking account of a number of factors that affect their formation. As the main indicator for the study were selected statistics about the allocation of the total population of Ukraine for certain categories by the level of income including all kinds of profit – wages, benefit and mixed income, property income, social assistance, and transfers. The reasons of decreasing incomes and the emergence of a new term in the economy, «the sudden poverty» were analyzed. It has been concluded about prognosticated improving the economic situation of the country, which will significantly impact the balance of incomes of population.
Review paper on wind turbine aerodynamics
DEFF Research Database (Denmark)
Hansen, Martin Otto Laver; Aagaard Madsen, Helge
2011-01-01
The paper describes the development and description of the aerodynamic models used to estimate the aerodynamic loads on wind turbine constructions. This includes a status of the capabilities of computation fluid dynamics and the need for reliable airfoil data for the simpler engineering models....... Also a discussion of the use of passive and active aerodynamic devices is included such as, e.g., Vortex Generators and distributed active flaps. Finally the problem of wakes in wind farms is addressed and a section of the likely future development of aerodynamic models for wind turbines is included...
Hypersonic Inflatable Aerodynamic Decelerator (HIAD) Project
National Aeronautics and Space Administration — The Hypersonic Inflatable Aerodynamic Decelerator (HIAD) project will focus on the development and demonstration of hypersonic inflatable aeroshell technologies...
Aerodynamics Laboratory Facilities, Equipment, and Capabilities
Federal Laboratory Consortium — The following facilities, equipment, and capabilities are available in the Aerodynamics Laboratory Facilities and Equipment (1) Subsonic, open-jet wind tunnel with...
Aerodynamic Aspects of Wind Energy Conversion
DEFF Research Database (Denmark)
Sørensen, Jens Nørkær
2011-01-01
This article reviews the most important aerodynamic research topics in the field of wind energy. Wind turbine aerodynamics concerns the modeling and prediction of aerodynamic forces, such as performance predictions of wind farms, and the design of specific parts of wind turbines, such as rotor......-blade geometry. The basics of the blade-element momentum theory are presented along with guidelines for the construction of airfoil data. Various theories for aerodynamically optimum rotors are discussed, and recent results on classical models are presented. State-of-the-art advanced numerical simulation tools...
Nonlinear dynamo action in a precessing cylindrical container.
Nore, C; Léorat, J; Guermond, J-L; Luddens, F
2011-07-01
It is numerically demonstrated by means of a magnetohydrodynamics code that precession can trigger the dynamo effect in a cylindrical container. When the Reynolds number, based on the radius of the cylinder and its angular velocity, increases, the flow, which is initially centrosymmetric, loses its stability and bifurcates to a quasiperiodic motion. This unsteady and asymmetric flow is shown to be capable of sustaining dynamo action in the linear and nonlinear regimes. The magnetic field thus generated is unsteady and quadrupolar. These numerical evidences of dynamo action in a precessing cylindrical container may be useful for an experiment now planned at the Dresden sodium facility for dynamo and thermohydraulic studies in Germany.
Zi-Wu, Guan
2014-01-01
The large active wing deformation is a significant way to generate high aerodynamic forces required in bat flapping flight. Besides the twisting, the elementary morphing models of a bat wing are proposed, such as wing-bending in the spanwise direction, wing-cambering in the chordwise direction, and wing area-changing. A plate of aspect ratio 3 is used to model a bat wing and a three dimensional unsteady panel method is applied to predict the aerodynamic forces. It is found that the cambering model has a great positive influence on the lift, followed by area-changing model and then the bending model. The further study indicates that the vortex control is a main mechanism to produce high aerodynamic forces, and the mechanisms for the aerodynamic force enhancement are the asymmetry of the cambered wing and the amplifier effects of wing area-changing and wing bending. The lift and thrust are mainly generated during the downstroke and almost negligible forces during the upstroke by the integrated morphing model-wi...
Directory of Open Access Journals (Sweden)
De Paolis P
2015-06-01
Full Text Available In this paper a computational aerodynamic prediction to support the aeromechanical integration of an advanced reconnaissance pod on a 5th generation fighter type aircraft is presented. The aim of the activity was to compare the aerodynamic characteristics of the new pod to a previous one already cleared on the same aircraft fleet, given verified inertial and structural similarity. Verifying the aforementioned aerodynamic similarity without involving extensive flight test activity was a must, to save time and to reduce costs. A two steps approach was required by the Certification Authority to verify, initially, the performance data compatibility in terms of aerodynamic coefficients of the old pod with the new one, in order to allow performance flight manual data interchangeability (a quantitative comparison was required; afterwards, a qualitative assessment was conducted to verify the absence of unsteadiness induced by the introduction in the external structure of the new pod of an auxiliary antenna case. Computational results are presented both for Straight and Level Un-accelerated Flight and SteadySideslip flight conditions at different Angles of Attack.
The basic aerodynamics of floatation
Energy Technology Data Exchange (ETDEWEB)
Davies, M.J.; Wood, D.H.
1983-09-01
The original derivation of the basic theory governing the aerodynamics of both hovercraft and modern floatation ovens, requires the validity of some extremely crude assumptions. However, the basic theory is surprisingly accurate. It is shown that this accuracy occurs because the final expression of the basic theory can be derived by approximating the full Navier-Stokes equations in a manner that clearly shows the limitations of the theory. These limitations are used in discussing the relatively small discrepancies between the theory and experiment, which may not be significant for practical purposes.
Study of interaction between shock wave and unsteady boundary layer
Institute of Scientific and Technical Information of China (English)
董志勇; 韩肇元
2003-01-01
This paper reports theoretical and experimental study of a new type of interaction of a moving shock wave with an unsteady boundary layer. This type of shock wave-boundary layer interaction describes a moving shock wave interaction with an unsteady boundary layer induced by another shock wave and a rarefaction wave. So it is different from the interaction of a stationary shock wave with steady boundary layer, also different from the interaction of a reflected moving shock wave at the end of a shock tube with unsteady boundary layer induced by an incident shock. Geometrical shock dynamics is used for the theoretical analysis of the shock wave-unsteady boundary layer interaction, and a double-driver shock tube with a rarefaction wave bursting diaphragm is used for the experimental investigation in this work.
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.
SPECTRAL FINITE ELEMENT METHOD FOR A UNSTEADY TRANSPORT EQUATION
Institute of Scientific and Technical Information of China (English)
MeiLiquan
1999-01-01
In this paper,a new numerical method,the coupling method of spherical harmonic function spectral and finite elements,for a unsteady transport equation is dlscussed,and the error analysis of this scheme is proved.
Biomimetic Approach for Accurate, Real-Time Aerodynamic Coefficients Project
National Aeronautics and Space Administration — Aerodynamic and structural reliability and efficiency depends critically on the ability to accurately assess the aerodynamic loads and moments for each lifting...
Unsteady Interaction Between a Transonic Turbine Stage and Downstream Components
Davis Roger; Yao Jixian; Clark John; Stetson Gary; Alonso Juan; Jameson Antony; Haldeman Charles; Dunn Michael
2004-01-01
Results from a numerical simulation of the unsteady flow through one quarter of the circumference of a transonic high-pressure turbine stage, transition duct, and low-pressure turbine first vane are presented and compared with experimental data. Analysis of the unsteady pressure field resulting from the simulation shows the effects of not only the rotor/stator interaction of the high-pressure turbine stage but also new details of the interaction between the blade and the downstream transition...
Finite difference methods for the solution of unsteady potential flows
Caradonna, F. X.
1985-01-01
A brief review is presented of various problems which are confronted in the development of an unsteady finite difference potential code. This review is conducted mainly in the context of what is done for a typical small disturbance and full potential methods. The issues discussed include choice of equation, linearization and conservation, differencing schemes, and algorithm development. A number of applications including unsteady three-dimensional rotor calculation, are demonstrated.
Unsteady Flow in a Supersonic Turbine with Variable Specific Heats
Dorney, Daniel J.; Griffin, Lisa W.; Huber, Frank; Sondak, Douglas L.; Turner, James (Technical Monitor)
2001-01-01
Modern high-work turbines can be compact, transonic, supersonic, counter-rotating, or use a dense drive gas. The vast majority of modern rocket turbine designs fall into these Categories. These turbines usually have large temperature variations across a given stage, and are characterized by large amounts of flow unsteadiness. The flow unsteadiness can have a major impact on the turbine performance and durability. For example, the Space Transportation Main Engine (STME) fuel turbine, a high work, transonic design, was found to have an unsteady inter-row shock which reduced efficiency by 2 points and increased dynamic loading by 24 percent. The Revolutionary Reusable Technology Turbopump (RRTT), which uses full flow oxygen for its drive gas, was found to shed vortices with such energy as to raise serious blade durability concerns. In both cases, the sources of the problems were uncovered (before turbopump testing) with the application of validated, unsteady computational fluid dynamics (CFD) to the designs. In the case of the RRTT and the Alternate Turbopump Development (ATD) turbines, the unsteady CFD codes have been used not just to identify problems, but to guide designs which mitigate problems due to unsteadiness. Using unsteady flow analyses as a part of the design process has led to turbine designs with higher performance (which affects temperature and mass flow rate) and fewer dynamics problems. One of the many assumptions made during the design and analysis of supersonic turbine stages is that the values of the specific heats are constant. In some analyses the value is based on an average of the expected upstream and downstream temperatures. In stages where the temperature can vary by 300 to 500 K, however, the assumption of constant fluid properties may lead to erroneous performance and durability predictions. In this study the suitability of assuming constant specific heats has been investigated by performing three-dimensional unsteady Navier
Correcting for response lag in unsteady pressure measurements in water
Energy Technology Data Exchange (ETDEWEB)
Conger, R.N. [John Graham Associates, Seattle, WA (United States); Ramaprian, B.R. [Washington State Univ., Pullman, WA (United States). Dept. of Mechanical and Materials Engineering
1993-12-01
There is not much information available on the use of diaphragm-type pressure transducers for the measurements of unsteady pressures in liquids. A procedure for measuring the dynamic response of a pressure transducer in such applications and correcting for its inadequate response is discussed in this report. An example of the successful use of this method to determine unsteady surface pressures on a pitching airfoil in a water channel is presented.
Aerodynamics of wind turbines emerging topics
Amano, R S
2014-01-01
Focusing on Aerodynamics of Wind Turbines with topics ranging from Fundamental to Application of horizontal axis wind turbines, this book presents advanced topics including: Basic Theory for Wind turbine Blade Aerodynamics, Computational Methods, and Special Structural Reinforcement Technique for Wind Turbine Blades.
Aerodynamic seal assemblies for turbo-machinery
Energy Technology Data Exchange (ETDEWEB)
Bidkar, Rahul Anil; Wolfe, Christopher; Fang, Biao
2015-09-29
The present application provides an aerodynamic seal assembly for use with a turbo-machine. The aerodynamic seal assembly may include a number of springs, a shoe connected to the springs, and a secondary seal positioned about the springs and the shoe.
Migration on Wings Aerodynamics and Energetics
Kantha, Lakshmi
2012-01-01
This book is an effort to explore the technical aspects associated with bird flight and migration on wings. After a short introduction on the birds migration, the book reviews the aerodynamics and Energetics of Flight and presents the calculation of the Migration Range. In addition, the authors explains aerodynamics of the formation flight and finally introduces great flight diagrams.
Indian Academy of Sciences (India)
MOHAMMADREZA AZIMI; ROUZBEH RIAZI
2017-03-01
Investigation for unsteady squeezing viscous flow is one of the most important research topics due to its wide range of engineering applications such as polymer processing and lubrication systems. The aim of the present paper is to study the unsteady squeezing viscous graphene oxide–water nanofluid flow with heat transfer between two infinite parallel plates. The governing equations, continuity, momentum and energy for thisproblem are reduced to coupled nonlinear ordinary differential equations using a similarity transformation. The transmuted model is shown to be controlled by a number of thermo-physical parameters, viz., moving parameter,graphene oxide nanoparticles solid volume fraction, Eckert and Prandtl numbers. Nusselt number and skin friction parameter are obtained for various values of GO solid volume fraction and Eckert number. Comparisonbetween analytical results and numerical ones achieved by fourth order Runge–Kutta method revealed that our analytical method can be a simple, powerful and efficient technique for finding analytical solutions in scienceand engineering nonlinear differential equations.
Leading Edge Device Aerodynamic Optimization
Directory of Open Access Journals (Sweden)
Marius Gabriel COJOCARU
2015-12-01
Full Text Available Leading edge devices are conventionally used as aerodynamic devices that enhance performances during landing and in some cases during takeoff. The need to increase the efficiency of the aircrafts has brought the idea of maintaining as much as possible a laminar flow over the wings. This is possible only when the leading edge of the wings is free from contamination, therefore using the leading edge devices with the additional role of shielding during takeoff. Such a device based on the Krueger flap design is aerodynamically analyzed and optimized. The optimization comprises three steps: first, the positioning of the flap such that the shielding criterion is kept, second, the analysis of the flap size and third, the optimization of the flap shape. The first step is subject of a gradient based optimization process of the position described by two parameters, the position along the line and the deflection angle. For the third step the Adjoint method is used to gain insight on the shape of the Krueger flap that will extend the most the stall limit. All these steps have been numerically performed using Ansys Fluent and the results are presented for the optimized shape in comparison with the baseline configuration.
Uncertainty Quantification in Numerical Aerodynamics
Litvinenko, Alexander
2017-05-16
We consider uncertainty quantification problem in aerodynamic simulations. We identify input uncertainties, classify them, suggest an appropriate statistical model and, finally, estimate propagation of these uncertainties into the solution (pressure, velocity and density fields as well as the lift and drag coefficients). The deterministic problem under consideration is a compressible transonic Reynolds-averaged Navier-Strokes flow around an airfoil with random/uncertain data. Input uncertainties include: uncertain angle of attack, the Mach number, random perturbations in the airfoil geometry, mesh, shock location, turbulence model and parameters of this turbulence model. This problem requires efficient numerical/statistical methods since it is computationally expensive, especially for the uncertainties caused by random geometry variations which involve a large number of variables. In numerical section we compares five methods, including quasi-Monte Carlo quadrature, polynomial chaos with coefficients determined by sparse quadrature and gradient-enhanced version of Kriging, radial basis functions and point collocation polynomial chaos, in their efficiency in estimating statistics of aerodynamic performance upon random perturbation to the airfoil geometry [D.Liu et al \\'17]. For modeling we used the TAU code, developed in DLR, Germany.
Aerodynamic Drag and Gyroscopic Stability
Courtney, Elya R
2013-01-01
This paper describes the effects on aerodynamic drag of rifle bullets as the gyroscopic stability is lowered from 1.3 to 1.0. It is well known that a bullet can tumble for stability less than 1.0. The Sierra Loading Manuals (4th and 5th Editions) have previously reported that ballistic coefficient decreases significantly as gyroscopic stability, Sg, is lowered below 1.3. These observations are further confirmed by the experiments reported here. Measured ballistic coefficients were compared with gyroscopic stabilities computed using the Miller Twist Rule for nearly solid metal bullets with uniform density and computed using the Courtney-Miller formula for plastic-tipped bullets. The experiments reported here also demonstrate a decrease in aerodynamic drag near Sg = 1.23 +/- 0.02. It is hypothesized that this decrease in drag over a narrow band of Sg values is due to a rapid damping of coning motions (precession and nutation). Observation of this drag decrease at a consistent value of Sg demonstrates the relati...
Directory of Open Access Journals (Sweden)
N. Sandeep
2016-03-01
Full Text Available We analyzed the unsteady magnetohydrodynamic radiative flow and heat transfer characteristics of a dusty nanofluid over an exponentially permeable stretching surface in presence of volume fraction of dust and nano particles. We considered two types of nanofluids namely Cu-water and CuO-water embedded with conducting dust particles. The governing equations are transformed into nonlinear ordinary differential equations by using similarity transformation and solved numerically using Runge–Kutta based shooting technique. The effects of non-dimensional governing parameters namely magneticfield parameter, mass concentration of dust particles, fluid particle interaction parameter, volume fraction of dust particles, volume fraction of nano particles, unsteadiness parameter, exponential parameter, radiation parameter and suction/injection parameter on velocity profiles for fluid phase, dust phase and temperature profiles are discussed and presented through graphs. Also, friction factor and Nusselt numbers are discussed and presented for two dusty nanofluids separately. Comparisons of the present study were made with existing studies under some special assumptions. The present results have an excellent agreement with existing studies. Results indicated that the enhancement in fluid particle interaction increases the heat transfer rate and depreciates the wall friction. Also, radiation parameter has the tendency to increase the temperature profiles of the dusty nanofluid.
Energy Technology Data Exchange (ETDEWEB)
Zhang, Ning; Yang, Minguan; Gao, Bo; Li, Zhong; Ni, Dan [Jiangsu University, Zhenjiang (China)
2015-10-15
This study experimentally and numerically investigates the unsteady flow in a centrifugal pump with special slope volute under various conditions to illustrate the detailed flow structures and pressure pulsation within the model pump. Whole flow passage is considered during the numerical simulation; pressure pulsation signals are extracted using nine fast-response pressure transducers. The Root mean square (RMS) method is introduced to deal with the discrete components at f{sub BPF} of the different monitoring points along the volute casing, which is an effective attempt to evaluate the overall pulsating level of the model pump. Results show that numerical method can predict the components at f{sub BPF} effectively; however, it has limited ability in capturing noise frequencies motivated by unsteady separate flow and non-linear interaction effect. Around the nominal flow rate, the predicted amplitudes at f{sub BPF} agree well with the experimental results, showing larger difference at the off-design conditions. To predict the pulsating level of the components at f{sub BPF}, two fitted equations of the RMS values versus the flow rate and specific speed are carried out, which would be very helpful in evaluating the pressure pulsation level in the centrifugal pump.
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.
Directory of Open Access Journals (Sweden)
M. Suali
2012-01-01
Full Text Available The unsteady stagnation point flow and heat transfer over a stretching/shrinking sheet with suction/injection is studied. The governing partial differential equations are converted into nonlinear ordinary differential equations using a similarity transformation and solved numerically. Both stretching and shrinking cases are considered. Results for the skin friction coefficient, local Nusselt number, velocity, and temperature profiles are presented for different values of the governing parameters. It is found that the dual solutions exist for the shrinking case, whereas the solution is unique for the stretching case. Numerical results show that the range of dual solutions increases with mass suction and decreases with mass injection.
Directory of Open Access Journals (Sweden)
Tirivanhu Chinyoka
2015-01-01
Full Text Available This article examines the combined effects of buoyancy force and asymmetrical convective cooling on unsteady MHD channel flow and heat transfer characteristics of an incompressible, reactive, variable viscosity and electrically conducting third grade fluid. The chemical kinetics in the flow system is exothermic and the asymmetric convective heat transfers at the channel walls follow the Newton’s law of cooling. The coupled nonlinear partial differential equations governing the problem are derived and solved numerically using a semi-implicit finite difference scheme. Graphical results are presented and physical aspects of the problem are discussed with respect to various parameters embedded in the system.
Sohail, Ayesha; Maqbool, K.; Sher Akbar, Noreen; Younas, Muhammad
2017-03-01
This paper investigate the effect of slip boundary condition, thermal radiation, heat source, Dufour number, chemical reaction and viscous dissipation on heat and mass transfer of unsteady free convective MHD flow of a viscous fluid past through a vertical plate embedded in a porous media. Numerical results are obtained for solving the nonlinear governing momentum, energy and concentration equations with slip boundary condition, ramped wall temperature and ramped wall concentration on the surface of the vertical plate. The influence of emerging parameters on velocity, temperature and concentration fields are shown graphically.
Aerodynamic Shape Optimization Using A Real-Number-Encoded Genetic Algorithm
Holst, Terry L.; Pulliam, Thomas H.
2001-01-01
A new method for aerodynamic shape optimization using a genetic algorithm with real number encoding is presented. The algorithm is used to optimize three different problems, a simple hill climbing problem, a quasi-one-dimensional nozzle problem using an Euler equation solver and a three-dimensional transonic wing problem using a nonlinear potential solver. Results indicate that the genetic algorithm is easy to implement and extremely reliable, being relatively insensitive to design space noise.
Institute of Scientific and Technical Information of China (English)
Tao Jun; Sun Gang
2016-01-01
With the progress of high-bypass turbofan and the innovation of silencing nacelle in engine noise reduction, airframe noise has now become another important sound source besides the engine noise. Thus, reducing airframe noise makes a great contribution to the overall noise reduction of a civil aircraft. However, reducing airframe noise often leads to aerodynamic perfor-mance loss in the meantime. In this case, an approach based on artificial neural network is intro-duced. An established database serves as a basis and the training sample of a back propagation (BP) artificial neural network, which uses confidence coefficient reasoning method for optimization later on. Then the most satisfactory configuration is selected for validating computations through the trained BP network. On the basis of the artificial neural network approach, an optimization pro-cess of slat cove filler (SCF) for high lift devices (HLD) on the Trap Wing is presented. Aerody-namic performance of both the baseline and optimized configurations is investigated through unsteady detached eddy simulations (DES), and a hybrid method, which combines unsteady DES method with acoustic analogy theory, is employed to validate the noise reduction effect. The numerical results indicate not merely a significant airframe noise reduction effect but also excel-lent aerodynamic performance retention simultaneously.
Directory of Open Access Journals (Sweden)
Tao Jun
2016-10-01
Full Text Available With the progress of high-bypass turbofan and the innovation of silencing nacelle in engine noise reduction, airframe noise has now become another important sound source besides the engine noise. Thus, reducing airframe noise makes a great contribution to the overall noise reduction of a civil aircraft. However, reducing airframe noise often leads to aerodynamic performance loss in the meantime. In this case, an approach based on artificial neural network is introduced. An established database serves as a basis and the training sample of a back propagation (BP artificial neural network, which uses confidence coefficient reasoning method for optimization later on. Then the most satisfactory configuration is selected for validating computations through the trained BP network. On the basis of the artificial neural network approach, an optimization process of slat cove filler (SCF for high lift devices (HLD on the Trap Wing is presented. Aerodynamic performance of both the baseline and optimized configurations is investigated through unsteady detached eddy simulations (DES, and a hybrid method, which combines unsteady DES method with acoustic analogy theory, is employed to validate the noise reduction effect. The numerical results indicate not merely a significant airframe noise reduction effect but also excellent aerodynamic performance retention simultaneously.
Numerical Study of Outlet Boundary Conditions for Unsteady Turbulent Internal Flows Using the NCC
Liu, Nan-Suey; Shih, Tsan-Hsing
2009-01-01
This paper presents the results of studies on the outlet boundary conditions for turbulent internal flow simulations. Several outlet boundary conditions have been investigated by applying the National Combustion Code (NCC) to the configuration of a LM6000 single injector flame tube. First of all, very large eddy simulations (VLES) have been performed using the partially resolved numerical simulation (PRNS) approach, in which both the nonlinear and linear dynamic subscale models were employed. Secondly, unsteady Reynolds averaged Navier- Stokes (URANS) simulations have also been performed for the same configuration to investigate the effects of different outlet boundary conditions in the context of URANS. Thirdly, the possible role of the initial condition is inspected by using three different initial flow fields for both the PRNS/VLES simulation and the URANS simulation. The same grid is used for all the simulations and the number of mesh element is about 0.5 million. The main purpose of this study is to examine the long-time behavior of the solution as determined by the imposed outlet boundary conditions. For a particular simulation to be considered as successful under the given initial and boundary conditions, the solution must be sustainable in a physically meaningful manner over a sufficiently long period of time. The commonly used outlet boundary condition for steady Reynolds averaged Navier-Stokes (RANS) simulation is a fixed pressure at the outlet with all the other dependent variables being extrapolated from the interior. The results of the present study suggest that this is also workable for the URANS simulation of the LM6000 injector flame tube. However, it does not work for the PRNS/VLES simulation due to the unphysical reflections of the pressure disturbances at the outlet boundary. This undesirable situation can be practically alleviated by applying a simple unsteady convection equation for the pressure disturbances at the outlet boundary. The
Aerodynamic seals for rotary machine
Energy Technology Data Exchange (ETDEWEB)
Bidkar, Rahul Anil; Cirri, Massimiliano; Thatte, Azam Mihir; Williams, John Robert
2016-02-09
An aerodynamic seal assembly for a rotary machine includes multiple sealing device segments disposed circumferentially intermediate to a stationary housing and a rotor. Each of the segments includes a shoe plate with a forward-shoe section and an aft-shoe section having multiple labyrinth teeth therebetween facing the rotor. The sealing device segment also includes multiple flexures connected to the shoe plate and to a top interface element, wherein the multiple flexures are configured to allow the high pressure fluid to occupy a forward cavity and the low pressure fluid to occupy an aft cavity. Further, the sealing device segments include a secondary seal attached to the top interface element at one first end and positioned about the flexures and the shoe plate at one second end.
Aerodynamic research on tipvane windturbines
Vanbussel, G. J. W.; Vanholten, T.; Vankuik, G. A. M.
1982-09-01
Tipvanes are small auxiliary wings mounted at the tips of windturbine blades in such a way that a diffuser effect is generated, resulting in a mass flow augmentation through the turbine disc. For predicting aerodynamic loads on the tipvane wind turbine, the acceleration potential is used and an expansion method is applied. In its simplest form, this method can essentially be classified as a lifting line approach, however, with a proper choice of the basis load distributions of the lifting line, the numerical integration of the pressurefield becomes one dimensional. the integration of the other variable can be performed analytically. The complete analytical expression for the pressure field consists of two series of basic pressure fields. One series is related to the basic load distributions over the turbineblade, and the other series to the basic load distribution over the tipvane.
The Aerodynamics of Frisbee Flight
Directory of Open Access Journals (Sweden)
Kathleen Baumback
2010-01-01
Full Text Available This project will describe the physics of a common Frisbee in flight. The aerodynamic forces acting on the Frisbee are lift and drag, with lift being explained by Bernoulli‘s equation and drag by the Prandtl relationship. Using V. R. Morrison‘s model for the 2-dimensional trajectory of a Frisbee, equations for the x- and y- components of the Frisbee‘s motion were written in Microsoft Excel and the path of the Frisbee was illustrated. Variables such as angle of attack, area, and attack velocity were altered to see their effect on the Frisbee‘s path and to speculate on ways to achieve maximum distance and height.
On cup anemometer rotor aerodynamics.
Pindado, Santiago; Pérez, Javier; Avila-Sanchez, Sergio
2012-01-01
The influence of anemometer rotor shape parameters, such as the cups' front area or their center rotation radius on the anemometer's performance was analyzed. This analysis was based on calibrations performed on two different anemometers (one based on magnet system output signal, and the other one based on an opto-electronic system output signal), tested with 21 different rotors. The results were compared to the ones resulting from classical analytical models. The results clearly showed a linear dependency of both calibration constants, the slope and the offset, on the cups' center rotation radius, the influence of the front area of the cups also being observed. The analytical model of Kondo et al. was proved to be accurate if it is based on precise data related to the aerodynamic behavior of a rotor's cup.
Rarefaction Effects in Hypersonic Aerodynamics
Riabov, Vladimir V.
2011-05-01
The Direct Simulation Monte-Carlo (DSMC) technique is used for numerical analysis of rarefied-gas hypersonic flows near a blunt plate, wedge, two side-by-side plates, disk, torus, and rotating cylinder. The role of various similarity parameters (Knudsen and Mach numbers, geometrical and temperature factors, specific heat ratios, and others) in aerodynamics of the probes is studied. Important kinetic effects that are specific for the transition flow regime have been found: non-monotonic lift and drag of plates, strong repulsive force between side-by-side plates and cylinders, dependence of drag on torus radii ratio, and the reverse Magnus effect on the lift of a rotating cylinder. The numerical results are in a good agreement with experimental data, which were obtained in a vacuum chamber at low and moderate Knudsen numbers from 0.01 to 10.
The basic aerodynamics of floatation
Davies, M. J.; Wood, D. H.
1983-09-01
It is pointed out that the basic aerodynamics of modern floatation ovens, in which the continuous, freshly painted metal strip is floated, dried, and cured, is the two-dimensional analog of that of hovercraft. The basic theory for the static lift considered in connection with the study of hovercraft has had spectacular success in describing the experimental results. This appears surprising in view of the crudity of the theory. The present investigation represents an attempt to explore the reasons for this success. An outline of the basic theory is presented and an approach is shown for deriving the resulting expressions for the lift from the full Navier-Stokes equations in a manner that clearly indicates the limitations on the validity of the expressions. Attention is given to the generally good agreement between the theory and the axisymmetric (about the centerline) results reported by Jaumotte and Kiedrzynski (1965).
On Cup Anemometer Rotor Aerodynamics
Directory of Open Access Journals (Sweden)
Santiago Pindado
2012-05-01
Full Text Available The influence of anemometer rotor shape parameters, such as the cups’ front area or their center rotation radius on the anemometer’s performance was analyzed. This analysis was based on calibrations performed on two different anemometers (one based on magnet system output signal, and the other one based on an opto-electronic system output signal, tested with 21 different rotors. The results were compared to the ones resulting from classical analytical models. The results clearly showed a linear dependency of both calibration constants, the slope and the offset, on the cups’ center rotation radius, the influence of the front area of the cups also being observed. The analytical model of Kondo et al. was proved to be accurate if it is based on precise data related to the aerodynamic behavior of a rotor’s cup.
Institute of Scientific and Technical Information of China (English)
刘昕; 林敬周; 陈亮中; 肖春华
2012-01-01
建立了适用于双三角翼大迎角非定常分离流场模拟的数值方法,研究双三角翼俯仰振荡时的动态流场特性,给出动态流场结构和气动力性能随迎角的变化规律,重点考察了减缩频率、转轴位置、平均迎角和振幅等参数对动态流场迟滞效应和气动力曲线迟滞环的影响.研究结果表明:俯仰振荡到相同大迎角时上仰和下俯的流场存在明显差异；减缩频率对气动力迟滞效应的影响相对大于转轴位置；平均迎角的变化导致双三角翼背风区流场结构呈现不同流态,而振幅的大小决定这些流态的数目,事实上俯仰运动时如果跨越的流态数目越多则流场结构的动态响应滞后现象就越显著.通过数值分析,有利于提高对双三角翼在俯仰振荡运动条件下的非定常特性和流场滞后效应等非线性现象的认识.%Numerical methods capable for computing the separated unsteady flow around a double-delta wing are established in this paper. The variation of the dynamic flow fields and aerodynamic performances following the change of the angle of attack Is studied, which concentrates on the investigation of the influences of several motion parameters on the time-lag effects of the dynamic flow fields and the hysteresis loops of the aerodynamic coefficients, such as reduced frequency, the position of rotation axis, the averaged angle of attack and the pitching amplitude. The numerical results show that there is great difference in the flow structure between pitch-up and pitch-down states at the same large angle of attack. The time-lag effect caused by the reduced frequency is relatively greater than that by the position of rotation axis. The variation of the averaged angles of attack causes different streamline forms on the leeward side of the double-delta wing; and the span of the streamline forms, which is related to the pitching amplitude, determines how much the dynamic response of the flow
Directory of Open Access Journals (Sweden)
O. D. Makinde
2014-01-01
Full Text Available This paper investigates the unsteady hydromagnetic-free convection of an incompressible electrical conducting Boussinesq’s radiating fluid past a moving vertical plate in an optically thin environment with the Navier slip, viscous dissipation, and Ohmic and Newtonian heating. The nonlinear partial differential equations governing the transient problem are obtained and tackled numerically using a semidiscretization finite difference method coupled with Runge-Kutta Fehlberg integration technique. Numerical data for the local skin friction coefficient and the Nusselt number have been tabulated for various values of parametric conditions. Graphical results for the fluid velocity, temperature, skin friction, and the Nusselt number are presented and discussed. The results indicate that the skin friction coefficient decreases while the heat transfer rate at the plate surface increases as the slip parameter and Newtonian heating increase.
Directory of Open Access Journals (Sweden)
P. LOGANATHAN,
2010-11-01
Full Text Available The numerical study of effects of thermal conductivity on unsteady MHD free convective flow over an isothermal semi infinite vertical plate is presented. It is assumed that the thermal conductivity of the fluid as a linear function of temperature. A magnetic field is applied transversely to the direction of the flow. The boundary layer equations of continuity, momentum and energy equations are transformed into non-linear coupled equations and then solved using implicit finite-difference method of Crank-Nicholson type. A parametric study is performed to illustrate the influence of thermal conductivity, magnetic parameter and Prandtl number on the velocity and temperature profiles. In addition, the local and average skin friction, Nusselt number at the plate are shown graphically for both air and water. An analysis of the results obtained shows that the flowfield is influenced appreciably by the strength of magnetic field, thermal conductivity at the wall of the plate.
Feasible domain of Walker's unsteady wall-layer model for the velocity profile in turbulent flows
Directory of Open Access Journals (Sweden)
MIKHAIL D. MIKHAILOV
2014-12-01
Full Text Available The present work studies, in detail, the unsteady wall-layer model of Walker et al. (1989, AIAA J., 27, 140 – 149 for the velocity profile in turbulent flows. Two new terms are included in the transcendental non-linear system of equations that is used to determine the three main model parameters. The mathematical and physical feasible domains of the model are determined as a function of the non-dimensional pressure gradient parameter (p+. An explicit parameterization is presented for the average period between bursts (, the origin of time ( and the integration constant of the time dependent equation (A0 in terms of p+. In the present procedure, all working systems of differential equations are transformed, resulting in a very fast computational procedure that can be used to develop real-time flow simulators.
Feasible domain of Walker's unsteady wall-layer model for the velocity profile in turbulent flows.
Mikhailov, Mikhail D; Freire, Atila P Silva
2014-12-01
The present work studies, in detail, the unsteady wall-layer model of Walker et al. (1989, AIAA J., 27, 140 – 149) for the velocity profile in turbulent flows. Two new terms are included in the transcendental nonlinear system of equations that is used to determine the three main model parameters. The mathematical and physical feasible domains of the model are determined as a function of the non-dimensional pressure gradient parameter (p+). An explicit parameterization is presented for the average period between bursts (T+B), the origin of time (t+0 ) and the integration constant of the time dependent equation (A0) in terms of p+. In the present procedure, all working systems of differential equations are transformed, resulting in a very fast computational procedure that can be used to develop real-time flow simulators.
Humphreys, A. P.; Paulson, J. W., Jr.; Kemmerly, G. T.
1988-01-01
Previous wind tunnel tests of fighter configurations have shown that thrust reverser jets can induce large, unsteady aerodynamic forces and moments during operation in ground proximity. This is a concern for STOL configurations using partial reversing to spoil the thrust while keeping the engine output near military (MIL) power during landing approach. A novel test technique to simulate approach and landing was developed under a cooperative Northrop/NASA/USAF program. The NASA LaRC Vortex Research Facility was used for the experiments in which a 7-percent F-18 model was moved horizontally at speeds of up to 100 feet per second over a ramp simulating an aircraft to ground rate of closure similar to a no-flare STOL approach and landing. This paper presents an analysis of data showing the effect of reverser jet orientation and jet dynamic pressure ratio on the transient forces for different angles of attack, and flap and horizontal tail deflection. It was found, for reverser jets acting parallel to the plane of symmetry, that the jets interacted strongly with the ground, starting approximately half a span above the ground board. Unsteady rolling moment transients, large enough to cause the probable upset of an aircraft, and strong normal force and pitching moment transients were measured. For jets directed 40 degrees outboard, the transients were similar to the jet-off case, implying only minor interaction.
Directory of Open Access Journals (Sweden)
Kyung Chun Kim
2014-11-01
Full Text Available A new type of horizontal axis wind turbine adopting the Archimedes spiral blade is introduced for urban-use. Based on the angular momentum conservation law, the design formula for the blade was derived using a variety of shape factors. The aerodynamic characteristics and performance of the designed Archimedes wind turbine were examined using computational fluid dynamics (CFD simulations. The CFD simulations showed that the new type of wind turbine produced a power coefficient (Cp of approximately 0.25, which is relatively high compared to other types of urban-usage wind turbines. To validate the CFD results, experimental studies were carried out using a scaled-down model. The instantaneous velocity fields were measured using the two-dimensional particle image velocimetry (PIV method in the near field of the blade. The PIV measurements revealed the presence of dominant vortical structures downstream the hub and near the blade tip. The interaction between the wake flow at the rotor downstream and the induced velocity due to the tip vortices were strongly affected by the wind speed and resulting rotational speed of the blade. The mean velocity profiles were compared with those predicted by the steady state and unsteady state CFD simulations. The unsteady CFD simulation agreed better with those of the PIV experiments than the steady state CFD simulations.
A Numerical Study of Aerodynamic Performance and Noise of a Bionic Airfoil Based on Owl Wing
Directory of Open Access Journals (Sweden)
Xiaomin Liu
2014-08-01
Full Text Available Noise reduction and efficiency enhancement are the two important directions in the development of the multiblade centrifugal fan. In this study, we attempt to develop a bionic airfoil based on the owl wing and investigate its aerodynamic performance and noise-reduction mechanism at the relatively low Reynolds number. Firstly, according to the geometric characteristics of the owl wing, a bionic airfoil is constructed as the object of study at Reynolds number of 12,300. Secondly, the large eddy simulation (LES with the Smagorinsky model is adopted to numerically simulate the unsteady flow fields around the bionic airfoil and the standard NACA0006 airfoil. And then, the acoustic sources are extracted from the unsteady flow field data, and the Ffowcs Williams-Hawkings (FW-H equation based on Lighthill's acoustic theory is solved to predict the propagation of these acoustic sources. The numerical results show that the lift-to-drag ratio of bionic airfoil is higher than that of the traditional NACA 0006 airfoil because of its deeply concave lower surface geometry. Finally, the sound field of the bionic airfoil is analyzed in detail. The distribution of the A-weighted sound pressure levels, the scaled directivity of the sound, and the distribution of dP/dt on the airfoil surface are provided so that the characteristics of the acoustic sources could be revealed.
Application of unsteady aeroelastic analysis techniques on the national aerospace plane
Pototzky, Anthony S.; Spain, Charles V.; Soistmann, David L.; Noll, Thomas E.
1988-01-01
A presentation provided at the Fourth National Aerospace Plane Technology Symposium held in Monterey, California, in February 1988 is discussed. The objective is to provide current results of ongoing investigations to develop a methodology for predicting the aerothermoelastic characteristics of NASP-type (hypersonic) flight vehicles. Several existing subsonic and supersonic unsteady aerodynamic codes applicable to the hypersonic class of flight vehicles that are generally available to the aerospace industry are described. These codes were evaluated by comparing calculated results with measured wind-tunnel aeroelastic data. The agreement was quite good in the subsonic speed range but showed mixed agreement in the supersonic range. In addition, a future endeavor to extend the aeroelastic analysis capability to hypersonic speeds is outlined. An investigation to identify the critical parameters affecting the aeroelastic characteristics of a hypersonic vehicle, to define and understand the various flutter mechanisms, and to develop trends for the important parameters using a simplified finite element model of the vehicle is summarized. This study showed the value of performing inexpensive and timely aeroelastic wind-tunnel tests to expand the experimental data base required for code validation using simple to complex models that are representative of the NASP configurations and root boundary conditions are discussed.
Added Mass Effect and an Extended Unsteady Blade ElementModel of Insect Hovering
Institute of Scientific and Technical Information of China (English)
Xingyao Yan; Shanan Zhu; Zhongdi Su; Hongjun Zhang
2011-01-01
During the insect flight,the force peak at the start of each stroke contributes a lot to the total aerodynamic force.Yet how this force is generated is still controversial.Two current explanations to this are wake capture and Added Mass Effect (AME)mechanisms.To study the AME,we present an extended unsteady blade element model which takes both the added mass of fluid and rotational effect of the wing into account.Simulation results show a high force peak at the start of each stroke and are quite similar to the measured forces on the physical wing model.We found that although the Added Mass Force (AMF) of the medium contributes a lot to this force peak,the wake capture effect further augments this force and may play a more important role in delayed mode.Furthermore,we also found that there might be an unknown mechanism which may augment the AME during acceleration period at the start of each stroke,and diminish the AME during deceleration at the end of each stroke.
Energy Technology Data Exchange (ETDEWEB)
Shaha, Poly Rani; Poddar, Nayan Kumar; Mondal, Rabindra Nath, E-mail: rnmondal71@yahoo.com [Department of Mathematics, Jagannath University, Dhaka-1100 (Bangladesh); Rudro, Sajal Kanti [Department of Mathematics, Notredame Colleage, Motijheel, Dhaka (Bangladesh)
2016-07-12
The study of flows through coiled ducts and channels has attracted considerable attention not only because of their ample applications in Chemical, Mechanical, Civil, Nuclear and Biomechanical engineering but also because of their ample applications in other areas, such as blood flow in the veins and arteries of human and other animals. In this paper, a numerical study is presented for the fully developed two-dimensional flow of viscous incompressible fluid through a loosely coiled rectangular duct of large aspect ratio. Numerical calculations are carried out by using a spectral method, and covering a wide range of the Dean number, Dn, for two types of curvatures of the duct. The main concern of the present study is to find out effects of curvature as well as formation of secondary vortices on unsteady solutions whether the unsteady flow is steady-state, periodic, multi-periodic or chaotic, if Dn is increased. Time evolution calculations as well as their phase spaces are performed with a view to study the non-linear behavior of the unsteady solutions, and it is found that the steady-state flow turns into chaotic flow through various flow instabilities, if Dn is increased no matter what the curvature is. It is found that the unsteady flow is a steady-state solution for small Dn’s and oscillates periodically or non-periodically (chaotic) between two- and twelve-vortex solutions, if Dn is increased. It is also found that the chaotic solution is weak for small Dn’s but strong as Dn becomes large. Axial flow distribution is also investigated and shown in contour plots.
Shaha, Poly Rani; Rudro, Sajal Kanti; Poddar, Nayan Kumar; Mondal, Rabindra Nath
2016-07-01
The study of flows through coiled ducts and channels has attracted considerable attention not only because of their ample applications in Chemical, Mechanical, Civil, Nuclear and Biomechanical engineering but also because of their ample applications in other areas, such as blood flow in the veins and arteries of human and other animals. In this paper, a numerical study is presented for the fully developed two-dimensional flow of viscous incompressible fluid through a loosely coiled rectangular duct of large aspect ratio. Numerical calculations are carried out by using a spectral method, and covering a wide range of the Dean number, Dn, for two types of curvatures of the duct. The main concern of the present study is to find out effects of curvature as well as formation of secondary vortices on unsteady solutions whether the unsteady flow is steady-state, periodic, multi-periodic or chaotic, if Dn is increased. Time evolution calculations as well as their phase spaces are performed with a view to study the non-linear behavior of the unsteady solutions, and it is found that the steady-state flow turns into chaotic flow through various flow instabilities, if Dn is increased no matter what the curvature is. It is found that the unsteady flow is a steady-state solution for small Dn's and oscillates periodically or non-periodically (chaotic) between two- and twelve-vortex solutions, if Dn is increased. It is also found that the chaotic solution is weak for small Dn's but strong as Dn becomes large. Axial flow distribution is also investigated and shown in contour plots.
Aeroelasticity of Axially Loaded Aerodynamic Structures for Truss-Braced Wing Aircraft
Nguyen, Nhan; Ting, Eric; Lebofsky, Sonia
2015-01-01
This paper presents an aeroelastic finite-element formulation for axially loaded aerodynamic structures. The presence of axial loading causes the bending and torsional sitffnesses to change. For aircraft with axially loaded structures such as the truss-braced wing aircraft, the aeroelastic behaviors of such structures are nonlinear and depend on the aerodynamic loading exerted on these structures. Under axial strain, a tensile force is created which can influence the stiffness of the overall aircraft structure. This tension stiffening is a geometric nonlinear effect that needs to be captured in aeroelastic analyses to better understand the behaviors of these types of aircraft structures. A frequency analysis of a rotating blade structure is performed to demonstrate the analytical method. A flutter analysis of a truss-braced wing aircraft is performed to analyze the effect of geometric nonlinear effect of tension stiffening on the flutter speed. The results show that the geometric nonlinear tension stiffening effect can have a significant impact on the flutter speed prediction. In general, increased wing loading results in an increase in the flutter speed. The study illustrates the importance of accounting for the geometric nonlinear tension stiffening effect in analyzing the truss-braced wing aircraft.
Minnowbrook V: 2006 Workshop on Unsteady Flows in Turbomachinery
LaGraff, John E.; Ashpis, David E.; Oldfield, Martin L. G.; Gostelow, J. Paul
2006-01-01
This CD-ROM contain materials presented at the Minnowbrook V 2006 Workshop on Unsteady Flows in Turbomachinery, held at the Syracuse University Minnowbrook Conference Center, New York, on August 20-23, 2006. The workshop organizers were John E. LaGraff (Syracuse University), Martin L.G. Oldfield (Oxford University), and J. Paul Gostelow (University of Leicester). The workshop followed the theme, venue, and informal format of four earlier workshops: Minnowbrook I (1993), Minnowbrook II (1997), Minnowbrook III (2000), and Minnowbrook IV (2003). The workshop was focused on physical understanding of unsteady flows in turbomachinery, with the specific goal of contributing to engineering application of improving design codes for turbomachinery. The workshop participants included academic researchers from the United States and abroad and representatives from the gas-turbine industry and U.S. Government laboratories. The physical mechanisms discussed were related to unsteady wakes, active flow control, turbulence, bypass and natural transition, separation bubbles and turbulent spots, modeling of turbulence and transition, heat transfer and cooling, surface roughness, unsteady CFD, and DNS. This CD-ROM contains copies of the viewgraphs presented, organized according to the workshop sessions. Full-color viewgraphs and animations are included. The workshop summary and the plenary discussion transcripts clearly highlight the need for continued vigorous research in the technologically important area of unsteady flows in turbomachines.
Mass and Aerodynamic Imbalance Estimates of Wind Turbines
Directory of Open Access Journals (Sweden)
Jenny Niebsch
2010-04-01
Full Text Available Due to its effect on the operation time of wind turbines, rotor imbalances of a wind turbine have to be detected early enough. We present a method that determines inhomogeneous mass distributions of the rotor as well as deviations in the pitch angles of the rotor blades from vibrational data only. To this end, a mathematical model connecting the load caused by the imbalances to the resulting vibrations was developed. After discretization, the resulting vibration equation was solved analytically. The inverse problem, i.e., the calculation of the mass and aerodynamic imbalance from vibrational data, was solved by using nonlinear regularization theory. Numerical simulations were performed using artificial vibration data.
Aerodynamic Efficiency Enhancements for Air Vehicles Project
National Aeronautics and Space Administration — The need for aerodynamics-based efficiency enhancements for air vehicles is presented. The results of the Phase I investigation of concepts for morphing aircraft are...
Aerodynamic Characterization of a Modern Launch Vehicle
Hall, Robert M.; Holland, Scott D.; Blevins, John A.
2011-01-01
A modern launch vehicle is by necessity an extremely integrated design. The accurate characterization of its aerodynamic characteristics is essential to determine design loads, to design flight control laws, and to establish performance. The NASA Ares Aerodynamics Panel has been responsible for technical planning, execution, and vetting of the aerodynamic characterization of the Ares I vehicle. An aerodynamics team supporting the Panel consists of wind tunnel engineers, computational engineers, database engineers, and other analysts that address topics such as uncertainty quantification. The team resides at three NASA centers: Langley Research Center, Marshall Space Flight Center, and Ames Research Center. The Panel has developed strategies to synergistically combine both the wind tunnel efforts and the computational efforts with the goal of validating the computations. Selected examples highlight key flow physics and, where possible, the fidelity of the comparisons between wind tunnel results and the computations. Lessons learned summarize what has been gleaned during the project and can be useful for other vehicle development projects.
Aerodynamic Efficiency Enhancements for Air Vehicles Project
National Aeronautics and Space Administration — The need for aerodynamics-based efficiency enhancements for air vehicles is presented. Concepts are presented for morphing aircraft, to enable the aircraft to...
Bloembergen, Nicolaas
1996-01-01
Nicolaas Bloembergen, recipient of the Nobel Prize for Physics (1981), wrote Nonlinear Optics in 1964, when the field of nonlinear optics was only three years old. The available literature has since grown by at least three orders of magnitude.The vitality of Nonlinear Optics is evident from the still-growing number of scientists and engineers engaged in the study of new nonlinear phenomena and in the development of new nonlinear devices in the field of opto-electronics. This monograph should be helpful in providing a historical introduction and a general background of basic ideas both for expe