Steady Aerodynamic Loads Research Articles

Influence of steady aerodynamic loads on hunting stability of high-speed trains

Influence of steady aerodynamic loads on hunting stability of high-speed trains

Study on Lateral Vibration of Tail Coach for High-Speed Train under Unsteady Aerodynamic Loads

As the speed of high-speed trains increases, the vehicle’s lateral stability steadily deteriorates. There have been observations of abnormal vibrations in the tail car, particularly on certain sections of the railway line. This study built a high-speed train aerodynamic simulation model for a three-car consist, and a multibody dynamics simulation model for an eight-car consist based on numerical simulations of train aerodynamics and multibody dynamics. It investigated both steady and unsteady aerodynamic loads, flow field characteristics, and the dynamic performance of vehicles under varied aerodynamic loads at 400 km/h. The results indicate that the aerodynamic loads generated during high-speed train operation exhibit highly unsteady characteristics. Steady aerodynamic loads have a relatively minor impact on the vehicle’s dynamic performance, whereas unsteady loads exert a more significant influence. Under unsteady aerodynamic forces, the tail car experiences severe lateral vibrations. The lateral stability index, displacement, velocity, and acceleration of the tail car under unsteady conditions were measured at 2.26, 7.54 mm, and 0.53 m/s2, respectively. These values represent increases of over 17.71%, 148.84%, and 111.24%, respectively, compared to the steady loads. Large oscillation amplitudes result in more significant lateral displacements and accelerations of the vehicle. This phenomenon is a crucial factor contributing to the “tail swing” effect observed in high-speed trains. This study emphasizes the importance of considering unsteady aerodynamic effects in assessing the lateral stability of high-speed trains and highlights the significance of mitigating the adverse impacts of such dynamic responses, particularly in the tail car.

VAWT support structure mass sensitivity due to aerodynamic load scaling

The X-rotor wind turbine is an X-shaped hybrid vertical axis wind turbine whose power take-off is done by horizontal axis rotors located at the tip of the lower blades. Based on an initial basic study, the present study developed a preliminary jacket design as the turbine support structure. Steady aerodynamic loads were obtained from an actuator cylinder model and dynamic load simulations including wave loads were performed. The structure was checked according to fatigue damage and maximum yielding for representative site-specific load cases for fatigue and ultimate limit states. Even though the use of a conventional jacket was shown to be feasible for the new turbine concept, the overall mass of the support structure obtained by the higher fidelity model was higher than the initial prediction. The design was driven by the fatigue damage, caused by large cyclical loads on every rotor rotation. The effect of a hypothetical aerodynamic load reduction on the jacket mass was investigated. The developed design methodology was also applied to the design of equivalent jackets after a load reduction of 75% and 50% and the mass of the structure was shown to be sensible, with a respective reduction of 25% and 48%. This result demonstrates that different design strategies that influence the magnitude of the aerodynamic loads (e.g. the control strategy) could lead to a more cost-efficient jacket design.

Aerodynamic load analyses of less-emission HTS maglev train in evacuated tube transport system

An evacuated tube transport (ETT) system is proposed by combining evacuated tube technology and high temperature superconducting (HTS) maglev technology in this paper. It can be predicted that this future transport mode can own the advantages of less emission, low noise, high efficiency, and suitable for high-speed or super-high-speed application. The train running at a high speed will inevitably cause complex aerodynamic load behaviors in an enclosed low-pressure tube. It further affects the real energy consumption and the fatigue life of the components. In order to explore how the aerodynamic load behaves in an ETT-HTS Maglev system, we established a three-dimension numerical calculation model based on ANSYS FLUENT software. The steady aerodynamic loads on the train’s surface and the tube’s inner surface are investigated under different pressures and different operation speeds. It is found that the aerodynamic load on the surface of the train and tube is significantly affected by the pressure inside the tube and the running speed of the train. The aerodynamic load fluctuations at the rear of the train are relatively more violent than those at the head. We also found that the impact of compression wave and expansion wave on aerodynamic loads at different positions of the tube is related to the size of the flow field space between the tube and the train. These results can provide some reference for the less-emission train body design and the whole ETT-HTS Maglev system structural strength in the near future.

Theoretical analysis for the effect of static pressure differential on aeroelastic stability of flexible panel

The static pressure differentials have been neglected in almost all of theoretical analysis models for panel flutter in the supersonic flow, which are established on the basis of the classic aeroelastic model by Dowell in 1966. However, in actual engineering, flexible panels are still subjected to the static pressure differentials under some circumstances. By using the numerical methods, Dowell et al. found that the static pressure differentials as small as 10−2 psi may significantly alter the flutter boundary. In this paper, a novel strategy for a theoretical analysis model is proposed to study the effect of static pressure differential on aeroelastic stability of flexible panel in the supersonic airflow. We regard the final total displacement of the panel as the superposition of dynamic displacement and static deformation, which is in accord with the actual situation of physicality. The static deformation is obtained by solving the static aeroelastic equation. Using the curve/surface fitting method, the static deformations are described by two approaches with/without considering the interaction between the static deformation and steady aerodynamic loads. And then the static deformation is introduced into the dynamic aeroelastic equations in the form of the stiffness through the nonlinear induced loading. The dynamic aeroelastic equation is solved by using the Galerkin discrete method, which can truncate the partial differential equations into a set of ordinary equations. Lyapunov indirect method is utilized to evaluate the aeroelastic stability of the flexible panel. According to the known expression of static deformation and Routh-Hurwitz criterion, a theoretical solution for the aeroelastic stability boundary under the action of the arbitrary static pressure differentials is derived. The theoretical results show that (1) The static pressure differential can significantly enhance the aeroelastic stability of the flexible panel, which is consistent with the numerical results. (2) Whether the actual coupling between the static deformation and aerodynamic loads is considered or not, the stability boundaries obtained are quite different. (3) The increase of the stiffness of structure induced by the static deformation can increase the critical flutter dynamic pressures, but it is not the dominant factor to lead to such a remarkable improvement of the stability of the flexible panel under the action of the static pressure differential. The actual coupling between the static deformation and aerodynamic loads plays a significant role in substantially improving the aeroelastic stability of the flexible panel.

Hunting Stability of High-Speed Railway Vehicles Under Steady Aerodynamic Loads

With the rising speed of high-speed trains, the aerodynamic loads become more significant and their influences on the hunting stability of railway vehicles deserve to be considered. Such an effect cannot be properly considered by the conventional model of hunting stability analysis. To this end, the linear hunting stability of high-speed railway vehicles running on tangent tracks is studied. A model considering the steady aerodynamic loads due to the joint action of the airflow facing the moving train and the crosswind, is proposed for the hunting stability analysis of a railway vehicle with 17 degrees of freedom (DOF). The key factors considered include: variations of the wheel–rail normal forces, creep coefficients, gravitational stiffness and angular stiffness due to the actions of the aerodynamic load, which affects the characteristics of hunting stability. Using the computer program developed, numerical calculations were carried out for studying the behavior of the linear hunting stability of vehicles under steady aerodynamic loads. The results show that the aerodynamic loads have an obvious effect on the linear critical speeds and instability modes. The linear critical speed decreases monotonously as the crosswind velocity increases, and the influences of pitch moment and lift force on the linear critical speed are larger than the other components of the aerodynamic loads.

Hunting stability of high-speed railway vehicles on a curved track considering the effects of steady aerodynamic loads

Aerodynamic loads may have effects on the hunting stability, and the factor of curved track makes it more complicated. Therefore, considering the steady aerodynamic loads generated by crosswind and airflow in the opposite advancing direction of train, the hunting stability of high-speed railway vehicle on a curved track is studied in this paper. The changes of gravitational restoring force and creep coefficients which are caused by aerodynamic loads are considered, and the change of equilibrium position due to aerodynamic loads, centrifugal force and the factor of curved track is also in consideration. A mathematical model of a high-speed railway vehicle during curve negotiation with aerodynamic loads is set up. A program based on the model is written and verified. Using this program, the linear critical speed considering the effects of aerodynamic loads is determined by the eigenvalue analysis. This paper investigates the critical speeds in three aerodynamic conditions. Considering the aerodynamic loads, the dependence of critical speed on curve radius and super-elevation is analyzed, and the impact of aerodynamic loads on instability mode is analyzed as well. In addition, this paper obtains the dominant factors affecting critical speed and the variation tendency of critical speed with primary longitudinal stiffness by orthogonal experiments. The results show that the critical speed decreases or increases while the wind is blowing to outer rail or inner rail respectively. The aerodynamic loads produce obvious effects on the instability mode. The variation tendency of critical speed dependence on curve radius in the conditions with aerodynamic loads keeps consistent with the case without aerodynamic loads. It is seen from the orthogonal experiments that, aerodynamic loads and curve radius are the dominant factors affecting linear critical speed of vehicle on a curved track, and the linear critical speed decreases with the increasing of primary longitudinal stiffness.

Downslope Gusty Wind Loading of Vehicles on Bridges

AbstractDownslope crosswind bora gusts impacting vehicles represent a significant traffic safety issue, and vehicles on bridges are particularly vulnerable to such crosswinds. Wind tunnel experiments were carried out to investigate the effects of the vertical wind incidence angle and vehicle position on the resulting transient aerodynamic loads. When considering accident risk for the vehicle/infrastructure scenario investigated in this study, the higher risk for vehicles exists at lower vertical wind incidence angles up to 30° and closer to the upwind edge of the bridge deck with respect to steady aerodynamic loads. Shed vortices and wind gusting determined the unsteady aerodynamic loading of a vehicle on the bridge. Effects of shed vortices decreased at larger vertical wind incidence angles, with the wind gusts driving the unsteady aerodynamic loads. Difficulties associated with vehicle maneuvering and stability in the upwind traffic lane in terms of unsteady aerodynamic loading are expected to occur at ...

Evaluation of Aerodynamic Loads via Reduced-Order Methodology

Centroidal Voronoi tessellation, leave-one-out cross validation, proper orthogonal decomposition, and multidimensional interpolation are integrated to define a reduced-order modeling approach for the parametric evaluation of steady aerodynamic loads. The proper orthogonal decomposition-based methodology allows reducing the number of degrees of freedom of the problem while maintaining good accuracy for the solution of complex three-dimensional viscous turbulent flows. As a result, it yields fairly accurate solutions at a fraction of the time required by standard computational fluid dynamics approaches. Three-dimensional examples for fixed- and rotary-wing cases of industrial relevance are used to assess the method in the cases of subsonic and transonic flow conditions.

Influences of aerodynamic loads on hunting stability of high-speed railway vehicles and parameter studies

The influences of steady aerodynamic loads on hunting stability of high-speed railway vehicles were investigated in this study. A mechanism is suggested to explain the change of hunting behavior due to actions of aerodynamic loads: the aerodynamic loads can change the position of vehicle system (consequently the contact relations), the wheel/rail normal contact forces, the gravitational restoring forces/moments and the creep forces/moments. A mathematical model for hunting stability incorporating such influences was developed. A computer program capable of incorporating the effects of aerodynamic loads based on the model was written, and the critical speeds were calculated using this program. The dependences of linear and nonlinear critical speeds on suspension parameters considering aerodynamic loads were analyzed by using the orthogonal test method, the results were also compared with the situations without aerodynamic loads. It is shown that the most dominant factors affecting linear and nonlinear critical speeds are different whether the aerodynamic loads considered or not. The damping of yaw damper is the most dominant influencing factor for linear critical speeds, while the damping of lateral damper is most dominant for nonlinear ones. When the influences of aerodynamic loads are considered, the linear critical speeds decrease with the rise of crosswind velocity, whereas it is not the case for the nonlinear critical speeds. The variation trends of critical speeds with suspension parameters can be significantly changed by aerodynamic loads. Combined actions of aerodynamic loads and suspension parameters also affect the critical speeds. The effects of such joint action are more obvious for nonlinear critical speeds.

Computational Aerodynamic Analysis of Offshore Upwind and Downwind Turbines

Aerodynamic interactions of the model NREL 5 MW offshore horizontal axis wind turbines (HAWT) are investigated using a high-fidelity computational fluid dynamics (CFD) analysis. Four wind turbine configurations are considered; three-bladed upwind and downwind and two-bladed upwind and downwind configurations, which operate at two different rotor speeds of 12.1 and 16 RPM. In the present study, both steady and unsteady aerodynamic loads, such as the rotor torque, blade hub bending moment, and base the tower bending moment of the tower, are evaluated in detail to provide overall assessment of different wind turbine configurations. Aerodynamic interactions between the rotor and tower are analyzed, including the rotor wake development downstream. The computational analysis provides insight into aerodynamic performance of the upwind and downwind, two- and three-bladed horizontal axis wind turbines.

Dynamic Nonlinear Aeroelastic Model of a Kite for Power Generation

This paper presents a numerical modeling approach for the flight dynamics and deformation of tethered inflatable wings, which are central components of many contemporary airborne wind energy systems. A geometrically nonlinear finite element framework is used to describe the large quasi-static deformations caused by changing bridle line geometry and by varying aerodynamic loading. The effect of the external flow is described in terms of discrete pressure distributions for the different wing sections. The empirical model takes into account the shape parameters of chord length, camber, and thickness per section, and it is derived by fitting precomputed data from computational fluid dynamic analysis. To reduce computation times, local dynamic deformation phenomena are neglected. For each integration time step, the steady aerodynamic loading is determined first and then used to update the static equilibrium shape of the wing. This static aeroelastic model is embedded in a dynamic system model that includes the tether, bridle lines, and kite control unit. The iterative approach can accurately describe bending and torsion of the wing, which contribute to the aerodynamic steering moments. The presented approach is complemented with a flight controller and used to simulate figure-eight flight maneuvers of a leading-edge inflatable tube kite used for traction power generation.

Study on wheel/rail adhesion force and its control of high-speed trains considering aerodynamic loads and track excitations

The wheel/rail vertical loads are strongly affected by the aerodynamic loads and track excitations, and will further influence the wheel/rail adhesion forces. With the increasing of train speed, the influence of aerodynamic loads becomes more and more significant. In order to probe into this problem, a simplified train dynamic model with three vehicles is established in which each vehicle system has 14 degrees of freedom. The track irregularity spectrum of a high speed line in China and steady aerodynamic loads are taken as the inputs to the vehicle system. Numerical simulation is carried out by using MATLAB. It is found that the aerodynamic loads obviously affect the wheel/rail contact forces for the high-speed train. Under the same train speed, with the increasing of crosswind velocity, the wheel/rail contact forces for cars at different positions in the train set are reduced gradually. Under the same crosswind velocity, the impact of aerodynamic loads on the different-position vehicle is different. The model of wheel/rail adhesion fuzzy control is built and preliminary analysis is conducted. The strategy of predictive control based on the vehicle system is introduced.

The aeroelastic effects on the scatter phenomenon of wind-tunnel data

The unsteady Reynolds-averaged Navier-Stokes equations coupled with the k-ω SST turbulence model are solved to obtain the steady and unsteady aerodynamic forces for airfoils and wings. The effects of vibration types and amplitudes on aerodynamic forces of airfoils and wings are studied. The deformation characteristics of a swept wing induced by steady aerodynamic load are presented. It is found that for a vibrating elastic wing at small and medium incidences, its mean aerodynamic loads are almost the same as those obtained from the static one. On the contrary, at high incidences especially around the stall incidence, the vibration may change the mean values. In addition, the larger amplitude is, the larger discrepancy will be. For a swept wing, the steady aerodynamic loads usually lead to the “pitching down” effect on the wing tip which delays the stall compared with a rigid one; But this phenomenon dose not occur on a aeroelastic wing which can induce the separation ahead and trigger the stall. The above conclusions are in good agreement with the scatter characteristics of wind-tunnel data. The reason why the data obtained from wind tunnel and CFD are different is also analyzed. Meanwhile, it can be an explanation for scatter phenomenon of wind-tunnel data, especially for high incidence cases, which remains a puzzle so far.

Non-linear reduced order models for steady aerodynamics

Abstract A reduced order modelling approach for predicting steady aerodynamic flows and loads data based on Computational Fluid Dynamics (CFD) and global Proper Orthogonal Decomposition (POD), that is, POD for multiple different variables of interest simultaneously, is presented. A suitable data transformation for obtaining problemadapted global basis modes is introduced. Model order reduction is achieved by parameter space sampling, reduced solution space representation via global POD and restriction of a CFD flow solver to the reduced POD subspace. Solving the governing equations of fluid dynamics is replaced by solving a non-linear least-squares optimization problem. Methods for obtaining feasible starting solutions for the optimization procedure are discussed. The method is demonstrated by computing reduced-order solutions to the compressible Euler equations for the NACA 0012 airfoil based on two different snapshot sets; one in the subsonic and one in the transonic flow regime, where shocks occur. Results are compared with those obtained by POD-based interpolation using Kriging and the Thin Plate Spline method (TPS).

Optimal Scheduling of Control Surfaces Flexible Wings to Reduce Induced Drag

An aircraft wing structure is a complex assemblage of interconnected elements composed of both metallic and composite materials. To capture the physics of the structural response at an appropriate level of accuracy the finite element method is employed to model the aircraft structure. The external aerodynamic loads distribution in both the chord and span direction are predicted using the USSAERO paneling method. The Automated StRuctural Optimization System[1] (ASTROS) is used for modeling the structure, the steady aerodynamic loads, and carrying out the trim analysis of a free flying flexible air vehicle. Two wing models are selected for this investigation. The first model, referred to as the Goland Wing[2], has a “beam-rod” structural model. The second model considered is a built-up model typical of a fighter type aircraft[3] and is shown in Figure 7 with the corresponding aerodynamic panel model. Both models have 20 discrete control surfaces along the trailing edge of each aerodynamic model. The aerodynamic effects of gaps between each of the discrete surfaces are ignored to simulate a “so-called” conformal control surface[4]. R.T. Jones[5] has demonstrated that wings having an elliptical spanwise lift distribution ensures minimum induced drag. Therefore, in the present study, the control surfaces are scheduled to obtain an elliptical spanwise load distribution. It is worth noting that the methodology developed in this work is general and can be used to obtain any desired distribution, not just elliptical. In addition, as demonstrated by Munk[7], induced drag is independent of the distribution of lift in the chordwise direction. For the current study induced drag calculations are carried out considering the “Trefftz-plane”[6] downstream from the trailing edge. The wing is held at a trimmed level flight condition using the angle of attack while the control surfaces are used only to obtain the desired elliptical spanwise pressure distribution.

Numerical Simulation of Aerodynamic Damping for Flutter Analysis of Turbomachinery Blade Rows

This paper describes the calculation of aerodynamic damping for prediction of e utter characteristics of turbomachinery bladerows.Theunsteady aerodynamicbladeloadsareobtainedbysolving theNavier ‐Stokesequations on a dynamically deforming, body-e tted grid. Phase-lagged boundary conditions are used to model the nonzero interbladephaseangleoscillations,and theenergy exchangemethod isused to calculatetheaerodynamicdamping. The analysis is applied to calculate e utter of a transonic forward-swept fan cone guration, which showed e utter at part speed conditions in wind-tunnel tests. The analysis successfully identie ed the most critical mode and the e ow characteristics responsible for the observed e utter. The location of shock wave and variation of its strength were found to strongly ine uence the aerodynamic damping, with outboard stations providing the main contribution. The results also demonstrate that changes in blade shape impact the calculated aerodynamic damping, indicating the importance of using an accurate blade operating shape under centrifugal and steady aerodynamic loading. Sensitivity of thecalculated aerodynamic damping to variation in inlet and exit conditions, the computational time steps, and blade natural frequency are also reported.

Oscillating Airfoil Aerodynamics of a Rotating Compressor Blade Row

Experiments are performed in a research compressor directed at investigating the aerodynamic damping unsteady aerodynamics of a rotor blade row. Specie cally, the torsion mode unsteady aerodynamics of the e rst-stage rotor of a research compressor are investigated and quantie ed, including the effects of oscillation amplitude and steady aerodynamic loading. An experimental ine uence coefe cient technique is implemented in conjunction with a unique torsion mode drive system that provides rotor blade torsion mode oscillations without other motor drive systems.Theoscillatingairfoilsurfaceunsteady pressureine uencecoefe cientdataareacquiredwith dynamicpressure transducers embedded in the rotor blades. The resulting rotor blade aerodynamic damping oscillating airfoil data are then correlated with a linear theory prediction. In general, the unsteady pressure ine uence coefe cient data decay rapidly with increasing distance from the reference blade, with different ine uences on thepressure and suction surfaces. Oscillationmagnitudeand steadyloading havea signie canteffectonboththeine uence coefe cient data and the equivalent all-airfoils-oscillating unsteady pressure data.

Analysis of steady and unsteady aerodynamic loads on the Ariane 5 lauch vehicle rear part during flight ascent

Les lanceurs sont soumis a un champ de pression stationnaire et instationnaire en phase transsonique et pression dynamique maximale. Ces champs de pression peuvent etre tres severes dans certaines zones du lanceur, qui presentent d'importantes variations locales de geometrie. Ces variations de geometrie conduisent a des decollements dans des zones significatives des lanceurs. Les charges aerodynamiques, dependent de la geometrie, du nombre de Mach et de la trajectoire, peuvent endommager les structures ou les sous-systemes, En consequence, ces charges doivent etre prises en compte dans le dimensionnement des lanceurs. Cet article se limite aux charges aerodynamiques appliquees en phase transsonique sur la partie arriere du lancear ARIANE 5. Il traite des campagnes experimentales (sous la responsabilite d'Aerospatiale dans le cadre d'un contrat avec le CNES) destinees a caracteriser le champ de pression stationnaire et instationnaire. Deux campagnes experimentales ont ete realisees dans les souffleries de l'ONERA S2, en utilisant une maquette au 60 e du lanceur ARIANE 5. L'experience acquise lors des deux campagnes d'esais est d'une grande importance pour les versions ameliorees d'ARIANE 5 Plus. Pour cette version d'ARIANE 5, la tuyere de l'etage central cryotechnique EPC est plus longue que la version standard, et munie d'un tore central, qui devrait augmenter localement les charges aerodynamiques.

Considerations of Gravity Effects on VAWT Rotor Configurations Which Minimize Flatwise Moments and Stresses

Anticipating that composite materials will permit greater freedom when future VAWT rotor blades are configured, this paper further examines the benefits of adopting true Troposkien shapes for blades which do not use horizontal struts. Two parameters are identified which control blade geometry under combined rotational and gravitational loads. Representative zero-bending-moment shapes are calculated, both for constant mass distribution and for several new variable-mass families. The latter include one case whose mathematical solution proves remarkably simple. Steady design stresses are found to be severely affected by deviations from the ideal shape. The concept of “aerodynamic Troposkien,” which preserves zero bending moments in the presence of 1-P cyclic normal forces, is extended to account for gravity as well as inertial effects on blade shape. This concept is limited to unstalled flow and it is found to require unrealistic blade chord distributions near the tower when gravity effects are included. It is noted that both steady gravitational loads and nonsteady aerodynamic normal force loads will become increasingly important in achieving high-cycle fatigue life with larger-scale rotor blades. It is indicated that this achievement will depend primarily on configuring the rotor blades to minimize the cyclic flatwise bending moments and stresses due to the nonsteady normal forces.