Steady Crosswind Research Articles

Effects of Crosswind on Pantograph–Catenary Wear Using Nonlinear Multibody System Dynamic Algorithms

In this study, a multibody system (MBS) computational framework is developed to determine the exact location of the contact point and wear prediction resulting from the pantograph–catenary interaction. The railroad vehicle models in the MBS computational framework comprise rigid-body railroad vehicles, rigid-body pantograph systems, and flexible catenary systems. To avoid incremental rotation, the nonlinear finite element absolute nodal coordinate formulation is used to model a flexible catenary system in the MBS computational framework. To avoid co-simulation processes, the rigid-body railroad vehicle and the pantograph and flexible catenary systems were integrated into the MBS algorithms. The pantograph–catenary interaction is modeled using an elastic contact formulation developed to include the effect of pantograph–catenary separation and sliding contact. The proposed MBS approach evaluates the location of the contact point, contact force, and normal wear rate (NWR) from the mechanical and electrical contributions. This investigation considers the vibration caused by a crosswind scenario and determines the numerical result in the case of a steady crosswind scenario. The steady crosswind scenario contains the advantage of pantograph–catenary aerodynamic design, and the vibration of the catenary system remains significant after the excitation of a steady crosswind. In the case of a steady crosswind, the higher value of the steady crosswind effect significantly increases the mean contact force and the NWR from the mechanical contribution. After crosswind load disturbances, the mean contact force decreases, but the standard deviation of the contact force increases. Therefore, the NWR from the electrical contribution increases significantly. However, the total NWR increases with the crosswind velocity.

Optimization of aerodynamic drag reduction for vehicles with non-smooth surfaces and research on aerodynamic characteristics under crosswind

Energy consumption and environmental pollution problems have become increasingly prominent in China. The drag reduction of vehicles is an effective method to improve the fuel economy of cars and reduce greenhouse emissions. In this paper, based on the MIRA squareback model, the influence of the shapes, arrangements, layout positions, and dimensions of the non-smooth units on the aerodynamic characteristics of vehicles are investigated through the computational fluid dynamics (CFD) method. The depth, longitudinal spacing, and horizontal spacing are taken as the design variables and the aerodynamic drag coefficient is used as the optimization objective. The optimal Latin hypercube experimental design method is adopted to select sample points, and the response values of each experiment sample point are calculated through the integrated platform in Isight software. According to the response values, the Kriging approximation model is built and validated. Furthermore, the multi-island genetic algorithm is applied to optimize the dimensions of pit non-smooth units. The aerodynamic characteristics of the smooth surface model and the optimized non-smooth surface model under steady crosswind are conducted using numerical simulation. The findings obtained from the investigation will provide a certain reference for the application of non-smooth units in the field of automobiles.

Analysis of the Aerodynamic Characteristics of Small-Sized Car Vehicles under the Influence of Steady Crosswind

The crosswind is one of the factors that can lead to a car accident. Crosswind is defined as a side force that causes a vehicle to become unstable and deviate from its desired path. This article focuses on evaluating the flow behaviour and aerodynamic loads that affect vehicle stability when driving in a steady crosswind. In this study, a numerical approach is used with the ANSYS Fluent software as a platform to run the simulation. In this research, the crosswind flow angle (Ψ) is varied from 0° to 90°. The incompressible flow surrounding the vehicle is solved using the Reynolds-Averaged Navier-Stokes (RANS) equations in conjunctions with the k-ε turbulence model. The Reynolds number is utilized depending on the velocity of the vehicle which are 2.8×106 for high Reynolds number and 7.2×105 for low Reynolds number respectively. According to the findings, the crosswind has a significant quantitative and qualitative impact on aerodynamics. In terms of aerodynamic load, the side coefficient (Cs) increases as the crosswind yaw angle increases. When the crosswind yaw angle reaches 60°, there is a significant drop, but it remains almost constant when the crosswind yaw angle reaches 90°. In terms of flow structure, as the crosswind yaw angle increases, the vortex formation on the leeward region expands, increasing the vehicle stability imbalance. Finally, there is no significant difference in the quantitative aerodynamic characteristics of high and low Reynolds numbers.

Deflector effect on flow behavior and drag of an Ahmed body under crosswind conditions

This study investigates the effect of a deflector on Ahmed model drag and the flow on the slant during steady crosswind conditions by experimental methods at a based-height Reynolds number of 2.45 × 105. The length deflector is 0.09 times the length of the slant. The deflector was fixed at the leading edge of the slant with an upward angle of 5° to the horizontal axis. Force, pressure, and global skin-friction measurements were conducted to understand the relation between drag, pressure distribution, and flow fields on the slant surface. The results showed that the deflector reduces aerodynamic drag at low yaw angles. This result is due to the breakdown structure of longitudinal vortexes and the separation bubble, which leads to fully separated flow on the leading edge of the slant. However, at yaw angles above 8°, a large reversed flow region forms on the slant and the drag of the model increases. A similar flow structure on the slant is observed for yaw angles of 12° and 15°. Conversely, the model lift is reduced with the deflector at all yaw angles tested. Detailed pressure distribution and complex flow structure on the slant provide insight in this study.

Drag reduction mechanisms on a generic square-back vehicle using an optimised yaw-insensitive base cavity

Regulations on global greenhouse gas emission are driving the development of more energy-efficient passenger vehicles. One of the key factors influencing energy consumption is the aerodynamic drag where a large portion of the drag is associated with the base wake. Environmental conditions such as wind can increase the drag associated with the separated base flow. This paper investigates an optimised yaw-insensitive base cavity on a square-back vehicle in steady crosswind. The test object is a simplified model scale bluff body, the Windsor geometry, with wheels. The model is tested experimentally with a straight cavity and a tapered cavity. The taper angles have been optimised numerically to improve the robustness to side wind in relation to drag. Base pressures and tomographic Particle Image Velocimetry of the full wake were measured in the wind tunnel. The results indicate that a cavity decreases the crossflow within the wake, increasing base pressure, therefore lowering drag. The additional optimised cavity tapering further reduces crossflow and results in a smaller wake with less losses. The overall wake unsteadiness is reduced by the cavity by minimising mixing in the shear layers as well as dampening wake motion. However, the coherent wake motions, indicative of a balanced wake, are increased by the investigated cavities.Graphical abstract

Aerodynamic Characterization of a Full-Scale Compact Car Exposed to Transient Crosswind

The transient surface pressure over a full-scale, operational compact automotive vehicle—a Volkswagen Golf 7—exposed to transient crosswinds with relative yaw angles of β = 22-45° has been characterized. Experiments were performed at the BMW side-wind facility in Aschheim, Germany. Measurements of the incoming flow in front of the car were taken with eleven five-hole dynamic pressure probes, and separately, time-resolved surface pressure measurements at 188 locations were performed. Unsteady characteristics (not able to be identified in quasi-steady modelling) have been identified: the flow in separated regions on the vehicle’s leeward side takes longer to develop than at the windward side, and spatially, the vehicle experiences local crosswind as it gradually enters the crosswind. The total effects of these localized unsteady pressure characteristics have also been predicted to affect the vehicle globally, with the evaluation of the transient forces and moments—through pressure integration—exhibiting unsteady characteristics of overshoots, undershoots, and temporal lag; relative to steady crosswind. These results provide new insight into both the characteristics and the causes of the unsteady crosswind response of a real, operational vehicle operating in real-world conditions. This insight can be used in the design of future vehicles to make them less sensitive to unsteady gusts. Further these results can be used to develop and validate numerical and reduced-scale experimental methods that can test and assess new vehicle geometry designs during the early stages of vehicle development.

Aerodynamic drag improvements on a square-back vehicle at yaw using a tapered cavity and asymmetric flaps

Emissions of greenhouse gasses from passenger vehicles is a concern globally. One of the factors that influence the vehicles energy consumption is the aerodynamic drag, continuing to be an active topic of interest. This work investigates the vehicle wake in relation to aerodynamic drag in steady crosswind conditions.The vehicle used is a modified version of the generic Windsor geometry with wheels and a rearward-facing base cavity with nine angled surfaces, or flaps, distributed at the trailing edge of the cavity along the roof and sides. A surrogate model-based optimisation algorithm was used to minimise the drag coefficient by optimising the angle of each flap individually. The experiments were performed in the Loughborough University Large Wind Tunnel. The time-averaged and unsteady results of both the base pressures and tomographic Particle Image Velocimetry indicate that the optimised flap angles improve drag primarily by altering the wake balance. This is achieved by reducing the strength of a large leeward side vortex, reducing the crossflow within the wake.

Numerical investigation for the influence of the car underbody on aerodynamic force and flow structure evolution in crosswind

To investigate the aerodynamic behavior of underbody structure in crosswind conditions, two numerical simulation models have been developed by using computational fluid dynamics method. First, to validate the accuracy of these models, the wind tunnel experiment of model with simplified flat underbody has been designed. The computationally predicted results of realizable k-e model show consistency with experimental data, and the correlation deviation of aerodynamic force is less than 10%. By using such model, the aerodynamic force and flow field of car under steady crosswind are simulated using underbody structure, and the influence on the aerodynamic characteristic has been analyzed. It can be found that the aerodynamic force increased significantly under different yaw angle. The physical mechanism response has been clearly shown by investigating the flow field around car body by vortices visualization technique. The results of this study can be served as a suggestion for studying the vehicle stability of high-speed under crosswind.

Experimental investigation of the flow around a simplified ground vehicle under effects of the steady crosswind

Crosswinds which stem from on-road flow conditions can deteriorate a ground vehicle's driving performance. In spite of the numerous studies investigating aerodynamics of the ground vehicles in the previous literature, there is still a need for thorough understanding of the underlying flow phenomena related to crosswind sensitivity of the ground vehicles. Therefore, the present study is aimed to investigate characteristics of the flow features around the ground vehicles under steady crosswind conditions within a range of yaw angles 0° ≤ β ≤ 15° using the Ahmed vehicle model with rear slant angles of α = 25° and 35°. Throughout the investigations, flow visualizations using dye injection technique and velocity measurements using particle image velocimetry PIV technique are conducted. The Reynolds number of the flow which is based on the free stream flow velocity U = 200 mm/s and height of the model H = 72 mm is ReH = 1.4 × 104. Results are presented in terms of time-averaged vorticity <ω> contours and streamline <ψ> patterns together with velocity magnitude ((<u>2+<w>2)1/2/U) of the flow fields. Additionally, turbulence quantities such as Reynolds stresses <u'w'>/U2 and turbulent kinetic energy TKE are presented and discussed in details. Results of the present study show that characteristics of the flow features in the near wake region downstream of the Ahmed model are very sensitive to the effects of the crosswind.

Simplified model of offshore Airborne Wind Energy Converters

Airborne Wind Energy Converters (AWECs) are promising devices that, thanks to tethered airborne systems, are able to harvest energy of winds blowing at an altitude which is not reachable by traditional wind turbines. This paper is meant to provide an analysis and a preliminary evaluation of an AWEC installed on a floating offshore platform. A minimum complexity dynamic model is developed including a moored heaving platform coupled with the dynamics of an AWEC in steady crosswind flight. A numerical case study is presented through the analysis of different geometrical sizes for the platform and for the airborne components. The results show that offshore AWECs are theoretically viable and they may also be more efficient than grounded devices by taking advantage of a small amount of additionally harvested power from ocean waves.

Simulation Research on Aerodynamic Characteristics of Vehicle under Steady Crosswind Based on XFlow

The aerodynamic characteristics of vehicle play a crucial role in steering stability, comfort and safety of vehicle. The crosswind will affect the aerodynamic characteristics of vehicle. In this paper, the aerodynamic characteristics of ASMO model under steady crosswind is simulated by XFlow software, and the changes of aerodynamic characteristics under different steady crosswind are analyzed. It turned out that the asymmetry of wake flow field is enhanced with the increasing of crosswind, and the body surface pressure of windward is amplified, the six components of aerodynamic coefficient are also increased. It is found that the vehicle aerodynamic characteristics changed obviously under steady crosswind.

Aerodynamic Simulation of Road Vehicle in Steady Crosswind

Because crosswind affects drivers to control their vehicles safely, the research on flow characteristics in automotive crosswind has a great significance to improve the crosswind stability of the vehicle. By the steady state numerical simulation method, the aerodynamic characteristics of external flow field of Ahmed body in crosswind was investigated. The Ahmed body with 25° slant angle is built in UG NX. The external flow field of the Ahmed body in the wind direction of 0°, 15º, 30° angle is simulated in XFlow software. According to the map of the pressure and velocity distribution, the flow field both before and after, as well as left and right has significant change as the wind direction angle increased, and the trail turbulence intensity also changes. The changes of aerodynamic force and moment affect the driving stability of a motor vehicle.

Shape influence on mean forces applied on a ground vehicle under steady cross-wind

In this paper the flow around a vehicle under constant cross-wind is studied. The influence of shape changes on aerodynamic forces and moments as well as on flow structures is studied experimentally in a wind-tunnel. Tests are run at a flow velocity of 40 m/s on a 1/5th model of a mini-van type vehicle, which is yawed to an angle of − 30 ∘ . It is shown that small variations of the A-pillar radius have an important effect on the side-force and yawing moment. A link is made to the A-pillar vortex and its changes in intensity. The use of wind-tunnels represents a quite high budget in aerodynamic development. It is therefore quite important to limit the use of sophisticated measurement techniques to a strict minimum. In this context, the PIV-plane position proposed in this paper yields useful additional information to analyse the impact of form changes for example on cars under side-wind influence.

Energy conversion efficiency of the pumping kite wind generator

This paper is devoted to analytical modelling and numerical simulation of the so-called pumping kite wind generator whose operating principle is to mechanically drive a groundbased electric generator using tethered kites. On the basis of the refined crosswind motion law, the mathematical model of steady crosswind motion of the tethered kite is constructed. Necessary conditions for optimality of the mean mechanical power functional are derived. Optimal control of the tether length rate is studied for the cases of open-loop and closed-loop figure-of-eight trajectories. The performance coefficient of the pumping kite wind generator is introduced. Simple formulas for the mechanical power output are obtained.

Effect of Side Wind on a Simplified Car Model: Experimental and Numerical Analysis

A prior analysis of the effect of steady cross wind on full size cars or models must be conducted when dealing with transient cross wind gust effects on automobiles. The experimental and numerical tests presented in this paper are performed on the Willy square-back test model. This model is realistic compared with a van-type vehicle; its plane underbody surface is parallel to the ground, and separations are limited to the base for moderated yaw angles. Experiments were carried out in the semi-open test section at the Conservatoire National des Arts et Métiers, and computations were performed at the Ecole Centrale de Nantes (ECN). The ISIS-CFD flow solver, developed by the CFD Department of the Fluid Mechanics Laboratory of ECN, used the incompressible unsteady Reynolds-averaged Navier–Stokes equations. In this paper, the results of experiments obtained at a Reynolds number of 0.9×106 are compared with numerical data at the same Reynolds number for steady flows. In both the experiments and numerical results, the yaw angle varies from 0 deg to 30 deg. The comparison between experimental and numerical results obtained for aerodynamic forces, wall pressures, and total pressure maps shows that the unsteady ISIS-CFD solver correctly reflects the physics of steady three-dimensional separated flows around bluff bodies. This encouraging result allows us to move to a second step dealing with the analysis of unsteady separated flows around the Willy model.

Nonlinear free vibrations of coupled spans of overhead transmission lines

The weakly nonlinear, freely vibrating motion of a system of coupled spans of suspended overhead transmission lines is studied. It is shown that the natural vibration is the gravity mode, of which the tension component vanishes in the first harmonic. The problem originates from a study of the phenomenon of galloping, which is a high-amplitude periodic oscillation of overhead transmission lines due to steady crosswind. Particular attention is given to an intermodal resonance, which may be interesting for galloping control.

Time-dependent geometrical optics

The basic relations of geometrical optics for the case of an isotropic, time-dependent medium are derived from Fermat’s principle. The time-dependent theory is applied by discussing the Debye-Sears effect and the frequency fluctuations in a plane light wave induced by atmospheric turbulence and a steady cross wind. In the former case it is shown that the Brillouin scattering relation Δω = VΔk holds in the geometrical optics limit where V is the sound velocity, while in the latter case we find, using a method due to Tatarski, that the fluctuations in frequency are of the order of a few kilohertz under the most extreme conditions of turbulence, wind speed, and range. The intensity law of geometrical optics, Iσ = constant, is generalized to read Iσ/ν2 = constant, where ν is the frequency of the light wave.

Chimney plumes in neutral and stable surroundings

A theoretical study of the rise of turbulent smoke plumes in a steady cross-wind and a density-stratified atmosphere is presented. The theory is based on the analogy between the rise of a plume and the rise of turbulent, two-dimensional vortex-pairs. Conservation laws for volume, buoyancy and energy, and a hypothesis of self-similarity are used. The theory proposed predicts that the rise of a buoyancy-dominated smoke plume in a homogeneous atmosphere is proportional to the 2 3 power of its lateral distance from the stack. This is in agreement with previously proposed theories, such as by F ay et al. (1969), and S Slawsdon and C sanady (1967). When the plume rises in a stably density-stratified atmosphere, it will rise initially according to the 2 3 power law, then level off and finally fall back. According to the analysis presented herein, the maximum plume rise in such cases is proportional to the cube root of the ratio of a buoyancy parameter, G (which is a dimensionless measure of the plume buoyancy flux, F), and the atmospheric stratification parameter, S; the lateral distance downwind from the stack at which this maximum is reached is proportional to the square root of the same ratio. Comparisons are made between theory and available full scale data, showing generally good agreement.

The round turbulent jet in a cross-wind

The flow of a jet directed normal to a uniform, steady cross-wind is considered. Experimental results show that for various jet strengths, the position of the jet in space, when stretched by the ratio of jet to cross-wind momenta, is described by a single function. Exceptions exist at very low velocity ratios where a shift of the potential core is evident. A natural system of axes is used to define important directions of the flow. The integrated equation of motion along the primary jet flow direction is made dimensionless after the general method of Morton (1961) and a virtual source is defined for the flow. It is shown that a single functional behaviour of the axial jet velocity exists for various velocity ratios if the jet is considered to originate from this source. Lateral velocity profiles show a similarity when scaled by appropriate lengths and velocities but true self-preservation is not attained.