Crosswind Conditions Research Articles

Identification of wake vortices using a simplified automobile model under parallel running and crosswind conditions

Previous studies have revealed that the change in aerodynamic drag on a test automobile under a parallel running condition is mainly because of the pressure effect, which is caused by the pressure field of the parallel running vehicle, and the effect of the change in wind direction caused by the parallel running vehicle. Apart from the drag change, which can be estimated by assuming a uniform crosswind, the change in wind direction has other effects. In this study, to clarify the other effects, the differences in the wake vortices associated with the change in drag between parallel running and uniform crosswind conditions were identified from the numerical simulation results. The surface pressure on the back excluding the pressure effect under the parallel running condition was lower on the opening side than that under the uniform crosswind condition. In addition, the wake vortices near the region of low surface pressure and their related vortices were focused. Visualizing the flows related to these vortices indicates that the non-uniformity of the flow along the upstream side and the strengthening of the entrainment at the rear end owing to the interference affect the change in the drag in the parallel running condition compared with the uniform crosswind condition. These results are useful for developing control methods to suppress the increase in drag in the parallel running condition.

A field study on the aerodynamics of freight trains with different stacking configurations

A full-scale 48-foot shipping container was instrumented with surface pressure taps and loaded onto a number of single- and double-stacked container freight trains. Surface pressure data enabled the container pressure drag coefficient to be evaluated for a range of different train loading configurations, container positions along the train, and atmospheric wind conditions. Field-based measurements show that for low and high crosswind conditions surface pressure distributions measured on the front face of the instrumented container are in good agreement with those reported in past studies. However, the magnitude of the pressure drag coefficient was found to be typically 50% lower for all loading cases analysed compared with previous seemingly analogous wind-tunnel and numerical investigations. For high crosswind conditions, the drag coefficient was found to increase and correlated well with the level of asymmetry observed in the measured pressure distributions. This was true for all cases regardless of the position along the length of the train. In the absence of direct information of the incident free-stream wind conditions, the level of asymmetry in the pressure distributions was found to provide a viable indirect method for assessing the impact that crosswinds have on the aerodynamic drag of freight trains.

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.

Effects of wind-rain coupling on the aerodynamic characteristics of a high-speed train

Simultaneous effect of crosswind and rainfall on railway vehicles has raised concern lately as it threatens the operational safety. In this study, the wind-rain coupling effects on the train aerodynamics have been systematically investigated by means of Euler-Lagrangian approach. The aerodynamic computational model is established based on non-spherical raindrops, and model verification is conducted with the aid of existing measurement results. The flow features as well as the train aerodynamic coefficients under wind-rain environments are systematically studied. The results show that, the mass concentration of raindrops around a train increases with rainfall intensity. The aerodynamic coefficients show linear relationship with the increase of rainfall intensity. Unlike that of a crosswind condition, train aerodynamic coefficients exposed to combined wind and rain are dependent not only on train shape and yaw angles, but also on resultant wind velocity and rainfall intensity. The formulae for predicting the aerodynamic coefficients of the train operating in wind-rain environments are finally obtained in this paper.

Base wake dynamics and its influence on driving stability of passenger vehicles in crosswind

The unsteady flow around a travelling vehicle induces fluctuating aerodynamic loads. Automotive manufacturers usually set targets on the time-averaged lift forces to ensure good straight-line stability performance at high speeds. These targets are generally sufficient in preventing unstable vehicle designs. Yet, small changes in averaged values occasionally yield unexpectedly large differences in the stability performance, indicating that the changes in averaged normal loads cannot solely explain these differences. The unsteady aerodynamic effects on driving stability are, therefore, an interesting topic to study. The objective of the present work is to investigate the differences in wake dynamics and fluctuating aerodynamic loads for two variants of a roof spoiler on a sports utility vehicle: a baseline that was known to cause stability issues and an improved design which resolved them. The vehicle designs were investigated using accurate time-resolved CFD simulations for a set of crosswind conditions. The unsteady aerodynamic response was coupled to a vehicle dynamics model to analyse the resulting impact on driving stability. It was shown that in crosswinds the baseline spoiler, contrary to the improved spoiler, has bi-stable wake dynamics that induce lift force fluctuations at frequencies close to the 1st natural frequency of the rear suspension.

Unsteady Analysis of Aeroengine Intake Distortion Mechanisms: Vortex Dynamics in Crosswind Conditions

Abstract The formation of a ground vortex and its ingestion into an aero-engine intake under crosswind conditions play a significant role in the aerodynamic excitation of the fan. Using steady and unsteady numerical simulations, an analysis of the dynamics of several distortion features is presented. For a simplified intake at high crosswind velocities, there is a substantial movement of the ingested ground vortex at the aerodynamic interface plane (AIP). The ingested ground vortex follows a specific trajectory while varying both in size and strength. The transition from a periodic to an aperiodic regime of the intake distortion at the AIP occurs as the crosswind velocity is increased. Circumferential mode decomposition shows that the largest amplitude of the distortion occurs at the first circumferential mode, and the amplitudes of the higher modes decrease monotonically. Furthermore, the amplitude of the spatial harmonics is time-dependent, which may be an influential feature at the time of assessing fan forced response.

Numerical Simulation on Temperature and Moisture Fields Around Cooling Towers Used in Mine Ventilation System

For heat rejection, small air-cooling towers are widely used in mine ventilation systems. However, the thermal efficiency of the cooling towers can be significantly affected by their geometrical arrangement and crosswind conditions. In certain ambient conditions, heated air coming from an exit of one tower can flow to intakes of other towers, which leads to a reduction in the thermal efficiency of the entire ventilation system. The aim of this study was to investigate the influence of crosswind speed and tower spacing on the temperature and moisture content of intakes of cooling towers. For this purpose, a three-dimensional CFD model of the non-isothermal turbulent flow of moist air around cooling towers is proposed. The model is based on the Reynolds-averaged Navier–Stokes equations with a standard turbulence model which are supplemented by heat transfer and moisture transport equations. The investigation of the effects of the crosswind speed and the tower spacing was carried out for two cooling towers by multiparametric numerical simulation using the CFD model. It was shown that the upstream tower protects the downstream one from the effect of the crosswind. The increase in the crosswind speed causes a rise in temperature and moisture content at the intakes of the downstream tower. The increase in the tower spacing, in general, contributes to a decrease in air temperature at the intakes of the downstream tower. However, at low crosswind speed, the heat transfer at the intakes can rise with the tower spacing due to a reduction in the protection possibilities of the upstream tower. Results of the numerical simulation of airflow around three cooling towers indicated that the increase in the number of cooling towers contributes to a rise in temperature and moisture content at the intakes.

Experimental investigation of the burning characteristics of aviation fuel under atmospheric crosswind conditions

Pool fires caused by leaks of aviation fuels such as RP-5 can result in severe catastrophes. This problem is especially more pronounced in ships and oil tankers. Accordingly, investigation of wind-exposed pool fires is of great significance to the safety of ships. In the present study, an experimental platform was designed and constructed to study the evolutions of flame shape, burning rate, and downstream gas temperature in square aviation fuel pool fires exposed to crosswind. In this regard, different pool side lengths (D = 0.32–0.55 m) and crosswind speeds (V = 0–6.5 m/s) were analyzed. The obtained results show that as the wind speed increased, the flame length and flame tilt angle increased first and then stabilized, and the maximum values almost reached 2.5 m and 90°, respectively. Based on the force analysis, the normalized flame length (L/LV=0) and tangent of flame tilt angle (tanθ) can be expressed by the power function of Forde number (Fr). It is found that the burning rate grew steadily first, followed by a level-off value, and the maximum value is 0.0481kg/(m2.s). Accordingly, a piecewise function based on the boundary theory was proposed to estimate the burning rate. The performed analyses reveal that the downstream gas temperature increased first to a peak value (within 1000 °C) and then decreased. A modified exponential correlation of the decay of the downstream gas temperature (ΔT/ΔTpeak) with the fire distance (x/D') was developed in terms of the heat transfer balance.

Effects of crosswinds and tip configurations on the initial phase of wingtip vortex evolution

Wingtip vortex is the initial phase of aircraft wake flow that jeopardizes flight safety. Previous studies have focused on the effect of incidence angle on tip vortex flow; thus, investigations on tip vortex in the roll-up stage under crosswind conditions are limited. In the present study, two NACA0012 wings with different tip shapes (round and square) were numerically analyzed to explore the effects of wingtip configurations on tip vortex. In addition, the effects of crosswinds on wingtip vortex evolution were also investigated. It was found that sharp edges of the square wingtip generated a multi-vortex system, resulting in a larger turbulent wake vortex core radius. The lift and vortex strength of the square wingtip were 23% higher and only 12% stronger than those of the round wingtip, respectively. Furthermore, crosswinds changed both the pressure distribution and the vortex structure. Crosswinds made the flow field unstable; hence, upwind lower edge vortices of the square wingtip burst earlier and merged faster. Consequently, the tightness of the upwind vortex of the square wingtip increased, and the corresponding vortex strength was enhanced. The downwind vortex of the square wingtip was weakened by 2.7% under a crosswind velocity of 4 m/s, whereas the downwind tip vortex of the round wingtip was strengthened under the same conditions.

Flow Structure Investigation of a Truck under Crosswinds

This paper investigates the flow structures on the near- and far-wake of a 1/8th scaled simplified heavy vehicle model called Ground Transportation System (GTS) model using a steady-state Reynolds-averaged Navier-Stokes (RANS) with k-ω Shear Stress Transport (SST) turbulence model at Reynolds number (Re) of 1.6 × 106 and yaw angles (Ψ) = 0o-14o. The current CFD results have been validated using experimental data from the literature. Two crosswind conditions based on the crosswind incidence angle (β) are adopted; β < 90o is called crosswind, and β = 90o (perpendicular to the GTS side surface) is called pure crosswind. Vortex detection scheme based on Ω method and total pressure coefficient (Cpt) contours is used to visualize the wake structure. With Ψ, vortices on the GTS roof take birth as a result of pressure differences between the windward and leeward sides. These vortices grow in size as they travel downstream. The growth in size is related to the Helmholtz theorem of vorticity and Kelvin’s Circulation Theorem. The vortices merged at Z/W > -4 (Z/W = 0 is the GTS rear surface) downstream of the GTS for Ψ = 7.5o and 14o. The merged vortex dissipates at Z/W > -6 and Z/W > -8 for Ψ = 7.5o and 14o, respectively. In the pure crosswind condition, the merged vortex attaches to the ground due to the velocity difference between the freestream and the moving computational ground used in the present simulation. At Ψ = 14o, surface streamlines on the GTS surface show the creation of two co-rotating vortices on the windward roof. For the present Ψ, similar flow structures between the two crosswind conditions are shown. Initial results show that the aerodynamic crosswind stability of a truck is related to the spanwise pressure difference between the windward and leeward surfaces of the truck.

Aerodynamics of a short intake in crosswind

The next generation of turbofan aero-engines are likely to have an increase in fan diameter to reduce the specific thrust and increase the overall propulsive efficiency. More compact nacelles with possibly shorter intakes may be used to reduce weight and drag and achieve a net reduction of fuel consumption. For these compact nacelles a key consideration is the design of the short intake at the off-design conditions such as crosswind and high incidence operations. The close coupled interaction between a short intake and the fan at these off-design conditions is one of the key challenges. Previous work focused on the impact of short intake aerodynamics on the fan but there is a similar requirement to understand the impact of the fan on the viable short intake design space. This paper addresses the influence of the fan on the separation onset of the flow within a short intake under crosswind conditions. The effect of the fan on the separation characteristics of the intake boundary layer was considered both from a steady and an unsteady point of view. A hierarchy of fan computational models was used to separately assess the different aerodynamic contributions and to evaluate a net effect of the fan on the intake critical condition. Steady computational fluid dynamics analyses showed a notable positive effect of the fan on total pressure loss at post-separation conditions relative to a configuration without the fan. However, unsteady analyses revealed that fan unsteadiness has an adverse impact on the intake separation characteristics which reduces the intake critical conditions by about 15%. The main mechanisms behind the unsteady interaction were identified. Overall this work addresses, for the first time, the role of fan unsteadiness on the separation characteristics of the boundary layer within a short intake in crosswind.

The research on plume abatement and water saving of mechanical draft wet cooling tower based on the rectangle module

To realize plume abatement and water saving of mechanical draft wet cooling tower (MCT), a rectangular module with plume abatement and water saving performance is proposed in this study. The plume, water saving, and thermal performance of MCT under different the environmental parameters, circulating water parameters, and crosswind conditions are analyzed. The result shows that, with the increase of relative humidity, circulating water temperature, and circulating water flow rate, the probability of plume generated increases. When the dry-bulb temperature increases, the probability of plume generated decreases. With the crosswind velocity increasing, the probability of plume generated decreases under the crosswind angle of 0°, and that increases under the crosswind angle of 90° and 180°. After using the rectangular module, the variation range of water saving amount is from 0.018 to 0.046 L/min, and the water saving rate is 4.3% ⁓ 16.2%. The plume can be abated, and the outlet water temperature is increased by about 2 °C in this study.

Effects of different wind directions on soil erosion and nitrogen loss processes under simulated wind-driven rain

“Wind-driven rain” is the main form of natural rainfall. Wind affects runoff, soil, and nutrient loss processes on slopes by changing rainfall characteristics. Wind direction is one of the main factors affecting the falling trajectory of raindrops, raindrop splash angle, and direction of the rainfall erosivity force. However, existing research on soil displacement and nitrogen loss driven by different wind directions and rainfall is still lacking. Based on a simulated wind-driven rain experiment, this study explored the influence of different wind directions (leeward, windward, and crosswind) on runoff, sediment yield, and nitrogen loss on slopes. The results showed that wind direction had a significant influence on runoff, sediment yield, and nitrogen loss in both runoff and sediment. The influence of wind direction on the slope runoff and sediment yield rates was leeward > crosswind > windless > windward. Compared with windless rainfall, the average runoff rate and sediment yield rate under leeward rainfall and crosswind rainfall increased by 6.17%–11.56% and 37.75%–41.58%, and 1.80%–2.40% and 13.31%–18.12%, respectively, while under windward rainfall, they decreased by 5.13%–7.38% and 7.86%–13.02%, respectively. Hydrodynamic parameters are physical parameters that characterize the process of sand-bearing shallow flow acting on surface soil particles. The mean flow velocity and unit stream power affected by the wind direction were ranked: leeward > windless > crosswind > windward. The mean flow velocity and unit stream power under leeward conditions were both 1.31 times those under windless conditions, indicating that leeward wind strengthened the erosion effect of the slope flow on the soil. The mean flow velocity and unit stream power caused by different wind directions may be the main reasons for soil erosion processes. The average nitrogen loss rate in runoff was ranked: windward > crosswind > windless > leeward. The law of nitrogen loss rate in the sediment is consistent with the regularity of the sediment yield rate in all wind directions, which increased respectively by 60.18%–163.86% and 19.39%–69.57% under leeward and crosswind conditions, respectively, and decreased by 10.23%–25.15% under windward conditions when compared to windless treatment. Therefore, when the intensity of wind-driven rain is constant, the impact of wind direction on slope runoff, sediment yield, and nitrogen loss is uncertain and may be either positive or negative. The angle between the raindrop movement direction and the runoff flow direction on the slope changes owing to the influence of different wind directions. This leads to changes in the slope infiltration rate, hydrological characteristics, and soil crusting process, and is one of the main reasons for the difference in soil erosion and nutrient loss rates.

Numerical Simulation of the Smoke Recirculation Behavior in Street Canyons with Different Aspect Ratios and Cross-Wind Conditions.

This study investigated smoke dispersion inside a street canyon in a series of numerical simulations. The building height and street width as well as the cross-wind velocity were changed during the simulation, and the smoke recirculation behavior inside the canyon is presented and discussed. The results show that the smoke recirculation behavior could be distinguished into two different stages, i.e., the “fully recirculation stage” and “semi recirculation stage”, which is strongly determined by the canyon aspect ratio (the building height divided by street width). It was found that the critical wind velocity at which the smoke recirculation would take place was almost constant for an ideal street canyon with an aspect ratio of 1; however, this velocity was decreased with increasing building height or decreasing street width, indicating a much more dangerous circumstance when the aspect ratio is greater. Finally, a new piecewise function is proposed for the critical smoke recirculation velocity for all cases, which can provide some theoretical basis for building designs and emergency rescue for human beings inside the street canyon.

Numerical study of the dynamic response of the natural draft dry cooling tower under crosswind condition

The turbulences from the cooling system have a significant impact on the thermal efficiency and safety operation of the power plant. The crosswind effect, which is one of the most frequent turbulence from the natural draft cooling system, is studied using a three-dimensional transient CFD model. Two common unsteady fluctuations: the emergence of the crosswind and the disappearance of the crosswind are simulated with different crosswind speeds. The changing rules of the aerodynamic characteristics and the heat transfer performance of the cooling tower under transients are presented and their mechanisms are discussed. The results show that the characteristic parameters of the cooling tower vary significantly with the turbulence of the crosswind. In terms of the response period, it is easier for the tower to resist the disturbance of the crosswind with lower speed. Due to the difference in the air flow driving force, the dynamic response of the cooling tower to crosswind emergence and disappearance is not mirrored. For the cooling tower experiencing minor crosswind speed changes, the response periods of the wind disappearing cases are longer than that of wind emerging. Whereas for the cooling tower experiencing major crosswind speed changes, the response periods of wind emerging cases are longer.

Drag reduction of a square-back bluff body under constant cross-wind conditions using asymmetric shear layer forcing

Highly resolved computations using Delayed Detached Eddy Simulations (DDES) of a canonical Windsor body are carried out. The flow around the car model, which is investigated imposing different yaw angles (up to 10°), is perturbed via a small square cylinder. This control element, whose length covers the whole height of the car model, is positioned at different streamwise locations on the windward face of the model. Depending on the location of the cylinder and the initial yaw angle of the model, drag increase or decrease up to 8% are observed. This sensitivity of the drag to the streamwise location of the cylinder is connected with the relative position of the flow reattachment on the side of the model after separation, which is caused by the cylinder. In the drag-optimal case where the flow reattachment occurs just at the streamwise location of the base, the asymmetry of the wake is reduced and the pressure in the wake is globally recovered. The flow mechanisms by which the drag reduction occur are twofold: (i) the flow is deviated inwards by the in-wash induced by the flow reattachment at the trailing-edge, thus acting as an inward-oriented flap, and (ii) the windward shear layer is forced by the turbulent field developing along the separated region of the perturbing cylinder.

Nonlinear aeroelastic analysis of a damped elastica-aerofoil system

This work formulates a comprehensive model of a nonlinear aeroelastic system developed for the analysis of complex aeroelastic phenomena related to structural and aerodynamic nonlinearities. The system is formulated as a two-dimensional cantilevered elastica with a rigid airfoil section firmly attached at its tip undergoing large displacements in the crosswind conditions. The system can demonstrate a wide range of domain specific as well as coupled nonlinear phenomena. The structural model is developed by means of the Rayleigh–Ritz approach, with shape functions discretizing both vertical and horizontal displacements and Lagrangian multipliers enforcing inextensibility. Damping is modeled based on a non-local strain-based mechanism in the Kelvin–Voigt arrangement. The resulting structural model is examined through studying the behavior under a follower load and with a tip-attached tendon under tension to study the shape convergence properties and the alignment of the results with known characteristics in the literature. The ONERA dynamic stall model is used to model the aerodynamics of the problem to accurately capture post-stall behavior at large deformations. The LCO responses of the aeroelastic problem are evaluated through time-marched simulations, and the combined airspeed–damping interactions are studied in this manner.

Stall flutter instabilities on the IEA-15 reference wind turbine in idling conditions: code-to-code comparisons and physical analyses

The present study investigates stall-induced vibrations on a IEA-15-RWT wind turbine blade. At standstill and under specific strong crosswind conditions, simulations using the codes OpenFAST and DeepLines WindTM exhibit large-amplitude vibrations. Results of both codes are first compared, showing an overall good agreement. Then, the influence of the wind misalignment angle is assessed as well as the choice of aerodynamic polar datasets. Vibrations are observed within two well-marked angular sectors, and the high sensitivity of the phenomenon to the choice of polars is highlighted. Finally, a simplified model based on a spring-mounted aeroelastic section is used to help identifying which type of unstable aeroelastic modes may be at play.

Identification of wake vortices in a simplified car model during significant aerodynamic drag increase under crosswind conditions

Identification of wake vortices in a simplified car model during significant aerodynamic drag increase under crosswind conditions

Effects of Curved Wind Barrier on the Aerodynamic Characteristics of a Train–Bridge System and Its Static Wind Load

Wind barriers are important measures that guarantee the running safety of high-speed trains under crosswind conditions, however, they can change the aerodynamic coefficients of a train–bridge system and the distribution of the flow field around a train and bridge, and studies have often ignored the static wind load characteristics of wind barriers. In this paper, the effects of height and porosity on the curved and vertical fence-type wind barriers on the aerodynamic characteristics of a train–bridge system are investigated by using numerical simulation and wind tunnel test methods. The static wind loads of the two types of wind barriers are analyzed by comparing the drag coefficients and the surface wind pressure distributions. The results show that, compared with the vertical wind barrier, the curved wind barrier can reduce the drag force and moment of a train while reducing the impact of the aerodynamic forces on a bridge. The static wind load of the curved wind barrier is less than that of the vertical wind barrier, when a train is on the windward side of a bridge, the drag coefficient of the curved wind barrier is only about 35% of that of the vertical wind barrier.