Effect Of Crosswind Research Articles

EFFECTS OF CROSSWIND ON THE DRAG OF MEDIUM SPEED TRAINS

Aerodynamic research on medium-speed trains is trying to map the flow of fluid around trains. The train model testing is conducted to study Cd values experimentally using a closed-loop wind tunnel at the Balai Besar Teknologi Aerodinamika, Aeroelastika, dan Aeroakustika. In addition to the experimental method, the computational method can be used to validate the experimental results, map the fluid flow around the train model, and calculate Cd values. The computational results of Cd obtained using ANSYS are compared against Cd values from wind tunnel tests. Further analysis using the ANSYS program with variations in the yaw angle can predict crosswind effects on the train model. It is found that vortices are formed around the train body, and modifying the head shape and adding fairing increases Cd values.

Capability analysis of computational fluid dynamics models in wind shield study on Queensferry Crossing, Scotland

Bridge aerodynamic studies are essential in ensuring the safety and acceptable performance of long-span bridges vulnerable to the effects of cross-winds. Aerodynamic studies were traditionally carried out in wind tunnel facilities, but there are now greater opportunities for using computational fluid dynamics (CFD) modelling. Few three-dimensional (3D) aerodynamic simulations of lightweight vehicles on bridges exist, but limited validation and verification work has been carried out. In the study reported in this paper, 3D CFD models were developed for Queensferry Crossing – a cable-stayed bridge in Scotland – containing wind shields and sample vehicles. The models considered the wind effects from a range of yaw wind angles and subsequently determined the aerodynamic coefficients of vehicles. The models were verified by means of a mesh sensitivity study, a domain sensitivity study and comparisons with wind tunnel tests. The models were then validated using the same modelling process but with a different type of wind shield and again comparing the results with wind tunnel test data for the same configuration. The results showed that CFD modelling can determine aerodynamic coefficients to a level of accuracy similar to that of wind tunnel tests.

Structural optimization to reduce the environmental crosswind negative influence on the performance of a solar chimney power plant system

The solar chimney power plant system (SCPPS) is a clean and pollution-free facility for generating electric power. To further improve the heat collection efficiency of SCPPS, reduce the influence of external unsteady environment crosswind, a bank of transparent baffles was proposed to be installed at the entrance of transparent cover in SCPPS. Combined with the discrete ordinates (DO) radiation model and solar load model in Fluent, the latitude and longitude of Hohhot and actual weather parameters were taken as boundary conditions. Numerical simulation of SCPPS model with external air domain and different number of baffles were carried out. The accuracy of numerical simulation was verified by experimental results. There are three different types of models discussed here: the SCPPS with no baffle, the SCPPS with one baffle, the SCPPS with two baffles. Under the condition of different baffle number, the distribution of temperature, velocity, pressure, turbulence and heat collecting efficiency were given to determine the optimal baffle number. The results show that the average temperature of chimney inlet with one baffle and two baffles are 0.92% and 3.92% higher than that with no baffle, respectively; the average velocity of chimney inlet with one baffle and two baffles are 11.83% and 18.70% higher than that with no baffle, respectively; the average collector efficiency of one baffle and two baffles are 28.45% and 58.52% higher than that of without baffle, respectively. Compared with without baffle and one baffle, adding two baffles can more effectively reduce the heat loss of SCPPS in Hohhot under different environmental crosswind speeds, and alleviate the negative effects of environmental crosswind.

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.

Unsteady aerodynamic characteristics on trains exposed to strong wind and rain environment

Crosswind associated with rainfall is a common weather condition, which threatens the operational safety of trains. This paper focuses on an investigation of the effect of crosswind associated with rainfall on train aerodynamics. The methodologies for reproducing the turbulent wind speed and instantaneous rainfall intensity are first described, and the calculation method of unsteady aerodynamic forces of trains operating in a wind-rain environment is set up using the quasi-steady method and weighting function method. Then the CFD technology is used to obtain the aerodynamic load coefficients of a train exposed to a wind-rain environment, and the computational model is verified with the experimental results. Finally, the unsteady aerodynamic load time histories, as well as the corresponding statistical characteristics of the train are investigated. The results demonstrate that the aerodynamic load coefficient is a function of yaw angle, rainfall intensity and wind velocity relative to the train under wind-rain conditions. The aerodynamic loads approximately obey normal distribution both for the quasi-steady method and weighting function method. The mean values of aerodynamic loads obtained by the two methods are almost the same, whereas the standard deviations computed by the weighting function method are smaller than those computed by the quasi-steady method. The dimensionless standard deviations of aerodynamic loads increase with the rainfall intensity, and are approximately linearly related to the rainfall intensity. The wind velocity relative to the train also has an impact on the dimensionless standard deviations of aerodynamic loads, and the impact becomes more obvious when the rainfall intensity increases. The dimensionless standard deviations of the aerodynamic loads can be expressed as quadratic polynomial functions of yaw angle, rainfall intensity and wind velocity relative to the train.

Mitigating crosswind effect on high-speed trains by active blowing method: a comparative study

ABSTRACT To reduce the crosswind effect on high-speed trains, in this paper, by using the Improved Delayed Detached Eddy Simulation (IDDES) method and the SST turbulence model, a novel blowing measure is studied and compared by considering different positions of blowing slots on the train surface. The concerned blowing positions on the train surface include the top position (Top); windward side (WWS): the upper position (WU), middle position (WM), and lower position (WL); and leeward side (LWS): the upper position (LU), middle position (LM), and lower position (LL). The results show that in regard to the rolling moment coefficient around the leeward rail, CMx lee, the mitigation effect with LM for the head car is the largest, and the mitigation effect with WL for the middle car and tail car is superior to other cases. The corresponding drop percentages are 18.5%, 21.7%, and 30.8% for the head car, middle car, and tail car, respectively. The flow structures indicate that the blowing positions on the lower half of WWS and upper half of LWS would form a protective air gap to weaken the impact of coming flows and delay the vortex separation on LWS, and thus the train aerodynamic performance is improved.

CFD Analysis of the Flow around Simplified Next-Generation Train Subjected to Crosswinds at Low Yaw Angles

The development of Next-Generation Trains (NGT) made of lightweight materials is a challenging task for the transport industry. It reduces axle loads, which saves money by lowering rail track maintenance costs and the amount of energy needed to drive vehicles. However, the increasing speed and decreasing mass of high-speed trains, on the other hand, raises concerns about the effects of strong crosswinds on their aerodynamics and train stability. As a result, the purpose of this research is to investigate the unsteady flow structure around an NGT in crosswind using a Computational Fluid Dynamics (CFD) technique known as Unsteady Reynolds Averaged Navier-Stokes (URANS). Based on the height of the train model and the velocity, the Reynolds number for the simulation used was . The simulation run in four different crosswind angles: 5°, 10°, 15°, and 20°. The simulation results were compared with experimental results. The findings revealed that a larger yaw angle, which is primarily determined by the incoming wind velocity, can lead to higher flow separation and a more complex three-dimensional flow around the train. Additionally, when the wind angle is small, separation of flow and wakes is limited to the train's end; however, as the wind angle increases, separation of flow occurs from the train's upper and lower corners, indicating that the vortices formed as a result of the flow passing over the roof top and underbody. Finally, the study's findings will contribute to a better understanding of the flow characteristics around an NGT in crosswinds, which is simply impossible to achieve through full-scale testing due to the cost, resources, and accuracy.

Effect of crosswind and shroud mounting height on thrust characteristics of drone propeller

This study investigated the effects of crosswind and shroud mounting heights on the thrust characteristics of a shroud and a propeller for a drone using wind tunnel experiments. The shroud mounting height ht/hr was varied from 0 to 0.75 (with ht being the distance between the height of the top of a shroud and the height of the tips of the propeller and hr being the length of the inlet part of the shroud). Three kinds of shrouds were tested, and crosswind speeds of 0, 2, and 5 m/s were set in the wind tunnel. All required aerodynamic data were obtained using a 6-component balance. The results showed using an elliptical inlet shroud at a crosswind speed of 2 m/s provided the highest thrust at each shroud mounting height compared to other combinations of shrouds and crosswind speeds. In all shroud cases, as the ht/hr increased, the total thrust on the shroud and the propeller, the power output of the motor, and the efficiency of the propeller with a shroud generally increased. In contrast, the thrust on a propeller was independent of the ht/hr. Therefore, the thrust improvement from the shroud mounting is considered to be due to the increase in thrust on the shroud, which is caused by a decrease in pressure in the vicinity of the shroud inlet part.

Numerical study on water distribution of natural draft wet cooling towers under crosswind

In order to improve the thermal performance of natural draft wet cooling tower under crosswind, a three-dimensional numerical model for heat and mass transfer of cooling towers was established. The comparison with the design parameters of the cooling tower shows that this model satisfies the requirements of the thermal performance computation of cooling tower. According to the numerical calculation of the cooling tower and the analysis of the temperature, humidity and velocity field under various crosswinds velocities, a scheme of partition water distribution of cooling tower was proposed to deal with the effect of crosswind. Using this scheme, the influence of various spray water density ratio k on the thermal performance of cooling tower were researched, and the results show that the heat transfer performance of the cooling tower can be effectively improved under a certain comparing with uniform water distribution. When the cross wind speed is in the range of 2-6 m/s and this partition water distribution scheme is applied, maximum reduction of the outlet water temperature will reach 1.01K comparing with uniform water distribution.

Crosswind Effects on Truck Platoon and Cooperative Strategy to Counteract Crosswind

Crosswind Effects on Truck Platoon and Cooperative Strategy to Counteract Crosswind

Crosswind Effects on Current Collection Quality of Railway Pantograph–Catenary: A Case Study in Chengdu–Chongqing Passenger Special Line

As a common disturbance to the railway pantograph–catenary system, the crosswind usually deteriorates the current collection quality and threats to operational safety. The main topic of this article is to evaluate the effect of crosswind on the interaction performance of pantograph–catenary considering the aerodynamic forces acting on both the pantograph and catenary. The pantograph–catenary system of the Chengdu–Chongqing passenger special line is adopted as the analysis object. The absolute nodal coordinate formulation (ANCF) is employed to model the catenary. The numerical accuracy is validated via the comparison with the field measurement data collected from an inspection vehicle operating at 378 km/h. According to the quasi-steady theory, the wind load acting on the catenary is derived. Computational fluid dynamics (CFD) is employed to calculate the lift and drag forces acting on each component of the pantograph, which are used to derive the equivalent aerodynamic force that can be applied in the lumped-mass model. A special spatial grid is defined for the pantograph–catenary system to generate the fluctuating wind field based on the empirical spectrum. The simulation results indicate that the pantograph–catenary system of Chengdu–Chongqing passenger special railway has an acceptable performance with a crosswind speed of 20 m/s. However, when the crosswind increases up to 30 m/s, some contact force statistics exceed the safety threshold with a turbulence intensity of more than 17%. Through the analysis of the operational safety, it is found that the contact wire always works within the safety range of the pantograph head with a crosswind speed of 30 m/s. However, some safety issues can be seen from the maximum uplift of the pantograph head with a turbulence intensity of more than 21%.

A Novel Control Strategy of Crosswind Disturbance Compensation for Rack-Type Motor Driven Power Steering (R-MDPS) System

The wind suddenly blown to the side of the car (i.e, cross-wind effect) is considered as one of the major lateral disturbances, which causes the unstable motion of the vehicle and the persistent driving fatigue for the driver who tracks the desired travel path. In particular, a commercial vehicle having a large side area is greatly affected by this effect. Therefore, many related automotive/car manufacturers still wish to equip their Advanced Driving Assistant System (ADAS) with the crosswind disturbance compensation control system. Meanwhile, in recent advanced vehicle systems, a rack-type motor-driven power steering (R-MDPS) system is more widely used than a column-type MDPS (C-MDPS) due to the structure advantage and the effective steering assistance. Recognizing those two issues, this paper investigates a novel anti-control and estimation strategy of crosswind disturbance for the R-MDPS system of vehicles with non-negligible side surfaces. Specifically, an adaptive disturbance observer (D.O.B) has been proposed to estimate the crosswind effect. Furthermore, using optimal control theory, the compensation control system is designed to assist the driver in two possible situations. One is for when the driver continues to steer the vehicle under the effect of the crosswind, and the other is for when the driver temporarily loses steering control due to the effect. In addition, the control mode selection conditions between two controls are clearly presented to maximize the efficiency and performance of the proposed control system. Finally, the effectiveness of the proposed control system has been evaluated based on the Simulink/Carsim Co-simulation and HILS environments.

Flexible modeling of parafoil delivery system in wind environments

Wind disturbances usually affect the motion states and aerodynamic distributions of a parafoil, changing the dynamics of the delivery system and deteriorating the control accuracy. This paper establishes an accurate flexible dynamic model for a parafoil delivery system in wind environments. Combined with identified wind fields, an accurate aerodynamic model is established, using aerodynamic coefficients calculated by fluid–structure interaction simulations to ensure its validity under crosswind effects. Good agreement between results of simulations and experiments demonstrates the accuracy of the dynamic responses. The model can be applied to the research of precise control algorithms for real parafoil systems.

Influence of noise barrier and louver on ventilation and thermal performance of wet cooling towers under crosswind conditions

Aiming at the influence of noise barrier and louver on the thermal performance of wet cooling towers, a three-dimensional numerical model of wet cooling towers was established in this paper. Based on this model, the influence of the noise barrier and louver on ventilation and thermal performance was studied under crosswind conditions (crosswind velocity varies from 0 m/s to 10 m/s and crosswind direction α is 0°, 90°, 180°). To analyze the influence of noise barrier and louver on the air intake characteristics, the inlet air uniformity coefficient Cff and the effective inlet air velocity vave were defined. Simulation results manifested that the noise barrier increases the internal low wind speed area in the rain zone and the high water temperature area on the collecting basin surface. Compared with the original cooling tower, although the Cff increases, the vave and the cooling capacity contribution of the fillings zone CF decrease after installing the noise barrier, so the water temperature drop ΔTW decreases. Additionally, the louver can relieve the adverse effect of crosswind on thermal performance, and the Cff, vave, CF, and ΔTW all have an increasing trend under crosswind conditions after installing the louver. The louver can improve remarkably the thermal performance when the crosswind velocity is 6 m/s and α = 90°, and compared with the original cooling tower, the Cff, vave, CF, and ΔTW increase by 0.02, 1.33 m/s, 1.33%, 0.31 °C, respectively.

Experimental study on the effect of canyon cross wind on temperature distribution of buoyancy-induced smoke layer in tunnel fires

Abstract Experiments were conducted in a 1:20 arced tunnel model to investigate the effect of canyon cross wind on buoyancy-induced smoke flow characteristics of pool fires, involving smoke movement behaviour and longitudinal temperature distribution of smoke layer. The canyon wind speed, longitudinal fire location and fire size were varied. Results show that there are two special smoke behaviours with the fire source positioned at different flow field zones. When the fire source is positioned at the negative pressure zone, with increasing canyon wind speed, the smoke always exists upstream mainly due to the vortex, and the smoke temperature near the fire source increases first and then decreases. However, when the fire source is located in the transition zone and the unidirectional flow zone, there is no smoke appearing upstream with a certain canyon wind speed. Meanwhile, the smoke temperature near the fire sources are decreases with increasing canyon wind speed. The dimensionless temperature rise of the smoke layer ΔTs* along the longitudinal direction of the tunnel follows a good exponential decay. As the canyon wind speed increases, the longitudinal decay rate of ΔTs* decreases. The longitudinal decay rate of ΔTs* downstream of the fire is related to the fire location and canyon wind speed, and independent of the fire size. The empirical correlations for predicting the longitudinal decay of ΔTs* downstream of the fire are established. For a relatively large-scale fire, the longitudinal decay rate of ΔTs* upstream of the fire increases as the distance between the fire source and the upstream portal increases, especially for larger canyon wind speeds.

Investigation on heat exchanger arrangement in solar enhanced natural draft dry cooling towers under various crosswind conditions

Solar enhanced natural draft dry cooling tower (SENDDCT) is a novel heat rejection device for thermal power plant, which uses solar energy to reheat the air after the heat exchanger and therefore improves the ventilation of the tower for performance enhancement. This paper develops 3-D models to compare the effects of circular/sawtooth arrangements of heat exchanger on cooling performance of a 140 m high SENDDCT. The result shows that sawtooth arrangement can improve the ventilation and heat dissipation rate of SENDDCTs. Under no crosswind condition, the flow field distributions of sawtooth and circular arrangements are similar in the tower. The ventilation and heat dissipation rate of sawtooth arrangement increases by 34.0 % and 46.8 % respectively when compared with circular arrangement under no crosswind condition. Under crosswind condition, the flow field of sawtooth arrangement is less affected by crosswind than that of circular arrangement. The ventilation rate and heat dissipation rate of sawtooth arrangement increases by 38.5 % and 65.0 % respectively when compared with circular arrangement at crosswind speed of 3 m/s. This study verifies that the sawtooth arrangement can weaken the crosswind effect and improve the cooling performance of SENDDCT and provides guidance for the optimal arrangement of heat exchanger for the SENDDCT.

Experimental study on thermal stratification characteristics in tunnel fires under the effect of canyon cross wind

In order to investigate the thermal stratification characteristics induced by pool fire and canyon cross wind, a set of tests were carried out in a 1:20 model tunnel. Experimental parameters were the canyon wind speed, longitudinal fire location and fire size. Results show that the dimensionless smoke layer thickness h∗ (the ratio of smoke layer thickness to hydraulic diameter) downstream the fire generally increases with increasing canyon wind speed until reaching the maximum value, and h∗ of a smaller-scale fire is slightly greater than that of a larger-scale fire at most canyon wind speeds. However, h∗ value upstream the fire is almost between 0.2 and 0.3 (h∗ = 0 is not considered). The smoke stratification downstream the fire gradually worsens with increasing canyon wind speed and decreasing distance between the fire source and the upstream portal Df in the cases of 0.194 ≤ Df∗ < 1 (Df∗ represents the ratio of Df to the tunnel length), while the smoke stratification upstream the fire is always obvious unless there is no smoke. As Df increases, the critical Froude number for judging the smoke stratification status decreases first for 0 ≤ Df∗ < 0.028 and then increases for 0.028 ≤ Df∗ < 0.306, and tends to be a constant value for 0.306 ≤ Df∗ < 1.

Coupling vibration response analysis of wind-train-bridge system considering the train-induced wind effect

Considering the wind loads and track irregularity as external excitation, the wind-train-bridge dynamic analysis model considering the longitudinal freedom of train is established in the present study. In the model, the wind load of train-bridge system under the train-induced wind field and the combined wind field is obtained by employing Computational Fluid Dynamics (CFD) method. With the CRH2 high-speed train and a 10-span simply-supported box girder bridge as an example, the whole history of the train running on the bridge under the combined effect of train-induced wind and crosswind is simulated to analyze the dynamic response of the train-bridge system. In addition, the operational safety indicators of the train are evaluated. According to the obtained results, the dynamic response of vehicles and bridges increases with the train speed without the consideration of the crosswind. In the combined wind field, the train-induced wind exerts a greater impact on the dynamic response of the vehicle, but has a less influence on that of the bridge simultaneously. Moreover, the influence of wind velocity is greater than that of train speed. When the wind-train-bridge dynamic response analysis is carried out based on traditional methods, the calculated wind load of the train-bridge system is too high, making the calculated responses too large to be consistent with actual values.

Crosswind effects on a train-bridge system: wind tunnel tests with a moving vehicle

To better understand the aerodynamic characteristics of a train-bridge system under crosswind, an in-house experimental apparatus was developed in a wind tunnel at Central South University (CSU). The new facility consists of trains, a bridge, U-shaped slide rails, and positioning systems with winches. A wireless data acquisition system for pressure measurements was mounted within the train carriage to avoid any potential aerodynamic interference. A 1:25 scaled model of CRH2 running over a simply supported girder bridge was tested in a wind tunnel. The aerodynamic characteristics of the train-bridge system under various combinations of crosswind speed, train speed, and vehicle location on the bridge were identified. The experimental results reveal that the cosine law for surface wind pressure on a train under crosswind is no longer valid when the train runs on the bridge. The moving model method can better capture the more practical aerodynamic characteristics and the impact of train movement on the bridge. The present study indicates that the wind tunnel experiments using the stationary model cannot fully reveal the aerodynamic characteristics of both the train and bridge during crossing. The results captured using this unique approach provide insight into the aerodynamic characteristics of trains and bridges.

The optimum model determination of porous barriers in high-speed tracks

In the railway industry, safety is an essential factor that has been modified by all societies and railroad managers. Against the background of increasing speed of rolling stock, risk factors such as cross wind and train stability have received more extensive attention. In this study, the porous wind barriers that are widely used in this industry have been surveyed. Also, to decrease the harmful effects of crosswind, the work attempts to find an optimum porous barrier design. This numerical simulation was based on a modern computational fluid dynamic in microscopic space model called the Lattice Boltzmann Method. Also, to find the optimum type of barrier design, the Multi-Objective Genetic Algorithm had been used. Two aspects of barrier design, including the porosity levels and distance between barriers, have been studied and, finally, a candidate design proposed for the barriers. It was found that porousity levels up to 15% have a positive effect in reducing the lift force coefficient, but beyond that it has a negative effect. On the other hand, increasing the porosity level leads to a decrease in the drag coefficient. The velocity vectors, velocity counter, vorticity, and turbulence intensity of the flow field around the model plotted for the candidate barrier.