Crosswind Sensitivity Research Articles

New retrofit method to improve the thermal performance of natural draft wet cooling towers based on the reconstruction of the aerodynamic field

Abstract The heat transfer deterioration that occurs in the inner rain zone weakens the thermal performance of natural draft wet cooling towers (NDWCTs). Existing NDWCT retrofit methods including the air deflectors and the cross wall have limited effects on this deterioration. In this paper, we propose a new retrofit method in which air ducts are installed in the rain zone and air deflectors are installed around the air inlet to improve the total tower thermal performance. To clarify the effect and mechanism of our retrofit method, a hot test for a NDWCT model is performed under various crosswind velocities, and a 3D numerical model for a NDWCT with air deflectors and air ducts is established and validated. Using the proposed method, the thermal performance of a NDWCT is substantially improved with less crosswind sensitivity. It is found that the flow diversion efficiency of the air deflectors weakens the adverse impact of the ambient crosswind on air inflow of the tower, and the additional ambient air introduced through the air ducts enhances the heat transfer in the central rain zone. Compared with the single effect of the air deflectors or the cross wall, the combined effect of the air ducts and air deflectors is more efficient in improving the thermal performance of NDWCTs.

Robust control of drag and lateral dynamic response for road vehicles exposed to cross-wind gusts

A robust closed-loop active flow control strategy for road vehicles under unsteady cross-wind conditions is presented. It is designed based on black-box models identified from experimental data for a 3D bluff body equipped with Coanda actuators along the rear edges. The controller adjusts the blowing rates of the actuators individually, achieving a drag reduction of about 15% while simultaneously improving cross-wind sensitivity. Hereby, the lateral vehicle dynamics and driver behavior are taken into account and replicated in the wind tunnel via a novel model support system. The effectiveness of the control strategy is demonstrated via cross-wind gust experiments.

Aerodynamic performances of rounded fastback vehicle

Experimental and numerical analyzes were performed to investigate the aerodynamic performances of a realistic vehicle with a different afterbody rounding. This afterbody rounding resulted in a reduction to drag and lift at a yaw angle of zero, while the crosswind performances were degraded. Rounding the side pillars generated moderate changes to the drag and also caused important lift reductions. A minor effect on the drag force was found to result from the opposite drag effects on the slanted and vertical surfaces. The vorticity distribution in the near wake was also analyzed to understand the flow field modifications due to the afterbody rounding. Crosswind sensitivity was investigated to complete the analysis of the aerodynamic performances of the rounded edges models. Additional tests were conducted with geometry modifications as spoilers and underbody diffusers.

Analysis of vehicle dynamics under sadden cross wind

In this paper, the way of calculating aerodynamic forces acting on a vehicle passing in the region of sadden cross wind was presented. The CarDyn, a vehicle dynamics simulation program, developed by the author was used. The effects of the cross wind were studied with a fixed steering wheel simulation. On the base of computer simulations the car cross wind sensitivity were determined, and vehicle responses such as lateral offset, side acceleration and yaw angular velocity are presented.

Detached Eddy Simulation of the flow around a simplified vehicle sheltered by wind barrier in transient yaw crosswind

This paper numerically investigates the flow around a moving vehicle sheltered by a wind barrier. Flow control strategy aimed at reducing the aerodynamic loads on the road vehicles requires a detailed knowledge of the reference flow. Exploratory study is conducted in under-standing the flow physics involved in the wind barrier vehicle protection. Transient nature of the crosswind gust is represented by the time-dependent boundary conditions in Detached Eddy Simulation. Three methods to quantify and visualize the effects of the transient crosswind on the moving vehicle are considered: aerodynamic coefficients, pressure mapping, and flow visualization. Aerodynamic forces and moments acting on the vehicle are considerably lower compared to the case without the barrier shelter. Vehicle's crosswind sensitivity is improved by wind barri-er application in crosswind protection. The aim of this paper is to quantify and visualize the barrier influence on the moving vehicle aerodynamics in transient crosswind scenario. (Less)

Crosswind sensitivity assessment of a representative Europe-wide range of conventional vehicles

The European Union Seventh Framework Programme research project AeroTRAIN aimed at delivering limit criteria for crosswinds to the ‘Rolling stock – locomotives and passenger rolling stock’ Technical Specification for Interoperability (CR LOC&PAS TSI) and for class 2 trains of the high-speed rolling stock TSI (HS RST TSI). A first objective was the assessment of characteristic wind curve (CWC) for identified class 2 and conventional vehicles with low, but sufficient, crosswind stability (as proven by their safe operational records) on the EN 14067-6: 2010 single track with ballast and rails (STBR) standard configuration. In the same manner, and as a second objective, Reference CWC and limit criteria for class 1 trains of HS RST TSI were planned to be determined. For all these trains, the aerodynamic coefficients were obtained in a unique wind tunnel campaign using the STBR ground configuration. Their crosswind sensitivity was assessed against a calculated CWC obtained from vehicle dynamics simulations. The resulting database will allow the derivation of the relevant limit criteria still needed for vehicle authorization regarding crosswind stability.

Effect of rear slant angle on vehicle crosswind stability simulation on a simplified car model

It is important to know the effect of the aerodynamic forces and moments on driving stability because it is responsible for the excitation and influences the response of the vehicle. The purpose of this paper is to study the effect of rear slant angle of a surface vehicle on crosswind sensitivity for stability analysis. The vehicle mathematical model used to conduct a dynamic simulation was based on a simple reduced order lateral dynamics of sideslip and yaw rate motion coupled with aerodynamics model. The intention here is to compare the effect of rear slant angles response to crosswind and to rank the crosswind sensitivity ratings. The aerodynamic loads are defined as the function of the aerodynamic derivatives from the static wind tunnel tests. Result shows a 20° rear slant angle demonstrates the highest rating of crosswind sensitivity, while zero degree slant exhibits the least.

1203 WIND TUNNEL EXPERIMENTS ON THE CONTROL OF THE LEE SIDE VORTEX OF HIGH-SPEED TRAINS

At cross wind conditions trains are subjected to strong moments, lift and side forces which reduce the stability of the vehicle. The cross wind sensitivity of trains is a safety relevant topic and train manufacturers are required to meet safety criteria defined in various national and international regulations. In an ongoing research project the lee-side vortex, sometimes called "delta vortex", which contributes to the critical rolling moments, is investigated in order to find methods to reduce its strength.

Modeling and Simulation Study on Crosswind Stability of the High-Speed Bus

Based on multi-body system dynamics, the model of Yutong high-speed bus was built by ADAMS/Car software to analyse the influence of crosswind on the high-speed bus' handing stability. Seven discrete wind pressure centers effects on the chasis were taken into account, so the crosswind model with a shifting pressure center was achieved. After improving the standard of the crosswind sensitivity test that is prescribed by American ESV (Experimental safety vehicle), the crosswind simulation tests with pressure center's shift and the immobile pressure center were carried out. The high-speed straight-line simulation test without the crosswind was also completed. By comparing the results of the three tests, the test data in consideration of wind pressure center's shift was more reasonable and provided the reference data for improving the crosswind stability of the bus.

Aerodynamic loads on buses due to crosswind gusts – on-road measurements

Bus and coach traffic is considered to be one of the safest means of travelling. Still, there is a problem with accidents due to crosswind gusts. Therefore there is a need to improve the crosswind performance of buses. As a part of the work with improving the crosswind performance, a method for estimating the aerodynamic loads on a bus when exposed to natural crosswind is proposed. The method is based on the measurements of the vehicle response and the tyre forces from which the aerodynamic loads are estimated using inverse simulations. The results are also shown to agree well with the results of other studies based on wind tunnel measurements. The estimated aerodynamic loads are intended to be used in a future study on crosswind sensitivity using a moving base simulator.

Aerodynamic design of high-sided coaches to reduce cross-wind sensitivity, based on wind tunnel tests

Aerodynamic properties of high-sided coaches with various body shapes were investigated in order to improve directional stability. The idea was to find out whether it would be possible, from an aerodynamic point of view, to suggest an optimal coach body design. The subject has previously been paid little attention in the scientific literature. The fact that during the last few years at least 10 wind-related coach crashes have occurred in Sweden indicates that here a serious problem exists and that cross-wind effects should be carefully considered by coach designers. The observations made in the present study suggest that it should be possible to find an ideal coach body shape. The ideal shape of the coach includes a rounded front face, rounded top sides and sharp rear corners.

The driver as a sensor for crosswind sensitivity

There are currently no standardized criteria for evaluating a vehicle’s crosswind behaviour. The application of conventional criteria to some vehicles results in different — and in some cases even contradictory — evaluations. The Research Institute of Automotive Engineering and Vehicle Engines Stuttgart (FKFS) of Stuttgart University is developing an approach that uses the driver as a sensor, making use of the fact that the driver adapts his steering actions in accordance with the vehicle’s behaviour. The driver’s subjective assessment of the vehicle’s crosswind behaviour is thus derived from the way in which he adapts his steering actions. The investigations are aimed at modelling an adaptive, virtual driver for the purpose of analyzing the vehicle’s crosswind behaviour even in the vehicle development stage.

Crosswind Handling Performance for Driver-Vehicle System.

Lateral trajectory and crosswind sensitivity with fixed control steering are often applied in evaluating for crosswind conditions. These indices, however, don't always represent the delicate feeling on steering correction. In this paper, a stability criteria of driver-vehicle system is derived analytically for straight running against crosswind, and then the quadratic form of state variables for handling performance is proposed as an active crosswind sensitivity, in order to evaluate objectively handling performance against wind gust and to optimize many design parameters as well as aero-dynamics.

Crosswind Sensitivity of Passenger Cars and the Influence of Chassis and Aerodynamic Properties on Driver Preferences

SUMMARY Results of vehicle crosswind research involving both full-scale driver-vehicle tests and associated analyses are presented. The paper focuses on experimental crosswind testing of several different vehicle configurations and a group of seven drivers. A test procedure, which utilized wind-generating fans arranged in alternating directions to provide a crosswind “gauntlet”, is introduced and described. Driver preferences for certain basic chassis and aerodynamic properties are demonstrated and linked to elementary system responses measured during the crosswind gauntlet tests. Based on these experimental findings and confirming analytical results, a two-stage vehicle design process is then recommended for predicting and analyzing the crosswind sensitivity of a particular vehicle or new design.

Influence of Aerodynamics and Suspension on the Cross-Wind Behaviour of Passenger Cars-Theoretical Investigation under Consideration of the Driver's Response

SUMMARY The handling behaviour in cross winds of fast, powerful passenger cars becomes more and more important as a result of the development of streamlined car bodies. Generally, bodies with low drag are more sensitive to cross wind. Up to now, one method of testing cross-wind sensitivity is by using a side-wind blower and evaluating the path deviation (fixed control). But unfavourable factors here are the normally large angle of approach, the constant velocity profile of the wind, the neglect of the driver's behaviour, etc. Therefore this paper points out results from simulation computations obtained from cruising in natural, stochastic cross winds under consideration of the driver's response. In the preliminary investigation for this work [4] the important and differing influences of (a) the aerodynamics of the body and (b) the handling properties of the chassis/suspension were identified. In this paper the body and chassis effects shall be investigated separately. Furthermore, a formula will be presen...