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Technical Paper

Comparison of Different Ground Simulation Techniques for Use in Automotive Wind Tunnels

1990-02-01
900321
The range of applicability and the physical restrictions for the use of ground-simulation techniques in automotive wind tunnels are elucidated. The techniques considered are the moving-belt technique, as well as boundary layer control techniques like tangential blowing and distributed normal suction for use in wind tunnels with stationary ground boards. Attention has to be paid to the question of whether the flow to be simulated is of boundary layer or Couette type. In the case of boundary layer flow, interaction of the ground-floor boundary layer with the inviscid flow in the gap between a vehicle and the road can be fully simulated by introducing a negative transpiration velocity along the stationary ground plane. In practise however, angularity effects on the external flow result from mismatched control parameters. Very small relative ground clearances give rise to the formation of a Couette flow between the road and the vehicle.
Technical Paper

Road Load Determination Based on Driving-Torque-Measurement

2003-03-03
2003-01-0933
This paper introduces a driving-torque measurement method for the determination of vehicle road load and its components. To increase the accuracy, the torque measurements are combined with rolling resistance measurements performed with a specially developed trailer. This method is a strictly experimental approach and does not use any mathematical models. The experimental techniques are described as well as the proceedings to compare test stand and road measurements. The results that are shown prove that this method is suitable for the investigation of single road load components. Furthermore, the comparison of different rolling resistance measurement devices shows the potential of the measurement trailer and the necessity to perform rolling resistance measurements on real road surfaces and not solely on test stands.
Journal Article

The Effect of High Turbulence Intensities on Surface Pressure Fluctuations and Wake Structures of a Vehicle Model

2009-04-20
2009-01-0001
The unsteady environment road vehicles are exposed to is subject of many investigations that are currently made. Yet, the approaching flow is only one aspect of unsteady forces acting on the vehicle. Unsteady wake structures also lead to time-varying surface pressures and consequently fluctuating forces even in steady and low turbulent flows. However, little is known about the influence of realistic flow conditions, i.e. as found on road, on the unsteady surface pressures and wake structures of a vehicle. Therefore, to derive a deeper understanding of the unsteady aerodynamic properties of a vehicle this paper presents results of measurements conducted on a vehicle body both in smooth and turbulent flow conditions in the IVK model scale wind tunnel. Unsteady surface pressure measurements in the area where separation occurs and the base of the vehicle were made together with time accurate total pressure measurements in the wake.
Journal Article

The Effect of Center Belt Roughness on Vehicle Aerodynamics

2009-04-20
2009-01-0776
Recently built or refurbished wind tunnel facilities show a trend towards a detailed simulation of road conditions. Therefore, these wind tunnel facilities are equipped with boundary layer conditioning systems and a rolling road consisting of one or several belts in order to simulate the rotation of the wheels and the relative motion between the vehicle underfloor and the road. Belts are either realized in rubber or steel. Steel belts offer the possibility to be coated with rubber to protect the belt itself. This coating additionally offers the possibility to attain a certain roughness to represent the road surface. This paper presents measurements of the roughness of the steel belt systems installed in the IVK Model Scale and Aero-Acoustic Full Scale Wind Tunnel in comparison to road surfaces. Additionally, the influence of roughness on the aerodynamic coefficients drag and lift is presented and discussed for the SAE reference body with different rear end configurations.
Technical Paper

The Influence of Rotating Wheels on Total Road Load

2007-04-16
2007-01-1047
Within in the scope of a road load investigation project at FKFS, the influence of rotating wheels on the road load of a passenger car was investigated. For this purpose an approach was developed to measure the ventilation resistance of a spinning wheel. This approach enables a comparison of different wheel sizes and rim designs. Together with aerodynamic drag measurements in the wind tunnel it is possible to evaluate different wheel configurations with respect to their contribution to the road load. The measuring approach and results of performed measurements are shown in this paper.
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