In the vehicle development process at Daimler thermal protection is an important task which has to be fulfilled. For this, CFD is a very important tool especially in the early stage of the development. As soon as first prototypes are available measurements are carried out in the wind tunnel and if possible also on the road. Differences in temperature between the results of road measurements and those of the other methods are observed in particular within the rear area of the car. One possible reason for these deviations is the influence of crosswind in the road measurements. For this reason measurements in the Daimler wind tunnel in Untertürkheim were performed, investigating the effect of crosswind on component temperatures. The vehicle used for these measurements was a current C-Class, the load case was the trailer towing uphill drive. The measured approach angles were 0 degree as reference, from both sides 15 degree and 30 degree and from one side additionally 40 degree, which corresponds to crosswind speeds of nearly up to 30 kph. The vehicle was equipped with about 300 measuring points, mostly for temperatures. These points are mainly located in the engine compartment, the tunnel and in the rear of the vehicle. In the engine compartment nearly no effect of the crosswind is present. Only the temperature of the air behind the radiator increases slightly at large angles, caused by a small reduction in the cooling air mass flow. This slight temperature rise sustains in the whole engine compartment. Along the transmission tunnel the influence of crosswind rises and in the rear end of the car the temperature difference reaches its maximum value. Here a temperature difference of about 50 K between the reference case and those with the maximum angles can be measured. Apart from the measurements computations were preformed with the commercial CFD program STAR CD. They are available for validating the results and for pointing out the physical effects in the fluid. The results of the calculations partially agreed well with measurement and were very helpful to understand the existing flow situation. For example the decrease of the cooling air mass flow can not only be verified but also determined quantitatively. However the effects of crosswind calculated by the present model are mainly too weak and in the rear end of the car the measured effects can not be observed. In conclusion it can be said that the effects of crosswinds are definitely visible in the transmission tunnel and the rear end and that temperatures in comparison with the straight flow have the tendency to drop. According to these investigations the wind conditions should be observed when testing vehicles on the road, in order to be able to evaluate the measured temperatures correctly. On the computational side more investigations concerning the grid resolution and the turbulence model have to be preformed.
The effect of crosswind on vehicle component temperatures
2008
15 Seiten, 10 Bilder, 5 Quellen
Aufsatz (Konferenz)
Datenträger
Englisch
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