1997-02-24

Assessing the Effects of Shear and Turbulence During the Dynamic Testing of the Crosswind Sensitivity of Road Vehicles 970135

With increasing speeds and the anticipated reduction in weight of modern cars, the issue of crosswind sensitivity is becoming increasingly important. In a previous paper by the same authors, the normal method of testing such aerodynamic characteristics at model scale, using static models at yaw to the freestream, was compared with dynamic testing, in which the model is propelled across a ‘gust’ simulated by a wind tunnel. A direct comparison using a similar gust profile for both static and dynamic tests was made with the conclusion that the simple static test technique was underestimating the true transient loads.
Further tests have been carried out, on a generic squareback (or estate) model, during which the effect of varying both the vertical velocity profile and the turbulence intensity within the gust was considered. Although these gust characteristics were not necessarily representative of an atmospheric boundary layer they give a good indication of the differences that might be expected between tests done using a static model at yaw and the more accurate dynamic simulation.
The data show a considerable variation in aerodynamic load on the model as the vertical velocity profile was altered but less variation with turbulence intensity. An attempt is made to determine, a simple relationship between a reference velocity, representative of the shape of the gust profile and the resultant forces and moments.

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