Towing Tank Experiments for Bluff Body Aerodynamics

Abstract

In ongoing studies on drag reducing devices for heavy vehicles wind tunnel experiments have been carried out at the Hermann-Föttinger Institute of the TU-Berlin. However, these wind tunnel experiments lack a moving belt or a suction system to remove the boundary layer of the wind tunnel floor. Therefore, the use of a towing tank which is available at the TU-Berlin was considered and realized. In order to gain experience with the towing tank as a tool for vehicle aerodynamic studies, preliminary experiments with a bluff body with out any ground effect were carried out. The box-shaped body corresponds to a simplified European trailer at a scale of 1:10. Towing speeds of up to 4 m/s leading to a Reynolds number of Re $=$ 5.2 $\times$ 10$^6$ were used. Comparative measurements in the wind tunnel and the towing tank were carried out with the box. They showed good agreement, however maximum deviations of up to 2.5 % for the axial drag coeefficient were observed. The effect of passive drag reducing devices, so called base flaps, were measured and also their positive effect was well reproduced in the towing tank. The towing tank has thus been established as an aerodynamic test facility.