Volvo employs Aeroprobe omniprobes to study the aerodynamics of car wheels

Aerodynamic resistance is significant energy consumption of an automobile at high speeds. But the upper-body drag accounts of only half of the overall aerodynamic losses. Considerable losses are due to the aerodynamics of the underbody, the wheels and the cavities in which they are placed. To study these phenomena, Volvo employed Aeroprobe Omniprobes to explore the velocity and pressure fields around a rotating wheel. These experiments were carried out with a full-scale Volvo automobile in the Volvo Aerodynamic Wind Tunnel. A moving-ground system was installed and tests were carried out with or without this system.

The Aeroprobe omniprobe was traversed along a plane around the spinning wheel.

A rake of two Omniprobes was traversed along planes normal or parallel to the free stream around the wheels of the automobile. In the figure below is shown the probe next tone of the wheels.

Typical results are shown in the figure below. In this figure the contours represent the total pressure measured, and the arrows correspond to the in-plane velocity components. Detailed results and important conclusions can be found in the SAE Paper No2009-01-0778 (Detailed flow structure in close proximity of rotating wheels on a passenger car by C. Landstrom, L. Lofdahl and T. Walker). Among others, the researchers identified two wakes downstream of the front wheel. The size and strength of the vortices appeared to be good indicators of the global aerodynamic drag.

Color contours indicate normalized reduced total pressure. The arrows represent in-plane velocity vectors.