Wind Tunnel Model Support Strut Interference

Road vehicle models are tested in a wind tunnel with a moving ground when an accurate simulation of the under-floor flow is required, for instance for the aerodynamic development of the underbody. The use of a moving ground necessitates that the model and wheels be supported using one or more struts. These struts can cause complex interference flow fields including three-dimensional separations in the area surrounding them. This work aims to quantify the magnitude of these interference effects for a saloon vehicle and to begin to explain the physics of the flow.

Models were mounted over a stationary ground plane using an under-floor balance to measure aerodynamic forces and moments on the model. Each model is tested with and without mock struts, which do not actually support the model. Comparisons are made between results from configurations with and without the mock struts in order to quantify their aerodynamic effects.

Tests performed on a typical four-door sedan show a slight increase in drag and greater increase in lift due to interference by an overhead support strut. Wheel support stings were found to produce an increase in lift. The compilation of both the overhead strut and wheel stings cause a combined effect on both lift and drag.