Coherent structure characterization in the wake of a ground vehicle with a large height to width ratio

The turbulent wakes of ground vehicles are as unique as the vehicles themselves. Their complex shapes and close proximity to the ground surface serve only to complicate the structure of the flow fields behind them. As a result of the random and chaotic nature of wake turbulence, researchers must utilize statistical measures such as averages of variables, correlations, and joint probabilities to identify the repeatable coherent structures which are now known to exist. The physical interpretation of statistical results generally requires an intuition based upon companion flow visualization results.

The wakes of three simply shaped van models were characterized with a flow visualization study in a water-filled tow tank. The effects of model width and ground clearance on the vortex shedding frequency and statistical properties such as those mentioned above were evaluated. The vortex shedding frequencies from the flow visualization results and auto-correlation results were compared. Mean velocity and turbulence intensity profiles at the lateral and vertical centerlines were produced and qualitatively analyzed.