A Study on Vortex Shedding Around a Bluff Body Near the Ground

A series of experiments and computational analysis were carried out on the flow around a bluff body. Some non-streamlined ground vehicles, buildings and pipelines near to the ground could encounter very dangerous situations because of the unsteady wind loading caused by the periodic vortex shedding behind the bluff body. A two-dimensional bluff body model was used to simulate flow in the wake region. Spectral analysis of the velocity profiles in the underbody region was also used to examine the influence of the underbody flow in the wake region. By using a flow visualization technique, the critical gap height and the separation line on the ground were investigated for various gap heights and boundary layer thicknesses.

Additionally, the 2-D Incompressible Navier-Stokes equation with an ε - SST (Strain Shear Stress Transport) turbulence model was used for comparison with experimental results. Through the experimental and computational results, the critical gap height due to the variation of the boundary layer thickness was identified. In addition, the existence of another transition region caused by the interaction between the vortex on the lee side of the bluff body and the separation bubble on the ground board. Through computational analysis the minima in the drag and lift coefficients were detected immediately after the critical gap height. These findings suggest that aerodynamic forces are caused by flow oscillations around the ground vehicle could be reduced by specifying an appropriate ratio between the gap height and ground vehicle height at the design stage.