Aerodynamics of the square-back Ahmed body under rainfall and turbulent conditions

We report an experimental investigation on the aerodynamics of the square-back Ahmed body, a simplified road vehicle, under rainfall conditions and different background turbulent flows. Wind tunnel tests using different grids (passive and active) and a uniform grid of injectors installed upstream of the body were used to characterize both the bi-stability and the base drag of the body. With this aim, a set of 81 pressure taps was installed at the body base. To study the role of rainfall in the dynamics of the Ahmed body, three different volume fractions of droplets were injected under passive-grid-generated turbulence conditions. On the other hand, the role of the turbulent inflow was assessed by testing the body in dry conditions, in an empty test section (laminar inflow), and under passive-grid- (low turbulence intensity) and active-grid-generated (moderate-to-high intensity) turbulence.

Our studies show that the bi-stability in the wake of the Ahmed body diminishes progressively when the void fraction of rainfall or the turbulence intensity of the inflow is increased. Furthermore, it is found that rainfall significantly damps the mean base pressure drag. A similar effect is found with respect to turbulence intensity, as the mean base pressure drag decreases when this quantity is increased.