Large Eddy Simulations are performed to investigate the bi-modal behavior of the flow past three-dimensional square - back bluff bodies. We consider two simplified road vehicle geometries: (i) the squareback Ahmed body and (ii) a simplified square -back truck geometry, with height greater than its width. The Reynolds numbers based on body height is chosen in the range 20,000 - 33,000, such that turbulent separation occurs for both. It is characteristic of such wakes to
exhibit slow random switching between asymmetric states. The accessibility of full flow - field data allows us to extract wake flow features that offer new insights. Finally we apply a single-input single
- output linear feedback control strategy to the flow. This consists of
sensing the base pressure force fluctuations, and actuating a zero-
net-mass-flux slot jet just ahead of separation to attenuate base pressure force fluctuations. Its effects on the symmetry of the wake and the mean pressure drag are investigated.