Boat-tail effects on the global wake dynamics of a flat-backed body with rectangular section

A three-dimensional body of rectangular section with a blunt trailing edge is studied for various angles of after-body boat-tailing. The Reynolds number of the flow is Re = 4.0 x 10(5) and the body is in the vicinity of the ground. It is found that the wake dynamics is strongly dependent on the coupling of top and bottom boat-tail angles, triggering either long-time bi-stability between two mirror static asymmetric states or an anti-symmetric periodic mode, both leading to large cross-flow force fluctuations. The transition is shown to depend on the aspect ratio of the vertical base and not on the flow orientations imposed by the coupling of angles. Within the limitation of the aspect ratio for which the static states persist and dominate the wake dynamics, as boat-tails are installed at the after-body, they generate a vertical base pressure gradient component on which the static states adapt according to the mechanism proposed by Bonnavion and Cadot (2018). (C) 2019 Elsevier Ltd. All rights reserved.