Unsteady phenomena in the flow field downstream of a two dimensional bluff body

摘要

An experimental investigation by LASER sheet flow visualization and LDV was performed on the flow immediately downstream of a bluff body. The model is a prismatic obstacle and extends over the whole width of a low speed wind tunnel. The measurements were carried out by means of a two component LDV system (TSI), working in the backward scattering mode and equipped with a Bragg cell. The simultaneous measurement of the horizontal and the vertical components of the instantaneous velocity allowed the detection of the averaged flow field and the turbulent quantities (standard deviation, Reynolds stresses, etc.). The results show a principal recirculation bubble downstream of the model, together with a secondary vortex, located in the region close to the obstacle back wall. The isolines concerning the standard deviation, the Reynolds stresses and the vorticity substantially confirm the strongly unsteady character of the flow which already appeared from the flow visualization test.