Wake characteristics of a circular cylinder with a short flat plate at an angle in one of the separated shear layers

Abstract

The flow over the circular cylinder and its wake is an important topic for many investigators because of its practical importance in engineering applications. It is a well-known fact that a plate at an angle of attack generates circulation. By keeping a flat plate in the wake at an angle of attack, its effect on the wake has not been studied. In the present investigation, a short flat plate is placed in one of the separated shear layers behind the circular cylinder to see its effect on the wake structure.

The investigation is carried out in three phases. Initially, flow visualization is done by colour dye injection method at R_e = 650; in the second phase, the surface pressure measurements are done by using surface pressure taps and manometers at R_e = 19300 and in the third phase, the wake measurements are done by using two-dimensional particle image velocimetry technique at R_e = 19300. The plate is placed asymmetrically at various angles, and it is moved at two streamwise locations, G/D = 0.5 and 1. The effect of a short flat plate on the suppression of vortex shedding, reduction of drag and changes in the wake structure is studied in the present investigation. It is seen from the flow visualization results that at a lower Reynolds number, a short flat plate suppresses the vortex shedding. At higher Reynolds number, pressure measurements show a considerable reduction in drag of 21 % for a short plate angle of α = 12 at G/D = 0.5. The turbulent kinetic energy and the Reynolds stresses, both normal and shear, decrease sharply in comparison with those for the bare cylinder by 47 %, 50 %, and 53 %, respectively.