An optimum suppression of fluid forces by controlling the separated shear layer. Control of one-sided shear layer separated from square prism.

Abstract

This paper deals with the suppression of the fluid forces by controlling a one-sided shear layer separated from a square prism. The control of the separated shear layer was established by setting up a small circular cylinder (the 'control' cylinder) in a one-sided shear layer near the square prism. Experimental date were collected to examine the effects on the fluid forces and vortex shedding frequency due to variation of the position and diameter of the control cylinder. The results show that (i) the position of the control cylinder corresponding to the minimum of he time-mean drag and fluctuating lift and drag was near what would ordinarily be considered the outer boundary of the shear layer ; (ii) the control of the separated shear layer by means of a small cylinder appeared to be effective in suppressing the fluctuating lift and drag rather than the time-mean drag ; (iii) the fluctuating fluid forces were reduced markedly below the plain prism value. For example with the control cylinder of 5 mm diameter, the fluctuating lift and drag were reduced to approximately 90% and 70% respectively ; (iv) the effectiveness of the control cylinder was attributed to the change of the position of the vortex formation region and suppression of vortex shedding.