Optimum suppression of fluid forces by controlling the separated shear layer. Control of shear layers on two sides of a square prism.

This paper deals with the suppression of fluid forces by controlling the shear layers separated from a square prism. Control of the spearated shear layers was established by two small circular cylinders placed in symmetry on two sides of the square prism. Experimental data were collected to examine the effects on the fluid forces due to variations of the position and diameter of the control cylinders. The results show that (i) the maximum reduction of the time-mean drag and fluctuating lift and drag occurred when the control cylinders were located near what would ordinarily be considered the outer boundary of the shear layers on two sides; (ii) the maximum reduction rate of the time-mean drag reached about 30%, and the fluctuating lift and drag reached approximately 90% and 80%, respectively, when the control cylinders with the diameter d = 3mm were located in symmetry on two sides; (iii) it was found that the bistable flow generated in the case of the controlling of the shear layer on one side can be perfectly prevented by the controlling of the shear layers on two sides; (iv) the relationship between the change of the fluid forces and the behavior of the separated shear layers was clarified by the observation of the flow patterns.