Modulation of aerodynamic characteristics of a finite wall-mounted square cylinder through steady jet injection

Abstract

This paper presents the results of an experimental study that investigates the flow behavior around a finite wall-mounted square cylinder (with the aspect ratio of AR = 7) subjected to a steady jet issued from the cylinder’s front face. Two wavy and continuous jets were considered to examine the jet velocity distribution effect. The wind tunnel measurements consist of smoke flow visualization, mean drag force, mean surface pressure, and velocity data obtained from hotwire probe, mostly at Reynolds number (Red, based on the cylinder width and inlet velocity) of 1.2 × 104. The ratio of the jet flow to the freestream, Г, was changed as 0 ≤ Г < 5. Both the wavy and continuous jets reduce the downwash flow contribution with the flow from the lateral faces. An increase of Г continuously amplifies this effect, and improves the flow control performance in drag reduction. The maximum pressure drag reduction of 29% and 16% were obtained for the wavy and continuous jets, respectively. Two characteristic continuous jet flow modes, namely deflected jet (Г < 1) and deflected oscillating jet (1 < Г < 2), were identified. The both continuous jet deflection mode have a leading role in the pressure reduction on the front face, and subsequently in drag reduction. Oscillation of the deflected continuous jet at high-Г also significantly increases the vortex shedding frequency in the upper half of the cylinder, and makes the mean wake flow asymmetrical. On the other hand, the base pressure recovery is the major reason for the drag reduction when the wavy jet is applied. The wavy jet shows a slight deflection at high-Г; however, the mean wake flow remains symmetrical. Finally, the influence of jet flow control on the flow topology was discussed.