Fluid dynamics of a cubic structure as affected by momentum injection and height

The concept of moving surface boundary-layer control (MSBC) as applied to a cubic structure is investigated experimentally at a subcritical Reynolds number of 6.7×104. Two high-speed rotating cylinders replaced adjacent vertical edges (W) of the cubeʹs nominal upstream face and controlled the momentum injection parameter Uc/U, where Uc is the cylinder surface velocity and U is the free-stream velocity. Three different configurations of the cube are considered: (i) the basic cube resting on a horizontal surface (H=W; H, vertical distance from the ground to the top face of the cube); (ii) H=2W; and (iii) H=3W. The focus is on the momentum injection and cube height on the fluid dynamical parameters represented by the surface pressure, drag and side force. The results suggest significant effect of the MSBC and the height on the boundary-layer separation and reattachment, thus affecting the fluid dynamical parameters. For the basis cube (Case (i)), the maximum drag reduction was observed to be around 67%, while the peak increase in the side force was as high as 900%. For H=2W (Case (ii)), the effect of Uc/U was to reduce the drag at virtually all angles of attack, however, the decrease was substantially less compared to that observed for the basic cube (Case (i)). This is primarily due to the lateral flow created on the side faces of the cube because of the gap formed by the proximity of the ground. However at the higher height (H=3W, Case (iii)), the trend reverses. Now the reduction in drag is significantly higher, even compared to that for the basic cube case. The fundamental information should prove useful to industrial aerodynamicists and practicing engineers.