Effects of Surface Roughness on Separated and Transitional Flows over a Wing

Abstract

Laminar separation bubbles are often found over the wing of micro air vehicles at low Reynolds numbers and strongly influence the lift, drag, and other aerodynamic performance parameters. A numerical investigation of passive separation control techniques using roughness bumps on a low-Reynolds-number wing is conducted in the present study. A high-order spectral difference unstructured-grid Navier–Stokes solver is employed in the simulations. The study of surface roughness on laminar separation and turbulent transition can provide insights into the design of future passive control devices on wings. The transitional flow with laminar separation bubble past a SD7003 rectangular wing with Reynolds number of 60,000 is used as the baseline (uncontrolled) case. In the controlled cases, roughness bumps are strategically placed near the leading edge of the wing for the purpose of improving aerodynamic performance in terms of the lift-to-drag ratio. The location, bump size, number of bumps, and angle of attack are varied to study the effects. The pressure drag forces in the controlled cases are found to be reduced significantly when the separation is reduced or avoided, resulting in much improved lift-over-drag ratio.