Flow channeling on airfoils with rough leading edges

In Kumar et al. (J. Turb., vol. 22(11), 2021, p. 735-760), we studied the flow over an airfoil with leading-edge roughness due to ice depositions. We found stationary spanwise inhomogeneities in the form of alternating regions of fast and slow-moving fluid, which were termed ``flow channels''. In the present study, we investigate further the channeling phenomenon by performing simulations of a NACA 4412 airfoil at three angles of attack. Downstream of the roughness zone, the fast regions slow down under the action of hairpin vortices generated by the roughness elements and merge with neighboring slow regions. The flow channels remain coherent over the entire airfoil and affect the trailing-edge separation. With an increasing angle of attack, the intensity of flow-channeling can increase or decrease depending on the topology of the leading-edge roughness. Its effect on the trailing-edge separation, however, remains significant. The mean separation line is highly distorted, and the separation length can vary by up to 30% along the span.