Counterclockwise Vortical-Gust/Airfoil Interactions at a Transitional Reynolds Number

Abstract

This paper presents high-fidelity implicit large-eddy simulations of parallel vortical-gust interactions with a NACA0012 airfoil operating at a transitional Reynolds number of and an angle of attack of . The gust is supplied upstream of the airfoil as a counterclockwise-oriented Taylor vortex. Upon impact with the leading edge, the gust splits, causing disruptions to the boundary layer on both surfaces of the airfoil. On the upper surface, the vortical gust causes an eruption of the laminar-separation bubble into a poorly formed turbulent leading-edge vortex that becomes more coherent as it overtakes and envelopes two-dimensional instability waves downstream. The gust and leading-edge vortex propagate as a dipole and induce a pressure disturbance upon departure from the trailing edge, an event significant enough to influence the lift. Beneath the airfoil, the lower section of the gust thickens the boundary layer and causes breakup into a series of spanwise coherent vortices. Both leading-edge vortex formation and lower boundary-layer disruption produce notable acoustic radiation. Three different initial vertical positions are considered for a counterclockwise-oriented gust. Gust position affects boundary-layer disruption such that higher encounters elicit a more coherent leading-edge vortex and lower encounters exhibit stronger lower-surface instabilities. All cases exhibit significant acoustic radiation emanating from the aforementioned flow transition events.