High-Fidelity Simulation of Transitional Flows Past a Plunging Airfoil”. AIAA

This investigation addresses the simulation of the unsteady separated flows encountered by a plunging airfoil under low-Reynolds-number conditions (Rec ≤ 6 × 104). The flow fields are computed employing a previously developed and extensively validated high-fidelity implicit large-eddy simulation (ILES) approach. In order to permit comparison with available experimental measurements, calculations are performed first for an SD7003 airfoil section at an angle of attack αo = 4 ◦ plunging with reduced frequency k = 3.93 and non-dimensional amplitude ho = 0.05. Under these conditions, it is demonstrated that for Rec = 104, transitional effects are not significant and that the dynamic-stall vortices remain fairly coherent as they propagate along the airfoil. For Rec = 4 × 104, the dynamic-stall vortex system is laminar at is inception, however shortly afterwards, it experiences an abrupt breakdown associated with the onset of spanwise instability effects. A de-tailed description of this transition process near the leading edge is provided. The computed phased-averaged structures for both values of Reynolds number are found to be in good agreement with the experimental data. As a second example, the suppression of static stall at high angle of attack (αo = 14◦) is investigated using high-frequency small-amplitude vibrations (k = 10, ho = 0.005). At Rec = 6 × 104, separation is completely eliminated in a time-averaged sense, and the mean drag is reduced by approximately 40%. The instantaneous flow is characterized by the periodic generation of dynamic-stall vortices near the leading edge and by thei