This investigation addresses the simulation of the unsteady separated flows encountered by a plunging airfoil under low-Reynolds-number conditions (Re(c) smaller or equal 6 x 10E4). The flowfields are computed employing an extensively validated high-fidelity implicit large-eddy simulation approach. Calculations are performed first for a SD7003 airfoil section at an angle of attack alpha(0) = 4 deg plunging with reduced frequency k = 3.93 and amplitude h(o)/c = 0.05. Under these conditions, it is demonstrated that, for Rec = 104, transitional effects are not significant. For Re(c) = 4 x 10E4, the dynamic-stall vortex system is laminar at its inception, however, shortly afterward, it experiences an abrupt breakdown due to the onset of spanwise instabilities. A description of this transition process near the leading edge is provided. As a second example, the suppression of stall at high angle of attack (alpha(0) = 14 deg) is investigated using high-frequency, small-amplitude vibrations (k = 10, h(o)/c = 0.005). At Re(c) = 6 x 10E4, separation is completely eliminated in a time-averaged sense, and the mean drag is reduced by approximately 40%. For larger forcing amplitude (ho/c = 0.04, Re(c) = 10E4), a very intriguing regime emerges. The dynamic-stall vortex moves around and in front of the leading edge and experiences a dramatic breakdown as it impinges against the airfoil. The corresponding phased-averaged flow displays no coherent vortices propagating along the airfoil upper surface. This new flow structure is also characterized in the mean by the existence of a strong jet in the near wake which produces net thrust. This study demonstrates the importance oftransition for low-Reynolds-number maneuvering airfoils and the suitability of the implicit large-eddy simulation approach for exploring such flow regime.
High-fidelity simulation of transitional flows past a plunging airfoil
Genaue Simulation der Übergangsströmung hinter einem Tragflügelprofil
AIAA Journal ; 47 , 11 ; 2685-2697
2009
13 Seiten, 25 Bilder, 3 Tabellen, 36 Quellen
Article (Journal)
English
High-Fidelity Simulation of Transitional Flows past a Plunging Airfoil
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