Impact of Surging Streamwise Flow on Laminar Separation Bubble Dynamics for a Finite-Span Wing*

The impact of unsteady streamwise flows on a finite, semi-span, NACA 0015 wing is examined for mean chord-based Reynolds Numbers of 100,000 and 150,000. The unsteady lift response is primarily dominated by the coupling of the surging streamwise flow with the laminar separation bubble dynamics at low to moderate angles of attack, and with the vortex shedding characteristics at angles of attack post-stall. For low reduced frequencies at low angles of attack, the laminar separation bubble elongates at the minimum velocity, thereby increasing the suction pressure on the suction surface and enhancing lift. For low reduced frequencies at post-stall angles of attack, shedding of low pressure coherent structures from the leading edge convect more slowly and coalesce, creating lift plateaus during the lower velocity portion of the cycle, but does not have an impact on the phase averaged lift.