Experimental Study of Pitching Airfoil Flow Structure Based on TR-PIV
The evolution of the pitching airfoil flow structure is complex,exhibiting interactions between various vortices.Based on TR-PIV(Time Resolved Particle Image Velocimetry),the spatio-temporal evolution of the flow structures on the near-wall surface of a pitching airfoil is quantitatively investigated under the conditions of Reynolds number is 3.0×105 and reduced frequency is 0.03.At the same angles of attack of upstroke and downstroke,the separation point is closer to the leading edge and the shear layer instability is more intense on the downstroke.This discrepancy is related to wall-normal component of velocity at the leading edge,relative to that of the incident flow.On the downstroke,the secondary counter-rotating vortex develops towards the trailing edge along the suction surface are observed in the flow field.The secondary vortex promotes the spanwise vortex shedding and merges with the spanwise vortex,causing violent changes in the flow field.On the upstroke,two types of vortex,leading-edge vortex and shear layer vortex are observed,with differ-ences in spatial location,structural morphology,convective velocity,etc.However,there is also a connection between them,as the shear layer vortex promotes the development of the leading-edge vortex,the merging between the leading-edge vortices forms large-scale dynamic stall vortex,and the development of the dynamic stall vortex is also influenced by the shear layer vortex.
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