Near-wall dynamics of laminar separation bubbles at low turbulence intensities

Abstract

The experiments are conducted at Rec=6⋅10^4 and 8⋅10^4 and an angle of attack of AoA=6°. The applied heating power at the lower Rec is 1764 W/m2 and 2545 W/m2 at the higher. SPOD analysis of the thermal fluctuations displays the footprints of the Kelvin-Helmholtz instabilities with temporary high levels of span-wise coherence. Instantaneous thermal snapshots display the propagation of simultaneously emerging V-shaped footprints in the stream-wise direction. Examples are shown in the paper. Some of the snapshots depict span-wise coherent footprints, which can only be assumed to be caused by Kelvin-Helmholtz vortices, in the same region as the V-shaped footprints, which implies that these are two distinct phenomena. Quasi-simultaneous PIV and TSP measurements confirm the assumption.