Affiliations: Institute of Theoretical and Applied Mechanics, SB
RAS, 630090, Novosibirsk, Russia | Novosibirsk State University, Novosibirsk,
Russia
Abstract: Flow visualization tests have been performed to examine the
structure of the near-wall flow over a low-aspect ratio straight wing installed
at various angles of attack &b.alpha; and chord Reynolds number Re_c = U
c/v = 1.76 ×10^5 . The experiments were carried out at two free-stream
turbulence levels, &b.epsiv; = 0.1% and &b.epsiv; = 1%, the latter one
having been achieved using a baffling grid. To visualize the flow, termochromic
cholesteric liquid crystals and digital processing of video images were used.
At the low turbulence level and &b.alpha; = 27°, a flow stall on the
lee side of the wing was observed, with a pair of large-scale vortices rotating
in the wing plane. Simultaneously, no vortex structures were observed on the
windward wing surface. It was found the flow patterns on either side of the
wing significantly changed with increasing free-stream turbulence level. A
separation bubble appeared near the leading edge on the lee side of the airfoil
at &b.epsiv; = 1%, and large-scale stationary longitudinal vortices
originated over the wing windward surface. The number and sizes of the
longitudinal structures were found to be dependent on the angle of attack.