2021 Volume 20 Pages 81-90
The visualization of flow field around NACA0012 airfoil under constant-pitch-rate motions was conducted using a towing tank. The effects of the pitch rate on the flow field were investigated by PIV, PTV, and pathline visualization at a Reynolds number of 50,000. The non-dimensional pitch rate r was set to 0.01 and 0.02. It was found that the effect of the pitch rate appeared at the pitch angles far smaller than the static stall angle. The separation point and the position of the separation bubble deviated from those in the steady condition. The angles at which the laminar separation bubble was observed under unsteady conditions were different from the angles under the steady condition. Due to the pitching up motion, the unsteady laminar flow separation was observed at r = 0.02. The delay in the formation of the laminar separation bubble was also observed at the smaller pitch rate (r = 0.01), although the unsteady laminar flow separation was not observed.
