Experimental study on the effect of angle of attack on airfoil boundary layer

In order to deeply understand the influence of the angle of attack on the airfoil boundary layer, a TR–PIV experimental study on the SD7003 airfoil is carried out. The distributions of statistics such as the average velocity of the airfoil suction surface and the Reynolds shear stress under the working conditions of the angle of attack α = 4°, 6° and 8° are compared. Proper orthogonal decomposition (POD) method is adopted for analysis of the experimental data. The flow structure in each mode and the frequency spectrum characteristics of the modes under different working conditions are analyzed in detail. The study finds that: with the increase of the angle of attack, the position of the separation bubble moves to the leading edge of the airfoil, and the thickness of the separation bubble increases; there is intensive shear motion inside the separation bubble and near the reattachment point; there are alternating positive and negative vortex structures near the reattachment point, and the vortex structures change continuously with the development of the boundary layer; the energy of each mode of POD decomposition is related to the scale of the structure contained and the mode frequency; with the increase of the angle of attack, the scale of the flow structures in the flow field increases, and the frequency domain distribution of flow field energy shifts from high frequency to low frequency.