Joint Computational-Experimental Investigation of Harmonically Pitching Airfoil Aerodynamics in Uniform-Shear Approach Flow

摘要

This work explores the aerodynamics of an airfoil oscillating in a uniform-shear flow at chord Reynolds number of approximately 1.2x104 using complementary two-dimensional Navier-Stokes computations and direct force measurements. A NACA-0012 airfoil is pitched harmonically about its quarter-chord, with 2 degrees amplitude and reduced frequency up to 12, in positive-shear approach flow for nondimensional shear rates in the range 0.0-1.0. The results show that the wake of the airfoil exhibits symmetry breaking that leads to a deflected wake toward the high-speed side as the reduced frequency increases beyond the reduced frequency for an aligned vortex street. The frequency at which the vortex alignment takes place is nearly independent of nondimensional shear rate. Interestingly, the presence of shear seems to have little or no effect on the average drag/thrust and root mean square (rms) of the lift and thrust fluctuation, whereas a prominent influence is seen on the average lift. The latter switches sign from negative to positive at a reduced frequency of approximately 3, and it increases in magnitude with both increasing nondimensional shear rate and reduced frequency.