Effects of compressibility, pitch rate and reynolds number on unsteady incipient boundary layer separation over a pitching airfoil

The effects of compressibility, pitch rate and Reynolds number on the initial stages of 2-D unsteady s separation of laminar subsonic flow over a pitching NACA-0012 airfoil have been.studied numerically. The approach involves the simulation of the flow by solving the two-dimensional unsteady compressible laminar Navier-Stokes equations employing the implicit approximate-factorization algorithm of Beam and Warming and a boundary-fitted C-grid. The algorithm has been extensively validated through comparison with analytical and previous numerical results. The computations display several important trends with regards to the "birth" of the primary recirculating region which is a principal precursor to leading edge separation. Increasing the non-dimensional pitch rate from 0.05 through 0.2 at a fixed Reynolds number and Macli number, delays the formation of the primary recirculating region. The primary recirculating region also forms closer to the leading edge. Increasing the Mach number from 0.2 to 0.5 at a fixed Reynolds number and pitch rate causes a delay in the formation of the primary recirculating region and also leads to its formation farther from the airfoil top surface. The length scale associated with the recirculating regions increase as well.