Simulation of starting/stopping vortices for a lifting aerofoil

In order to recreate Prandtl’s flow visualisation films dealing with starting and stopping vortices produced by a lifting aerofoil and expand on that research, direct numerical simulation was used to perform numerical experiments on the starting and stopping of lifting aerofoil by solving the two-dimensional incompressible Navier–Stokes equations. The simulation used a NACA 0012 aerofoil at angle of attack , the chord Reynolds number based on peak translation speed was, and was conducted using a spectral element simulation code. Trailing edge starting and stopping vortices and also a stopping leading edge vortex pair were produced. Net circulation was calculated and was found to have a small positive value, which fell as domain size was increased. The circulation agreed with the domain integral vorticity as expected. We examined the aerodynamics of the aerofoil by calculating the lift and drag coefficients and the lift-to-drag ratio. We found that CD was larger than CL when the aerofoil was accelerating and decelerating, but smaller during steady state velocity. Most of the drag was associated with pressure gradients as opposed to viscous skin friction. Details of circulation/vorticity generation and evolution will be presented