High Fidelity Computational Aeroelastic Analysis of a Plunging Membrane Airfoil

Abstract

Simulation results and analysis of a plunging one-dimensional membrane (string) are presented. A well-validated sixth-order Navier-Stokes solver coupled to a finite element solution of a two degree of freedom nonlinear string model are coupled and used to perform high fidelity aeroelastic computations. A low Reynolds number of 10 consistent with MAV flight is chosen and the effect of the plunging Strouhal number and reduced frequencies along with the static angle of attack of plunging is examined. At the lowest angle of attack studied (2 degrees) and a plunging with reduced frequency of 5.0, for both a Strouhal number of 0.2 and 0.5, the vorticity shed at the leading edge due to dynamic stall did not convect downstream and hence had a minimal effect on the overall flow field over the surface of the wing. In contrast, when the plunging occured at a Strouhal number of 0.5 and a reduced frequency of 1.5, for each static angle of attack investigated the vortex shed from the leading edge during the downward portion of the plunging is convected approximately one half of a chord downstream before it then convects back upstream during the upward portion of the motion. The convection of this vortex significantly effects the airfoil surface pressure distribution. It was also found that at low angle of attack (2 degrees) and a Strouhal number of 0.2, only a plunging with reduced frequency of 0.5, the lowest studied here, produced lift which was larger than the non-plunging flexible airfoil case. At 2 degree angle of attack plunging at a Strouhal number of 0.5 produced increased lift and drag over the stationary case for each of the reduced frequencies investigated. Finally, for the cases studied, the lift coefficient normalized by the corresponding stationary value was a weak function of angle of attack when plunging with a Strouhal number of 0.5 and a reduced frequency of 1.5.