Numerical simulation of thrust generating flow past a pitching airfoil

Earlier analytical and experimental studies predict that pitching motions at high frequency can generate thrust on the airfoil. The present work is an effort towards a systematic understanding of the influence of various parameters on thrust generation from a harmonically pitching airfoil. Quantitative instantaneous force computations have been discussed together with qualitative vortex patterns using a 2-D discrete vortex simulation of incompressible viscous flow. In general, thrust force increases with the oscillation frequency. The trend is very similar to the inviscid theory prediction. Further, the thrust force is seen to decrease with the increase in mean angle of attack. However, in a clear deviation from inviscid theory trends, pitching at high amplitudes about high mean angle of attack, only drag is observed for high values of reduced frequency considered. The effect of location of the pitching axis is also found to be significant on the propulsive characteristics of the airfoil.