Abstract
Unsteady flow field around a rigid 2D NACA 0012 foil perfoming pitching oscillations is studied numerically, changing the reduced frequency and pivot point location. Special attention is payed to the ability of thrust production.
Viscous flow simulation is based on solving the full 2D laminar incompressible Navier-Stokes equations in vorticity-stream function formulation, defined in moving noninertial frame of refrence. An implicit factored finite-difference numerical algorithm is used. Performed numerical tests for simulation indicate that, the simulated flow is of sufficient accuracy to merit a physical analysis. The computed flow pattern is compared with the flow visualized experimentally and both results seem to agree satisfactorily.
It was proved that, for large products of reduced frequency and distance to the pivot point location, the pitching hydrofoil is able to produce thrust but of low efficieny. However, the comparison with available results based on nonviscous flow investigations shows that the thrust and efficiency in these cases is highly overestimated. It is connected with the strong vortical structures near the leading edge. The same combination of parameters but in the case of pivot point located in front of the foil, is found more efficient. The flow pattern analysis shows that in this case the dominant leading edge vortex is weaker and it is washed downstream easier.
