Fluid Force and Flutter Stability of a Pitching Hydrofoil in Subcavitation Region

Abstract

The torsional flutter boundary of a pitching hydrofoil was experimentally investigated in the subcavitation region. Unsteady lift and moment were measured using load cells installed in a torsional vibration apparatus. The type and the degree of separation on the hydrofoil exert much influence on the unsteady fluid force and the flutter boundary in the subcavitation region. In the absence of separation, no unstable range of the flutter exists in the noncavitation or the subcavitation region. In the noncavitation region, the flutter boundary extends to the higher reduced frequency side as the angle of attack increases. In the subcavitation region, these flutter boundaries remain until the cavity length reaches the mid-chord. However, the flutter boundary shifts towards the higher reduced frequency side, keeping the width of the unstable range almost constant as the cavity length extends from the mid-chord to the full chord.