Unsteady forces and moments acting on a cantilevered rectangular hydrofoil with tip clearance in cavitating conditions

It is known that the lift and drag forces of hydrofoil increase then decrease with the decrease of cavitation number, i.e. the development of cavitation, in many cases. In our previous study, the measurement of lift and drag forces of cavitating Clark Y-11.7% hydrofoil was conducted under the assumption of two-dimensional flow, which showed the similar tendency to above common knowledge. However, since there was a tip clearance, the bending moment should present to some content due to the flow asymmetry. In the present study, by using hydrofoil supported by a cantilever equipped with totally 8 strain gauges, the lift and drag forces and their moments are separately measured. It is found that the time-averaged moments around midspan due to lift and drag forces change with the decrease of cavitation number as well as the lift and drag forces change. This means that the working points of lift and drag forces move in the spanwise direction, indicating the importance of the three-dimensionality of cavitation development including that due to tip clearance flow. Unsteady lift and drag forces and their moments also show the significant fluctuations due to periodic behaviour of cavitation instabilities.