Observations of Cavitation on a Three-dimensional Oscillating Hydrofoil

A test apparatus was designed and constructed to observe the effect of sinusoidal pitching oscillations on the cavitation of thredimensional hydrofoils. The apparatus is capable of oscillating hydrofoils at a rate up to 50 Hz and provides for adjustments in oscillation amplitude and mean angle of attack. Observations of the effect of pitching oscillation on cavitation have been made for a NACA 64-309 (modified) hydrofoil operating a its designed mean angle of attack of 7O with an oscillation amplitude of 2O. Photographs illustrating the interaction between natural cavity shedding frequencies and the foil reduced frequency are included. Nomenclature c = Foil chord length, 0.154m (6in) j = Excitation frequency in Hz k = Reduced frequency = wc/2Um P, = Water vapor pressure in kPa Pm = LTWT test section pressure in kPa Re = Reynolds number = Umc/v U, = LTWT test section velocity in m/s w -= Foil excitation frequency in rad/s a! = Hydrofoil angle of attack in degrees v = Kinematic viscosity in m2/s p = Fluid density in kg/m3 a = Cavitation number = (Pm P , ) / ( O . S ~ U ~ )