Characteristics of Bubble-Collapse Pressures in a Karman-Vortex Cavity

Flow patterns and bubble-collapse pressures in a Karman-vortex cavity behind a circular cylinder are investigated for several Reynolds numbers and cavitation numbers. The time histories and intensity distributions of the pressures are respectively measured by using a pressure transducer and pressure-sensitive films. The cavitation aspects are also observed by high-speed photography. The bubbles frequently collapse at the instant when the Karman-vortex cavity separates from the cylinder or the cavity itself. High impulsive pressures with spike pulses over 60MPa occur in the separation or the vortex formation region. With a decrease in cavitation number σ, these regions are combined into one. With an increase in Reynolds number Re, however, the distributions of the impulsive pressures show the same tendency, because they have the same Strouhal number St, but the pulse count rate and magnitude of maximum local impulsive pressures increase.