The influence of nuclei content on cloud cavitation about a hydrofoil

The dynamics of cloud cavitation about a 3D hydrofoil are investigated experimentally in a cavitation tunnel with both an abundance and dearth of freestream nuclei. The rectangular-planform, NACA 0015 hydrofoil was tested at a Reynolds number of 1:4 _ 106, a cavitation number of 0.55 and an incidence of 6°. High-speed photography of cavitation shedding phenomena was acquired simultaneously with unsteady force measurement to enable identification of cavity shedding modes corresponding with force spectral peaks. Two shedding modes are evident for both the nuclei deplete and abundant cases, although each are driven by different flow phenomena. The high-frequency mode for the nuclei deplete case is driven primarily by large-scale re-entrant jet formation during the growth phase, but shockwave propagation for the collapse phase of the cycle. The weaker low-frequency mode occurs because the strength of shedding at the hydrofoil tip varies at half the fundamental frequency. .e dominant mode for the abundant case is the low-frequency mode which is some 1.8 times slower than the nuclei deplete case. The high-frequency mode for the nuclei abundant case is due to the propagation of two shockwaves; the passage of the first only partially condenses the cavity, while the second condenses a much larger region of the cavity.