Cavitation generation and inhibition. I. Dominant mechanism of turbulent kinetic energy for cavitation evolution

摘要

Through energy conservation and transformation perspectives, we numerically investigated the physical mechanism of cavitation generation surrounding the two-dimensional NACA 0015 hydrofoil using the mass-transfer cavitation model and modified-RNG k-epsilon model. Cavitation generation is triggered by strong turbulent kinetic energy (TKE) with pressure below the saturation pressure. However, cavitation development absorbs TKE as phase-change energy and decreases kinetic energy in near-wall flow fields, thereby increasing pressure according to the energy conservation law. The increased pressure closes the cavity and generates an attached vortex or re-entrant jet, which causes cavitation collapse, conversely decreasing the pressure to the saturation pressure in the leading edge. Simultaneously, the cavitation collapse releases phase-change energy that increases TKE to a maximum so that a new period begins. Cavitation evolution is an interaction between the vapor and liquid flow fields associated with energy conservation and transformation among TKE, pressure, and phase-change energy. Beyond 50% of the chord length, the TKE and pressure-energy in the near-wall flow fields decrease, resulting in the cavitation instability. Within the cavity, the relationship between the local TKE intensity and the volume fraction of water vapor is quantitatively defined as a linear function. Two designs are proposed for the verification of the mechanism and cavitation inhibition, namely, grooves on the hydrofoil surface and bilateral wings in the tail. Grooves do not affect TKE intensity significantly and hence cannot change the cavitating flows. Bilateral tail-wings transfer TKEs from the leading edge to the wake flows and inhibit the cavitation remarkably. The TKE distribution is the dominant mechanism for cavitation generation and stability.