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

Abstract

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.

Investigation of the Performances of a Diesel Engine Operating on Blended and Emulsified Biofuels from Rapeseed Oil

“…The first core is located at the entrance to the hole, and the second core occurs where the fuel flow expands. The generation of TKE induced by cavitation zone collapse has also been reported in [68,69]. In comparison with DF, for R70E30, the turbulent core formed after the cavitation zone is connected with the turbulent core at the entrance to the hole and is far away from the hole outlet, and the generated TKE dissipates gradually downstream of the nozzle hole.…”

Study on reducing both flow force and cavitation in poppet valves

“…The generation of cavitation is caused by severe turbulent kinetic energy with pressure lower than the saturation pressure. 55 It is closely related to the distribution of turbulent kinetic energy and static pressure. Therefore, the vapor volume fractions, static pressure, and turbulent kinetic energy were used for the analysis of cavitation in the three poppet valves, the results are shown in Figures 13 and 14.

Figure 13.Contours of poppet valves under different pressure drops (valve opening x = 0.5 mm): (a) vapor volume fraction, (b) static pressure, and (c) turbulent kinetic energy.

Figure 14.Contours of poppet valves under different valve openings (pressure drop Δp =14 MPa): (a) vapor volume fraction, (b) static pressure, and (c) turbulent kinetic energy.

…”