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.

Finite element method is used to study the formations of the penetration jet, the bulge, and the burr in the designed reusable perforating gun. The attached layer of the soft metal on the perforator is studied for the controlling of the bulge height on the casing of the reusable perforating gun. Results indicate that the shaped charge jet is initially formed in the center of the shaped charge liner and then the material of the liner is driven to the centerline of the liner by the detonation wave. The attachment of the soft metal layer to the cartridge of the perforator can be beneficial to control the bulge height. The design on the blind holes on the casing can affect the burr height formed by the collision between the jet and the casing. With the increase in the liner angle, the penetration width on the cement wall of the wellbore is increased.

Internal velocity distribution is an important content of flow structure and reveals the gas loss mechanism for supercavitating flows. Considering the three-phase momentum interactions and the water-vapor mass transport, the water-gas-vapor multi-fluid model is established to simulate ventilated supercavitating flows at high speed in the frame of the nonhomogeneous multiphase flows theory. Based on the model, the gas velocity field inside supercavity is studied. In the case of supercavitating flows around disk cavitator, two vortex cores are formed in the longitudinal plane under the actions of the adverse pressure gradient in the tail and the viscous friction on cavity surface, and are symmetrically distributed about the longitudinal axis. Most inner regions in the cavity cross section are occupied by circulation flows, where the velocity is in the opposite direction of incoming flows and decreases in the radial direction. When passing the vortex center, the velocity changes direction and increases in the radial direction. Part of gas departs to wake flows from the outermost regions close to the section boundary. The results confirm Spurk’s assumption for gas entrainment in detail. It is also found that the gas velocity distribution in the cross section through vortex cores does not depend on cavitation number. Supercavitating vehicle has the similar internal velocity distribution and gas loss mechanism. Due to the added viscous effect of the enveloped body, there are multiple axisymmetrical distributed vortices inside the cavity. The relative distance between the vortex core and the cavity wall increases downstream. Computations of ventilated supercavitating flows at different Reynolds numbers show that the gas leakage is decreasing with increasing Reynolds number for a given cavitation number. This study deepens the understanding of gas loss for ventilated supercavity at high speed, and lays a foundation for further refinement of the dynamic model of the maneuvering ventilated supercavity and the control of ventilated supercavitating flows.

The cloud-cavitation shedding mechanism was numerically investigated around the NACA 0015 hydrofoil of α = 7° and σ = 0.7, 0.67 under the identical computational conditions as in Paper I [W. Jin, AIP Adv. 11, 065028 (2021)]. We discovered the invisible tail wing and self-inhibition effects of cloud cavitation. As the invisible tail wing of cloud cavitation swings up, the generated re-entrant jet causes cavitation shedding or collapse by the “sweeping and ejection” processes and simultaneously moves away turbulence kinetic energy (TKE) from the near-wall flow fields of the leeward hydrofoil surface, stopping the cavitation generation. In low pressure regions, non-uniform TKE intensity distributions cause different water-vapor volume fractions, resulting in discontinuity of cavitation generation. The attached vortex accompanying an individual cavity is defined, which causes fluctuations and cavitation instability on the bottom of the cavity. The cavity-bubble truncation and stretching are two primary transition mechanisms from the sheet to cloud cavitation. Compared with the invisible tail wing of cloud cavitation, the fixed unilateral wing can more effectively inhibit the cloud shedding because it can redistribute energies to two hydrofoil surfaces and transfer the strong TKE intensity from the minimum to the high-pressure region, which inhibits flow boundary layer separation and achieves non-cavitation control of the hydrofoil. Energy transfer and balance are the most effective mechanisms for inhibiting cloud cavitation. Larger unilateral wing sizes result in weaker TKE intensity along the leeward hydrofoil surface as well as more significant cloud-cavitation inhibition. The TKE intensity in the leading edge of the leeward hydrofoil surface determines the fluid boundary layer separation and cloud-cavitation stability.