Derivation of “double-loop” Theory and Mechanism of Cavitation-vortex Interaction in Turbulent Cavitation Boundary Layer

“Double-loop” theory was determined by deriving a correlation between turbulent fluctuating kinetic energy and water vapor volume fraction from the momentum equation, which further logically revealed the mystery of cavitation breaking around a three-dimensional symmetry hydrofoil based on the numerical results of large eddy simulation and Zwart-Gerber-Belamri cavitation model. When the second-order fluctuation moment V'xV'x and the streamwise velocity Vx are depleted, a vortex is generated, leading to alternating cavitation interface fluctuations. In one state, cavitation naturally breaks outward from the inner zone, triggering an up-and-down fluctuation in the normal velocity in the gap vortex and transferring external energy to the inner zone. In another state, it triggers a rise in an upward normal velocity in the attached vortex, creating an exchange of energy through the wake. Cavitation collapse caused by a reentrant jet stagnates the reverse Vx so that V'xV'x tends to zero. The pressure implosion resulting from the Shrinkage of the “Like-Rayleigh-Plesset” cavity at cavitation onset is stronger than the pressure implosion created by the vortex field during cavitation breaking.