Experimental and Numerical Analysis of Cavitation Inception in Jets

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ABSTRACT Proposal Number: CTS-9706701 Principal Investigator: Katz The present study is an integrated experimental and numerical effort to determine and explain the conditions for the onset of cavitation in high-Reynolds-number jets. Experimentally, high resolution PIV will be used to measure the unsteady velocity distribution within primary vortices, from which one can extract the vorticity and strain. Holography and video photography will be used to determine the motion of artificially-introduced microscopic seed bubbles. The pressure field within the primary eddies will be determined using microscopic bubbles as pressure sensors. The conditions for cavitation inception within observed secondary vortices (ribs) will be used to estimate the corresponding pressure minima. Computationally, Lagrangian simulations of primary structures will be conducted, with initial and boundary conditions provided by the experiments. The simulations will be first validated by comparison with the experimental results, and then used to analyze the impact of slenderness ratio on the pressure field within primary vortices and the strain field that they induce. The measured strain field will be used in direct numerical simulation of the rollup of streamwise vorticity perturbations in the braids. The experimentally-determined pressure minima within the ribs can then be used to select the appropriate streamwise vorticity perturbation levels. This combined approach will enable a mapping the pressure distribution within the near field of the jet.