Improved Prediction of Sheet Cavitation Inception Using Bridged Transition Sensitive Turbulence Model and Cavitation Model

Abstract

Sheet cavitation inception can be influenced by laminar boundary layer flow separation under Reynolds numbers regimes with transitional flow. The lack of accurate prediction of laminar separation may lead to massive over-prediction of sheet cavitation under certain circumstances, including model scale hydrofoils and marine propellers operating at relatively low Reynolds number. For non-cavitating flows, the local correlation based transition model, γ−Reθ transition model, has been found to provide predictions of laminar separation and resulting boundary layer transition. In the present study, the predicted laminar separation using γ−Reθ transition model is bridged with a cavitation mass transfer model to improve sheet cavitation predictions on hydrofoils and model scale marine propellers. The bridged model is developed and applied to study laminar separation and sheet cavitation predictions on the NACA16012 hydrofoil under different Reynolds numbers and angles of attack. As a reference case, the open case of the PPTC VP1304 model scale marine propeller tested on an inclined shaft is studied. Lastly as an application case, the predictions of cavitation on a commercial marine propeller from Kongsberg is presented for model scale conditions. Simulations using the bridged model and the standard unbridged approach with k−ωSST turbulence model are performed using the open-source package OpenFOAM, both using the Schnerr–Sauer cavitation mass transfer model, and the respective results are compared with available experimental results. The predictions using the bridged model agree well compared to experimental measurements and show significant improvements compared to the unbridged approach.

New proposals for coupling cavitation models with laminar/turbulent transition models: application to a cavitation sheet over a NACA 16 012

“…However, the cavity is strongly unsteady even at an incidence angle of 5 degrees, which is not observed experimentally. By multiplying the evaporation term with the intermittency (model 2), cavitation occurs away from the NACA surface and is not able to attach the surface as observed in [42]. Even if this feature could be in agreement with some observations for instance by Katz [18], who observed that cavitation first occurs in the shear layer and not at the wall, it seems that such a modelling approach is not able to capture the experimentally observed pattern.…”

“…Downstream the position x/c = 0.7 the pressure is equal to the saturation pressure whatever the model. As noticed by Ge et al [42], it seems that, by making the coefficient Cv proportional to the intermittency (see model 2), the cavitation sheet is not able to attach the wall surface. However, this feature is removed by using a threshold on the turbulence intensity or by making the coefficient Cv proportional to the turbulent intensity.…”

“…However, the simulations of propellers are considered not conclusive by the author, who proposes further validations and calibrations. Ge, Svennberg, and Bensow [42] propose to bridge the Schnerr & Sauer [29] cavitation model with the transition model of Menter et al [37] instead of making the coefficient constant Cvap dependent on the intermittency. They justify this choice by the fact that the latter prevents the development of cavitation at the wall surface.…”