Merging theory-based cavitation model adaptable with non-condensable gas effects in prediction of compressible three-phase cavitating flow

Abstract

The phenomenon of turbulent multiphase flow, such as cavitating flow, with phase change, becomes more complicated taking into account the non-condensable gas as an additional phase. The water, which is the operating fluid, contains a specified amount of dissolved air; as a result, the cavitating flow needs to be considered as a three-phase (i.e. water, vapor and air) flow. Although the existence of dissolved air is well known, most numerical models neglect it; as such, its effect is usually underestimated so far. To this end, the present work is devoted to developing a modified cavitation model based on the merging theory, taking into account the dissolved air in an Eulerian approach. The diffusion process is modeled to constitute the new bubble of the mixture; as a result, the bubble pressure is corrected based on the local air level. Also, the pressure fluctuation effect is applied in the calculation of the pressure of the mixture bubble. To have a more accurate estimation of the density of phases in the situation with a high-pressure difference, the liquid and gas phases are assumed as compressible fluids and modeled by the Tait equation and ideal gas law, respectively. To avoid overestimation of the turbulent viscosity while the standard turbulence model is used, the Density Corrected-Based model is employed to modify the turbulent viscosity employed in k−ε turbulence model. The dynamic characteristics of cavitating flow are analyzed using Power Spectral Density (PSD) and Continuous Wavelet Transform (CWT) techniques. In addition, the cavitating flow is visualized experimentally, and the captured frames are analyzed using image processing to provide temporal-spatial gray level distribution. The present work declares the major role of gas content on the cavitating flow and assesses the efficiency of the proposed numerical model in the prediction of three-phase cavitating flow.