Evaluation of modified turbulent viscosity on shedding dynamic of three-phase cloud cavitation around hydrofoil – numerical/experimental analysis

Abstract

Purpose This paper aims to focus on the cavitating flow around the Clark-Y hydrofoil when the dissolved air is taken into account as the third phase. As the RNG k-epsilon model yields poor prediction due to overestimation of viscosity, the modification approaches including density corrected method, filter-based model and filter-based density correction model are used, and the turbulence model is modified. Also, the numerical results are compared with the experimental data. Design/methodology/approach The cavitating flow is known as a complex multi-phase flow and appeared in the regions where the local pressure drops under saturation vapor pressure. Many researches have been conducted to analyze this phenomenon because of its significant impact on the erosion, vibration, noise, efficiency of turbomachines, etc. Findings The experiments are conducted in a rectangular test section equipped with Clark-Y hydrofoil providing cavity visualization, instantaneous pressure and vibration fluctuations. The simulations are carried out for different cavitation numbers with and without dissolved air. The Fast Fourier Transform, continues wavelet transform and temporal-spatial distribution of gray level are implemented to extract and compare the shedding frequency of experiments and numerical predictions and cavitation evolution. It is concluded that the flow structure, shedding frequency and time-averaged characteristics are highly influenced by the dissolved air. Also, the numerical prediction will be more satisfactory when the modified turbulence models are applied. Originality/value To the best of the authors’ knowledge, the originality of this study is the modification of the turbulence model for better prediction of cavitating flow, and the validation of numerical results with corresponding experimental data.

Experimental analysis on unsteady characteristics of sheet/cloud cavitating Venturi flow under the effect of dissolved air

“…Cavitation is known as a sudden phase change phenomenon, which usually can be observed in high-speed flow and is due to low-pressure regions falling below the local saturation pressure of the operating fluid. This phenomenon exists in many applications such as hydro-power turbines, high-speed propellers, pumps and rockets [1][2][3][4]. The existence of highly dynamic cavitating flow, in particular with intensive cavity breakup, may lead to severe destructive effects such as erosion on the surface of the object, vibration, noise and high-frequency pressure fluctuations [5][6][7][8][9][10].…”

Dissolved air effects on three-phase hydrodynamic cavitation in large scale Venturi- Experimental/numerical analysis

“…Their simulations were in good agreement with the experimental data in the same geometry and operating conditions. Malekshah et al [29] concentrated on the cavitating flow around the Clark-Y hydrofoil with dissolved air as the third phase. Because the RNG k-epsilon model overestimates viscosity and yields poor predictions, the turbulence model is changed using the density corrected model (DCM) and filter-based density correction model (FBM).…”