Numerical Simulation and Analysis of Cavitating Flow around Hydrofoil and in Injector Nozzle

Abstract

Cavitation occurs in flow regions where the hydrodynamic effect reduces the local pressure below the saturation vapor pressure of the liquid, causing the formation of vapor bubbles. When these vapor bubbles enter the region of higher pressure, they collapse violently producing enough force to damage the solid body. In case of hydrofoils, cavitation can affect the hydrodynamic and structural performance potentially. In injector nozzles, cavitation can cause a fuel injection instability and decreased fuel efficiency. Cavitation on hydrofoils and nozzles mainly depends on the flow parameters, shape and material of the hydrofoil or nozzle. In the present work to study the cavitation phenomenon three different studies have been made on hydrofoils and in injector nozzle. In first part of the work, the performance of two different cavitation model and four different turbulence models is compared with the available experimental data on cavitating NACA4412 and Clark-y hydrofoil in terms of lift coefficient, drag coefficient, Strouhal number and velocity profiles using ANSYS Fluent. Among all the turbulence models, the Realizable k-𝜖 turbulence was found to be more accurate, whereas the Zwart-Gerber-Belamri cavitation model is found to be more reliable. Using the Realizable k-𝜖 and Zwart-Gerber-Belamri cavitation model, the research was further extended to study the hydrodynamic and structural performance of 3D stainless steel MHKF-180 and NACA4418 cavitating hydrofoils using one-way fluid structure interaction (FSI). The simulation is performed at a chord-based Reynolds number, Re = 750000, for different cavitation numbers and angles of attack. On comparing the hydrodynamic performance of both the foils, in terms of lift coefficient, MHKF-180 found to perform better than NACA4418 under the cavitating condition. Whereas, from structural point of view, the MHKF-180 shows larger tip deformation and von Mises stress than NACA4418 hydrofoil. Further, in the last part of the work, the numerical investigation of cavitation characteristics of conventional (n-dodecane fuel) is compared with the alternative fuel (Oxymethylene ether, OME3) in Engine Combustion Network (ECN) Spray C037 nozzle using CONVERGE code. RNG 𝜅 − 𝜖 turbulence model is used to determine the effect of turbulence, and phase change inside the nozzle is predicted using the Homogeneous Relaxation Model (HRM) coupled with a multiphase mixture model. For model validation, the simulated mass flow rate and cavitation contour shape of n-dodecane fuel are compared with the experimental result provided in the literature. Among both the fuels OME3 found to be more cavitating as compared to n-dodecane fuel.