Development of Efficient and Accurate Parallel Computation Algorithm Using Moving Overset Grids on Background Multi-Domains for Complex Two-Phase Flows

Minho Ha,Hanshin Seol,Min-Jae Kim,Bu-Geun Paik,Young-Rae Jung,Cheolung Cheong

doi:10.3390/app8101937

Minho Ha, Hanshin Seol + Show 4 more

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https://doi.org/10.3390/app8101937

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Abstract

The goal of this study involves developing an efficient and accurate parallel computation method for two-phase flow problems including complex moving foreign bodies. The proposed parallel computing techniques are based on the moving body-fitted grids’ overset on background multidomains with grid-overlapping at their interface. First, the cavitation flow over the hemispherical head form is investigated using the two-phase flow solver, which is validated by comparing the numerical and experimental results. Subsequently, the parallel computing technique based on the multidomain method that divides the computational domain into several smaller subdomains is proposed to facilitate more efficient numerical simulations. At the interface of the subdomains, the grid-overlapping method is proposed for more accurate simulations. The illustrative computations indicate that the accuracy of the parallel computation combined with the grid-overlapping method on multidomains is identical to that of the serial computation based on a single block, albeit with a significant reduction in the computation time. Finally, the moving overset grid technique is combined with the background multidomain method and applied to simulate the gust flow that is generated by the pitching motions of the twin hydrofoils. The overset grid technique includes the following three sequential steps: hole-cutting, finding donor cells, and bilinear interpolation. The prediction results for the inflow gust generated by oscillating hydrofoils closely follow the measured results.

Highlights

Local static pressure in the vicinity of a foreign body in a liquid decreases to the vapor pressure when the object moves fast, and cavities are generated by the phase change from a liquid to gas
Efficient and accurate parallel computation methods for two-phase flow problems involving complex moving foreign bodies were developed using the parallel computation based on the moving body-fitted grids overset on background multidomain meshes
The solver was applied to predict the cavitation flow over a hemispherical head form, and its validity was confirmed by comparing its numerical results with the measured data

Summary

Introduction

Local static pressure in the vicinity of a foreign body in a liquid decreases to the vapor pressure when the object moves fast, and cavities are generated by the phase change from a liquid to gas. The vaporization of liquid due to decreases in the pressure is generally called cavitation. If the pressure increases again, the cavity explodes and generates high pressure and heat that can damage a foreign body such as a propeller, a pump, and a nozzle. The parts are designed for operating without cavitation in their normal operating conditions. The cavitation phenomena are used to reduce the viscous drag of a submerged vehicle. The viscosity of gas or vapor is lower than that of a liquid, and the frictional drag of the vehicle is reduced by covering the vehicle body with cavitation

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