ABSTRACT

The vortex shedding was simulated by viscous CFD technique when the linearly stratified fluid past a hydrofoil at a constant speed. Based on thermal density current model, the linear stratification of density was achieved by specifying the distribution of temperature. The RANS method was used to simulate the process. The results in this paper showed that the shape of the vortices was different from the angle of attack. The vortex shedding process in homogenous and stratified fluid were different. Compared to homogenous fluid, the vortex shedding occurred first in the linearly stratified fluid at a given Reynolds number. With the increase of the Reynolds number, the size of vortices and the lasting time became larger. It proved that the viscous CFD method was able to simulate the linearly stratified fluid passing a submerged body.

INTRODUCTION

A stratified fluid occurs very commonly in the atmosphere and in the ocean. Because of the sun's thermal radiation and oceanic salt circulation, the oceans are usually stratified and their density, temperature and salinity vary significantly in the vertical direction. When a submerged body moves in a stratified fluid, the fluid particles are subjected to a buoyant effect of volumetric effect that produces a hydrodynamic phenomenon that is different from a homogeneous environment. Large-scale vortex structures are widespread in nature and they play a crucial role in geophysical and industrial chaotic flows. These ordered structures are easily detectable and are visible to the naked eye in many quasi-two-dimensional liquid systems, particularly in the stratified ocean. They can effectively transport momentum, heat and salt, they play an essential role in ocean dynamics, determining the instantaneous fields of velocity, temperature and salinity.

Uniform flow past circular cylinder is a standard configuration for investigating vortex shedding and is well documented at low Reynolds numbers. However, at high Reynolds numbers, the vortex shedding in hydrofoil wake has been studied less despite its occurrence in numerous practical applications; for example in ship propulsion. In the process of simulating model ship propulsion, the Reynolds number is usually range from 105 to 106. So in this paper, we choose three high Reynolds numbers in this range to investigate the vortex shedding of hydrofoil. It will be a good foundation for simulating model ship propulsion.

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