Detection of free surface waves signature induced by submarine in the stratified environment has been a canonical question. In this paper, we investigate the main body aspect ratio of a generic submarine effect on the free surface waves using RANS simulation. The slenderness ratios L/D = 7, 8, 9, 10, 11 have been chosen, and the major axis (L) is aligned with the incoming flow. The Reynolds number based on the minor axis (D) and the incoming velocity (U) is Re = 106. All the simulations are placed in the linearly stratified fluid background with a constant buoyancy frequency. The linearly distributed stratification of density is achieved by specifying the distribution of water temperature. Take the Joubert BB2 submarine model as an example, the complex flow field when operating near the free surface is simulated and analyzed. The effect of the body slenderness on free surface waves is assessed by comparing the wave height and Kelvin angle. The results show that the bigger slenderness of the body, the smaller fluctuations on the free surface, that is, L/D = 11 achieves the lowest wave height and Kelvin angle.
A stratified fluid is defined by its mean density variation with depth as a result of any change in salinity and/or temperature. Density stratification is an important feature of oceans and the atmosphere. Stratification can have a significant effect on the mixing process and dynamics of the fluid. However, in previous studies, the flow field around marine vessels is usually studied by ignoring the effect of stratification for simplicity.
There are extensive experimental and numerical studies on the stratified flow around canonical geometries such as spheres, cylinders, and spheroids. For example, experimental investigations on internal waves generated by a sphere towed in a stratified fluid were presented by Hopfinger (1991), Chomaz (1991) and Bonneton (1993). They analyzed the internal waves and turbulence waves using the fluorescent dye technique. Recently, some researchers used computational fluid dynamics (CFD) methodology to simulate the stratified fluid. Ortiz- Tarin (2019) used the large-eddy simulation to elucidate the effect of ambient stratification on flow past a prolate spheroid. The influence of the body slenderness ratio is assessed by comparing the present results with previous work on a sphere. An overall result is that the flow past a slender body exhibits stronger buoyancy effects relative to a bluff body. Cao (2020) simulated the sphere wakes in both stratified fluid and nonstratified fluid and analyzed the drag force, turbulence wakes, density fluctuations and coherent vortex structures.
