Hydrodynamic Research Of Drag Reduction For High Speed Vehicle Underwater

In research of underwater weapons, reducing the drag of underwater high speed vehicle has been an important subject. And one of the hottest research topics is supercaviation technique, which can reduce the frication drag of the vehicle effectively. Another technique being put forward latest is the un-separated shape scheme, which aims to reduce the pressure drag. In this thesis, numerical simulations on the two sides were carried out with CFD software Fluent.This thesis was composed of three parts. In the first part, research was done on some problems of cavitator. Theoretical formulas for calculating supercavity's size and cavitator's drag coefficient were summarized. Numerical simulation was performed for supercavitation flows. The results of simulations were compared with classical experiment dates, which confirmed that numerical simulation with Fluent for supercavitating flows is feasible. Analysis was done on the law of how the supercavitation's size changed by varying the cavitation number, cavitator's shape and diameter. It was concluded that the supercavity's sizes were varied with different types of cavitator and would increase as the cavitator diameter increased or the cavitation number decreased. The drag coefficient of cavitator was calculated, and the results tallied well with theoretical dates. In the second part, simulation was done on 2D cavitator with fixed angle in steady and dynamic supercavitating flows. And the analysis of the effect of fixed angle on supercavity shape, drag and lift was done. The results indicate that the shape of supercavitation is affected by fixed angle slightly, and the drag coefficients decrease and lift coefficients increase with the increase of fixed angle in a range. In the last section, research was carried out on the notion of reducing pressure drag with an un-separated shape. Simulation was done on the flow of bodies which have un-separated flow pattern. The simulation results were analyzed to validate the pressure drag reduction theory and its feasibility. It is proved that this drag reduction scheme is only workable in a small range.