Numerical simulation of supercavitating flow created by cavitators with different shapes Presenter：Shuai Zhang Institute of Aerospace and Material Engineering National University of Defense Technology Changsha 410073, P.R. China

Contents Introduction Modeling and computational approaches 1 Introduction 2 Modeling and computational approaches 3 Results and discussions 4 Conclusion NUDT

Introduction Supercavitation, which could decrease more than 90% of the drag, is an outstanding method of anti-drag for high speed fully-submerged vehicles. As a result, it has attracted more and more interests resently. Cavitator is an important facility of supercavitating vehicle, its performance has a deep influence on cavitation effects and drag of the vehicle. NUDT

Introduction Experimental methods High-Speed Projectile Drag Analysis Water tunnel High-Speed Numerical methods NUDT

Introduction Singhal et.al established natural cavitating rate model based on once order Rayleigh-Plesset equation, successfully simulated the supercavity in comparison with the results of experiments. Then, plenty of natural supercaviting simulations are carried out based on the Singhal’s model. Especially, the model of Bakir et al. was utilized by the generic CFD code ANSYS CFX, which is the basement of this paper. NUDT

Modeling and computational approaches A. Governing equations The continuity, momentum equations of the mixture phase: The continuity equation of the vapor phase: The mixture property: NUDT

Modeling and computational approaches B. Natural cavitation model The Rayleigh-Plesset equation which provides the basis for the rate equation controlling vaporization and condensation is given by: NUDT

Modeling and computational approaches C. Turbulence model The standard turbulence model is used in this study: NUDT

Modeling and computational approaches The generic CFD code ANSYS CFX was utilized to investigate the supercavitation flow. The governing equations discretized by the Finite Volume Method(FVM). The convection terms were approximated by a high order resolution scheme while the diffusion terms were approximated by the second-order central difference scheme. NUDT

Results and discussions Figure 1 Schematic of the vehicle For the sake of simulating that the vehicle is navigating at the 10m depth underwater with the velocity of 100m/s and no angle of attack. The velocity of the incoming flow is 100m/s, with no angle of attack, and the pressure of the environment is 0.2MPa. Figure 2 Mesh of the simulation for supercavitation NUDT

Results and discussions Shape 1 Shape 2 Shape 3 Shape 4 Shape 1 Shape 2 Shape 3 Shape 4 Figure 3 Shapes of supercavity NUDT

Results and discussions Shape 1 Shape 2 Shape 3 Shape 4 Figure 4 Pressure distribution on the front surface of the cavitator NUDT

Results and discussions Shape 1 Shape 2 Shape 3 Shape 4 Figure 5 Water volume fraction distribution along the surface of the vehicle body NUDT

Results and discussions Shape 1 Shape 2 Shape 3 Shape 4 Figure 6 Friction coefficient distribution along the surface of the vehicle body NUDT

Results and discussions Shape 1 Shape 2 Shape 3 Shape 4 Table 1 Drag data under different cavitator conditions (N)   Shape 1 Shape 2 Shape 3 Shape 4 PC (relative decrease) 14520.8 13432.3 (7.5%) 10561.2 (27.3%) 8581 (40.9%) TP 14831.1 14210.9 11345 9375.3 Percentage of TP from PC 97.9% 94.5% 93.1% 91.5% TF 15.9 196.5 320.2 1141.3 RD 14847 14407.4 11665.2 10516.6 Percentage of RD from TF 0.1% 1.4% 2.7% 10.9% PC: the pressure drag force acting on the cavitator TP: the total pressure drag force acting on the vehicle TF: the total friction acting on the vehicle RD: the resultant drag force consisting of TP and TF NUDT

Conclusion A. Under the same conditions of diameter and income flow, disk cavitator owns the highest cavitating capability, but the pressure drag on cavitator is the largest of all. Convex conical cavitator has a opposite performance, there is wet part at the tail of the vehicle ,but the the pressure drag on cavitator decrease 40.9% relatively. The other two perform between disk cavitator and convex conical cavitator. NUDT

Conclusion B. The pressure drag on cavitator is higher than 90 percents of total pressure drag, indicating that the pressure drag on cavitator is the key part of total pressure drag, it is significant to reduce the total pressure drag through optimal design of the shape of cavitator. NUDT

Conclusion C. Good positive correlation is found between water volume fraction and friction coefficient distribution along the surface of vehicle body. If the surface touches water, the friction will jump sharply, indicating that the cavitating method of anti-drag is outstanding to reduce the friction of the underwater vehicle. NUDT

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