EXPERIMENTAL STUDIES ON HYDRODYNAMIC CHARACTERISTICS OF SUPERCAVITATING VEHICLES Associate Prof. Xulong Yuan College of Marine, Northwestern Polytechnical University, Xi’an, China Proceedings of the 8 th International Symposium on Cavitation CAV2012 – Abstract No. 87 August 14-16, 2012, Singapore NORTHWESTER POLYTECHNICAL UNIVERSITY

About Xi’an ——Ancient Capital of China About Xi’an ——Ancient Capital of China

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Overview 1. Why do we focus on this topic?2. Experiment Setup.3. Data analysis and conclusion.4. Discuss on tail hydrodynamic model.5. Summary

1. Why do we focus on this topic? (1)To develop high speed underwater vehicles and hydraulic machineries, supercavitation is unavoidable. (2)The hydrodynamic characteristics of supercavitating vehicles is very complicated, especially on the tail part. (3)The hydrodynamic characteristics of the tail part is multi-factor depended and could be parametric modeled 。

2. Experimental Setup (1) High speed water tunnel of NPU – It’s a closed cyclic water tunnel with cylinder test section – Equipped with complete force balances, distributed pressure measuring system, ventilation system, high-speed camera, PIV system and flow noise measuring and analysis system, etc. – Mainly used to study cavitation flow, hydrodynamic characteristic and flow noise characteristic of underwater vehicles. Test section size: Ø400×2000mm Velocity range: up to 18m/s Pressure range: 20kPa~300kPa Minimum cavitation number: 0.15 Digitalize velocity and pressure control system

2. Experimental Setup (2)Test Scheme ALICAT MC: 0~200 SLPM, 1% Kulite pressure sensor Range: 1.3bar,1‰ MEGA SPEED MS75K: 3-component embedded balance X force range: 0~3kg Y force range:-3~3kg Mz moment range: -0.6~0.6kgm Agilent 34972A Resolution: 6 1/2 Scan rate: 120/s

2. Experimental Setup (3)Test Models – M1~M3 – M4

2. Experimental Setup Cavities at different ventilation flow-rate M1 M2 M3

3. Data analysis and conclusion (1) Hydrodynamic coeffients of m4 – Drag coefficient vs angle of attack

3. Data analysis and conclusion (1) Hydrodynamic coeffients of m4 – Lift coefficient vs angle of attack

3. Data analysis and conclusion (1) Hydrodynamic coeffients of m4 – Moment of pitch vs angle of attack

3. Data analysis and conclusion (2)hydrodynamic characteristics of M1~M3

3. Data analysis and conclusion (3)Comparation of M1~M3 – With the decrease of diameter of cavitator – the slenderness of supercavity increase – drag coefficient gets lower – so does the attaching angle and critical angle

4. Discuss on tail hydrodynamic model (1)Attaching angle of attack At which the tail begins to attach the cavity wall. It is affected by the slenderness of supercavity, and it can be zero. (2)Critical angle of attack At which the tail provides max negative moment of pitch. It decreases with the increase of slenderness of vehicles. (3)Drag coefficient model of tail part (4)Lift coefficient model of tail part (5)Moment of pitch model of tail part

5. Summary (1)There are an attaching angle and a critical angle of attack that govern the hydrodynamic characteristic of supercavitating vehicles. (2)Within the attaching angle of attack, the drag coefficient is constant, lift and pitching moments curve take zero value. (3)Between attaching angle and critical angle, the cx, cy and mz can be described linear approximately. To be more precise, the curve should be described using polynomials. (4)The attaching angle and critical angle is determined by the slenderness of vehicles and the supercavitaty. By ventilation model experiment in water tunnel, the hydrodynamic coefficient can be acquired and formulated.

The End Thanks for your attention.