EXPERIMENTAL STUDIES ON HYDRODYNAMIC CHARACTERISTICS OF SUPERCAVITATING VEHICLES

Associate Prof. Xulong Yuan

College of Marine, Northwestern Polytechnical University, Xi’an, China

yuanxulong@nwpu.edu.cn

Proceedings of the 8th International Symposium on CavitationCAV2012 – Abstract No. 87

August 14-16, 2012, Singapore

NORTHWESTER POLYTECHNICAL UNIVERSITY

Xi’an City——Ancient Capital of China

Bell Tower —— the symbol of Xi’an

Terracotta Horses and Warriors——One of the eight wonders of the world

Big Wild Goose (Da Yan) Pagoda ——a holy place of Buddhism

An Introduction to NPU Founded in 1938 Research-oriented; Multi-disciplinary International Science and Technology

(Aeronautics; Astronautics; Marine Technology)

The Youyi campus takes an area of 198 acres.

Youyi Campus

38 kilometers from the Youyi Campus;

Taking an area of 645 acres.

Chang’an Campus

Faculty and Staff 3900Full and Associate Professors 1380Academicians of CAS/CAE 15

Students 25,700

Undergraduates 14,360

Postgraduates 11,340

1. School of Aeronautics

2. School of Astronautics

3. School of Marine Engineering

4. School of Materials Science

5. School of Mechatronics

6. School of Mechanics and Civil Construction

7. School of Power and Energy

8. School of Electronics and Information

9. School of Automation

10. School of Computer Science

11. School of Natural and Applied Sciences

12. School of Management

13. School of Humanities, Economics and Law

14. School of Life Science

14 Academic Schools

Overview1. 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。

So we arranged a series of experiments in water-tunnel to test the hydrodynamic characteristics of different supercavitating vehicles.

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: Ø400×2000mmVelocity range: up to 18m/sPressure range: 20kPa~300kPaMinimum cavitation number: 0.15Digitalize velocity and pressure control system

2. Experimental Setup

Compressed air

Embedded Balance

Pw Pt

Fx Fy Mz， ，

Pressure transducers

Pc

DAQ

DAQ

V

Camera

Angle adjusting system

Gas mass-flow-rate controller

Qm

• (2)Test Scheme

ALICAT MC: 0~200 SLPM, 1%

Kulite pressure sensor• Range: 1.3bar,1‰

MEGA SPEED MS75K:• 2000fps@504X506

3-component embedded balance• X force range: 0~3kg• Y force range:-3~3kg• Mz moment range: -

0.6~0.6kgm

Agilent 34972A• Resolution: 61/2

• Scan rate: 120/s

2. Experimental Setup

• (3)Test Models– M1~M3– M4

2. Experimental Setup• Cavities at different ventilation flow-rate of M1~M3

M1 M2 M3

3. Data analysis and conclusion• (1) Hydrodynamic coeffients of

m4– Drag coefficient vs angle of attack

0. 00

0. 05

0. 10

0. 15

0. 20

0. 25

0. 30

0. 35

0. 40

-2. 00 -1. 50 -1. 00 -0. 50 0. 00 0. 50 1. 00 1. 50 2. 00 AOA/ °

Cx Cxc Q40 Cxc Q60 Cxc Q100

3. Data analysis and conclusion• (1) Hydrodynamic coeffients of

m4– Lift coefficient vs angle of attack

- 0. 20

- 0. 15

- 0. 10

- 0. 05

0. 00

0. 05

0. 10

0. 15

0. 20

- 2. 00 - 1. 50 - 1. 00 - 0. 50 0. 00 0. 50 1. 00 1. 50 2. 00 AOA/ °

Cy Cyc Q40 Cyc Q60 Cyc Q100

3. Data analysis and conclusion• (1) Hydrodynamic coeffients of

m4– Moment of pitch vs angle of attack

- 0. 04

- 0. 03

- 0. 02

- 0. 01

0. 00

0. 01

0. 02

0. 03

0. 04

- 2. 00 - 1. 50 - 1. 00 - 0. 50 0. 00 0. 50 1. 00 1. 50 2. 00

AOA/ °

mz mzc Q40 mzc Q60 mzc Q100

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 attackAt 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

A

C

A

C

0

0

x A

x

x x A

CC

C C

xC

yC

zm0

( )

A

y

y A A C

CC

0

( )

A

z

z A A C

mm

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 EndThanks for your attention.