Experimental Investigation of Supercavitating Flows

Byoung-Kwon Ahn*, Tae-Kwon Lee, Hyoung-Tae Kim and Chang-Sup Lee

Dept. of Naval Architecture and Ocean EngineeringCollege of Engineering, Chungnam National Univ.

Background

2

Experimental Observations

Conclusions

General Features: Numerical Results

1

3

4

CONTENTS 2

Drag in water = 103 x Drag in air Greatly increased speed by significant reduction of the drag

Conventional Torpedo: less than 55knots Super-cavitating Torpedo: more than 200knots

Super-cavitation

3BACKGROUND

Shkval II VA-111 Shkval

Shkval Early 1990s Length: 8.2m Diameter: 533mm Weight: 2700kg Warhead weight: 210kg Opt. Range: 7km Speed: 200 + knots Thrust vectoring

Super-cavitating Torpedo (Russia)

4BACKGROUND

Barracuda (Germany)• 350+α knots

SuperCav (US Navy)• under-development

5BACKGROUND

Super-cavitating Torpedo (Germany & USA)

Key technologies of Super-Cavitating Torpedo (ONR)

6BACKGROUND

x

y

UC

U

UBy0()

Developed Numerical Method:• Ideal (Incompressible, Inviscid) flow + Irrotational flow• Dipole and Source distributions on the body and cavity surfaces

loglog

2 2B C C

x

S S S

r qU x ds rds

n

7NUMERICAL ANALYSIS

8NUMERICAL ANALYSIS

• Quiescence condition at infinity:

• Flow tangency condition on the body surface:

• Kinematic condition on the cavity surface:

• Dynamic condition on the cavity surface:

• Cavity closure condition:

• Linear termination model

U

/ 0 on Bn S

( , ) / 0 on c CDf x y Dt S

vp p

. . .( ) 0cC T Et x

Primary Boundary Conditions;

Governing Equation2 0

Typical results (2D):• Pressure and velocity distributions• Cavity length and volume according to the Cav. No.

x/c0 0.5 1 1.5 2 2.5 3

-Cp

,V

t

-1.5

-1

-0.5

0

0.5

1

1.5

PressureVelocity

Cavity length = 2.0ybase/c = 0.13

Wedge Angle(deg) = 15Cavitation Number = 0.27

212

vp p

U

9NUMERICAL ANALYSIS

10NUMERICAL ANALYSIS

Predicted super-cavity length and shape

11NUMERICAL ANALYSIS

Comparison with analytic solutions (by J. N. Newman)

Cavitation No. ( / 4 y 0)

Cavit

yL

en

gth

(no

nd

imen

sio

n)

0 0.5 1 1.5 2 2.5 30

1

2

3

4

5

6

7

8

9

10

Analytic SolutionPresent

Cavitation No. ( / 4 y 0)

Dra

gC

oe

ffic

ien

t(

Cd

/2(y

0)2

)

0.5 1 1.5 2 2.5 33

4

5

6

7

8

9

10

Analytic SolutionPresent

Wedge angle = 45 deg

x/c0 1 2 3 4 5 6 7 8 9 10 11 12 13

y/c

-3

-2

-1

0

1

2

3

4

5

Cavity length, on x-axis = 9.0Cavity length, girthwise = 9.39

Wedge Angle(deg) = 45ybase/Chord = 0.41

Cavitation Number = 0.35

x/c0 1 2 3 4 5 6 7 8 9 10 11 12 13

y/c

-3

-2

-1

0

1

2

3

4

5

Cavity length, on x-axis = 9.0Cavity length, girthwise = 11.4

Wedge Angle(deg) = 90ybase/Chord = 1.0

Cavitation Number = 0.72

Wedge angle = 90 deg

12NUMERICAL ANALYSIS

Super-cavity of the blunt body

13NUMERICAL ANALYSIS

Predicted cavity length and drag forces

Cavitation No. ()

Cav

ity

Len

gth

/Cav

itat

orW

idth

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.60

5

10

15

20

25

30

35

40

10 o

30 o

60 o

90 o

Cavitation No. ()

Dra

gC

oeff

icie

nt

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.5

1

1.5

10 o

30 o

60 o

90 o

14NUMERICAL ANALYSIS

Three dimensional analysis

15NUMERICAL ANALYSIS

Cavity length and maximum diameter

Cavitation number

Ca

vity

ma

xim

um

dia

me

ter

/C

avi

tato

rd

iam

ete

r

0 0.05 0.1 0.15 0.2 0.25 0.30

1

2

3

4

5

6

Cone(90°)

Disk

Cavitation number

Ca

vity

len

gth

/Ca

vita

tor

dia

me

ter

0 0.05 0.1 0.15 0.2 0.25 0.30

10

20

30

40

50

60

70

80

Cone(90°)

Disk

Self et. al (Cone)

Self et. al (Disk)

Self et. al (Cone)

Self et. al (Disk)

16NUMERICAL ANALYSIS

Drag coefficients (Disk)

Cavitation number

Dra

gco

eff

icie

nts

0 0.2 0.4 0.6 0.8 1 1.2 1.40

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Panel methodFisherArmstrong and DunhamPlesset and ShafferLinear

Circular Disk

17NUMERICAL ANALYSIS

Disk type cavitator w/ dummy body

σ CD LS LS/DC DS/DC

0.34 0.82 12,000 60.0 5.6knots

De

pth

(m)

Dra

g(k

N)

100 150 200 250 300-20

-10

0

10

20

30

40

50

60

0

50

100

150

200

250

300

350

400

Depth(m)Drag(kN)

DC(mm) DB(mm) LB(mm)

200 533 8,000

Speed(knots)

De

pth

(m)

100 150 200 250 300

0

10

20

30

40

50

60

70

80

Lcav/Dh = 30Lcav/Dh = 40Lcav/Dh = 50Lcav/Dh = 60

Drag(kN)

De

pth

(m)

0 50 100 150 200 250 300

0

10

20

30

40

50

60

70

80

Lcav/Dh = 30Lcav/Dh = 40Lcav/Dh = 50Lcav/Dh = 60

18NUMERICAL ANALYSIS

Predicted drag forces and required speed in practical conditions

19

CNU Cavitation Tunnel

EXPERIMENTAL OBSERVATIONS

2D Cavitator Analysis & Exp. observation: (V=8.10~10.32m/s)

20EXPERIMENTAL OBSERVATIONS

21EXPERIMENTAL OBSERVATIONS

V=9.4m/s, σ=1.11 V=9.8m/s, σ=1.13

V=9.4m/s, σ=1.16 V=9.8m/s, σ=1.17

V=9.4m/s, σ=1.16 V=9.8m/s, σ=1.17

30˚

45˚

Flat plate

w/o body w/ body

2D Cavitators

Hi-speed Camera

22EXPERIMENTAL OBSERVATIONS

Max Frame Rate 250,000 fps

Max Resolution 1,024 x 1,024

Max at Max Res. 3,000 fps

Max. Rec. Time at 1,000 fps (highest res.)

12.3 sec

23EXPERIMENTAL OBSERVATIONS

Hi-speed Camera (5,000 fps)Video Camera (30 fps)σ=0.83

2D Cavitators

24EXPERIMENTAL OBSERVATIONS

2D Cavitators

2D Cavitators

25EXPERIMENTAL OBSERVATIONS

σ=1.05 σ=0.70

26EXPERIMENTAL OBSERVATIONS

2D Cavitators

Value

Speed (m/s) 11

Temp (C°) 14.0

Density (kg/m3) 997.104

Vapor pressure (Pa) 1,598.14

Depressurized (bar) -0.412 ~ -0.657

σn 2.091 ~ 0.567

3D Cavitators

27EXPERIMENTAL OBSERVATIONS

30mm

30m

m

75mm 75mm

11

22

33 44

28EXPERIMENTAL OBSERVATIONS

Speed(m/s) Temp(C°) Density(kg/m3) Vapor pressure (Pa) Depressurized(bar) σn

11 14.0 997.104 1,598.14 -0.412 ~ -0.657 2.09 ~ 0.57

3D Cavitators

Disk

Disk w/ round

Cone

29EXPERIMENTAL OBSERVATIONS

1.25 0.98 0.88 0.83 0.65

Disk w/ hole

3D Cavitators

σ =

30EXPERIMENTAL OBSERVATIONS

3D Cavitators

Develop a numerical method to predict supercavity Investigate important features of supercavity: cavity length, diameter and drag forcesResults are validated by comparison with existing analytic and empirical values

Observe the early stage of the supercavity profiles generated by various 2D and 3D cavitatorsAccumulate experimental data for parametric information to design of the cavitatorAdditional experiments are on going; ventilation effects, pressure force measurements

Numerical Analysis:

31CONCLUSIONS

Experimental Observations:

Experimental Investigation of Supercavitating Flows

Byoung-Kwon Ahn*, Tae-Kwon Lee, Hyoung-Tae Kim and Chang-Sup Lee

Dept. of Naval Architecture and Ocean EngineeringCollege of Engineering, Chungnam National Univ.