Experimental Investigation of
Supercavitating Flows
Byoung-Kwon Ahn*, Tae-Kwon Lee, Hyoung-Tae Kim and Chang-Sup Lee
Dept. of Naval Architecture and Ocean Engineering
College of Engineering, Chungnam National Univ.
CONTENTS
1
Background
2
General Features: Numerical Results
3
Experimental Observations
4
Conclusions
2
BACKGROUND
 Super-cavitation
 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
3
BACKGROUND
4
 Super-cavitating Torpedo (Russia)
 Shkval








Early 1990s
Length: 8.2m
Diameter: 533mm
Weight: 2700kg
Warhead weight: 210kg
Opt. Range: 7km
Speed: 200 + knots
Thrust vectoring
Shkval II
VA-111 Shkval
BACKGROUND
 Super-cavitating Torpedo (Germany & USA)
 Barracuda (Germany)
•
350+α knots
 SuperCav (US Navy)
•
under-development
5
BACKGROUND
 Key technologies of Super-Cavitating Torpedo (ONR)
6
NUMERICAL ANALYSIS
7
 Developed Numerical Method:
• Ideal (Incompressible, Inviscid) flow + Irrotational flow
• Dipole and Source distributions on the body and cavity surfaces

x
 U  x 

SB SC
  log r
q
ds  
log rds
2 n
2
S
C
y
UC
UB
U

y0()
x
NUMERICAL ANALYSIS
8
 Governing Equation
2  0
 Primary Boundary Conditions;
• Quiescence condition at infinity:
  U
• Flow tangency condition on the body surface:
 / n  0 on SB
• Kinematic condition on the cavity surface:
Dfc ( x, y) / Dt  0 on SC
• Dynamic condition on the cavity surface:
p  pv
• Cavity closure condition:
• Linear termination model
t c ( xC.T .E. )  0
NUMERICAL ANALYSIS
9
 Typical results (2D):
• Pressure and velocity distributions
• Cavity length and volume according to the Cav. No.
1.5
1
Pressure
Velocity
0
-0.5
Cavity length = 2.0
ybase/c = 0.13
Wedge Angle(deg) = 15
Cavitation Number = 0.27
0
0.5
1
1.5
x/c
2
2.5
-1
3
-1.5
-Cp , V t
0.5
p  pv

1
2
U
2
NUMERICAL ANALYSIS
 Predicted super-cavity length and shape
10
NUMERICAL ANALYSIS
11
 Comparison with analytic solutions (by J. N. Newman)
10
10
Analytic Solution
Present
9
9
2
Drag Coefficient (Cd / 2 (y0) )
Cavity Length (nondimension)
8
7
6
5
4
3
8
7
6
5
2
4
1
0
Analytic Solution
Present
0
0.5
1
1.5
2
Cavitation No. ( / 4 y 0)
2.5
3
3
0.5
1
1.5
2
Cavitation No. ( / 4 y 0)
2.5
3
NUMERICAL ANALYSIS
12
 Super-cavity of the blunt body
5
5
Cavity length, on x-axis = 9.0
Cavity length, girthwise = 11.4
Wedge Angle(deg) = 90
ybase/Chord = 1.0
Cavitation Number = 0.72
4
3
4
3
2
1
0
1
2
3
4
5
6
7
8
9
10
11
12
y/c
2
1
0
0
-1
-1
-2
-2
-3
13
0
1
2
3
4
5
6
7
8
9
10
x/c
x/c
Wedge angle = 45 deg
Wedge angle = 90 deg
11
12
-3
13
y/c
Cavity length, on x-axis = 9.0
Cavity length, girthwise = 9.39
Wedge Angle(deg) = 45
ybase/Chord = 0.41
Cavitation Number = 0.35
NUMERICAL ANALYSIS
13
 Predicted cavity length and drag forces
40
1.5
o
o
35
30
Drag Coefficient
Cavity Length / Cavitator Width
10
o
30
o
60
90 o
10
30 o
o
60
o
90
25
20
15
1
0.5
10
5
0
0
0.2
0.4
0.6
0.8
1
Cavitation No. ()
1.2
1.4
1.6
0
0
0.1
0.2
0.3
0.4
0.5
0.6
Cavitation No. ()
0.7
0.8
0.9
1
NUMERICAL ANALYSIS
 Three dimensional analysis
14
NUMERICAL ANALYSIS
15
 Cavity length and maximum diameter
6
Cavity length / Cavitator diameter
70
Cone(90°)
Disk
Self et. al (Cone)
60
Self et. al (Disk)
50
40
30
20
10
0
0
0.05
0.1
0.15
0.2
Cavitation number
0.25
0.3
Cavity maximum diameter / Cavitator diameter
80
Cone(90°)
5
Disk
Self et. al (Cone)
Self et. al (Disk)
4
3
2
1
0
0
0.05
0.1
0.15
0.2
Cavitation number
0.25
0.3
NUMERICAL ANALYSIS
16
 Drag coefficients (Disk)
2
1.8
Circular Disk
1.6
Drag coefficients
1.4
1.2
Panel method
Fisher
Armstrong and Dunham
Plesset and Shaffer
Linear
1
0.8
0.6
0.4
0.2
0
0
0.2
0.4
0.6
0.8
Cavitation number
1
1.2
1.4
NUMERICAL ANALYSIS
17
 Disk type cavitator w/ dummy body
DC(mm)
DB(mm)
LB(mm)
200
533
8,000
60
400
Depth(m)
Drag(kN)
350
40
300
30
250
20
200
10
150
0
100
-10
σ
CD
LS
LS/DC
DS/DC
0.34
0.82
12,000
60.0
5.6
-20
100
50
150
200
knots
250
0
300
Drag(kN)
Depth(m)
50
NUMERICAL ANALYSIS
18
0
0
10
10
20
20
30
30
40
40
50
50
60
70
80
100
150
200
Speed(knots)
60
Lcav/D h = 30
Lcav/D h = 40
Lcav/D h = 50
Lcav/D h = 60
Lcav/D h = 30
Lcav/D h = 40
Lcav/D h = 50
Lcav/D h = 60
250
300
0
50
100
150
70
200
Drag(kN)
250
300
80
Depth(m)
Depth(m)
 Predicted drag forces and required speed in practical conditions
EXPERIMENTAL OBSERVATIONS
 CNU Cavitation Tunnel
19
EXPERIMENTAL OBSERVATIONS
 2D Cavitator
 Analysis & Exp. observation: (V=8.10~10.32m/s)
20
EXPERIMENTAL OBSERVATIONS
 2D Cavitators
w/o body
w/ body
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
21
EXPERIMENTAL OBSERVATIONS
 Hi-speed Camera
22
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
EXPERIMENTAL OBSERVATIONS
 2D Cavitators
σ=0.83
Video Camera (30 fps)
Hi-speed Camera (5,000 fps)
23
EXPERIMENTAL OBSERVATIONS
 2D Cavitators
24
EXPERIMENTAL OBSERVATIONS
 2D Cavitators
σ=1.05
σ=0.70
25
EXPERIMENTAL OBSERVATIONS
 2D Cavitators
26
EXPERIMENTAL OBSERVATIONS
27
 3D Cavitators
3
4
1
30mm
Value
30mm
2
75mm
Speed (m/s)
11
Temp (C°)
14.0
Density (kg/m3)
997.104
Vapor pressure (Pa)
75mm
1,598.14
Depressurized (bar)
-0.412 ~ -0.657
σn
2.091 ~ 0.567
EXPERIMENTAL OBSERVATIONS
28
 3D Cavitators
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
EXPERIMENTAL OBSERVATIONS
29
 3D Cavitators
σ=
1.25
Disk
Disk w/ hole
Disk w/ round
Cone
0.98
0.88
0.83
0.65
EXPERIMENTAL OBSERVATIONS
 3D Cavitators
30
CONCLUSIONS
 Numerical Analysis:
 Develop a numerical method to predict supercavity
 Investigate important features of supercavity:
cavity length, diameter and drag forces
 Results are validated by comparison with existing analytic
and empirical values
 Experimental Observations:
 Observe the early stage of the supercavity profiles generated
by various 2D and 3D cavitators
 Accumulate experimental data for parametric information to
design of the cavitator
 Additional experiments are on going;
ventilation effects, pressure force measurements
31
Experimental Investigation of
Supercavitating Flows
Byoung-Kwon Ahn*, Tae-Kwon Lee, Hyoung-Tae Kim and Chang-Sup Lee
Dept. of Naval Architecture and Ocean Engineering
College of Engineering, Chungnam National Univ.