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Proceedings of the 8 th International Symposium on Cavitation CAV2012 – Abstract No. 82 August 14-16, 2012, Singapore. On the re-entrant jet of a supercavitating body. Ya-dong Wang. Northwest Polytech Univ, Xi’an Shaanxi, P.R.China, 710072. Author Introduction. Ya-dong Wang - PowerPoint PPT Presentation
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On the re-entrant jet of a supercavitating bodyOn the re-entrant jet of a supercavitating body
Ya-dong Wang
Northwest Polytech Univ,Xi’an Shaanxi, P.R.China, 710072
Proceedings of the 8Proceedings of the 8thth International Symposium on International Symposium on CavitationCavitationCAV2012 – Abstract No. 82CAV2012 – Abstract No. 82August 14-16, 2012, August 14-16, 2012, SingaporeSingapore
Author Introduction
Ya-dong Wang
College of Marine, Northwestern Polytechnical University, Xi’an, Shaanxi, China
Email: roby868@ 163.com
Northwest Polytech Univ,Xi’an Shaanxi, P.R.China, 710072
Structure of Presentation
1. Introduction
2. Experiment setup
3. Results and discussion
4. Conclusions
1. Introduction
Various methods have been setup to study cavitating flow, they mainly fall to:
1. Potential method with modifications
2. Multiphase CFD simulation
3. Experiment technique
1. Introduction
Flow near the cavity closure region is the most complicated in cavitating flow. Several closure models have been setup:
Riaboushinsky Model
Efros Model
Pressure Recovery Model
1. Introduction
The Efros closure form, which assumes there is a re-entrant jet in the cavity closure region, is frequently observed in experimental studies:
Wosnik (2003)
Our experiment results
1. Introduction
According to the previous investigations, the re-entrant jet can induce the instabilityinstability of cavitation. The unstable cavity results in the undetermined dynamic undetermined dynamic featurefeature, which is a main problem of supercavitating vehicle design.
Therefore, the characteristics of re-entrant jet for a supercavitating body should be studied in the following aspects:
1. Main feature of re-entrant jet in cavitating flow
2. The factors affecting the re-entrant jet
3. Ways to restrain the adverse effects
2. Experiment Setup
Experiment was conducted in the high speed water tunnel of NPU, using the ventilation method to obtain supercavity, a series of instruments to acquire desired data.
2.1 Experiment Scheme
The experiment configuration is mainly composed of the measure and control system, ventilation system and the image capture system.
Compressed air
PwV
Pressure transducer array
Pc
M.C. system
Water tunnel control
V
Camera
Attack angle adjusting system
2.2 High Speed Water Tunnel in NPU
The water tunnel is a recirculating, closed jet facility with pressure regulation and is capable of velocities in excess of 18m/s.
Working Section Size: Φ400×2000mm, three side observations
2.3 Test Models
We mainly conducted three kinds of experiments: Pressure in closure region measurement Effects of head shape and attack angle to re-entrant jet Re-entrant jet restraining
2.3 Test Models
Pressure in closure region measurement:• Obtain the pressure distribution in the re-entrant jet
start location• An array of pressure transducers
2.3 Test Models
Effects to re-entrant jet:• Three model heads with different nose diameters• Same full model length• Adjust inflow angle
Φ29mm Φ25mm Φ20mm Full length: 385mmCylinder section diameter: 50mm
2.3 Test Models
Re-entrant jet restraining:• Two rings with different diameters• Arrange in the middle of test model
Φ55mm Φ60mm
2.4 Test Instruments
MICRO pressure transducer KULITE pressure transducer
ALICAT gas mass-flow-rate controller MEGA SPEED MS75K high speed camera
3. Results and Discussion
Through groups of experiments, we successfully got the pressure data, re-entrant jet images and the effect of re-entrant restraining method.
3.1 Pressure in Closure Region
Pressure distribution in the re-entrant jet start location
1 2 3 4 5 6 7 885
90
95
100
105
110
115
Pressure Monitor No.
P(K
Pa)
0
-1
1
-2
2No.1 ------ No.10
Pressure peak in the closure line
Vc
model
cavity
re-entrant jetγ VbVf
3.1 Pressure in Closure Region
Comparisons between upwind and downwind sides
0 2 4 6 885
90
95
100
105
110
115
Pressure Monitor No.
P(K
Pa)
-0.5
0.5
0 2 4 6 885
90
95
100
105
110
115
Pressure Monitor No.
P(K
Pa)
-1.0
1.0
0 2 4 6 885
90
95
100
105
110
115
Pressure Monitor No.
P(K
Pa)
-1.5
1.5
0 2 4 6 885
90
95
100
105
110
115
Pressure Monitor No.
P(K
Pa)
-2.0
2.0
3.2 Re-entrant jet effect to cavity feature
Cavities in different σc
Cavities generated by different cavitators Cavities of different lengths
3.2 Re-entrant jet effect to cavity feature
Cavities in different attack angles
Re-entrant jet disturbances are much weaker in upwind sides
Model 1
Model 2
Model 3Close line attached to model surface
Close out of model surface
3.3 Re-entrant jet induced instability
Two forms of cavity instability
Unstable cavity closure line
Unstable cavity shape
StretchedCompressed
Next period
Vertical disturbance
3.4 Re-entrant jet control method
Comparisons of model with/without re-entrant jet restraining ring
Front cavity is more clear and stable
3.4 Re-entrant jet control method
Comparisons of model with/without re-entrant jet restraining ring
Ф55mm ring Ф60mm ring
betterworse
best
4. Conclusions
1. A pressure peak exists in the re-entrant jet formation area;
2. Strength of re-entrant jet becomes greater as σc increases. Cavity closure location also plays a role in deciding re-entrant jet influence to cavity;
3. Re-entrant jet can induce the instability of cavity in cavity length and shape, and the cycle time is indeterminate;
4. Re-entrant jet can only be fully prevented if the blocking ring fits well with local cavity, improper designed blocking ring may worsen the disturbance of re-entrant jet to cavity.
Northwest Polytech Univ,Xi’an Shaanxi, P.R.China, 710072
