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On the re-entrant jet of a supercavitating body

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

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On the re-entrant jet of a supercavitating body

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  1. Proceedings of the 8th 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

  2. 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

  3. Structure of Presentation 1. Introduction 2. Experiment setup 3. Results and discussion 4. Conclusions

  4. 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

  5. 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

  6. 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

  7. 1. Introduction According to the previous investigations, the re-entrant jet can induce the instability of cavitation. The unstable cavity results in the undetermined dynamic feature, 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

  8. 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.

  9. M.C. system Compressed air Pc Pressure transducer array V Attack angle adjusting system Camera Water tunnel control Pw V 2.1 Experiment Scheme The experiment configuration is mainly composed of the measure and control system, ventilation system and the image capture system.

  10. 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

  11. 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

  12. 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

  13. 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: 385mm Cylinder section diameter: 50mm

  14. 2.3 Test Models Re-entrant jet restraining: • Two rings with different diameters • Arrange in the middle of test model Φ55mm Φ60mm

  15. 2.4 Test Instruments MICRO pressure transducer KULITE pressure transducer ALICAT gas mass-flow-rate controller MEGA SPEED MS75K high speed camera

  16. 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.

  17. 3.1 Pressure in Closure Region Pressure distribution in the re-entrant jet start location Pressure peak in the closure line No.1 ------ No.10

  18. 3.1 Pressure in Closure Region Comparisons between upwind and downwind sides

  19. 3.2 Re-entrant jet effect to cavity feature Cavities in different σc Cavities of different lengths Cavities generated by different cavitators

  20. 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 Close out of model surface Model 2 Close line attached to model surface Model 3

  21. 3.3 Re-entrant jet induced instability Two forms of cavity instability Vertical disturbance Stretched Compressed Unstable cavity shape Unstable cavity closure line Next period

  22. 3.4 Re-entrant jet control method Comparisons of model with/without re-entrant jet restraining ring Front cavity is more clear and stable

  23. 3.4 Re-entrant jet control method Comparisons of model with/without re-entrant jet restraining ring better worse best Ф55mm ring Ф60mm ring

  24. 4. Conclusions • A pressure peak exists in the re-entrant jet formation area; • Strength of re-entrant jet becomes greater as σcincreases. Cavity closure location also plays a role in deciding re-entrant jet influence to cavity; • Re-entrant jet can induce the instability of cavity in cavity length and shape, and the cycle time is indeterminate; • 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.

  25. Thank you! Northwest Polytech Univ, Xi’an Shaanxi, P.R.China, 710072

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