Experimental Research on Supercavitation Flows during Water Exit of Blunt Bodies Hong-Hui Shi, Hao-Lei Zhou, Jun-Hui Hu, Qing-Qing Hu College of Mechanical Engineering & Automation, Zhejiang Sci-Tech University, Hangzhou , Zhejiang Province, China The 8th Int. Symp. on Cavitation, Singapore, August 2012

Interset of Research  Water exit of a supercavity concerns with two free surfaces at the open water level and the supercavity boundary itself, which have non-linear and transient characteristics, the existed numerical and experimental results can not well describe the problem yet.

Experimental Set Up

Geometry of the test models

Experimental Conditions Test No.Model Driving Pressure P 0 (MPa) Incident Angle α(°) Vehicle Speed V 0 (m/s) 1a a a b b b b b

High speed photographs of water exit of hemi-spherical head cylinder. The body length and diameter are 36 mm and 6 mm respectively. The interframe time is 1 ms MPa nitrogen gas pressure.

High speed photographs of water exit of flat head cylinder. The body length and diameter are 36 mm and 6 mm respectively. The interframe time is 1 ms MPa nitrogen gas pressure.

Definition of the geometric sizes of a supercavity

Comparison with Theoretical Models

Conclusions  When a supercavity approaches free surface, it will first collapse in water. The body continuously moves upwards to create a new supercavity. The new supercavity will be carried by the underwater body to enter into air from water. Then, a second collapse of the cavity occurs in air. A supercavity can enter into air without a prior underwater collapse.  After water exit, an erupting splash is formed on the free surface, which is due to the rapid compression by the underwater vehicle, the effect of water inertia as well as the cavity collapse in air. The splash is fragmented and is unlike the regular water crown in water entry.  Comparison between the present experimental data and the models of Logvinovich and Savchenko shows that although the tendencies are basically same, the discrepancy in the magnitude is significant.