This study investigates the self noise from a ventilated supercavitating vehicle. A ventilated supercavity is a gaseous envelope surrounding an underwater vehicle that significantly reduces the drag felt by the vehicle. But the hydrodynamic noise generated by the creation of the supercavity could impact the successful deployment of the vehicle. A principal source of self noise for these types of vehicles is sound created by the ventilating gas jets impinging on the air-water interface. Analytical models of the radiated sound through the interface have been developed. Sometimes jets impinging on the interface entrain bubbles beneath the surface. This thesis outlines a theory to predict the influence of bubbles near the interface. Experimental measurements were made at the Naval Undersea Warfare Center (NUWC) in Newport, RI to test the accuracy of the model. These measurements include the unsteady force spectrum of a gas jet impinging on a rigid wall. The acoustic pressure spectrum of a gas jet striking the air-water interface was also recorded. The experimental results were compared to theoretical models for validation.

The objective of this dissertation was to investigate physical characteristics of high speed gas-liquid interfaces for the cases of subsonic, transonic, and supersonic gas jets submerged underwater and the transient development of an underwater projectile reaching the supercavitating state. These studies are motivated by the need to understand the basic physics associated with a novel submersible missile launcher termed the Water Piercing Missile Launcher (WPML). This dissertation presents the first study of high speed round and rectangular gas jets submerged underwater utilizing a global optical measurement technique. This technique allows quantitative measurement of the entire gas jet and the interfacial motion. Experimental results indicate that the penetration of the gas jets into a quiescent liquid is strongly influenced by the injection mass flow and the nozzle geometry. In contrast, the oscillations of the interface are influenced by the injection Mach number. The transition from a momentum driven to a buoyant jet is determined using a characteristic length scale that appears to be in good agreement with experimental observations. Moreover, the unsteadiness of the interface appears to be governed by both Kevin-Helmholtz and Rayleigh-Taylor instabilities. This dissertation also contains the first study of a projectile accelerating to reach the supercavitating state. Experimental results show that the transient development of the supercavity is governed by the formation of a vortex ring. Nuclei are shed from the forebody of the accelerating projectile and are entrained in the vortex ring core where they are subjected to low pressure and subsequently expand rapidly. A characteristic time scale for this supercavity development is presented. / Ph. D.

Supercavitating torpedoes pose new threats to submarines, surface ships, and shore targets whose current countermeasures are inadequate against this technology. These torpedoes have the advantage over their predecessors and companion weapons of dramatically increased speed, which reduces the reaction time available for deploying a countermeasure heightening the threat to their intended target. Proliferation of supercavitating torpedoes has motivated research on countermeasures against them as well as on the fluid phenomenon which makes them possible. The goal of this research was to investigate an envisaged countermeasure; an acoustic field capable of slowing or diverting the weapon by disrupting the cavitation envelope. The research focused on the interactions between high-level sound signals and a supercavity produced by a small free-flying projectile. In order to conduct this study it was necessary to achieve three preliminary accomplishments involving the design of: 1) experimental apparatus that allowed for the study of a small-scale supercavitating projectile in the laboratory environment; 2) apparatus and software for measuring and recording information about projectile dynamics and supercavity geometry; and 3) an acoustic array and power source capable of focusing the desired sound signal in the path of the supercavitating object. Positive results have been found which show that the accuracy of a supercavitating projectile can indeed be adversely affected by the sound signal. This research concludes with results that indicate that it is acoustic cavitation in the medium surrounding the supercavity that is responsible for the reduced accuracy. A hypothesis has been presented addressing the means by which the acoustic cavitation could cause this effect. Additionally, corrugations on the cavity/water interface imposed by the pressure signal have been observed and characterized.

A mesh-less method for solving incompressible, multi-phase flow problems has been developed and is discussed along with the presentation of benchmark results showing good agreement with theoretical and experimental results. Results of a systematic, parametric study of the single phase flow around a 2D circular cylinder at Reynolds numbers up to 1000 are presented and discussed. Simulation results show good agreement with experimental results. Extension of the method to deal with multiphase flow including liquid-to-vapor phase transition along with applications to cavitating flow are discussed. Insight gleaned from numerical experiments of the cavity closure problem are discussed along with recommendations for additional research. Several conclusions regarding the use of the method are made.

The main goal of this thesis is the examination of hydraulic characteristics for different cavity nozzles, influence of liquid rotation and visualization of cavitating flow. Thesis is divided into two parts, theoretical and practical. Theoretical part deals with the description of cavity - creation, development and its extinction. This part also contains description of vortex flow and basic vertex models. Practical part compares nozzles performance experimentally. The aim of experiment was to measure hydraulic characteristics and their comparison. Jet performance was judged using visualizations and measured data was processed in Microsoft Excel and Parametr.