Session: 04-02 Cavitation and Bubbly Flows

Paper Number: 87588

87588 - On the Transition Between Re-Entrant Jet and Condensation Shock Mechanism in Sheet to Cloud Cavitation 

Cavitation refers to the formation of vapor when the pressure in liquid falls below vapor pressure. It occurs in a wide variety of situations such as valves, orifices, and propulsor blades. The formation of vapor is often followed by a growth of the vapor cavity and its violent collapse under a high-pressure gradient. The physical consequences of this collapse include noise, vibration, and surface erosion. Sheet cavitation and its transition to cloud cavitation are of great practical interest since the highly unsteady flow can induce significant fluctuations in the thrust and torque of marine propellers. The collapse of the cloud also causes material damage to the blades. Hence a fundamental understanding of this phenomenon is necessary to mitigate and control the detrimental effects of the sheet to cloud cavitation.

The transition of a sheet cavity to a cloud cavity occurs primarily due to two mechanisms: liquid re-entrant jet and condensation shock. While the role of the liquid re-entrant jet in sheet to cloud cavitation has been investigated by many authors in detail, the fundamental knowledge behind the condensation shock mechanism has not been explored in detail yet. Hence the aim of this study is to conduct a systematic parametric investigation of the sheet to cloud cavitation through high-fidelity numerical simulations, focusing especially on the condensation shock mechanism and the physical conditions that lead to the transition between the re-entrant jet mechanism and condensation shock mechanism. We choose a flow over a wedge configuration based on the experiments of Ganesh et al (2016), at Reynolds number of 200,000 and several cavitation numbers from ranging σ=1.5 to σ=2.1. The multiphase medium is represented using a finite rate homogeneous equilibrium model that assumes thermal equilibrium between the liquid and the vapor phase. The governing equations are the compressible Navier Stokes equations for the liquid/vapor mixture along with a transport equation for the vapor mass fraction. The solution method is based on the numerical methodology developed by Gnanaskandan and Mahesh (2016). The numerical approach is first validated by comparison with the experimental measurements showing acceptable agreement, and then a systematic parametric investigation is carried out. The preliminary numerical results confirm that the attached sheet cavity forms at the apex wedge and grows up to a critical length, after which it sheds into a cloud cavity. The simulations also predict both re-entrant jet and condensations shocks to be the physical mechanisms of the transition

The numerical simulations will be further analyzed to identify the precise physical conditions that lead to the transition between the mechanisms. Once identified, the properties across the condensation shock will be extracted and analyzed using Rankine-Hugoniot jump conditions for a homogenous mixture system.

Presenting Author: Aswin GNANASKANDAN Worcester Polytechnic Institute