The Role of Unsteady Cloud Shedding on Cavitation Intensity
Abstract
The dynamics and break-up of vapor and gas sheets is an important flow process for many navalapplications. Off-design operation can lead to sheet cavitation on propulsor blades and control surfaces,as well as in waterjets. One of the most serious outcomes of unsteady cloud cavitation is the structuraldamage produced by the repeated collapse of bubbly clouds near the surfaces of hydrodynamiccomponents such as propulsor blades and housings. An important characteristic of cavitation activity inthe context of erosion is the intensity, or aggressiveness, or power of the cavitation, and there is evidencethat flow unsteadiness enhances the intensity of cavitation. Recent studies have shown that unsteadinessof sheet cavitation can be attributed to both the presence of re-entrant flows and the formation of strongbubbly shocks. And, unsteadiness occurring at the large scales affects the collapse of near surfacebubbles and the consequential erosion intensity at the small scales. The principal aim of the present studyis to identify the physical mechanism(s) linking large-scale cloud dynamics with increased small-scalecavitation activity. We hypothesize that the compressibility of bubbly flows (e.g., shocks driving thecollapse of cavitation clouds) is the mechanism responsible for increasing cavitation intensity, andsubsequent erosion. Our overall objective is to understand the role of free-stream unsteadiness oncavitation intensity. In particular, we seek to elucidate the relationship between the energy fed into thesystem at the large scales to the cavitation intensity causing erosion at the small scales through acoordinated experimental and modelling effort. We will experimentally produce a collapsing cloud ofbubbles near a solid surface that is similar to that produced by an unsteady attached spot or sheet cavityon a lifting surface, especially unsteady flow fields that lead to shock induced cloud collapse produced bya stationary and pitching hydrofoil, and in the unsteady wake of a wedge. The first phase of the modelingwill involve simulations of individual bubble collapse, and data-driven modeling. The second phase ofthe modeling and simulations involves implementation into a flow solver and simulations of thegeometries of interest, as well as verification/validation and investigation of the physics. Once the modelhas been integrated into the flow solver, we will simulate the geometries of interest (hydrofoil andtriangular wedge).
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 27, 2018
- Source ID
- N000141812699
Entities
People
- Steven Ceccio
Organizations
- Board of Regents of the University of Michigan
- Office of Naval Research
- United States Navy