Microbubble size distributions in the wake of cavitating flows

About the research project

The formation of microbubbles in the wake of maritime vessels is governed by a complex interplay of physical mechanisms, including air entrainment, turbulent bubble breakup, rectified diffusion, and cavitation. Of particular importance is cavitation associated with propulsors and control surfaces. When vapour cavities form on lifting surfaces, the local pressure reduction establishes strong concentration gradients that drive the rapid diffusion of dissolved gases from the liquid into the vapour phase. This diffusion can occur even in transient, shedding cavities where residence times are extremely short.

As these vapour cavities advect downstream and encounter regions of higher pressure, the vapour phase condenses. However, the incondensable gases that diffused into the cavity remain, forming persistent microbubbles approximately 0.1 mm in diameter. The resulting microbubble populations are of practical interest for naval hydrodynamics, vessel detectability, and wake persistence. Despite their importance, the size distributions produced and the fundamental physical processes governing their formation are not yet fully understood.

Beyond direct bubble generation by cavitation, lifting surfaces can substantially modify pre-existing microbubble populations through several interacting mechanisms. These include the activation of nuclei triggering further cavitation, growth via rectified diffusion, and fragmentation due to turbulent stresses. A key research challenge is that the influence of these processes is poorly characterised even at the level of a single bubble, making it difficult to predict or model collective bubble behaviour. Experimental investigation is further complicated by the wide range of spatial and temporal scales involved, spanning micrometre-sized bubbles evolving on millisecond time scales within highly unsteady, turbulent flows.

Recent advances in optical diagnostics, particularly digital holography and related high-resolution techniques, now provide powerful tools for addressing these challenges. These methods enable three-dimensional, time-resolved measurement of bubble size, spatial distribution, and evolution within complex flows. The Cavitation Research Laboratory offers access to controlled experimental facilities capable of producing representative cavitating flows and bubbly wakes, providing an ideal environment for high-fidelity measurements.

This project aims to experimentally investigate the production and modification of microbubble populations generated by cavitation on lifting surfaces. Through the application of advanced optical diagnostics, the research will elucidate the mechanisms governing bubble formation, growth, and breakup, contributing to improved physical understanding and modelling capability. The project is well suited to candidates with a strong interest in fluid dynamics, experimental methods, and optical measurement techniques.

Primary supervisor

Meet Doctor James Venning

Funding

Applicants will be considered for a Research Training Program (RTP) scholarship or Tasmania Graduate Research Scholarship (TGRS) which, if successful, provides:

• a living allowance stipend funded by University of Tasmania of $34,315 per annum for 3.5 years
• a relocation allowance of up to $2,000
• a tuition fees offset covering the cost of tuition fees for up to four years (domestic applicants only)

As part of the application process you may indicate if you do not wish to be considered for scholarship funding.

Other funding opportunities and fees

For further information regarding other scholarships on offer, and the various fees for undertaking a research degree, please visit our Scholarships and fees on research degrees page.

Eligibility

Applicants should review the Higher Degree by Research minimum entry requirements.

Ensure your eligibility for the scholarship round by referring to our Key Dates.

Additional eligibility criteria specific to this project/scholarship:

• Australian citizenship and ability to obtain and maintain a personal security clearance of Baseline.

Selection criteria

The project is competitively assessed and awarded. Selection is based on academic merit and suitability to the project as determined by the College.

Additional essential selection criteria specific to this project:

• Undergraduate degree in engineering or science with First Class Honours or equivalent.

Application process

1. Select your project, and check that you meet the eligibility and selection criteria, including citizenship;
2. Contact Doctor James Venning to discuss your suitability and the project's requirements; and
3. In your application:
   • Copy and paste the title of the project from this advertisement into your application. If you don’t correctly do this your application may be rejected.
   • Submit a signed supervisory support form, a CV including contact details of 2 referees and your project research proposal.
4. Apply prior to 1 October 2026.

Full details of the application process can be found under the ' How to apply ' section of the Research Degrees website.

Following the closing date applications will be assessed within the College. Applicants should expect to receive notification of the outcome by email by the advertised outcome date.

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