Vincent Wheatley

Multi-Fluid Computational Investigation of Plasma Fuel Engines

This PhD project expects to generate new knowledge in air-breathing hypersonic propulsion utilising a plasma for thrust. This approach could eliminate the physical limitations of current engines such as scramjets and enable flight within the atmosphere at speeds greater than three kilometres per second, or 10,000 kilometres per hour. The Plasma Fuel Engine (PFE) is a new technology based on a Hall thruster concept applied to an air-breathing engine. UQ has been awarded an ARC Linkage Project to experimentally and computationally investigate the performance of these engines. The objective of this PhD project is to develop the capability accurately simulate the flow physics within a PFE and validate this against experimental data produced in the broader Linkage Project. The simulation results will then be used to gain new insights into the details of PFE operation.

UQ Centre for Hypersonics has developed a continuum multi-fluid plasma simulation capability within the AMReX adaptive mesh refinement framework (Bond et al., (2017)). This solves for the momentum of ions, electrons and neutrals separately and thus models the fundamental transport processes governing all particle movements in the PFE. It is fundamentally different to the approaches previously utilized to simulate the physics of PFEs. The capability to simulate ionising air flows within this solver is being developed as part of a separate linkage project (LP180100107). In this PhD project, boundary conditions will be developed to enable the simulation of PFE operation utilizing AMReX’s embedded boundary routines. In addition, further development of our ionization modelling capability may be required to accurately simulate air ionization by electron beams. Once the new modelling capability has been experimentally validated, simulations of PFE operation at a range of conditions will be conducted. The results of these simulations will yield new understanding of the flow physics underpinning PFE performance, which could inform design improvements.

Expanding the scramjet operating envelope through oxygen enrichment

UQ, USQ, Hypersonix Launch Systems and the European Space Agency have been awarded an ARC Discovery Project to investigate the benefits of expanding the operating envelope of scramjets to higher altitudes and speeds by enriching their fuel with oxygen. This is expected to enhance the performance and flexibility of hypersonic air-breathing engines designed to form the core of a more reliable and economical access to space system. Expected outcomes of this project are a validated understanding and mapping of how oxygen enrichment can augment scramjet thrust at high altitudes and speeds, and a performance evaluation of a launch system optimised for this approach. This could provide significant benefits to the performance of reusable, air-breathing launch technology, where Australia is leading the push towards commercialisation

There are three PhD topics planned as part of this Discovery Project, one of which will be supported by a UQ Earmarked PhD scholarship. The topics include the following:

1. Predict and understand how oxygen enrichment can expand the scramjet operating envelope to low dynamic pressures and augment thrust at high Mach numbers using numerical simulations
2. Experimentally explore oxygen scramjet enriched performance and map engine performance
3. Conduct vehicle design studies to evaluate the system-wide benefits of oxygen enrichment

Advanced Combustion Modelling for Scramjets and Rotating Detonation Engines

UQ, together with USyd and RMIT, have been awarded an ARC Discovery Project to develop new fundamental knowledge and engineering models underpinning air-breathing high speed propulsion engines employing complex hydrocarbon fuels. Extensive data and new physical understanding will be garnered through analysis of direct numerical simulations (DNS) of supersonic reacting mixing layers including impinging shock waves. That data will be employed to isolate, test and develop computationally efficient engineering models that are accurate and efficient for high speed combustion in rotating detonation engines and scramjets. Expected outcomes are knowledge and tools needed to develop practical and effective supersonic propulsion engines for access to space, defence and high speed point-to-point flight.

As part of this project, UQ is offering a PhD project on the following topic:

• Large-Eddy Simulation (LES) of scramjet combustor experiments with Multiple Mapping Condition (MMC) and Conditional Moment Closure (CMC) models for highly compressible combustion. These simulations will be used to validate the newly developed models and gain new insight turbulent combustion within scramjets. The successful candidate will also contributed the development of the CMC model for supersonic flow and its verification against DNS data.

Computational Investigation of Distributed Fuel Injection in Hypersonic Inlets and Combustors

Preliminary experimental and computational investigations indicate that distributed fuel injection to maintain a fuel-rich film along hypersonic engine walls has multiple potential benefits:

• Provide film/transpiration cooling to reduce hypersonic heat transfer loads, one of the main technical roadblocks currently associated with sustained hypersonic flight
• Reduce skin friction drag, which can be a significant proportion of vehicle drag at high Mach numbers, through a combination of film effects and boundary layer combustion
• Trip the laminar boundary layer on the vehicle forebody to turbulence, removing the requirement for trip devices and thereby eliminating the excessive heating and drag associated with them
• Provide a low free-stream stagnation pressure loss mechanism to deliver fuel into the engine
• The forebody injected fuel film resides in the relatively low speed, high temperature lower boundary layer where has enhanced opportunity to form radicals, providing a potential ignition aid

Recent developments in the production of porous ceramic matrix composites as well as the optimization of dense small port-hole injector arrays has provided multiple options for distributed fuel injection that are suitable for scramjets. Fully understanding and maximizing the benefits of these approaches requires the capability to accurately model them using Computational Fluid Dynamics (CFD). The first aim of the proposed project is to develop and validate the capability to model the injection of fuel through porous walls into a hypersonic cross-flow in both Reynolds-averaged Navier Stokes (RANS) and Large-Eddy Simulations (LES). The LES capability will then be used to understand and quantify the effects of porous injection and multi-port injector arrays on boundary layer transition, film cooling, skin friction reduction and ignition for both hydrogen and hydrocarbon fuels. These fundamental simulations can be used to evaluated the accuracy of the RANS capability, which can potentially be used to evaluate the impact of distributed fuel injection on the performance of full engines. This study will also investigate the effect hot walls has on the performance.