Reducing instabilities in aircraft engine combustion systems

With HPC Midlands compute power the Rolls-Royce UTC in Combustion System Aerothermal Processes at Loughborough University achieves rapid turnaround on advanced CFD simulations which replicate the complex physical processes that occur within an engine at high pressures and temperatures.

Challenge

Instabilities in combustion systems are one of the key challenges faced by manufacturers of modern low-emission aircraft engines. Details of the air flow into the combustor through complex swirling passages are crucial in determining the unsteady system response. Predicting and understanding the response of the air flow to pressure waves is therefore important to the team at the Rolls-Royce University Technology Centre (UTC) as they help to develop stable, low emission combustors.

Computational Fluid Dynamics (CFD) can be used to produce predictions of this type. However the air flows into the combustor through complex swirling passages, the details of which are crucial in determining the unsteady system response. This complexity must be included in the simulations which must also be run at a range of acoustic frequencies for each design. This makes the method too slow to be practical without the use of high performance computing.

Solution

Using HPC Midlands, simulations of the unsteady flow though complex geometries can be carried out with a rapid turnaround. Typically the simulations are carried out using 96 cores. This number is relatively small by modern HPC standards but the real benefit of using HPC Midlands in this case is that simulations can be launched with different acoustic frequencies, or even different geometries, simultaneously.

For a particular design, to perform the simulations over the necessary range of frequencies requires in the region of 30,000 CPU hrs. Using HPC Midlands it is possible to complete these calculations in a matter of days. With this sort of turnaround time the CFD method employed becomes feasible as a design tool.

Impact

Using this method, excellent agreement has been obtained with experimental data. Not only this, but the simulation gives a level of detail that experiment alone is not able to. This, together with the ability to investigate multiple designs in a short space of time, is allowing novel designs with improved unsteady responses to be developed. This is contributing to the successful development of low emission engine designs.