Numerical investigation of the behaviour of confined, impinging jets with assessment of advanced concepts to reduce unsteady pressure fluctuations in gas turbine testing facilities

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Large test cells are used to evaluate the performance of modern jet engines. MDS Aero Support Corporation is a leading design and manufacturer of these test cells. They have observed large amplitude, low frequency unsteady pressure fluctuations on some of the components in the facilities when large engines are operated in them at high flow rates. These are significant enough to cause damage to the components over time. This leads to test cell downtime for repairs which is undesirable for MDS and their customers. This project will investigate approaches to reduce the unsteady pressure fluctuations and will also lead to new knowledge related to the air flow behaviour which gives rise to and governs the magnitude of the pressure fluctuations.The problem is related to jet impingement, but the geometry and flow speeds which are relevant have not been extensively studied in the past. To try to solve the problem, a two-pronged approach will be employed: on one hand, an investigation will be carried out to determine how changes to the shape of the components most directly affected by the pressure fluctuations can alter the fluctuation magnitudes; simultaneously a more fundamental study of the underlying physical processes at play will take place and this will yield design proposals for passive devices which could be added to the test cells to prevent or mitigate the pressure fluctuations. Both approaches will employ numerical simulations of the air flow in the test cell. In particular, a very accurate but complex simulation approach called Large Eddy Simulation will be used to capture the details of the relevant physical processes. Various design ideas and modifications will be assessed using these simulations to determine which have the most potential benefit, and why.