CFD evaluation of a turbine rear structure with an integrated heat exchanger

Abstract

The expanding aviation industry is currently experiencing a substantial transition in order to become more sustainable. A more environmentally friendly alternative to traditional jet fuel is liquid hydrogen, an option that has been investigated by GKN Aerospace among others. Employing liquid hydrogen imposes many engineer ing challenges, one of which is the design on the turbine rear structure part (TRS) of the engine. This section of an aeroplane engine is of special interest to GKN as it is one of their main products. As liquid hydrogen has to be kept at low temperatures in order to remain in its liquid state, a state most suited for use in aircraft due to the low energy density of gases, and as the air exiting an engine is typically very hot this opens the possibility, if not necessity of heat exchange between the fluids. A model of a heat exchanger that can be used for this purpose was constructed by GKN and tested at Chalmers university of technology where the hydrogen was replaced by heated water. A patent for the heat exchanger model had been filed but not obtained during the thesis work which meant that the exact geometry of it was omitted from the thesis. In this thesis the tests at Chalmers were used in order to perform CFD simulations of the turbine rear structure with an integrated heat exchanger. The results obtained from the CFD were then validated by comparing turbulence models and boundary condition specification methods after which the results were compared to the test data. The validity of the used CFD model was confirmed using tests and reasoning although the CFD model was shown to over predict the magnitude of separation zones. The measured outlet temperature of the water was shown to be accurately predicted by the CFD simulations. Additional simulations of a TRS without the heat exchanger were also carried out to highlight the difference between using and not using a heat exchanger. Finally the performance of the heat exchanger was assessed by calculating its effectiveness for the different simulations which gave indications for the optimal air flow through it.