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

Sammanfattning

The expanding aviation industry is currently experiencing a substantial transitionin order to become more sustainable. A more environmentally friendly alternativeto traditional jet fuel is liquid hydrogen, an option that has been investigated byGKN Aerospace among others. Employing liquid hydrogen imposes many engineer ing challenges, one of which is the design on the turbine rear structure part (TRS) ofthe engine. This section of an aeroplane engine is of special interest to GKN as it isone of their main products. As liquid hydrogen has to be kept at low temperaturesin order to remain in its liquid state, a state most suited for use in aircraft due tothe low energy density of gases, and as the air exiting an engine is typically veryhot 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 constructedby GKN and tested at Chalmers university of technology where the hydrogen wasreplaced by heated water. A patent for the heat exchanger model had been filed butnot obtained during the thesis work which meant that the exact geometry of it wasomitted from the thesis.In this thesis the tests at Chalmers were used in order to perform CFD simulations ofthe turbine rear structure with an integrated heat exchanger. The results obtainedfrom the CFD were then validated by comparing turbulence models and boundarycondition specification methods after which the results were compared to the testdata. The validity of the used CFD model was confirmed using tests and reasoningalthough the CFD model was shown to over predict the magnitude of separationzones. The measured outlet temperature of the water was shown to be accuratelypredicted by the CFD simulations. Additional simulations of a TRS without the heatexchanger were also carried out to highlight the difference between using and notusing a heat exchanger. Finally the performance of the heat exchanger was assessedby calculating its effectiveness for the different simulations which gave indicationsfor the optimal air flow through it.