Computational Fluid Dynamics (CFD) of transpiration cooling and noise reduction in jet engines

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In recent years, the reduction of noise emissions in airports has gained more importance due to the increase in air traffic. Airbus global market forecast predicts a 4.4% global annual air traffic growth over the next 20 years. Studies also concluded that aircraft noise has a negative impact on people's quality of life and health. In the UK alone over 1 million of people are living in areas where aircraft noise is above levels recommended for health. The Advisory Council for Aviation Research and innovation in Europe (ACARE) has set goals to reduce the perceived noise emission by 65% until 2050 with respect to the year 2000. In the past, jet engine noise was predominantly due to jet noise and fan noise. Jet noise has been reduced by increasing the bypass of turbofan engines while fan noise has been reduced through effective acoustic liners and complex designs of fan blade geometry. These efforts on the reduction of jet and fan noise have left combustion noise as an important remaining contributor. The total noise radiated by a gas turbine combustion chamber system consists of "direct" and "indirect" noise. Fluctuation in heat release rate from the turbulent flame causes an unsteady volumetric expansion and contraction, leading to a pressure wave which constitutes the "direct" acoustic noise. The "indirect" noise is generated due to the acceleration of entropy waves through the combustor, and in particular turbine blade rows. Recent studies showed that the level of indirect entropy noise could be on the same order of magnitude or larger than the direct acoustic noise. This requires more investigation of underusing the generation and dissipation of entropy noise as they convect through the turbine blade rows. In this PhD project a high fidelity CFD analisys will be performed using an open source software (i.e. OpenFoam) to investigate the detailed flow physics involved in the convection of entropy waves as they convect through the nozzle guide vane and turbine rotor blade rows. This will enable us to understand passive and active techniques to reduce the contribution of indirect entropy noise to the generation of the total noise in a gas turbine. This will have a great impact in designing new gas turbines but ultimately on peoples life affected by noise emission.