| dc.description.abstract | Modern gas turbine engines require a sophisticated cooling system design to achieve higher power output and efficiency. Film cooling is an indispensable part of the turbine external cooling mechanism. In this study, systematic tests were carried out to evaluate the potential effect of non-cylindrical inlet geometries on the performance of laid back, fan-shaped film cooling holes using the steady state pressure sensitive paint (PSP) measurement technique. “Racetrack” shaped inlet geometries with aspect ratios of 2:1 and 4:1 were selected as the subjects of this study, due to their possible potential of improving the film cooling effectiveness. The outlets of the tested film cooling holes share the same geometric parameters of a fan-shaped hole design studied in open literature, while the inlet geometry varies. The coolant flow conditions range from blowing ratios of M=0.3-1.5 and density ratios DR=1 and 2. The mainstream turbulence intensity is fixed at 6%. Results show that the shaped inlets can provide a higher area-averaged film cooling effectiveness, η, over the traditional cylindrical inlet design using the same amount of coolant, but the performance varies with flow conditions. For the 2:1 inlet, an advantage of 20% higher η could be maintained for DR=1, while for DR=2 this advantage is reduced to 10%. For the 4:1 inlet, when the coolant momentum flux ratio I<0.5, a similar or slightly higher improvement can be obtained, but when I>1 , the advantage diminishes with the growing momentum flux ratio to approximately 5% at I=2.25. The coolant coverage for the 2:1 inlet is better than the other two geometries downstream at higher momentum flux ratios (I>1). While the 4:1 inlet enjoys a more concentrated film coverage in regions closer to the hole (X/Dh <5) when I<0.5. The discharge coefficients results show that the 2:1 inlet geometry is similar to the cylindrical inlet in terms of discharge coefficients under most flow conditions. For the 4:1 inlet, its discharge coefficient is 0.02-0.04 lower than the fan-shaped holes with a cylindrical inlet under the same flow condition. | en |
