Gas turbines have been widely used in the aviation, marine, power plant, etc., which plays an indispensable role in modern industries. Nowadays, higher efficiency and larger output power is demanded, consequently, the turbine inlet temperature (TIT) has to be increased to up to 2260K in some turbofan engines. The turbine blades or vanes operate in a harsh environment and the operating temperature significantly surpasses the melting point of the turbine blade material. Therefore, the turbine cooling technology is of vital importance aiming to guarantee the lifespan of the turbine blades and the safe operation. Apart from the internal cooling methods, the external film cooling is a necessary and effective solution to protect the outer surface of the blades against the extreme high temperature mainstream from the combustion chamber. In this thesis, the thermal performance of the laidback fan-shaped film hole structure was numerically studied, which is known as 7-7-7 laidback fan-shaped film hole proposed by Thole [1]. Large eddy simulation (LES) method was implemented to investigate the thermal performance of the shaped film hole, and the LES result was compared with the RANS simulation with various turbulent models and verified by the experimental data from Thole. Besides, a comparative study was conducted between the conventional cylindrical film hole and the 7-7-7 shaped film hole. The results show the better cooling effectiveness with sufficient spread in spanwise direction as the blowing ratio increases, and proper orthogonal decomposition (POD) method was employed to present the coherent structure in flow field. Additionally, the effects of the blowing ratios M on the shaped film hole were simulated with LES in the range of M=0.5-3.0. Three different mainstream inlet turbulence intensities included between Tu=0.5% and Tu=20% were chosen to research the effects on the cooling effectiveness. Three mainstream inlet velocity profiles were applied for the LES calculation. The convex curved bottom surface was also investigated and compared with the flat bottom wall. The results show that M=1.5 can obtain a relative better performance for the same turbulence intensity of 0.5%. The cooling effectiveness deteriorates as the mainstream turbulence intensity increases from 0.5% to 20%. The mainstream inlet velocity profile causes less effects on the effectiveness relative to the blowing ratio and inlet turbulence intensity. The effectiveness of the convex curved bottom surface decays at higher blowing ratio condition. In addition, aerothermal performance of film cooled C3X vane was analyzed, and a comparison between the cylindrical and shaped film hole cases was presented. The effects of the two different film hole structures on the pressure and temperature distributions were studied. The present work evaluated the LES accuracy through a comparison with the experimental data and presented the reason of the different predictions between the LES and RANS. The numerical research on the film cooling can be considered as a baseline for further comparison and investigation of the film cooling in turbine blades or vanes.

AEROTHERMODYNAMIC INVESTIGATION OF THE TURBINE BLADE FILM COOLING WITH LARGE EDDY SIMULATION METHOD

YANG, LIANFENG
2022

Abstract

Gas turbines have been widely used in the aviation, marine, power plant, etc., which plays an indispensable role in modern industries. Nowadays, higher efficiency and larger output power is demanded, consequently, the turbine inlet temperature (TIT) has to be increased to up to 2260K in some turbofan engines. The turbine blades or vanes operate in a harsh environment and the operating temperature significantly surpasses the melting point of the turbine blade material. Therefore, the turbine cooling technology is of vital importance aiming to guarantee the lifespan of the turbine blades and the safe operation. Apart from the internal cooling methods, the external film cooling is a necessary and effective solution to protect the outer surface of the blades against the extreme high temperature mainstream from the combustion chamber. In this thesis, the thermal performance of the laidback fan-shaped film hole structure was numerically studied, which is known as 7-7-7 laidback fan-shaped film hole proposed by Thole [1]. Large eddy simulation (LES) method was implemented to investigate the thermal performance of the shaped film hole, and the LES result was compared with the RANS simulation with various turbulent models and verified by the experimental data from Thole. Besides, a comparative study was conducted between the conventional cylindrical film hole and the 7-7-7 shaped film hole. The results show the better cooling effectiveness with sufficient spread in spanwise direction as the blowing ratio increases, and proper orthogonal decomposition (POD) method was employed to present the coherent structure in flow field. Additionally, the effects of the blowing ratios M on the shaped film hole were simulated with LES in the range of M=0.5-3.0. Three different mainstream inlet turbulence intensities included between Tu=0.5% and Tu=20% were chosen to research the effects on the cooling effectiveness. Three mainstream inlet velocity profiles were applied for the LES calculation. The convex curved bottom surface was also investigated and compared with the flat bottom wall. The results show that M=1.5 can obtain a relative better performance for the same turbulence intensity of 0.5%. The cooling effectiveness deteriorates as the mainstream turbulence intensity increases from 0.5% to 20%. The mainstream inlet velocity profile causes less effects on the effectiveness relative to the blowing ratio and inlet turbulence intensity. The effectiveness of the convex curved bottom surface decays at higher blowing ratio condition. In addition, aerothermal performance of film cooled C3X vane was analyzed, and a comparison between the cylindrical and shaped film hole cases was presented. The effects of the two different film hole structures on the pressure and temperature distributions were studied. The present work evaluated the LES accuracy through a comparison with the experimental data and presented the reason of the different predictions between the LES and RANS. The numerical research on the film cooling can be considered as a baseline for further comparison and investigation of the film cooling in turbine blades or vanes.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11567/1093755
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