In modern gas turbine engine, turbine inlet temperature is increasing to meet requirement of high thermal efficiency. However, up to present, the gas temperature in first stage of gas turbine is much higher than the melting point of blade material, which presents great challenge for the aero-thermal design of turbine blades. For the rotor blade, the tip clearance is subjected to very high thermal load and mechanical stresses, which need a careful considerations of heat transfer and film cooling effect in design process. As a commonly used tip configuration, the squealer tip exhibits good aerodynamic performance and heat transfer characteristic in high pressure turbine stages, thus is under active research in the published literature. However, in the realistic operation process, wear damages in squealer tip is inevitably occurred as the high temperature gas passes the tip gap, which affect the aerodynamic, heat transfer and film cooling performance in tip region, significantly. In response to this issue, the present paper utilized a numerical method to investigate the effects of squealer tip wear on heat transfer and film cooling in squealer tip gap. Firstly, the numerical methods are carefully validated with the experimental data with respect to the tip heat transfer coefficient and film cooling effectiveness distributions. Secondly, the flow patterns in the worn squealer tip with different degrees of wear damage are illustrated and also compared with the unworn cases. Thirdly, heat transfer coefficients and film cooling effectiveness on squealer tip, as well as total pressure loss in cascade, are analyzed at three different wear locations and five wear depths of squealer tip. The results show that the wear damages have a great influence on aerodynamic, heat transfer and film cooling performance in the squealer tip gap. As the wear location moves towards the leading edge and the wear depth increases, the total pressure loss in cascade and the heat transfer coefficient on cavity floor are increased, but the heat transfer coefficient on rims and the overall film cooling effectiveness on the entire squealer tip are reduced. As the wear depth increases, the intensity of leakage vortex is increased while the intensity of passage vortex is decreased. As the wear depth increases from 1cm to 5cm, the averaged total pressure loss in cascade is increased by 0.68% and the overall film cooling effectiveness on squealer tip is decreased by 7.9%. The heat transfer coefficient on cavity floor is increased by 29.1% but the heat transfer coefficient on rims is decreased by 26.3% as the starting location of wear is at 25% axial chord. As the starting location of wear moves to trailing edge, the influence of wear damage on heat transfer and film cooling effect in squealer tip gap is reduced, correspondingly.


Investigations of Heat Transfer and Film Cooling Effect on a Worn Squealer Tip

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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