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The present work first introduces and studies the blade tip with a discrete trapezoidal slot scheme. The film-cooling characteristics of the discrete trapezoidal slot scheme on the blade tip with the partial pressure side squealer and full suction side squealer is experimentally investigated by the Pressure Sensitive Paint technique in transonic flow. The effects of the mass-flow-ratio and tip-clearance-gap are investigated, and the experiment is carried out at four mass-flow-ratios of 0.1% + 0.05%, 0.14% + 0.07%, 0.17% + 0.085%, and 0.21% + 0.105% and three tip-clearance-gaps of 0.7%, 1.1%, and 1.5%. The cascade exit Mach numbers is 1.05. The flow characteristics of the blade tip is studied by the calculation. The results indicate that the coolant can cover the whole blade tip bottom surface at the tip clearance of 1.5% and high mass-flow-ratios; With the tip-clearance-gap increasing, the adiabatic film effectiveness near the squealer rim of the suction side is significantly improved; The adiabatic film effectiveness near the leading edge at the small tip-clearance-gap is higher than that at the large tip-clearance-gap under the mass-flow-ratio of 0.1% + 0.05% condition due to the mainstream-blockage-effect; With the tip-clearance-gap increasing, the high aerodynamic loss coefficient region is significantly enlarged. At three tip-clearance-gaps, changing the mass-flow-ratio shows a slight effect on the aerodynamic loss coefficient distribution. [ABSTRACT FROM AUTHOR]

• Aerothermal performance of the rib-slot blade tip is studied in transonic flow. • A superior film cooling performance is obtained by rib-slot blade tip scheme. • The rib-slot blade tip with the jet decreases aerodynamic loss near the shroud. • The high-density jet improves film coverage near the tip trailing edge. A rib-slot blade tip is proposed to improve the film cooling performance of an unshrouded gas turbine blade tip in the current paper. The rib-slot blade tip is formed by arranging the slot into ribs of the multi-cavity squealer tip. The film cooling performance of the rib-slot blade tip is experimentally studied by using the Pressure Sensitive Paint (PSP) technique in transonic flows. The inlet Reynolds number is 370,000 based on the blade axial chord length. The exit Mach numbers is 1.05. Effects of density ratios and mass flow ratios on the film cooling characteristics are investigated, and the experiments are carried out at four mass flow ratios and three density ratios. The numerical simulation is used to predict the flow field and analyze the film cooling characteristics. The multi-cavity squealer tip consists of cavity 1-4. The results indicate that at the high mass flow ratio, the film can cover the whole squealer tip bottom surface downstream of rib-slots at three density ratios. Increasing the mass flow ratio has a slight effect on the film cooling effectiveness (η) near the tip pressure side upstream of the cavity 3. There is a low η region near the suction side of the cavity 2 and cavity 3 at low mass flow ratios, particularly for the high-density jet due to the leakage flow reattachment. A low η region is formed in the middle region of the cavity 4 at the low mass flow ratio. The blade tip with the jet shrinks the high aerodynamic loss coefficient region formed by the counter vortex, whereas, it expands the high aerodynamic loss coefficient region formed by the leakage vortex in the blade span-wise direction. The pitch-wise averaged aerodynamic loss coefficient of the blade tip with the jet is lower than that of the no film case near the shroud. [ABSTRACT FROM AUTHOR]