Aerodynamic loss measurements are presented for a state-of-the-art film cooled transonic gas turbine rotor blade tested in a two-dimensional cascade. A mixture of carbon dioxide and air, which correctly simulated engine coolant-to-mainstream density ratio and blowing rate, was ejected from each of five individual cooling hole rows in the aerofoil suction surface. The temperature of the coolant was equal to the cascade inlet stagnation temperature. The dependence of blade row efficiency and turning on outlet Mach number, blowing rate, and coolant-to-mainstream density ratio was investigated. Measured surface static pressure distributions were compared with time-marching predictions for both the datum aerofoil and film cooled blades. Detailed suction surface boundary layer measurements both upstream and downstream of a cooling film were compared with available differential calculation procedures. Unexpectedly, films downstream of the throat, even at blowing rates near unity, did not generate significantly higher losses compared to prethroat suction surface films on this aerofoil.

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A computational study is carried out on the influence of turbine inlet temperature distortion (hot streak). The hot streak effects are examined from both aeromechanical (forced blade vibration) and aero-thermal (heat transfer) points of view. Computations are firstly carried out for a transonic HP turbine stage, and the steady and unsteady surface pressure results are compared with the corresponding experimental data. Subsequent analysis is carried out for hot-streaks with variable circumferential wavelength, corresponding to different numbers of combustion burners. The results show that the circumferential wavelength of the temperature distortion can significantly change unsteady forcing as well as the heat-transfer to rotor blades. In particular, when the hot-streak wavelength is the same as the nozzle guide vane (NGV) blade pitch, there is a strong dependence of the preferential heating characteristics on the relative clocking position between hot-streak and NGV blade. However, this clocking dependence is shown to be qualitatively weakened for the cases with fewer hot streaks with longer circumferential wavelengths.

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This paper is part one of a two part paper which considers a shroud film-cooling system designed using a two-dimensional approach. Heat transfer to rotor-casings has reached levels that are causing in-service difficulties to be experienced. Future designs are likely to need to employ film-cooling of some form. There is currently very little information available for film-cooling on shroudless turbine rotor-casing liners. Heat transfer literature on uncooled configurations is not extensive and in particular, spatially-detailed, time-accurate data are rare. This paper describes the aero-thermodynamic design and validation of a rotor casing film-cooling system for a transonic, high-pressure shroudless turbine stage. The design was carried out using a boundary layer code with the film-cooling hole geometry representative of an engine configuration and, has been subjected to mechanical constraints similar to those for an engine component. The design consists of two double rows of cooling holes and two ‘cooling-hole’ shape configurations, cylindrical and fan shaped. The design was tested in the QinetiQ short duration turbine test facility (TTF). Measurements taken include casing heat transfer using thin film gauges and stage exit total pressure, Mach number and flow angle using a three-hole pressure probe. Results showed that while the cooling produced a reduction in the heat transfer rate close to the injection point, the film was stripped off the casing and entrained in nozzle guide vane secondary and rotor overtip flow, where it was transported spanwise towards the hub in the rotor passage. Using the results obtained from this deign a second cooling design was carried out, using a three-dimensional approach this gave significantly better cooling performance. The thee-dimensional design and validation is reported in GT2009-60246 as part 2 of this paper.