Heat Transfer Investigations at the Over-Tip Casing of a High Pressure Turbine Stag

Abstract

The development of gas turbines aims to an increase of power and efficiency, account environmental and economical aspects. Meanwhile combustion temperature reaches values far above of the acceptable material temperatures. Thus the thermal highly loaded components have to be cooled strongly. These parts are besides the blades, the platform and the casing of the first stages. Up to now the aero-thermal loading of the shroud above the rotor blades was investigated poorly. This final report contributes to a better understanding of the major phenomena governing the heat flux to the shroud. Using a HP-Turbine at different flow conditions extended measurements were performed at DLR’s wind tunnel for rotating cascades, Göttingen, concerning the flow field above the rotor and close to the shroud. The data collected include time averaged values as well as time resolved ones as i.e. static pressure at the shroud, wall temperature and calculated heat flux coefficient, hot film measurements; additionally the passage near the casing was investigated using probes (stationary and instationary ones). The sensors and inserts necessary to perform the measurements were developed and manufactured; the procedures for evaluating the gained data were developed too. From this investigation an extended data basis was generated used to proceed in getting some information about work process within the tip clearance and about the heat flux into linear segments. The procedures to develop (simple) correlations for a better estimation of the thermal load of the shroud are describe