Effect of Clocking on the Heat Transfer Distribution of a Second Stator Tested in a One and a Half Stage HP Turbine

Abstract

This paper reports detailed heat transfer measurements on the second stator of a one and a half stage HP turbine. The tests are performed under engine representative conditions. Four vane-to-vane clocking positions are investigated. The second stator inlet and outlet flowfield is monitored. The heat transfer measurements are performed with thin-film gauges around the blade profile at 15%, 50% and 85% span as well as on the hub and casing endwalls. On a time-averaged point of view, the inlet conditions of the second stator vary noticeably as a function of clocking. This variation is due to a change of relative position of the total pressure pitchwise distribution, linked to the first stator, with respect to the pitchwise variation of the static pressure, linked to the second stator. On the hub platform, the location of a zone of high heat transfer, probably due to high velocity levels, moves in conjunction with the clocking. When this zone is in the center of the passage, the time-averaged thermal load around the airfoil profile is significantly lower. On a time-resolved point of view, the rotor exit Mach number undergoes periodically short excursions in the transonic regime. The passing of these shock/potential distortion events can be clearly seen on the second stator profile. Thanks to a model of isentropic compression, it is demonstrated that the heat flux variations originate in static pressure fluctuations that are causing variations in the gas temperature. The clocking changes not only the mean levels of the heat transfer but also the intensity and the trajectory of the fluctuations.