Heat Transfer and Pressure Measurements for the Forward Purge Cavity, Inner Endwall, and Rotor Platform of a Cooled Transonic Turbine Stage

Abstract

An experiment is performed using a cooled transonic high-pressure turbine stage operating at design-corrected conditions. Pressure measurements are taken at several locations within the forward purge cavity between the high-pressure stator and rotor, as well as on the blade platforms and vane inner endwalls. Double-sided Kapton heat-flux gauges are installed on the upper surface of the rotor blade platform (open to the hot gas path flow) and underneath the platform (exposed to coolant and leakage flow). The blade airfoil and purge flow cooling are supplied by the same flow circuit and must be varied together, but the influence of the airfoil cooling has previously been shown to be negligible in the platform region flow of interest to this study. A separate cooling circuit supplies the aft purge flow between the rotor and downstream components. The vane cooling holes have been blocked off for this experiment to simplify analysis. In order to determine the effect of the purge flow on the blade aerodynamics and heat transfer, the forward and aft cooling flow rates are varied independently. Both time-averaged and time-accurate results are presented for the pressure and heat-flux data to illustrate the complex interactions between the purge cavity flow structures and the external flow. Time-accurate data are presented using both Fast-Fourier Transforms (FFTs) to identify driving frequencies and ensemble average plots to highlight the impact of different wake shapes.

The Aero-Thermal Performance of Purge Flow and Discrete Holes Film Cooling of Rotor Blade Platform in Modern High Pressure Gas Turbines: A Review

“…In [34], measurements based upon double sided heat flux gauges were presented by Nickol et al to discuss the heat transfer capability of a cooled transonic turbine stage at design-corrected operating conditions. The measurements evidenced that the presence of coolant flow does not directly alter the heat transfer magnitude, instead it has an impact on the characteristics of the passage vortex.…”

“…Most of these researches were carried out at Texas A and M University on a five-blade cascade test facility [13][14][15][16][17][18][19][20], at the University of Bergamo on a seven-blade cascade test facility [21][22][23][24][25][26] and at Whittle Laboratory of the University of Cambridge [27,28]. Meanwhile, the latter family of experiments (rotating platforms) were carried out in the TPFL-research turbine facility at Texas A and M University [29,30], in the CT3 compression tube turbine test rig at the von Karman Institute [31], at Ohio State University Turbine Test Facility (TTF) [32][33][34], at the LISA research turbine available at ETH Zurich [35,36] and, more recently, at the Large Annulus Rig (LAR) of the University of Bath [37,38]. Clearly, different measurement set-ups belonging to the same family are characterized by different cooling slot and hole dimensions and positions, as well as related geometrical characteristics.…”

Calibration of thermopile heat flux gauges using a physically-based equation

“…Nickol et al. 6 used a double-sided gauge consisting of a Kapton (polyimide) insulating layer (51-µm thick) sandwiched between two nickel resistance thermometers. This was used to measure high-frequency response (>100 kHz) heat flux on the platform of a transient, cooled transonic turbine stage with transient temperatures up to 280 °C.…”