Film-Cooling Effectiveness on a Rotating Turbine Platform Using Pressure Sensitive Paint Technique

Abstract

Film-cooling effectiveness is measured on a rotating turbine blade platform for coolant injection through discrete holes using pressure sensitive paint technique. Most of the existing literatures provide information only for stationary endwalls. The effects of rotation on the platform film-cooling effectiveness are not well documented. Hence, the existing three-stage turbine research facility at the Turbomachinery and Flow Performance Laboratory, Texas A&M University was redesigned and installed to enable coolant gas injection on the first stage rotor platform. Two distinct coolant supply loops were incorporated into the rotor to facilitate separate feeds for upstream cooling using stator-rotor gap purge flow and downstream discrete-hole film cooling. As a continuation of the previously published work involving stator-rotor gap purge cooling, this study investigates film-cooling effectiveness on the first stage rotor platform due to coolant gas injection through nine discrete holes located downstream within the passage region. Film-cooling effectiveness is measured for turbine rotor frequencies of 2400 rpm, 2550 rpm, and 3000 rpm corresponding to rotation numbers of Ro=0.18, 0.19, and 0.23, respectively. For each of the turbine rotational frequencies, film-cooling effectiveness is determined for average film-hole blowing ratios of Mholes=0.5, 0.75, 1.0, 1.25, 1.5, and 2.0. To provide a complete picture of hub cooling under rotating conditions, simultaneous injection of coolant gas through upstream stator-rotor purge gap and downstream discrete film-hole is also studied. The combined tests are conducted for gap purge flow corresponding to coolant to mainstream mass flow ratio of MFR=1% with three downstream film-hole blowing ratios of Mholes=0.75, 1.0, and 1.25 for each of the three turbine speeds. The results for combined upstream stator-rotor gap purge flow and downstream discrete holes provide information about the optimum purge flow coolant mass, average coolant hole blowing ratios for each rotational speed, and coolant injection location along the passage to obtain efficient platform film cooling.