Blade tip clearance effect on the performance and flow field of a three stage axial turbine

Abstract

The effect of a 1.5 % blade tip clearance on a rotating three stage turbine under different operating points was investigated using radially and circumferentially traversed five hole pressure probes. The probes were used to obtain flow field total and static pressures, absolute and relative velocities and angles, as well as calculate the blade span distribution of total pressure loss coefficient. Total temperature thermocouple probes were traversed radially and circumferentially to obtain temperature profiles under running conditions. Results showed high discrepancies especially in the blade tip region which is due to high circulation flows occurring at the tip that produce an out of probe calibration range type flow. Engine efficiency and massflow rate was also measured using a venturi flow meter in order to discern the effect the blade tip clearance has on the engine efficiency and performance. Results have shown that the blade tip clearance losses appear to play a smaller role when compared to other losses such as exit losses. This was because the engine efficiency was slightly affected when run using a blade tip clearance.