Blade Tip Leakage Loss Reduction by Means of Passive Tip Injection: Linear Cascade Wind Tunnel Results

In the open literature, an innovative concept for turbine blade tip leakage loss reduction by means of passive tip injection was recently proposed. The present paper presents experimental results obtained for an unshrouded turbine blade corresponding to a 50 % reaction stage. The experiments were performed in a low-speed linear cascade wind tunnel facility with air as working fluid. The effect of passive tip injection on the resulting loss was investigated by detailed five-hole-probe measurements. Cascades with three different tip gap heights and blades with and without passive injection were considered. Special attention was spent to the actual upstream conditions. The detailed flow field measurements showed that at the blade tip exit the leakage flow merged with the main flow and rolled up to a tip leakage vortex. The linear cascade wind tunnel results indicated a slight reduction of the resulting total pressure loss coefficient due to the passive tip injection. The observed tip leakage loss reduction was well comparable with the predictions of simplified analytical model.