Tip leakage flow reduces both efficiency and performance of axial turbines and damages turbine blades as well. Therefore, it is of great importance to identify and control tip leakage flow. This study investigated the effect of flow injection (from the casing), alongside flow structure, on turbine performance. Additionally, the effect of different injection parameters, including injection mass flow rate, angle, location, and diameter on the turbine performance are evaluated. A numerical analysis of the flow in a two-stage axial turbine was employed by using CFX software. To ensure the accuracy of the results, turbine performance curves were compared with the experimental results, which are in good agreement. Analyses revealed that active control method reduces tip leakage flow, improves turbine performance, and increases the efficiency by 1% to 5% as well. A parametric investigation of the tip injection has sought to identify how various parameters affect the turbine performance. The cross-section diameter and the angle of injection had no significant increase on efficiency. Additionally, results showed that at a point 9 mm further from the leading edge, the injection degree of effectiveness is optimum. Finally, analysis of the flow structure in the tip clearance region supported the tip leakage flow reduction.

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