Effect of clearance height on tip leakage reduced by spontaneous tip injection

The steady cascade flow field with different tip clearance height was obtained by numerically solving three-dimensional Reynolds-averaged N-S equations(RANS)and energy equations under the condition of single-hole spontaneous tip injection.The influences of clearance height on the interaction characteristics of the spontaneous injection with the tip leakage flow,the mass flow rate of leakage flow and the blade load were analyzed.The results show that the spontaneous jet has significant blocking effect on the leakage flow, the leakage ratio decreases by 0.06% with 1mm(t/H=0.5%) tip clearance,and meanwhile the blade load increases by 1.39%.The blocking effect decays with the increasing clearance height and can be ignored when the clearance height rises to 4 mm (t/H=2%);decreasing clearance height can effectively improve the controlling effect of spontaneous jet on leakage flow and reduce the flow losses caused by flow separation;the presence of spontaneous tip injection significantly changes the flow field of tip gap and the distribution of static pressure coefficient near the suction.The calculation results show that a vortex similar to the Karman vortex street appears downstream the jet flow when the leakage flow moves around the spontaneous jet.