An experimental investigation of the effect of tip clearance on the performance of a shrouded supersonic impulse turbine was performed in this study. A single-staged axial flow impulse turbine designed to have a rotor inlet relative Mach number of 1.7 was used for the experiment. Turbine efficiency was measured at various settings of tip clearances, rotational speeds, and turbine pressure ratios to observe the characteristics of the efficiency gradient. The overall efficiency of the supersonic impulse turbine was largely affected by rotational speed. For a fixed rotational speed, local maximum efficiency was found near a turbine pressure ratio at which the turbine nozzle was fully expanded. At a reference test point, the linearly estimated efficiency gradient was 0.09. However, efficiency variation with respect to tip clearance was nonlinear, and relatively larger efficiency gradients were found at small tip clearances and high rotational speeds. It has been found that the efficiency gradient varies linearly with the cube of rotational speed and shows its minimum value near the reference turbine pressure ratio.
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