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In this paper, a numerical investigation was conducted into the impact of the tip clearance height and the relative motion between the casing and the strake wall tip on the tip clearance leakage flow of a supersonic expander. Besides, an analysis was carried out to characterize the flow under varying operating conditions. Numerical results show that the remarkable characteristics of motion within the tip gap region are the leakage fluid around the trailing edge passing through the tip gap and then returning to the pressure side. As the tip clearance height increases, the intensity and scale of the tip leakage vortex show an upward trend. Also, the mix with the surrounding airflow contributes to a significant increase in the leakage losses and a reduction of the losses in the rampart and the mainstream region. It can be found that an excellent aerodynamic performance will be achieved when the tip clearance height ranges between 0.9% h0 and 1.5% h0. The relative motion of the casing not only reduces the transverse motion of the leakage vortex but also increases the tip leakage mass flow and the intensity of the tip leakage vortex, thus causing a significant rise in the flow losses. A lower [Formula: see text] will result in a severe deterioration in the performance of the supersonic expander. Furthermore, when the [Formula: see text] reaches a certain threshold (or above 12 times the atmospheric pressure to be precise), the main performance parameters of the supersonic expander will show no change with the increase of [Formula: see text]. Nevertheless, the continued improvement of [Formula: see text] means that the requirement becomes more demanding on engine performance.

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