The windage loss caused by protrusion in a rotor-stator cavity has been studied in detail,and there are abundant fitting formulas that have been summarized to calculate the moment coefficients.Some other theorists have emphasized its effect on the sealing efficiency,proposing that installation of protrusion could alleviate gas ingestion.However,the protrusion shape which is an influential factor on the sealing efficiency has not been focused in previous research.Using the experimental method of measuring CO2 volume fraction,cavity pressure,and power consumption,we investigated the effects of several typical protrusion shapes on various parameters for two sealing structures,in order to obtain the optimal shape.Results showed that a variation of the protrusion shape had little impact on the static pressure,but the total pressure and the sealing efficiency increased in different degrees.Furthermore,even though the hexagon shape resulted in the highest sealing efficiency,we observed that the drop shape had the best overall performance in all of the eight models,which could result in higher efficiency of the turbine cavity.The combination of a radial seal structure and protrusion could improve sealing efficiency better.