This paper presents a detailed investigation on the impact of protrusion parameter including both radial position and amount on the efficiency of cavity with protrusion converting additional windage loss for ingress alleviation in rotor–stator system. Experiment is conducted to explore the effect of protrusion parameter on ingress, and the corresponding additional windage loss is also calculated. During the experiment, rotor-mounted protrusions are circumferentially assembled at three different radial positions (0.9b, 0.8b, and 0.7b) each with four different amounts (32, 24, 16, and 8). Measurements of CO2 concentration and pressure inside turbine cavity are conducted. In the experiment, the annulus Reynolds number and rotating Reynolds number are set at 1.77 × 105 and 7.42 × 105, respectively, while the dimensionless sealing air flow rate ranges from 3047 to 8310. Experimental result shows that the cases of protrusion set at 0.8b achieve higher sealing efficiency than other cases as the cavity pressure is enhanced. The effect of protrusion amount on ingress could be obviously seen when CW is small or protrusion set in 0.7b. Furthermore, a parameter to evaluate which case obtains higher efficiency of converting additional windage loss for ingress alleviation, or alleviates ingress more efficiently for short, is applied for discussion. It is found that the case “C, N = 8” alleviates ingress most efficiently among all the cases. Therefore, proper setting of the protrusion could lead to high efficiency of converting additional windage loss for ingress alleviation in rotor–stator system.