Test of the annular supersonic air inlet with isentropic compression in the wind tunnel

In this paper, the practical implementation of the previously proposed design method of the annular supersonic air inlet with isentropic compression is considered. In the beginning, the contour of the annular supersonic nozzle is calculated. Here, the ideal gas is isentropically accelerated from $\mathrm{M}=1$ to $\mathrm{M}=3$. When the flow direction turns around $180$ degrees, the walls of the nozzle and each flow line can be considered as compression surfaces for the supersonic air inlet. In this study, two flow lines with relative mass flow rate equal to $1.0$ and $0.6$ were chosen as inlet compression surfaces. Then, the theoretical contour was transformed into a real inlet profile in accordance with the given restrictions. The profile was transformed into four sectors with possibilities of both folding and unfolding inside and outside the central cylindrical body of $120$ mm in diameter. The movement of the sectors is implemented by pneumatic cylinder at air pressure up to $10$ MPa.
The resulting air inlet model was tested in the wind tunnel at Mach number varying from $\mathrm{M}=2.5$ to $\mathrm{M}=4$. Over the course of experiments, the process of both inlet folding and unfolding in the supersonic air flow was demonstrated. The time of folding and unfolding was $0.25$ and $0.05$ s, respectively. According to the shadow visualization results in each inlet sector in the working position, the flow pattern complies with theoretical predictions.