Experimental investigation of the structure of overexpanded supersonic stream

Аuthors

Ponomarev A. A.^*, Ponomarev N. B.^**, Kirillov E. B.^***

Keldysh Research Centre, 8, Onezhskaya str., Moscow, 125438, Russia

*e-mail: ponomar_aa@mail.ru
**e-mail: ponomarevnb@mail.ru
***e-mail: kirilloveb@mail.ru

Abstract

The main purpose is to investigate the properties and features of free shock and restricted shock flow separation in supersonic nozzles. According to earlier articles on this subject, the main feature of the restricted shock separation is cap shock formation. Also the reverse flow zone is formed near the nozzle axis of symmetry. This fact was derived from indirect results and must be proved.
Overexpanded supersonic stream that flows from the nozzle is researched. The flow pattern of the stream is visualized and shadow pictures of the stream are obtained. A thick wire with small steel flags is placed perpendicular to the symmetry axis of the stream. Flags can rotate around the wire almost without friction. Such wire with flags is a good instrument to measure the direction of the velocity vector in different points of the stream. Two different nozzles are used. One of them has relatively small expansion ratio and is used to obtain free shock separation. Another one’s expansion ratio is significantly larger, so this nozzle is suitable to obtain restricted shock separation.
Experimental results show that flow velocity vector is directed away from the nozzle exit in all points of the stream in the case of free shock separation. The appearance of restricted shock separation really results in the formation of reverse flow zone near the symmetry axis of the stream. The stream flows around this zone as it is a solid obstacle. One can see that cap shock is formed.
In conclusion, we can say that restricted shock separation formation in high-area-ratio nozzles can result in great increasing of the amplitude of unsteady side loads and wall heat flux. Consequently, it is strongly recommended to carry out the liquid rocket engine tests in the conditions that prevent restricted shock separation formation.

Keywords:

ionosphere, ionosphere heating facilities, HAARP, space system for monitoring, natural ELF/VLF antennas

References

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