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Description
The ED nozzle is a type of altitude compensation nozzle that can be used for space launch vehicles. The ED nozzle forms an open wake with an effective area smaller than the normal nozzle exit area at low altitude. When the nozzle pressure ratio increases at high altitude, a closed wake is formed that increases the nozzle effective area. Transition is when the flow in an ED nozzle changes from an open wake to a closed wake as a function of the nozzle pressure ratio. In this paper, the before and after flow transition of the ED nozzle was studied.
An open wake occur in overexpansion before transition. Unlike typical bell nozzles, ED nozzles do not cause flow separation on the nozzle wall when it is over-expanded. The flows along the nozzle wall, and shock waves and expansion waves are repeatedly generated. This phenomenon is similar to RSS (Restricted Shock Separation) of a typical over-expanded bell nozzle. RSS of a typical bell nozzle generates a normal shock inside the nozzle. In the ED nozzle, the rear surface of the pintle located in the nozzle expansion serves as a normal shock wave, and a reflected shock occurs on the upper surface of the pintle. In the closed wake after the transition, flow separation occurs at the nozzle wall according to the nozzle pressure ratio. This is similar to the transition of flow from RSS to FSS (Free Shock Separation) as the nozzle pressure ratio increases in a typical bell nozzle. The separation point of the flow moves toward the nozzle exit as the nozzle pressure ratio increases.
The ED nozzle exhibits an RSS flow pattern at low nozzle pressure ratios due to the pressure of a pintle. Since the flow is unstable in the RSS, a large side load occurs when transitioning to FSS. In the future, it is necessary to study the side load during the flow transition of the ED nozzle.
References
[1] J. Choi and H. Huh, Performance analysis of an expansion-deflection (E-D) nozzle based on pintle inflection angle, Trans. Korean Soc. Mech. Eng. B, Vol. 36, No. 12, 2022, pp. 6065-6072.
[2] J. Lee, V. Lijo, and H. Kim, A Study on the Transitional Shock Separation Patterns in an Over-Expanded Nozzle, Journal of the Korea Society of Propulsion Engineers, Vol. 14, No. 3, 2010, pp. 9-15.
| Keywords | Expansion-Deflection Nozzle, Open Wake, Closed Wake, Transition, Nozzle Pressure Ratio |
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