Experimental and numerical investigation on design parameters of slot nozzles

Slot nozzles are altitude compensation nozzles. In the overexpansion mode, slots in the expansion section can affect the flow separation and improve the thrust. In this study, cold-flow experiments and numerical simulation are performed to study the design parameters of slot nozzles. The effects of slot location, number, and vented area on the flow field, thrust, and average specific impulse of the first-stage rocket are investigated. The results show that the thrust increases due to two reasons: the advance of the separation position and the rise of wall pressure in the recirculation zone. Moreover, the slot location is more important than other parameters in the design of slot nozzles. Only when a slot is close to the flow separation point, the influence of the slot on the flow field is apparent, thus, the thrust significantly and efficiently increases. The performance of the first-stage rocket can be significantly improved by replacing the traditional bell nozzles with slot nozzles. The average specific impulse increase of the space shuttle solid rocket booster and first-stage rocket of the nano launch vehicle (NLV) is 5.1 s and 7.9 s, respectively; further analysis of NLV shows that its payload can be increased by 16.1%.