Numerical Simulation of Reactive Flows in Overexpanded Supersonic Nozzle with Film Cooling

Mohamed Sellam,Amer Chpoun

doi:10.1155/2015/252404

Abstract

Reignition phenomena occurring in a supersonic nozzle flow may present a crucial safety issue for rocket propulsion systems. These phenomena concern mainly rocket engines which use H2gas (GH2) in the film cooling device, particularly when the nozzle operates under over expanded flow conditions at sea level or at low altitudes. Consequently, the induced wall thermal loads can lead to the nozzle geometry alteration, which in turn, leads to the appearance of strong side loads that may be detrimental to the rocket engine structural integrity. It is therefore necessary to understand both aerodynamic and chemical mechanisms that are at the origin of these processes. This paper is a numerical contribution which reports results from CFD analysis carried out for supersonic reactive flows in a planar nozzle cooled with GH2film. Like the experimental observations, CFD simulations showed their ability to highlight these phenomena for the same nozzle flow conditions. Induced thermal load are also analyzed in terms of cooling efficiency and the results already give an idea on their magnitude. It was also shown that slightly increasing the film injection pressure can avoid the reignition phenomena by moving the separation shock towards the nozzle exit section.

Highlights

One of the major challenges that the aerospace industry continues to face is the continued increase in launchers payload
At sea level and at low altitudes, the nozzle operates in overexpanded flow conditions; that is, the ambient pressure is higher than the nozzle exit pressure
Case 3 shows a typical behavior of film cooling applications as it was observed in several works [2]. In this case the temperature of the film cooling grows gradually by mixing with the hot main flow gas (Figure 11(c)) and the corresponding efficiency (η > 0.8) is within the range of the expected values (Figure 12(c)). This numerical study was conducted with the goal of reproducing some experimental tests carried out previously

Summary

Introduction

One of the major challenges that the aerospace industry continues to face is the continued increase in launchers payload. There are two challenges here: the increase in payload and the performance consolidation in terms of reliability These challenges promote development of nozzles with higher performances, which are substantially achieved by increasing the nozzle expansion area ratio or by developing new innovative nozzle concepts. The rocket engine nozzles, with high expansion area ratio, are generally optimized for operating at high altitudes. The ensuing side loads may be detrimental for both nozzle and other engine components These nozzles are designed to expand and accelerate combustion gases at high temperature. For Vulcain-II rocket engine, the cooling system is designed in two parts: a dump cooling for the first expansion part of the nozzle and GH2 film cooling for the second part [1, 2]

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Conclusion