Numerical Study on Flow Induced Vibration of LOX Post in Liquid Rocket Engine Preburner

Abstract

In a preburner of liquid rocket engines, some liquid-oxygen (LOX) posts, which introduced oxygen into combustion chamber, experienced severe flow-induced vibration due to unsteady cryogenic hydrogen flow. The mechanism of the vibration has not been fully understood because of the complexity of the flow field. In the present study, a new numerical method was developed to analyze the flow field of hydrogen, whose characteristic properties lie in its non-idealness and compressibility. The unsteady hydrogen flow inside the preburner unit was analyzed to investigate the details of hydrogen flow field as well as the mechanism of LOX post vibration. It was clarified that hydrogen flow inside the manifold and fluid dynamic forces on LOX posts were strongly affected by vortices shed from the junction at the upstream of the inlet. A baffle plate put inside the manifold was shown to reduce unsteady fluid forces on the LOX posts. INTRODUCTION In liquid rocket engines, a preburner is equipped at an upstream position of turbines to generate combustion gas for driving turbo pumps. A lot of liquid-oxygen (LOX) posts are arranged in the preburner to lead oxygen and hydrogen into the combustion chamber. A combustion chamber unit, schematically shown in Fig.1, is mainly consisted of a hydrogen manifold, an oxygen manifold, hundreds of LOX posts, and a combustion chamber. Figure 2 shows a cross-sectional view of hydrogen flow channel projected on the plane A-A’ in Fig.1. During the development of Space Shuttle Main Engine, some LOX posts were reported to experience harmful flow induced vibration (A.Kanmuri, 1983). Since the vibration was thought to be due to the unsteady hydrogen cross flow around the posts, some fluid dynamics studies have been carried out so far to clarify the mechanism of the vibration (S.S.Chen and J.A.Jendrzejczyk, 1984) (M.Williams, 1987). However, the detailed flow field in the preburner and the vibration mechanism have not been understood yet because of the complexity of the hydrogen flow field inside the preburner. The non-ideal characteristics of hydrogen itself inside the manifold also made it difficult to understand them. Recently, some LOX posts in a preburner of Japanese liquid rocket engine experienced a strong vibration, too. In the engine system, the hydrogen flow into the preburner was observed to have significant non-uniformity in the hydrogen manifold, though the details of the flow were still unclear. To obtain full understanding of the flow and vibration phenomena, detailed flow simulations should be performed in which the effect of all the LOX posts are taken into account and the hydrogen is treated as compressible and non-ideal fluid. In the present study, a new numerical method has been developed and proposed for simulating the complex flow field of compressible non-ideal hydrogen in the preburner. As a fundamental study, two-dimensional flow field, shown in Fig.2, was analyzed by the developed method to clarify the unsteady complicated flow field, and to investigate the mechanism of the flow induced vibration. The effect of a countermeasure of the strong vibration of LOX posts was also studied. NOMENCLATURE D tube diameter [m] e internal energy [J/kg] f frequency of shed vortices [Hz] Hs area fraction of solid [ ] Hv volume fraction of solid [ ]

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Cite this paper

@inproceedings{Inoue2007NumericalSO, title={Numerical Study on Flow Induced Vibration of LOX Post in Liquid Rocket Engine Preburner}, author={Chihiro Inoue and Toshinori Watanabe and Takehiro Himeno}, year={2007} }