Miki Nishimoto

LE-X -Japanese Next Liquid Booster Engine-

The LE-X engine is under study for Japan’s next flagship expendable launcher (post H2A) to be operated in the next decade with enhanced reliability and reduced cost. The goal of LE-X development is to meet the requirements from the vehicle for higher reliability, lower production cost and appropriate performance. Technology development itself is also a purpose of this investigation and will be applied to other forthcoming engines to be developed in Japan. The early-stage feasibility study of the LE-X engine was completed in 2005 through primary studies on system design, engine component design, cost reduction, reliability prediction, subscale testing, and computational simulation. In 2006, engine system analysis and fundamental studies on LE-X components by means of element tests were successfully conducted. In 2007, we have optimized the engine baseline configuration from aspect of cost reduction activities. Significant cost reduction will be achieved by drastic simplification of the engine system, and the innovation of the manufacturing process. Technology development will be ongoingly conducted to mitigate development risks, such as precise life prediction analysis of combustion chamber, prediction of combustion instability, and high-fidelity simulation.

Numerical Analysis of Flow-Induced Structural Vibration in the LE-7A Liquid Hydrogen Pump

The prediction of structural vibration generated from the turbopump is becoming increasingly important in developing highly reliable rocket engines. A potential risk that originates from the turbopump is the strong interaction between rotating impellers and stationary parts such as diffuser vanes and casing tongues. This will induce severe vibration to the turbopump casings, and damage other engine components with natural frequencies close to the casing vibrational frequency. The present paper describes the application of the numerical code developed by the authors (Kato and Yoshimura) to understand the flowinduced structural vibration in the liquid hydrogen pump of the LE-7A rocket engine. The source fluctuations of the flow field are computed by a large-eddy simulation (LES) with the Dynamic Smagorinsky Model (DSM) and the results are fed to the structural vibration analysis through our mesh matching and data transfer code. The vibration of the structural portion is simulated using an explicit dynamic finite element code. First, computations of the unsteady flow in the entire liquid hydrogen pump were carried out. Water tunnel experiments were also carried out to obtain validation data and the results were compared with the numerical results. The computed static pressure distribution, pressure fluctuation, and flow angle distribution agree well with the measured data. Next, after data interpolation, elastic wave propagating in the solid portion is solved. It was found that the phase difference of the first and second stage impellers had no affect on the structural vibration, but a major decrease was found to occur when the second stage impeller-diffuser clearance was expanded by only a few percent in the radial direction from the nominal configuration. The quantitative agreement of computed results with water tunnel experimental results and our findings in this study have shown that the proposed method can serve as a practical tool for predicting flow-induced structural vibrations in rocket engine pumps.