Mitsubishi Heavy Industries Ltd. Develop H-IIB Launch Vehicle with Flowmaster

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Project Introduction

At 2:01 am on September 11th 2009 (JST) the new Japanese H-IIB rocket launched successfully into space, carrying with it the H-II Transfer Vehicle (HTV) for re-supplying the ISS (International Space Station). Mitsubishi Heavy Industries Ltd (MHI) and Japan Aerospace Exploration Agency (JAXA) worked together to develop the H-IIB which was an upgrade version of the existing H-IIA launch vehicle. The success of the launch was critical to the continuation of the ISS.

The development of the H-IIB needed to be carried out in a short time frame, but without any increase to risk or cost. To achieve the new performance requirements, H-IIB adopted the cluster system of two engines for the first-stage instead of the single engine design of the H-IIA’s. The design of the feed lines, tank pressurisation system and other systems needed to be changed for the new vehicle. Various simulations and tests would have to be carried out to obtain the optimal system design.

MHI began using Flowmaster software for simulating launch vehicle systems in 1998. Back then, MHI used the software for troubleshooting the existing systems of the H-IIA. A specific example of this: Flowmaster could deliver complex transient behavioural information on the pressure and the flowrate change of the LOX and LH2 feed systems on valve opening. This previous success of using Flowmaster encouraged MHI to adopt system simulation software earlier into the design

phase of the H-IIB to overcome various initial design challenges, improve design robustness and increase development efficiency.

Development Challenges

One of the challenges faced by the propulsion system engineers was to stabilise the LOX (Liquid Oxygen) feed system due to the pressure interference resulting from clustering the engines (see Figure 1. H-IIB 1st stage LOX feed system schematic diagram). A couple of major factors had to be considered in trying to achieve a stable solution:

1. Pressure at the inlet of the engine changes transitionally in line with the level of LOX that the engine consumes. An excessive rise in pressure drop at the engine inlet due to interference between two feed systems would damage the engine. It was therefore very important to keep the change of the engine entrance pressure within design optimum limits.

2. When two engines are started, a pressure pulsation occurs. It was feared that the magnitude of the pressure pulsation at the entrance of the engine would be much higher compared with the existing H-IIA, due to the new cluster design. Therefore, it was necessary to evaluate the influence of the ignition timing and starting characteristics of the two engines.

Flowmaster system simulation was adopted early in the design process to overcome the above challenges.

Improving efficiency and overcoming design challenges through early adoption of system simulation into the development process.

Figure 1 - H-IIB 1st stage LOX feed system schematic diagram

Figure 2 - Photo showing H-IIB 1st & 2nd stage assembly (Photo Courtesy of JAXA)

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Modelling Approach

The simulation of the H-IIB system design was executed only after some verification tests had been conducted. MHI wanted to test the accuracy of Flowmaster’s simulation results against some existing measured past flight data of the current H-IIA rocket.

If Flowmaster’s simulated results were in close alignment with the true physical data from the past flight, MHI would then be confident to use the Flowmaster model. The Flowmaster model would then run parametric simulations to predict the influence of the new design variations on the engine inlet pressure, by considering the characteristic of two engines and the timing of the engine start. The simulation model and the predicted results would then be verified by the BFT (Battleship tank Firing Test). Figure 3 shows the flowchart of this modelling approach.

Simulation Model

An incompressible transient analysis was carried out for the simulation of the LOX feed system (See Figure 4).

In the model, the PSD (Pogo Suppression Device) which works as an accumulator to suppress the pressure change in the feed line, located at the engine inlet was a customised component that was modelled on design specification parameters. The fluid properties of LOX used the detailed data which was authorised in the actual design.

Figure 3 - flowchart of the modelling approach

Figure 4 - H-IIB 1st stage LOX feed system and its Flowmaster V7 simulation model

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Buildup simulation model

Verification of simulation model

Parametric study

Verification against BFT

Design of system

FeedbackPrediction of sytem characteristics

Comparing with simulation results and the measured data of the past flight

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Simulation Results and Validations

Figure 5 shows the comparison between predicted results from Flowmaster and measured data from BFT. The graph clearly shows a close fit between the predicted results and measured data. For the transient pressure behaviour and the peak pressure after starting the engines, the graph shows the predicted minimum pressure is smaller than the measured data, which means that the simulation results predict that the engine design has a good safety margin.

In Summary

MHI saw great savings in overall development time, by being able to analyse a transitional pressure behaviour at the inlet of two engines of H-IIB LOX feed system, at the very beginning of the design process. Flowmaster’s ease of use allowed MHI to quickly model and validate the previous H-IIA simulation results against existing flight data, helping provide confidence in the results delivered from the new developments of the H-IIB.

MHI was able to conduct a number of parametric transient analysis studies when designing the H-IIB LOX feed system considering the various outcomes that could occur. This enabled accurate prediction of the differing behaviour of the engine inlet pressure and reduced the amount of physical testing later in the development process.

Most importantly it was confirmed that the predicted results from the Flowmaster transient analysis were in close alignment

Figure 5 - LOX engine inlet pressure (comparing data to predicted profile)

Images courtesy of JAXAwith the test results of the BFT. This resulted in few design problems being encountered with this system further into the development process, enabling the development to advance efficiently towards a successful launch.

“The accuracy of Flowmaster’s results against pre-existing flight data allowed us to design the H-IIB launch vehicle confident in the knowledge that we could rely on the performance figures given from testing the new systems in a ‘virtual’ software environment.”

— Akihiro SATo, ProPulSion SyS-

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miTSuBiShi heAVy inDuSTrieS, lTD.