JAXA Supercomputer System Annual Report February 2025-January 2026

Report Number: R25ECMP35

Subject Category: Competitive Funding

PDF (to be added)

• Responsible Representative: Hideaki Nanri, Director, Research Unit IV, Research and Development Directorate
• Contact Information: Masahiro Takahashi(takahashi.masahiro@jaxa.jp)
• Members: Masaaki Fukui, Chihiro Fujio, Susumu Hasegawa, Taku Inoue, Masatoshi Kodera, Toshihiko Munakata, Sadatake Tomioka, Masahiro Takahashi

Abstract

Hypersonic air-breathing engines can be efficient for winged launch vehicles and high-speed vehicles for peer-to-peer transportation. For example, a high-speed vehicle with a Mach number above 5.5 in flight is reported to have a good potential market. However, no single airbreathing engine can operate over a wide range of speeds from takeoff to Mach 5.5 and above, so combined cycle engines are required for such applications. Various types of combined cycle engines have been proposed, and currently, turbine-based combined cycle engines are under development or in the technical demonstration phase, mainly for Mach 5 vehicles. A combination with scramjet is necessary for higher velocity, say Mach 6, bringing a further challenge to engine design technology, which is not mature yet. Therefore, JAXA is collaborating with several universities on a five-year research program to develop key technologies needed for the development of a TBCC engine, which is a combination of a turbo-ramjet and a scramjet with a flow-pass switching mechanism, and to demonstrate them through ground tests.

Reference URL

N/A

Reasons and benefits of using JAXA Supercomputer System

Taking scramjet research as an example, one of the main tasks of this research is to design the geometry of the air inlet, combustor flow path, fuel injector, and cavity flame holder. These are then manufactured and tested on the ground to confirm their performance. To keep the candidate geometry selection process on schedule, many parametric computations must be performed within a limited time frame. In particular, the computational cost of CFD of scramjet combustors increases significantly because the combustion process of hydrocarbon fuels involves many intermediate species, and the combustion reaction models are complex and extensive. Therefore, using JSS, which has high computational power, is essential.

Achievements of the Year

(1) Design study of scramjet combustors

This fiscal year, we determined the basic combustion chamber geometry with the aim of operating from cruise conditions down to the transition point to the Turbo-Ramjet (TRJ) engine (targeted between Mach 3 and Mach 4). We then conducted a parametric study using CFD on the fuel injectors and cavity flame holders to be installed in this combustor under cruise conditions (assuming flight conditions equivalent to Mach 6) and selected promising candidate geometries. Figure 1 shows the distribution of physical quantities within the spanwise midplane for three cases with different mounting positions of the fin-type fuel injectors, designed to supply fuel over a wide range in the vertical direction of the combustor. From top to bottom, the quantities are static pressure, static temperature, Mach number, and fuel equivalence ratio. The inflow condition was a Mach 3 airflow corresponding to the flow condition at the exit of air inlets. The fuel was a 64% ethylene / 36% methane mixture, commonly used as a surrogate for thermally decomposed jet fuel, and combustion CFD was applied using a 31-species air/ethylene/methane skeletal reaction mechanism. The fuel equivalence ratio was 0.6. By changing the injector position, the incident point of the reflected shock wave from the bottom wall, which originally formed around the fin, to the cavity flow moved and the shape of the shear layer and recirculation region within the cavity changed significantly. As a result, differences were observed in the mixing of fuel and the main airflow, as well as in the progression of combustion heat release. We have fabricated wind tunnel test models of the fuel injectors and cavity flame holders, whose configurations demonstrated effectiveness in the CFD evaluations and are conducting combustion tests to evaluate them.

(2) Design study of scramjet inlets

We evaluated the performance and starting characteristics at low-speed non-design points of a two-dimensional, multi-stage ramp mixed-compression type inlet—designed to meet the requirements of 100% air capture ratio, an overall pressure ratio of 30, and high total pressure recovery under cruise conditions (Mach 6)—using 2D CFD. First, the pressure ratio distribution to each ramp that maximizes the total pressure recovery rate of the multi-stage ramp inlet was investigated using GA-optimized design and CFD evaluation. Previous studies have analytically shown that, in the case of inviscid flow, it is optimal to distribute the pressure ratios of each compression stage equally within external and internal compression stages. We demonstrated that the optimal distribution remains nearly equal even when considering viscous losses such as total pressure loss due to boundary layers and heat loss to the wall. Furthermore, when the overall pressure ratio is the same, deflecting the direction of the airflow at the inlet exit from horizontal to downward reduces the ratio of the internal compression ratio to the overall pressure ratio, and a flow field in the started state was obtained under non-design point conditions at Mach 3.5 (Fig. 2). However, it was also found that the drag on the outer surface of the cowl increased significantly. These results suggest that designing the inlet based solely on its performance is insufficient, and that the design must be guided by the goal of maximizing the net thrust generated by the entire engine, including the combustor and nozzle. In response to this, we are currently working to update our design tools.

(3) Performance evaluation of turbo-ramjet engine

Two-dimensional performance calculations were performed on a turboramjet engine. The intake's peak performance point was investigated by installing a throat with a variable cross-sectional area at the intake outlet. Performance analysis of the turboramjet engine was then performed based on the intake outlet state variables, and the nozzle inlet boundary conditions were determined. The forces acting on the engine were calculated from the CFD results, and engine performance was evaluated.

Fig.1: Distribution of flow properties in the central cross-section of the combustor: from top to bottom, static pressure, static temperature, Mach number, and fuel equivalence ratio. The inflow is a Mach 3 combustion-heated airflow (corresponding to the Mach 6 cruise conditions). Fuel equivalence ratio was 0.6. The positions of the fin injectors were A: uppermost position (X = 0 mm), B: middle position (X = 27 mm), C: lowermost position (X = 83 mm).

Fig.2: Mach number distribution at the design point (Mach 6) and non-design point (Mach 3.5) of a two-dimensional multi-stage ramp mixed-compression type inlet: overall pressure ratio 30, three external compression stages with three internal compression stages.

Fig.3: Example of turbo-ramjet performance evaluation using two-dimensional CFD

Publications

- Non peer-reviewed papers

1) Takahashi, M., et al., ''Design Study of a Scramjet Combustor Operating Over a Wide Range of Mach Numbers,'' Proceedings of 69th UKAREN, 4K03 (2025).

2) Takahashi, M., et al., ''Design Study of a 2-dimensional Scramjet Inlet Operating over a Wide Range of Mach Numbers,'' HiSST-2025-0229 (2025).

Usage of JSS

Computational Information

• Process Parallelization Methods: MPI
• Thread Parallelization Methods: N/A
• Number of Processes: 48 - 4800
• Elapsed Time per Case: 50 Hour(s)

JSS3 Resources Used

Fraction of Usage in Total Resources*1(%): 1.74

Details

Please refer to System Configuration of JSS3 for the system configuration and major specifications of JSS3.

*1: Fraction of Usage in Total Resources: Weighted average of three resource types (Computing, File System, and Archiver).

*2: Fraction of Usage：Percentage of usage relative to each resource used in one year.

ISV Software Licenses Used

*2: Fraction of Usage：Percentage of usage relative to each resource used in one year.

JAXA Supercomputer System Annual Report February 2025-January 2026