JAXA Supercomputer System Annual Report February 2025-January 2026

Report Number: R25EFHC0320

Subject Category: Large-Scale Challenge

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• Responsible Representative: Yasuhito Okano, Postdoctral researcher, Research and Development Directorate, Unit III
• Contact Information: Yasuhito Okano, Research and Development Directorate, Research Unit III(okano.yasuhito@jaxa.jp)
• Members: Takanori Haga, Yasuhito Okano

Abstract

Accurate prediction of wall heat flux is crucial for liquid rocket engine combustors. Although wall-modeled LES (WMLES) can obtain high fedility results at a practical computational cost, simulations often blow up under extremely cold-wall conditions typical of rocket combustors because of numerical instabilities in the near-wall region. To address this issue, we are developing a robust WMLES framework by adding artificial viscosity only near the wall. We have already confirmed its effectiveness through comparison with DNS under moderately cold-wall conditions. However, reliable reference data for extremely cold-wall conditions are scarce. The lack of reference data makes quantitative validation difficult. Therefore, wall-resolved LES (WRLES) is performed in this study to obtain validation data. The validity of the proposed method is then assessed.

Reference URL

N/A

Reasons and benefits of using JAXA Supercomputer System

In WRLES, the viscous sublayer near the wall must be fully resolved, which imposes very strict requirements on the number of cells and the minimum grid spacing. Thus, the computational cost of WRLES is substantially high. In addition, for reacting flows, the computational cost per time step and the memory requirement are larger than for ideal-gas flows. Furthermore, in turbulent flows, discussions are often based on time-averaged fields, which requires long-time sampling. Therefore, the supercomputer is indispensable to obtain reliable reference data for validation.

Achievements of the Year

The WRLES of a turbulent channel flow with an extremely cold wall is performed to obtain reference data. The test gas was H2/O2 combustion products. The combustion temperature and wall temperature are approximately 3500 K and 800 K, respectively. The ratio of the recovery temperature to the wall temperature is about 0.2. The Q-criterion obtained by the WRLES is visualized in Fig. 1. Vortical structures can be clearly observed. The wall-normal profiles of the streamwise velocity, temperature, and Reynolds shear stress are shown in Fig. 2. The WMLES results are in good agreement with the WRLES results. In addition, the mass fractions of H2O, O2, and OH are shown in Fig. 3. Even in terms of species mass fractions, the WMLES results agree well with the WRLES results. Finally, the nondimensional heat fluxes obtained by WMLES and WRLES are 0.1768 and 0.1854, respectively. The error between them is within 5.1%. These results indicate that the proposed WMLES can accurately predict even the reacting channel flow. The proposed method is currently being applied to more practical problems, such as a single-element combustion chamber.

Fig.1: Isosurface of Q-criterion colored by streamwise velocity obtained by WRLES.

Fig.2: Streamwise velocity, temperature, and Reynolds shear stress profiles for wall-normal direction.

Fig.3: Mass fraction profiles of H2O, O2, and OH for wall-normal direction.

Publications

- Non peer-reviewed papers

1. Okano, Y., Haga, T., "Robust Isothermal-Wall WMLES with the Flux Reconstruction Method," 57th Fluid Dynamics Conference / 43rd Aerospace Numerical Simulation Technology Symposium (in Japanese).

2. Okano, Y., Haga, T., "Robust Wall-modeled LES with Flux Reconstruction Scheme toward Accurate Heat Flux Prediction in Rocket Engine Combustors," AIAA Paper, No. 2026-0387, 2026.

- Oral Presentations

1. Okano, Y., Haga, T., "Wall-Modeled LES of Reacting Flows under Cold-Wall Conditions Using the Flux Reconstruction Method," 39th Computational Fluid Dynamics Symposium, December 16, 2025, Kitakyushu, Japan (in Japanese).

Usage of JSS

Computational Information

• Process Parallelization Methods: MPI
• Thread Parallelization Methods: OpenMP
• Number of Processes: 112 - 336
• Elapsed Time per Case: 600 Hour(s)

JSS3 Resources Used

Fraction of Usage in Total Resources*1(%): 0.65

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