JAXA Supercomputer System Annual Report February 2025-January 2026

Report Number: R25EACA49

Subject Category: JSS Inter-University Research

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• Responsible Representative: Taku Nonomura, Professor, Nagoya University
• Contact Information: Taku Nonomura (Professor at Nagoya University)(nonomura@nagoya-u.jp)
• Members: Taku Nonomura, Takayuki Nagata, Naotaka Shigeta, Yuri Sato, Tentaro Uchida

Abstract

Large-eddy simulations (LES) are performed under compressible conditions of flow around symmetric airfoils, including flat plates with Reynolds numbers of O(10^3)-O(10^4), to elucidate the effects of compressibility on laminar separation bubbles and turbulent transition. In the low Reynolds number region investigated in this study, important phenomena for low Reynolds number aerodynamics are pronounced, such as the formation of laminar separation bubbles and turbulent transition. By precisely investigating the effects of compressibility on these phenomena, knowledge will be gained that will contribute to improving the performance of fluid machinery operated under high-speed and low-pressure conditions, such as the Mars aircraft.

Reference URL

N/A

Reasons and benefits of using JAXA Supercomputer System

In the present study, a parametric study by large-eddy simulations is conducted, and thus, a large-scale parallel calculation is required.

Achievements of the Year

At a Reynolds number of 1.0 x 10^4, direct numerical simulations (DNS) were performed for the NACA0006, NACA0012, and NACA0018 airfoils to investigate the effects of Mach number, airfoil thickness, and angle of attack on the flow field and aerodynamic characteristics. As in the case of 2.4 x 10^4 computed in the previous fiscal year, higher Mach numbers tended to delay the formation of vortex structures and the onset of three-dimensionality (Figs. 1 and 2). Comparisons were also made with wind tunnel experiments conducted under the same conditions. Figure 3 shows the lift coefficients for the NACA0006 and NACA0018 airfoils. In particular, for the thinner airfoil, the wind tunnel experiments tended to underestimate the lift coefficient compared with the numerical simulations. This is presumably because the wind tunnel experiments were affected by the boundary layers developing on the sidewalls, whereas the numerical simulations were not subject to this effect. Under the low-Reynolds-number conditions considered in this study, this influence is expected to be particularly significant. It was also found that the discrepancy between the wind tunnel experiments and the numerical simulations becomes especially large under conditions where a laminar separation bubble is formed.

Fig.1: Instantaneous velocity fields and vortical structure of flow around NACA0006 airfoil visualized by the second invariant of the velocity gradient tensor (perspective view). The threshold of the isosurface is Q/u_inf^2 = 5.

Fig.2: Instantaneous velocity fields and vortical structure of flow around NACA0012 airfoil visualized by the second invariant of the velocity gradient tensor (perspective view). The threshold of the isosurface is Q/u_inf^2 = 5.

Fig.3: Lift curves of NACA0006 and NACA0018.

Publications

- Oral Presentations

Uchida, T., Nagata, T., and Nonomura, T., "Wall-resolved LES evaluation of Mach number and angle of attack effects on the flow field around NACA airfoils at low Reynolds numbers under compressible conditions," 2026 AIAA SciTech, 1438, Florida, USA (2026).

Usage of JSS

Computational Information

• Process Parallelization Methods: MPI
• Thread Parallelization Methods: OpenMP
• Number of Processes: 44
• Elapsed Time per Case: 150 Hour(s)

JSS3 Resources Used

Fraction of Usage in Total Resources*1(%): 0.28

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