Thermal and Fluid Dynamics of the Atmospheric Reentry Capsule

JAXA Supercomputer System Annual Report February 2025-January 2026

Report Number: R25EDU10300

Subject Category: Space and Astronautical Science

Responsible Representative: Hideto Takasawa, ISAS, Dept. of Space Flight Systems
Contact Information: Takasawa hideto(takasawa.hideto@jaxa.jp)
Members: Shotaro Baba, Reo Iida, Tomohito Morimoto, Takahiro Miki, Hideto Takasawa

Abstract

During atmospheric entry, a capsule travels over a wide range of velocities from hypersonic to subsonic regimes. Consequently, this leads to severe aerodynamic heating and disturbances in its flight attitude. To elucidate and mitigate these phenomena, numerical simulations are conducted to provide detailed flow-field information that cannot be obtained from wind tunnel experiments or flight tests. In this year, wind tunnel experiments under single-degree-of-freedom free oscillation are numerically reproduced to clarify the mechanism of attitude instability. The target configuration is a thin-aeroshell capsule designed for deep-space sample return missions.

Reference URL

N/A

Reasons and benefits of using JAXA Supercomputer System

Regarding attitude instability, it is well known that the wake formed behind the capsule significantly influences attitude behavior. Moreover, the growth characteristics of the oscillation strongly depend on the numerical resolution of this wake region. Therefore, to properly capture the instability phenomena, high-order spatial accuracy and fine grid resolution in the wake region are required. Consequently, large-scale three-dimensional unsteady simulations become indispensable. To accommodate these computationally demanding conditions, a supercomputer was utilized in this study.

Achievements of the Year

To reproduce the wind tunnel experimental results under a Mach 1.3 flow condition, coupled simulations of single-degree-of-freedom free oscillation and the flow field were conducted under identical conditions. As shown in Fig. 1, the numerical analysis successfully reproduced the growth history of the oscillation observed in the wind tunnel experiments. As an example, the Mach number distribution is presented in Fig. 2. Under supersonic conditions, a shock wave is formed in front of the capsule, while the flow separated from the shoulder expands. In addition, a recirculation region is formed behind the capsule. On the forebody, a phase lead in pressure induced by the motion was observed, contributing to attitude stabilization. In contrast, in the wake region, a phase delay associated with the convection delay of the recirculating vortex was formed. These wake structures contribute to attitude destabilization, and it is suggested that the growth of the oscillation arises from the balance between the stabilizing effect on the forebody and the destabilizing effect in the wake.

Fig.1: Time history of the angle-of-attack oscillation. The red line indicates the numerical result, and the black circles represent the amplitude history obtained from the experiment.

Fig.2: Time-averaged density distribution over 0.4 ms around an angle of attack of 0 degrees.

Publications

- Oral Presentations

Takasawa Hideto, et.al., Effect of the flow field on the instability threshold during transonic one-degree-of-freedom oscillation, Symposium on Flight Mechanics and Astrodynamics, ISAS2025-SFMA-051, 2025.

Takasawa Hideto, et.al., Effect of Oscillation Frequency on the Transient Attitude Motion of a Thin Aeroshell Capsule under One-Degree-of-Freedom Oscillation, 69th Space Sciences and Technology Conference, 3I14, 2025.

Usage of JSS

Computational Information

Process Parallelization Methods: MPI
Thread Parallelization Methods: OpenMP
Number of Processes: 1 - 784
Elapsed Time per Case: 240 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.

Computational Resources
System Name	CPU Resources Used (Core x Hours)	Fraction of Usage*2(%)
TOKI-SORA	14658917.61	0.66
TOKI-ST	950405.60	0.98
TOKI-GP	0.00	0.00
TOKI-XM	0.00	0.00
TOKI-LM	7.75	0.00
TOKI-TST	0.00	0.00
TOKI-TGP	0.00	0.00
TOKI-TLM	0.00	0.00

File System Resources
File System Name	Storage Assigned (GiB)	Fraction of Usage*2(%)
/home	0.00	0.00
/data and /data2	0.00	0.00
/ssd	0.00	0.00

Archiver Resources
Archiver Name	Storage Used (TiB)	Fraction of Usage*2(%)
J-SPACE	0.00	0.00

*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

ISV Software Licenses Resources
	ISV Software Licenses Used (Hours)	Fraction of Usage*2(%)
ISV Software Licenses (Total)	384.13	0.27

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