CFD simulation of a rotor blade for high advance ratio flight

JAXA Supercomputer System Annual Report February 2025-January 2026

Report Number: R25EDA102C20

Subject Category: Aeronautical Technology

Responsible Representative: Kanako Yasue, Aviation Technology Directorate, team leader, Aircraft Integration Innovation Hub, Airmobility Design Team
Contact Information: Keita Kimura(kimura.keita@jaxa.jp)
Members: Fumihiro Kajiwara, Keita Kimura, Yasutada Tanabe

Abstract

In JAXA, research and technology demonstrations are being conducted on next-generation rotorcraft concepts, including winged compound helicopters capable of achieving approximately twice the flight speed of conventional helicopters. In this context, efforts are focused on accumulating and validating rotor blade design and operational technologies that are compatible with high-speed flight conditions.

The advance ratio, defined as the ratio of forward flight speed to rotor tip speed, is used to characterize flight conditions. High advance ratio conditions, in which the forward speed is large relative to the rotational speed, are referred to as high-mu conditions.

In this report, in addition to previous blade designs for high-mu rotors, analyses are conducted on lift offset conditions, which are considered effective for improving aerodynamic performance under high-mu conditions. Furthermore, changes in blade pitching moment associated with these conditions are investigated. The related results are presented in this report.

Reference URL

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Reasons and benefits of using JAXA Supercomputer System

For analyzing the performance of helicopter blades, it is necessary to use a high-fidelity tool (CFD) that can correctly represent complex flow fields, such as interference with the tip vortex. In order to perform analyses of a large number of cases while maintaining a high resolution, it is desirable to use a supercomputer.

Achievements of the Year

In this fiscal year, forward-flight analyses were conducted for a JAXA-designed compound helicopter model to investigate the application of lift offset technology. Lift offset is a concept aimed at improving rotor performance by effectively utilizing the high dynamic pressure on the advancing side of the rotor as lift. As the center of lift shifts toward the advancing side relative to the rotor hub, this configuration is referred to as "lift offset".

Figure 1 illustrates a conceptual diagram of a winged compound helicopter under lift offset conditions. In this concept, the rolling moment generated by the forward shift of the lift center is compensated by actuation of the main wing flaps. CFD analysis confirms that this configuration improves the effective lift-to-drag ratio of the rotor.

In addition, as a secondary effect of lift offset application, a reduction in the pitching moment acting on the rotor blade is suggested. Figure 2 shows the distribution of pitching moment over the rotor disk, while Figure 3 presents the radial distribution of the mean pitching moment.

Under high advance ratio conditions, a significant difference in dynamic pressure exists between the advancing and retreating sides. As a result, particularly large pitch angles are required on the retreating side, leading to increased pitching moments near the blade root. With the application of lift offset, the required control input is reduced, which in turn decreases the pitching moment acting on the blade.

Fig.1: Overview of Lift Offset Technology

Fig.2: Pitching Moment Distribution over the Rotor Disk (CmM²)

Fig.3: Radial Distribution of Pitching Moment (Lift Offset: LO)

Publications

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Usage of JSS

Computational Information

Process Parallelization Methods: N/A
Thread Parallelization Methods: OpenMP
Number of Processes: 1
Elapsed Time per Case: 72 Hour(s)

JSS3 Resources Used

Fraction of Usage in Total Resources*1(%): 0.30

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	1334907.04	0.06
TOKI-ST	1689742.91	1.75
TOKI-GP	0.00	0.00
TOKI-XM	0.00	0.00
TOKI-LM	0.00	0.00
TOKI-TST	564637.37	9.23
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)	65.62	0.05

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