A deep study of TEF/NTBT rotor based on CFD/CSD method

Modern helicopters often employ advanced rotor blade platforms such as swept blade, dihedral/anhedral blade-tip, and nonlinear twist to achieve preferable aerodynamic performance, but meanwhile the complex-shaped blades not only cause significant challenges in structural manufacturing but also tend to generate higher vibratory loads of the rotor disc. These vibratory loads are further transmitted to the fuselage through the rotor hub system, affecting the vibration level and fatigue life of the helicopter directly. Therefore, the vibration reduction designs for the NTBT rotor become one of the frontier technologies in rotor design area. As one of the smart rotor families, the TEF technology has been widely applied in rotor vibration suppression due to its strong compatibility and fast response.

Although the aeroelastic coupling method has been extensively adopted in academia for independent studies on both TEF technology and NTBT rotor, there remains a great gap in deep research on rotors that integrate both TEF and NTBT features. The CFD/CSD method is capable of integrating the impacts of unconventional blade platforms, unsteady flowfields, and structural time-dependent properties, making it particularly suitable for conducting aeroelastic studies on the NTBT rotor with TEF technology. Based on that, conducting research on TEF/NTBT rotor based on the CFD/CSD method holds significant theoretical value and engineering importance.

Recently, the team led by Professor Qijun Zhao from the National Key Laboratory of Helicopter Aeromechanics at Nanjing University of Aeronautics and Astronautics, in collaboration with the 60th Research Institute of China RongTong Asset Management Group Corporation Limited, has analyzed the aeroelastic coupling characteristics of TEF/NTBT rotor in forward flight using CFD/CSD method. The study has revealed the aeroelastic mechanisms of TEF rotor and the potential for vibration reduction. Further, a functional control strategy of TEF to suppress the hub vibration intensity of the rotor is proposed.

The team published their work in Chinese Journal of Aeronautics on July 18, 2025.

“In this study, the frequency, phase, and amplitude-sweeping parametric analyses of TEF are conducted thoroughly to reveal the influence mechanisms on the aeroelastic characteristics of NTBT rotor.” said Xiayang Zhang, associate professor at Nanjing University of Aeronautics and Astronautics, a senior expert whose research interests focus on the field of rotor fluid-structure interaction. “In the aerodynamic aspect, the variations of C_Ts and C_Qs (thrust and moment coefficient of a single blade) increase with the growth of δ_m (amplitude of the TEF); the oscillations of C_Ts and C_Qs become severe with the increment of k (frequency of the TEF), resulting in the rise of peak C_Qs and the decrease of rotor aerodynamic performance. In the structural aspect, higher δ_m will increase certain vibratory hub loads and Q_h (vibration intensity); k cannot reduce the vibratory hub loads entirely, in which certain load components even exceed the reference state.”

“At higher advance ratio μ, the TEF control leads to a reduction in the normal force coefficient C_n of the retreating blade root. Upon discovering a novel phenomenon, researchers must investigate and reveal its mechanisms.” emphasized Dr. Hualong Wang.

“At certain flight speed, the TEF-derived vortices from the front blade may impinge the root of the rear blade at the retreating side. It induces the opposite spanwise flows on the upper and lower surfaces of the rear blade and subsequently generates the opposite Coriolis forces. The opposite Coriolis forces ultimately affect the chordwise airflow and decrease C_n at blade root in the retreating side.” said Prof. Qijun Zhao.

An optimal TEF control method based on different TEF actuation frequencies is developed for vibration reduction. “By this method, Q_h can be further reduced by 45.72% and 52.26% relative to the single TEF control. Meanwhile, it is also demonstrated that the TEF control cannot ensure that all the vibratory hub loads can be suppressed.” said Dr. Xiayang Zhang.

To address this issue, the further vibratory control method could be improved by applying multiple TEFs. All six components of the vibratory hub load could be suppressed simultaneously with lower control angle deflections and power requirements of TEFs.

Other contributors include Li MA, Wei BIAN from the National Key Laboratory of Helicopter Aeromechanics at Nanjing University of Aeronautics and Astronautics in Nanjing, China; Shiming LIU, Yuan GONG from the 60th Research Institute of China RongTong Asset Management Group Corporation Limited in Nanjing, China.

Original Source

Hualong WANG, Xiayang ZHANG, Qijun ZHAO, Li MA, Wei BIAN, Shiming LIU, Yuan GONG. Aeroelastic characteristics and vibration reduction method of NTBT rotor with TEF technology[J]. Chinese Journal of Aeronautics, 2025, https://doi.org/10.1016/j.cja.2025.103690.

About Chinese Journal of Aeronautics 

Chinese Journal of Aeronautics (CJA) is an open access, peer-reviewed international journal covering all aspects of aerospace engineering, monthly published by Elsevier. The Journal reports the scientific and technological achievements and frontiers in aeronautic engineering and astronautic engineering, in both theory and practice. CJA is indexed in SCI (IF = 5.7, Q1), EI, IAA, AJ, CSA, Scopus.