Scholar - SciOpen

Objective

When an aircraft encounters external disturbances such as gusts or turbulence during flight, the lift structures of the aircraft, such as the wings, will be subjected to additional unsteady aerodynamic loads, resulting in sustained oscillations for a certain period of time. Gust response alleviation is mainly achieved by taking certain measures to reduce the amplitude of gust response or decrease the oscillation time, in order to reduce the vibration level and improve the stability and robustness of the aeroelastic system. The passive control technology for gust response alleviation is mainly achieved through some clever structural/mechanical designs, so it can be achieved without feedback from sensors, making it simpler, more reliable, and easier to implement. The vibro-impact absorber technology is mainly based on traditional linear absorbers. By setting certain displacement constraints within the range of the oscillator's motion, vibration energy is absorbed through the collision between the oscillator and the constraints, achieving the purpose of vibration reduction. Due to its short duration and high energy consumption, collision vibration can absorb vibration energy in a short period of time, which has a good effect on vibration control. In this paper, introducing vibro-impact absorbers into the aeroelastic system of high-speed wings aims to investigate the mitigation of wing gust response by vibro-impact absorbers. The goal is to reduce the amplitude of aeroelastic gust response, lower the vibration level, and improve the stability of the aeroelastic system.

Methods

A two degrees-of-freedom wing is selected to establish an aeroelastic gust response dynamic model of the wing with a vibro-impact absorber. The Hertz contact model is used to calculate the collision contact force between the oscillator and the wing skin, and the piston theory is used to calculate the unsteady aerodynamic force. The unsteady aerodynamic force generated by the gust can be calculated in the form of an equivalent angle of attack through the piston theory, and the gust velocity is calculated using the "1-cos" model. Finally, the Runge-Kutta method is used to solve the gust response dynamic model.

Results

(1) A comparative analysis was conducted on the influence of the presence or absence of vibro-impact absorbers on the aeroelastic gust response of the wing. The results indicate that the vibro-impact absorber can absorb and transfer the energy of the wing gust response by colliding with the wing skin, thereby achieving the effect of gust alleviation. The maximum decrease in vibration amplitude of the aeroelastic response compared to the uncontrolled system can reach 72.6%, the maximum decrease in vibration velocity amplitude can reach 18.7%, and the maximum decrease in root mean square acceleration value can reach 19.5%. (2) The variation of the gust response root mean square acceleration of the wing aeroelastic system with the natural frequency ratio of the vibro-impact absorber is analyzed. The results show that the root mean square value of acceleration decreases first and then increases with the natural frequency. At ω_p=0.2, the root mean square value of acceleration in the heave direction is 3.36E-8. When ω_p=3.4, it reaches the minimum of 3.11E-8. When ω_p=6, the root mean square value of acceleration increases to 3.21E-8. (3) The influence of collision absorber stiffness on aeroelastic gust alleviation was analyzed, and the results showed that as the collision stiffness increased, the root mean square value of gust response gradually increased. When the collision stiffness is 4E4, the root mean square value of acceleration in the plunge direction is 3.2E-8. When the collision stiffness increases to 3.6E7, the root mean square value of acceleration in the heave direction is 3.7E-8, an increase of 15.6%. (4) The influence of the initial gap between the vibro-impact absorber and the skin on gust alleviation is analyzed. When the gap is less than 6.4E-4, the root mean square acceleration of the gust response of the aeroelastic system increases with the increase of the initial gap. When the initial gap is greater than 6.4E-4, the root mean square value of acceleration in gust response will remain unchanged. At this time, the impact absorber will not collide with the wing skin and will degrade into a linear system composed of linear stiffness and damping. (5) The influence of the relative distance between the installation position of the vibro-impact absorber and the elastic axis on the gust reduction of the wing aeroelastic system is analyzed. The results indicate that as the distance d between the installation position and the elastic axis changes, the root mean square value of gust response acceleration shows a trend of first increasing and then decreasing. When d=-0.7, the root mean square value of the buoyancy direction is 3.16E-8. At d=-0.3, the root mean square value of acceleration reaches its maximum, and the direction of buoyancy is 4.52E-8. At d=0.5, the heave direction is 3.77E-8 and the pitch direction is 7.31E-8. Overall, when the collision absorber is closer to the leading edge of the wing, its response acceleration root mean square value is smaller, and the reduction effect of gust response is better.

Conclusions

In this paper, the vibro-impact absorber is applied to the gust response alleviation of high-speed wing aeroelastic systems, and the alleviation effect and influence law of vibro-impact absorber parameters on gust response are studied. (1) Under specific parameters, the impact absorber has a good alleviation effect on the aeroelastic gust response of the wing. Analysis from multiple aspects such as gust response displacement, response speed, and response acceleration shows that the vibro-impact absorber can absorb and transfer the energy of the wing gust response through the impact vibration with the wing skin, thereby achieving the effect of gust alleviation. (2) The parameters of the vibro-impact absorber have a significant impact on the alleviation effect of aeroelastic gust response. Reducing the impact stiffness and initial clearance can both enhance the gust response mitigation effect of the aeroelastic system. The natural frequency ratio of the vibro-impact absorber needs to be optimized and selected, and there exists an optimal frequency ratio that enables the system to have a good gust response alleviation effect. For the installation position of the impact absorber, the gust reduction effect is more significant when it is closer to the leading edge of the wing.

The subcritical problem of wing flutter system with freeplay nonlinearity was addressed by introducing the NES (nonlinear energy sink) technology to improve the critical velocity of the system′s limit cycle oscillation. A dynamic model of flutter system with NES control for wings with freeplay nonlinearity was established, and the suppression effects of NES parameters such as mass ratio, frequency ratio, damping ratio, and relative position on the limit cycle oscillation of the flutter system were analyzed. The influence of NES parameters on the critical speed of the limit cycle oscillation of the flutter system was also investigated. The results show that a larger damping ratio can stabilize the system at a smaller natural frequency ratio but required a more stringent location requirement for the NES, i.e., closer to the leading edge of the wing. On the other hand, a smaller damping ratio results in a smaller NES mass required to stabilize the limit cycle response of the flutter system. When the NES location is closer to the leading edge of the wing, increasing the natural frequency ratio significantly improve the suppression effect of limit cycle oscillation, and increasing the mass ratio also significantly improve the suppression effect and critical speed of limit cycle oscillation. Additionally, a smaller damping ratio of the NES results in better suppression of limit cycle oscillation in the flutter system.