Active stability augmentation system is an attractive and promising technology to suppress flutter and limit cycle oscillation(LCO).In order to design a good active control law,the control plant model with low order and high accuracy must be provided,which is one of the most important key points.The traditional model is based on low fidelity aerodynamics model such as panel method,which is unsuitable for transonic flight regime.The physics-based high fidelity tools,reduced order model(ROM) and CFD/CSD coupled aeroservoelastic solver are used to design the active control law.The Volterra/ROM is applied to constructing the low order state space model for the nonlinear unsteady aerodynamics and static output feedback method is used to active control law design.The detail of the new method is demonstrated by the Goland+ wing/store system.The simulation results show that the effectiveness of the designed active augmentation system,which can suppress the flutter and LCO successfully.
As the amplitude of the unsteady flow oscillation is large or large changes occur in the mean background flow such as limit cycle oscillation,the traditional proper orthogonal decomposition reduced order model based on linearized time or frequency domain small disturbance solvers can not capture the main nonlinear features.A new nonlinear reduced order model based on the dynamically nonlinear flow equation was investigated.The nonlinear second order snapshot equation in the time domain for proper orthogonal decomposition basis construction was obtained from the Taylor series expansion of the flow solver.The NLR 7301 airfoil configuration and Goland+ wing/store aeroelastic model were used to validate the capability and efficiency of the new nonlinear reduced order model.The simulation results indicate that the proposed new reduced order model can capture the limit cycle oscillation of aeroelastic system very well,while the traditional proper orthogonal decomposition reduced order model will lose effectiveness.
Traditional coupled multi-disciplinary design optimization based on computational fluid dynamics/computational structure dynamics(CFD/CSD)aims to optimize the jig shape of aircraft,and general multi-disciplinary design optimization methodology is adopted.No special consideration is given to the aircraft itself during the optimization.The main drawback of these methodologies is the huge expanse and the low efficiency.To solve this problem,we put forward to optimize the cruise shape directly based on the fact that the cruise shape can be transformed into jig shape,and a methodology named reverse iteration of structural model(RISM)is proposed to get the aero-structural performance of cruise shape.The main advantage of RISM is that the efficiency can be improved by at least four times compared with loosely-coupled aeroelastic analysis and it maintains almost the same fidelity of loosely-coupled aeroelastic analysis.An optimization framework based on RISM is proposed.The aerodynamic and structural performances can be optimized simultaneously in this framework,so it may lead to the true optimal solution.The aerodynamic performance was predicted by N-S solver in this paper.Test shows that RISM predicts the aerodynamic and structural performances very well.A wing-body configuration was optimized by the proposed optimization framework.The drag and weight of the aircraft are decreased after optimization,which shows the effectiveness of the proposed framework.
ZUO Ying TaoGAO Zheng HongCHEN GangWANG Xiao PengLI Yue Ming
Gust alleviation is very important to a large flexible aircraft.A nonlinear low-order aerodynamic state space model is required to model the nonlinear aeroelastic responses due to gust.Based on the proper orthogonal decomposition method,a reduced order modeling of gust loads was proposed.And then the open-loop and closed-loop reduced order state space model for the transonic aeroelastic system was developed.The static output feed back control scheme was used to design a simple multiple-in multiple-out(MIMO)gust alleviation control law.The control law was demonstrated with the Goland+wing model with four control surfaces.The simulation results of different discrete gusts show the capability and good performance of the designed MIMO controller in transonic gust alleviation.
