基于非定常气动力降阶的AGARD445.6硬机翼不同迎角颤振研究

以AGARD445.6硬机翼为研究对象，发展了基于计算流体力学与模态叠加的并行流固耦合方法，计算该机翼在不同初始迎角、不同来流速度的气动弹性时域响应，结果表明:初始迎角小于7°时，该机翼颤振速度随着初始迎角增加而降低；初始迎角7°~10°，颤振速度随着迎角增大而增加。在10°迎角条件建立了基于径向基神经网络的非定常气动降阶模型，准确预测不同速度、减缩频率的非定常气动力，并使用时域龙格库塔法和频域VG法预测10°迎角的颤振特性；建立考虑初始迎角输入的非定常气动降阶模型，预测机翼不同初始迎角的颤振特性。基于降阶模型的初始迎角对颤振边界影响的机理分析表明:小迎角时，随着迎角的增加广义力系数幅值比增加，导致颤振速度的下降；迎角大于7°后展向涡改变了机翼表面压强分布，导致一扭广义力系数幅值比降低，从而增加该机翼颤振速度。

RESEARCH ON THE FLUTTER CHARACTERISTCIS OF AGARD445.6 SOLID WING CONSIDERING THE INITIAL ANGLE OF ATTACK BASED ON REDUCED ORDER MODEL

The AGARD445.6 solid wing is considered as the object of this study. The fluid-structure interaction method based on CFD and modal superposition is developed, and the aeroelastic responses at various angles of attack and velocities are calculated. Results indicate that with the increase of initial angle of attack, the flutter velocity decreases when the angle of attack is under 7°, and the flutter velocity increases when the angle of attack is between 7° and 10°. Then, at 10° angle of attack, the unsteady aerodynamic reduced order model based on radial basis function neural network is developed to predict the unsteady aerodynamic forces at different velocities and reduced frequencies. The flutter characteristics at 10° angle of attack are predicted using the time domain Runge-Kutta method and the frequency domain VG method. Then the unsteady aerodynamic reduced order model considering the input of initial angle is established to predict the flutter characteristics at different angles of attack. The analysis on the effect of initial angle on the flutter boundary shows that, at small angle, the increase of the generalized force coefficient amplitude ratio with the increase of the angle leads to the decrease of flutter velocity. When the initial angle is greater than 7°, the flow separation region expands, which changes the pressure distribution on the wing surface, leading to the decrease of the generalized force coefficient amplitude ratio of torsional mode, and hence results in the increase of flutter velocity.