一种飞机垂尾抖振载荷识别的新方法

A New Approach to Identify Buffet Loads for Aircraft Vertical Tail

针对抖振载荷难以直接测量的问题,提出了一种由抖振加速度响应逐点识别翼面分布抖振载荷的频域方法。根据抖振载荷空间和时间的分布特性,将抖振载荷表示成一组空间正交函数与一组时间函数的线性组合,从而把频域内的抖振载荷识别问题转化为时间函数的识别问题。通过垂尾结构的气动弹性运动方程推导出加速度响应功率谱密度与广义力功率谱密度之间的关系式,再由谱分解理论得出广义力功率密度与抖振载荷功率谱密度的关系式,最后根据空间分布函数的正交性逐点识别出时间函数。为了解决上述逐点识别过程中遇到的不适定问题,提出了一种新的正则化处理方法,并用牛顿迭代法选取最佳正则化因子。对一个垂尾模型,先用计算流体力学(CFD)仿真软件计算出垂尾模型上的抖振载荷,然后将这些抖振载荷施加在垂尾结构上,并计算出垂尾结构的抖振加速度响应,利用计算出的加速度响应识别出抖振载荷,并与计算的抖振载荷进行比较,从而验证了本文所提出的抖振载荷逐点识别方法具有很好的识别精度。

It is difficult to perform direct measurement of the buffet loads acting on the vertical tail of an aircraft. This paper presents a novel frequency domain approach to identify buffet loads point by point from the measured acceleration respon- ses. Based on the statistical property of the buffet loads in the time domain and spatial domain, the buffet loads are ex- pressed as a linear combination of orthogonal functions in the spatial domain and random functions in the time domain. The spatial function is composed of a set of orthogonal functions, and the identification of buffet loads in the frequency domain is transformed into the estimation of the time function. First, the relationship between the acceleration spectral density and the generalized exciting force spectral density is obtained from the aeroelastic motion equation of the vertical tail; then, the rela- tionship of the exciting force spectral density and buffet loads spectral density is obtained in terms of spectral decomposition. The time function can be identified utilizing the orthogonality of the spatial functions point by point. In order to address ill-pos- edness, a new regularization process is introduced to guarantee the stability of identification, and the optimal regularization factor is selected by Newton＇s iteration. A vertical tail model is adopted to verify the feasibility and precision of the pro- posed method. A set of buffet loads are simulated by a computational fluid dynamics （CFD） code, and these buffet loads are exerted on the vertical tail to calculate the corresponding buffeting acceleration responses which are used to identify the buf- fet loads using the proposed method. Good agreements between the calculated buffet loads and estimated buffet loads vali- date the present method.