吸气式高超声速飞行器多学科动力学建模

Multidisciplinary dynamics modeling and analysis of a generic hypersonic vehicle

高超声速飞行器一体化设计中存在气动/热/推进/结构弹性相互耦合的问题,首先根据飞行器的机体/发动机一体化设计思想构造了二维高超声速飞行器模型,并基于激波/膨胀波原理和动量定理建立了气动力模型,采用Chavez和Schmidt建立的超燃冲压发动机推进系统模型;在飞行器结构方面,引入变截面和变质量分布的自由梁结构模型,并采用Eckert参考焓方法分析的气动加热过程中承力梁不同轴向位置温度随时间变化特征,在此基础上运用模态法计算了燃料消耗和气动加热条件下结构的固有频率和振型特征,获得结构弹性变形的模型;最后建立了考虑热气动弹性和推进系统作用的飞行动力学方程。研究结果表明:质量变化对结构弹性特性影响比较显著,而气动加热的影响主要表现在振动频率方面,且会随着加热过程的持续而逐渐增强;结构变形会改变飞行器静配平状态,特别是在机体质量较大的最初飞行阶段,气动加热会强化结构变形对配平特征的影响;线性化系统的动力学特征分析表明,质量减小和结构变形均会增加短周期模态和振荡模态的不稳定特性,而对高度特性的影响不大,气动加热效应会进一步增加飞行力学和气动弹性的耦合特征,并导致弹性模态的稳定性降低。

Fluid-thermal-propulsive-structural coupling exists during the design of generic hypersonic vehicles. A two-dimensional air-breathing generic hypersonic flight vehicle model has been developed according to the design concept of hypersonic vehicle＇s integrated airframe/scramjet configuration, and aerodynamic model is derived from oblique-shock/PrandtI-Meyer theory and momentum theorem. A free beam model of variant cross-section and mass distribution is introduced as the structure of the vehicle, and the approach of Eckert＇s reference enthalpy is used to obtain temperature distribution as a function of time along the axial direction of the beam, above which the assumed modes method is used to obtain the natural frequencies and mode shapes of the structure during the consumption of fuel and aerodynamic heating. Flight dynamics equations coupled with aerothermoelasticity are finally presented. The results indicate that the structural characteristic is dominated by the mass variation over the aerodynamic heating, the effect of which is enhanced as the aerodynamic heating progresses. Results also indicate that trimmed states are changed by the effect of the flexible deflection especially at the beginning of flight process, and the aerodynamic heating enhances the effect of flexible deflection. The dynamic eigenvalues of linearized system show that both structural deflection and mass decrease adversely increase the instability of the short period and ph- ugoid modes, while the altitude mode is slightly affected. Moreover, aerodynamic heating enhances the coupling between flight dynamics and aeroelasticity and decreases the stability of flexible modes.