This dissertation describes coupled fluid-thermal-structural modeling and analysis of a semi-infinite insulated metallic panel and a blade-stiffened carbon-carbon skin panel for aerothermoelasticity and forced response prediction in hypersonic flow.
The United States Air Force' goals of affordable, reusable platforms capable of sustained hypersonic flight and responsive access to space depend on the ability to predict the response, the degradation, and ultimately the life of structures under combined, extreme aerodynamic heating and fluctuating pressure loads. However, the necessary modeling and prediction capabilities are severely limited in current commercial software due to the inability to seamlessly address multi-coupled, multi-scale fluid-thermal-structural interactions. Moreover, because of the complexity and expense of coupled computational methods, the capability is needed to define the necessary level of coupling a priori.
The aim of this dissertation is to develop coupled fluid-thermal-structural analysis methodology for response prediction in combined, extreme environments. Furthermore, it seeks to identify key characteristics (e.g., trajectories, operating conditions, and structural configurations) that determine the level of coupling needed for different situations. An additional focus is the targeted use of simplified temporal coupling strategies for reducing the computational expense of hypersonic aerothermoelasticity and forced response prediction over long durations.
First, in order to efficiently study the effects of fluid-thermal-structural coupling, an approximate hypersonic aerodynamics model is developed. The approximate model is verified and validated by comparison to aerodynamic pressure and heating data from hypersonic wind tunnel experiments and computational fluid dynamics solutions of the Navier-Stokes equations. Next, thermal and structural models of the panels are developed. The insulated metallic panel is modeled using the two-dimensional heat equation with a finite difference solution and von Karman plate theory with an assumed modes solution. Thermal and structural models of the carbon-carbon skin panel are developed using commercial finite element software.
Partitioned fluid-thermal-structural solution strategies are developed and used to systematically study the impact of multiple physical coupling mechanisms and simplified temporal coupling procedures. The aerothermoelastic behavior of the insulated metallic panel is found to be dependent on mutual coupling of aerodynamic heating and structural deformation. Additionally, it is determined that simplified temporal coupling procedures offer substantial reductions in computational expense, with negligible loss of accuracy, for aerothermoelastic analysis over long-duration hypersonic trajectories.
Quasi-static and transient dynamic structural responses of the carbon-carbon skin panel are investigated. It is found that the level of coupling needed for quasi-static response prediction depends largely on the in-plane structural boundary conditions, since greater resistance to thermal expansion results in larger deformations. Including these deformations in the aerodynamic heating analysis results in: nonuniform skin temperatures, asymmetric deformation, and elevated stresses. Predictions of panel failure and mode (static stress or snap-through) are found to be dependent on: trajectory, degree of coupling, and stiffness of in-plane boundary conditions. Additionally, it is determined that dynamic response predictions are sensitive to: mutual coupling of aerodynamic heating and structural deformation and temporal coupling of thermal and structural solutions. The degree of coupling needed for accurate dynamic response prediction increases with increasing fluctuating pressure levels and aerodynamic heating rates.