Nonlinear systems for frequency conversion from IR to RF

Brian D. Dolasinski


The utilization of fuel as a heat sink can allow the design of higher performance aircraft that may normally be limited by heat loads. An energy model for the cross section of a wing with an internal fuel tank in flight is developed for determining its potential use as a heat sink in the conceptual design phase. The computations are aimed at being based more on physical dependencies than empirical correlations. The conservation of energy equation is solved separately using prior calculated information from the conservation of mass and momentum equations. The energy analysis is conducted using a series of control volumes around the airfoil surface with an integral method which can utilize various temperature profiles to model the thermal boundary layer. An unheated starting length followed by an isothermal surface approximates the heated fuel tank as a surface boundary condition. The performance of explicit and implicit methods for solving the resulting set of energy equations is compared with the implicit method proving to function more desirably. The implemented method is verified through analyzing the effects of refining the discretization along the surface as well as normal to it. Also, a flat plate analysis is compared to NACA 0001 airfoil results to demonstrate that XFOIL is coupled correctly with the program to enable computing flow information over arbitrary airfoils. Results of the developed method are compared to empirical correlations for validation purposes involving turbulent flow test cases over NACA 0001, NACA 0007, and NACA 0015 airfoils. The calculations are first conducted for a completely isothermal surface and then for an unheated starting length to isothermal surface. Four temperature profiles are initially considered, but are narrowed down to two profiles for the majority of the results. When modeling a fuel tank as a heat source using an unheated starting length to isothermal surface boundary condition, the results show reasonable agreement with empirical correlations and thus the proposed method could be used for conceptual design purposes.