This paper introduces a general computational model for electronic packages, e.g., cabinets that contain electronic equipment. A simplified physical model, which combines principles of classical thermodynamics and heat transfer, is developed and the resulting three-dimensional differential equations are discretized in space using a three-dimensional cell centered finite volume scheme. Therefore, the combination of the proposed simplified physical model with the adopted finite volume scheme for the numerical discretization of the differential equations is called a volume element model (VEM). A typical cabinet was built in the laboratory, and two different experimental conditions were tested, measuring the temperatures at forty-six internal points. The proposed model was utilized to simulate numerically the behavior of the cabinet operating under the same experimental conditions. Mesh refinements were conducted to ensure the convergence of the numerical results. The converged mesh was relatively coarse (504 cells), therefore the solutions were obtained with low computational time. The model temperature results were directly compared to the steady-state experimental measurements of the forty-six internal points, with good quantitative and qualitative agreement. Since accuracy and low computational time are combined, the model is shown to be efficient and could be used as a tool for simulation, design, and optimization of electronic packages.

A review of the status of reduced order modeling of unsteady aerodynamic systems is presented. Reduced order modeling is a conceptually novel and computationally efficient technique for computing unsteady flow about isolated airfoils, wings, and turbomachinery cascades. For example, starting with either a time domain or frequency domain computational fluid dynamics (CFD) analysis of unsteady aerodynamic flows, a large, sparse eigenvalue problem is solved using the Lanczos algorithm. Then, using just a few of the resulting eigenmodes, a Reduced Order Model of the unsteady flow is constructed. With this model, one can rapidly and accurately predict the unsteady aerodynamic response of the system over a wide range of reduced frequencies. Moreover, the eigenmode information provides important insights into the physics of unsteady flows. Finally, the method is particularly well suited for use in the aeroelastic analysis of active control for flutter or gust response. As an alternative to the use of eigenmodes, Proper Orthogonal Decomposition (POD) is also explored and discussed. In general POD is an attractive alternative and/or complement to the use of eigenmodes in terms of computational cost and convenience. Balanced modes, a concept widely used in control engineering, are also briefly discussed, as are input/output models. Numerical results presented include a discussion of the effects of discretization and a finite computational domain in the CFD model on the eigenvalue distribution, the effects of the Mach number and viscosity on reduced order models and representative results from linear and nonlinear aeroelastic analysis. Recent results for transonic flows with shock waves including viscous and nonlinear effects are emphasized.

The present paper demonstrates the aerodynamic feasibility of boundary-layer ingesting embedded-engine inlet designs with low total pressure losses and distortion harmonic content. The inlet was designed using a hierarchical multi-objective computational fluid dynamics optimization that combined global and local shaping. Global parameters including duct offset and length, wall curvature and shape, inlet aspect ratio, lip contour and thickness, and upstream airframe contour were used to identify optimal design space regions. Local inlet shaping optimization further reduced total pressure losses and harmonic distortion upstream of the fan. Coupled inlet/fan design iterations were carried out for selected inlet designs to assess the fan/engine stability and operability benefits. The resulting inlet design has the potential of achieving a 3-5% boundary-layer ingesting fuel burn benefit for NASA's Generation-After-Next aircraft relative to a baseline high-performance pylon-mounted propulsion system. It shows significantly improved performance when compared with NASA's "inlet A" reference geometry with a length-to-diameter ratio of 3. The new inlet was shortened to a length-to-diameter ratio of 0.6, total pressure losses were reduced by three times, dominant distortion harmonic amplitudes were reduced by 30-50%, and fan efficiency losses were reduced from 6 to 0.5-1.5%. No flow control was required.

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