An Interactive Preliminary Design System of High Speed Forebody and Inlet Flows

This paper demonstrates a simulation-based aerodynamic design process of high speed inlet. A genetic algorithm is integrated into the design process to facilitate the single objective optimization. The objective function is the total pressure recovery and is obtained by using a PNS solver for its computing efficiency. The system developed uses existing software of geometry definition, mesh generation and CFD analysis. The process which produces increasingly desirable design in each genetic evolution over many generations is automatically carried out. A generic two-dimensional inlet is created as a showcase to demonstrate the capabilities of this tool. A parameterized study of geometric shape and size of the showcase is also presented. I. Introduction The art of high speed inlet design is a trade-off among various factors, including weight, aerodynamic performance and pressure recovery. The primary consideration of the efficiency of an inlet is the total pressure recovery which represents the available work that can be extracted from the captured mass flow. Losses of total pressure are due to the oblique shock system in the supersonic section of the inlet, the viscous boundary layer, the terminal normal shock and shock-boundary layer interaction. The pay-off of a high recovery inlet is substantial. Most gas turbine engines require the Mach number at the engine face at a moderate subsonic speed, typically around Mach 0.4. A preferable high static pressure at the compressor face has compromised the high recovery objective. In Hypersonic flight regime, although ramjet or scramjet depending on high speeds to compress the air without the help from compressor machinery, either has to combine with turbojet to make the flight across the range of speeds possible. High speed inlet design has become a problem involving multiple parameters and multiple objectives, not to mention the multiple disciplines involved. The data of total pressure recovery at engine face has a determining effect on engine thrust and aerodynamic evaluation of a whole aircraft. Therefore, a design tool is needed. Due to the complexity of shock waves and boundary layers interaction, the use of the traditional techniques, like the method of characteristic or streamline tracing, becomes inadequate for preliminary design stage. Computational Fluid dynamics (CFD) has allowed engineers to test new designs quickly before carrying out experiments. Integrating CFD and other computer-aided simulation programs, a system has been developed for the preliminary design of high speed inlets and forebodies. A graphical user interfaces written in Matlab© is provided to designer for an interactive design environment. Continuing the development 1 , two new elements are added to the system. First, a geometry controller, Capri, is included. CAPRI provides a simple control and easy access to the CAD models for simulation driven design. Because the inlet must provide optimum performance over a wide range of speed, a large matrix of geometric and flow variables are mandated to obtain an optimum configuration. Those can be very time consuming and computationally intensive. Working as a checking mechanism, secondly, an optimizer is included to aid engineers in making multiple objectives selections and compromises, for instance those of the compression methods, number of oblique shocks or ramps and the cross section shape of supersonic section. As a result, not only is high –speed calculation required, but also the automation in finding optimum solution is desired. The automation of the system has been implemented and is driven by an optimizer. The resulting Inlet Preliminary and Optimizing Design System (IPODS) comprises six functions: geometry definition, geometry controller, flow grid generation, a Parabolized Navier-Stokes (PNS) flow solver, graphics post-processor and optimizer, 1 Aerospace Engineer, Multidisciplinary Design, Analysis, and Optimization Branch, 21000 Brookpark Rd., MS 5-11, AIAA