Propulsion/Airframe Integration and Optimization on a Supersonic Business Jet

Abstract

A parametric geometry generator, an advanced Euler CFD method, and a robust nonlinear optimizer are coupled to produce a powerful aerodynamic design tool. The application is used to integrate a propulsion system with the airframe of a supersonic business jet. More specifically, the inlet and nozzle installations are optimized sequentially in the presence of the airplane. For each problem, an appropriate objective function is selected to address the tradeoffs between engine performance and aircraft aerodynamic efficiency. Constraints are identified and selected to maintain realistic geometry and desired flow features. While the aircraft design continues to evolve, intermediate results of the optimization process are presented demonstrating the effectiveness of the design method. I. Background Aerion Corporation of Reno, Nevada has developed a unique design for a supersonic business jet which is depicted in Figure 1. Utilizing a patented feature, the wings are designed to sustain a significant extent of laminar flow during supersonic cruise to dramatically increase fuel efficiency and range. This wing design also allows for efficient transonic cruise. The propulsion system uses a slightly modified Pratt & Whitney JT8D engine with advanced nacelle, inlet, and nozzle designs. Mounted close to the fuselage and over the inboard strake of the wing, the engine nacelle poses a challenging integration problem. The need to operate efficiently with either fixed or minimally varying geometry over a wide range of Mach numbers also augments this challenge. The trade-offs between inlet performance, nozzle performance, and airframe aerodynamic efficiency must be properly addressed in order to make the design viable. Desktop Aeronautics of Palo Alto, CA has developed a design tool to address this difficult propulsion integration problem. The approach exploits multidisciplinary optimization techniques coupled with a powerful Euler solver and a versatile parametric geometry generator. Earlier incarnations of this design tool have been applied very successfully to similar but perhaps less difficult problems. The first published (Reference 1) application of the tool was the aerodynamic optimization of a generic swept-wing business jet. Reference 2 details the optimization of an axisymmetric, supersonic spike-inlet with the same design tool. However, for this problem, the tool was also extended to incorporate a propulsion system simulator forging a truly multidisciplinary design method. For the Aerion project, the design tool was further enhanced by extending the capabilities of the geometry engine to model the complex shapes that are present on the aircraft design. The design tool has been used on several parts of the entire aircraft design from the cockpit region to the empennage. For the purposes of this paper, only the design of the propulsion system is considered. This restriction limits the problem to the inlet, nozzle, nacelle outer surface, and any other part of the aircraft that is directly affected aerodynamically by the propulsion system. Because all optimization is conducted on the airplane at cruise conditions, this limits the design region significantly. Supersonic flight conditions also allow the inlet and nozzle to be