This paper describes a procedure, developed over several years at Virginia Tech, for the combined aerodynamic-structural design optimization of a high-speed civil transport (HSCT). The computational challenge associated with the optimization is the focus of the work and it is addressed by two techniques. First, we developed efficient parameterization of the design, which describes the wing, fuselage, tails, nacelle geometries, and mission profile with only 28 design variables. Second, we used a variable-complexity modeling (VCM) technique, which combines simple and complex models to construct various discipline approximations for use during the optmization process. Simple models for predicting aerodynamic performance and structural weight are conceptual-design-level methods. The more complex models are panel methods and finite-elementbased structural optimization. The VCM approach allows us to combine the computational efficiency of the simpler models with the accuracy of the more complex ones. Several examples are used to demonstrate design trade-offs for the HSCT.
The performance of NASA Rotor 37 with Circumferential Grooves Casing Treatment (CGCT) is studied with an in-house CFD code NSAWET. Based on the stall mechanism analysis, a number of CGCT configurations have been proposed and numerically tested. The computation results show that the stall mechanisms are strongly related with the width of tip clearance. With a small tip clearance, the stall process is dominated by the trailing edge separation, while the leading edge tip leakage vortex breakdown induced blockage causes stall in a large tip clearance configuration. Circumferential grooves at appropriate axial locations can be beneficial to the stall margin in these two types of stall processes. The effects of the groove width and depth are presented. The mechanisms of CGCT for different tip clearances are also discussed.
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