Successful design of aerospace vehicles must incorporate knowledge from various engineering disciplines, such as structures, propulsion, aerodynamics, heat transfer, and controls. In the last fifteen years true multidisciplinary design (not simply the analysis of a given design from the perspective of any given engineering discipline) has become possible due to the emergence of new tools. One such tool for the preliminary design of aerospace structures is the Automated Structural Optimization System (ASTROS).

As with many structural optimization programs, the aerodynamic modeling capabilities within ASTROS are based on linear panel methods and, thus, have a limited range of applicability. With the expanded flight envelopes being considered for maneuvering aircraft, it has become increasingly important to be able to model nonlinear steady and unsteady aerodynamics earlier in the design cycle. Including Computational Fluid Dynamics (CFD) models within ASTROS has the potential of extending significantly its range of applicability, flow conditions, and geometry capabilities. In doing so, adverse fluid-structure interactions can be detected early in the design cycle.

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The objective of this study was to demonstrate the feasibility of integrating modern CFD aerodynamic prediction technology in ASTROS. A detailed analysis was carried out, presenting how to make use of both steady and unsteady CFD-generated air loads in the design disciplines of ASTROS. Both NASA's Direct Iterative Surface Curvature (DISC) method and CFD automatic differentiation (ADIFOR) were evaluated to compute sensitivities to geometric design variables and formulate alternative Aerodynamic Influence Coefficient (AIC) matrices. A demonstration of a Computational Fluid Interface (CFI) was carried out by coupling ASTROS with NASA's transonic small disturbance computational aeroelasticity program CAPTSD. This demonstration involved the redesign of a composite wing under transonic and supersonic load conditions, subject to static aeroelastic constraints (see Figure). Finally, detailed plans were drawn to minimize the number of CFD runs required, since the overall computational cost is dominated by CFD. Unique solutions maximizing the use that can be made of each CFD run were developed, both to carry out nonlinear trim module enhancements and for the inclusion of unsteady aerodynamics.

Commercial Applications: The ability to accurately and efficiently incorporate CFD-generated aerodynamics into the multidisciplinary design capabilities of ASTROS is a significant leap in the design process, particularly for transonic flow and high angle of attack conditions. The benefits of this early multidisciplinary integration are: reduced design cycle time and reduced time-to-market for airframe manufacturers.

References:

Reisenthel, P. H., " Novel Concepts for a CFD-Enhanced ASTROS Capability." NEAR TR 510, Nielsen Engineering & Research, Mountain View, CA, April 1996.