Aerodynamic Parameter Adaptation of CFD-Based Reduced-Order Models

The proper orthogonal decomposition (POD) method has been shown to produce accurate reduced-order models (ROMs) for unsteady aerodynamic analyses at fixed flight conditions. However, changes in aerodynamic parameters such as the Mach number or angle of attack often necessitate the re-construction of the ROM in order to maintain accuracy, which destroys the sought-after computational eciency. Straightforward approaches to ROM adaptation — such as the global POD method and the direct interpolation of the POD basis vectors — are known to lead to inaccurate POD bases in the transonic flight regime. Alternatively, a new ROM adaptation scheme is described in this paper and evaluated for changes in the free-stream Mach number and/or angle of attack. This scheme interpolates the subspace angles between two POD subspaces, then generates a new POD basis through an orthogonal transformation based on the interpolated subspace angles. The resulting computational methodology is applied to unsteady flows for both aerodynamic and aeroelastic applications involving a complete F-16 configuration in various airstreams. The predicted aerodynamics loads and aeroelastic frequencies and damping coecients are compared with counterparts obtained from full-order nonlinear simulations and flight test data. Good correlations are observed, including in the transonic regime. The obtained computational results reveal a significant potential of the adapted ROM computational technology for accurate, near-real-time, numerical, predictions.