NEWPAN-MSC.Nastran™ Dynamic Aeroelastics: Flutter

With the introduction of the USNEWPAN product, Flow Solutions are able to offer an aerodynamic solution ideally suited to coupled dynamic aeroelastic analysis, including flutter.

A USNEWPAN based aeroelastic analysis of a high aspect ratio swept wing of airliner planform. Coupled MSC.Nastran™ analysis revealed a flutter mode - shown above with surface pressures varying around the cycle. A family of wings of different thicknesses were analysed for flutter over a range of incidences. The plot below shows the effect of incidence and thickness on the predicted flutter velocity - an effect which a classical method such as DLM is incapable of predicting.

In partnership with MSC.Software, a close coupling between NEWPAN/USNEWPAN and MSC.Nastran™ has been developed. The data exchange between USNEWPAN and the MSC.Nastran™ database is achieved via the NastAero toolkit (a set of functions developed by MSC.Software using their MSC.Nastran™ toolkit). Hence communication is performed directly with MSC.Nastran™, without using interface programs or files. The resulting aerodynamic or aeroelastic databases can be used to do flutter analysis, or maneuver simulations such as a pull up. Gust analysis is a step that will follow.

An important feature of USNEWPAN is that it allows for the unsteady perturbations of the full steady solution found by NEWPAN - it does not rely on the grossly linearized theory of classical methods. Hence the USNEWPAN implementation provides predictions for the effect of thickness and incidence on flutter velocity - an effect not seen with classical methods like DLM.

Two methods of USNEWPAN/MSC.Nastran™ coupling are provided, each of which have distinct advantages depending upon the analysis being performed. In both methods, USNEWPAN writes directly into the MSC.Nastran™ database - no intermediate files are necessary.

In the first method , USNEWPAN computes a full set of Aerodynamic Influence Coefficients (AIC's - matrices of the size number of panels squared), and these are passed across to MSC.Nastran™ and stored in the Aerodynamic Database (ADB). Since these matrices do not depend on the structure, they do not need to be recomputed if the structure is changed.

In the second method, MSC.Nastran™ provides USNEWPAN with a set of one or more structural modes, and USNEWPAN solves for the unsteady pressures for each of these modes directly. The advantage of this modal method is that storage is minimised and the USNEWPAN solution procedure is very fast (highly optimised for solution of this class of aerodynamic matrices). The disadvantage is that if the structure is modified, the coupled USNEWPAN run will need to be repeated.

The USNEWPAN/MSC.Nastran™ combination provides a fast and practical capability for flutter analysis of complex configurations in subsonic flow, and represents a logical and substantial advance over DLM. USNEWPAN supports execution in parallel on multiprocessor systems, even when running in MSC.Nastran™ coupled mode.

MSC.Nastran,MSC.Patran and MSC.Flightloads are trademarks of MSC.Software Corporation.