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
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.