Leveraging a Doublet Lattice Correction Method to Expedite Linearized Frequency-Domain Optimizations in MPhys

The Linearized Frequency-Domain method was recently implemented in FUN3D’s Stabilized Finite Element solver to allow for gradient-based optimization subject to aeroelastic flutter and gust constraints. This method, which linearizes about a nonlinear flow solution (thereby being more accurate than panel-based aerodynamics), makes computing these constraints much more tractable than equivalent responses with the full nonlinear time-domain solution. Computing these responses and their analytic derivatives, however, can still be quite costly depending on the number of structural modes and frequencies of interest. Correction techniques for Doublet Lattice Method aerodynamics have long been used in an effort to make panel-based
aerodynamics more accurate, while not incurring the cost of a time- or frequency-domain Computational Fluid Dynamics solution. This work presents an implementation of such a correction procedure using the authors’ toolset developed at NASA Langley Research Center, including FUN3D’s Linearized Frequency-Domain solver and an in-house Doublet Lattice Method implementation. The toolset leverages the MPhys library for OpenMDAO, which helps facilitate solver modularity and the computation of analytic design derivatives, among other advantages. Optimizations with flutter and gust (both continuous and discrete) constraints, and
with both shape and sizing design variables, are demonstrated for the AGARD 445.6 wing at a transonic flow condition.