2026 Balachandar Aeroelastic Vortex Particle Finite Element Solver

We present VarFlExT (Variable Fidelity Unsteady Flow–FEmIS Exchange Interface), a modular aeroleastic solver for modeling two-way fluid–structure interaction (FSI) of flexible lifting surfaces. The framework employs a reformulated Vortex Particle Method (rVPM) to solve the incompressible Navier–Stokes equations without the need for computationally expensive volumetric remeshing, while supporting variable-fidelity aerodynamic modeling using the FluidUnsteady framework. On the structural side, a Reissner-Mindlin plate formulation is discretized using the finite element method and integrated in time through the generalized-a method, with the nonlinear equilibrium equations solved using a Gauss-Newton procedure within the FEniCS framework. Fluid and structural solvers are coupled through an explicit staggered partitioned scheme, ensuring conservation of virtual work for load and displacement transfers across the non-matching interface. The framework is validated against water-tunnel experiments, demonstrating accurate prediction of the coupled aeroleastic response rather than independent validation of the constituent solvers. The computational efficiency of the meshless aerodynamic solver enables simulations at significantly lower computational cost while maintaining accuracy. The solver is further evaluated through sensitivity analyses and parameter studies spanning different flow conditions, structural properties, and coupling parameters.