Time-Synchronized EHD and CHT Coupling Strategies in an FEM-Based PHASTA Solver

We use an open-source FEM-based PHASTA code to study two coupling strategies for applications of Electrohydrodynamics (EHD) and Conjugate Heat Transfer (CHT). In the case of EHD, charge conduction in weakly conducting liquids is much faster than the fluid's time scale; therefore, the field is considered quasi-static. The Maxwell stress body force caused by the electric field is evaluated as a source term in the Navier-Stokes equation. For conjugate heat transfer, we couple a solid FEM conduction solver to the fluid domain using a Neumann-Dirichlet boundary interface, where the solid exports heat flux, and the fluid returns temperature to the solid. To ensure stability, we use Aitken-relaxed iterations at each major step, marching the solid with a fully implicit Crank–Nicolson solver that handles its larger thermal time scale. With this strong, conventional serial staggered (CSS) approach, the master-slave sub-cycling algorithm ensures coupling synchronization by executing multiple smaller solid sub-steps within each larger fluid time step, preventing physical time drifts. To reduce computational costs, we exchange interface data through an efficient mapping system that accommodates non-conforming meshes and transmits only necessary wall scalars, minimizing MPI communication even at large scales.