Adaptation of general purpose CFD code for fusion MHD applications

Abstract

Analysis of many fusion applications such as liquid metal blankets requires application of Computational Fluid Dynamics (CFD) methods for electrically conductive liquids in the geometrically complex regions and in the presence of a strong magnetic field. Current state of the art general purpose CFD code allows modeling of the flow in complex geometric regions, with simultaneous conjugated heat transfer analysis in liquid and surrounding solid parts. Together with Magneto Hydro Dynamics (MHD) capability general purpose CFD code will be a valuable tool for design and optimization of fusion devices. This presentation describes an introduction of MHD capability into a general purpose CFD code CFX part of the ANSYS Workbench. The code was adapted for MHD problems using magnetic induction approach. CFX allows introduction of user defined variables using transport, or Poisson equations. For MHD adaptation of the code three additional transport equations were introduced for the components of the magnetic field, with additional Poisson equation for electric potential. Lorentz force is included in the momentum transport equation as a source term. Fusion applications usually involve very strong magnetic field with the values of the Hartmann number of up to tens of thousands. In this situation system of MHD equations became very rigid with very large source terms, and very strong gradients of the variables. To increase system robustness, special measures were introduced during iterative convergence process, such as under-relaxation using source coefficient for momentum and magnetic field equations. MHD implementation in general purpose CFD code was tested against benchmarks specifically selected for liquid metal blanket applications. Results of numerical simulations using present implementation closely match analytical solution for the Hartmann number of up to 15000 for two-dimensional laminar flow in the duct of square cross-section, with conducting and non-conducting walls. Results for three dimensional test cases are also included in the presentation.

Acceleration of three-dimensional Tokamak magnetohydrodynamical code with graphics processing unit and OpenACC heterogeneous parallel programming

“…Because of the similarities between CFD and MHD, CFD solvers can be generalized to study MHD problems (Khodak 2015), and vice versa.…”