Implementation and Verification of a Variational Two Fluid Model in Ansys CFX*

A novel variational Two Fluid Model (TFM) in terms of the volumetric and drift fluxes has been derived by Clausse and Bertodano [1]. Their formulation yields the two natural modes of the TFM, i.e. the Drift Flux Model and the Two Fluid Wave Equation (TFWE). The variational method differs from the mechanistic method in that it allows a complete and objective definition of the inertial coupling based on the flow topology, resulting in a more complete dynamic TFM.

A variational TFM in terms of the primitive variables (velocities) equivalent to the two-mode variational TFM, is obtained and implemented in Ansys CFX. A non-linear void wave propagation problem is devised for the verification of the CFX TFM. Bubbly flow and slug flow simulations are performed, applying the corresponding inertial coupling models and drag laws. CFX TFM results are verified against TFWE results from a verified in-house FORTRAN program [2]. Converged CFX TFM results comparing well with the FORTRAN TFWE results are obtained.

[1] A Clausse & M Bertodano, "Natural Modes of the Two-Fluid Model of Two-Phase Flow", Physics of Fluids 33, 033324 (2021).

[2] R Ram, K Chetty, A Clausse, M Bertodano, “A New Two Fluid Model Verification Problem”, 2021 ANS Winter Meeting (2021).