Direct FEM simulation of multi-phase turbulent flow

Johan Jansson
Computational Science and Technology
CSC
KTH
Stockholm
and
CFD Computational Technology
Basque Center for Applied Mathematics
Bilbao, Spain


Abstract:

In our research we develop the general adaptive stabilized G2 General Galerkin / Direct FEM methodology [1] and the FEniCS [2] framework, specifically focusing on HPC [3, 4] and the Unicorn solver targeting turbulent continuum models. In this seminar we will present an overview of the Direct FEM methodology and recent new developments toward multi-phase flow with applications in marine energy, and a general do-nothing approach to adaptive error control. The methodology and software is the basis for several application projects based both at BCAM and KTH, for example the MSO4SC H2020 project where we develop an HPC cloud infrastructure, the EUNISON FP7 project on simulating the human voice based on fundamental mechanics, several projects on simulating marine energy generation, and aeronautics projects based on simulating jet engines and flight.

The methodology has several unique aspects which we hope can advance the field in new directions:

1. The incompressible Navier-Stokes Equations (NSE) are discretized directly, without applying any filter. Thus, the method does not approximate any Large Eddy Simulation (LES) filtered solution, but is instead an approximation of a weak solution, satisfying the weak form of the NSE.

2. For this method, we have a posteriori error estimates of quantities of interest with respect to a weak solution, which form the basis for our adaptive mesh refinement algorithm. The a posteriori error estimates are based on the solution of an associated adjoint problem with a goal quantity (such as a drag coefficient) as data.

3. We model turbulent boundary layers by a slip boundary condition which is a good approximation for small skin friction stress, which gives enormous savings in computational cost by not having to resolve a very thin boundary layer.

[1] J. Hoffman, J. Jansson, N. Jansson, R. V. de Abreu, and C. Johnson. Computability and Adaptivity in CFD. Encyclopedia of Computational Mechanics (2016).

[2] http://fenicsproject.org

[3] J. Hoffman, J. Jansson, and N. Jansson. FEniCS-HPC: Automated predictive high-performance finite element computing with applications in aerodynamics. Proceedings of PPAM 2015. Lecture Notes in Computer Science (2015)

[4] PRACE Tier-0 Call 8, FEniCS-HPC, J. Hoffman, J. Jansson, N. Jansson, C. Degirmenci, A. Larcher (2014-2015)

[5] J. Hoffman, J. Jansson, C. Johnson, New Theory of Flight, Journal of Mathematical Fluid Mechanics, 2015