Combining Boundary-Conforming Finite Element Meshes on Moving Domains Using a Sliding Mesh Approach

For most finite element simulations, boundary-conforming meshes have significant advantages in terms of accuracy or efficiency. This is particularly true for complex domains. However, with increased complexity of the domain, generating a boundary-conforming mesh becomes more difficult and time consuming. One might therefore decide to resort to an approach where individual boundary-conforming meshes are pieced together in a modular fashion to form a larger domain. This paper presents a stabilized finite element formulation for fluid and temperature equations on sliding meshes. It couples the solution fields of multiple subdomains whose boundaries slide along each other on common interfaces. Thus, the method allows to use highly tuned boundary-conforming meshes for each subdomain that are only coupled at the overlapping boundary interfaces. In contrast to standard overlapping or fictitious domain methods the coupling is broken down to few interfaces with reduced geometric dimension. The formulation consists of the following key ingredients: the coupling of the solution fields on the overlapping surfaces is imposed weakly using a stabilized version of Nitsche's method. It ensures mass and energy conservation at the common interfaces. Additionally, we allow to impose weak Dirichlet boundary conditions at the non-overlapping parts of the interfaces. We present a detailed numerical study for the resulting stabilized formulation. It shows optimal convergence behavior for both Newtonian and generalized Newtonian material models. Simulations of flow of plastic melt inside single-screw as well as twin-screw extruders demonstrate the applicability of the method to complex and relevant industrial applications

Design and Analysis of a Task-based Parallelization over a Runtime System of an Explicit Finite-Volume CFD Code with Adaptive Time Stepping

FLUSEPA (Registered trademark in France No. 134009261) is an advanced simulation tool which performs a large panel of aerodynamic studies. It is the unstructured finite-volume solver developed by Airbus Safran Launchers company to calculate compressible, multidimensional, unsteady, viscous and reactive flows around bodies in relative motion. The time integration in FLUSEPA is done using an explicit temporal adaptive method. The current production version of the code is based on MPI and OpenMP. This implementation leads to important synchronizations that must be reduced. To tackle this problem, we present the study of a task-based parallelization of the aerodynamic solver of FLUSEPA using the runtime system StarPU and combining up to three levels of parallelism. We validate our solution by the simulation (using a finite-volume mesh with 80 million cells) of a take-off blast wave propagation for Ariane 5 launcher.Comment: Accepted manuscript of a paper in Journal of Computational Scienc

Numerical Simulations on the PSP Rotor Using HMB3

This work presents CFD analyses of the isolated Pressure Sensitive Paint (PSP) model rotor blade in hover and forward flight using the structured multi-block CFD solver of Glasgow University. In hover, two blade-tip Mach numbers (0.585 and 0.65) were simulated for a range of blade pitch angles using fully-turbulent flow and the k-ω SST model. Results at blade-tip Mach number of 0.585 showed a fair agreement with experimental Figure of Merit and surface pressure coefficients obtained in the Rotor Test Cell (RTC) at NASA Langley Research Center. Comparisons are presented at blade-tip Mach number of 0.65 in terms of integral blade loads, surface pressure coefficients and position of the tip-vortex cores with published numerical data. Finally, the flow around the PSP rotor in forward flight was also computed at medium thrust (CT =0.006) and results were compared with published experimental data

Onshore Wind Farm Modelling

We present a Computational Fluid Dynamics (CFD) modeling strategy for onshore windfarms aimed at predicting and optimizing the production of farms using a CFD model that includes me-teorological data assimilation, complex terrain and wind turbine effects. The model involves the solutionof the Reynolds-Averaged Navier-Stokes (RANS) equations together with a κ-ε turbulence model spe-cially designed for the Atmospheric Boundary Layer (ABL). The model involves automatic meshing andgeneration of boundary conditions with atmospheric boundary layer shape for the entering wind flow.As the integration of the model up to the ground surface is still not viable for complex terrains, a specificlaw of the wall including roughness effects is implemented. The wake effects and the aerodynamic be-havior of the wind turbines are described using the actuator disk model, upon which a volumetric forceis included in the momentum equations. The placement of the wind turbines and a mesh refinement forthe near wakes is done by means of a Chimera method. The model is implemented in Alya, a HighPerformance Computing (HPC) multi physics parallel solver based on finite elements and developed atBarcelona Supercomputing Center.Laboratorio de Capa Límite y Fluidodinámica AmbientalGrupo Fluidodinámica Computaciona

A Chimera method based on a Dirichlet/Neumann(Robin) coupling for the Navier–Stokes equations

We present a Chimera method for the numerical solution of incompressible flows past objects in relative motion. The Chimera method is implemented as an iteration-by-subdomain method based on Dirichlet/Neumann(Robin) coupling. The DD method we propose is not only geometric but also algorithmic, for the solution on each subdomain is obtained on separate processes and the exchange of information between the subdomains is carried out by a master code. This strategy is very flexible as it requires almost no modification to the original numerical code. Therefore, only the master code has to be adapted to the numerical codes and the strategies used on each subdomain. As a basic flow solver, we a use stabilized finite element method

Onshore Wind Farm Modelling

We present a Computational Fluid Dynamics (CFD) modeling strategy for onshore windfarms aimed at predicting and optimizing the production of farms using a CFD model that includes me-teorological data assimilation, complex terrain and wind turbine effects. The model involves the solutionof the Reynolds-Averaged Navier-Stokes (RANS) equations together with a κ-ε turbulence model spe-cially designed for the Atmospheric Boundary Layer (ABL). The model involves automatic meshing andgeneration of boundary conditions with atmospheric boundary layer shape for the entering wind flow.As the integration of the model up to the ground surface is still not viable for complex terrains, a specificlaw of the wall including roughness effects is implemented. The wake effects and the aerodynamic be-havior of the wind turbines are described using the actuator disk model, upon which a volumetric forceis included in the momentum equations. The placement of the wind turbines and a mesh refinement forthe near wakes is done by means of a Chimera method. The model is implemented in Alya, a HighPerformance Computing (HPC) multi physics parallel solver based on finite elements and developed atBarcelona Supercomputing Center.Laboratorio de Capa Límite y Fluidodinámica AmbientalGrupo Fluidodinámica Computaciona

Cartesian Off-Body Grid Adaption for Viscous Time- Accurate Flow Simulation

An improved solution adaption capability has been implemented in the OVERFLOW overset grid CFD code. Building on the Cartesian off-body approach inherent in OVERFLOW and the original adaptive refinement method developed by Meakin, the new scheme provides for automated creation of multiple levels of finer Cartesian grids. Refinement can be based on the undivided second-difference of the flow solution variables, or on a specific flow quantity such as vorticity. Coupled with load-balancing and an inmemory solution interpolation procedure, the adaption process provides very good performance for time-accurate simulations on parallel compute platforms. A method of using refined, thin body-fitted grids combined with adaption in the off-body grids is presented, which maximizes the part of the domain subject to adaption. Two- and three-dimensional examples are used to illustrate the effectiveness and performance of the adaption scheme