Post on 27-Jul-2015
Adaptive Tetrahedral Remeshingfor Multiphase Flow Simulations in
OpenFOAM
Sandeep Menon and David P. Schmidt
Multiphase Flow Simulation LaboratoryUniversity of Massachusetts Amherst
June 3, 2009
Off-center Droplet Collision
M. Dai and D. P. Schmidt,
“Numerical Simulation of Head-On Droplet Collision: Effect of Viscosity on Maximum Deformation”,
Phys. Fluids, 17(4), 2005.
Motivation
Pros and Cons:Accurate interface representation.Direct application of interface boundaryconditions.Conserves mass very well.Complicated mesh manipulation withlocalized remeshing and interpolation.
Lagrangian interface tracking:Interface points move with the interfacenormal velocityThe interior mesh automatically adjusts tomaintain mesh qualityWe only use simplical meshes
Prior Work
Since last year:Two-dimensional version in OF completedDemonstrated for ink jetsPublished in ILASS 2008, ICLASS 2009
Interface tracking capabilities in OpenFOAM:interTrackFoam - Prior work on interfacetracking by Zeljko Tukovic and Hrvoje Jasak.Uses the freeSurface library, also developedby Tukovic and Jasak.Used mesh-motion only - limited deformationcapability.tetDecomposition mesh motion solver.
Three Major Code Components
Incompressible PISO solverMesh motionMesh reconnections
Tetrahedral Mesh Motion
Current state of techniques:Laplacian smoothing - fast,simple, but createsdegenerate cells.Need to associate meshmotion with mesh quality.Alternative:optimization-basedsmoothing.Optimize algebraic meshquality metrics.More expensive thanLaplacian smoothing, butvery effective.
Tetrahedral Mesh Motion
Mesquite Optimization Library:Developed by Sandia NationalLabs.OpenFOAM wrapper class -mesquiteSmoother.Run-time selection of:É Optimization algorithms: CG,
Steepest Descent, FeasibleNewton, Quasi Newton, etc.
É Quality metrics: ConditionNumber, Inverse Mean Ratio,Aspect Ratio, etc.
É Termination Criteria: RelativeQuality Improvement, L2 norm,iterations, CPU Time, etc
Mean Ratio =12(3V2)1/3∑6
iL2e
Atomic Topology Operations
Arbitrary number of tetrahedra sharing an edge.Dynamic Programming algorithm to define swap configuration.
3D Edge Flip2D Edge Flip
Combination of Swap Operations
3-2 swapEquitorial Polygon2-3 swap4 cells sharing an edge
Possible Configurations
7 sides, 42 ways
6 sides, 14 ways5 sides, 5 ways
Tetrahedral Bisection and Collapse
Test Case: Rotating & Translating Sphere
Test Case: Rotating & Translating Sphere
Test Case: Rotating & Translating Sphere
Ink Jet Simulation
Conclusion
Future work...Automated interface topology modifications for dropletbreak-up and coalesence.Effective divergence-free local interpolation.Hybrid parallelization efforts: MPI and pthreads.
Work In Progress...Non-Newtonian effects.Temperature-dependent viscosity and surface-tension effects.