The multiphase capabilities in Simcenter STAR-CCM+ are ever growing and the latest version, 2410, follows this trend as well. It is time again for some multiphase news and we will see, both for Eulerian and Lagrangian simulations, that there are new features that improve both accuracy, capabilities, and speed.
Dynamic Implicit Multi-Step for Constant timestep in VOF
The implicit multi-step for VOF was introduced a while back and it has now been improved. The implicit multi-step allows you when running, to keep implicit steps for the solution procedure of the volume fraction. This allows you to utilize the possibility of either a higher global timestep and still maintaining accuracy of the interface or maintaining the same timestep and increasing the sharpness of the interface as that is updated internally within a timestep. The new feature with a dynamic timestep (for a constant global timestep) allows the solver to decide how many implicit steps that are used inside the global timestep. This is done so that the CFL target is reached. With this introduction, the maximum number of implicit steps has been increased from 20 to 100.
The example below shows for a sloshing tank, the speed-up provided with increasing constant timestep and increasing number of average Implicit steps.
Schrage Boiling/Condensation Model for VOF and MMP
A new model for handling cryogenic boiling and condensation has been introduced. Cryogenic boiling is initiated at free surfaces rather than walls, requiring a new approach than the traditional methods. The Schrage model is based on kinetic theory and is applied where phases interact, at Large scale Interfaces for VOF and MMP and in the dispersed phase interaction area density for MMP. This creates a good framework for handling simulations including liquid hydrogen.
Compatibility of Generalized Non-Newtonian Cross Fluid with VOF
It is now possible to simulate Non-Newtonian fluids like mayonnaise using the Generalized Non-Newtonian Cross Law for VOF. Before you could use Carreau-Yasuda and (or?) Power Laws, but the fitting parameters for those models were not as easy to find. Often, data in the form of cross law is more readily available. Often, applications involving foodstuffs have turbulent flow and involve motion or mixing, making the VOF framework better than the Finite element approach used in computational rheology.
Lagrangian droplets vaporizing to VOF gas phase
Before, the continuous phase, in a Lagrangian evaporation simulation had to be single phase. This limitation is now lifted, making it possible to evaporate liquid droplets into the vapor component of the gas phase in a VOF-simulation. You now specify this physics in the multiphase interaction between the Lagrangian phase and the VOF gas phase. This is a strong feature for applications like Internal combustion engines and turbomachinery combustors.
Reduced mesh dependance of Lagrangian collision models
Previously, the NTC (No Time collision) model for particle collisions identified the collision pairs in each mesh cell. That method gave artifacts to the results that had a strong dependance for the collision outcomes on the mesh size and mesh topology. The animation below shows the “clover-leaf” shape in version 2406, but now in 2410 it is heavily reduced. This improvement is made possible by using cell clusters instead of cells as the location for collision pair identification. It is provided by specifying “collision mesh” as input for the collision detection instead of the “cell”.
Compatibility of collision model with Liquid-Solid-Gas particles
For spray drying applications the NTC collision model has now been made available. This now allows you to simulate e.g. REA spray drying together with NTC collision modeling. It is the liquid-solid-gas composition for particles that now is made compatible with NTC. This is a first step in improving spray drying where later down the road, also modification will be made possible of collision outcome maps for almost dry particles.
Liquid droplets deposition on solid particles
A new absorption model is now available for simulations involving the interaction between DEM with a solid-liquid-gas composition and liquid Lagrangian particles. It enables simulations of wetting, often used in pharmaceutical and chemical process applications. The model detects the collision between liquid droplets and DEM particles, and the instantaneous transfer of the whole droplet mass is transferred into the liquid component of the DEM particle. The transfer increases the DEM particle mass and size. Momentum and energy are equally transferred. This is possible to use in the mesh-based DEM (meaning not mesh-free DEM) workflow and works with all types of DEM-particles.
I hope this blog has been useful to read, and I also hope it provides ideas for what is possible to do with your multiphase simulations. This year’s updates for multiphase simulations have continued to give new possibilities in terms of hybridization. As usual, if you have any questions reach out to support@volupe.com.
Author
Robin Victor
+46731473121
support@volupe.com