With our recent release of PreonLab 5.2, which was a very special release for us, we introduced our new feature – Continuous Particle Size (CPS), where particles can have any size in a user defined range.
In this article, we shall take a look at the development of adaptive refinement and coarsening in PreonLab and the benefits of CPS along with the challenges and limitations that go with it.
Furthermore, during this step, the finer particles need to have similar velocities compared to each other, in order to conserve momentum upon merging. If these conditions cannot be satisfied, the particles cannot be merged, and we are left with the issue of left-over particles in the simulation.
Apart from this, the splitting and merging of particles introduces sampling and density noise, since the distribution of particles changes. This is one of the biggest challenges for particle-based approaches and needs to be addressed and rectified. This is touched upon in more detail in the article: Adaptive Particle-based Simulation in PreonLab.
The latest PreonLab 5.2 release saw the introduction of a game-changing new feature in the context of adaptive refinement for particle-based CFD applications – Continuous Particle Size or CPS. As is the case with most great achievements, this was the result of constant efforts and steady progress over the past few years. Let us have a quick look at the various stages of this journey:
The ability to have adaptive refinement was first introduced to PreonLab users with PreonLab 4.x, where two levels for particle size were introduced. Along with letting the particles in the regions of interest be as fine as required, the simulation for the rest of the bulk fluid volume could be performed with coarser particles. By doubling the size of the finer particles during coarsening, it was possible to reduce the number of particles in the simulation by up to eight times. Refinement was not carried out only within the region of interest, but rather a buffer zone was needed around it for the splitting and merging of particles.
With PreonLab 5.0, it became possible to include 3 levels of refinement within a simulation. This means that three distinct particle sizes could be defined within a single simulation setup. This can be visualized in figure 3 for the water-wading simulation setup. All particles in the region of interest i.e., close to the car geometry, have a particle size of 5 mm, while the particles away from the region of interest become coarser using three levels of refinement. The middle refinement level between the fine and coarse refinements offered some significant benefits. Most importantly, it allowed for an increase in the size ratio between the coarsest and finest particles, thereby reducing the number of particles in the simulation further, by up to sixty-four times. The resulting speed-up is discussed in the article: Getting the Same Result 12x Faster.