It this week’s blog post we will keep looking into the news of the latest Simcenter STAR-CCM+ version. This time we will specifically look at the news related to Langrangian multiphase models.

Langrangian multiphase and AMR

As mentioned, a couple of weeks back AMR was introduced for Langrangian multiphase. This can provide cell count reduction for cases where LMP droplets (or other type of particles) coexist with; either model based refinement for VOF, or user refinement based on field functions. It is possible to refine the mesh based on Lagrangian fields via parcel data mapper.

This compatibility is valid also in presence of overset mesh for moving geometries, reacting flows, etc. Animation on this slide illustrates the usage of AMR for simulating windshield wiper application with rain droplets modeled by LMP.

Improved control over size of cell clusters

This new feature can improve convergence and accuracy for 2-way coupling and reduce mesh dependency of simulation results. Source smoothing using cell clustering is a tool user can activate to spread coupling effects of LMP, including DEM, on the flow solution over a cluster of cells. This tool has proven to be very useful for improving the convergence and accuracy of the solution in many applications, including fuel sprays and Selective Catalytic Reduction. However, until now, it was not possible to use it for models with large cell size variation because the cluster size was required to be larger than the largest cell in simulation domain. Now, in version 2020.2, this limitation is removed. New methods for setting cluster size are available: Absolute, Relative to geometric mean, Relative to the largest cell, allowing user to set the size of cluster as required by particular physics and not bonded by the size of the largest cell.

On the left side is a screenshot of user interface related to the new feature. On the right side we have a comparison of the three levels of cell clustering for typical reacting fuel spray simulation with smaller cells in the middle to properly resolve hydrodynamics and reactions around the spray and large cells at the far boundaries, each cluster is marked by different random color. Previously users could not get the benefit of improving the stability and convergence of the simulation by using source smoothing with cell clustering because previous clustering algorithm can produce only coarse clusters, see middle and bottom images. New algorithm implemented in 2020.2 allows proper cluster resolution of the spray while still getting the benefits of source smoothing.

Flash boiling

In version 2020.2 we introduce the models and injection options to account for flash boiling. Flash boiling is a fast transition from liquid to vapor. It involves highly non-equilibrium and complex physics. Flash boiling is especially relevant for direct injection gasoline engines (GDI). The sudden onset of boiling can cause the breakup of the liquid jet in a catastrophic manner which alters the mixture formation process in the engine.

The new feature includes the models and options for both in-nozzle flash boiling and in-chamber flash boiling. In-nozzle modeling is set through new options of Nozzle Injector. It uses zero-dimensional cavitation and nucleation models to provide nozzle exit conditions.

In-chamber modeling is possible by using new Droplet Flash-Boiling model which account for enhanced vaporization of the droplets due to superheating and thermal breakup due to bubble growth.

Animations show the results of simulating the fuel spray with flash boiling. Top animation shows the result for the lower chamber pressure that is causing the higher degree of superheat, and bottom animation shows the result for the higher chamber pressure with lower degree of superheat. Both in-nozzle and in-chamber flash boiling physics is accounted for. Due to higher superheat in the first case part of the liquid is evaporated inside the nozzle so nozzle injector is injecting smaller size droplets and it is also providing higher mass flow rate for continuous phase, liquid vapor, being injected together with LMP droplets. It is for the first time in Simcenter STAR-CCM+ Lagrangian injector can inject both discrete and continuous phases.

Compatibility of collision and break-up models with VOF

There is improved realism in hybrid multiphase simulation, Simcenter STAR-CCM+ now allows Langrangian droplet collision and break-up to be modelled in simulations also including VOF. It is compatible with hybrid VOF-film and some applications include Vehicle water management, spray dryers, wet scrubbers and fuel.

I hope this has been useful to you as a Simcenter STAR-CCM+ user. Do not hesitate to contact me at robin.victor@volupe.com or at support@volupe.com if you have any questions. Tune in again next week for the conclusion of what version Simcenter STAR-CCM+ 2020.2 has to offer, we will then look e.g. at the news to data analysis together with some other news.

Langrangian multiphase and AMR

Improved control over size of cell clusters

Flash boiling

Compatibility of collision and break-up models with VOF

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