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It always seems a little odd to me when CFD engineers talk about "multiphase flow". After all, most real world flow scenarios usually involve more than one phase (i.e.solid,  liquid, gas or plasma).

The reason that multiphase flows get lumped into their own separate category is that historically, they've been perceived as being difficult to solve, either by using classical methods or through simulation. Part of the problem is that multiphase models were often restricted to a very narrow range of application. Many industrial-type problems fell into the gap between these models, to the extent that the multiphase influences are either ignored, or simplified as part of a legitimate modeling assumption.

CD-adapco is committed to the philosophy of "simulating systems". This gives our users the opportunity to take into account all the factors likely to influence the performance of their product in its operational life when building a simulation. As part of that commitment, one of our ongoing development themes in STAR-CCM+ involves making multiphase flows more accessible to all of our users. by introducing new features that allow you to tackle a wider range of industrial applications (bridging the "gaps" described above) by further improving solver performance, so that you can tackle them on an industrial scale.

Eulerian Multiphase

One application area that sees a number of significant benefits in this release is separation. This includes the separation of fluids of different densities in a cyclone, such as oil and water, or the refining or distillation of multi-component fluids with different boiling points.

There are two main advances in this area in STAR-CCM+ v8.06:

  • The Reynolds Stress Model for Eulerian Multiphase improves the accuracy of modeling swirling flows and vortices.
  • The new multicomponent boiling model allows components to evaporate individually, aiding in the modeling of refinery and distillation processes.

RSM turbulence is useful for swirling flows

Of course not all phases represented by the Eulerian Multiphase model are liquid or gas - you can also model granular flows. With the release of STAR-CCM+ v8.06, we introduce the Granular Temperature Transport Model. Granular Temperature is a measure of the average kinetic energy of the particles which is analogous to the temperature of molecules. Solving an additional transport equation for granular temperature allows the kinetic energy of the granules to be transported with their motion, adding significant accuracy benefits over the algebraic granular temperature model which estimates the granular temperature from local conditions.

Applications that involve arbitrarily moving components and fluid films, such as the spray painting automotive parts, or the film and ice buildup on aircraft wings with moving flaps, can be modeled with the overset mesh. In the example shown, a paint nozzle moves using a prescribed motion using overset mesh. Lagrangian droplets represent the paint spray, which then impinge on the fluid film, adding to its thickness which can then spread out over the panel surface using the Eulerian fluid film model.

Spray painting simulation using STAR-CCM+

Lagrangian and Discrete Element Models

Engineers in industries such as Energy, Chemical Process, and Life Sciences will benefit from the addition of passive scalars for the Lagrangian and DEM models. Passive scalars allow particles to carry additional information such as the thickness of a coating being sprayed onto the particles (via an Eulerian passive scalar), or the water content of particles being dried. Passive scalars enable you to determine the effectiveness of mixing processes where previously it would have been impossible to distinguish particles from each other, which in terms of the physics being modeled were otherwise identical.

Users of the DEM model will notice substantial performance improvements in STAR-CCM+ v8.06, with simulations taking as little as 1/3 of the time taken in previous versions. Central to these improvements have been optimizations to the core DEM algorithms and a new 'skinning' option to avoid repeated contact detection.

Gas turbine combustion modeling is another application area that will benefit from the release of STAR-CCM+ v8.06 withthe addition of the Stochastic Secondary Droplet (SSD) break up model for Lagrangian droplets. In such applications, where liquid spray atomization occurs, the correct modeling of the break-up of the fuel spray and prediction of thesubsequent droplet size distribution is important in producing an accurate simulation. The SSD model determines breakup based on the local conditions, and produces results that are less sensitive to the injected particle size, and improves numerical stability.

DEM performance enhancement

 While this is not an exhaustive list of the new multiphase features in STAR-CCM+ v8.06, hopefully it serves to whet your appetite to pursue some of those rewarding, infinite possibilities that you have always wanted to model that now are just a few clicks away.

STAR-CCM+ v8.06 will be released this fall. Stay tuned to the CD-adapco Blog for all the latest information.

 

 

Stephen Ferguson
Communications Manager
Dr Mesh
Meshing Guru
Brigid Blaschak
Communications Specialist
Sabine Goodwin
Senior Engineer, Technical Marketing
Jean-Claude Ercolanelli
Senior Vice President, Product Management at CD-adapco
Bob Ryan
President Red Cedar Technology
Joel Davison
Product Manager, STAR-CCM+
Deborah Eppel
Technical Marketing Engineer