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Julie Polyakh March 21, 2002 16:36

Cell size
 
Hello!

Is there some rule how to choose the cells size when dealing with droplets?

Thanks,

Julie Polyakh

Ossi March 22, 2002 04:35

Re: Cell size
 
Unfortunately there is not. With the Lagrangian spray formulation there are problems associated with too coarse grids as well as too fine grids. With too coarse grid the accuracy is, of course, compromised but with too fine grid there also starts to be problems if the evaporation is strong. That is, if the droplet is very big in comparison to the cell size, the source term from the evaporation can be problematic. Then, one has to make the grid coarser, unfortunately.

A very general estimate is that for a non-evaporating sprays a cell size of the order of 1mm is quite sufficient. But as I said, there is no exact solution to this problem.

Julie Polyakh March 22, 2002 09:55

Re: Cell size
 
Hi, Ossi!

And what can you advise for evaporating sprays?

Thank you for the answer,

Julie

HVN March 22, 2002 10:07

Re: Cell size
 
Hello,

In the manual page 13-20 it is recommanded that the total droplet volume should not exceed 40% of this cell volume.

Ossi March 22, 2002 10:18

Re: Cell size
 
I would start from the cold flow mesh and see if that works well. If not, I would make it coarser.

If you have a large volume to be meshed, then usually one cannot use very fine mesh (computational time is prohibitive). But you will have to optimize the mesh anyways between accuracy and computational effort.

Julie Polyakh March 22, 2002 12:03

Re: Cell size
 
Hi, I didn't get it. Are they talking about ALL droplets volume and ALL the control volume or it's about ALL droplets and ONE cell? Or I've confused everything?..

Thanks,

Julie

Julie Polyakh March 22, 2002 12:05

Re: Cell size
 
Stupid question: How can one deremine if the solution is good enough?

Julie

Ossi March 22, 2002 12:11

Re: Cell size
 
Against experiments, and comparing different grid densities.

Julie Polyakh March 22, 2002 12:43

Re: Cell size
 
But, Ossi, tell me please, what error in per cents, do you think, should I achieve between two solutions to say that my grid is OK?

Thanks,

Julie


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