Droplets breakup
 

Hi,

Does anybody have successful experience modeling droplets breakup with STAR-CD?

Regards,

Julie

Re: Droplets breakup
 

It depends on how you define "successful"...

Re: Droplets breakup
 

I want the computations to agree with experiment. (Now you will ask how do I define "agree"?)

Re: Droplets breakup
 

We have simuleted drops in diesel engines as well as in constant volume bombs. The constant volume bomb computations have been compared with experiments done in the same conditions (spray penetration, drop SMD, spray width and spray shape).

Re: Droplets breakup
 

Have you calculated drops breakup? I don't see that it works.

In general, I have problems with drops trajectory. It seems like the drag coefficient is too small.

Another question is cell dimensions. Can you give me specific example of cell dimensions from your model?

Re: Droplets breakup
 

I assume you are doing transient simulations because you are trying to breakup droplets. I have not observed problems in drop drag. In constant volume bomb simulations I am typically using cylindrical grid and the cell size is roughly 1mm in every direction near the nozzle. Gradually the cell size is getting bigger when moving away from the nozzle location.

Re: Droplets breakup
 

Hi Ossi,

I am performing steady-state simulation. There are nothing said about break-up model apliciability with simulation types. Moveover, they use the Reitz breakup in Tutorial 2.3 in steady-state calculation.

Can you explain the meaning of Droplet Trajectory Max File Size(MB) and of Maximum Tracking Time values, please? How one determinates their values and how do they influence the solution?

Thank you,

Julie

Re: Droplets breakup
 

I think one cannot use the droplet collision model for steady-state runs, sorry about that.

Max file size is the max allowed file size of the case.trk file, and max tracking time will ensure that if a drop for some reason will go to a never-ending loop, it will not be tracked more than the specified time.

Re: Droplets breakup
 

I was talking about droplets breakup (not droplets collision) model.

If I set max .trk file size smaller than it really is, what happens then?