Learning Forum

[Zwernjayden]

I am trying to model impinging jets where 1 jet is 75% ethanol and 25% water by mass, and the other is liquid oxygen. I am using the VOF to DPM method. I have defined a velocity inlet, with the specified volume fraction of water and ethanol at the inlet. Water and ethanol are defined as different phases, each with a respective DPM droplet injecton defined to store the particles converted from the VOF phase. For some reason, at the start of the transient solution, the iso surface breaks up due to interactions of the ethanol and water, and imediately convert into DPM particles, instead of waiting for primary impingment of the steams to occur. This then results in "floating point error". This doesnt happen to the impinging lox jet, or when I define the fuel jet as 100% ethanol instead of 2 phases.

Is there a solution to this? Or is there a way I can have the inlet be a single phase homogenous ethanol/water mixture? How would I define the DPM for the VOF-to-DPM method for that?

I tried defining a ethanol/water mixture template as a single VOF phase instead of 2 different phases, and a multicomponent DPM for the droplets, but kept getting an error about how the materials were inconsistent and how there was an error with the VOF-to-DPM mechanism

 

I need to maintain information about the c2h5oh (ethanol) and water species, as I will be implementing a combustion model, so I cant just make a custom material template with the precalculated properties of the mixture

 

 

[Rob]

Depending on how you're adding the water & ethanol phases (remember VOF is a free surface tracking model so there are rules about boundary volume fraction) you may not have a clean free surface to prevent transition. So, a species mixture of water & ethanol (do they mix?) for that phase may be needed. That would transition to a multicomponent droplet. 

[Zwernjayden]

Yep looks like that was the issue. Defined a mixture and setup a multicomponent DPM and now its working. Thanks!