## Fluids

#### DPM Volume Fraction

• shal3391
Subscriber

Hi,

I am modelling a fluid injection into air using a DPM model. I am injecting fluid parcels with diameter sizes equal to the jet nozzle diameter (0.686mm). I want to find the volume fraction along the centre line of the domain. The plot of the 'DPM volume fraction' is shown below, why does the volume fraction exceed 1?

Or if the values are as a %, why is it so low and not equal to 1 at the nozzle inlet?

Thanks

• Rob
Ansys Employee
Have a look at how the DPM model works. We assume a point mass, so if your particle is bigger than the cells and all of that mass is added where the centre point is the volume fraction will be over 1. nWhat are you trying to work out? n
• shal3391
Subscriber
Thankyou Rob,nnI am trying to determine the mean liquid volume fraction along the centreline of the domain. I am trying to create a plot similar to the one below.nnn
• Rob
Ansys Employee
Given that, do you think the DPM model is the correct choice? n
• shal3391
Subscriber
No, I have tried to use VOF model but have spent a lot of time on it and not been able to get a model working well. nIf I make every DPM volume fraction that exceed 1 equal to 1, would this be a kind of work around?.
• Rob
Ansys Employee
You'd still be tracking large droplets. DPM is designed for dispersed systems where the particles don't interact. nVOF is a free surface tracking model typically used for river/channel flows. If we refine the mesh we can also use it for fluid jets and their subsequent break up. One option to keep the cell count low enough for the Student version will be to use 2d axi-symmetric modelling. You can then use mesh adaption to refine around the free surface and hopefully pick up the jet break up. n