## Fluids

Topics relate to Fluent, CFX, Turbogrid and more

#### Adjusting diameter distribution in DPM.

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• Beb99
Subscriber

Hey all,

I'm trying to simulate DPM in Ansys, and having trouble matching the diameter distribution. I have to inject particles ranging from 0 to 3mm in diameter. For example, let's say I have 50% of the total mass injected in the range 0 to 0.4mm, 49% of the mass in between 0.4 to 2.3mm, and the rest 1% mass in 2.3mm to 3mm diameter particles.

I tried using Rossin Rammler distribution for 0 to 3mm but it doesn't give the right distribution after simulation. Now, I'm using multiple injections (in this case 3) (a. 0-0.4mm b. 0.4mm to 2.3mm c. 2.3m to 3mm). But still, I'm unable to increase or decrease the number of particles individually in these injections. And to get the required mass %, it seems I need to add a lot of lower diameter particles (around 10000 particles) for every 1 particle of higher diameter. This makes the data too big to process.

PS.: I'm exporting the particle data in an excel sheet for the domain( 0 to 1m cylinder) and creating diameter distribution for the section of (0.8 to 1m) to get the exit distribution.

Any help would be appreciated.

Thank you,

Beb99

• Rob
Ansys Employee
If you create multiple injections you can set up whatever mass flow with a diameter to suit what you're after.
• Beb99
Subscriber
But the mas flow rate doesn't seem to give me the right diameter distribution. As mentioned in the example above, I distributed the mass flow rate as 0.5:0.49:1. But, the diameter of the largest particle is almost ten times the smallest one, the diameter distribution is skewed onto the largest diameter.

PS.: When I say diameter distribution, I meant histogram of diameter on the x-axis and their corresponding mass fraction (out of 100%) on the y-axis.
I'm getting something like this: but what I need is 50:49:1

Let me know if you need more clarification.
Thank you Beb99
• Rob
Ansys Employee
Sorry, I missed the bit in the second paragraph.
Read the Theory Guide to understand parcel theory, and do NOT mess with the parcel method in the injection panel. That should (if you use a cone or other fixed size injection) mean each injection releases the same (manageable) number of parcels for each size. You then use a dpm.out file to figure out what went where, or post process particle tracks (steady state only) injection by injection to show their trajectories.