Fluent: Rosin-Rammler PSD – Spread parameter is altered by fluent!

- July 2, 2020 at 10:17 pm
  
  ai0013
  Subscriber
  
  Hello,
  
  I noticed my simulation is not using my specified spread parameter (3.5), rather is using 2.84!!! Why is this happening??
  
  I checked this with a manual calculation of the RR distribution based on particle sampling over a cross-sectional floating surface, and with the dpm summary report!!
  
  If someone knows how fluent deviates from my specified value, please let me know!
- July 3, 2020 at 5:08 am
  
  DrAmine
  Ansys Employee
  
  How did you get the RR? Also to get the theoretical value one would need zo have a lot of parcels/diameters. Where are you sampling?
- July 3, 2020 at 7:18 pm
  
  ai0013
  Subscriber
  
  Thanks for your kind reply
  
  I did a particle sampling for my combusting particles over a cross-sectional floating surface in my injector (where no reactions are taking place yet). I ran it for approx 2,000 particle injection time steps and then post-processed the data in the histogram tool. I weighted the data by parcel-mass and divided the frequency distribution by the bin size. Then compared this to the derivative (PDF) of the analytical RR.
  
  Blue line: my pre-defined (analytics)l PDF RR (n=3.5)
  
  Red line: fluent (analytical) PDF RR based on reported spread parameter (n=2.84) (summary report)
  
  Squares: fluent (numerical) PDF RR based on particle sampling
  
  From here I see Fluent is deviating my spread parameter, so don't know what is happening. Should I sample for a longer time?
- July 8, 2020 at 12:41 am
  
  ai0013
  Subscriber
  
  Does anyone in the community has noticed something similar to the above problem? Thanks