DPM: Sampling a surface and understanding the variables in the .dpm file.

    • nicko627
      Hello I ran a Transient simulation with a discrete phase and some trap boundary conditions. I sampled one of these trap boundaries so that I could get the coordinates on the surface and other characteristics of the particles landing on that surface. The injection is a cone injection with a 10-bin rosin-rammler size distribution and 20 streamlines (it seems 200 parcels are injected whenever they are injected). 
      The output file (.dpm extension) has the following variables for each trapped particle on the surface I'm sampling on:
      self-explanatory: x, y, z, u. v, w, diameter, t (temperature), flow-time
      I'm not sure how these work: parcel-mass, mass, n-in-parcel, time
      I'm assuming 'time' is the particle time while its being integrated by the DPM package.
      I expected 'n-in-parcel' to be an integer, like "5000 particles" to indicate how many particles are in the parcel, but instead they are floating-point values around 1e-5. I noticed that "parcel-mass" is related to "mass" and "n-in-parcel" by "parcel-mass = mass * n-in-parcel". Is this how it should function? And then, why does it function like this if the phase should be "discrete"? If n-in-parcel is much less than 0, it would seem that the parcel doesn't even represent a full particle.
      I was intending to use this dpm sampling in a comparison with some data that has particles landing at specific coordinates, so I didn't want to do a mass-based or mass-weighted comparison. 
      Furthermore; is there a way to write a user-defined dpm scalar to this file? I noticed that I don't have my defined scalar in this file, even though it was turned on. I'm thinking I'll have to use one of the DPM UDF's (maybe DEFINE_DPM_OUTPUT).

    • Surya Deb
      Ansys Employee


      The n-in-parcel can be less than 1 [not less than 0]. This depends on the particle mass and the parcel mass which in turn depends on the mass flow rate and the parcel release method. Yes, you can output your scalar using DEFINE_DPM_OUTPUT.

      You can find more information about parcels here [https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v221/en/flu_ug/flu_ug_sec_dpm_concepts.html?q=n-in-parcel]



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