Fluids

Fluids

Topics relate to Fluent, CFX, Turbogrid and more

why I get zero erosion?

    • Narges
      Subscriber

      I'm trying to calculate DPM erosion Rate, but no matter what method I use, I just get zero as the result! can anyone help about what the problem is from?

      System: fluid + nanoparticles are injected from the inlet of the microchannel

      I used: 3D-dp-pbns-steady state flow

      viscose model: SST k-omega

      DPM: 2-way coupled, injection type: surface-inlet

      BC: velocity-inlet, pressure-outlet, reflect-wall

    • DrAmine
      Ansys Employee
      Are you using the Boundary Trap for DPM at the walls?
    • Narges
      Subscriber
      I have used "reflect" and "wall-jet" and also "trap" and even UDF! not only Erosion rate, but also the "DPM wall force" and "DPM wall normal pressure" are zero!
      my fluid is Water. I resimulated my system with air and it worked! how can I solve it?
    • DrAmine
      Ansys Employee
      Please first focus on using Trap and check if any particles are declared to be trapped? Which version area you using?
    • Narges
      Subscriber
      I'm using Student version. when I change my fluid from "liquid water" to "air" I can get non-zero value. but I don't know how to do it with liquid Water.
    • DrAmine
      Ansys Employee
      The same way as with air: your particles are not hitting any wall perhaps..
    • Narges
      Subscriber
      This is the geometry of my microchannel. with 3m/s velocity and 0.5mm distance of inlet and wall, collision is inevitable. is there anything that I can do to resolve it?

    • DrAmine
      Ansys Employee
      Also again: if you set the wall to be a trapping wall: do you see the particle trapped there Yes or No?
    • Narges
      Subscriber
      when I use water as fluid there is no trapped particle.
      when I use Air as fluid, less than a third of particles are trapped and else escaped.
    • DrAmine
      Ansys Employee
      If you do not have any trapped particles then you won't see any erosion rate as your particles are not toughing the wall. Please add a screenshot of particle tracks and screenshot of particle DPM Summary.
    • Narges
      Subscriber
      Dear Dr. Amine this is my system mesh from inlet to the spherical wall:
      and this is the particle track:
      and this is the summery of tracking:
      could the problem be from my meshing?



    • DrAmine
      Ansys Employee
      The mesh does not look good for me but it is my flavor as I prefer uniform mesh and boundary layer resolved meshes. Moreover your particles are all escaping so your erosion rate will be zero. You said at it was air particles are trapped on the wall. Water has higher viscosity and this will affect the particle relaxation time. Can you estimate the Stokes number based on the properties you have?
      Consider changing the position of the outlet to avoid any numerical backflow which you are now just "avoiding" via artificial wall creation.
    • Narges
      Subscriber
      Dr. Amine, thank you for your answer. the Stocks number is 1.8575e-6 for this system.
      sorry, but I didn't get the "changing the position of the outlet". how can I do that?
    • DrAmine
      Ansys Employee
      you place your outlet bit more downstream to avoid any numerical backflow. Sometimes backflow will also happen due to the physics. Please disable the "prevent backflow" option and try to figure out why you have a backflow.

      Your Stokes number is very low so the particles will be like passive tracers and travel with the flow.
    • Narges
      Subscriber
      Thank you very much for your help. with increasing the particle relaxation time I can get non-zero wall force. I also I removed the "prevent backflow" option.
      would you please suggest me a method to improve my meshing?
    • Rob
      Forum Moderator
      likes inflation and hex, alternatively have a look at Fluent Meshing and use inflation with polyhedral cells.
      With a Stokes Number that low I'd be surprised if the particles hit anything: they'll follow the flow.
    • DrAmine
      Ansys Employee
      Assess some inflations layers :)
    • Narges
      Subscriber
      thank you . sure, I will do that
Viewing 17 reply threads
  • The topic ‘why I get zero erosion?’ is closed to new replies.