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Flow Simulation of a Hydrostatic Bearing Issues

Question asked by Joshua Thompson on Jan 4, 2021
Latest reply on Jan 8, 2021 by Joshua Thompson

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Hi,

I am currently undertaking Flow Simulation analysis of a Hydrostatic Bearing for my Honours Degree Project. This is my first time using the software and I am having a few issues with the simulation that I cannot seem to solve.

1. When running the simulation, a message appears stating negative pressure. I have checked the figures and directions of the pressure and all seem to be correct.

2. Once the simulation is complete and I run flow trajectories, the software crashes when I select more than 80 points but below 80 points doesn't seem to be enough to show the flow within the bearing pocket.

Any help or pointers in the right direction would be appreciated

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Sylvain Grondin Jan 4, 2021 11:55 AM
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Hello,

1 : Does the message disappear during the simulation or is it still there after hundreds of iterations ?

2 : The problem occuring may be linked to the message of negative pressure you have ; my guess would be the thin geometry (or anything which is link to) which is not resolved enough (mesh not fine enough) which could lead to false results

Could you provide your model so we can investigate what could be wrong ?
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- Joshua Thompson @ Sylvain Grondin on Jan 4, 2021 12:05 PM
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  Hello,
  Thank you for the reply.
  The message is still there after several hundred iterations.
  
  How would I go about attaching my model?
  
  Kind Regards
  Joshua Thompson
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  - Sylvain Grondin @ Joshua Thompson on Jan 5, 2021 3:02 AM
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    To attach your model :
    Then, when you post a message :
    And browse your file
    
    (For more : How can I attach a file to a forum post? )
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    - Joshua Thompson @ Sylvain Grondin on Jan 5, 2021 12:23 PM
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      Hi,
      
      I have followed the steps provided but the files seem to be too large to attach to the post. The File is coming out at 157MB. Is there any other way of attaching the file.
      
      Many Thanks
      Joshua Thompson
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      - Wayne Matus @ Joshua Thompson on Jan 5, 2021 3:52 PM
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        You do not need to include the results. The setup of the simulation is stored in the assembly file. We can run it to get the results.
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        Sylvain Grondin @ Wayne Matus on Jan 6, 2021 2:41 AM
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        Thanks ffor correcting me.
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Joshua Thompson Jan 6, 2021 12:19 AM
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Hi,
Thank you for your help.
I have managed to save it and attach it.
Hopefully it works correctly
Currently using Solidworks 2018 if there is any compatibility issues
Many Thanks
Attachments
- BEARING FLOW SIMULATION.zip639.8 KB
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- Wayne Matus @ Joshua Thompson on Jan 6, 2021 3:57 PM
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  Sorry, I did not realize you had special fluid. You will need to export it and attach so we can use it.
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  - Joshua Thompson @ Wayne Matus on Jan 7, 2021 11:40 AM
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    Hopefully this is the correct file. The fluid is an ISO VG10 Oil.
    Attachments
    ISO VG10.zip2.0 KB
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    - Wayne Matus @ Joshua Thompson on Jan 8, 2021 4:30 PM
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      I am not sure if it is. I was able to import it bout not sure it had all of the data. , When I opened in notepad, it had non ASCI characters in it.
      
      I did look closer at the model and think there are two issues. One of the projects has an extra environment pressure boundary condition on a surface. That would make it with four openings, the one Total Pressure opening, the Outlet Volume flow on two surfaces, and then the environment pressure.
      
      So I looked at the other project. In it, I think you have a wrong Outlet Volume flow rate. You have 20 cubic meters per second. That seams like way too much for this size of model. Also, I am not sure if Flow uses that rate per surface or that rate would be divided by the two selected surfaces. I would have to run a test to see if volume flow rate is total or per selected surface.
      
      The other issue is that the outlet faces are real thin openings. It is almost a 4 inch bearing opening, .003 inch on the diameter clearance between shaft and bearing.. With flow, you need at least three cells across flow passage ways. I have been experiementing in getting that to happen and have not been successful yet. Once, it would error out on mesh creation. Second try meshed it with 30,000,000 cells and it failed in the prep for calculation.
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      - Joshua Thompson @ Wayne Matus on Jan 8, 2021 5:14 PM
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        Hi Wayne,
        
        Thank you for your feedback.
        The project with environment pressure was a thought after i got the negative pressure as I wasnt sure if solidworks thought it was a vacuum within the bearing. I was under the impression applying environment pressure i would be able to put the pressure of the environment in the environment of the bearing. Am I correct in thinking this?
        
        Going back to the original project, i will look at the outlet volume flow and see if there is another way of doing it or reducing the figure. Also, would it be a better option to create the computational domain around that 1 pocket which I am trying see the flow of oil in. Would this then increase the number of cells across the clearance but have a lower amount of cells to prevent any calculation errors and reduce the calculation and simulation time?
        
        Many Thanks
        Joshua Thompson
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Flow Simulation of a Hydrostatic Bearing Issues

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