3 Replies Latest reply on Dec 12, 2011 3:48 PM by David Maxham

    Simulating Perforated Plates That Are Not on Domain Boundaries

    David Maxham

      I'm looking to simulate a perforated plate that is part of an internal subassembly within our electronic unit.  If I understand correctly, the perforated plate feature that's part of the electronics cooling module, must be used on either a fan surface, lid or other surface where an environmental pressure is specified.  That helps for those perforated plates that are on the external surface of our units and when we are modeling internal flows, but we have many situations where the perforated plates are internal, say, part of an EMI subassembly, where the perforated plate feature of Solidworks Simulation cannot be applied?

       

      Any ideas on how to simulate a perforated plate that is internal to the unit?  This problem of using a perforated plate in Solidworks also arises when we have an analysis where we don't want to consider the flow as internal since we want to model the external surfaces of the unit. I've started looking at using a porous material for the internal perforated plate but it seems like a lot of work.  I've been working in Flotherm for the last 12 years so I'm a little familiar with making numerical wind tunnel models of objects, but I'm not sure if the effort will pay off here.  Maybe there's an easier way?

       

      Thanks,

       

      Dave

        • Re: Simulating Perforated Plates That Are Not on Domain Boundaries
          David Paulson

          David,

           

          I use Flow 2009 and do not have the electronics module, but I do model air/gas spearation systems that use perforated plate that is internal and in the flow path.  I model the perforated plate to actual dimensions. hole size and spacing in SolidWorks and get good results from this method.  Obviously can add considerably to the mesh, and computational time will increase.  But you can also set some surface goals to determine the pressure loss due to the plate.  I do use porous media for wire mesh, but haven't tried it on perforated plate.  I guess you could always calibrate the porous media to yield the same PD as the actual perforated plate and your computational time will be reduced.

          • Re: Simulating Perforated Plates That Are Not on Domain Boundaries
            Bill McEachern

            I built a little "wind tunnel" (ideal walls with a reasonable length) and put in small bits of the perforated plate - say 4 holes by 4 holes. I then run a few studies - say 10 over the range of velocities of interest and get a pressure drop vs. flow rate curve. You can probably get away with 3 points) I then, in my system lelvel model put in a porous media with the properties I just computed. I usually thicken the plate in the model and adjust the depth parameter in the porous media definition to get the same properties with a much thicker plate. I do this to avoid having a lot of mesh cells through the thickness of the porous media. Works like a charm.

            • Re: Simulating Perforated Plates That Are Not on Domain Boundaries
              David Maxham

              David, Bill,

               

              Thanks for your helpful answers.  David - I've been running the model with the perforated plate as designed and I'm getting the same flow rate through the unit as I have when modeled with Flotherm.  I'm using Flotherm as the benchmark here since I've gotten good agreement with Flotherm and actual testing.  And I appreciate your point about the model size being larger with the actual perforated plate.

               

              Bill, I think I'll go ahead and try some wind tunnel modeling, as you've done.  The perforated section in our model is part of a sheet metal part that's typically .60 to .093 inch thick, so I'm wondering how I'll make out with a porous material that is the same thickness (or better said - same thiness?)

               

              On a related note, I located a copy of Idel'chik's classic on flow resistances - I'll pick it up from a local university library later tonight.  Although I haven't seen this reference yet, I understand that it's full of useful information for pressure drops versus different flow resistances, included perforated plates.  Maybe even some wire meshes?

               

              I'll keep you posted - thanks again, much appreciated!

               

              Dave