9 Replies Latest reply on Sep 19, 2014 2:56 PM by Jared Conway

    Flow through webs/thin material

    Amit Katz

      I have a model of a transfer roll which has already been simulated:

       

      cad.PNG

       

      I would like to add to this model a thin web of material that wraps around the face of the roll and see how that will affect the flow of air. I have experimental data regarding the speed of air that flows through the web for a given pressure difference.

       

      What would be the best way to approach this problem? My gut feeling is to model a thin shell and define a custom porous medium for it, but ideally I would like the material to be a simple planar resistance to flow. I don't want to get a lot of cells in the thickness of this material because I really don't care what happens inside of it, I just want to know how much pressure there will be on the wide surface normal to the roll.

        • Re: Flow through webs/thin material
          Jared Conway

          "simple planar resistance to flow"

           

          what do you mean here? are you saying like just telling the surface that it has a resistance vs modeling the part and applying the porous medium? i think i'm confused because you are saying "planar" when this is cylindrical.

           

          but in the end there are really only 2 ways:

          1. porous medium

          2. perforated plate

           

          maybe you need to consider making a "combined" porous medium that includes the surface that you want to add and the existing part

            • Re: Flow through webs/thin material
              Amit Katz

              Yes, it's not planar but rather the outer face of the cylinder that I was referring to. I would like just a resistance across that surface. I know it's possible in other CFD packages I've used, but SolidWorks seems to lack that capability.

               

              Perforated plates wont work, because I have an environmental lid over the assembly, rather than a boundary condition at the face of the roll. I suppose porous media are way to go.

            • Re: Flow through webs/thin material
              Amit Katz

              Well for a anybody who is curious, I managed to make this work with porous media. I'm not crazy about this implementation, however, because I was forced to make my porous fluid thicker than my original sample size (using the original sample thickness results in a non-converging simulation). This means that I'm probably not getting very accurate results.

                • Re: Flow through webs/thin material
                  Jared Conway

                  i don't understand this comment.

                  how thick did it start?

                  how thick did you have to make it?

                  what are the thicknesses relative to the other geometry?

                  what about relative to the size of the elements?

                  what does non convergence mean to you?

                    • Re: Flow through webs/thin material
                      Amit Katz

                      The sample I used to establish the flow data is very thin (it is a web after all), approximately 1 mm thick. When I created my custom  porous material I used the area and thickness of the test sample as in input parameters (for the flow, pressure, dimensions type of media.)

                       

                      Originally the web in the model was the same thickness, 1 mm, but this did not work. I tried making a very simple model of a box with negative relative pressure at one face and a web covering this outlet, and I got the same results. The solution would not converge (I flagged global static pressure max as a convergence goal, and it simply kept climbing and climbing to ridiculously high numbers.) I noticed that setting the material thickness to more than the thickness specified in the material definition gave a more reasonable answer, though the airflow still does not line up very well with what I would expect given the experimental data.

                       

                      The size of the web in the model of the roll is quite thin. 2 mm compared to the roll which has the diameter of over 500 mm.