2 Replies Latest reply on Mar 15, 2012 5:41 PM by Dan Hofstetter

    How to get nodal values from flow simulation?

    Dan Hofstetter

      I am currently taking a Finite Element Methods course, and wanted to set up a simple problem in Flow Simulation to compare results with values from a simple educational FEM solver and from hand calculations.  I set up a simple 2D problem using symmetry - flow between parallel plates around a rectangular obstruction.  By hand or when using the educational software, I come up with solutions to the system of linear equations for the various U values (potential for flow in this problem).  I don't see a way to get the nodal values that Flow Simulation must calculate when solving - is there a way I can find these?  The X and Y velocity components that Flow Simulation reports are close in value to my calculated values, but not exact.

       

      Another question I have related to this:  The mesh geometry (see attached jpeg below) for the problem I worked by hand had triangular elements.  Is there a way to force Flow Simulation to use a mesh based on a user-input list of coordinates for nodes so that I might get something closer to an exact match for the solution?  i.e. can I have Flow solve the problem using my own custom mesh? 

       

      Here is the six-element model.  The length of the top is 200cm, the left side is 100cm, and the rectangular obstruction is 10cm high x 20cm long (these are for the quarter section as shown).  Flow enters from the left hand side at 50cm/s.  I also did eight, sixteen, and thirty-two element versions of this to see how increasing the number of elements effects the final solution.

      Elements.jpg

        • Re: How to get nodal values from flow simulation?
          Bill McEachern

            I don't see a way to get the nodal values that Flow Simulation must calculate when solving - is there a way I can find these?  The X and Y velocity components that Flow Simulation reports are close in value to my calculated values, but not exact.

           

          Flow Sim is a finite volume code not a finite element code. Values are reported at the centers of the cells to thebest of my knowlegde. Also all plots are typically ellipticaly interpolated by default. I would suggest putting a sketch line through where you want the values and make a 2D plot and the values will be reported in the spreadsheet plot. Compare the profiles not individual locations would be my suggestion.

           

          Another question I have related to this:  The mesh geometry (see attached jpeg below) for the problem I worked by hand had triangular elements.  Is there a way to force Flow Simulation to use a mesh based on a user-input list of coordinates for nodes so that I might get something closer to an exact match for the solution?  i.e. can I have Flow solve the problem using my own custom mesh?

           

          Flow sim uses a structured orthoganal mesh with faceting at solid fluid interface. It doesn't work like your typical continuum mechanics code that typically develop a surface mesh first and then meshes the volume. Flow sim does it the other way round - it meshes the volume then defines the solid fluid interface on a cell by cell basis. So no you can't use any other shape cell other than a brick or a faceted brick.