11 Replies Latest reply on Dec 11, 2013 11:57 AM by Jared Conway

    Inaccurate results - suggest a solution.

    Sahajkumar Panchal

      Hi,

      This is Sahaj from Ahmedabad, India.

      I've been trying to simulate a nozzle with one inlet and 48 small exit holes. I've created a domain around the nozzle with a single exit face instead of 48 individual exits to study the flow behavior inside it, but I'm getting inaccurate results as compared to the practical data. Small variation is allowed but the simulation results are almost doubled than those obtained in a lab test! Practical data shows velocities to be roughly 25-30m/s whereas SolidWorks states it to be 70-80m/s. Increasing the initial mesh accuracy increases the values even further.

      What could possibly be wrong? I've attached an image to give you an idea about it. Am I performing the simulation incorrectly? What would be a work around for this?

      Any help would be appreciated.

      Thanks,

      Sahaj.

        • Re: Inaccurate results - suggest a solution.
          Chatura Elkaduwa

          Hi Sahaj,

           

          I tried the setup you've shown in the attachment, with a similar model.

          In my case, I defined it as an external study with environmental conditions specified as ambient conditions and left the outlet holes open; and the resultant maximum flow velocity was around 24m/s.

           

          It was a coarse (level 3) mesh; with a refined mesh, I would expect it to slightly increase.

           

          If you continue to face the same issue, upload the model with your setup for us to take a look at it.

           

          model.jpgcomp_domain.JPG

            • Re: Inaccurate results - suggest a solution.
              Sahajkumar Panchal

              Hi Chatura,

              Unfortunately I can't give you the geometry, but to give you a basic idea - it's a 2m(L) by .170m(W) by .230m(H) body with 48 holes of 17mm dia, 24 holes in two rows and with 1mm wall thickness

              Inlet conditions I'm specifying are the velocity inlet, fully developed flow - 20m/s and the default environmental conditions with initial conditions default as well. Wall roughness is 6.3.

              I've also tried performing an external flow simulation but it didn't work at refined mesh. I've even tried creating local mesh with certain level of refinements - but nothing. Velocities are much higher than expected.

              FYI - I'm creating 'caps' as shown to get velocity and other output parameters at each holes. These 'caps' were than excluded from the analysis, as they were nothing but individual bodies. Then creating surface parameter results will give me values like velocity, mass flow etc.

              Please let me know if anything seems wrong.

              Thanks,

              Sahaj.

              Capture.JPG

            • Re: Inaccurate results - suggest a solution.
              Jared Conway

              what is your convergence criteria? why did the solution complete? do the input properties look correct? do you have the environment at 101325 and your inlet at 101325?