3 Replies Latest reply on Jan 11, 2018 5:38 PM by Mark Keown

    Pressure drop too low?

    Phillip Laplante

      Hello,

       

      I have been working with a basic gas turbine engine (ignoring the fuel for now) and added these orifice plates around the flame can, to help even out the flow.  However, these plates should create a huge pressure drop (~2psi) that doesn't seem to be showing up.  Instead Solidworks tells me the pressure drop is .1psi.

      I have an inlet mass flow of 2.75lb/s, an enviromental pressure on the bottom outlet of 54lbf/in^2 and a bleed port on the left side with an outlet mass flow of .6875lb/s.  The rest of the settings are by default (laminar and turbulent, air, gravity, adiabadic wall, zero wall roughness, etc).  The mesh was set to automatic 7, giving me 1.6million cells and took 2 hours to run.

       

      Dropbox link to files *Project(9) is the one displayed below: Dropbox - Flame Can Assembly.zip

       

      Is this pressure drop accurate or is there something wrong with the simulation (boundary conditions, mesh, etc)?

      Untitled.png Untitled2.pngUntitled2.png

        • Re: Pressure drop too low?
          Mark Keown

          Trying to follow what you are trying to accomplish.  Is the bleed a constant? you are really only putting 2.06lb/s through.  Not sure where you are measuring the pressure drop.

          Closing the gap and closing the bleed will increase drop. This may not be addressing your issue at all.  I did not fully solve due to time.

            • Re: Pressure drop too low?
              Phillip Laplante

              The bleed is constant of 0.875lbs/s (30% of original flow) through the suppressed exit (as labeled in your picture), which yes would lower the drop as a whole, but I am confused at the oriface plates' pressure drop.  I know that there is a small gap between the oriface plates and the flame can, but that is intentional since we need to keep those parts from touching (due to the heat that the flame can would experience).  I am just wondering if that pressure drop from the 54.82 to the 54.72 in my first picture is accurate since I would think that the pressure drop just across one of those oriface plates should be in the range of ~5% (or about ~2psi).  Or is my pencil math that came up with that ~5% wrong.

                • Re: Pressure drop too low?
                  Mark Keown

                  Not sure how you calculated the pressure drop.  You have multiple paths all at the same time and what type of restriction is it? ( purf plate, contraction, corner?).  Flow resistance is a function of 1/Area²  so the resistance will change rapidly with changes in area.

                  The best thing to do is make a simple model with a purf-plate (or a single hole in a plate) and simulate that.  Gain confidence that Flow are close to calculated values (what mesh and goals are needed to obtain good results).  Use calculations form Idelchik or equal for determining the loss in the simplified model.  Blindly accepting the Flow results is NOT the way to go.