3 Replies Latest reply on Feb 24, 2017 8:45 AM by Luis Alberto Salazar Salazar

    Surface goal without a surface

    Luis Alberto Salazar Salazar

      Hello, im working in a model of a dust collection duct line, im trying to estimate the VP equivalent of an elbow, for that first i need to find the diference in presure drop in both cases: first for a straight line without the elbowand next for the same lenght of duct but wit an elbow in the middle, i have a model for the straight line but in order to get the losses by produced in the entry of the duct i add a box with a bigger diameter and i specify the condition that you can see in the image, the quiestion is how can i specify a surface goal for the entry of the duct with out add a lid on that end of the duct? (surface goal2 in the image) i need to do that to get the static, total and dynamic pressures and also the z component of velocity.

      Wich pressure im getting when i run an x-y plot?

      Another question, why if i run 2 models one with a inner velocity (forced draft flow) and the other with a outer velocity (induced draft flow) (same value and same environment conditions) im getting different values for the static and the total pressures? (the model with the inner velocity gives me the same value that the one im getting making the calculation "by hand" using the ACGIH method).


      Best Regards

      Luis Salazar

        • Re: Surface goal without a surface
          Siavash Khajehhasani

          for your first question: if you want to have a face to be included into simulations goals, you can insets a dummy component and then exclude it from the analysis. About the 2nd question: please upload your simulation here if possible.

            • Re: Surface goal without a surface
              Amit Katz

              Yes, dummy geometry is the way to go here. You can turn off CAD geometry from being considered in your CFD model by using the "component control" tool.

                • Re: Surface goal without a surface
                  Luis Alberto Salazar Salazar

                  Hello, thanks for your comments, i already made that modification (dummy geometry), attached you can find 3 pages with the results.


                  The first page (R. Mott) includes the traditional method to calculate the delta p through the duct this gives a value of 0.114 inWg, this method considers that there are no changes in fluid velocity between points 1 and 2, this method also does not consider the losses caused by the entrance of the fluid to the duct.


                  The second page (ACGIH) includes the ACGIH method, this method considers lost by friction in the duct (0.157 inWg) and losses originated by the flow entering the duct (1.693 inWg), the total Static Pressure is 1.850 inWg


                  The tird page includes the flow simulation results

                  A.- forced draft flow: Delta SP = 0.166 inWg

                  B.- induced draft flow Delta SP = 0.139 inWg

                  C.- Study to take account of the duct entry loss Delta SP = 0.094 inWg


                  If i follow the ACGIH method to calculate the Total pressure = SP + VP i can solve the ecuation and obtain the Factor for the elbow i want to analyse, currently i only have the calcs and simulation for the single duct however as you can see there are a big difference in SP if i use the ACGIH method wich will affect the final TP, also i dont understand why im getting a lower value when i run the case C scenario

                  what do you think about all this guys???