14 Replies Latest reply on Mar 12, 2015 4:13 PM by Dhruv Malhotra

    fsae intake

    Dhruv Malhotra

      top centre final.png

      As seen in the flow trajectory, the flow in the c-d nozzle isn't uniform in the end which results in much more flow entering the second(from left) runner. On what basis does solidworks makes this analysis, as conventionally flow should be somewhat more in the middle two runners than the extreme two as they(middle) are more closer to the restrictor axis??

      In this case i am doing cfd for conservation of mass flow rate.

      Inlet bc: mass flow rate   

      Outlet bcs: env.pressure

      Rather the primary cfd i want to do is to check the pressure at the outlet(loss). That i discussed on another forum and answers came out to be env.pressure at inlet(that is also during practical conditions), and mass flow at outlet. Now the problem is that how can i decide the values of mass flow at outlet to put as boundary cond.as there is no uniformity of flow even between the middle two and between the two extreme runners?!?

      Dhruv Malhotra

      Engine deptt, Mechsonic Racing

        • Re: fsae intake
          Amit Katz

          Is this behavior consistent for further mesh refinements and higher density meshes? Did you try putting in goals on your outlets and seeing that they converge to consistent values? It is a strange outcome...

            • Re: fsae intake
              Dhruv Malhotra

              mesh cut plot.png

              This is centre plane cut plot. I chose result resolution to level 5. From the previous picture flow seem to get non uniform from the nozzle only. I don't understand at all what is happening! I don't know much about changing mesh settings  but just know the theory that more meshing is gonna make more grids which in turn will produce more accurate results.

              what to do?? 

                • Re: fsae intake
                  Amit Katz

                  Here is what I would do in your place.

                   

                  Start with resolution 3. Set mass flow rate goals for each outlet and then observe their convergence using a goal plot.

                   

                  Clone your project and go up another meshing level. Observe the results again and compare them to the previous run.

                   

                  Continue to do this until your goals converge to a specific value, then you can have confidence that your simulation is mesh independent. If you still have results that are unusual then the issue is something else.

              • Re: fsae intake
                Jared Conway

                i don't think i understand your methodology

                 

                are you using mass flow rate in and environmental pressure at the outlet or are you using the opposite?

                 

                I think you're trying to connect those 2 simulations together but I don't see how.

                 

                if you are using mass flow in and env pressure out, what are the actual mass flow rate differences between them? are you sure you're not just getting tricked by the flow trajectories?

                  • Re: fsae intake
                    Dhruv Malhotra

                    In this simulation I am putting mass flow rate at inlet and pressure at outlet, and then solving for conservation of mass and noting individual values of mass flow at runners. Doing this as I have no other value to put at outlet!

                    I wished to collect the mass flow values at outlet of diff.runners from the solver and put them as boundary conditions on another cfd where i will be checking pressure loss in the manifold( in this case i ll put env. pressure at inlet and then solve for pressure loss). I don't know if taking values from a solver of one cfd and putting them as bound. cond. in another cfd is right or wrong. But for doing that too, the values should be comparable according to the geometry.Then in the picture in my question, one can see that the flow is becoming non-uniform in the c-d nozzle only, resulting in heavy flow through one runner and less flow through other three.

                    Rather according to the geometry the flow should be comparable in middle two runners and should be somewhat less in the extreme two.. Resolution level chosen is 5 in this cfd with no other changes! What to do now?!?

                      • Re: fsae intake
                        Jared Conway

                        meshing looks fine.

                         

                        when you say different CFD do you mean a different program all together or another analysis within flow simulation? I don't see any benefit of your methodology either way as the problem should solve the same in both if you change tools or if you feed one problem into another.

                         

                        I think it would still be helpful to know what mass flow rate you are getting at each of the outlets and how much they differ and to look at a CUT PLOT of the results, not just flow trajectories.

                         

                        beyond that, I'd recommend looking into boundary conditions that you can trust. it sounds like you're throwing something at the problem and not really sure what the outcome will be.

                          • Re: fsae intake
                            Dhruv Malhotra

                            cut plot.png

                                     

                            Assem top centre.SLDASM [Project(1) [Default]]
                            Goal NameUnitValueAveraged ValueMinimum ValueMaximum ValueProgress [%]Use In ConvergenceDeltaCriteria
                            SG Mass Flow Rate inlet [kg/s]0.0750.0750.0750.075100Yes07.5E-05
                            SG Mass Flow Rate 1 [kg/s]-0.015745507-0.016637049-0.017334437-0.01553752321.9Yes0.000665660.000146002
                            SG Mass Flow Rate 2 [kg/s]-0.014182489-0.014457213-0.015294123-0.0138633465.9Yes0.0005072330.0003346
                            SG Mass Flow Rate 3 [kg/s]-0.015227955-0.01529089-0.015567729-0.01508267346.6Yes0.0003108010.00014497
                            SG Mass Flow Rate 4 [kg/s]-0.029841217-0.028614913-0.030160573-0.02687622641.1Yes0.0009678270.000398388
                            Equation Goal 1 [kg/s]-0.074997168-0.075000065-0.075004823-0.074994953100Yes4.00812E-070.000181225

                            Iterations:  200

                             

                            I meant another analysis within flow simulation. Well boundary conditions i am using are mass flow at inlet which is reference max.in the cd nozzle( calculated at throat at choke conditions) and pressure at outlet as recommended in solidworks tutorial.

                              • Re: fsae intake
                                Jared Conway

                                you have less than 50% convergence on your 4 goals if i'm reading things correctly

                                 

                                and only 1 of them is out of whack

                                 

                                did the software complete because the goals converged or because you hit max iterations/travels?

                                 

                                also i'm not following the reasoning behind the setup change

                                 

                                the method you have seems reasonable. most FSAE teams actually go a lot deeper and do time dependency to account for the cylinders firing. usually they only do pure flow on the CD nozzle

                        • Re: fsae intake
                          Dhruv Malhotra

                          100% convergence is just reaching for the inlet( bound. cond.) and the equation goal. Others don't full converge but the calculation ends! And yeah, most fsae teams either go into deep and do time dependent transient analysis or just do cfd on the c-d nozzle!!

                          Rather can someone tell me some valid explanation about giving env. pressure at outlet? 'I dont have any b.c. at oulet that's why giving preesure' doesnt seem a logical reply!

                            • Re: fsae intake
                              Amit Katz

                              It doesn't seem like the simulation is converged. Check your calculation parameters and see that you don't have some failsafe stop like max travels/time/iteration...

                              • Re: fsae intake
                                Jared Conway

                                I'm not sure what you are asking about the environmental pressure condition. It is just a reference to tell the software fluid goes out there and it is a particular flow rate. Your analysis as it is defined right now says flow is coming in at a particular flow rate at the inlet and at the outlet flow goes out.

                                 

                                This is fine.

                                 

                                Like we've said a couple times, another analysis that i've seen is mass flow rate out using the flow rate from the engine. Generally this is cycled. This can be calculated. In this case the inlet would be environmental pressure.

                                 

                                But what you should focus on first is rerunning your simulation and telling the software in the calc control options to only stop when all the values converge.

                                 

                                And then second, sit down with your team and talk about how you would test this and what you know about that testing and how it would apply to setting up a virtual simulation that matches.