9 Replies Latest reply on May 6, 2010 2:42 PM by 1-DWWB94

    Simulating Jet Turbine Exhaust impinging on a plate

      I have been given a task to analyze the temperature distribution in a flat plate directly underneath the exhaust nozzle of a jet engine.

       

      In terms of thermodynamic properties, the jet is described by using the coefficient of convective heat transfer adjacent to the nozzle, the size of the impingement area, and the gas temperature.

       

      Becuase of my lack of experience with FEA in general, and especially FlowSimulation, I am not sure what tools are available in SW to do this.  My first thought was to use a fan, but I do not know the characteristics of the flow other than the diameter of the impingement zone and h.

       

      So, I settled on using a boundary condition, where I could specify direclty the coefficient of convective transfer.  To do this, I created a circular split on my surface and defined h inside the circle.  When I run the model, I get results that are not meaningful.  In a past exercise, I converted my h to a heat load, and placed a surface source on the surface of my flat plate.  When I run that model, I get a temperature distribution that is as expected, but the temperatures are too high, as the temperature of the plate reaches the exhaust temperature.  I know that this will happen at equillibrium, but not initially.

       

      The question is, I guess, then;  What "tools" or methods would you use with Flow Simulation if you had to model a jet of fluid (in this case, air) impinging on a flat surface.  in my case, I am given h, T and A.

       

      Thanks in advance for your assistance,


      Wes

        • Re: Simulating Jet Turbine Exhaust impinging on a plate

          Well, this seems to be a very popular thread, and while I haevn't yet received an answer, I thought I'd post what I have learned so far for the enlightenment of all.

           

          1.  The only method that I have found that works in a manner that seems reasonable is when I create a split sketch on my surface, and apply a convective boundary condition at that location.  Since h is prescribed, in this case, I apply that value to the surface where the jet would impinge.  This leads me to solutions that I can believe, as the surface temperature where the jet impinges is just slightly below the temperature of the gas in the impinging jet.

           

          2.  Any attempt to model the system using a fan with data from real Jet Engines, compression ratio, mass flow rate, etc, results in Mach Numbers that are like 1.34E23.  This, obviously, is meaningless.  Further, the temps that the solver calculates in these cases come up to E 33 values.  Again, meaningless.

           

          I'll post more as I learn, as I feel that this is an interesting topic.  Feel free to weigh in here, even if you haven't got the solution.


          W

            • Re: Simulating Jet Turbine Exhaust impinging on a plate
              Bill McEachern

              Hi Wes,

               

              I haven't got a great idea of what you are after but if you know the heat transfer coefficient and don't really care much about the actual flow then you can shut of off the flow part and just do a conduction problem with the convection coefficient. You can use the fea tool for this.

              If I was running the flow code I would put in a model of the jet (say a solid rod) and I would assign an inlet and an out let to the tube that matches the inlet and outlet conditions to the jet engine. The fans are primarily for electronic cooling or ventilating apps where the pressure drop the fan is working against determines the fan operating point. It isn't a good use for modeling a jet engine.

              Why are you pointing a jet engine at the ground by the way? If might be helpful to know what the objective is. further, if you use the flow code you do not need to know "h" - the flow code will figure it out for you. It will show you the variation of h spatially on the plate once you get the right sort of flow happening. This is a pretty simple problem really.

              • Re: Simulating Jet Turbine Exhaust impinging on a plate
                Derek Bishop
                You will probably find that there are not many people on the forum who understand what you are talking about at the moment. Hence the lack of responses. I am not familiar with Flow Simulation. I use the Structural Simulation. Suggest that you have a good idea of the answers to expect from hand calculations. You seem to be doing this. As the saying goes. To err is human. To really screw things up you need a computer. The problem sounds interesting though. To add to our interest in reading your progress how about adding some annotated diagrams or sketches. We might learn something! Also once you post your results all the arm chair critics will have a chance to point out the flaws in your methodology.
                  • Re: Simulating Jet Turbine Exhaust impinging on a plate

                    There is plenty of literature out there approaching this problem from the analytical or empirical approach, so I have a pretty good idea of where I should land at the end of the simulation.  We've shelved this project for now due to lack of funding, but we might pick it up again.  If we do, I'll certainly keep the community abreast of my attempts to solve this.

                     

                    Thanks,


                    Wes

                  • Re: Simulating Jet Turbine Exhaust impinging on a plate
                    Drew Castle

                    I'm always interested in seeing other peoples' results for problems like this. I am consistently running into problems where I know what the results *should* be, but even with all the information can't get the numbers to line up right. While this sounds like a relatively simple problem, I'm sure after attempting to solve it I would be in the same position you are. I like Bill's solutions, as they sound exactly like what I would have tried.

                     

                    Good luck, and keep us posted.

                     

                    D.

                    • Re: Simulating Jet Turbine Exhaust impinging on a plate
                      Rich Bayless

                      Hello,

                       

                      (sorry I missed the beginning of this one)

                       

                      Previous work like this has been done to study heating metal with a flame and also heating of a vehicle heat shield during reentry from orbit.

                       

                      Have you done some literature searches on "flame impingement heat transfer"?  Look for authors such as Sibulkin and Hustad.  They came up with some equations to calculate "semianalytical solutions" for flame impingement.

                       

                      see attached example of a nozzle spraying a flame on a flat plate.

                       

                      Cheers,  Rich.