7 Replies Latest reply on Mar 16, 2013 3:53 PM by Jared Conway

    Conduction through rocket nozzle insulation and housing

    Addison Mauldin

      Hi all,

       

      I am learning my way with Simulation as I am new to this world.  I am trying to figure out how I can conduct a transient thermal analysis that will show the heat conducting through the layers of a rocket nozzle as a function of time.  Here is what I do know upfront.  I know the stagnation (recovery) temperature at several locations through the nozzle along with the material properties.  I also know the heat transfer coefficients for each of the given areas where the insulation is coming in contact with the combustion stream.  Is this something I could run by applying my initial temperature condition and by some way using the heat flux under the thermal load options?  Again, new to this world and appologize for my lack of understading.

       

      Thanks

          • Re: Conduction through rocket nozzle insulation and housing
            Addison Mauldin

            I think I have it figured out.  Instead of running with the heat flux, I think switching over to a convection load would be better.  I know the convection coeffiecients at several locations along the axial direction of the nozzle.  At these sames locations I know the stagnation temp.  I assume I can set the stagnation temp as my bulk ambient air temperature (~5900 deg F) for the duration of the motor burn.  In other words make the bulk ambient air temp time dependent at the known surface locations inside my nozzle.  Does this seem logical?

              • Re: Conduction through rocket nozzle insulation and housing
                Bill McEachern

                Yes. If you have the Sim Premium product you maybe able to do a 2D axisymmetric model - might run a lot quicker if htat is a suiatble assumption. Any radiation going on or is it just smeard out in the convection coefficients that you are using? If only conduction then the time steps can be rather large with out running into much inthe way of issues.

                • Re: Conduction through rocket nozzle insulation and housing
                  Mike Pogue

                  It's been a long time, but isn't the stagnation temperature very different from the bulk temperature when the velocity is supersonic?

                  • Re: Conduction through rocket nozzle insulation and housing
                    Jared Conway

                    What are you calling the stagnation temp? I agree with miKe, double check the convection equation to make sure the bulk temp that flow uses matches your definition of stagnation temp.

                     

                    Something you might be missing is that you'll need to apply some split lines on the inside surface to apply your different convection coefficients. But you'll potentially have some discontinuities at the boundaries. This could be improved with smaller surfaces or running the fluid problem in flow feat and transferring the coefficients. But at that point, I'd you don't care about thermal stress, you can solve the whole problem in flow.

                     

                    As bill mentioned, if you want thermal stress over time, you need to go nonlinear. And simplifying down to 2d will solve your problem fast. Both are part of sim premium.

                      • Re: Conduction through rocket nozzle insulation and housing
                        Addison Mauldin

                        I am attaching a graphic that I hope explains what I am dealing with.  I got some clarification on what I have been calling stagnation temperature...It is actually the recovery temperature at each of the surface locations within the nozzle.  I guess this goes back to assuming boundary layer theory at surface locations (temp/velocity gradient_flow zero at surface).  As said before, I have tabular data for the heat transfer coeff and Trec as a function the rocket motor burn time at each of these locations too.  Do I set this Trec as a function of time in the bulk temp box of the convection load?  I guess the way I am going about would be to do a different time varying heat trans coeff for each nozzle location,  associated with time varying bulk temp.

                         

                        Also noticed when I clicked on the time variation button under the bulk temp box, it said data must be entered in the columns as time vs temp (in K).  Is it different than entering time vs. some multiplier as you do with other time varying selection boxes within Simulation?

                         

                        Jared....I have set up split lines for my model just for the reason you explained.  I also am running Simulation Professional 2013 x64 SP1.0.  I do not care about thermal stress, as that is for another day and time.

                         

                        Nozzle_Capture.JPG