6 Replies Latest reply on Feb 16, 2018 4:32 PM by Tom Cipollone

    Flow simulation: Can there be velocity from two directions simultaneously?

    Tom Cipollone
    Tom Cipollone Feb 16, 2018 1:04 PM

      In other words, can I subject an object/part to two distinct gas vectors at the same time? This is very important in terms of aerodynamic design work (propellers/wings).

      For example, when using the flow simulation wizard I can see a way to set up a vector in the XYZ direction. However, what I desire to do is to set up at least two of these vectors.

       

      Thank You

      Tom

        • Re: Flow simulation: Can there be velocity from two directions simultaneously?
          Bill McEachern
          Bill McEachern Feb 16, 2018 1:42 PM (in response to Tom Cipollone)

          Are you after an angle of attack? Just put in the two components and you have it.

            • Re: Flow simulation: Can there be velocity from two directions simultaneously?
              Tom Cipollone
              Tom Cipollone Feb 16, 2018 2:26 PM (in response to Bill McEachern)

              Thank you for the reply. Is creating two vectors a "simple" matter of creating two different boundary conditions? That would be nice.

               

              In answer to your question, yes, I am after angle of attack, as a final result, but for different vectors of relative wind.

               

              I'm going to assume that you know that it is much easier to simulate angle of attack for a wing than it is for a prop. I need the two vectors because one is from the forward direction and one will be from the vertical direction (with an equation being used to simulate the increase in speed of the wind relative to the radius of the prop).

               

              Tom

                • Re: Flow simulation: Can there be velocity from two directions simultaneously?
                  Bill McEachern
                  Bill McEachern Feb 16, 2018 3:18 PM (in response to Tom Cipollone)

                  In the initial conditions dialog you can specif the components of the vector for X, Y & Z. For the propeller you can use a rotating region (rotating frame approximation - azimuthal averaging) around the prop set to the speed of the prop (opposite direction). You might want to do some small experiments to ensure it all works the way you want. What are you try to figure out? This would help a lot as there are other options depending on what you are modeling/designing. If its the prop then the above might work, if the airplane then you could use and internal fan might do the trick for example.

                    • Re: Flow simulation: Can there be velocity from two directions simultaneously?
                      Tom Cipollone
                      Tom Cipollone Feb 16, 2018 3:53 PM (in response to Bill McEachern)

                      Bill, again, thank you for your reply. Clearly you have experience, which I am grateful that you are sharing.

                       

                      I am aware that one can use rotating regions in the manner which you suggest, but my aim is something more basic. I only want to show the resultant pressure gradient along the prop from the base to the tip. For example, in a wing, theoretically, if the angle of attack is correct, one would like to see an area of relative low pressure on top of the wing, resulting from Bernoulli, which will provide lift. For a prop, in order for the angle of attack to be somewhat constant over the length of the blade, there needs to be a twist, to account for the changing relative wind over the length of the blade as it rotates. I would like to show how the twist allows for this relative low pressure area to exist. Nothing more.

                       

                      I'm a retired electronics engineer, nearing the end of my A&P training (at the advanced age of 62). Since there are no video's on youtube showing precisely this, I decided to do the simulation myself.

                       

                      Regards

                      Tom

                        • Re: Flow simulation: Can there be velocity from two directions simultaneously?
                          Bill McEachern
                          Bill McEachern Feb 16, 2018 4:01 PM (in response to Tom Cipollone)

                          There is a global rotation option that will probably do what you want. It would be the prop in a rotating flow, I think you can add an axial component as well so the whole flow domain would be rotating as a helix. That should probably work. You need to select the global rotation option in the wizard. I have not used this myself so just do some coarse runs to make sure it is doing what you want.

                          A & P training? Not sure what that is. 62? Not so old.....you only have a couple on me.

                            • Re: Flow simulation: Can there be velocity from two directions simultaneously?
                              Tom Cipollone
                              Tom Cipollone Feb 16, 2018 4:32 PM (in response to Bill McEachern)

                              Thanks Bill, I'll research your suggestion in a bit. I'm not familiar with using the global rotation option myself, so as you say, it will take some trial and error.

                               

                              A&P means "Airframe and Powerplant (engine)" mechanic. It is an FAA certification. It is a 2 year program of vocational training that allows one to take a reciprocating aircraft down to the nuts and bolts, including the engine, and return it to service. I'm in a program with people, some of which, are almost the age of my grandson (not quite but not all that far). I want to buy a small plane but can't see myself bringing it to a mechanic every time it needs service, so I figured that I would get the certification. After nearly two years of crawling around, upside down, in small planes, in bad weather, I'm ready to be an engineer again :-).

                               

                              Tom