4 Replies Latest reply on Jul 17, 2013 3:55 PM by Jared Conway

    Question about flow simulator

    Ariel Elboim
    Ariel Elboim Jul 17, 2013 12:21 PM

      I dont understand whats going on with the angle of attack?????

       

       

      Dear whoever can help,

       

      I have recently started using solidworks to model flow around an s809 aerofoil and my results for Cl and Cd are very different when i change the angle of attack by either changing the velocities in general setting or physically rotating the model!!!!!

       

      I do not understand why this is the case.

       

      If anyone has an answer or way to deal with it, or even suggestion as to which method i should use i would be very appreciative

       

       

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        • Re: Question about flow simulator
          Bill McEachern
          Bill McEachern Jul 17, 2013 1:55 PM (in response to Ariel Elboim)

          aren't the values suppose to change with angle of attack? Or do you mean you get different values depending on how you change the angle of attack?  If it is the latter it would not be surpising. While it is possibly a bit less convenient chanigng the velocity components to get the angle of attack you want it would be the preferred methond at least for low angles of attack as the meshes will be identical. Changing the angle relative to the global coordinate system will require a new mesh on each run, hence mesh induced errors may occur. Getting a fine enough mesh in either case is probably required to get close to experimental values. Still getting close values for the "Somers" series migh be a bit tricky as they are typically tailored to deal with some aspect of low to moderate R' numbers - like laminar separation bubbles. Not that I have checked it out in Flow Sim but I would not expect it to capture such phenomena.

          • Re: Question about flow simulator
            Jared Conway
            Jared Conway Jul 17, 2013 1:56 PM (in response to Ariel Elboim)

            are you saying Cl and Cd change when you change the angle of attack? because the is likely going to be the case.

             

            or are you saying the values aren't what you expect?

             

            if the latter, i'd start by checking the solidworks knowledgebase. there are several articles about this. if you're expecting the results to be exact, you're going to have to reset your expectations. that being said, if you follow the recommendations with respect to the meshing and size of the computational domain you should be able to get reasonable results and also good trends between studies. there are mayn discussion about this on the forum. check for one recently by someone looking at 2d wing sections.

            • Re: Question about flow simulator
              Ariel Elboim
              Ariel Elboim Jul 17, 2013 3:52 PM (in response to Ariel Elboim)

              i am getting very different results when changing the method of which i change the angle of attack

               

              method 1: change velocity vector

              method 2: change angle of aerofoil wrt coordinate system

               

              I have attached a localized mesh to the aerofoil which rotates with it when i physically move the blade. This result gives me results that are similar in shape to what i should expect the Cl and Cd curves to look like, just underestimated. I assumed that changing the velocity vector would cause the flow to come at the mesh from and angle which may not be captured as well in the simulation, plus the flow seperates anbout 6 degrees to early in this scenario?

               

              p.s how accurate can i expect to get my results as i am trying to validate them against experimental. I am currently at about 40-50000 cells about 10000are on the local mesh. i dont have a huge amount of time to simulate either and this is kinda my limit in terms of the cpu power i can use