3 Replies Latest reply on Dec 17, 2013 10:35 PM by Jared Conway

    still air = .2 m/s ?

    Mark Keown

      I see in some papers that for equipment that is to be tested in still air (natural convection) one of the domains will have a 0.2 m/s velocity.  I'm not sure if that is vertical or horizontal.  Is this best practice or your comments.  Cheers.

        • Re: still air = .2 m/s ?
          Jared Conway

          still air to me means 0 m/s to start and then let the software determine what the flow velocity is based on the buoyant forces

            • Re: still air = .2 m/s ?
              Mark Keown

              What I was getting at was the comparison between CFD and the real world.  I will have some gear made and then put it in a heat chamber or a room with a fan, convection off the walls, HVAC , a window…  MIL-810 considers 0.2 m/s ‘still air’.  So what is best practice in CFD?  Secondly putting in some velocity initially and then taking it out after 20 iteration may help to solve quicker.

                • Re: still air = .2 m/s ?
                  Jared Conway

                  If you perform an internal analysis your input of 0.2m/s is just an initial condition anyways. If the final answer is near 0.2 you will iterate it to it faster but the results will be based on the buoyant forces. If you want to maintain 0.2 you'd have to add a fan or similar. And if that was the case, I'm sure it would be called for in the standard. But if you are comparing flow to physical, a sealed box is as I described above. Gravity on only, add initial conditions if you wish but not required.