7 Replies Latest reply on Dec 8, 2016 3:12 PM by Txon Aguirre

    Propeller flow simulation. Wrong force/torque

    Odd Ramone

      Hello people

       

      I`m quite new to the "Flow Simulation" part of my SolidWorks 2014. So when I tried to simulate my first part, a propeller, I followed this YouTube video:

       

      propeller thrust and flow trajectories using solidworks flow simulation - YouTube

       

      I don`t know the language, but I just followed the video:)

      The propeller is made from 4 separate parts. So I made a assembly of all the parts, also the big round extruded part that surround the propeller. And after that I run the simulation like the one att the youtube video.

       

      Everything seams good so far, except one thing. I use the "Goals" function to find out how much force/torque that is needed to run this propeller in water att 540rpm. But when I try with "SG Torque (Z) 1" I get the value 39 884Nm. And that`s absolutely wrong, because I have used this propeller in real life with a engine. And that engine deliver 2000-3000 Nm att maximum. So what have I done wrong? Really hope anyone can help me!:)

        • Re: Propeller flow simulation. Wrong force/torque
          Jaja Jojo

          I think your RPM is to high 540rad/sec is equivalent to about 5000RPM. Is the propeller can be crank up to 5000RPM?, What is RPM of the propeller you use in real life?

          • Re: Propeller flow simulation. Wrong force/torque
            Amit Katz

            Keep us posted Odd. I have seen this issue come up several times in these forums, and I've yet to see somebody reproduce actual physical testing results with the software. There is usually a 30-50% error.

              • Re: Propeller flow simulation. Wrong force/torque
                Odd Ramone

                Hello. It took some time, but I just did some new simulations on the propeller. Here is a picture of the propeller simulation.

                 

                rondell353_kraft.jpg

                First; I`m not quite sure what all the numbers mean.

                Min, max, averaged value and value I guess is the value of how much force is needed to turn the propeller round at 540rpm in water?

                What about the Delta and Criteria numbers, what are they? But all the numbers on this measurements where to high, because the motor torque output is about 590NM. So something isn`t quite right.

                 

                But I made a new simulation, with much bigger "Computational Domain" and bigger "Extruded boss" (cylinder where the propeller is inside). That helped to get more realistic resaults.

                rondell353(2)_kraft.jpg

                The Delta and Criteria numbers are very close to the real numbers, but what exactly do they mean?

                  • Re: Propeller flow simulation. Wrong force/torque
                    Amit Katz

                    Sorry for the late reply, but I just wanted to address your last question.

                    Delta and criteria, these numbers have to do with convergence. "Delta" is the range of values recorded during the last X iterations, where X is your convergence interval. This number is usually determined automatically by the software, but you can set it manually as well. "Criteria" is the largest value of delta that is considered acceptable for convergence to have occurred, again this is usually determined automatically by the software. So in your case the software determined that a range of ~500 N force with an average of 3500 N was sufficiently converged. Not sure I would agree with that personally, it's a pretty big chunk of your average.

                • Re: Propeller flow simulation. Wrong force/torque
                  Txon Aguirre

                  Hi Odd Ramone, and Hi all, of course.

                  In most propeller simulations, the advance velocity is missed in the setup, arriving to wrong results. Did you set any Vz velocity ? Otherwise, what you've got is the "bollard pull", not the navigation condition of the propeller.

                   

                  Regards