11 Replies Latest reply on Jun 23, 2010 2:48 AM by Ameer Chilakala

    Warning Errors

    John Ashton
      I often get the warning: "A vortex crosses the pressure opening". The results of an analysis when this warning is displayed are generally suspect.
      I have tested physical models equivalent to the 3D flow models and I know they work much better than the analysis results (when warning is present). How do I deal with this problem? Refine the mesh? Other comments?

      Thanks,
      JA
        • Warning Errors
          Bill McEachern
          take a look at the whole warning message. At the far right it will give the ratio of the inflow to the outflow. If htis number is small thatn I would say you are safe to ignor ehte message. Otherwise extend the domain to contain the wortex. Put a room after it if that is wat happens....well not quite but a bigger space or extend the out let geometry. It should be a big problem typically.
            • Re: Warning Errors
              amar nivarthi

              I am also having the same problem. I keep getting the error at the out let where I have specified environment pressure condition (also tried static pressure condition). I extended the outlet duct from 25mm to 100mm but am still getting the same error. Also the ratio of inlet to outlet flows at the vortex is 0.19. are the results still acceptable? Is there any other way of getting rid of this error?

                • Re: Warning Errors
                  Bill McEachern

                  it is not an error it is a warning. typically it is not a big issue unless you are very interested in the area near where it is occurring. Otherwise extend the domain to contain the vortex or move the boundary away from the area of interest.

                    • Re: Warning Errors
                      amar nivarthi

                      thanks for the prompt reply bill. It's just that the solidworks documentation(read tutoril) states that such a warning indicates that the results might not be reliable. Also I was wondering why lengthening the duct did not get rid of the warning? And could you tell me if I should continue with environment boundary condition or use the static pressure condition?

                        • Re: Warning Errors
                          amar nivarthi

                          Hi Bill

                           

                          The reason I am interested in getting rid of the vortex warning is because I am interested in the total pressure drop across the system.

                          • Re: Warning Errors
                            Bill McEachern

                            Env BC is static out total in.

                             

                            At some length of duct the message will go away - it might be something like 10 diameters at most, and probably only a few. I haven't seen what is being modeled so take it all with a grain of salt.

                             

                            What is the ratio of out flow to inflow? Expand the message and it will tell you. If it is small like 1 or 2 percent I wouldn't worry about it.

                              • Re: Warning Errors
                                amar nivarthi

                                Hi Bill

                                 

                                 

                                I have attached the model I am working on. Please do take a look and let me know if the total pressure drop in

                                this model is unaffected by the vortex at the outlet BC.

                                 

                                Thanks

                                Amar

                                  • Re: Warning Errors
                                    Satit Nilyai

                                    I have question in the model. In original model chamber outlet , How many size? "(width x length) of chamber ?

                                      • Re: Warning Errors
                                        amar nivarthi

                                        Hi Satit,

                                         

                                        The chamber is 12mm dia by 25 mm length and outlet pipe is 14mm dia by 100 mm length.

                                         

                                        @Bill

                                         

                                        Thanks  a lot. the vortex did indeed disappear at about 6 diameters length. I did have one more Q though,

                                        I am getting significantly different numbers when I run the same simulation twice (the entire configuration stays

                                        the same). I remeshed and ran a new calculation each time. Is this differerence in numbers (pressure drop) a

                                        function of the way solidworks solves the problems or is there something I should change in the calculation control options?

                                          • Re: Warning Errors
                                            Bill McEachern

                                            it could be a lot of things. The numbers should not change for identical setting and mesh though. Like all other simulations you should increase the mesh density till the numbers stop changing. I would not change any other setting when you do this though. Try reading the Solving Engineering problems guide in the lang section of the install directory.

                            • Re: Warning Errors
                              Ameer Chilakala

                              Hi,

                               

                              for your issue this is the solution from solidworks.

                               

                              When flow both enters and exits the same opening, the accuracy of the results will worsen. In such cases, one would typically add the next component to the model (such as a pipe extending the computational domain) so that the vortex does not occur at an opening. Or the user can apply an Environment Pressure boundary condition at the opening which improves the accuracy at the vortex flow.

                               

                              The Environment pressure condition is interpreted by COSMOSFloWorks as a total pressure for incoming flows and as a static pressure for outgoing flows. If, during calculation, a vortex crosses an opening with the Environment pressure condition specified at it, this pressure considered as the total pressure at the part of opening through which the flow enters the model and as the static pressure at the part of opening through which the flow leaves the model.