13 Replies Latest reply on May 16, 2008 8:32 PM by Bill McEachern

    drag and lift analysis of car model

    Anil Singh
      Hi Guys,

      I am currently trying to use cosmosflow to do some aerodynamic simulations of flow around a car model. I have been having some problems though and i wish i could get some help.

      1) Having stated my fluid velocity, how do i develop a moving road beneath the car to immitate a moving boundary.

      2) How do i make the wheels of the car rotate while running the simulations as it is important for me to study flow around the wheels and wheel housings as well.

      I would be grateful for any help. Furthermore, if anybody has case studies on car flow analysis using cosmos, please share or advice. I am in distress.
        • drag and lift analysis of car model
          Basil Gello
          Anil,

          I would try to answer your questions in the order you specified:

          1.) COSMOS/Flo can't operate with moving walls, so you have to specify a running fluid. You can specify the fluid velocity in General Parameters. To use the effect of moving road, you can apply the Real Wall condition.

          2.) You have to disable the wheels assemblies or parts in the Component Manager and make them the rotating region.

          I also operate with vehicle aerodynamics, and I prefer to use ANSYS/CFX or Fluent for that, cause it is much more powerful than CFW. But, if you want to make the study for training or education purposes, you will get enough accurate results.

          If you have any questions, don't hesitate to ask them.

          Regards,
          Basil Gello.


          P.S. What is the purpose of your modelling? Is it related to only aerodynamics or to more complexed things? Maybe you will paste here a screenshot of the model so I will be able to consult you?
            • drag and lift analysis of car model
              An Si
              Hi Basil,

              This is Anil Singh. I had some problems with my previous account and had to change it. Thank you so much for your reply. Yes i am actually doing a simple study to show how the rotation of wheels and the presence of wheel housing affect the aerodynamic properties of the car. I basically would like to have a few drag and lift values at the end of the studies. These are my queries for you:

              1) Assuming i have got a 3D model of the car on screen, what do i need to do to create a real wall? I cant seem to select the bottom boundary to make it a real wall. How do i go about creating a wall. Do i have to design another part in solidworks that can act like a road and assemble it to the wheels of the car?

              2) I tried disabling the wheels and making them rotating regions however i was given a warning that 'there is no fluid flow through the volume' when i was trying to solve. How do you specify the axis around which the wheel will spin in cosmos. When i tried, i could only type in the angular velocity.

              Regards,
              Anil Singh
                • drag and lift analysis of car model
                  Basil Gello
                  Hi Anil,
                  about the first task you have to create the simple plain part representing the road and to define its upper surface as a real wall. About the error with wheels, it is maybe because the wheel part is solid and there is no place for fluid or gas, besides CW interprets it as a rotating volume of fluid. So you have to define the all space in wheel envelope as a boundary part and make it the rotating region. The axis I prefer are the Z for rotation or a fluid flow direction.
                  Regards, Basil.
                    • drag and lift analysis of car model
                      An Si
                      Dear Basil,

                      I still have the following problems:
                      If lets say before i actually use a car model i just want to see the flow over a rotating cylinder with a moving floor, how do i go about doing it?

                      1) Firstly, how do i get the cylinder to rotate. I dont really understand how to get the wheel to become a rotating region. Am i correct to use a local rotating region setting in the initial cosmos project wizard? Do i also have to consider the wheel as a real rotating wall by setting a boundary condition with the same angular velocity of the rotating region. Can you explain what shape i could best use to envelope the cylinder to create a rotating region?

                      2) For the moving wall how big a part should i create? Does it completely have to be in the computational domain and cover the bottom of the domain or must i adjust the domain such that only the surface of the road is in the computational domain?

                      3) When i assemble the cylinder to the road, how should i assemble it. My cylinder is fixed and road is able to move along only 1 axis while being tangent to cylinder. Is that ok?

                      Also i do not have icq, do you happen to use MSN or email by any chance? And if you have any tutorial or example using cosmosflow for a car, i would appreciate it if i could take a look so i know the parameters. Basil thank you so much for helping me out. I am really short on time here and you so far have been my only help. Really appreciate it.


                      Anil Singh
                        • drag and lift analysis of car model
                          Basil Gello
                          Dear Anil,

                          I will look for a suitable tutorial for you among my works... if not I will compose the simple one what will help you to understand all you are asking for
                          However, you can mail a model here and I will have a look on it.

                          1.)
                          a) You have to define the mate of the wheel as a concentric/coincident combination of joints relative to the car body.
                          b) You really have to use local rotating regions, but you have to fix the body and make the wheels rotatable by the joints (see above).
                          c)And you have NOT to make intersections with the wheel and body, cause the region will fail. Also, you have NOT to place the wheels STRICTLY TANGENT to the road, because currently CFW does not support it and generates the error in this case. You have to UP them slightly (on 0.01 to 0.03 mm) over the road.

                          The shape of the region of rotation while keeping this rules can be the any.

                          2.) About the road part it has to be twice - three times longer than the car body, e.g for the car 4m long you have to design 8-10m long road. The size of the domain has to cover ALL the car ad the road NOT only the road.

                          3.) As I said you have to fix the road and car body and make wheels rotating.

                          Hope my mentions will be useful for you )

                          Regards, Basil.
                            • drag and lift analysis of car model
                              An Si
                              Dear Basil,

                              Hi this is Anil Singh from the solidworks forum. If you do have any examples, tutorials please send them to plasticbagkite@yahoo.co.uk. I have attached a image of a cylinder and road and emailed it to you. I want to imagine the cylinder to the be the wheel of a car and the rectangular plate to be the road.

                              1) When creating a moving wall, can i just select the top surface of the plate when setting the boundary conditions or do i have to select all 6 surfaces of the plate?

                              2) I am still very confused on creating a rotating region. How do i make the cylinder spin. How do i create the local rotating region. It would be good if you could show me an example and show me which faces of the part i need to select when making a rotating region

                              3) Do you know how i can learn to model a car in solidworks. I just need a simple car model. Maybe shaped like a honda civic.

                              Thank you very much Basil for your help. I hope i am not being to much trouble.

                              Anil Singh
                              • drag and lift analysis of car model
                                An Si
                                Dear Basil,

                                I hope i am not being too much trouble. I might need the example more than i thought as i just found out that my deadline for my initial report is in three weeks. I have come up with a lousy looking car model. I would just need to use your example to find out the settings for creating a rotating region around the wheels and for the moving road. Thank you so much for your help. Happy New Year!

                                Regards,
                                Anil Singh
                      • drag and lift analysis of car model
                        Tan  TS
                        hi Basil, i'm currently using CFW in simulating a naca0012 airfoil to obtain the drag and lift coefficient. did few simulations and i am unable to get the flow trajectories, cut plots, 3D profile plots, surface plots and isosurfaces etc. keeps prompting me " failed to complete". however, i am able to produce the xy plot.

                        is it something regarding the input data for boundary conditions?

                        regards

                        TS
                          • drag and lift analysis of car model
                            Basil Gello
                            Tan,
                            Are you running a simulation on 2D airfoil? Try finite-length wing and I an sure you will get the 3D plots. Also, have a look on VLAERO+ software. It gives more accurate results cause it uses the VLM method. Download the package and get a time demo license. Hope it helps. Also, you may have a look on Zhukovskiy profiles generator and calculator, but I have got different results comparing to its ones.
                            Regards, Basil
                          • drag and lift analysis of car model
                            Bill McEachern
                            you can do all you that want. Put in a part to represent the road and pick the upper surface make it a wall and give it a velocity equal to the free stream - just check the help for how to do this. This was added quite awhile ago. Same goes for the wheels but htey will get a rotational velocity in the direction of rotation. Use an appropriate roughness.