19 Replies Latest reply on Jan 10, 2014 10:29 AM by Rodrigo Jimenez

    what's wrong in this simulation setup

    Rodrigo Jimenez

      Hi all.

      I've modeled a formula car, in the better way I could, but i've been struggling to make the flow simulation working without lucky.

      I've configure a air flow in X direction of 50m/s, with 3 boundary conditions (ground, front and rear wheels).

      ground at the same speed and direction of the flow.

        and the wheel the equivalent radians over axis which cross the center of the wheels.

       

      Moreover i can no find the static preassure as parameter in the results surface, cut plots etc...

      How i can solve this?

       

      Here is a example that shows that something is not working properly in the simulation.

      (cut plot of top plane (centerline of the car about flow velocity)

      Seems the the front wing the aft bodywork and many other parts are not covered.in the plot.

      What i'm doing wrong now

      I also attached the project, if somebody wants to have a look,

       

      [IMG]http://imageshack.us/a/img819/2972/3y41.jpg[/IMG]

      [IMG]http://imageshack.us/a/img17/5025/s71l.jpg[/IMG]

       

       

      Thanks.

      Regards, Rodrigo

        • Re: what's wrong in this simulation setup
          Jared Conway

          pressure parameter = static pressure

           

          what do you mean by "not covered"? it looks like to me that your scale is too broad that you can't see the changes. if you change the scale so that you're only seeing the values that are green, you'll see some changes around the front wing for example.

           

          you may want to look through the forum, there have been several posts on this type of problem. to get good accurate results, you're going to need to simplify this assembly further, make the comp domain bigger, and add a lot more cells. you also will want to fix some of the surface bodies in this model because flow will not recognize them.

            • Re: what's wrong in this simulation setup
              Rodrigo Jimenez

              Hi jared

              About the static preassure, I can not find it, only i can select total preassure, dinamic preassure, relative preassure, but not the static preassure, I should add something at initial conditions to make it visible?

               

              With not covered, I mean that seems that has not recognized by the flow, anyway I 've made some fixes in the body, and at least after chech geometry and see the fluid solid, I can see all the parts of the car.

               

              Why I should increase the computational domain?, is not enough with 1 meter more for each side of the car, and 1,5 for the aft and rear?.

               

              I've set about 150 cells in X and 100 for Y and Z

               

              Anyway i 'm facing with many problem during calculation and mesh generation with the memory and I'm runing 64 bits win and sw with 4 gb ram.to resolve this I can simplify the model or also split the car in different computational domains and make the simulations separately ?


              I will have a look on other threads.

              Thanks

              Regards, rodrigo

                • Re: what's wrong in this simulation setup
                  Jared Conway

                  The parameter pressure is static pressure

                   

                  You could use half symmetry in this case

                   

                  As for comp domain, you probably need one length in front, 5 to the rear and 1 to each side and 1 to the top for Starters

                   

                  4gb will probably not be enough, you will probably have to deal with slow solve times unless you can simplify further. What exactly are you trying to learn?

                    • Re: what's wrong in this simulation setup
                      Rodrigo Jimenez

                      Basically i'm trying is to analalize some changes that i would like to introduce in my car, end plates wings, diffuser and other misc.

                      I simplified the model,removing some cavities from the bodywork, wheels, giving me una estamation of 1000 horas, mmm that is quite lot...

                      There are something when i remove a feature other one that is not related with, is removed also, and i can not find out why. any idea how i can know ?

                        • Re: what's wrong in this simulation setup
                          Jared Conway

                          hi rodrigo, 1000 hrs to solve wouldn't blow my mind, you have a pretty big problem. formula 1 teams throw millions of dollars at CFD to be able to replace wind tunnel testing. software, hardware and people cost a lot of money. my suggestion would be that rather than trying to solve the whole car problem, maybe look at some individual components and infer how they will affect the system.

                           

                          regarding your second problem, you'll have to elaborate

                            • Re: what's wrong in this simulation setup
                              Rodrigo Jimenez

                              Luckely. In my case is only a hobby   I'm not looking for something really accurate, only a aprox should be enough for me.

                               

                              Now having only half car in computational domain and (150,50,45) cells is running for 100 hours.

                               

                              Do you see something not correct or missing in this summary for this kind of simulations, and taking in account that i'm not looking for really accurate results ?

                               

                               

                              Initial Mesh Settings

                                              Automatic initial mesh:   Off

                               

                               

                                      Basic Mesh Dimensions

                                              Number of cells in X:   150

                                              Number of cells in Y:   50

                                              Number of cells in Z:   44

                               

                               

                                      Control Planes

                                              Control planes in X direction

                                              Name             Minimum             Maximum             Number of cells             Ratio

                                              X1             -2.293             -1.764             -             2.9764276

                                              X2             -1.764             5.180             -             1.0000000

                                              Control planes in Y direction

                                              Name             Minimum             Maximum             Number of cells             Ratio

                                              Y1             0.192             1.176             -             2.0786272

                                              Y2             1.176             1.334             -             0.4191351

                                              Control planes in Z direction

                                              Name             Minimum             Maximum             Number of cells             Ratio

                                              Z1             -1.344             -0.796             -             4.1151004

                                              Z2             -0.796             -0.268             -             1.0000000

                                              Z3             -0.268             0.259             -             1.0000000

                                              Z4             0.259             0.335             -             0.2461512

                               

                               

                                      Solid/Fluid Interface

                                              Small solid features refinement level:   5

                                              Curvature refinement level:   6

                                              Curvature refinement criterion:   0.644 rad

                                              Tolerance refinement level:   5 

                                              Tolerance refinement criterion:   0.001 m

                               

                               

                                      Refining cells

                                              Refine fluid cells:   Off

                                              Refine partial cells:   Off

                                              Refine solid cells:   Off

                                              Advanced narrow channel refinement:   Off

                               

                               

                                  Computational Domain

                               

                               

                                      Size

                                              X min:   -2.293 m

                                              X max:   5.180 m

                                              Y min:   0.192 m

                                              Y max:   1.334 m

                                              Z min:   -1.344 m

                                              Z max:   0.335 m

                               

                               

                                      Boundary Conditions

                                              2D plane flow:   None

                                              At X min:   Default

                                              At X max:   Symmetry

                                              At Y min:   Default

                                              At Y max:   Default

                                              At Z min:   Default

                                              At Z max:   Default

                               

                               

                              Physical Features

                                              Heat conduction in solids:   Off

                                              Time dependent:   Off

                                              Gravitational effects:   On

                                              Flow type:   Laminar and turbulent

                                              High Mach number flow:   Off

                                              Humidity:   Off

                                              Default roughness:   0 micrometer

                               

                               

                                      Gravitational Settings

                                              X component:   0 m/s^2

                                              Y component:   -9.81 m/s^2

                                              Z component:   0 m/s^2

                                              Default wall conditions:   Adiabatic wall

                               

                               

                                  Ambient Conditions

                               

                               

                                          Thermodynamic parameters

                                              Static Pressure:   101325.00 Pa

                                              Temperature:   293.20 K

                               

                               

                                          Velocity parameters

                                              Velocity vector

                                              Velocity in X direction:   50.000 m/s

                                              Velocity in Y direction:   0 m/s

                                              Velocity in Z direction:   0 m/s

                               

                               

                                          Turbulence parameters

                                              Turbulence intensity and length

                                              Intensity:   2.00 %

                                              Length:   1.000e-004 m

                               

                               

                                  Material Settings

                               

                               

                                      Fluids

                                              Air

                               

                               

                                  Boundary Conditions

                               

                               

                                          front wheels

                                              Type:   Real wall

                                              Faces:   Face<1>@Extrude left front wheel

                                              Coordinate system:   Global coordinate system

                                              Reference axis:   X

                               

                               

                                          Moving wall parameters

                                              Translation velocity:   0 m/s

                                              Angular velocity:   190.000 rad/s

                                              Direction:   Reference axis

                                              Reference feature:   Axis5

                               

                               

                                          rear wheels

                                              Type:   Real wall

                                              Faces:   Face<2>@Extrude left rear wheel

                                              Coordinate system:   Global coordinate system

                                              Reference axis:   X

                               

                               

                                          Moving wall parameters

                                              Translation velocity:   0 m/s

                                              Angular velocity:   190.000 rad/s

                                              Direction:   Reference axis

                                              Reference feature:   Axis6

                               

                               

                                          ground

                                              Type:   Real wall

                                              Faces:   Face<3>@Boss Extrude Ground

                                              Coordinate system:   Face Coordinate System

                                              Reference axis:   X

                               

                               

                                          Moving wall parameters

                                              Translation velocity:   50.000 m/s

                                              Angular velocity:   0 rad/s

                                              Direction:   Axis of coordinate system

                                              Axis:   Y

                                • Re: what's wrong in this simulation setup
                                  Jared Conway

                                  don't worry about gravity

                                   

                                  and to reduce the calc time, simplify your model further

                                   

                                  also to reiterate, if you're not going to improve the mesh or lengthen the comp domain, take the results with a grain of salt.

                                    • Re: what's wrong in this simulation setup
                                      Rodrigo Jimenez

                                      the gravity is not quite relevant, right ?. I Think i'm going to removed it.

                                       

                                      I'll try to simplify the model a bit more, but there are some features that i can not remove them, as other not related features are also beign removed

                                       

                                      improve the mesh means more cells ?

                                      what do you mean with grain of sal ?

                                       

                                      I also having messages about mach number exceeded.

                                       

                                      Yesterday i saw a warning (now has vanish i don't know how) about supersonic flow in a considerable amount of cells, how this can be.

                                      If my velocity flow is about 50 m/s ?

                                       

                                       

                                      Seeing the doc about flow freezing. maybe is possible to apply this feature from travel 1 permanently. in this case without affecting quite much the results. what do you think ?

                                        • Re: what's wrong in this simulation setup
                                          Jared Conway

                                          the gravity is not quite relevant, right ?. I Think i'm going to removed it.

                                           

                                          >>your flow is much stronger than any natural convection effects

                                           

                                          I'll try to simplify the model a bit more, but there are some features that i can not remove them, as other not related features are also beign removed

                                           

                                          >>this is always the case. you have to balance solve time with accuracy, this is one of the reasons i suggested looking at individual components and estimating the effect in the larger model. you could also look at EFD zooming.

                                           

                                          improve the mesh means more cells ?

                                           

                                          >>more cells and concentration of cells.

                                           

                                          what do you mean with grain of sal ?

                                           

                                          >>see above comment about balancing solve time with accuracy. if you do a bunch of coarse mesh runs, you can't assume the results to be absolutely accurate.

                                           

                                          I also having messages about mach number exceeded.

                                           

                                          Yesterday i saw a warning (now has vanish i don't know how) about supersonic flow in a considerable amount of cells, how this can be.

                                          If my velocity flow is about 50 m/s ?

                                           

                                          >>if you have a small gap in the model or similar it could create a high flow in that one region. this is one reason i recommended generating a more simple model where you have eliminated these types of things.

                                           

                                          Seeing the doc about flow freezing. maybe is possible to apply this feature from travel 1 permanently. in this case without affecting quite much the results. what do you think ?

                                           

                                          >>don't think it applies in your case, you shouldn't need heat transfer in the solids enabled.