Week 3 Challenge : CFD meshing on Turbocharger

1] AIM -

To generate volumetric mesh for the given turbocharger model.

2] OBJECTIVE -

* To perform geometry checks and check for single cons.
* To perform topology cleanup,generate PID's and generate surface mesh.
* To generate volumetric mesh from the surface mesh.

3] INTRODUCTION -

ANSA is a computer-aided engineering tool for Finite Element Analysis and CFD analysis widely used in the automotive industry.It carries several proprietary algorithms for meshing suitable for both CFD and structural models.

                              

We have been provided with a CAD model of a turbocharger with some geometrical errors.As from the model we can see there are many single coons(in red) and glitchy surfaces are present,which we need to resolve before performing meshing operation also,we need to patch any open surfaces as in CFD analysis surfaces should be close to do volumetric mesh.There are also some default PID's which we will delete to create our own PID's.

4] PROCEDURE -

4.1] Topology Cleanup -

As we open our model in ANSA,first we will perform checks on the geometry to see all the errors that are present in the model .Beside script tool there is arrow botton,click on it and select ckecks and select geommetry.Then from the bottom part of the window we will select the things which we wants to check then click execute.We can see many errors listed.Lets resolve them.

                            

First we will use topo tool.Topo is opposite of release.Release will create 2 single cons from a double con and 3 single cons from a triple con.Topo will do the same in opposite manner i.e. from 3 surfaces it will create triple con and from 2 surfaces will create double cons.Topo is useful when, we see triple cons but there are no overlapped surface then we can release and do topo again just to show  that there aren't any triple cons present or any overlapped surfaces present.

For Turbo casing first we will create multiple hot points using parametric option,then will create surfaces one by one as follows,
rom faces select => New => then use from existing surf,planar,fitted and coons options to patch the surfaces.We have created so many hot points to have smooth surfacea and to avoid intersection with already existing surfaces.

    

On rotor shaft there are many triple cons.They are caused by overlapping surfaces.Thus we will delete them to resolve the triple cons and also to create common volume for the blades and the rotor shaft. Overlapped surfaces may cause an error while going in the volumetric mesh.Once we go in the volumetric mesh ,we may get generation error,that error is basically showing us overlapped surfaces.

    

   

    

   

    

    

   

   

    

    

    

   

4.2] PID Creation -

Now lets create PID's which will come handy during meshing.To do that follow below procedure ,
Click Properties => right click and select New => select PSHELL => again select PSHEL => Give name as Compressor casing => ok. Simillarly create turbo casing,inlet casing cover,blade stage 1,blade stage 2,impeller,shaft rotor,casing inlet,casing outlet , bottom casing inlet and bottom casing outlet PID's.

Now ,to assign each PID to it's respective part follow below steps,
Right click on PID name => Apply => select the respective part => click middle mouse button to confirm. Simillarly assign all the PIDs.

   

   

   

   

                                               

Now if we try to delete the shell properties we got an error as "Selected ID is used by a deleted face and can not be deleted" .But there aren't any surfaces showing after selecting show only for Shell_Property PID.Thus we will delete it using brute force .Thus select arrow symbol beside the measure tool and select compress then press ok.This will delete the unnessary PIDs.

4.3] Meshing -

Now here we need to create mesh for various PID's by using below data,
Blade stage 1 = 1 mm
Blade stage 2 = 1 mm
Impeller = 2 mm
Shaft Rotor = 1 mm
Turbo Casing = 5 mm
Compressor Casing = 5 mm
Inlet Casing Cover = 5 mm

A] Compressor Casing,Casing Inlet and Casing Outlet -

* CLick on Quality Criteria =>minimum length 3 mm and max. lenght 7 mm.
* Mesh Parameters => Target Length 5 mm and select element type as tria.
* In Perimeter and Macros set length as 5 mm.
*In mesh generation => Select Spot Mesh => Select Visible.

  

                                                             

B] Inlet Casing Cover,Bottom Casing inlet,Bottom Casing Outlet,Inlet Casing Cover -

* CLick on Quality Criteria =>minimum length 3 mm and max. lenght 7 mm.
* Mesh Parameters => Target Length 5 mm and select element type as tria.
* In Perimeter and Macros set length as 5 mm.
*In mesh generation => Select Spot Mesh => Select Visible.

C] Impeller -

* CLick on Quality Criteria =>minimum length 1 mm and max. lenght 3 mm.
* Mesh Parameters => Target Length 2 mm and select element type as tria.
* In Perimeter and Macros set length as 2 mm.
*In mesh generation => Select Spot Mesh => Select Visible.

D] Blade stage 1 and 2 -

* CLick on Quality Criteria =>minimum length 0.5 mm and max. lenght 2 mm.
* Mesh Parameters => Target Length 1 mm and select element type as tria.
* In Perimeter and Macros set length as 1 mm.
*In mesh generation => Select Spot Mesh => Select Visible.

E] Shaft Rotor -

* CLick on Quality Criteria =>minimum length 0.5 mm and max. lenght 2 mm.
* Mesh Parameters => Target Length 1 mm and select element type as tria.
* In Perimeter and Macros set length as 1 mm.
*In mesh generation => Select Spot Mesh => Select Visible.

Now we can see,that on some surfaces mesh is getting erased,that because both connecting surfaces have different mesh sizes.Now select the PID whose mesh got erased and do the mesh again,but this time don't change macros or perimeter.If macros has perticular range so dont enter any value,same thing apply to perimeter also.If there is range present the leave it as it is,otherwise input the desired target length.So now we can see transition region,as we go away from the boundary of two surfaces,mesh length smoothly changes.

 

4.4] Volumetric Mesh -

Volumetric mesh is nothing but 3D elements,while surface mesh is mesh with the help of 2D elements which are tria elements .One important thing to do before volumetric mesh is to make sure that all of our surfaces are meshed.As surface mesh is pre-requisite for volumetric mesh.Click on mesh deck and make sure there aren't any unmeshed surfaces.

                  

First we need ANSA to detect all volumes present.To do that follow below steps,
Click on V.Mesh deck => Volumes => Define => Right click and select Auto Detect => Work on whole db => OK.

                                     

As we can ANSA auto detected 8 volumes.Now we need to figure out required and non required volumes.As we are meshing for CFD,we will only take volumes which are not occupied or taken by our parrent geometry thickness,i.e. only consider the volumes where fluid may flow and we will try to 3D mesh it and delete the rest of the volumes.

Thus we will delete the volumes occupied by the thickness of blade stage 1 and 2,impeller and also rotor shaft.Simmillarly will
delete the volume for the outer casing thickness.Hence will keep 4 volumes as shown below.

                             

To do volumetric mesh for the required volumes follow below steps,we will select smallest volume first then go on to larger ones,In unstructured mesh => select Tetra CFD => select the desired volume => middle click.

    

We have selected Tetra CFD as we want elements for CFD application.Always check type and status after finishing meshing of perticular component or PID.Also make sure not to have any unmeshed volumes.

                                                   

5] RESULTS AND OUTCOMES -

                            

                         

                         

In the axial cross section we can see that at the blades location elements are really small and gets bigger away from them,because elements near blade are 1 mm and away from them they are 5 mm.Also the transition from 1 mm mesh to 5 mm mesh is really smooth.

Geometrical details got capture precisely and accurately.This is evident if we look at the blade surfaces and compressor casing
bends.But as we reduce the mesh lenght number of elements and volumes increases drastically,which increases comutational cost as well as memory usage.

6] CONCLUSION -

* We have successfully performed topology cleanup on the given turbocharge model and resolved single cons and removed all overlapped surfaces.
* Successfully generated surface mesh,which is pre requisite for volumetric mesh.
* Also learned what is volumetric mesh and how to performe volumetric mesh.
* Thus we have successfully generated volumetric mesh for the give turbo charger model.