Geometry cleanup and meshing of turbocharger model
Statement- To perforem geometry cleanup and meshing of the given geometry model of turbocharger.
Methodology-
1. Geometry Cleanup
a. Missing parts
As we can see from the initialization of the given file various vital components of the turbocharger are missing, there are some graphical glitches as well as there are some extruded parts.
Steps for geometry clean up:-
1. For the glitching part, one can delete it using universal delete option once other parts are hidden using not option.
2. In the geometry some portion near the compressor casing outlet is missing, this can be corrected using fitted option under the new option in faces tab and then select manually all the cons connected to it and then press middle mouse button to get the surface.
3. The next is the turbo casing, in this a major portion is missing which can be corrected by using coons surface in the new option under faces tab, but before that we have to insert hot points between the curves so as to make get the required surfaces. This can be done by using parametric optin under hot points and then selec the direction in which hot points are required to be measured from then provide a value at which the new hot point is required to be inserted by clicking ok button. Make sure to provide ample points so as to avoid interference between geometries.
4. Next is the extruded part which can be deleted, but to do so first we have to project the single con to the extruded surface using project option under cons menu and then use topo option to join all the surfaces with the extruded part so that it can be finally be deleted using universal delete option.
5. The next error is the intersection error in the compressor casing, which can be resolved using the intersect option under faces and then select the first and the second surfaces which are extruded surface and the entire casing after clicking the middle mouse button we can select the parts that we require and delete the unnecessary parts so as to keep the geometry as symmetrical as possible.
b. Naming PIDs and single volume creation of blade assembly
1. Click on the property icon and convert the already available entries to required names based on the part which gets highlighted when clicked on the property list. These are compressor casing, Inlet casing cover, impeller,turbo casing, shaft rotor, blade stage 1 and blade stage 2.
2. Combining the blade assemblies into single volume is done in parts, firstly the impeller blades and the rotor shaft is joined for that first select the topo option and then drag and drop between the intersection this leads to forming of triple cons between impeller blade intersection, so to completely convert the intersection a triple con we can use cut option and then use it to seperate the surfaces, then use topo option again to get uniform triple con at intersection.
3. Now delete the common surfaces between the intersection and now the rotor shaft and the impeller blades have a single volume.
4. We can mimic this above procedure to get single volume between stage 1 and stage 2 blades with the rotor shaft.
5. For extruded part use project option under cons and project the circle to rotor shaft which will lead to irregular connection which can be corrected using mesh mode and then using length option under parameter option and then select the near circle and then click ok to get the perfect circle.
6. Now delete the common geometry using universal delete option to remove the overlapping.
7. After the single volume creation of the blade assembly is complete we can use compress option to get rid of all the unassigned PIDs.
2. Meshing
a. Free mesh
In this method after selecting mesh mode, under parameters option we give 5mm as the length and then divide the geometry into divsions of 5mm between nodes.
Now we choose free option under mesh generation tab and then select the entire geometry by right click drag and then click on the middle mouse button to get the required mesh.
b. PID specific meshing
The specifications of the each PID region is as follows and tria mesh is used as element type
blade stage 1 = 1mm
blade stage 2 = 1mm
compressor casing = 5mm
impeller = 2mm
inlet casing cover=5mm
shaft rotor = 1mm
turbo casing= 5mm
The method in this case is to group the PIDs with similar specifications using property window and then using ctrl and left click and then click on right click to select the option show only. Now use drag method to select all the visible parts under parameter and then give the required value. Now after completing this go to free mesh option and hold left click and select the visible option and generate the required mesh.
Problems
In this approach was the mismatch of divsions at the interface as a result of which the mesh gets cancelled sometime during meshing process. To overcome this the intersection of shaft rotor as well as the impeller was given as 1mm and rest of the mesh of impeller as well as the rotor shaft was unchanged as per specifications.
Another discontinuity in the mesh was observed in the intersection of rotor shaft and compressor casing as well as the intersection of the rotor shaft and the turbo casing.
Both of the discontinuity was observed in the form of overlapping in the topo mode.
Steps to remove the disontinuity:-
1.First remove the common intersection among both i.e the extruded part of both the casings into the rotor shafts by using delete option to remove the overlapping.
2. Then convert the newly formed single cons to triple cons using project option.
3. Now the mesh of the removed parts are destroyed so in order to remesh them without any length parameter issue just select the remesh macros option on while giving the length divsions to the unmeshed parts.
Steps to improve quality of the interface mesh:-
At the interface of the two components there is an abrupt change in mesh length which leads to a bad quality mesh. So to improve it, a path of area is created with dense mesh around the interface.
1. we can use mark/unmark option under hot points to manually mark the points and then using perimeter option under length give size as 3mm and then recreate mesh.
2. We can use cut option under macros to do the patch directly and then recreate the patch divisions and then recreate the mesh.
Both this process have to be done on the outside as well as the inside of the geometry at intersections.
c. Volumetric mesh:-
Before moving to volumetric mesh we have to fix all the openings in the geometry so that no leakage will occur during CFD anaysis. For this new PIDs are created for compressor casing inlet, outlet as well as turbo casing inlet and oulet using fitted and coons option under faces option. After which meshing is done on the new created surfaces by going to mesh mode and then meshing all visible option under free mesh option.
Now we have to define various volumes required in the geometry. The steps are:-
1. Go to the menu in which various modes are present like topo mode, mesh mode etc there click the arrow icon to bring hidden menu in which select V. Mesh.
2. Now click on define under volume tab and then select in volume detect option window.
3. Select the required volumes through which flow is occuring inside the geometry and delete the rest unrequired thickness models.
4. Now under the unstructured mesh select tetra mesh and then select the entire geometry using left click and then click on the middle mouse button.
Results
1. Before
2. After
Learnings-
1. Undelete option can be used to revert back the changes in the geometry so that previous parts can be restored if considered as critical parts
2. Topo option can be used to join various intersecting geometries to create an equal volume entity.
3. Free mesh option can be selected using a single con which will inturn select all the cons in link with it.
4. Erase mesh option with ENT on can enable us to select an entire surface
5. Both free mesh and erase mesh can be done seperately by holding the left mouse button and selecting the visible option.
6. Under length option in mesh window perimeter option allows us to choose a length while macros option allows us to use both ENT mode as well as PID region mode to select as per the geometry requirement.
7. Remesh macros option under the length tab in mesh mode helps to mesh the current surface as well as the attached mesh so that both mesh can co exist in the same geometry.
8. Ctrl + left click on any of the icons in the right hand side will open the help menu and give its detailed funcion.
9. F1,F2 F3 etc are different view shortcuts in ANSA.
10. Not option can be used to check the inner mesh after volumetric mesh is completed , that is slices can be made within geometry to see inner mesh quality.