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Vashishth Patel November 6, 2008 12:01

Very simple question
Hi Guys, I have a very simple question. I am not that familiar with CFD/CFD packages. Any information would be high appreciated.

We have a very simple axial flow impeller design (just like a hercules screw). All I want to know is how many rotations would be required to draw certain volume of blood(fluid) from a reservoir.

What would I need to solve the problem?? I have fluent, gambit, ANSYS CFX without TurboGrid.

Any approach would be appreciated.

Thanks for the help!

Georg November 7, 2008 01:42

Re: Very simple question
You can use Fluent+Gambit or CFX+CFX-Mesh. First you should create geometry of fluid domain (your CAD or DesignModeler). It would be bounded by inlet, outlet, shroud and hub surfaces. You can use rotation periodicity to model only one-blade symmetric part (not whole impeller). After you get the geometry you should generate the mesh then select and name boundary surfaces. Next import the mesh to CFX/Fluent and set physics. If you prefer CFX you can make this setting easier to use Torbo mode of CFX-Pre.

Vashishth Patel November 7, 2008 08:44

Re: Very simple question
Thanks a ton Georg! I have the impeller geometry and for the simplicity it has only one blade (i actually had two or three blades). However, do I need the TurboGrid to set up the mesh? Or a normal mesh set up in CFX would do? any specifics required if you generate a blade/impeller mesh in CFX?

i'll have to look up what rotation periodicity - one blade symmetric ..

Thanks again!

Georg November 8, 2008 13:34

Re: Very simple question
TurboGrid can be fast and convenient way for your case. But CFX-Mesh or ICEM-CFD is good choice too. I recommend you take a look at ANSYS CFX Tutorials | Tutorial 12: Flow in an Axial Rotor/Stator. There you can find basic steps which you need in your work.

Vashishth November 11, 2008 14:30

Re: Very simple question
hey Georg, thanks again for the response

i tried working with turbogrid, but it reads only bladegen file *.inf or something like that .... i tried to create a bladegen file *.inf using the import wizard of through all the steps from 1.importing :a *.iges file of my impeller with housing 2.defing hub, shroud, blade curves

But could not get pass "edit meridional....." it kept on showing red triangles, despite my editing with the "bad points"

So i went back and looked at the tutorial flow around blunt body ...

so what i'm trying is 1. creating fluid domain + body (here impeller) mesh and then 2. run cfx as shown in tutorial for stationary impeller (as blunt body)

somehow i need to know if i can import this mesh and use in "turbo mode" of cfx-pre ...

Thanks again

Georg November 12, 2008 01:56

Re: Very simple question
BladeGen Import wizard isn't very comfortable tool. I heard this step will be more convenient in ANSYS 12.0. To pass "edit meridional" you should slightly change coordinates of red points. There is angle value limitation. Piecewise curves have to change smoothly. Try to correct "red" coordinates. If you export iges to BladeGen you can get (by TurboGrid) good hexa-mesh more easily. If you want to model only fluid dynamics without structural analysis you don't need solid body domain. You need only fluid domain. Are you going to use Tutorial 5? It's not for your case. You should use Tutorial 12: Flow in an Axial Rotor/Stator. You can import and use in Turbo mode all types of available grids (CFX-Mesh, ICEM CFD, ANSYS, Workbench Meshing, etc.).

Vashishth November 14, 2008 10:48

Re: Very simple question
Thanks Georg for all the help all this way!!

axial rotor/stator tutorial is good! but it is slightly different

i think my case has to use 'pump' axial inducer impeller/pump

i've been successful in simulating the run so far, but getting weird results. So just have perfect what to do ...

i have a cylindrical tube containing a axial impeller something like this

i defined blade (as i know it is needed for sure)

but i am not sure about hub and shroud ..... when i used a shround as the outer shell of cylinder gave weird result becuase it was assuming the shroud rotates too ....but it stays stationary in my case

only the central thing with blades on it rotates ... currently i am trying a case without selecting hub and shroud domain let's see what i get ...

thanks again ...

Georg November 17, 2008 07:13

Re: Very simple question
If shroud surface is stator you should use "counter rotating wall" for your shroud. Open your model in Standard Mode of CFX-Pre. Open Boundary Details Tab in shroud boundary object. Activate check-box "Wall velocity" and set "Counter rotating wall". Good luck!

yuvarajmdesign November 8, 2011 01:46

Hi Georg,
I need a small clarification from you on Bladegen.
I have modeled the rotor blade for axial flow compressor in NX and tried to import the iges format of it in blade editor. But it didn't work. I can try to import to the same file in workbench geometry modeler.
If it worked, while exporting the model to turbogrid, I need to mention the leading edge and trailing edge curve. But in my case I have created the fillets at these regions and hence I'll be having two curves on either side.

Can you please tell me how can I represent it inorder to get a good quality of hex mesh in turbogrid? Blade shape is too much curvy throughout its span. Will this works fine in Turbogrid?

Amp November 8, 2011 05:13

Is it difficult to hand calculate it? seems to be a simple calculation to me!

Graham81 November 8, 2011 05:26

If you model only the axial impeller you will get a certain head at any flowrate you prescribe or vice versa. In other words, the amount of fluid you draw from a reservoir will depend on the QH curve of the impeller and the system curve. If you have no curve of the impeller you can use CFD to come up with an idealized version.

If you ask: how much flow will this pump do?
The correct answer is: what is your system curve?

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