# Fundamental Problem

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 July 18, 2007, 13:21 Fundamental Problem #1 Naghman Khan Guest   Posts: n/a Hello, I'm finding it difficult to picture the domain in which flow occurs. I have a geometry, 3D centrifugal fan without any casing i.e. just the impeller. I have made the blades and the two ends which hold the blades, all are volumes and meshed and successfully exported. But what about the hollow space in the impeller? Is this space hollow and therefor not subject to any calculations by fluent? Do I need to make a separate volume in this space, mesh it and then define this as what (Boundary types)? And also would I define my blades as walls, for the air to flow around them and then through the impeller and out past the opposing blades? And where would the flow out from, do I need to explicitly define outflows as the spaces between the blades? Thanks people, I'm new to CFD, still can't picture it.

 July 18, 2007, 16:34 Re: Fundamental Problem #2 red lemon Guest   Posts: n/a Dont think you have a clear idea of what you are doing. Look at some other turbo style meshes for pumps/turbochargers etc or turbo examples available from Fluent.

 July 18, 2007, 17:33 Re: Fundamental Problem #3 Naghman Khan Guest   Posts: n/a Red Lemon, Hi you are right I'm not completely sure of what I am doing. Unfortunately my department does not have the Turbo add on. Anything else you can suggest? Thanks

 July 19, 2007, 18:02 Re: Fundamental Problem #4 red lemon Guest   Posts: n/a You dont need GTurbo to access the turbo tutorials. Just go to fluentusers.com or learningcfd.com and advanced tutorials. All setups for pumps & fans (MRF or sliding) are there.

 July 24, 2007, 01:14 Re: Fundamental Problem #5 Raj Guest   Posts: n/a Hi, To start with, what is the significance of that hollow space? I meant rhetorically. If there is no heat transfer calculation going on, then you dont have to worry abt the conduction, if at all, in the impeller blade. So you dont have to create that volume and hence no meshing involved there. Yes, just define the faces of that hollow region as walls and zero heat flux. Now, lest consider just one blade...ok... Here, if the space around that blade has been meshed, then you would have six faces(if the meshed region is cuboid in shape). One would be inlet, one would be outlet. Two would be walls and two more would be given periodic, ie peridic interfaces between the previous blade and the next blade. That way you can do the analysis for only one blade and then replicate the others in post processing. I hope this helps. Later. Raj.

 July 24, 2007, 07:09 Re: Fundamental Problem #6 Naghman Khan Guest   Posts: n/a Raj, Hi there, thanks so much for your reply. I am beginning to picture things now. So what you are saying is that I only need to physically make and mesh one blade and adjacent open space and define them as periodic. Or do i need to make two blades with the space in between defined as inlet, outflow, walls etc? What if I wanted to use a multiple reference frame i.e. to make the blades rotate, should I still just model one blade or in this case would I ahve to model all of them? Thanks Raj, hope my questions make sense. Best wishes Khan.

 July 24, 2007, 11:21 Re: Fundamental Problem #8 Naghman Khan Guest   Posts: n/a Raj, Thanks bro, for all your help. Your advice does make a lot of sense, I'll give it a go. By the way, I am using Gambit but I don't have the Turbo function as this is an extra which you have to pay extra for. On the question of MRF, when I define a fluid as having a rotational velocity of say 20 rpm, in the rotation axis origin and rotation axis direction what input need I give? For the rotation axis origin, is this asking me which coordinate does the actual axis about which rotation takes place originate, e.g. 0,0,0 (x, y, z)? And for rotation axis direction under x, y, z values do i need to put basically the length of the rotating body? For example if my axis started at 0,0,0 and was 10 units in positive z direction, would I put 0,0,0 as the origin and 0,0,10 as the rotation axis direction values? Thanks again bro,

 August 1, 2007, 11:01 Re: Fundamental Problem #9 Remsy Tharakan Guest   Posts: n/a I WOULD LIKE TO SEE A ROTATING MOTION OF THE PROPELLER INSIDE A PIPE. What is the way to introduce this function in the Fluent. There is already a liquid flowing through the pipe and through the propeller an another liquid flows out. How can I simulate this in Fluent. Which way to proceed to get the end result.

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