Dynamometer, 2D Axisymmetric!

hadikhayyamian · June 2, 2012, 17:29

Hi All;

I am working on a dynamometer (you dont need to know what it is!!!), and for simplicity I changed its geometry as in Fig.1, as you can see water is inside a cylinder which contains a rotor spinnnig with angullar velocity of 5500 rpm. I set my Computational Domain like in Fig. 2. Note that there is no any inlet and outlet in this analysis to decrease computational difficulty.

Through my case setup in Fluent I did following:

1- Pressure Based- 2d Axisymmetric swirl (I dont know why I cant use just 2D Axisymmetric ??)- Absolute Velocity Formulation

3-Viscouse: I used Laminar, k-e and spalart-...

2- Material water; I assumed constant density

3- BC:

Fluid zone as single rotating frame (its rotation axis is x-axis as stated in Fluent Docs) , angular velocity of 5500 rpm

Rotor: rotating moving wall with relative velocity of zero (However I think I could set it as stationary wall as well. right????)

wall: rotating wall with absolute velocity of zero.

4- First Order Discritization Scheme for starting iteration and then shift 2 2nd order. For pressure I selected PRETSO! though.

5- operating pressure: about 3 bars, since I know from experiment its pressure is in that range.

6- initialization: just changed pressure from zero to 2 bar.

My results: Although solution converges, result is crazy. for example the inside pressure varies for -3 bar to 100 bar!

I also checked my Y+ value. it was alright.

I would appreciate if you reply anything you may think useful regarding my problem!

Regards.

xrs333 · June 3, 2012, 04:45

Nihao, Khayyamian,
I think i can explain your puzzle. Your model has no flow inlet and outlet, and the flow is imcompressible, so the pressure in the model is floating. To overcome this, define the operating pressure at a position in the domain.

hadikhayyamian · June 7, 2012, 13:10

Thanks xrs333 for your fast reply!

I will check out what you mentioned, it takes some days though. I will notify then.

But I asked another question, what if used 2D Axisymmetric without Swirl but wall still moving?

delaneyluke · June 8, 2012, 06:41

2D axisymmetric without swirl with not capture the effect of the rotating wall on the fluid and hence your results will look the same as when your wall does not rotate.

Regards
Luke

vahid.najafi · July 27, 2012, 03:06

Im produse 2Daxisymetric.
but after run , my results is not one with 3D???and incorrect!!!!
Have i correct boundary type?

axis:empty (empty or symmetryPlane is correct?????? )
wall:wall
inlet: patch
outlet: patch
frontAndBackPlanes:empty
frontAndBackPlanes_pos:wedge
frontAndBackPlanes_neg:wedge

please tell me my mistake!

flotus1 · July 27, 2012, 04:05

The case you have is not axisymmetric. The main velocity component is the tangential component, which is not even computed in an axisymmetric case.
The right way to model your case is with a periodic boundary condition and a 3D geometry or as axisymmetric swirl.

vahid.najafi · July 27, 2012, 07:36

Hi dear Alex S.
Thanks for your answer.axisymmetric swirl???
please learn me more for this idea!!!

flotus1 · July 27, 2012, 08:26

You will learn much more about it by reading the section "axisymmetric swirl" in the Fluent manual.

vahid.najafi · July 27, 2012, 09:29

I worked with openFoam!!!why you tell me fluent???please tell me Details about it.

flotus1 · July 27, 2012, 10:24

Because this is the FLUENT subsection of the forum.
I know nothing about open foam.

vahid.najafi · July 27, 2012, 10:29

ohhhhh!!!!!Im very sorryyyyyy!!!!
thanks.

hadikhayyamian · July 27, 2012, 13:29

reply to #3
Thanks xrs333
Your solution was right. I did your instructions and pressure ditribution became fine.

July 27, 2012, 07:36	an other question	#7
vahid.najafi Member vahid Join Date: Feb 2012 Location: Mashhad-Iran Posts: 80 Rep Power: 13	Hi dear Alex S. Thanks for your answer.axisymmetric swirl??? please learn me more for this idea!!!

July 27, 2012, 10:29	ohhhh	#11
vahid.najafi Member vahid Join Date: Feb 2012 Location: Mashhad-Iran Posts: 80 Rep Power: 13	ohhhhh!!!!!Im very sorryyyyyy!!!! thanks.

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June 3, 2012, 04:45		#2
xrs333 Senior Member xrs333 Join Date: Aug 2010 Posts: 125 Rep Power: 16	Nihao, Khayyamian, I think i can explain your puzzle. Your model has no flow inlet and outlet, and the flow is imcompressible, so the pressure in the model is floating. To overcome this, define the operating pressure at a position in the domain.

June 7, 2012, 13:10		#3
hadikhayyamian Member Khayyamian Join Date: Dec 2010 Posts: 46 Rep Power: 15	Thanks xrs333 for your fast reply! I will check out what you mentioned, it takes some days though. I will notify then. But I asked another question, what if used 2D Axisymmetric without Swirl but wall still moving?

June 8, 2012, 06:41		#4
delaneyluke Senior Member Join Date: Mar 2009 Location: Indiana, US Posts: 186 Rep Power: 17	2D axisymmetric without swirl with not capture the effect of the rotating wall on the fluid and hence your results will look the same as when your wall does not rotate. Regards Luke

July 27, 2012, 04:05		#6
flotus1 Super Moderator Alex Join Date: Jun 2012 Location: Germany Posts: 3,399 Rep Power: 46	The case you have is not axisymmetric. The main velocity component is the tangential component, which is not even computed in an axisymmetric case. The right way to model your case is with a periodic boundary condition and a 3D geometry or as axisymmetric swirl.

July 27, 2012, 08:26		#8
flotus1 Super Moderator Alex Join Date: Jun 2012 Location: Germany Posts: 3,399 Rep Power: 46	You will learn much more about it by reading the section "axisymmetric swirl" in the Fluent manual.

July 27, 2012, 10:24		#10
flotus1 Super Moderator Alex Join Date: Jun 2012 Location: Germany Posts: 3,399 Rep Power: 46	Because this is the FLUENT subsection of the forum. I know nothing about open foam.

July 27, 2012, 13:29		#12
hadikhayyamian Member Khayyamian Join Date: Dec 2010 Posts: 46 Rep Power: 15	reply to #3 Thanks xrs333 Your solution was right. I did your instructions and pressure ditribution became fine.