# Cylinder tutorial

 Register Blogs Members List Search Today's Posts Mark Forums Read

 June 13, 2008, 05:07 If the pressure equation that #21 New Member   Roberto Join Date: Mar 2009 Posts: 17 Rep Power: 10 If the pressure equation that potentialFoam solves is not laplacian(p)=0 then the manual should be corrected! From the relation I've posted after some rearrangements it turns: laplacian(p)=-rho*(d^2(phi)/(d(x_i)d(x_k)))^2 wich is different from the equation that you have posted. Also laplacian(p)=div(phi) is not dimensionally correct! and also: is it possible to define the divergence of a scalar field? nice weekend to you! Roberto

 June 13, 2008, 10:14 Hi I am wondering if we are #22 Senior Member   Niels Gjoel Jacobsen Join Date: Mar 2009 Location: Deltares, Delft, The Netherlands Posts: 1,746 Rep Power: 29 Hi I am wondering if we are chasing something which is not present in the solution. Have found the analytical solution of the potential around a cylinder, and it writes: phi = -u_0 x (1 + R^2 / (x^2 + y^2)) Thus in increases for decreasing x and varies linearly in the farfield of the cylinder. Could it be that the solution is actual for phi and not p? / Niels __________________ Please note that I do not use the Friend-feature, so do not be offended, if I do not accept a request.

 June 13, 2008, 14:18 The pressure field shown varie #23 New Member   Roberto Join Date: Mar 2009 Posts: 17 Rep Power: 10 The pressure field shown varies linearly in the whole field, not only in the farfield. I don't know exactly what is the solution for the potential flow but if it is the one that you write you can write it in polar coordinates as: phi=-u_o*(1+R^2/r^2) where r^2 is the generical radius far from the cylinder. In this way the potential contours must be concentrical circles around the cylinder... and this is not the case of the field shown. So the pressure field shown is not the potential field... Roberto

 June 14, 2008, 03:56 Please note the 'x' after u_0. #24 Senior Member   Niels Gjoel Jacobsen Join Date: Mar 2009 Location: Deltares, Delft, The Netherlands Posts: 1,746 Rep Power: 29 Please note the 'x' after u_0. - Niels __________________ Please note that I do not use the Friend-feature, so do not be offended, if I do not accept a request.

 June 14, 2008, 05:22 i missed that parsicular! i've #25 New Member   Roberto Join Date: Mar 2009 Posts: 17 Rep Power: 10 i missed that parsicular! i've plotted the function you posted and it shows good agreement with the pressure field shown... but why potentialFoam plots the potential field instead of the pressure field? Roberto

 March 10, 2010, 12:38 #26 Senior Member   Kevin Smith Join Date: Mar 2009 Posts: 104 Rep Power: 10 Did this issue ever get resolved? Both tutorials for potentialFoam seem to give incorrect pressure distributions if you run the simulation with the '-writep' argument. It does seem the pressure field resembles phi more than anything.

 March 10, 2010, 12:42 #27 Senior Member   Kevin Smith Join Date: Mar 2009 Posts: 104 Rep Power: 10 Also, the field phi is a scalar field - taking divergence of that field seems nonsensical.. What am I missing?

 March 17, 2010, 08:55 Modeling the flow inside an annulus?! #28 New Member   Sawi Join Date: Mar 2010 Posts: 7 Rep Power: 9 I' am trying to model the behavior of a non newtonian fluid inside an eccentric annulus. I need to get a profile of the annular velocity of the fluid for the whole cross section. I just discovered the OpenFoam and i was wondering if the "nonNewtonianIcoFoam" solver would manage a problem like this? Since i am new in this area any further help or suggestions is appreciated. What should i read to get started? Is there another solver that is more specialized in Annular flow? Will i need a mesh generation program(Boundary conforming grid generator) or Will the Openfoam handle the whole problem? Really appreciate any help

March 17, 2010, 16:25
#29
Senior Member

Sebastian Gatzka
Join Date: Mar 2009
Location: Frankfurt, Germany
Posts: 729
Rep Power: 13
Quote:
 Originally Posted by Aelsawis I' am trying to model the behavior of a non newtonian fluid inside an eccentric annulus. I need to get a profile of the annular velocity of the fluid for the whole cross section. I just discovered the OpenFoam and i was wondering if the "nonNewtonianIcoFoam" solver would manage a problem like this? Since i am new in this area any further help or suggestions is appreciated. What should i read to get started? Is there another solver that is more specialized in Annular flow? Will i need a mesh generation program(Boundary conforming grid generator) or Will the Openfoam handle the whole problem? Really appreciate any help
I'm pretty sure your question is in not related to this thread.
Open you own discussion!
__________________
Schrödingers wife: "What did you do to the cat? It's half dead!"

 March 17, 2010, 18:33 #30 New Member   Sawi Join Date: Mar 2010 Posts: 7 Rep Power: 9 yeah maybe ur right i am sorry for the disturbance.i just thought since the discussion began with the cylinder example ..that maybe someone would know something about the annular flow between two cylinders...

 March 17, 2010, 19:44 #31 Senior Member   Cean Join Date: Feb 2010 Posts: 128 Rep Power: 9 The p in the program has a dimension of m^2/s^2, so it is not simple a pressure. I think it is p/density. Becasue: p - kg/(ms^2) density - (kg/m^3) p/density=kg/(ms^2)/(kg/m^3)=m^2/s^2 For potential flow, usually we start from solving phi, then get U by differentiation of phi. Then get pressure from Bernolli's equation. The U is correct here, so we could try to get pressure from it. BTW, There is an analyticalFoam folder under the cylinder tutorial folder. Where this output is saved? Cean Last edited by shirazbj; March 18, 2010 at 23:45.

 March 25, 2010, 12:32 #32 Senior Member   Kevin Smith Join Date: Mar 2009 Posts: 104 Rep Power: 10 Cean - That's what I ended up doing - since my case had a uniform free stream velocity it was relatively trivial to modify the potentialFoam solver to calculate pressure.

April 2, 2010, 08:43
#33
Senior Member

Cean
Join Date: Feb 2010
Posts: 128
Rep Power: 9
Quote:
 Originally Posted by kev4573 Did this issue ever get resolved? Both tutorials for potentialFoam seem to give incorrect pressure distributions if you run the simulation with the '-writep' argument. It does seem the pressure field resembles phi more than anything.
phi is the flux through the cell surface.

Does the equation means flux due to pressure change in the cell?

 April 6, 2010, 09:25 #34 Senior Member   Kevin Smith Join Date: Mar 2009 Posts: 104 Rep Power: 10 By phi I really meant potential, sorry for the confusion.

 May 11, 2010, 01:52 Cylindrical boundary condition #35 New Member   Joseph Join Date: Mar 2010 Posts: 14 Rep Power: 8 Hi Could you send me your code about cylindrical boundary condition? TANX Joseph

 May 11, 2010, 02:58 Hi #36 Senior Member     ata kamyabi Join Date: Aug 2009 Location: Kerman Posts: 323 Rep Power: 10 Hi I think that in that file which I have send for you, is a link to cylindrical B.C. Best regards

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post Jason ANSYS Meshing & Geometry 29 October 30, 2015 09:59 CH FLUENT 8 April 2, 2014 10:56 pilli4u FLUENT 2 April 2, 2007 05:09 sachin bhalerao FLUENT 0 February 28, 2006 04:05 Ngoctq FLUENT 0 December 29, 2005 21:46

All times are GMT -4. The time now is 01:36.