CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Phoenics

someone can explain this.....

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

Reply
 
LinkBack Thread Tools Display Modes
Old   June 4, 2001, 11:59
Default someone can explain this.....
  #1
mazza
Guest
 
Posts: n/a
I will try to explain better my problem and I hope with this information someone can help me. Using polar system with KE-EP turbulence model, the GXSQUR gives the production of turbulence energy by shear stress like (when NX=1):

GENK = LENG1 = 2*( (DU/DX + V/R)**2 + (DV/DY)**2 + (DW/DZ)**2) + (DU/DY ľU/R+ (1/R)*DV/DX)**2 + ( (1/R)*DW/DX + DU/DZ)**2 + (DV/DZ + DW/DY)**2

If I print out the field of LGEN variable at the end of subroutine GXSQUR, I get:

IZ = 10 -> 7.19E+01 1.07E+04 1.46E+04 1.04E+04 7.64E+03 5.73E+03 4.42E+03 3.50E+03 2.84E+03 2.48E+03

IZ = 9 -> 5.62E+01 1.01E+04 1.35E+04 9.60E+03 6.97E+03 5.19E+03 3.98E+03 3.15E+03 2.55E+03 2.21E+03

IZ = 8 -> 4.39E+01 8.39E+03 1.11E+04 7.92E+03 5.67E+03 4.17E+03 3.18E+03 2.50E+03 2.01E+03 1.72E+03

IZ = 7 -> 3.47E+01 6.38E+03 8.54E+03 6.15E+03 4.36E+03 3.19E+03 2.41E+03 1.89E+03 1.52E+03 1.28E+03

IZ = 6 -> 2.80E+01 4.52E+03 6.15E+03 4.50E+03 3.17E+03 2.31E+03 1.74E+03 1.36E+03 1.09E+03 9.06E+02

IZ = 5 -> 2.32E+01 2.98E+03 4.12E+03 3.06E+03 2.15E+03 1.56E+03 1.17E+03 9.12E+02 7.30E+02 6.02E+02

IZ = 4 -> 1.98E+01 1.78E+03 2.48E+03 1.87E+03 1.31E+03 9.47E+02 7.12E+02 5.54E+02 4.43E+02 3.62E+02

IZ = 3 -> 1.75E+01 9.00E+02 1.26E+03 9.62E+02 6.74E+02 4.86E+02 3.65E+02 2.84E+02 2.27E+02 1.84E+02

IZ = 2 -> 1.61E+01 3.25E+02 4.55E+02 3.49E+02 2.44E+02 1.76E+02 1.32E+02 1.03E+02 8.19E+01 6.64E+01

IZ = 1 -> 1.54E+01 1.45E+02 2.04E+02 1.57E+02 1.10E+02 7.87E+01 5.89E+01 4.57E+01 3.65E+01 2.95E+01

IY 1 2 3 4 5 6 7 8 9 10

But, if I store the GENK variable in q1, I get:

IZ = 10 -> 1.96E+06 4.59E+05 6.14E+04 4.51E+04 3.55E+04 2.83E+04 2.31E+04 1.93E+04 1.64E+04 1.48E+04

IZ = 9 -> 5.62E+01 1.01E+04 1.35E+04 9.60E+03 6.97E+03 5.19E+03 3.98E+03 3.15E+03 2.55E+032.21E+03

IZ = 8 -> 4.39E+01 8.39E+03 1.11E+04 7.92E+03 5.67E+03 4.17E+03 3.18E+03 2.50E+03 2.01E+03 1.72E+03

IZ = 7 -> 3.47E+01 6.38E+03 8.54E+03 6.15E+03 4.36E+03 3.19E+03 2.41E+03 1.89E+03 1.52E+03 1.28E+03

IZ = 6 -> 2.80E+01 4.52E+03 6.15E+03 4.50E+03 3.17E+03 2.31E+03 1.74E+03 1.36E+03 1.09E+03 9.06E+02

IZ = 5 -> 2.32E+01 2.98E+03 4.12E+03 3.06E+03 2.15E+03 1.56E+03 1.17E+03 9.12E+02 7.30E+02 6.02E+02

IZ = 4 -> 1.98E+01 1.78E+03 2.48E+03 1.87E+03 1.31E+03 9.47E+02 7.12E+02 5.54E+02 4.43E+02 3.62E+02

IZ = 3 -> 1.75E+01 9.00E+02 1.26E+03 9.62E+02 6.74E+02 4.86E+02 3.65E+02 2.84E+02 2.27E+02 1.84E+02

IZ = 2 -> 1.61E+01 3.25E+02 4.55E+02 3.49E+02 2.44E+02 1.76E+02 1.32E+02 1.03E+02 8.19E+01 6.64E+01

IZ = 1 -> 1.54E+01 1.45E+02 2.04E+02 1.57E+02 1.10E+02 7.87E+01 5.89E+01 4.57E+01 3.65E+01 2.95E+01 IY 1 2 3 4 5 6 7 8 9 10

Comparing the two fields I see that all values are equal, except for IZ = 10 for all IY. This control volume is the region of wall boundary condiction, which I define in q1 like:

PATCH( PH, HWALL1,NX, 1,NY,NZ,NZ,1,1)

COVAL(PH,W1,GRND2, 0.0)

COVAL(PH,U1,GRND2,GRND)

At GROUND I define a function that calculates the U1 velocity at this wall.

This is the problem. At wall boundary condition the LGEN values calculated by GXSQUR are different from GENK. I was expecting the same values for all control volume. Initially, I think that the LGEN that I printed out at end of GXSQUR was wrong. To check for this, I calculated with velocity field the LGEN value using Excel program and LGEN definition above. To evaluate the differential I used second order central difference, except for the system boundary where I used a first order upwind or downwind. All the values that I got with this procedure were the same calculate for LGEN by GXSQUR subroutine. After this check I think that the GENK field is not the same used to calculate the turbulence sources. To check, I found the location in the GXTURB subroutine where the turbulence source was calculated and I printed out the LGEN field. I got the same values presented by GENK variable, instead of LGEN values calculated by GXSQUR. I think this is very strange and I can't understand why the values at wall boundary for GENK and LGEN are different and I can't find where the change is made. For this reason I wrote the first message. I hope with this explanation someone would understand my problem. Tanks.

RM
  Reply With Quote

Reply

Thread Tools
Display Modes

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 Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Can someone explain the Y plus value jeff bennet Main CFD Forum 17 April 1, 2014 14:34
Can someone please explain this jaswi OpenFOAM 2 July 3, 2007 08:19
Please explain Abby CFX 1 April 25, 2006 06:18
please explain these terms kiran Main CFD Forum 0 June 28, 2005 17:40
can some one explain this to me? docsri Main CFD Forum 2 December 11, 2002 22:43


All times are GMT -4. The time now is 19:53.