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-   -   someone can explain this..... (http://www.cfd-online.com/Forums/phoenics/51206-someone-can-explain.html)

mazza June 4, 2001 11:59

someone can explain this.....
 
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


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