yPlusLam() in RASModel.C

guanghaowu · August 17, 2009, 02:41

In $SRC/turbulenceModels/incompressible/RAS/RASModel.C, Line148

scalar RASModel::yPlusLam(const scalar kappa, const scalar E) const
{
scalar ypl = 11.0;

for (int i=0; i<10; i++) <== ???
{
ypl = log(max(E*ypl, 1))/kappa;
}

return ypl;
}

I cant understand the for{...}, how about as follows?

scalar RASModel::yPlusLam(const scalar kappa, const scalar E) const
{
scalar ypl = 11.0;

ypl = log(max(E*ypl, 1))/kappa;

return ypl;
}

Also, in $SRC/turbulenceModels/compressible/RAS/RASModel.C, Line153

scalar RASModel::yPlusLam(const scalar kappa, const scalar E) const
{
scalar ypl = 11.0;

for (int i=0; i<10; i++)
{
ypl = log(E*ypl)/kappa;
}

return ypl;
}

=>

scalar RASModel::yPlusLam(const scalar kappa, const scalar E) const
{
scalar ypl = 11.0;

ypl = log(max(E*ypl, 1))/kappa;

return ypl;
}

Thanks in advance.

ngj · August 17, 2009, 03:12

Good morning

It is because it is a non-linear equation, hence you need to solve it in an iterative manner.

Best regards,

NIels

guanghaowu · August 17, 2009, 03:20

Hi, NLels

Just now I found its my misunderstanding.
You've replied before I delete my thread.

However, thank you very much.

feldy77 · March 20, 2012, 19:45

Dear friends,
I am also puzzled about the above for loop.
Can you please explain in more detais which non linear equation it
supposed to solve and how it does it
Mnay tahnks, Yuri

AlexC · March 18, 2014, 14:06

Two years later, I too have a question about this - why only iterate 10 times?

I am getting an error where the product E*ypl was negative in:

Quote:

ypl = log(E*ypl)/kappa;

I ran gdb and here's the output that shows a log of a negative number, and the values of kappa, and E:

Quote:

(gdb) bt
#0 0x00007ffff162ead4 in log () from /lib64/libm.so.6
#1 0x00007ffff5bd67ad in Foam::log (s=-0.0072670797110974744)
at /home/achan/foam/foam-extend-3.0/src/foam/lnInclude/Scalar.H:242
#2 0x00007ffff3af7d9e in Foam::compressible::RASModel::yPlusLam (this=0xd3bb10, kappa=0.40999999999999998,
E=0.95255364484361649) at RASModel/RASModel.C:162
#3 0x00007ffff3bca35a in Foam::compressible::RASModels::mutRoughWallFunctio nFvPatchScalarField::calcMut (
this=0xd41d10)
at derivedFvPatchFields/wallFunctions/mutWallFunctions/mutRoughWallFunction/mutRoughWallFunctionFvPatchScalarField.C:98
#4 0x00007ffff3bc9321 in Foam::compressible::RASModels::mutWallFunctionFvPa tchScalarField::updateCoeffs (
this=0xd41d10)
at derivedFvPatchFields/wallFunctions/mutWallFunctions/mutWallFunction/mutWallFunctionFvPatchScalarField.C:192
#5 0x00000000004c0ff5 in Foam::fvPatchField<double>::evaluate (this=0xd41d10)
at /home/achan/foam/foam-extend-3.0/src/finiteVolume/lnInclude/fvPatchField.C:237
#6 0x00000000004b12d9 in Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh>::GeometricBoundaryField::evaluate (this=0xd3c350) at /home/achan/foam/foam-extend-3.0/src/foam/lnInclude/GeometricBoundaryField.C:308
#7 0x000000000049ba1e in Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh>::correctBoundaryConditions (this=0xd3c278) at /home/achan/foam/foam-extend-3.0/src/foam/lnInclude/GeometricField.C:880
#8 0x00007ffff3b37e4c in Foam::compressible::RASModels::kEpsilon::correct (this=0xd3bb10)
at kEpsilon/kEpsilon.C:335

How could that product be negative?

randolph · July 11, 2018, 12:57

Quote:

Originally Posted by AlexC

Two years later, I too have a question about this - why only iterate 10 times?

I am getting an error where the product E*ypl was negative in:

I ran gdb and here's the output that shows a log of a negative number, and the values of kappa, and E:

How could that product be negative?

ypl = log(max(E*ypl, 1))/kappa;

mAlletto · September 23, 2020, 04:17

Just for clarification: The function calculates the intersection between the velocity profile of the laminar sublayer

and the velocity profile in the log layer $U+ = 1/\kappa \ ln(E y+)$ which results in the non linear equation solved:

$y+ = 1/\kappa \ ln(E y+)$

August 17, 2009, 02:41	yPlusLam() in RASModel.C	#1
guanghaowu New Member Guanghao Wu Join Date: Mar 2009 Location: Tokyo, Japan Posts: 15 Rep Power: 17	In $SRC/turbulenceModels/incompressible/RAS/RASModel.C, Line148 scalar RASModel::yPlusLam(const scalar kappa, const scalar E) const { scalar ypl = 11.0; for (int i=0; i<10; i++) <== ??? { ypl = log(max(Eypl, 1))/kappa; } return ypl; } I cant understand the for{...}, how about as follows? scalar RASModel::yPlusLam(const scalar kappa, const scalar E) const { scalar ypl = 11.0; ypl = log(max(Eypl, 1))/kappa; return ypl; } Also, in $SRC/turbulenceModels/compressible/RAS/RASModel.C, Line153 scalar RASModel::yPlusLam(const scalar kappa, const scalar E) const { scalar ypl = 11.0; for (int i=0; i<10; i++) { ypl = log(Eypl)/kappa; } return ypl; } => scalar RASModel::yPlusLam(const scalar kappa, const scalar E) const { scalar ypl = 11.0; ypl = log(max(Eypl, 1))/kappa; return ypl; } Thanks in advance.

August 17, 2009, 03:12		#2
ngj Senior Member Niels Gjoel Jacobsen Join Date: Mar 2009 Location: Copenhagen, Denmark Posts: 1,900 Rep Power: 37	Good morning It is because it is a non-linear equation, hence you need to solve it in an iterative manner. Best regards, NIels

August 17, 2009, 03:20		#3
guanghaowu New Member Guanghao Wu Join Date: Mar 2009 Location: Tokyo, Japan Posts: 15 Rep Power: 17	Hi, NLels Just now I found its my misunderstanding. You've replied before I delete my thread. However, thank you very much.

March 20, 2012, 19:45		#4
feldy77 Member Yuri Feldman Join Date: Mar 2011 Posts: 30 Rep Power: 15	Dear friends, I am also puzzled about the above for loop. Can you please explain in more detais which non linear equation it supposed to solve and how it does it Mnay tahnks, Yuri

September 23, 2020, 04:17		#7
mAlletto Senior Member Michael Alletto Join Date: Jun 2018 Location: Bremen Posts: 615 Rep Power: 15	Just for clarification: The function calculates the intersection between the velocity profile of the laminar sublayer and the velocity profile in the log layer $U+ = 1/\kappa \ ln(E y+)$ which results in the non linear equation solved: $y+ = 1/\kappa \ ln(E y+)$