[itsme_kit]

Hi This is my source term for turbulent dissipation gradient in z direction

DEFINE_SOURCE(dissipation_gradient,cell,thread,dS, eqn)
{
real source;
source=C_D_G(cell,thread)=-0.000003;
dS[eqn]=0.;
return source;
}

Hopefully the above structure is correct

After interpreting in Fluent, I got following message: invalid lvalue in assignment (in line starting with source=C_D_G(cell,thread)=-0.000003

I couldn't understand the meaning of this message

Actually I just wanna have a source term for depsilon/dz

Can anyone help me sort it out?

Thanks in advance

[pakk]

What do you want to achieve with the line "source=C_D_G(cell,thread)=-0.000003"?

Does the variable "source" needs to be set to the value of C_D_G(cell,thread), or to -0.000003? Or do you want the value of C_D_G(cell_thread) to change? The compiler does not understand what you want...

[itsme_kit]

Originally Posted by pakk

What do you want to achieve with the line "source=C_D_G(cell,thread)=-0.000003"?

Does the variable "source" needs to be set to the value of C_D_G(cell,thread), or to -0.000003? Or do you want the value of C_D_G(cell_thread) to change? The compiler does not understand what you want...

Hi pakk

Thanks for your reply first of all

Currently I have a formula: depsilon/dz=constant

I wanna add this formula into fluid zone in the form of source term

Just now I found I missed one component in that line: [2] direction vector

Now the compiler can read my code without any warning

However, in terms of my case, do you have any comment? I wonder if I'm doing this correctly

[pakk]

You did not answer my questions, so I don't know what you want your code to do. Therefore I don't know what your code should look like.

[itsme_kit]

Originally Posted by pakk

You did not answer my questions, so I don't know what you want your code to do. Therefore I don't know what your code should look like.

Hi PAKK

I wanna apply a shear stress in my fluid zone

In order to do this, I derived du/dz and depsilon/dz which are acting in the effect of shear stress

Look forward to hearing from you

[pakk]

My questions were:

Does the variable "source" needs to be set to the value of C_D_G(cell,thread), or to -0.000003? Or do you want the value of C_D_G(cell_thread) to change?

These ones need an answer.

[itsme_kit]

Originally Posted by pakk

My questions were:

Does the variable "source" needs to be set to the value of C_D_G(cell,thread), or to -0.000003? Or do you want the value of C_D_G(cell_thread) to change?

These ones need an answer.

the value of C_D_G is -0.000003

The source is a constant value in -0.000003

[pakk]

But in a programming language, you are giving instructions to the computer. What do you want the computer to do?

-Computer, please change the value of C_D_G into -0.000003.
-Computer, please change the value of source into -0.000003.
-Computer, please change the value of source into the value of C_D_G.

Which one is it? With the code you had before, the computer did not know which one you meant.

(You say "the value of C_D_G is -0.000003", but that does not make clear if C_D_G already has that value, or if you want to change it into that value.)

[itsme_kit]

Originally Posted by pakk

But in a programming language, you are giving instructions to the computer. What do you want the computer to do?

-Computer, please change the value of C_D_G into -0.000003.
-Computer, please change the value of source into -0.000003.
-Computer, please change the value of source into the value of C_D_G.

Which one is it? With the code you had before, the computer did not know which one you meant.

(You say "the value of C_D_G is -0.000003", but that does not make clear if C_D_G already has that value, or if you want to change it into that value.)

I have to say I got a little bit confused now

I only want to add a source term in U equation to act like a shear stress

Currently I got: depsilon/dz=-0.000003

In terms of my case, how can I let PC know depsilon/dz=-0.000003?

Do you mind modifying what I wrote in code in a correct way?

[pakk]

I think what you mean is:

source = -0.000003;

It looks like you added C_D_G(cell,thread) in the code to inform Fluent that you are talking about depsilon/dz, am I right? If so, this is not the correct place; you do that by selecting in Fluent where you add this source.
Honestly, I don't know if there is a place where you can hook it to the turbulent dissipation gradient in z direction, that is beyond my knowledge.

[itsme_kit]

Originally Posted by pakk

I think what you mean is:

source = -0.000003;

It looks like you added C_D_G(cell,thread) in the code to inform Fluent that you are talking about depsilon/dz, am I right? If so, this is not the correct place; you do that by selecting in Fluent where you add this source.
Honestly, I don't know if there is a place where you can hook it to the turbulent dissipation gradient in z direction, that is beyond my knowledge.

Yes, I noticed this problem too, I will try to sort it out and let you know any update

In terms of velocity gradient: du/dz

DEFINE_SOURCE(shear_stress,cell,thread,dS,eqn)
{
real source;
source=C_DUDZ(cell,thread)=0.003251;
dS[eqn]=0.;
return source;
}

I put this source term in the x momentum equation

Do I think I wrote this code correctly?

Thanks

[pakk]

No. You make exactly the same mistake. The solution is therefore exactly the same.

[itsme_kit]

Originally Posted by pakk

No. You make exactly the same mistake. The solution is therefore exactly the same.

What mistake do you mean?

I think the place to hook this source term is correct

Maybe some problems existed in the structure of code

I found that the unit of source term in momentum equation is n/m3

I also noticed that du/dz is a constant in my code, there is no variable for derivation, right?

[pakk]

You have the same code, only with C_DUDZ instead of C_D_G and 0.003251 in stead of -0.000003.

Everything I said before therefore also applies to this code, only replace "C_D_G" in my comments by "C_DUDZ", and "-0.000003" by "0.003251". Literally.

[itsme_kit]

Originally Posted by pakk

You have the same code, only with C_DUDZ instead of C_D_G and 0.003251 in stead of -0.000003.

Everything I said before therefore also applies to this code, only replace "C_D_G" in my comments by "C_DUDZ", and "-0.000003" by "0.003251". Literally.

I think C_DUDZ can be hooked in x momentum equation

Only except C_D_G (maybe turbulent dissipation rate equation)

Just I have no idea how to modify my code in a correct structure

[pakk]

I showed you how to modify your code for the turbulent dissipation gradient case. For the x momentum equation case, the modification is exactly the same, only replace "C_D_G" by "C_DUDZ", and "-0.000003" by "0.003251". Literally.

[itsme_kit]

Originally Posted by pakk

I showed you how to modify your code for the turbulent dissipation gradient case. For the x momentum equation case, the modification is exactly the same, only replace "C_D_G" by "C_DUDZ", and "-0.000003" by "0.003251". Literally.

Hi

I didn't get your point of modifying the code

I do want the computer to know that C_DUDZ=0.003251, perhaps source will not be equal to 0.003251

[pakk]

Then please re-read my message of today, 09:32. I gave you a direct answer, and tried to explain you why your way of thinking failed here.

[itsme_kit]

Originally Posted by pakk

Then please re-read my message of today, 09:32. I gave you a direct answer, and tried to explain you why your way of thinking failed here.

do you mean I get rid of C_DUDZ and C_D_G?

Only put source = constant value in the momentum equation or epsilon equation?

This is my understanding

[pakk]

That is indeed what I am saying.