[Nurzhan]

Dear CFX experts,

I am trying to set different initial temperatures within one geometry and look how the temperature will achieve the equilibrium within the body.

I built all eight parts separately (using DM) and meshed the parts in ANSYS meshing application. Then, I represent each part as a separate domain and made interface connections between the domains.

Was my philosophy is right? Is it possible to set different initial conditions within a single body in any other way? I was advised to try "IF" statement, where I have to specify coordinates of each part (e.g. IF x<0.5 and y<0.4 than T=50).

Any help and advise will be highly appreciated.

Best regards,
Nurzhan

[Lance]

You can use nested if statements or step functions to get what you want.

"IF x<0.5 and y<0.4 than T=50" can be written in a CEL expression as

if(X < 0.5 [m],(if(Y< 0.4 [m], 50 [C],0 [C])),0 [C])

It would give you 50 [C] at x<0.5 and y<0.4 and 0 [C] everywhere else.

[Nurzhan]

Hi Lance,

Thanks for quick response and it is exactly what I wanted.

In addition I want to ask:

If I want to specify temperatures for another parts of a geometry , for example:

1st part of the geometry: x<0.5 and y<0.4 then T= 50oC
2nd part of the geometry: x<1 and y< 0.6 then T= 60oC
3d part of the geometry: x<1.2 and y<0.7 then T= 70oC
4th part of the geometry: x<1.5 and y<0.8 then T= 80oC

Will the expression look like this:

if(X < 0.5 [m],(if(Y< 0.4 [m], 50 [C],if(X < 1 [m],(if(Y< 0.6 [m], 60 [C],if(X < 1.2 [m],(if(Y< 0.7 [m], 70 [C],80 [C])),80 [C]))),80 [C]))),80 [C])

?

Thanks again Lance.

Regards,
Nurzhan

[ghorrocks]

Your expression is becoming pretty messy. If you have lots of regions like this I would consider using a 1D interpolation function instead.

[Nurzhan]

Hi Glenn,

I got your idea, but does 1-D interpolation will work for my case (see attached photo)? As per my understanding if temperature was uniform at given x value than 1-D interpolations make a sense.

[ghorrocks]

No, 1D interpolation would not work for your 2D case.

You could use a 3D interpolation where you set the 3rd dimension to zeros. That would be a single function, but note it uses nearest neighbour interpolation and that means the transitions between temperature regions can be a little weird sometimes.

Maybe your nested if statements are the best way to go.

[Nurzhan]

Thank you guys for given advises. I will try IF expression then.

[Nurzhan]

I found mistake IF function for my case perfectly.

Regards,
Nurzhan

[Opaque]

I am bit confused by your description. If you already meshed the parts, I imagine they show up as mesh entities under Mesh in CFX-Pre. If you already created the domains using such parts, the domains should also show up on the outline tree, correct ?

If you want to set the initial temperature distribution within one of the domain you have defined, you can open the Domain Editor, Click on the Domain Initialization tab, and input your temperature (x,y,z) distribution via a CEL expression.

If you want to set the initial temperature distribution within a mesh region (2D, or 3D), you can do so by creating your CEL expression for the distribution, and multiply it by the "inside()@Locator" function. For example, let's assume you have mesh regions named "Part 1", and "Part 2", and you want to specify the temperature as a quadratic function in "Part 1", and cubic in "Part 2", you will input

Temperature = (x * x + y * y) * inside()@Part 1 + (x * x * x + y * y * y) * inside()@Part 2.

If you want to do so for domains, the syntax is similar:

Temperature = (x * x + y * y) * inside()@Domain 1 + (x * x + y * y) * inside()@Domain 2

or on 2D locators

Temperature = (x * x + y * y) * inside()@TheInlet + (x * x + y * y) * inside()@MyWall

In summary, if the coordinates describing your expressions match the mesh region boundaries, there is no need for IF statements anywhere.

Hope the above helps,

[Nurzhan]

If you already meshed the parts, I imagine they show up as mesh entities under Mesh in CFX-Pre. If you already created the domains using such parts, the domains should also show up on the outline tree, correct ?

I already simulated this problem by using domain interface and setting each part as a separate domain. However, when I will complicate my model the domain interface may cause some problem and mistakes in my calculations. Hence, I was trying to use another method to solve this problem and as it was proposed I tried IF function.

Your idea with "inside()@Locator" also sounds interesting, as "IF" function is quite "messy". Moreover, I personally found "IF" function quite inconvenient and limited, as its principle is IF(test, res1, res2) and I have to specify only one condition at test parameter.