[QaisKhraisat]

Hi Everyone,
I am trying to simulate a water lubricated bearing on CFX. With that in mind, I want to take into consideration the viscosity variation with temperature. The attached photo shows the relation between the kinematic viscosity [cSt] and Temperature [K]. I would like to import this formula into CFX, and I tried writing an expression, but without any success.

Can anyone explain to me on how do that please?

Note:
a, n, and m are constants.

Thank you very much in advance!


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[Opaque]

That is an implicit formula for kinematic viscosity as a function of T.

Which explicit form of that formula did you attempt to use? We (forum members) can then help you with the CEL details

[QaisKhraisat]

Thanks for the reply Opaque!

The formula was based on MacCoull and Walther's relation which is provided in the literature in its implicit form. The image in this link (https://1drv.ms/u/s!AkCnaOk1rReFzULinQPjc1_aurxy) shows the formula in its original form.

Is it possible to write it in this form into CFX?

[Opaque]

ANSYS CFX expects a formula for viscosity explicitly, say

Dynamic Viscosity = F (T)

In your case, you must solve for "nu" as a function of T

nu = density * ( 10** ( 10 ** ( ...) ) - a)

Just be careful to keep all the evaluations within bounds.

[QaisKhraisat]

Thanks for the advice!

[evcelica]

MathCAD is great at algebra, see attached image.

And then viscosity written in CEL: = -Aconstant + (10^((10^Nconstant)/((TempUnitless)^Mconstant)))
Define TempUnitless as Temperature*1[K^-1] (if it is in units of K)
You can plot your expression when defining it to make sure it is what you expect.

[QaisKhraisat]

Thanks for the reply and advice Evcelica!

[Mayank Shakya]

Hello
I am also working on the same problem, but facing problem. The solver is ending up with error.
If any one can help please suggest what I can do.
I want to use temperature dependent viscosity in my model.
Thank and Regards

[QaisKhraisat]

Hi,

Make sure you specify the units at the end only. This is the formula that I wrote:

((10^(10^(n-(m*(log(T*1[K^-1]))))))-a)*(1000)*(10^-6) [Pa s]

In the formula (n, m , a) are constants. T represents the temerature, but notice that I added (k^-1) to make it a dimensionless value. At the very end, I specify the unit which is (Pa s)

BE CAUTIOUS with the UNITS in your case.

Hope this was helpful.
Qais Khraisat

[Mayank Shakya]

Hello,
Thank you very much the problem is solved.
Do you know how I can calculate Frictional Torque in Hydrodynamic Thrust Pad Bearing.

[ghorrocks]

Use the CEL expressions like torque_x(), torque_y() etc on the boundary face which is the face you want the torque from.

[Mayank Shakya]

Hello
Thank you very much I got all the problem solved.