Temperature dependent viscosity
 

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!


Attachment 86944

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

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?

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.

Thanks for the advice!

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.

Thanks for the reply and advice Evcelica!

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

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

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

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

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