CFD Online Discussion Forums

CFD Online Discussion Forums (
-   CFX (

Roberto Salvador July 13, 2006 09:03

I have made pressure loss calculations with ansys cfx. I have programmed the basic darcy weisbach equation in order to get such losses. I have validated it comparing the results of the simulation with calculations by hand using the same model. The proccess is as follows:

1.- I have done a model of a straight tube. 2.- I have given as constant value for the problem the friction factor in darcy-weisbach equation. This factor can be obtained by use of Moody's chart, but I want to use the cfx capabilities in order it can calculate it directly.

so I have an equation that gives the same result than Moody's chart. This is the colebrook-white equation. This equation solves the friction factor as a funtion of itself, so if you want to solve it you must solve it by iteration.

This is the first question:

Is there anybody who knows how can i program an iteration in ansys cfx?

colebrook-white equation is as follows:


The second problem is the following:

I have given initial conditions to the model. I have specified a determined flow rate, but it's constant. So if i want to obtain pressure losses for several flow rates I should run the same simulation several times varying the flow rates in ordel to get such losses.

The question is:

Is there any way to do this in such a way that I can specifiy a flow rate range and ansys can execute the simulation in the flow range specified?

How could I program a bath proccess in ansys cfx?

Thanks in advance

Patrick July 14, 2006 01:19

Batch mode: CFX Community, Technical Tips: Running solver jobs in batch and job scheduling 27 October 2005

Dr. Bian July 14, 2006 10:04

More commands can be viewed from the command line (DOS window) started through CFX launcher by running:

cfx5solve -help

Robin July 14, 2006 12:23

Hi Roberto,

I'm not sure I understand what you are trying to do. Are you calculating the friction factor to apply at a boundary condition?

To calculate the friction factor directly, use the Swamee-Jain equation instead

Regards, Robin

Roberto Salvador July 15, 2006 12:22

Hi, Robin. I have seen the Swamee-Jain ecuation, and I have validated it by comparing it with the colebrook white ecuation. I have found that it gives results within 0.0001 accuracy so this time you have helped me to solve the friction factor without the use of iterative proccesses.

So now I need to investigate the advice given to me respect to batch proccessing.

Roberto Salvador July 15, 2006 12:30

Hi Patrick, where should I find the document that you are refering to?

All times are GMT -4. The time now is 07:24.