CFD Online Discussion Forums

CFD Online Discussion Forums (
-   CFX (
-   -   Efficiency calculation (

ayothicfd May 14, 2012 11:56

Efficiency calculation
Dear all,
I am doing fan (forced draft) simulation to predict performance curve in Ansys CFX. From the simulation, I don't know how to calculate the efficiency of fan from each simulation result. I have thought that
efficiency= (Del P*discharge)/(Torque of blades*omega)
Is this expression correct way of calculating efficiency?
And moreover, Is it possible to drive the same from Turbo workspace? What is the main purpose of turbo workspace?

Thank you all...

ghorrocks May 14, 2012 18:46

The turbo workspace is a set of macros to make calculating standard turbomachinery performance parameters easier. I am pretty sure it contains efficiency calculations. Also I strongly recommend you do the CFX tutorials and the CFD-post tutorials on rotating machinery, and read the best practises guide on rotating machinery.

ayothicfd May 15, 2012 10:34

Dear Glenn,
First of all, I am thanking you to reply. Actually my geometry consists of 4 different parts such as suction duct, Inlet guide vane, Impeller and Volute. To work in turbo workspace, I need to isolate the domain into single one for initialization. May I get an isolated domain by setting composite region? or any other method will be available to create an isolated domain?
By doing manual calculation, I will get the efficiency from the corresponding result (values gathered from simulation). What could be the deviation between turbo workspace result and manual result? Will it be more significant?

ghorrocks May 15, 2012 19:29

I do not work with rotating machinery so am not familiar with the macro or how to use it. But have you done the tutorials showing how to use it? That seems the obvious place to start.

ayothicfd May 16, 2012 12:36

Dear Glenn,
I am reading ansys manual on turbo workspace. I am going to do the turbo workspace tutorial problems. After dictating the tutorial problems, I will share the details. Eagerly seeking your support. Thank you.

ayothicfd May 17, 2012 09:54

Dear Glenn,
I have gone through turbo workspace tutorials. The result file of Gas turbine (Periodic domain of Stator with Rotor) has been given. By working on the result, I have noticed that macros are available for the following cases only
1. Liquid pump performance
2. Gas turbine performance
3. Gas compressor performance
4. Liquid turbine performance
5. Fan noise
Other than there will be curves for field variables available by generating a line which is passing through the domain. By seeing the macro itself, the required values are retrieved from the result file to calculate the performance.

ghorrocks May 17, 2012 18:39

Don't forget to have a look at the best practises guide for turbomachinery. That has further information which may be useful.

Far May 18, 2012 01:28

Turbospace uses the integrated pressure and temperature values at inlet and outlet, not just the mass averaged or area averaged .

olegmang May 18, 2012 04:48

I do such thing (performance curve) in Workbench. You need to create expression for your efficiency and "Del P*discharge" all other parameters are already present in expressions of CFX Post. Then you set your efficiency (pressure ratio) as the output parameter (read workbench tutorials) and rotation speed (in cfx pre) as the input parameter. as a result - you can get performance curve.

Regards, Oleg.

ayothicfd May 21, 2012 21:40

2 Attachment(s)
I have done a practice on post file given in bin directory. In the attached image (, you can easily understand that geometry has stator and rotor. To enable turbo workspace, I have taken this model (actually the problem is about turbine). By using macros on fan, there is study on noise analysis of fan alone is available. I have attached my geometry image ( for your understanding. By enabling report of the simulation, I can easily get the total torque applied on blades. Has it calculated through only by manual or setting expression in Pre?

Thanks to all.

olegmang May 22, 2012 05:01

You can create expression in Post. And then set it as the workbench output parameter. In fact i've already mentioned necessary steps before. But if you dont have Workbench i'm not sure how can i help you.

ayothicfd May 22, 2012 12:24

Hi Oleg,
You were right. Thank you for giving your command. Actually, I puzzled that the macros available in Turbo workspace will help to evaluate the efficiency. But they will be only available for turbine or compressor to evaluate compression or expansion efficiency(either isentropic or polytropic). By considering my case, Fan is working under Incompressible and Isothermal flow. I got cleared. Once again, I thank you.

All times are GMT -4. The time now is 22:31.