# Efficiency calculation

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 May 14, 2012, 11:56 Efficiency calculation #1 New Member   Ayothi Ramanathan Join Date: Sep 2011 Posts: 28 Rep Power: 8 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...

 May 14, 2012, 18:46 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 14,202 Rep Power: 110 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.

 May 15, 2012, 10:34 #3 New Member   Ayothi Ramanathan Join Date: Sep 2011 Posts: 28 Rep Power: 8 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?

 May 15, 2012, 19:29 #4 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 14,202 Rep Power: 110 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.

 May 16, 2012, 12:36 #5 New Member   Ayothi Ramanathan Join Date: Sep 2011 Posts: 28 Rep Power: 8 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.

 May 17, 2012, 09:54 #6 New Member   Ayothi Ramanathan Join Date: Sep 2011 Posts: 28 Rep Power: 8 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.

 May 17, 2012, 18:39 #7 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 14,202 Rep Power: 110 Don't forget to have a look at the best practises guide for turbomachinery. That has further information which may be useful.

 May 18, 2012, 01:28 #8 Super Moderator   Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,358 Blog Entries: 6 Rep Power: 45 Turbospace uses the integrated pressure and temperature values at inlet and outlet, not just the mass averaged or area averaged .

 May 18, 2012, 04:48 #9 Member   Oleg Join Date: Nov 2011 Location: Ukraine, Kharkov Posts: 57 Rep Power: 8 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.

May 21, 2012, 21:40
#10
New Member

Ayothi Ramanathan
Join Date: Sep 2011
Posts: 28
Rep Power: 8
Hi,
I have done a practice on post file given in bin directory. In the attached image (http://www.cfd-online.com/Forums/att...1&d=1337650094), 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 (http://www.cfd-online.com/Forums/att...1&d=1337650155) 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.
Attached Images
 Screen.jpg (91.3 KB, 161 views) Screen2.jpg (90.5 KB, 127 views)

 May 22, 2012, 05:01 #11 Member   Oleg Join Date: Nov 2011 Location: Ukraine, Kharkov Posts: 57 Rep Power: 8 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.

 May 22, 2012, 12:24 #12 New Member   Ayothi Ramanathan Join Date: Sep 2011 Posts: 28 Rep Power: 8 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.

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