# How to calculate the average of torque in transient Ansys CFX Simulation

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 April 3, 2013, 07:18 How to calculate the average of torque in transient Ansys CFX Simulation #1 New Member   Benjamin Stanke Join Date: Sep 2011 Posts: 18 Rep Power: 6 Hi, I am trying to calculate the power of a wind turbine in a transient simulation. My simulate of a rotor blade works well but as a result I need the torque of the blade as mean over many time steps. For my CFD simulation I am using Ansys CFX 14.5. I can get the torque in CFD-Post ->Calculators -> Function Calculator -> Fuction:torque (Location). But just for the current time step I chose. Those anyone know how I can get the torque Results over all my time steps? As a plot, a file or somehow else? Thanks ahead.

 April 3, 2013, 07:28 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 11,946 Rep Power: 93 I would export the torque versus time history and do the averaging in another package like excel, matlab or whatever you wish. To get the full time history, make a monitor point set to torque_x/y/z()@location and then export this point in the solver manager.

 April 3, 2013, 08:07 #3 New Member   Benjamin Stanke Join Date: Sep 2011 Posts: 18 Rep Power: 6 Thanks @ghorrocks. It works just perfect in this way!

 April 4, 2013, 09:27 #4 Senior Member   Matthias Voß Join Date: Mar 2009 Location: Berlin, Germany Posts: 446 Rep Power: 12 in case you did not set the monitor point before calculating, here is a little script which loops through each time step for a given res-file. start it from the cfx command line via cfx5perl. res-file needs to be next to the script (or viceversa). Code: ```>load filename=YOURRESFILE.res ! \$Liste = getValue("DATA READER","Timestep List"); ! @TIMELIST = split(/,/,\$Liste); ! print "@TIMELIST \n"; ! open OUT, ">YOURDATA.dat"; ! print OUT "Time;Massflow Inlet;Massflow Düse;Massflow Mündung\n"; #HEADER ! foreach \$TS(@TIMELIST){ > load timestep = \$TS ! print "calculating timestep \$TS \n"; ! (\$time, \$timeunits) = evaluate("Time"); ! \$pin=massFlow("INLET"); ! \$pduese=massFlow("Domain Interface 1 Side 2"); ! \$pmuendung=massFlow("Domain Interface 2 Side 1"); ! print "\$time;\$pin;\$pduese;\$pmuendung \n"; ! print OUT "\$time;\$pin;\$pduese;\$pmuendung\n"; ! }; ! close OUT; > close``` n0ukh3z007 likes this.

March 13, 2014, 14:19
#5
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Fernando Ruviaro
Join Date: Mar 2014
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Quote:
 Originally Posted by ghorrocks I would export the torque versus time history and do the averaging in another package like excel, matlab or whatever you wish. To get the full time history, make a monitor point set to torque_x/y/z()@location and then export this point in the solver manager.
Hello. I can't set a torque monitor point. When I created it, torque wasn't in the output variable list. I've typed "torque_z()@pa" ("pa" was the name of the surface I've wanted to evaluate the torque around the z axis) in the box and it just goes empty again as I press "Apply". Is there any special way to do it?

 March 13, 2014, 14:36 #6 New Member   Benjamin Stanke Join Date: Sep 2011 Posts: 18 Rep Power: 6 "torque_z()@pa" should actually work. Do you need torque over time or are you simulate 'steady state'?

 March 13, 2014, 14:43 #7 New Member   Fernando Ruviaro Join Date: Mar 2014 Posts: 9 Rep Power: 4 Torque over time. I'm simulating a vertical axis wind turbine and I need in the torque vs angular position curve.

 March 13, 2014, 14:53 #8 New Member   Benjamin Stanke Join Date: Sep 2011 Posts: 18 Rep Power: 6 If you create a output expression with "torque_z()@pa" in CFX-Setup you should get the curve as User Points in CFX-Solver.

 March 13, 2014, 15:18 #9 New Member   Fernando Ruviaro Join Date: Mar 2014 Posts: 9 Rep Power: 4 I will try it.

March 13, 2014, 16:16
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Fernando Ruviaro
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Is it what I should do? I type "torque_z()@pa", press enter and apply and the field doesn't go empty. But, if I press ok, then open again the monitor point, the output variable goes automatically to "Absolute Pressure".
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 March 13, 2014, 17:00 #11 New Member   Benjamin Stanke Join Date: Sep 2011 Posts: 18 Rep Power: 6 Ok you have to change the Option drop down menu from "Cartesian Coordinates" to "Expression" then CFX will accept the torque-espresssion. God luck

 March 14, 2014, 13:35 #12 New Member   Fernando Ruviaro Join Date: Mar 2014 Posts: 9 Rep Power: 4 It works now. Thank you very much The unit of the torque measured is relative to the solution units, right?

March 14, 2014, 16:56
#13
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Fernando Ruviaro
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I was testing the results with this method and noticed that the value of torque obtained with the monitor point differed a bit from the value acquired by using the 'Function Calculator' (in Calculators) in a given timestep.

So, to have an idea of this difference I've made a simple simulation of a rotating "square" in an air flux, first with it still, to have the inicial values, and then with it moving, and a monitor point measuring the force in the x direction in the sides of the square (defined as "paredes").

After, I've compared the data exported from the monitor point and the force in the x direction evaluated at each timestep using the 'Function Calculator'. The data is shown in the third image (in the table, data refers to "exported data", and manual to data obtained with the function calculator).

It seems that the x axis using the monitor point is refers to a frame of reference fixed in the rotating domain. I've tried marking the "Coord Frame" box and selectinig the "Coord 0" (the only one that appear), but the result is the same.

How can I export the data referred to the global coordinate system?
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 Capturar.JPG (51.5 KB, 72 views) Capturar2.JPG (94.6 KB, 100 views) Capturar3.JPG (81.9 KB, 124 views)

 April 24, 2014, 11:13 Average Temperature #14 Banned   Join Date: Feb 2013 Posts: 16 Rep Power: 0 Hello, The subject treated here is very interesting. I would like to ask a question in my turn. My simulation on CFX is on heating a large block into contact with a combustion chamber. A heat flow is transmitted to the block and the temperature of the block varies with time. So I get for each time step the temperature profiles of tho block. When I want to see the transient variation of the block temperature with XY - transient or sequence in Chart I can do it for points only (not all the domain). Does anyone can tell me, please, how to plot the average temperature of all my block function of time? Or how to export at each timestep the average temperature of my block. Thank you in advance for your help.

 April 24, 2014, 12:29 #15 Senior Member   Matthias Voß Join Date: Mar 2009 Location: Berlin, Germany Posts: 446 Rep Power: 12 You can create an expession like volumeAve(T)@block And use it instread of the Point in the Chart schematic. For the export via script see #4 above.

 April 24, 2014, 14:08 #16 Banned   Join Date: Feb 2013 Posts: 16 Rep Power: 0 Thank you so much.

 May 16, 2014, 07:00 #17 New Member   Walter Join Date: May 2014 Posts: 2 Rep Power: 0 Thank you so much for all of this information! I would like to monitor the pressure of a moving wall. Unfortunately it doesn't work like that: "pressure()@MOVING_WALL" Ansys doesn't know the word "pressure". What can I do?

 May 16, 2014, 09:22 #18 Senior Member   Edmund Singer P.E. Join Date: Aug 2010 Location: Minneapolis, MN Posts: 510 Rep Power: 11 The variable goes into the parenthesis. The first part is how you want to evaluate the variable. In your case for example: areaAve(Pressure)@moving_wall maxVal(Pressure)@moving_wall minVal(Pressure)@moving_wall can give you the area average, the max value and min value. Please look up CEL in the help.

 May 16, 2014, 10:40 #19 New Member   Walter Join Date: May 2014 Posts: 2 Rep Power: 0 Thank you very much! I'm new in CFX. I will look up CEL. Saved me a lot of hours! Thank you!

January 25, 2016, 07:27
#20
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Ronald Thompson
Join Date: Mar 2015
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Quote:
 Originally Posted by ghorrocks I would export the torque versus time history and do the averaging in another package like excel, matlab or whatever you wish. To get the full time history, make a monitor point set to torque_x/y/z()@location and then export this point in the solver manager.
Hi Glenn,
I want to do something similar with what you showed Benjamin how to do, but I'm using fluent, I want to export the torque at each time step of my analysis to determine what is the optimum angle of attack throughout the rotation,

I tried creating a monitoring point and setting the expression as stated above in the calculation activities in fluent but when I run it is says invalid

what am I doing wrong thanks

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