# High torque coefficient Cm for Vertical Axis Wind Turbine (VAWT)

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 February 28, 2010, 08:33 High torque coefficient Cm for Vertical Axis Wind Turbine (VAWT) #1 New Member   Join Date: Nov 2009 Posts: 22 Rep Power: 7 Hello, I am modelling the 2D vertical axis wind turbine (VAWT). The turbulence model is k-epsilon with std wall function. I simulate 4 angular velocities: 5, 10, 15 and 20 rad/s. Wind velocity is 11 m/s. Model is using U-RANS with sliding mesh. Problem is that I obtain excessively high torque calculated from the Cm (4 to 5 times larger than it should be). Cm is obtained from Fluent, torque calculated with the Cm definition(Cm=T/(0.5 x rho x v^2 x A x R). Time step: tried both time steps corresponding to 1 degree and 1/8th degree. Results perfectly match so the 1deg step is fine enough. I would be very grateful to the one who can spot if and/or where I am making a mistake and can contribute to making this simulation happen the best way. Thanks All the best TonyMac Last edited by tony00; March 17, 2010 at 06:25. Reason: wrote seconds instead of degrees to define the angular step increment

 March 16, 2010, 17:34 #2 Member   benoit paillard Join Date: Mar 2010 Posts: 42 Rep Power: 7 that might sound - and actually be - silly but check that you actually divided the torque by the appropriate value, to get a reduced coefficient instead of a Nm torque. That happened here not too long ago.

 March 19, 2010, 09:26 #3 New Member   Join Date: Nov 2009 Posts: 22 Rep Power: 7 Hello Benoit, all solved and getting pretty good results now. As you suggested it was indeed a problem with the constants entered in report-> reference values. Thanks Tony

 March 22, 2010, 23:43 Change fluent reference values #4 Member   Haris Hameed Join Date: Oct 2009 Posts: 37 Rep Power: 7 Change fluent reference values compute velocity form inlet and change reference area to swept area your cm will change hope this work

April 1, 2010, 00:59
#5
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SHIVA
Join Date: Feb 2010
Posts: 7
Rep Power: 7
Quote:
 Originally Posted by tony00 Hello, I am modelling the 2D vertical axis wind turbine (VAWT). The turbulence model is k-epsilon with std wall function. I simulate 4 angular velocities: 5, 10, 15 and 20 rad/s. Wind velocity is 11 m/s. Model is using U-RANS with sliding mesh. Problem is that I obtain excessively high torque calculated from the Cm (4 to 5 times larger than it should be). Cm is obtained from Fluent, torque calculated with the Cm definition(Cm=T/(0.5 x rho x v^2 x A x R). Time step: tried both time steps corresponding to 1 degree and 1/8th degree. Results perfectly match so the 1deg step is fine enough. I would be very grateful to the one who can spot if and/or where I am making a mistake and can contribute to making this simulation happen the best way. Thanks All the best TonyMac
Dear Tony,

I m also facing the same problem. still i m not able to reasolve the fluent case. please give some idea to predict the Torgue and Co efficient of the performance (Cp) of the wind Turbine.

With Regards

S.SIVAKUMAR

 June 11, 2010, 05:15 #6 New Member   Join Date: Jan 2010 Posts: 28 Rep Power: 7 Hi tony, maybe I'm affected by the same problem you solved. I hope you will share with me your solution. Thanks

 February 21, 2014, 01:07 Doubt #7 New Member   dynamic Join Date: Oct 2013 Posts: 3 Rep Power: 3 In the Cm definition, what is A(area)?

March 25, 2014, 02:56
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Join Date: Feb 2014
Location: malaysia
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Quote:
 Originally Posted by harishameed33 Change fluent reference values compute velocity form inlet and change reference area to swept area your cm will change hope this work
what is the swept area in 2D model for vawt ?

June 2, 2014, 02:25
high value of Cm
#9
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Aalisha
Join Date: Jan 2014
Posts: 18
Rep Power: 3
Quote:
 Originally Posted by skshivas Dear Tony, I m also facing the same problem. still i m not able to reasolve the fluent case. please give some idea to predict the Torgue and Co efficient of the performance (Cp) of the wind Turbine. With Regards S.SIVAKUMAR
Hey I am also facing the same problem. I am trying to change the values for the references. IF you can share how you have solved this problem? Thanks.

-Aalisha

 January 9, 2015, 23:27 #10 New Member   Join Date: Jan 2015 Posts: 1 Rep Power: 0 For a 2D case should I take the area = 1, and in this case what should be the depth.

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