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-   -   High torque coefficient Cm for Vertical Axis Wind Turbine (VAWT) (https://www.cfd-online.com/Forums/fluent/73134-high-torque-coefficient-cm-vertical-axis-wind-turbine-vawt.html)

 tony00 February 28, 2010 08:33

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

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

 bennn March 16, 2010 17:34

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.

 tony00 March 19, 2010 09:26

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

 harishameed33 March 22, 2010 23:43

Change fluent reference values

Change fluent reference values

compute velocity form inlet
and change reference area to swept area
hope this work

 skshivas April 1, 2010 00:59

Quote:
 Originally Posted by tony00 (Post 247776) 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

 esp-m1000 June 11, 2010 05:15

Hi tony, maybe I'm affected by the same problem you solved.
I hope you will share with me your solution.

Thanks

 Poojitha February 21, 2014 01:07

Doubt

In the Cm definition, what is A(area)?

 shahizare March 25, 2014 02:56

Quote:
 Originally Posted by harishameed33 (Post 251189) 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 ?

 aalisha June 2, 2014 02:25

high value of Cm

Quote:
 Originally Posted by skshivas (Post 252643) 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

 mshaheen January 9, 2015 23:27

For a 2D case should I take the area = 1, and in this case what should be the depth.

 nima2472 March 27, 2017 01:51

CM coefficient

hi