Hi,
I am studing the performances of Darrieus wind turbine composed of three Naca profiles.
I have set these values at the "reference values" in order to estimate the torque coefficient. In fact, I suggest two possibilities. Could I have please your feedbacks.
Cheers,
Possibility 1: (the study is done on 2D)
1 - Area: corde length * 3(number of blade) * 1 (depth)
2 - Depth: 1
3- Length: Radius of the rotor
Possibility 2:
1 - Area (swept area): diametre of the rotor * 1 (depth)
2 - Depth: 1
3- Length: Radius of the rotor
If you want to extract the torque value (for example in each timestep) no need to make yourself confused with all those values.
Run your simulation at least for one timestep and print the moment on your blades in Fluent console using the Force Reports dialog box. And Try to make the Net Moment and Net Coefficient values as close as possible by changing just one of the fields in the Reference Values menu while keeping others unchanged.
thanks M.Mahdi for your answer. I have tried it five times but I still don't find identical results. I have two questions if you don't mind M.Mahdi:
- Cp is a non-dimensional number (cp = (P - P,ref)/(1/2*Rho*U²*A) ) and the unit of Moment is (Nm), so why both of those values should be the same? is there any link between the torque and the pressure (physically yes but how fluent models this relation ) ?
- I have to set my moment center instead of the default value (1, 0) ?
You're welcome Fertahi.
Moment coefficients are computed, using the reference values specified in the Reference Values panel. The moment coefficient is defined as the moment divided by ½ ρv2AL where the density, velocity, area, and length explicitly specified in the Reference Values panel. When you make the value of above equation equal to 1 then the output value for both moment and moment coefficient will be same.
The moment center should locate at the rotor column coordinates.
Dear Fertahi and Mahdi
I am also working in same field and trying to simulate Savonius turbine in water channel in order to get Cp (power coefficient) with respect to different TSR.
I am
I am trying calculate Cp by using formula as follow:
Cp= Torque*omega / (0.5* Rho* swept area * V^3)
where omega is defined as input parameter at turbine walls, Torque is as output parameter in CFD post. Problem which I am facing is, Cp is always increasing with respect to TSR (angular velocity). Need help in this case
Dear Sir,
further from above discussion , I have some question if you don't mind :
Question 1 why are we trying to get identical value of moment and moment coefficient ?
Q2 If I am getting directly moment from Fluent then how Coefficient of moment is helpful in calculation of Torque or Coefficient of power?
Q3 In above discussion one formula is written cp = (P - P,ref)/(1/2*Rho*U²*A)....
does Cp stand for coefficient of power or pressure coefficeint
what are P and P,ref and how one can get these value from Fluent.
thanks in advance
It is better to refer to the literature in this case to know how these parameters are defined. Yes you can calculate the torque easily in Ansys Fluent, but the the value of torque coefficient is very important if you wish to compare with any other available work and any mistake in defining the coefficient will affect greatly the comparison.
Dear Anuj,
The effectuve way to calculate Cp coefficient is to use this formula:
Cp = Lambda*Cm
where Lambda (Tip speed ratio) = tangential velocity / Velocity of the flow at the inlet.
You can monitor Cm coefficient each time step that corresponds to an angle of rotation of savonius. For exemple, if you get Cm each 1° of rotation then you will have results that are in good agreaments with experiments.
The procedure is as follow:
1 - You fixe the angulare velocity (it depends on the technic that you are using to simulate the rotation of savonius (sliding mesh, single rotating frame etc)) and the velocity of the flow.
2- You monitor Cm, make sure the you introduce the accurate origine of rotation of savonius and also the direction of its rotation !!
3- You deduce Cp.
Thanks Fertahi Sir,
Further I have a doubt as :
monitoring Cm coefficient for each time step is a transient type simulation or steady type.
I have fixed all the velocity (angular velocity for single rotating frame and velocity of flow) also defined direction and origin of rotation for rotor. Also getting value of Coefficient of moment (single value). I am simulating it as a steady type.
But How Can i get values of Cm for each time step or each 1° of rotation. What Step should I follow in Fluent in order to get the same ?
Dear Yasser Sir,
Identical value of Coefficient of moment and Moment in Fluent can be achieved by hit and trial method by playing with reference area and reference length.
Reference area is Swept area of rotor. Generally, Reference length is the radius of rotor. By using these values, Cm and M has different value.
however, by changing Reference length (using hit and trial ), we will get same torque with different coefficient of moment.
So why are we trying to get identical values for both parameters (Cm and M). how will it affect my simulation results and comparison with experimental data
I am trying to simulate 2d Savonius rotor using Ansys Fluent 15. The reference values are Swept area is diameter of the rotor, depth 1m, length is radius of the rotor, But i am not getting proper result. Please help me
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