Calculating lift force of a wind turbine blade problem

LittleBart · June 23, 2011, 04:58

Hello everyone!

After long vacations I'm again face to face with my blade problem and again asking for your help. Thank to Simon now I can build relatively stable and adjustable unconstructed mesh for the blade. And now I'm trying to model the problem in CFX (13). Actualy, this problem is my old one, the one that made me turning to ICEM CFD and master the Mesh Skill. Thats because I thought that the results I've received are bad because of the bad mesh quality.

In my previous problem I've made a blade geometry and meshed it with CFX Mesh. The CFX problem had the following parameters:

CF:
Z - rotational axis; X - tangent in the rotor plane; Y - lengthwise the top blade

Domain:
1. Air - fluid domain - ref. pressure = 1 atm; fluid - air; CF - rotational cf with 13 rad/s velocity (expected velocity of the modeled blade at 10 m/s wind).
2. Blade - solid domain (Aluminum).

BCs:
1. Inlet - inlet surface of the air volume - Velocity = 10 m/s
2. Outlet - outlet surface of the air volume - Static pressure = 0 atm. (= ref. pressure)
3. External surface - wall - no slip wall (FF)
4. Side surfaces - domain interface Air/Air - rotational periodicity
5. Air/Blade - domain interface - fluid/solid - frozen rotor

That was the model. And these are the results:

But my main question is quality of the blade. In order to answer this question I've tried to evaluate the overall Lift Force of the blade and, as a result, Momentum or Torque. In order to compare this force with the one calculated with beam element theory.

I've calculated this with an expression

aveInt(Force X)@Blade_surf

and got the value of 13.4 N

Which made me sad.

And now I've made the same procedure with new mesh and result is 12.5 N which is proximately the same.
to be continue...

ghorrocks · June 23, 2011, 08:14

And what is the question?

LittleBart · June 26, 2011, 06:48

I'm total beginner in that kind of simulation and I'm completely not sure that I've done everything right. Especially with BCs and domains' conditions and settings.
Because the results seem not real to me. I don't know how to verify them at all.

ghorrocks · June 26, 2011, 07:17

http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F

LittleBart · June 29, 2011, 03:33

I've seen this for many times. But you didn't get me right. I can't estimate is the whole workflow is correct. I mean, am I on the right way. For example, I have Outlet BC = 'Static pressure=0'. But I'm not sure that this will be correct for that kind of analysis . So I need someone to tell me that I'm right in this or visa versa - to tell me that correct BC is 'Constant speed' or some like that.

The most important for me is the question of force. Will it be correct to estimate the Lift as stated (intArea(Force X)@bladearea) ? that the crucial point.

And how to calculate efficiency coefficient of the blade?

June 23, 2011, 04:58	Calculating lift force of a wind turbine blade problem	#1
LittleBart New Member LittleBart Join Date: Jan 2011 Posts: 20 Rep Power: 15	Hello everyone! After long vacations I'm again face to face with my blade problem and again asking for your help. Thank to Simon now I can build relatively stable and adjustable unconstructed mesh for the blade. And now I'm trying to model the problem in CFX (13). Actualy, this problem is my old one, the one that made me turning to ICEM CFD and master the Mesh Skill. Thats because I thought that the results I've received are bad because of the bad mesh quality. In my previous problem I've made a blade geometry and meshed it with CFX Mesh. The CFX problem had the following parameters: CF: Z - rotational axis; X - tangent in the rotor plane; Y - lengthwise the top blade Domain: 1. Air - fluid domain - ref. pressure = 1 atm; fluid - air; CF - rotational cf with 13 rad/s velocity (expected velocity of the modeled blade at 10 m/s wind). 2. Blade - solid domain (Aluminum). BCs: 1. Inlet - inlet surface of the air volume - Velocity = 10 m/s 2. Outlet - outlet surface of the air volume - Static pressure = 0 atm. (= ref. pressure) 3. External surface - wall - no slip wall (FF) 4. Side surfaces - domain interface Air/Air - rotational periodicity 5. Air/Blade - domain interface - fluid/solid - frozen rotor That was the model. And these are the results: But my main question is quality of the blade. In order to answer this question I've tried to evaluate the overall Lift Force of the blade and, as a result, Momentum or Torque. In order to compare this force with the one calculated with beam element theory. I've calculated this with an expression aveInt(Force X)@Blade_surf and got the value of 13.4 N Which made me sad. And now I've made the same procedure with new mesh and result is 12.5 N which is proximately the same. to be continue...

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June 23, 2011, 08:14		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	And what is the question?

June 26, 2011, 06:48		#3
LittleBart New Member LittleBart Join Date: Jan 2011 Posts: 20 Rep Power: 15	I'm total beginner in that kind of simulation and I'm completely not sure that I've done everything right. Especially with BCs and domains' conditions and settings. Because the results seem not real to me. I don't know how to verify them at all.

June 26, 2011, 07:17		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F

June 29, 2011, 03:33		#5
LittleBart New Member LittleBart Join Date: Jan 2011 Posts: 20 Rep Power: 15	I've seen this for many times. But you didn't get me right. I can't estimate is the whole workflow is correct. I mean, am I on the right way. For example, I have Outlet BC = 'Static pressure=0'. But I'm not sure that this will be correct for that kind of analysis . So I need someone to tell me that I'm right in this or visa versa - to tell me that correct BC is 'Constant speed' or some like that. The most important for me is the question of force. Will it be correct to estimate the Lift as stated (intArea(Force X)@bladearea) ? that the crucial point. And how to calculate efficiency coefficient of the blade?