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Please Help...Effect of wind tunnel size on coefficient of drag & drag force..

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Old   March 3, 2013, 08:08
Default Please Help...Effect of wind tunnel size on coefficient of drag & drag force..
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adi
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I am getting different value of Drag Force Fd & Coefficient of Drag for a verticle plate of 1 m^2 cross sectional area and 100 mm thickness while changing the wind tunnel size in project Falcon by autodesk (I attached photo of analysis with different wind tunnel size..take a look). plz help me to decide optimal size of virtual wind tunnel in falcon so that i can get correct answer..


2. Wht is the volume stand for that i highlighted in the pics??


plz reply..
Thanks & Regards..
Attached Images
File Type: jpg 100 MM.jpg (31.3 KB, 25 views)
File Type: jpg 100 MM 2.jpg (31.7 KB, 18 views)
File Type: jpg 100 MM 3.jpg (31.4 KB, 15 views)
File Type: jpg 100 MM 4.jpg (30.5 KB, 13 views)
File Type: jpg MM 100 5.jpg (38.2 KB, 10 views)
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Old   March 3, 2013, 09:34
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Quote:
Originally Posted by addy01 View Post
I am getting different value of Drag Force Fd & Coefficient of Drag for a verticle plate of 1 m^2 cross sectional area and 100 mm thickness while changing the wind tunnel size in project Falcon by autodesk (I attached photo of analysis with different wind tunnel size..take a look). plz help me to decide optimal size of virtual wind tunnel in falcon so that i can get correct answer..
What is the correct answer? (In the non-virtual world companies spend large amounts of money finding which independent commercial experimental facilities give the "best" answer.)
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Old   March 5, 2013, 10:24
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You have to desired based on characteristics length of model
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Old   March 5, 2013, 12:52
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Quote:
Originally Posted by addy01 View Post
I am getting different value of Drag Force Fd & Coefficient of Drag for a verticle plate of 1 m^2 cross sectional area and 100 mm thickness while changing the wind tunnel size in project Falcon by autodesk (I attached photo of analysis with different wind tunnel size..take a look). plz help me to decide optimal size of virtual wind tunnel in falcon so that i can get correct answer...
I am not familiar with Project Falcon but, ideally, you don't want the wind tunnel's walls to affect your "measurements" therefore, they should be placed as far from the model as possible. In the case of an actual wind tunnel, an experimenter makes the model smaller so that there's no (or minimum anyway) interaction with the walls. In the case of the virtual wind tunnel you can have the actual dimensions of your model and make the wind tunnel as big as you computer can handle. For example, when we're dealing with airfoils, we place the boundaries at approximately 20c away from the airfoil... From the numerical point of view, this is done as well, to avoid influence of the boundary conditions on the solution.

Maybe someone who is more familiar with the specific application can give you more insight into it.
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Old   March 9, 2013, 02:57
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Dear friend I checked a research done on this issue before but the researcher was using ansys fluent and please note that there is no standard dimensions for wind tunnel and conclusion is take from the right, left, top and up stream a distance equale 5 times your model width and take after the model in the down stream about 10 to 12 times the model width too,

hope you are getting a good results with this dimensions, and there is anothe way to check your results because your model shape is regular so you can check the avarage drag and left coeff. from any code like BS, thank you


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Old   March 12, 2013, 14:38
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If you specifically study the force and the drag, so you must create a very large wind tunnel for your purpose. It's supposed to have a wind tunnel with the typical length scale of 30 times at the typical length scale of the model.

I have one individual idea like that. Try to resize your wind tunnel until the result is independent or weakly dependent on the wind tunnel size, say, if the results are about 5% different in some norms. Then you will get the ideal size of your wind tunnel for the test case.
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