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Old   September 27, 2009, 10:12
Default calculating Cl and Cd
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s.k
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Hi,
i am a university student and am completing a thesis using the CFD Fluent software program. Im relatively new to the program and i need a little help with a few problems i have encountered.
Im trying to calculate the Coefficient of lift and Coefficient of drag values for varying angles of attack on an aerofoil. How do i get fluent to display these varying values on screen? (not just convergence graph)

also, i have been told that the values of Cl and Cd which fluent gives out are not the absolute correct values. Do these values have to be altered in some way, e.g. imposed onto a vector?

i would really appreciate any advice you could give me,

thanks!
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Old   October 21, 2009, 13:35
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Try this tutorial.
It explains the meshing in Gambit and also the set up it Fluent.

http://courses.cit.cornell.edu/fluent/airfoil/step1.htm

For chaning the angles you have to change the velocity in the x and y direction.

Enjoy
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Old   November 24, 2009, 14:59
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Rich
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hi, i have two questions concerning the cl and cd monitor.

1) just to be sure, the last value you geton your cl/cd convergence graph is the cl and cl value for the surface you chose before you started the calculation?

2) now in case we have a 3d car (e.g. Porsche)and we want to caluclate cl over the cars spoiler if one picks x=0 y=0 and z=1, that means that the spoiler has zero attack coming from the airflow at the inlet.

but in reality i think the airflow over the car isn't flowing parallel to the x axis, but its flowing angled over the cars back/rear window where it reaches the spoiler. does fluent that take into account or does one need to find out the angle of the cars back window?

thanks
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Old   November 24, 2009, 18:10
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Chris
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Quote:
Originally Posted by dralosdir View Post
hi, i have two questions concerning the cl and cd monitor.

1) just to be sure, the last value you geton your cl/cd convergence graph is the cl and cl value for the surface you chose before you started the calculation?

2) now in case we have a 3d car (e.g. Porsche)and we want to caluclate cl over the cars spoiler if one picks x=0 y=0 and z=1, that means that the spoiler has zero attack coming from the airflow at the inlet.

but in reality i think the airflow over the car isn't flowing parallel to the x axis, but its flowing angled over the cars back/rear window where it reaches the spoiler. does fluent that take into account or does one need to find out the angle of the cars back window?

thanks
1) yes

2) You set a reference force vector, not the flow direction. So if the flow was in the x direction, for example, then the lift force is in the y direction, and the reference vector for lift would be {0, 1, 0}.
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Old   November 25, 2009, 06:48
Post energy eqation in flow past a sphere
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Muhammed Asmail
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Dear Sir
how are you?
i have problem is flow past a sphere,3-dimension,unsteady state
if the energy equation is applied in flow past a sphere,how the mean value of heat tranfer calculated on surface of the sphere at each time by using FLUENT?,please can you give me the options of FLUENT in order to calculate mean value of heat tranfer calculated on the surface of sphere at each time .
i am waiting your reply quickly
please,please help me
many thanks to you
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Old   December 19, 2009, 07:36
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Muhammed Asmail
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Quote:
Originally Posted by Chris D View Post
1) yes

2) You set a reference force vector, not the flow direction. So if the flow was in the x direction, for example, then the lift force is in the y direction, and the reference vector for lift would be {0, 1, 0}.
Dear Chris
the cd on cylinder appeared sin wave but on the sphere not appeared sin wave why?
many thanks
i am waiting your reply quickly
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