# NACA0012 airfoil Critical reynolds number

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 December 7, 2012, 13:58 NACA0012 airfoil Critical reynolds number #1 New Member   Kianoosh Join Date: Jul 2012 Posts: 20 Rep Power: 7 hi guys i need a resource for critical Reynolds number over NACA0012 and NACA0015 and NACA0018 airfoils. I search a lot but i can't find a paper or part of book that report these numbers. can any body help me and recommend me a valid resource. thx

 December 7, 2012, 15:31 sajid #2 New Member   Chaudhary Join Date: Dec 2012 Location: Pakistan Posts: 8 Rep Power: 7 dear it can be calculated by using hydraulic dia meter kianoosh_py likes this.

December 7, 2012, 18:43
#3
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Kianoosh
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Quote:
 Originally Posted by sajid dear it can be calculated by using hydraulic dia meter
thx, but how i can calculate the critical Reynolds umber via hydraulic diameter for airfoils?

 December 7, 2012, 19:34 #4 Senior Member   Join Date: Jul 2009 Posts: 247 Rep Power: 12 If you are trying to establish the transition point, the first approximation is to use the flat plate value of Re = 500000, where the distance is measured from the nose of the airfoil (or the attachment point for high angles of attack). Googling critical Reynolds airfoil may provide you with more info.

December 7, 2012, 19:45
#5
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Kianoosh
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Quote:
 Originally Posted by agd If you are trying to establish the transition point, the first approximation is to use the flat plate value of Re = 500000, where the distance is measured from the nose of the airfoil (or the attachment point for high angles of attack). Googling critical Reynolds airfoil may provide you with more info.
i use google with different keyword but ican't find nothing proper. but i found it's diffrent value for diffrent angles of attack and a major question for me:
in angle of attack of 0 degrees we don't have a separation point on NACA 0012 airfoil (i use the fluent for simulation) at re=500,000 , it that mean the flow is laminar. but it shouldn't be correct, because over the flat plate the flow is turbulent for re>500,000 and on the airfoils we have thickness on the critical Reynolds number should be smaller.

is it correct?

otherwise in the Huang et al. work (2004), this is my base type for validation, the flow with re=500,000 was introduced fully turbulent flow over NACA0012 airfoil.

 December 7, 2012, 23:58 #6 Senior Member   Join Date: Jul 2009 Posts: 247 Rep Power: 12 I'm not sure what you are saying here, but laminar flow over a NACA0012 will separate. Like I said, Re = 500000 is only a rough guide. For more info you could look here www.risoe.dk/rispubl/VEA/veapdf/RIS-R-987.pdf if this link works. I found it by googling "critical reynolds number airfoil"

December 8, 2012, 08:28
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Use X-foil
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December 8, 2012, 08:39
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Kianoosh
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 Originally Posted by truffaldino Use X-foil
thx a lot
i don't know how to use X-foil. can you explain how to run X-foil?

 December 8, 2012, 09:28 #9 Senior Member     Join Date: Jan 2011 Posts: 248 Blog Entries: 5 Rep Power: 10 It is extremely easy to lern and use. Google x-foil tutorial or x-foil manual or look at Session for NACA0012 will look as follows: opening x-foil you will get prompt XFOIL c>, you just enter naca0012 like this XFOIL c> NACA0012 + enter the x-foil will generate naca0012 coordinates and will print the foil description followed by XFOIL prompt, then you put XFOIL c> OPER + enter you will get new prompt .OPERi, it means that you entered flow analysys subroutine. Then you put .OPERi c> visc 5E5 + enter i.e. you fixed your reynolds number to 500K and you will get prompt OPERv then you put .OPERv c> alfa 0 +enter it means your angle of attack is 0: the xfoil will show you analysys data, if it writes that computation does not converce, put again alfa 0 etc unil it converges. If you want re-initialize computations put init To exit from analysys subroutine (or any other sub-routine) to higer level routine just press enter. To change free stream turbulence parameters enter .OPERv c> vpar + enter you will get prompt VPAR. By default Ncrit=9, to decrease free stream turbulence put higer Ncrit, e.g. ..VPAR c> N 15 + enter then just press enter to return to OPERv and put your alfa For help press ? + enter To see transition and separation points use command ..OPERv c> vplot + enter you will get prompt VPLO Then put ...VPLO c> CF + enter you will see plot Cf vs X, the point where Cf=0 is the separation point kianoosh_py likes this.

December 8, 2012, 10:16
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Kianoosh
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Quote:
 Originally Posted by truffaldino It is extremely easy to lern and use. Google x-foil tutorial or x-foil manual or look at Session for NACA0012 will look as follows: opening x-foil you will get prompt XFOIL c>, you just enter naca0012 like this XFOIL c> NACA0012 + enter the x-foil will generate naca0012 coordinates and will print the foil description followed by XFOIL prompt, then you put XFOIL c> OPER + enter you will get new prompt .OPERi, it means that you entered flow analysys subroutine. Then you put .OPERi c> visc 5E5 + enter i.e. you fixed your reynolds number to 500K and you will get prompt OPERv then you put .OPERv c> alfa 0 +enter it means your angle of attack is 0: the xfoil will show you analysys data, if it writes that computation does not converce, put again alfa 0 etc unil it converges. If you want re-initialize computations put init To exit from analysys subroutine (or any other sub-routine) to higer level routine just press enter. To change free stream turbulence parameters enter .OPERv c> vpar + enter you will get prompt VPAR. By default Ncrit=9, to decrease free stream turbulence put higer Ncrit, e.g. ..VPAR c> N 15 + enter then just press enter to return to OPERv and put your alfa For help press ? + enter To see transition and separation points use command ..OPERv c> vplot + enter you will get prompt VPLO Then put ...VPLO c> CF + enter you will see plot Cf vs X, the point where Cf=0 is the separation point
thx a lot, it was very useful

 December 9, 2012, 23:43 #11 Senior Member   Mehdi Join Date: Jan 2011 Location: Iran Posts: 130 Rep Power: 9 Dear Kianoosh; I don't want to make you confused, but it is so hard to say the exact Re in which transition starts. It depends on a lot of parameters, such as turbulence intensity, pressure gradient. __________________ Best Regards; Mehdi E-mail: mb.pejvak[at]Gmail[dot]com

December 10, 2012, 02:15
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Kianoosh
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Quote:
 Originally Posted by mb.pejvak Dear Kianoosh; I don't want to make you confused, but it is so hard to say the exact Re in which transition starts. It depends on a lot of parameters, such as turbulence intensity, pressure gradient.
i agree with you absolutely, this is very difficult work.
i try to define th critical Re in this way. for naca0012 airfoil i starting to found the separation point from Re=5e5. in this Re number the separation point was at aboiut 0.85 C. I try with different Re Number 4e5, 3e5, 2e5, e5, 8e4 until the flow over airfoil to be laminar or separation point be in 1. this mean is we don't have any separation on the airfoil surface at Critical Re.

i the Critical Reynolds Number for NACA0012 about e5 and for NACA 0015 about 3.5e4. whats you idea?

 December 10, 2012, 03:43 #13 Senior Member   Mehdi Join Date: Jan 2011 Location: Iran Posts: 130 Rep Power: 9 Dear kianoosh; I recommend you to read "Boundary-Layer Measurements on an Airfoil at Low Reynolds Numbers" by M. Brendel. it is very helpful paper in describing transition and how it can be found out where flow starts laminar to turbulent transition. I hope it can answer your questions. __________________ Best Regards; Mehdi E-mail: mb.pejvak[at]Gmail[dot]com

 December 15, 2012, 10:04 #14 New Member   Choose one... Join Date: Oct 2012 Posts: 8 Rep Power: 7 Is the paper by Brendel available online. If yes, kindly post the link. else kindly mail me at debanik1@gmail.com

December 15, 2012, 12:07
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Kianoosh
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Quote:
 Originally Posted by debanik1 Is the paper by Brendel available online. If yes, kindly post the link. else kindly mail me at debanik1@gmail.com
The paper available online. You can find it by googling the title of paper. If you can't find it message me to send it for you.

 December 15, 2012, 12:10 #16 New Member   Choose one... Join Date: Oct 2012 Posts: 8 Rep Power: 7 kindly mail me at debanik1@gmail.com

December 15, 2012, 12:15
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Kianoosh
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Quote:
 Originally Posted by mb.pejvak Dear kianoosh; I recommend you to read "Boundary-Layer Measurements on an Airfoil at Low Reynolds Numbers" by M. Brendel. it is very helpful paper in describing transition and how it can be found out where flow starts laminar to turbulent transition. I hope it can answer your questions.
I read this paper , but i can't find that my way to found critical Re number is correct or no. What's your idea to my describe way above. It's important that I found critical Raynolds number In angle of attack of zero degree.

December 15, 2012, 12:18
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Kianoosh
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 Originally Posted by debanik1 kindly mail me at debanik1@gmail.com
Sure, But i'm not at home now. I send it in next 4 hours.

 January 14, 2014, 10:51 #19 Senior Member   Join Date: Feb 2010 Posts: 213 Rep Power: 10 please, send to vaina74@hotmail.com. thanks.

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