Fluid Flow Around NACA2412 Airfoil

muratgunes · December 9, 2016, 17:25

Hi everyone,

I have a GRADUATION THESIS that is Fluid Flow Around NACA2412 Airfoil. I'll discuss Cl and Cd at different attack angle.However, I have a problem after zero attack angle in fluent. For example, at the 5 attack angle Cl and Cd values don't match with the experimental values, so I can't have costant value for Cl/Cd. What is the problem? mesh or boundary conditions or y+ value? I need help immediately.

Best Regards,

Murat Gunes

fanch33 · December 13, 2016, 11:52

Hi,

the y+ value depends on the turbulence model (SA, k-e, SST etc.) you are using and if you use or not wall functions. Describe your case.

Fanch

muratgunes · December 13, 2016, 14:40

I'm using the sst turbulent model.

fanch33 · December 16, 2016, 18:16

So you need y+<1

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Antanas · December 17, 2016, 03:09

Quote:

Originally Posted by fanch33

Hi,

the y+ value depends on the turbulence model (SA, k-e, SST etc.) you are using and if you use or not wall functions

Fanch

This is misleading statement.

Quote:

Originally Posted by fanch33

So you need y+<1

Sent from my iPhone using CFD Online Forum mobile app

Really? Why?

fanch33 · December 17, 2016, 06:26

The SST allows the resolution of the boundary layer all the way down to the wall and work as a low Reynolds number, so you need to ensure that y+<1

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Antanas · December 17, 2016, 07:45

Quote:

Originally Posted by fanch33

The SST allows the resolution of the boundary layer all the way down to the wall and work as a low Reynolds number, so you need to ensure that y+<1

Sent from my iPhone using CFD Online Forum mobile app

Yes it allows it, but it doesn't mean that one needs it and that y+ needs to be < 1 for this.

fanch33 · December 17, 2016, 07:52

It means that the sub viscous layer must be resolved so y+<5 ...
But y+<1 is better ...
Do as you want

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Antanas · December 17, 2016, 08:09

Quote:

Originally Posted by fanch33

It means that the sub viscous layer must be resolved so y+<5 ...
But y+<1 is better ...
Do as you want

Sent from my iPhone using CFD Online Forum mobile app

y+ = 1 is the lowest limit.

mali28 · December 19, 2016, 16:03

The performance of a wing has a critical influence on the overall performance of the airplane impacting the range, speed, climb rate, payload, maneuverability, runway length, etc. Performance degradation is often the result of flow separation over the wing. Adverse pressure gradient with low flow velocities in the boundary layer causes flow separation on the wing leading to significant reduction in lift. The prediction of flow behavior over the range of operating conditions in a flight is thus very crucial for optimal design and safety consideration.

December 9, 2016, 17:25	Fluid Flow Around NACA2412 Airfoil	#1
muratgunes New Member MURAT GÜNEŞ Join Date: Nov 2016 Location: Osmaniye/TURKEY Posts: 2 Rep Power: 0	Hi everyone, I have a GRADUATION THESIS that is Fluid Flow Around NACA2412 Airfoil. I'll discuss Cl and Cd at different attack angle.However, I have a problem after zero attack angle in fluent. For example, at the 5 attack angle Cl and Cd values don't match with the experimental values, so I can't have costant value for Cl/Cd. What is the problem? mesh or boundary conditions or y+ value? I need help immediately. Best Regards, Murat Gunes

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December 13, 2016, 11:52		#2
fanch33 Member Join Date: Feb 2015 Posts: 32 Rep Power: 11	Hi, the y+ value depends on the turbulence model (SA, k-e, SST etc.) you are using and if you use or not wall functions. Describe your case. Fanch

December 13, 2016, 14:40		#3
muratgunes New Member MURAT GÜNEŞ Join Date: Nov 2016 Location: Osmaniye/TURKEY Posts: 2 Rep Power: 0	I'm using the sst turbulent model.

December 16, 2016, 18:16		#4
fanch33 Member Join Date: Feb 2015 Posts: 32 Rep Power: 11	So you need y+<1 Sent from my iPhone using CFD Online Forum mobile app

December 17, 2016, 06:26		#6
fanch33 Member Join Date: Feb 2015 Posts: 32 Rep Power: 11	The SST allows the resolution of the boundary layer all the way down to the wall and work as a low Reynolds number, so you need to ensure that y+<1 Sent from my iPhone using CFD Online Forum mobile app

December 17, 2016, 07:52		#8
fanch33 Member Join Date: Feb 2015 Posts: 32 Rep Power: 11	It means that the sub viscous layer must be resolved so y+<5 ... But y+<1 is better ... Do as you want Sent from my iPhone using CFD Online Forum mobile app

December 19, 2016, 16:03		#10
mali28 Member Join Date: Jun 2011 Posts: 86 Rep Power: 14	The performance of a wing has a critical influence on the overall performance of the airplane impacting the range, speed, climb rate, payload, maneuverability, runway length, etc. Performance degradation is often the result of flow separation over the wing. Adverse pressure gradient with low flow velocities in the boundary layer causes flow separation on the wing leading to significant reduction in lift. The prediction of flow behavior over the range of operating conditions in a flight is thus very crucial for optimal design and safety consideration.