Epsilon and mixing length value for airfoil simulation

gian_ing · January 29, 2009, 06:50

Hi all,
I'm trying to simulate a turbulent flow around an airfoil. I have some difficulties in evaluating the correct value for epsilon.
In particular I don't know which value of the mixing length I should use.
The domain is 3 meters long and 2 high.
The airfoil is located at 1 meter from the inlet and in the middle of the height, the chord length is 0.1 m, the speed is 100 m/s, Re=1e6.
Thank you in advance for your suggestions.

Bye
Gianluca

gian_ing · January 29, 2009, 08:33

Hi, this is what I obtained so far.
I attach the directory of the case and a screenshot.
Thanks again.

airfoil_simulation.zip

Gianluca

wolle1982 · January 29, 2009, 11:32

hi,

your U value seams to be 10m/s instead of 100. you also will have to raise the size of your mesh to 40-100 times the chordlength.

antonio_ing · January 29, 2009, 14:17

Actually, Gianluca and I tried to do a different simulation with the k and epsilon of a simulation of prof.Jasak on a naca 0012. with the same chord length and the same distance. but you see the result (it is embarassing :-) )

maruthamuthu_venkatraman · January 30, 2009, 16:32

Hello Antonio and Gianluca,
Try to keep y+ approx 1 to 5 and use sst k-w model. You shall check the best practise guidelines in ERCOFTAC for such flow.

Naca profile example is there in it... May be it helps you.

good luck

ivan_cozza · January 31, 2009, 13:15

Mmmm,
the k-Omega SST coded in OF is based on a wall functions approach, so it should be necessary to use an y+ of about 30...
egards, Ivan

antonio_ing · February 1, 2009, 03:55

thanks Ivan and Maruthamuthu. We find out our bug :-). In the boundary file we did not specify that the profile surface was of wall type. There are other types in OpenFOAM (inlet, outlet, etc...)

Is it so important to specify the other types (apart wall of course)?

January 29, 2009, 06:50	Hi all, I'm trying to simulat	#1
gian_ing New Member Gianluca VZ Join Date: Mar 2009 Posts: 6 Rep Power: 17	Hi all, I'm trying to simulate a turbulent flow around an airfoil. I have some difficulties in evaluating the correct value for epsilon. In particular I don't know which value of the mixing length I should use. The domain is 3 meters long and 2 high. The airfoil is located at 1 meter from the inlet and in the middle of the height, the chord length is 0.1 m, the speed is 100 m/s, Re=1e6. Thank you in advance for your suggestions. Bye Gianluca

January 29, 2009, 08:33	Hi, this is what I obtained so	#2
gian_ing New Member Gianluca VZ Join Date: Mar 2009 Posts: 6 Rep Power: 17	Hi, this is what I obtained so far. I attach the directory of the case and a screenshot. Thanks again. airfoil_simulation.zip Gianluca

January 29, 2009, 11:32	hi, your U value seams to b	#3
wolle1982 Senior Member Wolfgang Heydlauff Join Date: Mar 2009 Location: Germany Posts: 136 Rep Power: 21	hi, your U value seams to be 10m/s instead of 100. you also will have to raise the size of your mesh to 40-100 times the chordlength.

January 29, 2009, 14:17	Actually, Gianluca and I tried	#4
antonio_ing Member antonio segalini Join Date: Mar 2009 Posts: 75 Rep Power: 17	Actually, Gianluca and I tried to do a different simulation with the k and epsilon of a simulation of prof.Jasak on a naca 0012. with the same chord length and the same distance. but you see the result (it is embarassing :-) )

January 30, 2009, 16:32	Hello Antonio and Gianluca,	#5
maruthamuthu_venkatraman Member Maruthamuthu Venkatraman Join Date: Mar 2009 Location: Norway Posts: 80 Rep Power: 17	Hello Antonio and Gianluca, Try to keep y+ approx 1 to 5 and use sst k-w model. You shall check the best practise guidelines in ERCOFTAC for such flow. Naca profile example is there in it... May be it helps you. good luck

January 31, 2009, 13:15	Mmmm, the k-Omega SST coded	#6
ivan_cozza Senior Member Ivan Flaminio Cozza Join Date: Mar 2009 Location: Torino, Piemonte, Italia Posts: 210 Rep Power: 18	Mmmm, the k-Omega SST coded in OF is based on a wall functions approach, so it should be necessary to use an y+ of about 30... egards, Ivan

February 1, 2009, 03:55	thanks Ivan and Maruthamuthu.	#7
antonio_ing Member antonio segalini Join Date: Mar 2009 Posts: 75 Rep Power: 17	thanks Ivan and Maruthamuthu. We find out our bug :-). In the boundary file we did not specify that the profile surface was of wall type. There are other types in OpenFOAM (inlet, outlet, etc...) Is it so important to specify the other types (apart wall of course)?

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