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• ## Re: [CFDBible] How to DRAW CURVE ON GAMBIT??

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• Dear Mr mahdi Thanks for your reply. I ll try ^^. I ve other question for you, when i wanna simulate an airfoil GOE type. there is some thing wrong. The value
Message 1 of 8 , Nov 9, 2009
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Dear Mr mahdi

Thanks for your reply. I'll try ^^. I've other question for you, when i wanna simulate an airfoil GOE type. there is some thing wrong. The value of Cl is close to hand book but Cd is far to hand book. what's wrong with my simulation??
teguh
--- On Sat, 10/31/09, mahdi hosseinali <anishtain4@...> wrote:

From: mahdi hosseinali <anishtain4@...>
Subject: Re: [CFDBible] How to DRAW CURVE ON GAMBIT??
To: CFDBible@yahoogroups.com
Date: Saturday, October 31, 2009, 1:26 AM

• Hello Mr Prakash Thank you for your answer. I ll try it. If I have problem, I ll ask you. Teguh Hady A ... From: singh prakash Subject:
Message 1 of 8 , Nov 13, 2009
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Hello Mr Prakash

--- On Sat, 11/7/09, singh prakash <sprakash29@...> wrote:

From: singh prakash <sprakash29@...>
Subject: Re: [CFDBible] How to DRAW CURVE ON GAMBIT??
To: CFDBible@yahoogroups.com
Date: Saturday, November 7, 2009, 4:37 AM

 hi,for curve geometries like airfoil or turbine blade in gambit is difficult to draw if it is not arc of a circle. when drawing a curve in gambit, we have to either specify three points on arc or by center and two points on the circle, but airfoil is not a single arc so the way is, draw the geometry in cad software like proe or autocad or solid work then generate the coordinate of the point required for gambit as told earlier this will generate accurate geometry other direct method may approximate the geometry in gambit..the other method may be complex for a beginner, save the cad geometry in iges format and import the vertex data in gambit, this is fast process but may have problem in big geometries.hope this may help you..singh prakash, M. Ae. SIscientist DRDL

• Dear Teguh, Cd is always hard to predict with CFD, in fact its the trickiest part of CFD to match your value of Cd with that of authenticated experimental
Message 1 of 8 , Nov 14, 2009
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Dear Teguh,
Cd is always hard to predict with CFD, in fact its the trickiest part of CFD to match your value of Cd with that of authenticated experimental value. Firstly you need to have an authenticated data to compare your results with. In case you have the authenticated experimental data and you can't match your Cd with that, you need to check your turbulence model. Drag in CFD simulations consists of two components i.e. pressure drag and viscous drag. Its the viscous drag that is problematical if your turbulence model is not correct. I don't know which turbulence model you are using, you should try using a different turbulence model. Also keep a track of the Y+ values on the wall, there is different requirement of wall y+ for each turbulence model. But before doing all this check you solution properly for convergence and y+.

Regards,
Awais Ali

To: CFDBible@yahoogroups.com
From: huget_teguh@...
Date: Mon, 9 Nov 2009 05:29:26 -0800
Subject: Re: [CFDBible] How to DRAW CURVE ON GAMBIT??

Dear Mr mahdi

Thanks for your reply. I'll try ^^. I've other question for you, when i wanna simulate an airfoil GOE type. there is some thing wrong. The value of Cl is close to hand book but Cd is far to hand book. what's wrong with my simulation??
teguh
--- On Sat, 10/31/09, mahdi hosseinali <anishtain4@yahoo. com> wrote:

From: mahdi hosseinali <anishtain4@yahoo. com>
Subject: Re: [CFDBible] How to DRAW CURVE ON GAMBIT??
To: CFDBible@yahoogroup s.com
Date: Saturday, October 31, 2009, 1:26 AM

• Dear Awais, Well,  I use experiment data of Sandia National Laboratories. My turbulence is k-w SST. I ve read that the correct value of Y+ = 1-2. But it s
Message 1 of 8 , Nov 16, 2009
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Dear Awais,
Well,  I use experiment data of Sandia National Laboratories. My turbulence is k-w SST. I've read that the correct value of Y+ = 1-2. But it's hard for me to make boundary layer to get that value of Y+. Any suggestion??
Thank you
regards

--- On Sat, 11/14/09, Awais Jaffari <awais_4u@...> wrote:

From: Awais Jaffari <awais_4u@...>
Subject: RE: [CFDBible] How to DRAW CURVE ON GAMBIT??
To: cfdbible@yahoogroups.com
Date: Saturday, November 14, 2009, 6:42 PM

Dear Teguh,
Cd is always hard to predict with CFD, in fact its the trickiest part of CFD to match your value of Cd with that of authenticated experimental value. Firstly you need to have an authenticated data to compare your results with. In case you have the authenticated experimental data and you can't match your Cd with that, you need to check your turbulence model. Drag in CFD simulations consists of two components i.e. pressure drag and viscous drag. Its the viscous drag that is problematical if your turbulence model is not correct. I don't know which turbulence model you are using, you should try using a different turbulence model. Also keep a track of the Y+ values on the wall, there is different requirement of wall y+ for each turbulence model. But before doing all this check you solution properly for convergence and y+.

Regards,
Awais Ali

To: CFDBible@yahoogroup s.com
From: huget_teguh@ ymail.com
Date: Mon, 9 Nov 2009 05:29:26 -0800
Subject: Re: [CFDBible] How to DRAW CURVE ON GAMBIT??

Dear Mr mahdi

Thanks for your reply. I'll try ^^. I've other question for you, when i wanna simulate an airfoil GOE type. there is some thing wrong. The value of Cl is close to hand book but Cd is far to hand book. what's wrong with my simulation??
teguh
--- On Sat, 10/31/09, mahdi hosseinali <anishtain4@yahoo. com> wrote:

From: mahdi hosseinali <anishtain4@yahoo. com>
Subject: Re: [CFDBible] How to DRAW CURVE ON GAMBIT??
To: CFDBible@yahoogroup s.com
Date: Saturday, October 31, 2009, 1:26 AM

• Dear Teguh, As far as I know k-w is used for modeling turbulence flow through complex geometries. Yes, controlling Y+ on wall is not easy, but again its the
Message 1 of 8 , Nov 18, 2009
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Dear Teguh,
As far as I know k-w is used for modeling turbulence flow through complex geometries. Yes, controlling Y+ on wall is not easy, but again its the only solution. If you are using some turbulence model you should try to closely match its Y+ requirements or at least the deviation from standard y+ values must not be very large, how large?, its another question.
Another Solution to your problem could be use of some other turbulence model. Like k-e or S-A. k-e has a y+ requirement of 30-300 and S-A has a y+ requirement of 0<y+<1 or 30<y+. If you could elaborate your problem a bit it would get more easy to suggest some more close and possible solution.
Regards,
Awais

To: CFDBible@yahoogroups.com
From: huget_teguh@...
Date: Mon, 16 Nov 2009 15:09:44 -0800
Subject: [CFDBible] What is the Value of Y+ for Airfoil??

Dear Awais,
Well,  I use experiment data of Sandia National Laboratories. My turbulence is k-w SST. I've read that the correct value of Y+ = 1-2. But it's hard for me to make boundary layer to get that value of Y+. Any suggestion??
Thank you
regards

--- On Sat, 11/14/09, Awais Jaffari <awais_4u@hotmail. com> wrote:

From: Awais Jaffari <awais_4u@hotmail. com>
Subject: RE: [CFDBible] How to DRAW CURVE ON GAMBIT??
To: cfdbible@yahoogroup s.com
Date: Saturday, November 14, 2009, 6:42 PM

Dear Teguh,
Cd is always hard to predict with CFD, in fact its the trickiest part of CFD to match your value of Cd with that of authenticated experimental value. Firstly you need to have an authenticated data to compare your results with. In case you have the authenticated experimental data and you can't match your Cd with that, you need to check your turbulence model. Drag in CFD simulations consists of two components i.e. pressure drag and viscous drag. Its the viscous drag that is problematical if your turbulence model is not correct. I don't know which turbulence model you are using, you should try using a different turbulence model. Also keep a track of the Y+ values on the wall, there is different requirement of wall y+ for each turbulence model. But before doing all this check you solution properly for convergence and y+.

Regards,
Awais Ali

To: CFDBible@yahoogroup s.com
From: huget_teguh@ ymail.com
Date: Mon, 9 Nov 2009 05:29:26 -0800
Subject: Re: [CFDBible] How to DRAW CURVE ON GAMBIT??

Dear Mr mahdi

Thanks for your reply. I'll try ^^. I've other question for you, when i wanna simulate an airfoil GOE type. there is some thing wrong. The value of Cl is close to hand book but Cd is far to hand book. what's wrong with my simulation??
teguh
--- On Sat, 10/31/09, mahdi hosseinali <anishtain4@yahoo. com> wrote:

From: mahdi hosseinali <anishtain4@yahoo. com>
Subject: Re: [CFDBible] How to DRAW CURVE ON GAMBIT??
To: CFDBible@yahoogroup s.com
Date: Saturday, October 31, 2009, 1:26 AM