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Range of Transitional Reynolds Number for NACA0012

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Old   November 4, 2007, 23:00
Default Range of Transitional Reynolds Number for NACA0012
  #1
Mohammad Faridul Alam
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What is the range of Transitional Reynolds Number for NACA0012 airfoil?

Thanks in advance.

Farid
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Old   November 5, 2007, 18:12
Default Re: Range of Transitional Reynolds Number for NACA
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Glenn Horrocks
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Hi,

What do you mean transitional Reynolds number? Anyway, for general information like this Google is a good start. There are plenty of references for NACA0012 airfoils on the web.

Glenn Horrocks
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Old   November 6, 2007, 05:34
Default Re: Range of Transitional Reynolds Number for NACA
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Mohammad Faridul Alam
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Hi Glenn, Thanks. I wanna know about the Reynolds number for which I can run simulation using Gamma Theta Transition Model.

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Old   November 6, 2007, 05:50
Default Re: Range of Transitional Reynolds Number for NACA
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Mohammad Faridul Alam
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Hi Glenn,

I have run a simulation using SST Model with Fully turbulent option and I got good result for Cp distribution. But when I ran the simulation using Gamma Theta Transition model, I didnt get good result.

Could you tell me the reason behind it?
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Old   November 6, 2007, 06:21
Default Re: Range of Transitional Reynolds Number for NACA
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Glenn Horrocks
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Hi,

What airfoil Reynolds number are you running at? If it is fairly high and you have a grid with a large y+ then a fully turbulent model will give a good result but transitional turbulence model will not.

Regards, Glenn Horrocks
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Old   November 6, 2007, 06:57
Default Re: Range of Transitional Reynolds Number for NACA
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Adam
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It also depends on the inlet conditions used. The gamma-theta model is very sensitive to the inlet boundary conditions.

The first thing you need to do is find out where transition is actually happening and then compare it to where the model predicts it to be.

The gamma-theta model should not have a great effect on cp, unless you expect laminar separation or a separation towards the trailing edge.

Unless you know where transition is and how to properlly use the model, its best not to use it.

Adam
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Old   November 7, 2007, 04:01
Default Re: Range of Transitional Reynolds Number for NACA
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Mohammad Faridul Alam
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Hi Glenn, Thanks for the reply. My Re=0.54 Million for the simulation and I have set y+ value for Re= 2 Million during the Mesh generation. so, I think for y+ value I am in safe side.
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Old   November 7, 2007, 18:47
Default Re: Range of Transitional Reynolds Number for NACA
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Glenn Horrocks
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Hi,

At this Re number you will likely get a significant region of laminar flow (providing the upstream flow is not too turbulent and the surface condition is pretty good) so a transition model will help accuracy.

The transitional model is very sensitive to mesh density perpendicular to the surface and sometimes sensitive to mesh density along the surface. Have you done a mesh refinement study to check your mesh is OK? What y+ range do you have on your airfoil?

Glenn Horrocks
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Old   November 8, 2007, 05:15
Default Re: Range of Transitional Reynolds Number for NACA
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Mohammad Faridul Alam
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Hi Glenn, Thank you again for the reply.

I didnt go through the Mesh Refinement. I took y+=1.0, Re=2 million , Cf=10E-3 and then calculated the y value(height of the first inflation layer around the airfoil).

Faridul Alam
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Old   November 8, 2007, 05:28
Default Re: Range of Transitional Reynolds Number for NACA
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Dr. Flow Squad
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Often for airfoils, CFD has high problems in predicting the right drag coefficient. I once were told that,"lift is easy, drag is hard and moment is impossible" when it comes to do CFD calculations on airfoils. But it is getting better. I would check javafoilhttp://www.mh-aerotools.de/airfoils/javafoil.htm before doing the cfd calculations to see where my transition zone is based on empirical formulas. from the bottom left choose "The Applet" and type 0012 in the "Name field" and click "create airfoil". Turn to "Boundary Layer" and press "analyze it". That gives you a prediction of the transition switch from laminar to turbulent. Based on that, Re number and angle of attack (AOA) you can set up you cfd calculations.Otherwise paste the data from javafoil into you report and take the day off (optional) - Dr. Flow Squad
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Old   November 8, 2007, 16:57
Default Re: Range of Transitional Reynolds Number for NACA
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Mohammad Faridul Alam
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Enormous Thanks to All for your cordial help.
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