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DES for Airfoil Analysis

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Old   April 10, 2007, 02:17
Default DES for Airfoil Analysis
  #1
asd
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Has anyone used DES for airfoil analysis? I am particularly interested in capturing the onset of boundary layer transition and maximum CL for airfoils at Re 6 million and mach of 0.35 I have used k-e and k-w models to predict aerodynamic coefficinets with lift and drag varying approximately 5%-7% over experimental data for an AOA range of 0-10 degress, for the case where the boundary layer has been fixed. The case for free or natural transition using DES is the focus now, and i would be interseted to know how others have studied this in particular the process of natural transtion.
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Old   April 10, 2007, 05:54
Default Re: DES for Airfoil Analysis
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to
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Hi,

In a few words, DES is not designed to compute BL transition. Basically, in the DES approach, BL are computed with a RANS model. And the latter is usually not able to compute transition without including some magic tricks.

Regards

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Old   April 10, 2007, 19:29
Default Re: DES for Airfoil Analysis
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ag
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To echo the other poster's comments, DES is designed to capture the free vortices due to separated layers. In traditional RANS models these vortices are overdamped due to the eddy viscosity. In a DES model, only the scales that can't be resolved by the grid are modeled (at least that's the theory). Most studies of natural transition make use of the Orr-Sommerfeld equations or some similar set of equations to determine stability, and correlate transition with an N-factor approach. Recently I believe Menter published a paper detailing an approach using a modified turbulence model to model transition, but you will need to search for it - I don't have it handy and I am presently several hundred miles from my desk.
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Old   April 13, 2007, 06:54
Default Re: DES for Airfoil Analysis
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sguna
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You should expect better prediction for cl, even with EVM. Transition modeling is always a problem and matching experiment condition may not be possible or give the same results.
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Old   April 13, 2007, 10:30
Default Re: DES for Airfoil Analysis
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akm
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Hi asd you can check this http://www.tfd.chalmers.se/~lada/pro...t.html#starten. it may help

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