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Viewing streamlines using LES simulations

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Old   February 5, 2017, 09:02
Default Viewing streamlines using LES simulations
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raunak jung pandey
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Hello, everyone.

I carried out RANS and LES simulation of a fluidic oscillator. No of nodes is 4.5 million. Time step size is 10^-5. Reynolds number is 37500. I have experimental data of streamlines of the internal flow field. When compared to experimental data the streamline by LES is streaky and the smaller vortices aren't captured. Also, the big vortices look messy and not coherent. The results look close to experimental data using SST model where structures are coherent and distinctive.

I am unsure if this is normal using LES. Please help me analyse my results and suggest improvements. Thank You





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Old   February 5, 2017, 12:26
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Julio Mendez
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Are you sure that your grid lies on the inertial subrange. This is my main question. Without that information the les computation is not more but number without sense
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Old   February 5, 2017, 13:47
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Santiago Lopez Castano
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Is the LES field shown an instantaneous field or is it averaged in time?

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Old   February 5, 2017, 18:34
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Quote:
Originally Posted by Santiago View Post
Is the LES field shown an instantaneous field or is it averaged in time?

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This is not instantaneous field. its averaged in time
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Old   February 5, 2017, 18:44
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1. Over how many circulation times have you averaged your solution?
2. From the plots, no conclusion can be drawn about coherence and vorticity. Regions of non-zero circulation are not, in general, coherent structures.
2. What LES model are you using? The Re is a bit high. Are you resolving the wall directly?
4. Is the grid structured?
5. Have you done any higher order statistics?

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Old   February 5, 2017, 18:49
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Quote:
Originally Posted by juliom View Post
Are you sure that your grid lies on the inertial subrange. This is my main question. Without that information, the les computation is not more but number without sense
How to determine if grid is on inertial subrange? I carried out RANS simulation prior to LES simulation to find Turbulent Kinetic Energy and turbulent dissipation energy. This was used to find the length scale and taylor micro scale

Turbulent length scale L=k^(3/2)/ε
Taylor microscale λ=√(10kν/ε)
Kolmogorov scale η=L*Re^((-3)/4)
Turbulence Reynolds number Re*L=k^2/εν


v = kinematic viscosity
I am using the following estimator to calculate the mesh resolution
Δ=max⁡( λ,L/10)

My mesh size is 0.1 mm.

Last edited by raunakjung; February 6, 2017 at 05:16.
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Old   February 6, 2017, 04:50
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Quote:
Originally Posted by Santiago View Post
1. Over how many circulation times have you averaged your solution?
2. From the plots, no conclusion can be drawn about coherence and vorticity. Regions of non-zero circulation are not, in general, coherent structures.
2. What LES model are you using? The Re is a bit high. Are you resolving the wall directly?
4. Is the grid structured?
5. Have you done any higher order statistics?

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I am trying to use WALE and LES smagorinsky model. I plan to use wall modeling. No the grid isn't structured. I have used hexahedral mesh. I haven't carried out higher order statistics.

Why is the Reynolds number high? What would be the grid point requirements? It is wall bounded flow.

Thank YOU
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