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February 5, 2017, 08:02 |
Viewing streamlines using LES simulations
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#1 |
Senior Member
raunak jung pandey
Join Date: Jun 2016
Posts: 102
Rep Power: 9 |
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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February 5, 2017, 11:26 |
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#2 |
Senior Member
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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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February 5, 2017, 12:47 |
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#3 |
Senior Member
Santiago Lopez Castano
Join Date: Nov 2012
Posts: 354
Rep Power: 15 |
Is the LES field shown an instantaneous field or is it averaged in time?
Sent from my GT-I8190L using CFD Online Forum mobile app |
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February 5, 2017, 17:34 |
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#4 | |
Senior Member
raunak jung pandey
Join Date: Jun 2016
Posts: 102
Rep Power: 9 |
Quote:
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February 5, 2017, 17:44 |
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#5 |
Senior Member
Santiago Lopez Castano
Join Date: Nov 2012
Posts: 354
Rep Power: 15 |
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? Sent from my GT-I8190L using CFD Online Forum mobile app |
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February 5, 2017, 17:49 |
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#6 | |
Senior Member
raunak jung pandey
Join Date: Jun 2016
Posts: 102
Rep Power: 9 |
Quote:
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 04:16. |
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February 6, 2017, 03:50 |
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#7 | |
Senior Member
raunak jung pandey
Join Date: Jun 2016
Posts: 102
Rep Power: 9 |
Quote:
Why is the Reynolds number high? What would be the grid point requirements? It is wall bounded flow. Thank YOU |
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Tags |
cfd - post, les, streamlines |
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