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Integral Length scale and Reynolds stress tensor |
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#1 |
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ssa
Join Date: Sep 2018
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Hi all,
I have a velocity time series data (U vs time) from an wind tunnel experiment for a number of points along the height of the wind tunnel. I need to calculate the integral length scale and reynolds stress tensor from this data for my simulation. How to obtain these values.? Is there any matlab script available. ? Thanks. ssa. |
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#2 |
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Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
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U is the full 3D vector or just one component? You can't calculate the Reynolds stress with only one velocity component. Reynolds stresses are straight forward to calculate. You determine u'(t)=u(t)-umean, v'=v(t)-vmean, w'=w(t)-wmean and then take all their products. Hopefully you don't need anyone else's code to do this...
For estimating length scale, there's several methods mentioned in doi: 10.1115/1.1391277 needing only the u' at a single point. |
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#3 |
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ssa
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I have three velocity components.
So If I take a time series, say may be 100 values over a period of 5 seconds, I should calculate the u mean from those values and then get u'(t). so I will have 100 u'(t) values and then I should average those values to get u'. Am I correct.? |
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#4 | |
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Lucky
Join Date: Apr 2011
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Quote:
You will need a lot more than 100 values! But okay, supposing you have a lot of them... If you average 100 u'(t) values you will get 0. The Reynolds stresses are calculated by taking pairwise products u'(t)*u'(t) and then averaging the 100 product-pairs. There are 6 stresses from u'u', u'v', u'w', v'v', v'w', w'w'. This is all done at 1 point in the wind tunnel. You can repeat this across all the points in the wind tunnel if you like. The Reynolds stresses are a tensor field over the domain, just like the velocity is a vector field over the entire domain. Similarly, the integral length scale is not one number for the entire wind tunnel but a local flow property. |
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