Abstract
Stationary and non-stationary grid-generated turbulence was studied using a complementary technique that combines empirical mode decomposition (EMD) and triple-decomposition. Non-stationary conditions were generated by superimposing periodic and random fluctuations on the original flow. Empirical mode decomposition (EMD) was applied as a filter to separate these fluctuations from the turbulent velocity component. Triple-decomposition was then used and the turbulent intensity, the integral length scales and the Power Spectral Density of the velocity were determined. How to use EMD in order to optimize this decomposition is discussed. Finally, the properties of the turbulence are compared to those characterized without addition of fluctuations and a good agreement is found.
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Abbreviations
- d :
-
Diameter of holes in the grid
- D :
-
Diameter of the flow jet pipe
- E 1 (n) :
-
Distribution function of the u component energy
- Fc :
-
Cutoff frequency
- M :
-
Mesh size of the turbulence grid
- n :
-
Frequency
- R E :
-
Eulerian time correlation function
- U :
-
Measured velocity along the x axis
- \( \overline{U} \) :
-
Mean velocity component of U
- u :
-
Turbulent velocity component of U
- \( \bar{u} \) :
-
Mean turbulent velocity component of U
- \( \tilde{u} \) :
-
Perturbation component of U
- \( u^{\prime } = \sqrt {\overline{{u^{2} }} } \) :
-
RMS value of the turbulent fluctuation
- \( \tilde{u}^{\prime } = \sqrt {\overline{{\tilde{u}^{2} }} } \) :
-
RMS value of the perturbation fluctuation
- \( {\frac{{u^{\prime } }}{{\overline{U} }}} \) :
-
Relative turbulence intensity
- x :
-
Distance between the probe and the grid
- Λ f :
-
Integral length scale
- σ :
-
Solidity of the grid
- τ r :
-
Time response of the hot-wire probe
- τ e :
-
Integral time scale
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Foucher, F., Ravier, P. Determination of turbulence properties by using empirical mode decomposition on periodic and random perturbed flows. Exp Fluids 49, 379–390 (2010). https://doi.org/10.1007/s00348-009-0804-5
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DOI: https://doi.org/10.1007/s00348-009-0804-5