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Probability density function of turbulent velocity fluctuations in a rough-wall boundary layer
Hideaki Mouri1, Masanori Takaoka, Akihiro Hori
1Meteorological Research Institute, Nagamine 1-1, Tsukuba 305-0052, Japan. hmouri@mri-jma.go.jp
Summary
Turbulence velocity fluctuations tend to Gaussian in ideal conditions. Intermittent motions in rough-wall boundary layers cause non-Gaussian fluctuations, deviating from ideal turbulence models.
Area of Science:
- Fluid Dynamics
- Turbulence Theory
- Statistical Mechanics
Background:
- Turbulence is characterized by complex velocity fluctuations.
- Understanding the probability density function (PDF) of these fluctuations is crucial.
- Deviations from Gaussian distributions indicate non-ideal turbulent behavior.
Purpose of the Study:
- To systematically study the PDF of single-point velocity fluctuations in turbulence.
- To investigate the influence of Fourier coefficients in the energy-containing range on fluctuation PDFs.
- To analyze deviations from Gaussian behavior in specific turbulent flows.
Main Methods:
- Analysis of Fourier coefficients within the energy-containing range of turbulent flows.
- Comparison of theoretical predictions for ideal turbulence with experimental data.
- Experimental investigation of a rough-wall boundary layer flow.
Main Results:
- In ideal turbulence, Fourier coefficients are Gaussian and independent, leading to Gaussian velocity fluctuations.
- Intermittency or bounded motions cause non-Gaussian Fourier coefficients and dependent behavior.
- Experimental data from a rough-wall boundary layer exhibit non-Gaussian velocity fluctuations.
Conclusions:
- The study confirms that deviations from Gaussian velocity fluctuations are linked to intermittent or bounded energy-containing motions.
- Fourier coefficient analysis provides a method to identify non-ideal turbulence characteristics.
- Rough-wall boundary layers present a real-world example of non-Gaussian turbulence.