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National Repository of Grey Literature 2 records found  Search took 0.00 seconds. 
Temporal, Spatial, and Spatio-temporal correlation of the velocity fluctuations
 Jurčáková, Klára
Taylor's hypothesis about frozen turbulence [1] says that if the turbulence intensity is small compared to the mean velocity then the advection of a turbulent flow field past a fixed point can be taken entirely due to the mean flow. This means that in the “frozen turbulent field” spatial and temporal dimensions can be interchanged. Although the main assumption of Taylor's hypothesis is not met in the atmospheric boundary layer (the intensity of turbulence is usually between 10 and 20%) the hypothesis is commonly used to calculate integral length scales of turbulent fields from point measurements. Particle image velocimetry with high temporal resolution (TR-PIV) allows us to analyze both temporal and spatial cross-correlations in the turbulent flow fields and to evaluate obtained results.
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Spatial and temporal correlations in turbulent boundary layers
 Jurčáková, Klára ; Kellnerová, Radka
The experimental data from time-resolved particle image velocimetry measurement of the boundary-layer flows over various aerodynamically rough surfaces are presented. Temporal, spatial, and time-space correlation are analyzed and used for calculation of integral length and time scales. Temporal and spatial integral scales are connected via convection velocity. Taylor's hypothesis on frozen turbulence says that the convection velocity is equal to the local mean velocity. The experimental data shows that the convection velocity is larger than local mean velocity in the lower third of the boundary layer and greater in the upper two thirds. The cross-over line is higher over surfaces with higher roughness.
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