Bursts in turbulent shear flows

Abstract

The burst frequency or frequency of regions in a turbulent flow where the energy dissipation is large has been measured in both laboratory and atmospheric shear flows. The laboratory measurements were made in two slightly heated flows, a boundary layer in zero pressure gradient and an axisymmetric jet with a co-flowing external system. The atmospheric data were obtained in the first few meters above a wheat canopy. For the laboratory data, the burst frequency, as determined from either velocity or temperature signals, is found to be approximately equal to one half the zero crossing frequency of these signals. In the atmosphere, the burst frequency is very roughly twice the zero crossing frequency. The burst intermittency factor and the ratio of the burst width to Kolgomoroff length scale are found to be very weakly dependent on the Reynolds number. Available data in the literature on the intermittency factor and width of bursts exhibit extensive scatter and conflicting Reynolds number trends.