Scaling the characteristic time of the bursting process in the turbulent boundary layer

Abstract

Characteristic time scales associated with bursting events in the turbulent boundary layer were examined over a very large range of Reynolds numbers based on momentum thickness of 1010, 2870, 4850, and 5×10^6. Well-resolved hot-wire measurements were obtained at the lowest three Reynolds numbers in a low-speed wind tunnel with a long development length and compared to hot-wire and sonic anemometer measurements in the near-neutral atmospheric surface layer over the salt flats of Utah's western desert. Bursting events were detected using the modified U-level threshold-crossing algorithm outlined by Luchik and Tiederman (1987) [1]. The same procedure and codes were used to analyze all time series records from both the wind tunnel and field experiments. The time between events, T_e, and the event duration, ΔT, were calculated and normalized using four different types of scalings: inner, outer, mixed, and Taylor microscales. It was found that both Reynolds number and wall-normal trends in the mode of T_e were eliminated when scaled by the Taylor microscale. Furthermore, constant (Reynolds number independent) values of the nondimensional mean T_e and ΔT were found in a narrow wall-normal region near the top of the buffer layer when the data were normalized by the Taylor microscale.

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