Scaling the characteristic time of the bursting process in the turbulent boundary layer
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) . 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.
© 2009 Elsevier B.V. Available online 22 September 2009. Support for the 2005 field experiments was provided by NSF, ONR, and US Dugway Proving Ground. Support for the data analysis was provided by ONR. The authors also gratefully acknowledge Dr. J. Klewicki for making his wind tunnel data available. Finally, the authors would like to thank an anonymous reviewer for suggesting the weighted mixed scaling approach.