Author(s): Hubert Chanson

Linked Author(s): Hubert Chanson

Keywords: Turbulent events; Unsteady transient breaking bores; Physical modelling; Turbulent mixing;

Abstract: A breaking tidal bore is a highly turbulent transient process that may affect the natural estuarine system. Like many natural process flows, the tidal bore flow motion is dominated by coherent structure activities and turbulent events, with significant impact in terms of sediment processes. Herein an unsteady turbulent event analysis was developed for highly-unsteady rapidly-varied breaking bore flows. New experimental data were collected in a large size facility under controlled flow conditions. The data analysis was based upon basic concepts, in which turbulent bursting events were defined in terms of the instantaneous relative turbulent flux, and applied to the rapidly-varied highly-unsteady bore motion. The instantaneous three-dimensional velocities were recorded using an Acoustic Doppler Velocimetry. Rapid longitudinal deceleration, transient recirculation and large velocity fluctuations were observed during the bore passage, especially more intensive next to the sidewall. A turbulent event analysis was performed in the transient flow. The threshold constant k =1 was obtained from a sensitivity analysis. The unsteady turbulent event results highlighted an intense bursting process during the flow deceleration, in terms of the relatively large event duration, event amplitude and relative magnitude compared with the early flood flow phase. The unsteady event amplitude and relative magnitude exhibited a quasi-symmetrical distribution about the zero amplitude. The majority of turbulent events lasted between 0.005 s to 0.06 s. Overall, the results showed that the turbulent event analysis provided valuable quantitative details into the turbulent bursts that are responsible for major mixing and sedimentary processes.

DOI: https://doi.org/10.3850/38WC092019-0279

Year: 2019