Probability distribution mapping of velocity changes in turbulenttime-series: a tool for the empiric analysis of the interaction between suspended solids andturbulent fluid flow

摘要

Sediment particles modulate the turbulence in moving fluids compared to single-phase flows. This modulation is a feedback mechanism between transported sediment and sediment transport process. Bulk statistical measures such as turbulence intensity and skew are insufficient to fully describe this effect. Fourier and wavelet analysis may indicate frequency modulations but cannot describe the shape (in time and space) of turbulent events. Better methodologies are needed to quantify the character of turbulence in velocity time-series obtained from sediment-laden flows if the interaction between suspended sediment and flow dynamics is to be studied empirically. Here, a methodology is proposed in which the probability distribution of velocity change from one data-point to the next is mapped as a function of the magnitude of the velocity. The resulting probability landscapes are an image of the full range of turbulent events that took place in the measured time-series. The architecture of these probability landscapes changes spatially within flows. The primary parameters that govern the architectures are sampling time (i.e. a methodological constraint) and position relative to the frictional boundaries (indicative of the flow structure).