Study of Large-Scale Turbulence Horizontal Coherent Structures Under Ice-Covered Conditions

Large-scale turbulence coherent structures are defined as the largest conglomerations of eddies with a prevailing sense of rotation. They can be vertical (i.e., rotating around horizontal axes) or horizontal (rotating around vertical axes), and both have already been the object of intensive research in open-channel and river flows. The focus of this work is on large-scale horizontal coherent structures (LSHCSs). In addition to playing an important role in the transport of sediment and pollutants in rivers, LSHCSs have also been related to various fluvial bed and plan forms. Yet, despite numerous literature on the topic, no studies have been carried out so far on LSHCSs in ice-covered flows. This work aims to fill this gap by addressing the existing lack of information on the characteristic scales and life cycle of LSHCSs in such flows. The analysis is based on a series of instantaneous velocity measurements conducted in an 11-m-long and 0.382-m-wide flume. The velocity was measured with the aid of a 2D Micro Acoustic Doppler Velocimeter. The simulated ice cover was made of extruded polystyrene covered with a mesh; a 5-mm gravel was used as bed material. Low-pass filters and continuous wavelet transform were used for the detection and establishment of the length and time scales of the LSHCSs. The results indicate that the simulated ice cover impacts the amplitude of the velocity oscillograms as well as markedly reduces the power intensity of the LSHCSs. Ice covers may also have an effect on the time and length scales of LSHCSs but not a significant one. The results of this work must be viewed as preliminary, as the number of measurements is limited.