| Résumé | Frazil ice tends to form in a water column that is both supercooled and turbulent. Since the 1950's, there has been a considerable number of laboratory studies focusing on frazil ice and related phenomena. Three requirements for generating that ice in a laboratory are a water containment, a means to bring down the water temperature and a source of turbulence. The water containments in which frazil ice was generated by investigators are divided into: flow in a loop, absorbed flow, Lagrangian flow, vertical flow and no flow. For supercooling the water column, most work was conducted inside a cold room, or with a test set-up incorporating a chilling system. To induce turbulence in the water column, the various equipment used to deliver that energy included: wave makers, propellers, oscillating grids, water thrusters, ventilators and river bed roughness. Frazil-monitoring instruments were based on different principles, including photo detection, water conduction, calorimetry, imaging systems, flow rate and acoustic devices. Frazil ice dynamics involve a complex amalgamation of thermomechanical and hydraulic processes. For instance, secondary (as opposed to primary) nucleation is the mechanism generally alluded to explaining the sudden and massive generation of frazil ice. It accounts for the reduction in supercooling of the water column, and is influenced by cooling rate. Higher salinities promote frazil generation but that ice is less cohesive and adhesive than frazil ice grown from low salinity or freshwater. Rising velocity of frazil particles in the water column has been shown to increase with particle and floc sizes. The ability of frazil ice to capture foreign particles suspended in the water column. referred to as sediment entrainment, has also been investigated – coarser particles are preferentially captured, with implications on glacigenic sedimentation patterns. Anchor ice is known for its ability to transport material and its tendency to clog submerged structures (such as trash racks). Release conditions, shape and growth rate of that ice was related to the Froude and Reynolds numbers. Interestingly, anchor ice has been shown to grow more readily in freshwater than in saline water. Wave damping of frazil ice, after it has built an ice layer at the water surface, has also been studied – for instance, wave patterns were shown to vary with travel distance and ice layer thickness. Finally, a series of investigations, addressing frazil adhesion as well as particular scenarios of structures exposed to clogging by frazil, are described – these include cables, trash racks, ice booms and water intakes. Doing so, investigators explored methods to collect or characterize frazil ice and to evaluate the performance of mitigating measures. |
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