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The effect of zero-mean-flow external turbulence on the topology of the scalar turbulent/turbulent interface (TTI) has recently been studied in axisymmetric jets (Kohan & Gaskin, J. Fluid Mech., vol. 950, 2022, p. A32). The present study aims to understand the process of turbulent entrainment into a jet, as affected by background turbulence, using scalar statistics. Planar-laser-induced fluorescence was employed to capture the orthogonal cross sections of the jet at a fixed downstream station with varying background turbulence intensities. The ambient turbulence is generated using a random jet array. The conditional scalar profiles revealed that the thickness of the TTI is greater than that of the traditional turbulent/non-turbulent interface (TNTI), and that the interfacial thickness is an increasing function of the background turbulence intensity. External forcing tends to suppress the net rate of entrainment into the jet by increasing the contribution of detached jet patches (i.e., ‘islands’) to that of the main jet, despite a larger jet area, implying an increase in the local detrainment events. Furthermore, an increased occurrence of concentration ‘holes’ within the jet in the presence of ambient turbulence suggests a more significant role of engulfment in the turbulent/turbulent entrainment process. Lastly, the lowered entrainment in the turbulent ambient as compared to the quiescent background is manifested as less negative values of scalar skewness deep within the jet, while positive skewness at far radial positions from the jet centerline indicates intense detrainment episodes, induced by external fluctuations., Résumé de la communication présentée lors du congrès international tenu conjointement par Canadian Society for Mechanical Engineering (CSME) et Computational Fluid Dynamics Society of Canada (CFD Canada), à l’Université de Sherbrooke (Québec), du 28 au 31 mai 2023.

Hydropower is a renewable energy source, but its environmental impacts must be minimized. Flows downstream of the turbine must meet minimum dissolved oxygen levels, which can be achieved using draft tube aeration, a low-impact retro-fit option. The diffusion of oxygen from air to water is governed by the rate of diffusion through the air-water interface and by the flow velocity. The oxygenation transfer efficiency, , is obtained by integrating the mass transfer equation of time, , where C refers to the dissolved oxygen concentration and Cs corresponds to dissolved oxygen saturation concentration at equilibrium, is the liquid film coefficient for bubble-water oxygen transfer, is the specific surface area of bubbles, is the time and are the concentration and time at which the oxygenation process was started. A high air masstransfer rate requires a large interfacial area and thus a small bubble size. A physical scale model was built to study and predict oxygenation efficiency of air injected into the lee of a deflector over a range of flow velocity, void ratio (or air/water volume ratio) and initial dissolved oxygen concentrations. An initial study optimized an ultrasonic deaeration method to produce the low dissolved oxygen water required for the test rig. A customized ultrasonic probe (QSonica) driven at a frequency of up to 20 kHz decreased the dissolved oxygen concentration from 8 mg/l to 4 mg/l within 30 mins for the conditions of a water temperature of 23 ºC and an applied vacuum pressure of 68 kPa. The time evolution of the dissolved oxygen concentration downstream of the air injection can be studied using four dissolved oxygen measuring stations located along the conduit. A preliminary investigation of the oxygenation rate of the flow due to air injected at a standard elbow deflector validated the data acquisition system and the ability to determine the evolution of the oxygen transfer over time, and the magnitude of the oxygen transfer coefficient. F, Résumé de la communication présentée lors du congrès international tenu conjointement par Canadian Society for Mechanical Engineering (CSME) et Computational Fluid Dynamics Society of Canada (CFD Canada), à l’Université de Sherbrooke (Québec), du 28 au 31 mai 2023.

Impact assessments on river systems of the combined effect of bed and suspended sediment loads from quarries are difficult to find. In this study, bed and suspended loads were measured to determine the impact of a 20-ha limestone quarry on the river system of its 5,000-ha steep, diverse land use/land cover but mostly forested catchment. A network of hydrologic and sediment monitoring instruments was deployed over the catchment during two separate study periods when sediment loadings were measured from captured storms. Results showed that the quarry stood to make a disproportionately large contribution to the catchment's estimated 2.1 Mg ha(-1) yr(-1) suspended sediment load. Large storm events contributed most of the loadings with five events supplying 92% of total loadings at the outlet. A paired method approach to compare suspended sediment loads between two subcatchments showed that during eight storm events, the quarry yielded between 2 and 49.2 Mg ha(-1) per event, whereas the forest never yielded more than 0.1 Mg ha(-1). Furthermore, the contribution of sediments from the quarry to bed load was more than 75% at a section located 1.2 km downstream. Future management activities to reduce sediment and bed loads, not only from this catchment but also from all others with similar land use/land covers, should focus on improving quarry operations.