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Abstract: In this study, the performance of the horizontal large eddy simulation module, developed at the University of Leuven (HLES-KULeuven module) is assessed. A comparison between different subgrid scale models has been carried out. The study is concerned with the non-rotating and unstratified flows. The results of the simulation for an oscillatory backward facing (BFS) flow are presented in case of an expanding flume based on a one-length scale approach and a two-length scale approach. Three subgrid scale (SGS) models have been tested: Smagorinsky SGS model (Smagorinsky, J., (1963). General circulation experiments with the primitive equations, I. the basic experiments. Monthly Weather Review, 91(3), 99–164), Uittenbogaard SGS model (Uittenbogaard, R.E., and van Vossen, B., (2004). Subgrid-scale model for quasi-2D turbulence in shallow water. Shallow Flows. Jirka and Uijttewaal (Eds.), Taylor & Francis Group, London, ISBN 90 5809 700 5) and a proposed two-length scale approach. The first two models are considered to be a one-length scale models. A simulation without a subgrid scale model for the horizontal mixing has also been conducted. In all simulations, a quadratic friction model parameterizes the dissipation produced by the 3D-subdepth scale turbulence. The two-length scale concept uses a newly mixing length formulation for the quasi-2D turbulence and doesn''t depend on the filter width in contrast to the one-length scale approach, in which the mixing length is function of the filter width. The outputs of the HLES-KULeuven module have been compared with the experimental data taken from Stelling, G.S., and Wang, L.X., (1984). Experiments and computations on separating flow in an expanding flume. Dept. Civil Engineering, Delft University of Technology, Report 2–84.). The two-length scale approach has been validated with experimental data from SERC Flood Channel Facility at HR Wallingford. In general, there is a qualitative agreement with the experimental data. It has also been found that the two-length scale approach produces more elongated and less isotropic vortex than the one-length scale models. [Copyright &y& Elsevier]

Eulerian equations for the vertical flux and momentum of suspended particles in dilute sediment-laden open-channel flow in equilibrium have been derived using the two-fluid approach. Reynolds averaging has been applied in order to allow validation of individual terms with experimental data. Consideration of the various terms of the vertical momentum balance with experimental flume data indicates that the drag force has to be separated into a mean and a turbulent contribution with different timescales, respectively, the (gravitational) particle timescale and the integral turbulence timescale. The resulting formulation further provides a new theoretical closure for the turbulent Schmidt number. [ABSTRACT FROM AUTHOR]

The means by which mud is conditioned for use in laboratory experiments affects the behaviour of the mud during the experiments, and hence the results and reproducibility. This study discusses the impact of different mud conditioning techniques and procedures using multiple series of short-term consolidation tests. The mud used originates from the Zeebrugge docks of the Port of Antwerp-Bruges, Belgium. For all experiments the initial density of the mud was around 1.08 g ⋅ cm−3, which is below its gel density. This has the advantage that the comparison can be limited to the behaviour during the typical initial settling phases, allowing experiments to be restricted in time to seven days. Each series of experiments is repeated multiple times using two separate batches of mud. The objective is to quantify the repeatability across these different series of experiments, and to identify the ideal conditioning procedure for optimal reproducibility for future laboratory experiments using mud. Distinct differences in settling curves are observed which confirm the intended influence of each mixing technique. A conditioning procedure based on a combination of axial and radial mixing yields the most control over settling behaviour during the initial stages of the sedimentation process and therefore results in the best repeatability of settling behaviour. It is recommended that such a mud conditioning procedure is further used for experiments with mud to allow for a better uniformity in research where the behaviour of mud is critical. • The way mud is conditioned influences its behaviour during sedimentation. • Today, there is no generally known uniform method for conditioning mud. • Experimental fluid dynamics with mud needs better reproducibility of mud behaviour. • A combination of shear and axial mixing yields the highest level of reproducibility. [ABSTRACT FROM AUTHOR]