This study investigates the influence of multiple jet parameters on the flow field of translating impinging inclined water jets. We conducted full-scale stereoscopic particle image velocimetry and pressure measurements and three-dimensional computational fluid dynamics simulations for Reynolds numbers in the range of. Considering the complex mechanism of a translating impinging jet, a good concordance is observed between the experimental and numerical results. The translation-to-jet velocity ratio is identified as a critical parameter in determining whether the jet flow predominantly exhibits impinging characteristics or behaves as a jet in cross-flow. It is found that, for, jet impingement is minimal. The stand-off distance to nozzle diameter ratio determines the relative influence of the cross-flow on the jet flow. The effect of is similar to a stationary impinging jet, with the potential core extending up to, but entrainment is enhanced by the relative cross-flow. For an inclined jet, i.e. jet angle, the direction of the jet, either backward or forward, governs the deflection of the flow. Higher pressures are recorded for a backward directed jet compared with a forward directed jet for supplementary angles.

A common way to transport solids in large quantities is by using a carrier fluid to transport the solids as a concentrated solid/liquid mixture or slurry through a pipeline. Typical examples are found in dredging, mining and drilling applications. Dependent on the slurry properties and flow conditions, horizontal slurry pipe flow is either in the fixed-bed, sliding-bed or fully-suspended regime. In terms of non-dimensional numbers, the flow is fully characterized by the bulk liquid Reynolds number (Re), the Galileo number (Ga, a measure for the tendency of particles to settle under gravity), the solid bulk concentration (ϕ_b), the particle/fluid density ratio (ρ_p/ρ_f), the particle/pipe diameter ratio (D_p/D_pipe), and parameters related to direct particle interactions such as the Coulomb coefficient of sliding friction (μ_c). To further our fundamental understanding of the flow dynamics, we performed experiments and interface-resolved Direct Numerical Simulations (DNS) of slurry flow in a horizontal pipe. The experiments were performed in a transparent flow loop with D_pipe=4 cm. We measured the pressure drop along the pipeline, the spatial solid concentration distribution in the cross-flow plane through Electrical Resistance Tomography (ERT), and used a high-speed camera for flow visualization. The slurry consisted of polystyrene beads in water with D_p=2mm, ρ_p/ρ_f=1.02, Ga between 40–45 and ϕ_b between 0.26–0.33. The different flow regimes were studied by varying the flow rate, with Re varying from 3272 till 13830. The simulations were performed for the same flow parameters as in the experiments. Taking the experimental uncertainty into account, the results from the DNS and the experiments are in reasonably good agreement. The results for the pressure drop agree also fairly well with popular empirical models from literature. In addition, we performed a parametric DNS study in which we solely varied Re and Ga. In all flow regimes, a secondary flow of Prandtl's second kind is present, ascribed to the presence of internal flow corners and a ridge of densely packed particles at the pipe bottom during transition towards the fully-suspended regime. In the bulk of the turbulent flow above the bed, secondary flow transport of streamwise momentum dominates over turbulent diffusion in regions where the secondary flow is strong and vice versa where it is weak. The transition between flow regimes appears to be governed by the competition between the net gravity force on the particles and shear-induced particle migration from particle–particle interactions. This competition can be expressed by the Shields number, θ. For θ≲0.75, gravity is dominant and the flow is in the fixed-bed regime. For θ≳0.75, shear-induced migration becomes progressively more important for increasing θ. Low-concentration zones flanking the sliding bed start to form at the top corners of the bed, and gradually expand downwards along the pipe wall till the pipe bottom is reached. For θ≳1.5, shear-induced migration is responsible for lifting the particle bed away from the wall, associated with the onset of the suspended regime. For θ≫1, gravity is of minor importance and the mean flow eventually reaches axi-symmetry with a high-concentration particle core at the pipe center and negligible secondary flow.

Accurate characterization of mechanical perturbations on the seabed is essential for developing models assessing the environmental impacts from physical disturbances. Furthermore, understanding the relationship between (1) seabed resistance and (2) penetration depth, can also facilitate the development of more efficient and less impactful fishing gears. This study examines these two aspects of tickler chain rigged beam trawling via large-scale physical experiments. Three scaled down models (“light,” “medium,” and “heavy” designs) were developed to represent the impacts from typical beam trawl configurations used in the North Sea and were towed at various speeds on a saturated sand bed. Results reveal that increasing the towing speed reduces the mean penetration depth and the steady-state towing resistance of the gears. Smaller scale physical model tests incorporating tickler chains in sand, demonstrate that the towing resistance is significantly influenced by the soil compaction and particle sizes. Moreover, our study offers a simple and efficient method to estimate the penetration depth and towing resistance of prototype beam trawl gears in sand. This approach, along with the associated research, may be valuable for marine scientists assessing trawling impacts and demersal fishing gear designers seeking to optimize efficiency while minimizing seabed disturbance.

In submerged sandy slopes, soil is frequently eroded as a combination of two main mechanisms: breaching, which refers to the retrogressive failure of a steep slope forming a turbidity current, and instantaneous sliding wedges, known as shear failure, that also contribute to shape the morphology of the soil deposit. Although there are several modes of failures, in this paper we investigate breaching and shear failures of granular columns using the two-fluid approach. The numerical model is first applied to simulate small-scale granular column collapses (Rondon et al., Phys. Fluids, vol. 23, 2011, 073301) with different initial volume fractions to study the role of the initial conditions in the main flow dynamics. For loosely packed granular columns, the porous medium initially contracts and the resulting positive pore pressure leads to a rapid collapse. Whereas in initially dense-packing columns, the porous medium dilates and negative pore pressure is generated stabilizing the granular column, which results in a slow collapse. The proposed numerical approach shows good agreement with the experimental data in terms of morphology and excess of pore pressure. Numerical results are extended to a large-scale application (Weij, doctoral dissertation, 2020, Delft University of Technology; Alhaddad et al., J. Mar. Sci. Eng., vol. 11, 2023, 560) known as the breaching process. This phenomenon may occur naturally at coasts or on dykes and levees in rivers but it can also be triggered by humans during dredging operations. The results indicate that the two-phase flow model correctly predicts the dilative behaviour and the subsequent turbidity currents associated with the breaching process.

Background: Both influenza and SARS-CoV-2 viruses show a strong seasonal spreading in temperate regions. Several studies indicated that changes in indoor humidity could be one of the key factors explaining this. Objective: The purpose of this study is to quantify the association between relevant epidemiological metrics and humidity in both influenza and SARS-CoV-2 epidemic periods. Methods: The atmospheric dew point temperature serves as a proxy for indoor relative humidity. This study considered the weekly mortality rate in the Netherlands between 1995 and 2019 to determine the correlation between the dew point and the spread of influenza. During influenza epidemic periods in the Netherlands, governmental restrictions were absent; therefore, there is no need to control this confounder. During the SARS-CoV-2 pandemic, governmental restrictions strongly varied over time. To control this effect, periods with a relatively constant governmental intervention level were selected to analyze the reproduction rate. We also examine SARS-CoV-2 deaths in the nursing home setting, where health policy and social factors were less variable. Viral transmissibility was measured by computing the ratio between the estimated daily number of infectious persons in the Netherlands and the lagged mortality figures in the nursing homes. Results: For both influenza and SARS-CoV-2, a significant correlation was found between the dew point temperature and the aforementioned epidemiological metrics. The findings are consistent with the anticipated mechanisms related to droplet evaporation, stability of virus in the indoor environment, and impairment of the natural defenses of the respiratory tract in dry air. Significance: This information is helpful to understand the seasonal pattern of respiratory viruses and motivate further study to what extent it is possible to alter the seasonal pattern by actively intervening in the adverse role of low humidity during fall and winter in temperate regions. Impact: A solid understanding and quantification of the role of humidity on the transmission of respiratory viruses is imperative for epidemiological modeling and the installation of non-pharmaceutical interventions. The results of this study indicate that improving the indoor humidity by humidifiers could be a promising technology for reducing the spread of both influenza and SARS-CoV-2 during winter and fall in the temperate zone. The identification of this potential should be seen as a strong motivation to invest in further prospective testing of this non-pharmaceutical intervention.

Dredging is the relocation of soil. Before the soil can be transported, it has to be loosened. This can be done hydraulically (jetting) or mechanically (cutting). Often, water jets are used to erode the soil layer. Over time, pickup functions have been derived to predict the amount of erosion corresponding to the flow conditions. However, existing pickup functions are inaccurate at high flow velocities. During the current study, erosion experiments have been done at high flow velocities (up to 4.7 m/s) corresponding to a bed shear stress of up to 60 Pa and a Shields parameter (θ) of up to 30. The results of these experiments were compared with a number of well-known data sets and pickup functions.

This article presents a new turbulence closure based on the k-ω SST model for predicting turbulent flows of Herschel–Bulkley fluids, including Bingham and power-law fluids. The model has been calibrated with direct numerical simulations (DNS) data for fully-developed pipe flow of shear-thinning and viscoplastic fluids. The new model shows good agreement in the mean velocity, average viscosity, mean shear stress budget and friction factor. The latter compares well also against correlations from the literature for a wide range of Reynolds numbers. With the new model, improvements are also observed in the iterative convergence, which is often difficult for calculations with yield-stress fluids. Additionally, three eddy-viscosity models for Newtonian fluids, namely the k-ω SST, k-kL and Spalart–Allmaras model, have been tested on turbulent Herschel–Bulkley flows. Results show that (i) the new model produces the best prediction; (ii) the standard SST model may be considered for simulations of weakly shear-thinning/viscoplastic fluids at high Reynolds numbers; (iii) the k-kL and the Spalart–Allmaras models appear to be unsuitable for turbulent Herschel–Bulkley flows. The new model is simple and appealing for engineering applications concerned with turbulent wall-bounded flows and is presented in a formulation that can be easily adapted to other generalised Newtonian fluids.