Range Of Froude Numbers Research Articles

Theoretical investigation of hysteresis loops in free-surface flow under sluice gates for power-law channels

ABSTRACT In the present study, a new theoretical framework and analytical solutions to the problem of hysteresis loops due to hydraulic jump in power-law open channels under supercritical flows are introduced. This investigation primarily focuses on the flow dynamics encountered at a vertical sluice gate across channels of various shapes: rectangular, parabolic, and triangular. By the application of energy and momentum conservation principles, the dual flow configurations emerging under identical initial conditions are shown. An intensive analytical computational analysis led to the development of approximate theoretical models, facilitating the prediction of hysteresis loops for a wide range of Froude numbers and dimensionless channel geometry parameters. Several illustrative examples were treated and the results show a high degree of accuracy of the proposed models in predicting the hysteresis loops. The present research contributes to a novel methodology for enhancing predictions regarding the behavior of supercritical flows and the design of open channels for specific scenarios of the hysteresis phenomenon.

Turbulence Modulation By Large Heavy Particles In Wall-Bounded Turbulence

"Most studies on particle laden flows have focused either on small heavy particles or large neutrally buoyant particles. We present, for the first time (to the best of our knowledge), results in the regime of large and heavy particles, investigating the particle-turbulence dynamics over a parameter space covering a wide range of particle-volume fractions, Stokes and Froude numbers. We consider a flow in a pipe aligned with the gravitational vector, thus allowing for the investigation of the two-way coupling between particles and carrier phase turbulence, while excluding the effect of gravity on the wall-normal migration of particles. Time-resolved images of both tracers (10 micrometers particles) and the dispersed particles (700 micrometers in diameter) were taken in the streamwise-wall-normal pipe plane using a planar particle image velocimetry (PIV) system consisting of a high speed camera (Phantom VEO 440), and an Nd:YLF Laser as light source. Using Voronoi tessellations to analyze the inertial particle dynamics, we show a strong deviation from Poisson behaviour for cases with and without turbophoresis. From the time-resolved PIV measurements, we also show that the carrier phase turbulence is modulated even at particle concentrations as low as 0.3% indicating that particle-induced stresses due to distortion of fluid streamlines cannot be neglected. An increase or decrease in the peak streamwise velocity fluctuation in the particle laden flow was observed, depending on the Stokes number, while the radial velocity fluctuation was found either to be the same as in the single phase flow case or higher. Furthermore, pressure drop measurements indicate a linear increase in the skin friction coefficient with volume fraction of particles. This was true for all Stokes and Froude numbers considered. The growth rate (β) of the skin friction coefficient was however observed to be only a function of the Froude number. A power-law fit to the data shows that β scales inversely with the Froude number indicating that for Froude numbers less than 1, the influence of gravity cannot be neglected. "

Study on the Coefficient of Apparent Shear Stress along Lines Dividing a Compound Cross-Section

A compound channel’s discharge capacity and boundary shear force can be predicted as a sum of the discharge capacity of different sub-regions once the apparent shear stress of the dividing line is reasonably quantified. The apparent shear stress was usually expressed as a coefficient multiplied by the difference between two squared velocities of two adjacent regions. This study investigated the range of the coefficient values and their influencing factors. Firstly, the optimal values of the coefficient were obtained based on experimental data. Then, comparisons between the optimal values and several parameters used in quantifying the apparent shear stress were conducted. The results show that the coefficient is mainly related to a morphological parameter of the floodplain and the ratio of resistance coefficients between the floodplain and the main channel. An empirical formula to calculate the coefficient was developed and introduced to calculate the flow discharge and boundary shear stress. Experimental data, including 142 sets of test data of symmetric-floodplain cases and 104 sets of one-floodplain cases, have been used to examine the prediction accuracy of discharges and boundary shear stress. For all these tests, the ranges of water depth of the main channel and the total width of the compound cross-section are about 0.05~0.30 m and 0.3~10 m, respectively; the Q range and the range of Froude numbers of the main channel flow are about 0.0033~1.11 m3/s and 0.3~2.3, respectively. Comparison with other methods and experimental data from both rigid and erodible compound channels indicated that the proposed method not only provided acceptable accuracy for the computation of discharge capacity and boundary shear stress of compound channels in labs but also gave insights for calculating discharge capacity in natural compound channels.

Planing Hull Hydrodynamic Performance Prediction Using LincoSim Virtual Towing Tank

This work shows the performance of LincoSim, a web-based virtual towing tank enabling automated and standardized calm water computational fluid dynamics (CFD) data sampling, extending previous published applications to the case of a high-speed hull. The calculations are performed for a 1:10 scale model of a 43 ft powerboat hull form in the Froude number range from 0.3 to 2.0. The counterpart physical model is the experimental fluid dynamics (EFD) campaign performed at the University of Naples Federico II, where the resistance, sinkage and trim data have been measured. The EFD/CFD data comparison is performed and shown with a discussion of the spotted differences. The average percentage differences between the EFD and CFD data for the whole speed range are 1.84, 6.87 and 6.94 for the resistance, dynamic trim, and sinkage, respectively. These results confirm the maturity of the standardized and automated CFD modeling for calm water hydrodynamic analysis included in LincoSim, even at very high Froude numbers. The wetted length of the keel and chine and the wetted surface are calculated from numerical data using the advanced post-processing. Finally, as a work in progress, we test a first comparison for the same hull of the EFD and CFD data, considering two seakeeping conditions for head waves at a given wavelength for two velocity conditions. Also, this kind of analysis confirms the tight correlation between the measured and computed outcomes. This synergic interplay of EFD and CFD can link the advantages of both methods to support hull design but also requires experiment planning and final data analysis to obtain physical parameters not easily measurable in laboratory, such as the wetted surface, wetted lengths, proper viscous contribution, and pressure distribution both in calm water and in waves.

Equations and methodologies of inlet drainage system discharge coefficients: A review

Abstract Accurate determination of grate inlet discharge coefficients is crucial in reducing modeling uncertainties and mitigating urban flooding hazards. This review critically examines the methods, equations, and recommendations for determining the weir/orifice discharge coefficients, based on the inlet parameters and flow conditions. Reviewing previous studies for inlets showed that the discharge coefficient of rectangular inlets under subcritical flow ranges from 0.53 to 0.6 for weirs and from 0.4 to 0.46 for orifices, while in grated circular inlets, it falls between 0.115 and 0.372 for weirs and between 0.349 and 2.038 for orifices. For circular non-grated inlets under subcritical flow, the weir and orifice coefficients are in the range of 0.493–0.587 and 0.159–0.174, respectively. However, the orifice discharge coefficients of grated and non-grated inlets with unknown Froude number range between 0.14–0.39 and 0.677–0.82, respectively. For supercritical flow, the weir and orifice discharge coefficients of grated and non-grated rectangular inlets are 0.03–0.47 and 1.67–2.68, respectively. Previous studies showed that it is recommended to correlate the discharge coefficients with the approaching flow and Froude number under subcritical and supercritical flows, respectively. Yet, additional studies are recommended for a better understanding of the limits and parameters governing the flow transitional stage between weir and orifice and between subcritical and supercritical conditions. Moreover, further research is required to determine the weir and orifice discharge coefficients of circular inlets under supercritical flow as well as the orifice discharge coefficient range of rectangular non-grated inlets under subcritical flow. Finally, it is recommended to increase the road surface roughness to reduce Froude number, and thereby, increase discharge coefficients of street inlets. The aim of this review is to help inlet designers and authorities promote sustainable cities with resilient urban drainage systems and reduce the environmental, economic, health, and social impacts of urban drainage failure.

Experimental and Numerical Study on Influence of Wheel Attachments on Resistance Performance of Amphibious Vessel for Marine Debris Collection

This study aims to investigate the influence of wheel configurations on hydrodynamic resistance of an amphibious vessel through experiments and simulations. To evaluate the resistance performance associated with wheel attachments, three configurations were examined: vessel without attachments, with caterpillars, and with both caterpillars and shoe−paddles. A comprehensive series of computational fluid dynamics (CFD) simulations were conducted for these attachment types, complemented by experimental validations. The Volume-of-Fluid (VOF) model was employed in CFD simulations to capture the free surface movement, and the Dynamic Fluid–Body Interaction (DFBI) model was adopted to represent the two-degree-of-freedom motion of the vessel, specifically trim and sinkage. The total resistance derived from CFD simulations was calculated across a range of Froude numbers (Fns), including the design speed of the target vessel, and validated through model tests conducted in a wave basin equipped with a towing facility. The analysis indicated a general increase in resistance when attachments were added to the amphibious vessel. Remarkably, at the design speed (Fn = 0.27), the total resistance with both caterpillars and shoe−paddles exceeded that of the configuration without any attachments by more than 75.7%. These results provide crucial insights for the preliminary design stage of amphibious vessels, particularly those intended for marine debris collection in hard-to-reach areas.

Experimental investigation and application of soft computing models for predicting flow energy loss in arc-shaped constrictions

Abstract This investigation focuses on flow energy, a crucial parameter in the design of water structures such as channels. The research endeavors to explore the relative energy loss (ΔEAB/EA) in a constricted flow path of varying widths, employing Support Vector Machine (SVM), Artificial Neural Network (ANN), Gene Expression Programming (GEP), Multiple Adaptive Regression Splines (MARS), M5 and Random Forest (RF) models. Experiments span a Froude number range from 2.85 to 8.85. The experimental findings indicate that the ΔEAB/EA exceeds that observed in a classical hydraulic jump with constriction section. Within the SVM model, the linear kernel emerges as the best predictor of ΔEAB/EA, outperforming polynomial, radial basis function (RBF), and sigmoid kernels. In addition, in the ANN model, the MLP network was more accurate compared to the RBF network. The results indicate that the relationship proposed by the MARS model can play a significant role resulting in high accuracy compared to the non-linear regression relationship in predicting the target parameter. Upon comprehensive evaluation, the ANN method emerges as the most promising among the candidates, yielding superior performance compared to the other models. The testing phase results for the ANN-MLP are noteworthy, with R = 0.997, average RE% = 0.63%, RMSE = 0.0069, BIAS = −0.0004, DR = 0.999, SI = 0.0098 and KGE = 0.995.

Experimental and numerical investigation of bow wave and wake flows around towed surface-piercing cylinders

An investigation was conducted to study the flow characteristics around towed surface-piercing cylinders and understand the mechanisms behind the bow wave and wake region formation. The experiments took place in a towing tank using three different cylinder models, covering a range of Froude numbers based on cylinder diameter from 0.28 to 1.73. Three-cylinder models are considered M1 is circular, M2 is semicircular ellipse and M3 is elliptical. Numerical simulations were performed using the OpenFOAM framework, considering turbulence effects through the unsteady Reynolds-Averaged Navier Stokes equations with the Shear Stress Transport k-ω turbulence model. The numerical results matched well with the experimental data. The bow wave's general features were similar across all cylinder models, with the height increasing as the Froude number rose. Froude numbers between 0.28 and 0.58 displayed a smooth surge surface, transitioning to a rough surface with roll-up initiation between 0.87 and 1.15. At Froude numbers 1.44 to 1.73, a fountain-like bow wave formed. Models M1 and M2 had the same average bow wave height, approximately 15% higher than that of Model M3. The depression depth or air ventilation at the trailing edge of the cylinders increased with the Froude number. Model M1 exhibited a greater depression depth than Models M2 and M3 at Froude number 1.15, and this difference further increased at Froude number 1.73 due to high vorticity and adverse pressure gradient generated by Model M1. Vortex coherent structures visualization revealed that at a low Froude number of 0.58, only the Karman vortex at the trailing edge was observed. At Froude number 1.15, the deep wake region maintained predominantly two-dimensional vortex structures, while the free surface displayed pronounced three-dimensional vortex structures. Model M1 had a drag coefficient approximately 40% higher than Model M3. These findings are valuable for engineering applications, particularly in the design of submarine masts.

Evolution of a Stratified Turbulent Cloud under Rotation

Localized turbulence is common in geophysical flows, where the roles of rotation and stratification are paramount. In this study, we investigate the evolution of a stratified turbulent cloud under rotation. Recognizing that a turbulent cloud is composed of vortices of varying scales and shapes, we start our investigation with a single eddy using analytical solutions derived from a linearized system. Compared to an eddy under pure rotation, the stratified eddy shows the physical manifestation of a known potential vorticity mode, appearing as a static stable vortex. In addition, the expected shift from inertial waves to inertial-gravity waves is observed. In our numerical simulations of the turbulent cloud, carried out at a constant Rossby number over a range of Froude numbers, stratification causes columnar structures to deviate from vertical alignment. This deviation increases with increasing stratification, slowing the expansion rate of the cloud. The observed characteristics of these columnar structures are consistent with the predictions of linear theory, particularly in their tilt angles and vertical growth rates, suggesting a significant influence of inertial-gravity waves. Using Lagrangian particle tracking, we have identified regions where wave activity dominates over turbulence. In scenarios of milder stratification, these inertial-gravity waves are responsible for a significant energy transfer away from the turbulent cloud, a phenomenon that attenuates with increasing stratification.

Flow Visualization on Submerged Flow Conditions in Open Channel Weir Downstream

Submerged flow regimes are common phenomena observed in open channel flow, such as rivers and spillways, with or without weirs. These flow regimes involve a sudden rise in the liquid surface downstream when high-velocity liquid discharges into a region of lower velocity. The rapid deceleration of the flowing liquid results in an increase in height and a conversion of kinetic energy into potential energy, with some energy dissipated as turbulence and heat. In this study, flow visualization techniques were employed to investigate the two-dimensional hydrodynamic characteristics of submerged hydraulic jumps within the Froude number range of 1.0 to 5.4 over a fixed bed. The obtained results were compared with existing literature data, showing a good agreement. This research contributes to the understanding of submerged flow phenomena and provides valuable insights into the hydrodynamics of submerged hydraulic jumps.

A scaling law for the length of granular jumps down smooth inclines

Granular jumps commonly develop during granular flows over complex topographies or when hitting retaining structures. While this process has been well-studied for hydraulic flows, in granular flows such jumps remain to be fully explored, given the role of interparticle friction. Predicting the length of granular jumps is a challenging question, relevant to the design of protection dams against avalanches. In this study, we investigate the canonical case of standing jumps formed in granular flows down smooth inclines using extensive numerical simulations based on the discrete element method. We consider both two- and three-dimensional configurations and vary the chute bottom friction to account for the crucial interplay between the sliding along the smooth bottom and the shearing across the granular bulk above. By doing so, we derived a robust scaling law for the jump length that is valid over a wide range of Froude numbers and takes into account the influence of the packing density. The findings have potential implications on a number of situations encountered in industry as well as problems associated with natural hazards.

Novel wall-attached multidirectional jets: Mathematical formulation, CFD modeling and experimental validation

Achieving a healthy and comfortable indoor air environment has long been an objective of human endeavors. For a novel ventilation system, the wall-attached multidirectional jet pattern, the mathematical model describing the jet trajectory, temperature and velocity changes was first proposed to predict airflow attachment and separation moments from walls, covering a densimetric Froude number range from 0.5 to 4.0. Subsequently, this mathematical model was solved using a comprehensive numerical methodology and validated by full-scale experiments, which demonstrated that this established model could accurately depict the wall-attached multidirectional jet flow, with controllable errors — 16.4% for jet trajectory and 8.2% errors for jet axis temperature — when maintaining a supply velocity of 0.2 m/s. Also, the flow characteristics within a room featuring internal heat sources were analyzed, varying air supply velocities from 0.1 to 0.8 m/s and jet angles from 0° to 60°. Finally, this flow pattern of the wall-attached multidirectional jet was further confirmed and reproduced through CFD modelling which illustrated temperature stratification ranging from 18.1 °C to 25.2 °C, similar to the pattern observed in displacement ventilation. Present research could be valuable for the development of wall-attached multidirectional jet and the establishment of a healthy indoor air environment in practical applications.

Effects of pitch angle on a near free surface underwater vehicle

Simulations of an underwater vehicle were conducted to investigate the effects of steady pitch angle, Froude number, and submergence depth. A shallow submerged (D* = 1.1) to a deeply submerged (D* = 6.6) SUBOFF was investigated over a range of steady pitch angles and Froude numbers. Results show that proximity to the free surface causes increased resistance, heave and pitch moment and that free surface effects diminish rapidly with increased submergence depth. Even though D* = 3.3 is typically quoted as being the deeply submerged threshold, free surface effects can still be observed especially at large pitch angles. At pitch angle, asymmetry can be seen between the pressure distribution of the upper and lower surfaces of the SUBOFF, with a phase shift of the hydrodynamic forces and moments. At smaller pitch angles, the changes in hydrodynamic forces and moments stay relatively linear at an offset from zero degrees. At larger pitch angles, the hydrodynamic forces and moments become non-linear due to crossflow separation and air entrainment over the bow/stern. Additionally, the potential of the stern planes to cope with free surface effects were investigated, showing the safety threshold with respect to Froude number, submergence depth, and hull pitch angle.

Experimental study of the influence of catamaran parameters on water resistance

The advantages of multihulls over monohulls are better running characteristics at high speeds and a larger deck area, which is critical for passenger ships. When designing, it is necessary to choose geometric parameters, which include the distance between the hulls. A brief description of the existing methods for calculating the towing resistance of multihull vessels is provided in the paper. New results of an experimental study of the effect of transverse clearance and the ratio of the one hull width to draft on the resistance of a displacement catamaran are also provided. The studies are carried out by testing a small non-self-propelled model of a multihull vessel in the towing tank. The model length is 1.84 m; the width of one hull is 0.15 m; the draft varies from 0.07 m to 0.11 m. The experiment is carried out in the towing tank of the Admiral Makarov State University of Maritime and Inland Shipping. The results are processed according to the Froude method without taking into account dynamic heel and they are presented as a dependence of the residual resistance coefficients on the Froude number. By approximating the experimental data, an expression allowing evaluating the influence of these parameters on the value of the residual resistance in the range of Froude numbers 0.30–0.70 is obtained. One hull is also tested at two draft values in the same speed range. These data are not approximated, but they are presented in the paper in the form of experimentally obtained points. The results of the work can be used at the initial stages of designing catamarans and at studying the influence of these factors on the residual resistance.

Hydrodynamic performance of high-speed displacement vessel with hull vane

The hydrodynamic performance of high-speed displacement vessels can be enhanced by installing basic stern fittings such as stern wedges, stern flaps, interceptors, and hull vanes. The hydrodynamic performance of a high-speed displacement vessel with hull vane is analysed and compared to the bare hull condition in this study. The hull vane is a hydrofoil wing attached transversely to the bottom of the transom that focuses largely on minimising the wave-making resistance of the vessel by altering the flow at the stern. It increases flow on its upper surface, which interferes favourably with the stern wave system, hence lowering wave-making resistance. This research investigates the effects of installing the hull vane on a high-speed displacement vessel at various locations in the X and Z directions from the transom edge. The tests were carried out on model ship with and without a hull vane to verify the accuracy of the computational findings. The experiments were carried out in the towing tank facility available at Indian Institute of Technology Madras (IIT Madras), Department of Ocean Engineering (DOE). Computational fluid dynamics (CFD) simulations were carried out for model vessel with and without hull vane for a range of Froude numbers from 0.17 to 0.42 using RANSE-based commercial software. The research examines the resistance, trim, pressure distribution, and stern flow development of the vessel at various speeds and in calm water conditions. The results indicate that installing a stern hull vane reduces resistance and trim of the vessel. The effect of a hull vane is enhanced when it is positioned away from the stern of the vessel.

A comprehensive experimental investigation of total drag and wave height of ONR Tumblehome, including uncertainty analysis

A comprehensive hydrodynamic investigation of the 48.9 scale ONR Tumblehome (ONRT) form has been made by experiments carried out in Ata Nutku Ship Model Testing Laboratory of Istanbul Technical University (ITU-AN). Starting from the bare hull of ONRT hull, drag tests w/or w/o rudders, shafts and brackets, and the fully appended ONRT hull have sequentially been performed in the range of Froude number, 0.16≤Fr ≤ 0.36. The repeatability of drag tests of fully appended ONRT hull has been presented by uncertainty analysis between 0.10≤ Fr ≤ 0.42. The total drag (RTM) of ONRT form with the expanded uncertainty was estimated as 4.615 ± 1.098% N at Fr = 0.20, and 11.121 0.636% N at Fr = 0.30. At Fr = 0.20, it was concluded that the total drag (RTM) of fully appended model was 79.21% bare hull, 7.10% rudders, 8.78% shafts and brackets, and 4.91% bilge keels. The drag tests of fully appended ONRT performed at ITU-AN was also compared with those of carried out at IOWA-IIHR and OU-NAOE. New wave heights at two planes (namely, y/LWL = 0.1557 and y/LWL = 0.3623) of ONRT were also measured and presented at five different Fr numbers. These measurements were compared with those of CFD performed before. A very good agreement has been obtained.

Investigation of heavy gas dispersion characteristics in a static environment: Spatial distribution and volume flux prediction

The unexpected release of hazardous gases due to natural/industrial accidents or man-made disasters can have tragic consequences. Compared with other gaseous pollutants, heavy gases easily accumulate in personnel working areas and are more difficult to eliminate through existing mechanical ventilation systems. In this paper, to improve air quality in enclosed environments, the spatial characteristics of heavy gas dispersion were obtained based on an analysis of the basic properties of heavy gas dispersion. Schlieren experiments and image processing were conducted with shadow correction and noise reduction. The computational fluid dynamics (CFD) was used for predicting the dispersion of heavy gas. The numerical simulations cover a wide range of the densimetric Froude number (Fr) from 6.45 to 25.79, and a best-fit relation of Fr and the height of heavy gas fountain was provided. The radial velocity, radial density and axial density at cross-section of heavy gas dispersion were normalized using the unified scaling law. The axial density reached a minimum value at a height of 10 times the inlet diameter. Further decreases in the inertial force or decreases in the buoyant force can reduce the dilution of heavy gas by ambient fluids, which means that heavy gases diffuse faster and farther. An alternative method for estimating volume flux during gas dispersion using Fr was also proposed.

Investigation of the optimum longitudinal single transverse step location for a high-speed craft

One of the crucial aspects of the conceptual design of a stepped planing hull is the prediction of its performance. To improve performance, the prediction of total resistance must become more accurate. In the field of research, both towing tank experiments and numerical analysis may be used to achieve this goal. In this study, experiments were conducted initially to investigate total resistance of a relatively high-speed craft without a transverse step. Later, numerical computations were carried out to validate the experimental results. After it was determined that the test results and CFD methods were in good agreement, the experimental method continued to investigate the resistance properties of the hull with four different configurations to evaluate the optimal longitudinal position of a single transverse step. The ideal longitudinal position of the single transverse step was evaluated based on a similar relatively high-speed hull with a velocity of up to beam Froude number (FrB) 2.56 in this study, focusing on the FrB range between 2.30 and 2.45.

Wake and air entrainment properties of transom stern over a wide range of Froude numbers

In the present study, high-fidelity simulations of the wake behind a transom stern are performed with a block-based adaptive mesh refinement technology. By transom stern, we mean a square-ended stern of a ship, which is a favorable design for the high-speed ship. The sharp volume of fluid method is adopted to capture the gas–liquid interface, and the immersed boundary method is applied to simulate the boundaries of ship hull. Simulation results show that the V-like diverging wave along with air entrainment constitute the main characteristics of the wake. Air cavity of various scales is captured and tracked by the cavity-detection algorithm. Thus, the spatial and temporal distribution of the number and volume of air cavity is obtained in the simulation. Different draft Froude numbers are considered to analyze their influence on the wake. The wave profile, distribution of air cavity, turbulence kinetic energy, and the air entrainment features of the wakes behind dry and wetted stern are compared quantitatively. Numerical results demonstrate the present solver is capable of reproducing the main characteristics of wake behind a high-speed transom stern.

Characterisation of the granular dynamics at the interface between a pipe and a granular flow in a rotating drum

A new mobile bed heat exchanger is presented in this work which is composed of a flowing granular material in a rotating drum and a cylindrical pipe with potential interest in different energy applications as cooling, heating or heat recovery processes. An optimal design of the device requires a characterisation of the phenomena involved at the interface between the granular flow and the pipe. The process is modelled by the discrete element method and a global classification of the flow patterns around the pipe is presented with respect to the three main control parameters of the problem: the Froude number, the diameter ratio and the relative filling height of the drum. The second part is devoted to the characterisation of the structure of the flow at the interface (velocity field, density field) in particular in a so-called Biflow regime where granular motion occurs above as well as below the pipe which is favourable to transfer by convection. A typical behavior at the interface with the pipe consists of a zone I with high velocities of particles at the top of the pipe, a second zone with quasistatic particles or low velocity particles at the front and at the bottom of the pipe and a last zone III of depletion of particles at the back of the pipe. The Froude number has a limited effect on the features of this structure on the first layer in the range of Froude numbers considered whereas the relative height is a more determinant parameter to control the relative magnitude of velocities in zone I and zone II as well as the extent of the depletion zone. This first hydrodynamical characterisation can shed light on the dynamical regimes with improved transfer between the particles and the pipe boundary.