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The presence of sediment particles in open-channel flow has an important effect on turbulence; thus, an empirical, turbulent eddy viscosity formula was established for application in the limit for low concentrations. The current study establishes a theoretical relation for the mixture viscosity based on the two-phase mixture model. The percentage contribution of the three mechanisms of mixture viscosity, namely, fluid turbulence (FT), particle turbulence (PT), and inter-particle collisions (IPCs), was calculated under different conditions. The study results indicate that the contribution of FT is dominant, whereas those of PT and IPCs are not significant when the particle inertia (PI) is small, suggesting that the movement of sediment-laden flows is mainly controlled by the fluid properties. The effects of PT and IPCs increase with increases in sediment concentration and PI. Specifically, the effect of collisions among particles generally becomes dominant near the bed surface. A good agreement between the calculated velocity profile of the mixture and available experimental data for large particle sizes and high concentrations proves that the proposed relation for mixture viscosity is more reasonable than the previous empirical relation owing to the consideration of the effects of PT and IPCs, and, thus, can be applied to both dilute and dense suspensions. • Particle collision and particle turbulence effects were investigated. • Effect of particle collisions becomes dominant in the vicinity of the bed surface. • Resistance coefficient decreased with decrease in particle inertia. • Proposed formula provides better results in comparison to the empirical relation. [ABSTRACT FROM AUTHOR]

This study presents the application of physics-informed neural networks (PINN) to reconstruct the velocity and pressure of wave-in-deck (WID) loading phenomena based on particle image velocimetry (PIV) experiments in a 2D wave tank. The Euler equation for inviscid and incompressible fluids was adopted as the governing equation, and two boundary conditions were applied, with zero gauge pressure in air and zero vertical velocity on the deck bottom for the PINN. The free surface was reconstructed accurately by incorporating the loss term of the volume fraction into the total loss function. A learning rate annealing method and minibatch training strategy were used to achieve better training convergence. For a faster training process, the volume fraction was incorporated with the residual of the continuity equation and velocity loss. The velocity profile and pressure reconstructed by the PINN were compared with the velocity profile and pressure measured in the experiments and the pressure estimated by the PIV-based estimation methods, which revealed the advantages of the PINN in flow field reconstruction. The results showed that the PINN could be applied to reconstruct the velocity and pressure for the WID loading phenomena, and the pressure reconstructed by the PINN generally showed better agreement with the measured pressure than the pressure estimated by the PIV-based estimation methods. Additionally, proper implementation of governing equations and boundary conditions proved effective in mitigating the influence of measurement noise on the reconstructed results. [ABSTRACT FROM AUTHOR]

Natural revegetation alters local hydrodynamic conditions in coastal lagoons. To investigate vertical flow structures in revegetated lagoons, a series of flume experiments are implemented on an immobile bed with Phragmites australis by a certain staggered configuration. Six incident wave heights and five inflow discharges are considered. The experimental results demonstrate that wave dominates turbulent kinetic energy (TKE) distributions under wave-current conditions. Vegetation morphology plays an important role in wave-current-vegetation interactions, which regulates TKE distributions by diminishing wave effects within 70% of water depth especially (0.3 < z / h < 1). The increasing inflow discharge has positive effects on diminishment of wave effects, while the reduction of mean streamwise flow velocity is stable under the present vegetation configuration. Moreover, the practical values of vertical mean flow velocity can be obtained from the empirical equation, which includes wave effects by a quadratic polynomial relationship between the ratio of experimental values to theorical values (U / U p) and the relative wave height H 0 / h. Furthermore, two relationships are established between the reduction of mean streamwise flow velocity r and z / h , involving a logarithmical relationship in the lower layer (0 < z / h < 0.3), and a cubic polynomial relationship in the upper layer (0.3 < z / h < 0.7). • Natural vegetation is investigated in flume experiments under wave-current conditions. • Vegetation morphology takes an important place in wave-current-vegetation interactions. • An empirical equation of vertical mean flow velocity is modified by including wave effects. • Relations between vegetation-induced reduction of flow velocity and relative water depth are established. [ABSTRACT FROM AUTHOR]

Abrasive waterjet (AWJ) is an effective tool for manufacturing parts from multi-layered structures (MLSs) due to its capability in machining a wide range of materials. However, the challenge in employing AWJ in producing the desired kerf geometry in MLS can be attributed to the complex nature of the jet's interaction with multiple layers that possess different material properties. Hence, a model that captures the interaction of the jet with MLS, and predicts the whole kerf geometry is required to gain control over the kerf quality. On the other hand, the kerf generated in a layer is affected by the presence of preceding-/following- layers. In this context, it is essential to develop a comprehensive model for the prediction of kerf profile during the penetration of the jet in each layer. Although, several models exist to predict the process response (erosion depth, top (w t), and bottom kerf width (w b), kerf taper), very limited models available on kerf profile prediction. Further, neglecting the actual jet characteristics limits their ability to predict accurately. By considering the above, this work proposes a model for the prediction of the kerf geometry (profile and characteristics) in a single layer of MLS along with its kerf characteristics apart from considering the non-linearities, such as jet characteristics and the effects of AWJ process parameters. A discretized form of the jet, abrasives mass flow distribution, and their velocity in the jet plume to realize a more realistic model for predicting kerf geometry. Further, a new parameter, ' depth of damaged region ' was defined towards realizing the w t. The model was evaluated by comparing the kerf geometry formed on mild steel (MS) and aluminum (Al) materials by using root mean square and mean absolute error. The proposed model was found to predict the kerf geometry accurately. • First model to predict AWJ generated kerf profile considering abrasive particle velocity profile and mass flow rate distribution. • Development of analytical model to accurately predict the complete kerf profile in a single layer cut by AWJs. • Erosion theories combined with discretization approach in the development of model. • Effective representation of the top kerf width in different materials based on depth of damaged region. [ABSTRACT FROM AUTHOR]

Savonius turbines are utilized on low-density open urban rooftops. Array of these rotors significantly increase energy production. Many studies on arrays employ two-dimensional Unsteady Reynolds-Averaged Navier-Stokes (URANS) approach to simulate flow. However, insufficient exploration exists in literature between studies of single rotor and of Savonius arrays, particularly in understanding wake of Savonius turbines. Thorough understanding of wake characteristics using three-dimensional computational fluid dynamics (CFD) is crucial for efficient setup of arrays. This study examines wake by adjusting operational conditions of Savonius rotor. For a tip speed ratio (TSR) 1.0, approximately 50 % and 75 % of streamwise velocity is recovered at downstream distances of 4 and 7 rotor diameters (D) from centroid. Two-dimensional simulations cannot capture the wake accurately, as significant entrainment on advancing side occurs from z-direction. Vortical structures, characterized by Q-criterion and z-vorticity, are smaller at higher TSRs due to increased interaction with returning blade side. Novel integral momentum approach determines optimal downstream turbine position without simulating downstream rotor. It segregates downstream region into nine areas and analyzes momentum flux to account for varied recovery rates across z-planes. Additionally, velocity profiles are estimated using hyperbolic secant function. Present findings provide critical insights for efficient arrangement of Savonius turbine arrays. • Velocity deficit of Savonius wind turbine for different tip speed ratio is studied. • Vortical structures and vorticity at different vertical planes are presented. • New integral momentum approach to determine optimum position of downstream rotor. • Estimation of velocity profile using hyperbolic secant function. • Analysis useful for optimization of off-grid arrays of Savonius wind turbines. [ABSTRACT FROM AUTHOR]

Consideration of roughness effects in the flow in a minichannel has been a major scientific problem for many decades. Roughness can alter the momentum diffusion, heat transfer conditions or laminar-turbulent transition. These effects are even more pronounced in minichannel flows where the roughness can occupy a large part of the cross-section. Modelling methods applied so far usually fall short in internal flows with high relative roughness. The presented paper pertains to the analytical flow model in Tesla turbine components with consideration of roughness on the rotor walls. The model uses the equivalent sand grain approach to modify dynamic viscosity in the governing equations to achieve a desired downward shift of the dimensionless velocity profile. The model solves two-dimensional equations of continuity, momentum and energy. The semi-empirical function was derived to consider the change in the shape of the radial velocity. The applied model incorporates Euler's turbomachinery equation to determine the influence of roughness on the turbine performance under varied operating conditions. Roughness shortens the streamlines inside the rotor, but the overall turbine's performance is improved. The roughness equal to 10−5 m increased the power generated and isentropic efficiency by factors of 3 and 2.5, respectively, compared to the smooth rotor. • Modification of fluid viscosity is used to account for roughness in the Tesla turbine. • Blockage effect of roughness elements in microchannels is considered. • Semi-empirical function for velocity profile is used to improve modelling accuracy. • Roughness can increase power three-fold and efficiency two-fold. [ABSTRACT FROM AUTHOR]

Addressing the need for innovative burner designs to optimize combustion characteristics and meet energy efficiency goals, this study introduces a novel concept rooted in swirl-induced flames. The proposed burner employs a unique approach to generate air and fuel swirl using four opposing slots in two sets, each set at distinct angles. Incorporating of a channel within the outer casing allows for fine-tuning of entry angles, optimizing the double swirling process. The objective of this research is to enhance combustion characteristics through the implementation of the swirl principle, introducing a tangential velocity component to the airflow or fuel-air mixture upon entry into the burner. Systematic measurements at various entry angles (0°, 15°, 30°, 45°, and 60°) are conducted to identify optimal or near-optimal conditions. The research covers a comparison between flow fields generated by traditional swirled vanes and swirl-induced injection ports at identical inlet conditions, revealing enhanced flame stability and combustion efficiency in the latter configuration. The formation of recirculation zones around the burner, facilitated by increased outer air jet velocities, promotes better mixing and stability. This research contributes valuable insights into burner design and optimization, with implications for improved combustion efficiency and environmental sustainability. • Swirl induction was done by a tangential velocity component to the airflow or fuel-air mixture upon entry into the burner. • Numerical simulations of LPG diffusion flames at different equivalence ratios are conducted. • Thermal inflame contours measurements are agreed with numerical calculations. • The locations of the generated recirculation zones are shown via flow field simulation analysis. [ABSTRACT FROM AUTHOR]

The nearshore zone turns out to be the area with the higher concentration of plastic debris and, for this reason, it is important to know the processes that affect the transport and the fate of this type of litter. This study focuses on investigating the dynamics of various plastic types under several hydrodynamic conditions primarily induced by waves. 2D tests were carried out at the Hydraulic Laboratory of the University of Messina reproducing the main phenomena that occurred during the wave propagation on a planar beach. More than 200 different conditions were tested changing the wave characteristics, the water depth, the plastic debris characteristics (density and shape), and the roughness of the fixed bottom. In general, it can be observed that the reduction in particle displacement occurs due to: i) a decrease in wave steepness; ii) an increase in depth; iii) an increase in particle size; iv) an increase in plastic density. However, the experimental investigation shows that some plastic characteristics and bed roughness, even when hydraulically smooth, can alter these results. The experimental data analysis identified a criterion for predicting the short-term fate of plastic debris under wave action. This criterion to determine equilibrium conditions, based on an empirical relationship, takes into account the wave characteristics, the bed roughness and slope, and the weight of the debris. • Various types of plastics were subject to hydrodynamic forcing to test their motion. • The displacement of the plastic increases as the wave steepness increases. • The bed roughness determines a nonlinear plastic displacement behaviour. • A methodology to understand the short-term fate in wave-driven transport was defined. [ABSTRACT FROM AUTHOR]

[Display omitted] • Boundaryand elastohydrodynamic lubrication models with additives under sinusoidal load were studied by NEMD. • The additive's solidification degree reflects the interlacing strength, thus relative motion less occurs in the BL regime. • The liquefaction degree and the velocity difference of base oil and additive regions, affect friction in the EHL regime. The evolution of lubricating oil containing additives under dynamic conditions is very significant, since its oil film structure, velocity distribution, and adsorption characteristic have an obvious impact on friction and wear. In this work, a boundary lubrication (BL) and elastohydrodynamic lubrication (EHL) models under sinusoidal load were carried out by nonequilibrium molecular dynamics (NEMD), using iron oxide as the substrate, hexadecane, and stearic acid molecules as lubricants. It was discovered that the friction in the BL regime is positively correlated with the degree of additive's solidification. The greater the solidification degree of additive layers, the less the interlacing between them, making the relative motion between them easier and reducing compression oscillation within them, thus diminishing friction in the BL regime. The degree of liquefaction of base oil and additive regions, as well as the velocity difference within their interlacing zones, are connected to the friction force in the EHL regime. At high frequencies as well as large amplitudes, the oil film has a very high degree of liquefaction, which facilitates internal shear in it, and there is essentially no relative motion between the base oil and additives, resulting in low friction. [ABSTRACT FROM AUTHOR]

• The physical principles and typical challenges of acoustic techniques applied to fluid-particle systems are explained. • Signal processing for obtaining velocity profiles, solid volume fractions, and PSD of the dispersed phases are discussed. • Acoustic-based methods can advance the fundamental understanding of fluid-particle flows. • Ultrasound techniques can be further applied to three phase flows, bubbly flows and liquid-liquid or liquid gas flows. Acoustic methods applied to opaque systems have attracted the attention of researchers in fluid mechanics. In particular, owing to their ability to characterise in real-time, non-transparent and highly concentrated fluid-particle systems, they have been applied to the study of complex multiphase flows such as fluidised beds. This paper gives an overview of the physical principles and typical challenges of ultrasound and acoustic emission AE methods when applied to fluid-particle systems. The principles of ultrasound imaging are explained first. The measurement techniques and signal processing methodologies for obtaining velocity profiles, size distribution of the dispersed phases, and solid volume fraction are then discussed. The techniques are based on the measurement of attenuation, sound speed, frequency shift, and transit time of the propagated sound wave. A description of the acoustic emission technique and applications to fluid-particle systems are then discussed. Finally, extensions and future opportunities of the acoustic techniques are presented. [ABSTRACT FROM AUTHOR]

• (1) A velocity prediction model based on multi-factor-dependent drag coefficient is proposed. • (2) The relationship between flow characteristics and drag coefficient in steady flow with submerged flexible vegetation is quantified. • (3) The effect of water depth on drag coefficient in steady flow with emergent flexible vegetation is explored. Flexible submerged vegetation plays a pivotal role in ecosystem. Understanding the complex impact of flexible vegetation bending on flow drag is crucial. The wide variability in drag coefficients within flexible vegetation poses challenges in accurately predicting flow drag. In this paper, the developed prediction model of velocity profile based on multi-factor-dependent drag coefficient is derived based on Euler-Bernoulli beam assumption, dual-layer averaged velocity model and the relationship between the averaged inclination angle of bent vegetation and Cauchy number. This model makes it possible to calculate the drag coefficients and velocity profiles at the same time, instead of using an assumed constant drag coefficient, and the application of this prediction model is highly favorable with experimental data. Meanwhile, new function of the depth-averaged drag coefficient applicable to submerged and emergent vegetation are presented, describing its relationship with the deformation angle of canopy, Reynolds number, submergence and water depth. The result shows that the drag coefficients for the same vegetation are smaller at higher submergence and Reynolds number. The findings of this study may provide valuable insights into the variability of drag coefficients and the flow structure with submerged flexible vegetation, and being applicable for the restoration and management of freshwater ecosystems. [ABSTRACT FROM AUTHOR]

• A CSN injector was designed and a simplified non-ignited entrained flow gasifier model was built. • Several equations based on the assumption of free turbulence flow were proposed. • Compared with single nozzle injector, the designed CSN injector could reduce the gasifier volume about 50%. • The CSN injector could improve overall rate for gasification reaction and carbon conversion rate. As one of the key equipment of a gasifier, the injector unit of a gasifier has significant impacts on its flow filed, and further, the performance of gasifier. With the growth demand for higher gasification efficiency, new gasifier injector designs were kept being invented. In this paper, a pilot cluster-six nozzles (CSN) injector was designed and implemented on a simplified non-ignited entrained flow gasifier model in order to exam its performance, the formulated flow fields were compared with traditional single nozzle injector, results showed that the mean velocity profile along radial direction for CSN injector was similar to a Gaussian curve. Several equations based on the assumption of free turbulence flow were proposed in order to analyze the characteristics of the flow field. Compared with single nozzle injector, the centerline mean velocity of CSN injector decay more serious, which could reduce the gasifier volume about 50%, and the flow features, for example: the flow rate and the half-thickness under the same experiment conditions and cross section are about twice as much as in the single nozzle injector, and energy dissipation rate were also became faster. Experiment results also showed a better particle dispersion effect from the CSN injector, that the solid particles ejected from CSN injector were occupying more gasifier space and kept a longer residue time in gasifier, which could cause larger overall rate for gasification reaction and carbon conversion rate. These results indicated that the CSN injector can effectively improve the gasification performance and also provide more information for new gasifier injector design. [ABSTRACT FROM AUTHOR]

A series of experimental observations are presented in the current study to discuss the effects of artificial bed roughness on the turbidity current flowing in a rectangular channel with an abrupt change in bed slope. For this purpose, two different types of elements, sinusoidal and trapezoidal, with various heights and arrangements are considered as artificial bed roughness. A Vectrino velocity meter was used to measure the velocity and sediment concentration profiles. The effects of inlet sediment concentration on front velocity, body velocity, unit discharge, sediment concentration, and suspended load transport rate also were investigated. Accurate equations were developed for estimation of the velocity of a turbidity current over smooth and rough beds. The unexpected experimental results showed that unlike the effect of roughness height, a change in the roughness arrangement has no significant influence on the velocity of a turbidity current. Also, the effect of bed roughness on the front velocity of a denser current is more significant. [ABSTRACT FROM AUTHOR]

Underwater wall shear stress measurement based on a newly developed MEMS sensors array is experimentally verified utilizing a set of flat plate benchmark tests conducted in a precision water flume. The array is firstly calibrated in a well-defined 2D flow and then flush embedded on the plate surface to measure WSS directly. The local freestream velocities ranging from 0.1 m/s to 0.7 m/s are adopted for the test cases of naturally developing flow and deliberately stimulated turbulence. The boundary layer profiles of interests are correspondingly detected with LDV, and mean WSS values are extrapolated from suitable fits to known profile shapes for flat plate with a zero pressure gradient. The results from the MEMS sensors match well with those from the LDV velocity profile fits and are in good agreement with empirical estimations with an overall bias of less than 5%. Also, the direct simultaneous measurements from multiple sensors on the MEMS array favorably exhibit the streamwise variation of the wall-bounded flow. Generally, the MEMS sensors array-based underwater wall shear stress measurement is characterized by desirable accuracy and spatial resolution for further practical applications. • Researches on detailed measurement of wall shear stress for flat plate model are carried out with MEMS sensor array. • MEMS sensor array is calibrated in flume and measurements are verified with LDV results and empirical estimations results. • A comparative study of wall shear stress in flat plate naturally developing flow and stimulated turbulence is demonstrated. [ABSTRACT FROM AUTHOR]

• An analytical model for water transport capacity through nanopores is proposed. • Water slip mechanism and heterogeneous water physical properties are seriously captured in the proposed model. • Effect of water slip on nanoconfined water flow capacity will become weak with the increase of pore radius. • Enhance factor will increase with increasing contact angle at a certain pore radius. Currently, a key scientific question has been urgently raised up by nanoscale associated industry that how to generate precise prediction results of transport capacity for nanoconfined water. The proper solution for the aforementioned issue will directly contribute to the development as well as economic interests of the related industry. Notably, unlike well-established theory for water transport through conventional pore scale, flow behavior of nanoconfined water remains unclear nowadays to a large extent resulting from the varying intermolecular interactions between water and pore surface. The interplay between water molecules and pore surface has tremendous effects on near-wall water physical properties, including viscosity, density as well as the boundary condition. These effects can be reasonably overlooked at the macroscopic scale, however, play crucial roles when it comes to nanoscale and should be properly treated. Herein, a novel model is developed to characterize water transport capacity within nanopores, in which above physical properties of nanoconfined water are related to surface wettability explicitly representing water-wall interactions. Meanwhile, apparent permeability, a concept from the petroleum industry is employed here to describe the transport capacity of nanoconfined water. Results show that (a) effect of surface wettability will become stronger within smaller pore dimension and enhance factor will increase with the increase of contact angle at a certain pore radius as a result from the stronger water slip phenomenon; (b) Due to the weak effect of surface wettability on nanoconfined water transport capacity at large pore size, enhance factor will close to one with the increase of pore size. (c) Through analyzing effect of critical thickness of the interfacial region, it can be demonstrated that the proposed model can be applied to the majority of pore surface of contact angle larger than 100° with high accuracy. Moreover, utmost caution should be paid when using the proposed model to pore surface with contact angle is relatively small (<40°). Finally, it is necessary to mention that the proposed model possesses analytically formulas, which greatly facilitate predicting nanoconfined water flow performance under various conditions. The above feature of the proposed model presents broad application potential in the related industry, like water purification, energy storage, and geophysical processes. [ABSTRACT FROM AUTHOR]

Highlight • Sudden contraction into the inlets of two parallel jets was investigated with PIV. • Velocity vectors evolve with a position in the contraction. • The size and shape and position of vortices change with Reynolds number. • Turbulence started at the fast and slow flow partitions and intensifies with Reynolds number. Abstract The inlets to parallel rectangular jets are unique and a critical component of its design. A sudden contraction (contraction ratio = 4.2) of a vertically upward entry flow into two inlets has been investigated experimentally. Changes in velocity profile close to the inlets were measured, while the corner vortices, fluid separation and the development of axial and lateral turbulent intensities were observed from the result of particle image velocimetry analysis. The velocity profiles in the fluid adjacent to the inlets are independent of the Reynolds number, generally the same for similar geometries, concave but changes rapidly before finally adapting to the positions of the inlets. The radii of the corner vortices decreased and became elliptical with an increase in Re. Also, the detachment length shrunk by 60% when the Re was doubled. Lateral and axial turbulence increased and more fluid flowed parallel to the wall as Re increased. The trend and magnitude of the lateral to axial velocity agree with those of similar works. [ABSTRACT FROM AUTHOR]

The velocity profiles of the electrohydrodynamic flow generator were investigated experimentally and numerically. The generator of a needle-to-cylinder electrode configuration with varying interelectrode distance and supply voltage was studied. Experimental results were obtained with constant temperature anemometry technique and the numerical simulations were performed with Multiphysics Object-Oriented Simulation Environment (MOOSE) framework. The current-voltage characteristic of the device and the relationship between flow velocity and electric current were found out to qualitatively match the results from previous studies. Velocity profiles obtained experimentally and numerically showed varying degree of agreement throughout studied configurations of interelectrode distance and supply voltage. Generally, better agreement was found in cases with lower interelectrode distance, lower turbulence strength and better accuracy of the solution of the electric part of the problem. Some similarities between studied flow and the flow specific for confined jet arrangement were observed, although recorded turbulence intensity values were much higher. Turbulence intensity profile for the lowest interelectrode distance indicated the existence of the shear layer between jet core and the boundary layer. For other values of the interelectrode distance the shear layer and boundary layer could no longer be distinguished. Nondimensional velocity profiles for all investigated configurations showed high degree of similarity in the jet core region, however the similarity was lost in the remaining part of the flow. • Better accuracy of the velocity prediction was observed for the jet region and for low values of the interelectrode distance. • The resemblance between investigated flow and confined jet arrangement was pointed out. • The existence of the jet region and boundary layer separated by shear layer was observed. • Dimensionless velocity profiles for all investigated configurations showed significant similarity within the jet region. [ABSTRACT FROM AUTHOR]

Highlights • A pulse-wave ultrasonic Doppler industrial measurement system is established. • Velocity profiles of four typical dispersed oil-water two-phase flow patterns were measured in a horizontal pipe. • Velocity profiles were separately for flow patterns of different continuous phase. Abstract Flow velocity is an important parameter in oil-water two-phase flow, which is closely related to the oil production estimation and production safety. In recent years, pulse-wave Doppler is widely studied because it can obtain the velocity profile along the ultrasound beam. In this paper, a new Pulse-wave Doppler system based on the industrial bus was designed to measure the velocity profile of oil-water two-phase flow. This system was used to study the velocity profile of a horizontal tube oil-water two-phase flow, the flow patterns include dispersion of oil in water and water (Do/w & w), oil in water emulsion (O/W), dual dispersions of water in oil and oil in water (Dw/o & Do/w) and water in oil emulsion (W/O). The velocity profile obtained was compared with the Laser Doppler Velocimetry (LDV) data under similar flow conditions. The results showed that, in water continuous flow patterns, the velocity profile of the two-phase flow can be described by a modified Nikuradse equation that describes the velocity profile of single phase pipe flow; in oil continuous flow patterns, the velocity profile also can be described by a modified Nikuradse equation with different parameters. [ABSTRACT FROM AUTHOR]

Highlights • A mathematical model is presented for prediction of RTD in laminar flow tubes. • The model predicts the RTD in a wide range of flow regimes in tubular reactors. • The presented PTIS model combines the axial diffusion and velocity profile. • Comparison of model results with experimental data showed a well compatibility. • The PTIS is able to predict the RTD of intricately structured micro-reactors. Abstract The residence time distribution is an important characteristic in the analysis of non-ideal reactors. In micro- reactors that operate predominantly under low Reynolds number, the axial dispersion is important. Since the channel length or residence time of fluid is usually not long enough, the axial dispersion model cannot predict an accurate RTD of the fluid in micro-reactors. In order to overcome this dilemma, a new model has been developed in the present work that combines the axial dispersion and velocity profile using the parallel tanks-in-series compartment model. The model comprises of two parameters, including the velocity profile exponent and Peclet number. It can be used for Newtonian and non-Newtonian fluid flow in the reactors with a wide range of Reynolds number and in all ranges of flow regime, including plug, laminar, perfectly mixed, and other profiles between these regimes. After verifying the model, the effects of velocity profile and Peclet number on the RTD of fluid in the tube for m-laminar and y-laminar velocity profiles were evaluated. Then, the RTDs of some previously reported systems such as straight Polytetrafluoroethylene (PTFE) tube, multi-laminated/elongational flow micro-mixer (MEFM-4) and standard T-junction micro-mixer (TjM) were adjusted to the proposed model. [ABSTRACT FROM AUTHOR]

Abstract Many industrial processes use bins for storage of granular particles. However, the discharge of granular particles through bins is not well described quantitatively. Monitoring and analysis of the flow of particles inside bins is a challenge faced in many industrial operations. Understanding particle flow during discharge can lead to significant improvements in the design and construction of bins. The paper presents a technique to detect the particle flow pattern inside a silo using X-ray radiography. The particle flow patterns for a mass-flow bin and a funnel-flow bin were detected by the in-situ tracking of tagged granular particles during discharge. X-ray radiographs of the silo were obtained at different times of discharge, which were then analyzed using image processing techniques, and the tagged particles in the silo were tracked. The individual particle trajectories obtained explain the particle flow pattern in the silo. Graphical abstract Radiographic tracking of tagged particles inside the silo identifies the actual path of individual particles. By combining all the individual particle trajectories, the particle flow pattern is established. Unlabelled Image Highlights • Particle flow patterns for mass-flow and funnel-flow bins were detected. • In-situ tracking of tagged granular particles during discharge was obtained. • Individual particle trajectories explained the particle flow pattern in the bin. [ABSTRACT FROM AUTHOR]

Highlights • Granular flows over a static pile have been investigated in an inclined channel. • The velocity profiles of the avalanches follow a pure parabolic decrease. • The velocity profiles can be predicted with the flow rate. • A shear-thinning viscosity model accounting for the velocity profile is deduced. Abstract Granular flows over a static pile have been investigated in an inclined channel. Instead of dividing the granular motions into fast flow with linear velocity profile and creeping motion with exponential velocity profile, we set the boundary of the flowing layer as the locus of points where the particle velocity decreases down to 1% of the surface velocity, and unify the granular motions with a single velocity profile making the application more convenient. The velocity profile of the granular flows follows a parabolic form, and can be predicted once the surface velocity or the flow rate is determined. Moreover, we propose a viscosity model to account for the parabolic velocity profile in the flowing layer, and validate this model by employing FT4 Powder Rheometer. The apparent viscosity is approximated as the sum of frictional and collisional-translational contributions. In analogy with the turbulent mixing-length theory, the momentum transfer is enhanced by the fluctuation, and the apparent viscosity in the granular flows depends both on the flowing-layer thickness and the local shear rate. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

Abstract This paper describes a novel dual-frequency inductive flow tomography (IFT) system, which relies on the use of a multi-electrode electromagnetic flow meter (EMFM). This flow meter is currently capable of imaging the velocity profile of the conducting continuous phase of both single phase and highly asymmetric multiphase flows ten times every second. Uniform and anti-Helmholtz magnetic fields are simultaneously applied to the cross section of the flow tube of the EMFM. This enables flow induced potentials to be measured, at an array of electrodes, flush mounted on the inner wall of the EMFM, ten times every second using a multi-channel analogue signal conditioning system. These measured flow induced potentials are then used in an image reconstruction algorithm to reconstruct the water velocity profile in the flow cross section at 0.1 s time intervals. A series of experiments were carried out in water continuous, upward, air-water flows inclined at 15° to the vertical to measure the water velocity profile using the IFT system. The water velocity profiles were compared with air velocity profiles previously obtained for inclined air-water flows at similar flow conditions using local probing techniques. For all of the flow conditions investigated it was found that both the local axial water and air velocities were significantly greater at the upper side of the inclined pipe than at the lower side. The high local water velocities were probably due to upward momentum of the air bubbles being locally transferred to the water at the upper side of the inclined pipe. A comparison of the local axial air velocity distribution and the local axial water velocity distribution also showed that the local slip velocity between the phases varied markedly in the flow cross section – indicating that previous assumptions that the local slip velocity is constant in the flow cross section are clearly incorrect. Highlights • Fast imaging of water velocity using novel dual frequency inductive flow tomography system. • Water velocity profiles measured in air-in-water flows inclined at 15° to the vertical. • Local axial water velocity significantly greater at the upper side of the inclined pipe than at the lower side. • Local slip velocity varied markedly when local axial air velocity distribution was compared with local axial water velocity distribution. [ABSTRACT FROM AUTHOR]

Abstract In this paper a recently theoretically deduced rill flow resistance equation, based on a power-velocity profile, was tested experimentally on plots of varying slopes and soil texture in which mobile bed rills are incised. Measurements of flow velocity, water depth, cross section area, wetted perimeter and bed slope conducted in rill reaches incised on experimental plots, having different slope values (9, 14, 22, 24 and 26%) and soil texture (clay fraction ranging from 42 to 73%), and literature data were used to calibrate the flow resistance equation. In particular, the relationship between the velocity profile parameter Γ, the channel slope, the flow Froude number and texture fractions was firstly calibrated using 147 rill reach data. Then this relationship was tested using 126 measurements carried out with soils having different texture (percentage of clay ranging from 9.6 to 73%) and slopes (6.9%–26%). The measurements allowed to establish that a) the Darcy-Weisbach friction factor can be accurately estimated using the proposed theoretical approach, and b) the data were supportive of the soil texture influence on rill velocity and flow resistance. Highlights • The effect of soil texture on rill flow resistance is experimentally investigated. • The relationship between rill flow resistance and velocity profile is investigated. • The flow resistance law is theoretically deduced by dimensional analysis. • The equation of the velocity profile parameter is calibrated by 147 rill data. • The equation of the velocity profile parameter is tested by 126 rill data. [ABSTRACT FROM AUTHOR]

Highlights • The incoming flow will enter both porous and non-porous regions. • The foam block causes a higher pressure drop than a solid block of the same size. • The effect of blockage on pressure drop is more dominant than pore density and inlet velocity. • The predicted friction factor is in agreement with the experimental data. Abstract This study experimentally investigates the effects of pore density, inlet velocity and blockage ratio on fluid flow behaviour and pressure drop in channels partially filled with a metal foam block. The fluid velocities in the free stream region, which is a clear (from foam) region on the top of foam block, are measured using Laser Doppler Anemometry (LDA) and hot-wire anemometry. The metal foam data are compared to those of solid blocks with the same size. For low blockage ratios, i.e. thin foam layers, the pressure drop caused by a solid block is higher than that of the foam when tested under identical conditions. Interestingly, nonetheless, beyond a threshold blockage ratio value, the pressure drop induced by the metal foam block exceeds that of the solid block of the same height tested at the same air flow rate. This behaviour is best described as the interplay between resistance caused by blockage versus that of the wake forms downstream and over the objects and additional frictional effects within the porous region and on the interface. Furthermore, a correlation, with ±16% deviation, is developed to predict the flow resistance caused by the solid and foam blocks across the partially filled channel. [ABSTRACT FROM AUTHOR]

An experimental study is presented on air-water two-phase flow in a 10.5-m-long annular duct with an external diameter of 155 mm and an inner diameter of 60 mm. Particle image velocimetry (PIV) is applied to obtain instantaneous velocity measurements of the flow field. The annular duct inclination is of 5 Â ° from the horizontal. A CCD camera ( 2448 pixel  × 2050 pixel, 5 Mpixel, 12-bit ) was positioned in the test section to record the seeding particles. The illumination was provided by a double pulsed PIV laser (Nd:YAG, frequency doubled to 532 nm) with a measured pulse intensity of 70 mJ/pulse. It was used at 15 Hz (resulting in the independence of the velocity samples). Based on the instantaneous local velocities, Probability Density Functions (PDF) and mean velocities are calculated. Two-phase flow arranged in the slug-flow pattern is observed, at superficial velocities of j w  = 0.154 m/s and j a  = 0.044 m/s. 3000 samples per case are processed using cross-correlation procedure, for the PIV analysis. A home-made Annular Wire-Mesh Sensor (AWMS) was applied to obtain time-signal-measured void-fraction data as a function of the electrical permittivity. The average bubble velocity is estimated by two techniques, (i) High-Speed Video Recording and (ii) Particle Image Velocimetry (PIV) together with the AWMS. A comparison of the two techniques is presented. A new technique based on AWMS for the measurement of bubble-passage frequency, bubble length and slug length is proposed. It was observed: (i) deceleration of the water phase beneath the bubble as it passes, shown by velocity profiles at different bubble locations, (ii) an increase in bubble velocity as air superficial velocity is increased and (iii) the complexity of the flow pattern, shown in details by AWMS cross-sectional images. The new experimental results are of great value for comparison with CFD models and for the development of more refined pressure-drop prediction tools in two-phase annular-duct flows. [ABSTRACT FROM AUTHOR]

Bubbly flows are frequently encountered in many industrial applications where multiphase contact is used to promote heat, mass and momentum transfer. These include applications where both chemical and physical processes occur, such as wastewater treatment and biological aeration systems. We investigated the behaviour of underwater-generated bubble swarms, which were produced at the bottom of a 1-m 3 square tank from a 5-mm nozzle and allowed to rise by buoyancy in still water. Instantaneous velocity fields around the bubbles were obtained using Particle Image Velocimetry (PIV) seeded with 10–15-µm poly-dispersed fluorescent particles and gas flow rates ranging from 2 to 15 L/min (1.7–12.8 m/s). A continuous laser was used to obtain the time-resolved field, and a pulse laser was used to obtain the mean velocity fields. Images were captured at up to 2000 fps. After interrogation, a post-processing validation algorithm was employed to identify and remove vectors produced by bubbles and the interface, essentially producing vector fields of the liquid phase only. Proper orthogonal decomposition analysis was carried out on 1000 realisations of each gas flow case to identify dominant flow structures, and the flow was decomposed into its constituent spatial and temporal modes. We established that induced vortices in the liquid phase more clearly manifest at far streamwise locations shown by the spatial mode at lower gas flow rates and are clearer in the temporal mode at high gas flow rates. The mean streamwise and spanwise liquid velocities increased with the gas flow rate, and the streamwise bubble velocities can be well described by a top-hat profile curve. Finally, an analysis was done to estimate the bubble entrainment coefficient using the slip velocity and the gas buoyancy flux. [ABSTRACT FROM AUTHOR]

Computational Fluid Dynamics (CFD) approach, encoded on STAR-CCM+ was used to simulate air and highly viscous liquid two-phase slug flow in a 50.8-mm (2-in.) ID and 18.9-m (62 ft.) long horizontal pipe. The Volume of Fluid (VOF) method, the Continuum Surface Force (CSF) model and the High Resolution Interface Capturing (HRIC) scheme were utilized. The liquid viscosity varied from 161 to 567 mPa s based on the experimental data. A sensitivity analysis of the sharpening factor, the angle factor, and the Interface Momentum Dissipation (IMD) model was carried out to obtain the best combination of parameters. Besides, comparison with experimental measurements concerning slug frequency, average liquid holdup and velocity profiles in the liquid region was carried out. The comparison shows a fair correspondence in terms of behavior and magnitude with the experimental results obtained by Particle Image Velocimetry (PIV). It was observed that the velocity profile is not fully developed near the bottom of slug body. Finally, extrapolation to the extended velocity conditions was performed. The reduction of translational velocity at higher mixture velocity conditions was investigated. A certain amount of gas passing from the tail to the front of the liquid slug body was visualized by three-dimensional velocity profiles. This phenomenon supports the reduction of translational velocity above the certain level of mixture velocity. [ABSTRACT FROM AUTHOR]

This work explains the motivation, advantages, and novel approach of using velocity magnetic resonance imaging (MRI) for studying the hydrodynamics in a complicated structural biomedical device such as an intravenous catheter needleless connector (NC). MRI was applied as a non-invasive and non-destructive technique to evaluate the fluid dynamics associated with various internal designs of the NC. Spatial velocity maps of fluid flow at specific locations within these medical devices were acquired. Dynamic MRI is demonstrated as an effective method to quantify flow patterns and fluid dynamic dependence on structural features of NCs. These spatial velocity maps could be used as a basis for groundtruthing computational fluid dynamics (CFD) methods that could impact the design of NCs. [ABSTRACT FROM AUTHOR]

In this paper, we investigate avalanches during the fully developed stage of the discharge in a quasi-two-dimensional wedge-shaped hopper. The velocity profiles of the avalanches are measured by employing a high-speed camera. The velocity profiles vary along the flow, but remain invariant in shape and follow a pure parabolic decrease from the surface. The velocity profiles can be expressed by two parameters of surface velocity and flowing layer thickness. These two parameters increase along the flow, and are both functions of the descending height. Therefore, the velocity profile can be predicted with the descending height. Moreover, a shear-thinning viscosity model is deduced to account for the granular flow behaviour. [ABSTRACT FROM AUTHOR]

In this paper, a new method is proposed to measure the air velocity profile around a fence structure with consideration of snow effects. This includes the consideration of snow particle size and its distribution. In this method, a simple wind tunnel powered by a fan was utilized to generate the wind for outdoor test. Considering drifting snow particles might cause damage to the equipment, different materials with different surface roughness height are introduced to simulate the influence of drifting snow particles on boundary layer of velocity profile. According to the test and analysis, the materials with 0.1 –3 cm surface roughness height can adequately characterize the effect of drifting snow particles on boundary layer of velocity profile. The snow depth distribution measured in this study agrees well with the reference value reported in the previous research. The measurement method proposed in this paper can be employed for further snow drifting tests while the wind tunnel is not needed in the experiment. [ABSTRACT FROM AUTHOR]

Echocardiography is the leading imaging modality for cardiac disorders in clinical practice. During an echocardiographic exam, geometry and blood flow are quantified in order to assess cardiac function. In clinical practice, these image-based measurements are currently performed manually. An automated approach is needed if more advanced analysis is desired. In this article, we propose a new hybrid framework for the construction of a disease-specific atlas to improve Doppler aortic outflow velocity profile segmentation. The proposed method is based on combining realistic computational simulations of the cardiovascular system for common cardiac conditions (using CircAdapt) with a validated image-based atlas construction method. The coupling is realized via model-based generation of echocardiographic images of virtual populations with a statistically approved parameter variation. We created virtual populations of 100 healthy individuals and 100 patients with aortic stenosis, synthesized their aortic Doppler velocity images and constructed the corresponding atlases. We validated atlases’ performances by comparing their segmentation of real clinical images with the manually segmented ground truth. The experimental results show that the segmentation accuracy obtained using the proposed atlases is comparable to the accuracy obtained using classical clinical image-based atlases. Moreover, this framework eliminates the time-consuming acquisition of a sufficient number of representative images in clinical practice, offering a substantial time efficiency and flexibility in creating a disease specific atlas and ensuring an observer-independent automated segmentation. The proposed approach can easily be extended towards the creation of atlases for segmenting any Doppler trace in the cardiovascular circulation in a specific disease. [ABSTRACT FROM AUTHOR]

In piping systems, the flow through a bend is typically undeveloped, unsteady, and complicated. In this study, we proposed a novel method to accurately predict downstream flow in bent pipes based on radial basis function neural network (RBFNN) and ultrasound Doppler velocimetry (UDV). An improved UDV method was developed for the measurement of complex flow in bent pipes. The downstream flow characteristics of three different bend configurations were investigated using computational fluid dynamics (CFD). The proposed RBFNN models established the relationships between the velocity profile along the symmetric axis and the velocity distribution over the pipe cross-section. Numerical data were used for model training and validation, whereas the combined datasets with UDV data as inputs and the corresponding CFD data as outputs were used for model modification. The model prediction performance was then evaluated with new UDV inputs by comparing the predicted velocities with the associated CFD results. The results indicated that the velocity profiles obtained using modified UDV agreed well with the present numerical simulation. Finally, the trained model exhibited satisfactory flow reconstruction performance and high flowrate prediction accuracy, with a maximum error of approximately 3%. This work contributes to the application of the UDV method in complex flow measurements and further demonstrates that artificial neural networks (ANNs) are promising for modeling fluid mechanics. • An improved ultrasound Doppler velocimetry (UDV) was developed for bend pipe flow. • Radial basis function neural network (RBFNN) was employed for flow reconstruction. • Three types of in-plane piping configurations were considered. • Flowrate prediction error by the proposed model was less than 3%. [ABSTRACT FROM AUTHOR]

• The investigation of the correction factor consists in the combination of analytical and computational techniques. • The main source of errors for meters consists in the difficulty of taking into account the actual flow velocity profile. • The actual flow velocity was obtained by results of integrating flow profiles models based on inverse Abel's transform. The aim of this work is to combine analytical and computational techniques in investigation of correction factor for ultrasonic flow meters to improve their accuracy. Exploring velocity profiles that do not have axial symmetry we applied reconstruction of two-dimensional velocity field based on the inverse Abel's transform. For velocity profiles that do not have rotational symmetry around the axis of the pipeline, the value of the correction factor will depend on the angle of measuring plane orientation relative to the diametrical plane of the flow meter. The calculation of the actual average flow velocity in the cross section of the meter was obtained from a specific mathematical dependencies describing velocity distribution by integration technique. This study allows us to conclude that even under conditions of distorted non-symmetric flows it is possible to determine the performance of ultrasonic flowmeters with sufficient accuracy using both methods of theoretical research and computational hydrodynamics. [ABSTRACT FROM AUTHOR]

• We analyzed three regimes of boundary layers: sub-, trans-, and supercritical. • Theoretical profiles are computed by self-similar solution. • Two-phase transcritical boundary layers have the sub-layer. • There is no transcritical boundary layer at small Mach number. • Wall temperature may be greater than inflow total temperature. Boundary layers can be defined as sub-, trans-, and supercritical regime according to whether their temperature profiles cross the Widom line. The transcritical boundary layers which contain liquid and supercritical phases are hard to solve. In this paper, adiabatic flat plate laminar boundary layers of supercritical carbon dioxide (SCO 2) are preliminarily explored by the self-similar solution. We analyze the difference of boundary layer profiles at 8 MPa - inflow pressure by varying inflow temperature T e and Mach number M a. The influence of T e and M a on the velocity profiles exhibits complex diversity at three boundary layer regimes. Compared with subcritical and supercritical boundary layers, transcritical boundary layers with smaller skin friction coefficients are the most special, and they include the "sub-layer". Notably, there is no transcritical boundary layer when T e increases to pseudo-critical temperature T p c at small M a. The wall temperature T w of transcritical boundary layers may be greater than inflow total temperature T 0 at larger M a. [Display omitted] [ABSTRACT FROM AUTHOR]

Realistic oceanographic conditions are essential to consider in the design of resilient tidal-stream energy devices that can make meaningful contributions to global emissions targets. Depth-averaged or simplified velocity profiles are often used in studies of device performance, or device interaction with the environment. We improve representation of flow at tidal-stream energy regions by characterising the velocity profile. At two potential tidal-stream energy sites, the 1/7th power-law with a bed-roughness coefficient of 0.4 accurately described the observed velocity profile on average (>1 month ADCP deployments). Temporal variability in the power-law fit was found at both sites, and best characterised with Generalised Extreme Value distribution; with correlation of variability to tidal condition, wind speed and wave conditions found. The mean velocity profile was accurately simulated using a 3D hydrodynamic model (ROMS) of the Irish Sea (UK) but with temporal variability in accuracy of power-law fits. For all potential tidal sites, the spatial-mean velocity profile was also found to be similar (characterised with ∼1/7th power-law and 0.4 bed-roughness value). Therefore realistic flow conditions can be characterised for tidal-energy research, but dynamically coupled wind-wave-tide models, or long-term observations, are needed to fully characterise velocity profile temporal variability. [ABSTRACT FROM AUTHOR]

An approximate analytical solution for forced convection of power-law fluids in the entrance region of parallel-plates ducts with the uniform heat flux boundary condition (H condition) is presented and analyzed. It is based on the assumption of similarity between the profiles of the velocity and the temperature in the respective boundary layers and in the fully developed region where exact analytical profiles are obtained from the differential conservation equations. The axial evolutions of the hydrodynamic and thermal boundary layers, of the pressure loss, of the skin friction coefficient and of the Nusselt number are also obtained by applying the integral form of the conservation equations in the entrance region. For a flow behavior index equal to unity (Newtonian fluid) the predicted values of these parameters are in good agreement with corresponding data from the literature. [ABSTRACT FROM AUTHOR]

The present study explores the effect of upstream disturbances like a single 90°bend, double 90° bends (in plane and out of plane) on the performance of wafer cone flowmeters with same beta ratio ( β ) of 0.77 but different half cone angles ( α ) of 30° and 45°. The influence of these disturbances on the upstream and downstream axial velocity ( u ) profiles are studied experimentally. The orientation effects, if any, are also studied experimentally. The minimum upstream distances required to get a fully developed flow for these disturbances vary with type of upstream disturbance, beta ratio ( β ) and half cone angle ( α ) of the wafer cone flowmeter. The study is carried out for a single phase flow with air as working medium at high Reynolds number ( Re D = 144000). From the results obtained from this study, it may be concluded that the wafer cone flowmeter with a beta ratio ( β ) of 0.77 and a cone angle of 30° requires less upstream distance compared to the wafer cone flowmeter with a beta ratio ( β ) of 0.77 with a cone angle of 45° for all the disturbances under consideration. [ABSTRACT FROM AUTHOR]

This short communication considers a video-based approach to quantify near bed and sheet flow swash zone sediment particle velocities over a mobile bed in a laboratory setting and relate the profile shape to sheet thickness and a velocity that can be measured outside the sheet layer (by for instance a current meter) Near bed high speed imagery was recorded during a dam-break driven swash event in a flume with optically clear walls. Repeated swash events for two different median sediment sizes were tested. Optical Current Meter (OCM) analysis was applied to bed parallel image time stacks extracted at elevations from below the at rest bed to within the lower water column. OCM results were compared to in situ velocity measurements, where possible, obtained with an acoustic Doppler profiling velocimeter (ADPV). OCM results compared well with ADPV measurements for moderate suspended sediment concentrations (based on visual observation; sediment concentrations were not measured). Too high of a sediment concentration over saturated the image and did not provide distinct sediment particle trajectories in a consistent direction for OCM analysis. This saturation occurred during uprush for both sediment sizes. Too little of a sediment concentration provided an inadequate number of sediment particle trajectories to track, such as during flow reversal for the coarser sediment. For coarser sediment, backwash velocities were well resolved in OCM analysis with velocities comparing well (correlation coefficient > 0.8) to ADPV estimates. The dimensionless backwash sheet flow sediment particle velocity profile (normalized by the velocity at the top of the sheet) scaled with the dimensionless elevation (normalized by the sheet layer thickness) to the 0.62 power with 95% confidence intervals for the exponent ranging from 0.47 to 0.76. [ABSTRACT FROM AUTHOR]

The effect of the stator geometry, cavity gap and fluid volume on the turbulent aggregation, hydrodynamics and flow pattern in rotor-stator vortex reactors have been investigated using a digital 2D Particle Image Velocimetry (PIV) and visual observation. The results of the study showed a more uniform distribution of the quantified flow parameters—velocity profile and vorticity map in the continuous reactor when compared to the batch reactor. In addition, a high velocity recirculating jet which creates a diverging flow as the jet hits the reactor wall was observed in the batch reactor creating two distinct vortex structures (core and marginal vortex). Frictional losses across the cavity account for much of the difference between the theoretically computed and measured values of the hydrodynamic parameters. The stream pattern obtained from the PIV analysis unexpectedly shows a fairly good correlation with the flow pattern created from the digital video recordings of the pellet motion during the wet agglomeration experiments. [ABSTRACT FROM AUTHOR]

A method of tidal stream energy resource assessment around the Ushant Island in the Iroise Sea, using surface velocity time series from High Frequency radars (HFR) and ADCP measurements, is presented. Remotely sensed velocities provided by the radars allow to augment the industry standard approach of 3D numerical modeling and in-situ ADCP surveying to make a large-scale quantification of tidal stream resource. They capture the real ocean dynamics and thus provide context on the complex spatial variability of tidal currents that are so often feature at potential tidal energy sites. The observations show current velocities of 4 m/s northwest of the Island and in the Fromveur Strait, with 1 m/s value exceeded 60% and 70% of time respectively. Emphasis is given to the peculiarities in tidal flow asymmetry and to the study of the variation of vertical velocity profiles during different tidal stages. Radar derived velocities reveal a pronounced asymmetry between the flood and ebb flow around the Ushant Island, quantified by dimensionless number a - velocity asymmetry. The largest range of asymmetry variation, from 0.5 to 2.5, is observed in the Fromveur Strait. Harmonic analysis demonstrated that a joint variation of phase of the principal semi-diurnal (M 2 ) and quarter-diurnal (M 4 ) tidal velocity component accounts for flow asymmetry variation in the strait. Asymmetry in current direction is also quantified. ADCP measurements show that the vertical velocity profiles follow a 1/α power law with a power law exponent mostly depending on geographic location than on tidal stage. It was demonstrated that, in the Fromveur Strait, the 1/7 power law is appropriate to characterize the velocity profile. The combination of two sources of data enables characterization of the velocity variations in three spatial dimensions and in time thus increasing accuracy of the hydrokinetic resource assessment from HF radar observations. The estimation shows that the mean technical resource is 50% smaller in the lower half than in the upper half of the water column. The theoretical resource on average is three times higher than the technical resource and appears to be more sensitive to variations in the shape of the velocity profile in the lower layer. [ABSTRACT FROM AUTHOR]

Sluice gates have been widely used and intensively studied, however their submerged flow conditions still call for in depth attention. A large scale experimental setup equipped with Acoustic Doppler Velocimetry, ADV, and electromagnetic flow-meter was used to thoroughly investigate various aspects of the hydraulics of submerged sluice gate. In this study, new experimental data sets are provided, that help better understand and quantify the flow features for submerged sluice gates. According to the experimental data generic fitting are provided for the velocity profiles from which the velocity correction factors can be obtained. Then, the experimentally obtained submerged head loss coefficient is presented and discussed. The results of this study showed that current classical Energy-Momentum methods (EM) failed to accurately determine the flow rate for the cases of highly submergences, while employing the interaction of the energy correction factors and head loss values in the EM model would result in more accurate head-discharge estimation. The new data set provided in this work can be used effectively for the validation of numerical modeling of submerged sluice gates. [ABSTRACT FROM AUTHOR]

Qualification and quantification of mixing processes are crucial requirements for process engineering and energetic optimization in chemical and pharmaceutical industry as well as in wastewater treatment and biogas production. The analysis of mixing processes in stirred systems becomes a challenging task, especially when using opaque substrates. With Electrical Resistance Tomography (ERT), a powerful measuring technique is provided to allow a comprehensive and non-intrusive quantification of mixing processes of complex suspensions. Combined with advanced cross-correlation techniques, ERT offers the possibility to derive the axial flow velocity profile inside a stirred system. Investigations in different scales are an essential prerequisite regarding the evaluation and optimization of large-scale mixing processes under consideration of similarity laws. The experimental tests presented in this paper are carried out in reactor systems with volumes of 0.1 m 3 and 1 m 3 . The validity of scale-up methodologies was ensured by comparable flow conditions and velocity distributions between the lab and pilot plant scale. For biogas plants, as an example of the importance of efficient mixing, the scale-up principles ‘geometric similarity’, ‘constant impeller tip speed’, ‘similar viscosity and flow characteristics’ as well as ‘scale-up of particles and fibers of the dispersed phase’ are proved to be valid by the Fraunhofer Institute for Ceramic Technologies and Systems (IKTS). Within the scope of further investigations, reliable information related with Computational Fluid Dynamics (CFD) are ought to be derived for the continuing evaluation of mixing processes at any scale to establish a foundation for the dimensioning and operation of stirring systems, especially for highly concentrated, non-Newtonian fluids. [ABSTRACT FROM AUTHOR]

• Lateral distribution of velocity may have two dramatically increasing segments. • Lateral distribution of the Reynolds stress shows a bimodal characteristic. • Large-scale quasi-2-D coherent structures exist in the shear layer and mixing layer. • Ejections and sweeps events are dominant in the shear layer and mixing layer. Aquatic plants can alter flow structure, affect sediment transport and contaminants diffusion, and is noteworthy for channel restoration and navigation. In the present work, experiments are conducted to investigate the velocity and turbulence structures in a compound channel with varying coverage of riparian vegetation. Lateral profile of velocity may change from a traditional single sharply increasing segment to two sharply increasing segments, the shear layer (SL) and the mixing layer (ML), which are influenced by bed morphology and vegetation. Lateral profile of Reynolds stress is bimodal, with a crest value that decreases with increasing ratio of the width of nonvegetated floodplain to the bankfull height (B NV / h). Quasi-two-dimensional (Quasi-2-D) coherent structures can be found in both SL and ML when B NV / h is small according to power spectral density and temporal autocorrelation function, which have a significant influence on Reynolds stress. Brief and intense ejections and sweeps events dominate the contribution to Reynolds stress, and according to quadrant analysis, an ejections event of the SL may occur simultaneously with each event of the ML. [ABSTRACT FROM AUTHOR]

• New analytical velocity model is proposed for vegetation with spherical canopy. • New power series, exponential and trigonometric methods are used in flow model. • New formula of penetration length scale is proposed. Vegetation exists widely in natural rivers, resulting in unique characteristics of flow movement, affecting river flood processes and water quality. The flow movement of vegetated channels is defined as vegetated flow, and is currently receiving close attention. Influenced by vegetation, the classical logarithmic velocity profile turn into a more complex function according to the vegetation morphology and flow pattern. Several research teams have studied analytical models for simple cylinder-type vegetation; however, few studies have been conducted on analytical velocity models for vegetation with spherical canopy, and previous models cannot make accurate prediction of velocity profile in this case. To address this issue, new analytical models are proposed adopting the power series, exponential and trigonometric models. A comparison between the measured velocity profile and the analytical solution confirms that the newly proposed models are suitable for vegetation with spherical canopy. This analytical model can capture the vertical non-monotonic characteristics of velocity profile, which is what the previous models lack. Moreover, in contrast to numerical models, which require a lot of computational cost, this analytical model allows a quick and intuitive description of the flow profile, which provides hydrodynamic support for the restoration of vegetated channels. [ABSTRACT FROM AUTHOR]

CO 2 fracturing is a critical technique for carbon capture, utilization, and storage (CCUS). It has a crucial role in oil-gas development and combating climate change. However, the high flow friction severely affects the fracturing construction. The micro-mechanism of CO 2 vertical flow friction in fracturing pipe string is unclear, and it is difficult to experimentally simulate the fracturing conditions. Computational Fluid Dynamics model is used to investigate the micro-mechanism of CO 2 flow friction in fracturing conditions to reduce friction. A turbulence model was optimized to accurately calculate the friction of CO 2 pipe flow. Subsequently, the relationships between the velocity profile, friction factor, and thickness of viscous sublayer of pure CO 2 and thickened CO 2 were analysed in fracturing pipe string, wherein the temperature and pressure were in the range of 253.15–343.15 K and 10–60 MPa, respectively. In this paper, the micro-mechanism of CO 2 flow friction in fracturing pipe string was revealed and the situation of thickened CO 2 was additionally considered, since the effect of the thickener has generally been ignored in previous numerical investigations. The results demonstrated that a uniform velocity profile reduced the friction factor. The temperature and pressure changed the relationship between the thickness of viscous sublayer and roughness, which caused the variation in the friction factor of pure CO 2 and thickened CO 2. The effect of roughness height on flow was different in the viscous sublayer and turbulent core region. A method was proposed to reduce the friction by optimizing the CO 2 thickener and changing flow temperature and pressure. • CFD model used because experiment is hard to reflect fracturing conditions. • The micro-mechanism of pure and thickened CO 2 flow friction is investigated. • A uniform velocity profiles produce a small friction factors. • The effect of roughness is different in the viscous sublayer and turbulent core area. • Optimizing thickener and varying temperature and pressure can reduce friction. [ABSTRACT FROM AUTHOR]

In this paper, a theoretical open channel flow resistance equation was verified using flow depth and discharge measurements carried out by Freeman et al. in a large channel, 2.44 m wide, for ten different types of uniform-sized plants (shrubs and woody vegetation). The plants, which are broadleaf deciduous vegetation commonly found in floodplains and riparian zones, were placed in staggered rows inside the channel whose bed was constructed to accept plants with their root systems. For each species, the available measurements were carried out by Freeman et al. with plants having different values of plant density, height, and bending stiffness. The available literature database (87 measurements) was divided into two groups which were separately used to calibrate and test the theoretical approach. In particular, 46 measurements were used to calibrate the relationship between the scale factor Γ of the velocity profile, the Froude number, and the channel slope. This relationship was calibrated using the entire available dataset or varying the scaling coefficient a with the investigated vegetation type. The measured values of the Darcy-Weisbach friction factor, obtained by the measured flow velocity, water depth and slope values, were compared with those calculated by the theoretical flow resistance law, coupled with the relationship for estimating the Γ function having a scaling coefficient different for each investigated vegetation type. This comparison allowed to demonstrate that an accurate estimate of the Darcy-Weisbach friction factor (errors less than or equal to ±10% for 87% of the investigated cases) can be obtained. However, for the investigated vegetation species, that are characterized by a large range of bending stiffness, also a mean value of the scaling coefficient a equal to 0.3283 allows an accurate estimate of the Darcy-Weisbach friction factor. • A theoretical flow resistance law was tested for shrub and woody vegetation. • Effects of different species on flow resistance was verified. • The calibrated flow resistance law allowed an accurate estimate of friction factor. • Effect of vegetation type is represented by the values of a single coefficient. [ABSTRACT FROM AUTHOR]