Assessment of dam impacts on river flow regimes and water quality:a case study of the Huai River Basin in P.R.China

The Huai River Basin is a unique area in P.R.China with the highest densities of population and water projects.It is also subject to the most serious water pollution.We proposed a distributional SWAT(Soil and Water Assessment Tool) model coupled with a water quality-quantity balance model to evaluate dam impacts on river flow regimes and water quality in the middle and upper reaches of the Huai River Basin.We calibrated and validated the SWAT model with data from 29 selected cross-sections in four typical years(1971,1981,1991 and 1999) and used scenario analysis to compensate for the unavailability of historical data regarding uninterrupted river flows before dam and floodgate construction,a problem of prediction for ungauged basins.The results indicate that dam and floodgate operations tended to reduce runoff,decrease peak value and shift peaking time.The contribution of water projects to river water quality deterioration in the concerned river system was between 0 to 40%,while pollutant discharge contributed to 60% to 100% of the water pollution.Pollution control should therefore be the key to the water quality rehabilitation in the Huai River Basin.

Two-Phase Flow Regimes and Discharge Characteristics of a Plasma Electrohydrodynamic Atomization

Experimental investigation was conducted to study the flow regimes and discharge characteristics of plasma electrohydrodynamic atomization （EHDA） for decane （CloH22） under pulsed applied negative voltage. The experimental parameters were set as the flow rate of decane from 0 mL/min to 10 mL/min and the DC charging voltage from DC 0 V to 12 V with a pulse repetition rates of 200 Hz. The flow regime of decane was observed and the volume-to-electrical charge ratio was measured. Unlike a conventional EHDA system, the results show that a corona discharge was initiated at the edge of the hollow electrode at a specific corona on-set voltage of -17 kV or -20 kV in the case with or without decane flow, respectively. This phenomenon was defined as plasma EHDA.

The properties of dilute debris flow and hyper-concentrated flow in different flow regimes in open channels

Particle Image Velocimetry(PIV) technique was used to test the analogues of hyperconcentrated flow and dilute debris flow in an open flume. Flow fields, velocity profiles and turbulent parameters were obtained under different conditions. Results show that the flow regime depends on coarse grain concentration. Slurry with high fine grain concentration but lacking of coarse grains behaves as a laminar flow. Dilute debris flows containing coarse grains are generally turbulent flows. Streamlines are parallel and velocity values are large in laminar flows. However, in turbulent flows the velocity diminishes in line with the intense mixing of liquid and eddies occurring. The velocity profiles of laminar flow accord with the parabolic distribution law. When the flow is in a transitional regime, velocity profiles deviate slightly from the parabolic law. Turbulent flow has an approximately uniform distribution of velocity and turbulent kinetic energy. The ratio of turbulent kinetic energy to the kinetic energy of time-averaged flow is the internal cause determining the flow regime: laminar flow(k/K<0.1); transitional flow(0.1< k/K<1); and turbulent flow(k/K>1). Turbulent kinetic energy firstly increases with increasing coarse grain concentration and then decreases owing to the suppression of turbulence by the high concentration of coarse grains. This variation is also influenced by coarse grain size and channel slope. The results contribute to the modeling of debris flow and hyperconcentrated flow.

Investigation on gas–solid flow regimes in a novel multistage fluidized bed

Gas–solid flow regime in a novel multistage circulating fluidized bed is investigated in this study.Pressure fluctuations are first sampled from gas–solid flow systems and then are analyzed through frequency and time–frequency domain methods including power spectrum and Hilbert–Huang transform.According to the flow characteristics obtained from pressure fluctuations,it is found that the gas–solid motions in the multistage circulating fluidized bed exhibit two dominant motion peaks in low and high frequencies.Moreover,gas-cluster motions become intensive for the multistage circulating fluidized bed in comparison with the fast bed.Unlike the traditional methods,the fuzzy C-means clustering method is introduced to objectively identify flow regime in the multistage circulating fluidized bed on the basis of the flow characteristics extracted from bubbling,turbulent,fast,and multistage fluidized beds.The identification accuracy of fuzzy C-means clustering method is first verified.The identification results show that the flow regime in the multistage circulating fluidized bed is in the scope of fast flow regime under examined conditions.Moreover,the results indicate that the consistency of flow regime between two enlarged sections exists.In addition,the transition onset of fast flow regime in the multistage circulating fluidized bed is higher than that in the fast bed.

Comparative CFD-DEM study of flow regimes in spout-fluid beds

Spout-fluid beds are unique systems that require thorough study prior to their industrial application.In this study,the hydrodynamics of spout-fluid beds were investigated using 3D computational fluid dy-namics coupled with discrete element method(CFD-DEM).Three flow regimes,including jet-in-fluidized bed,spouting-with-aeration,and intermediate/spout-fluidization were studied,and the particle mixing was quantified in these regimes using the Lacey mixing index.The results showed that both axial and lateral mixing rates are better in jet-in-fluidized bed and the spouting-with-aeration flow regimes,with the axial mixing being superior to the lateral in all flow regimes.Examining the diffusivity coefficient revealed that mixing in the jet-in-fluidized bed flow regime is better due to the formation and eruption of bubbles in the annulus.Additionally,the granular temperature was analyzed in all flow regimes,and higher particle velocity fluctuations were observed in the spouting-with-aeration and the jet-in-fluidized bed flow regimes due to the higher spout gas velocity and formation of bubbles in the annulus.This study provides valuable insights into the hydrodynamics of spout-fluid beds in different flow regimes,which can aid in the design and optimization of spout-fluid bed reactors for various industrial applications.

Adaptive partitioning-based discrete unified gas kinetic scheme for flows in all flow regimes

To improve the efficiency of the discrete unified gas kinetic scheme(DUGKS)in capturing cross-scale flow physics,an adaptive partitioning-based discrete unified gas kinetic scheme(ADUGKS)is developed in this work.The ADUGKS is designed from the discrete characteristic solution to the Boltzmann-BGK equation,which contains the initial distribution function and the local equilibrium state.The initial distribution function contributes to the calculation of free streaming fluxes and the local equilibrium state contributes to the calculation of equilibrium fluxes.When the contribution of the initial distribution function is negative,the local flow field can be regarded as the continuous flow and the Navier-Stokes(N-S)equations can be used to obtain the solution directly.Otherwise,the discrete distribution functions should be updated by the Boltzmann equation to capture the rarefaction effect.Given this,in the ADUGKS,the computational domain is divided into the DUGKS cell and the N-S cell based on the contribu-tion of the initial distribution function to the calculation of free streaming fluxes.In the N-S cell,the local flow field is evolved by solving the N-S equations,while in the DUGKS cell,both the discrete velocity Boltzmann equation and the correspond-ing macroscopic governing equations are solved by a modified DUGKS.Since more and more cells turn into the N-S cell with the decrease of the Knudsen number,a significant acceleration can be achieved for the ADUGKS in the continuum flow regime as compared with the DUGKS.

Extending homogeneous fluidization flow regime of Geldart-A particles by exerting axial uniform and steady magnetic field

The homogeneous/particulate fluidization flow regime is particularly suitable for handling the various gas–solid contact processes encountered in the chemical and energy industry.This work aimed to extend such a regime of Geldart-A particles by exerting the axial uniform and steady magnetic field.Under the action of the magnetic field,the overall homogeneous fluidization regime of Geldart-A magnetizable particles became composed of two parts:inherent homogeneous fluidization and newly-created magnetic stabilization.Since the former remained almost unchanged whereas the latter became broader as the magnetic field intensity increased,the overall homogeneous fluidization regime could be extended remarkably.As for Geldart-A nonmagnetizable particles,certain amount of magnetizable particles had to be premixed to transmit the magnetic stabilization.Among others,the mere addition of magnetizable particles could broaden the homogeneous fluidization regime.The added content of magnetizable particles had an optimal value with smaller/lighter ones working better.The added magnetizable particles might raise the ratio between the interparticle force and the particle gravity.After the magnetic field was exerted,the homogeneous fluidization regime was further expanded due to the formation of magnetic stabilization flow regime.The more the added magnetizable particles,the better the magnetic performance and the broader the overall homogeneous fluidization regime.Smaller/lighter magnetizable particles were preferred to maximize the magnetic performance and extend the overall homogeneous fluidization regime.This phenomenon could be ascribed to that the added magnetizable particles themselves became more Geldart-A than-B type as their density or size decreased.

Impacts of hydropower-induced flow alterations on composition and diversity of riparian vegetation in the Western Himalayas: A case study in Uttarakhand, India

The increasing demand for water and energy resources has led to widespread dam construction,particularly in ecologically sensitive regions like the Himalayan Range.This study focuses on the Uttarakhand state in the Western Himalayas,where hydroelectric projects(HEPs)have significantly altered river flow regimes.The research investigates the impact of flow alterations on the composition and structure of riparian vegetation in the Garhwal Himalayas,specifically analysing four rivers regulated by hydroelectric projects.Utilizing the paired-reach comparison method,control(undisturbed),diverted(downstream of barrage/dam),and altered flow conditions(downstream of water outlet)were examined.The research reveals diverse and unique riparian ecosystems,with 89 genera and 113 taxa identified,showcasing the dominance of families like Asteraceae and Lamiaceae.The study unveils the structural importance of key species such as Berberis asiatica and Artemisia nilagirica.The density,diversity,and richness of shrub and herb species vary significantly across flow conditions.Notably,altered flow conditions demonstrate resilience in vegetation structure,while diverted conditions exhibit decreased species richness and density.The study emphasizes the importance of nuanced environmental flow management for mitigating adverse effects on riparian biodiversity in the fragile Himalayan region.These findings contribute to the global discourse on dam impacts and riparian ecology,shedding light on the complexities of this dynamic relationship in a vulnerable ecosystem.

FLOW REGIMES BELOW AERATORS FOR DISCHARGE TUNNELS

The flow regimes below an aerator influence directly the air entrainment and the cavitation damage control. Based on the theoretical considerations, the experiments of the aerator for a discharge tunnel were conducted, and the relationships between the flow regime and hydraulic and geometric parameters were investigated. The results showed that, there are two kinds of threshold values for the flow regime conversions. One is Fr1-2 standing for the conversion from the fully filled cavity to the partially filled cavity, and the other is Fr2-3 which shows the change from the partially filled cavity to the net air cavity. Two empirical expressions were obtained for the conversions of the flow regimes, which can be used in the designs of the aerators.

IDENTIFICATION OF GAS LIQUID FLOW REGIMES IN A HORIZONTAL FLOW USING NEURAL NETWORK

The knowledge of flow regimes is very important in the study of a two phase flow system. A new flow regime identification method based on a Probability Density Function (PDF) and a neural network is proposed in this paper. The instantaneous differential pressure signals of a horizontal flow were acquired with a differential pressure sensor. The characters of differential pressure signals for different flow regimes are analyzed with the PDF. Then, four characteristic parameters of the PDF curves are defined, the peak number (K 1 ), the maximum peak value (K 2 ), the peak position (K 3 ) and the PDF variance (K 4 ). The characteristic vectors which consist of the four characteristic parameters as the input vectors train the neural network to classify the flow regimes. Experimental results show that this novel method for identifying air water two phase flow regimes has the advantages with a high accuracy and a fast response. The results clearly demonstrate that this new method could provide an accurate identification of flow regimes.

PREDICTION OF FLOW REGIMES IN SPOUT-FLUIDIZED BEDS

Five main flow regimes in spout-fluidized bed were identified in this study, namely, fixed bed, spout with aeration, spout-fluidization, jet in fluidized bed and slugging, together with their corresponding major frequencies translated from pressure signals. The empirical equation A=aB^b, in which A=Fr^＊I（HIDi） and B=（Fr^＊I（HIDi））/（Ugt/Umf） are respectively the spout-geometry and spout-geometry-fluidization dimensionless numbers, was proposed to distinguish these flow regimes.

Identification of flow regimes and determination of the boundaries for magnetized fluidized bed with Geldart-B particles

The magnetized fluidized bed(MFB)with Geldart-B particles exhibits many distinct flow regimes depend-ing on the magnetic field intensity(H)and gas velocity(U_(g)).The identification of these regimes was reviewed for the MFB with magnetizable particles and that with binary admixture of magnetizable and nonmagnetizable particles.Meanwhile,methods for determining the boundaries between two adjacent flow regimes were clarified.The MFB state was found to depend not only on H and Ug but also on their application sequence(i.e.,operation mode)within certain operating zones.The dependence feature arose from that the MFB therein could have different equilibrium states for the same combination of H and Ug.Furthermore,such a polymorphic characteristic of the MFB was revealed to result from the internal friction among the particles that were in unfluidized/packed state.Many of the MFB states were demon-strated to be in metastable equilibrium.Nevertheless,they differed significantly from the metastates well-known in the discipline of physical chemistry,such as supercooling and superheated.In fact,they belonged to the amorphous/glass state.This review will deepen our hydrodynamic understanding of the MFB and further promote its commercial application in the chemical and biochemical industries.

Nonlinear characteristics analyses of particle motion for predicting flow regimes

Gas-solid flow regimes have a significant impact on particle transport and separation in a fluidized bed reactor.In this study,to determine flow regime transitions in gas-solid fluidized beds,an acoustic technique was used to detect and analyze the behavior of gas and solids.Algorithm complexity,fluctuation complexity,and Shannon entropy analyses of acoustic emission signals were performed to examine non linear system characteristics,and to determine the flow regime transiti on velocities uc,uk,and ufd-Moreover,using the standard deviation of pressure signals,pressure measurements and acoustic measurements were compared.The relative deviations(RDs)between the experimental and empirical values of uk were 8.8%,13.7%,8.8%,and 30.4%for the algorithm complexity,fluctuation complexity,Shannon entropy,and pressure signal standard deviation,respectively,while the respective RDs for Ufd were 15.7%,23.9%,15.7%,and 97.8%.The RDs between the experimental and empirical values of uc were all 6.4%.The experimental values obtained from acoustic signal measurements were therefore closer to the empirical values.In summary,the integration of non-intrusive acoustic measurements,complexity analysis,and Shannon entropy analysis is suitable for identifying flow regime transitions.

Determination of groundwater flow regimes based on the spatial non-local distribution of hydraulic gradient:Model and validation

The groundwater flow in natural aquifers can change from the Darcy flow to the non-Darcian flow due to a variety of causes,such as the increase of the Reynolds number in the highly permeable media or the decrease of the hydraulic gradient below a threshold in the low-permeability media,while the representative flow regime cannot be reliably determined using the traditional criteria.To address this challenge,this paper proposes a new term called the equivalent hydraulic gradient(EHG)by generalizing the differential form of the Darcy’s law using a spatial integral of the upstream hydraulic head.The nonlocal spatial variation of the hydraulic head difference between upstream and downstream zones is assumed to be the potential cause of the transition of the groundwater flow regimes.This assumption is analogous to the common assumption used for quantifying the anomalous pollutant transport in the geological media.Applications of this idea show that the EHG concept could distinguish three main flow regimes,namely the Super-Darcy flow,the Darcy flow,and the Sub-Darcy flow,although the Super-Darcy flow regime is rarely observed in the laboratory column flow experiments.Results of this study therefore shed lights on the interpretation of the fundamental dynamics of the groundwater moving in various heterogeneous aquifers,and may lead to the rebuilding of the hydrodynamics of the surface water,the groundwater,and the soil.

Flow regimes of the immiscible liquids within a rectangular microchannel

Flow regimes of two immiscible liquids at the cross junction within a rectangular microchannel are experimentally investigated.Characteristics of the flow regimes including critical conditions and interfacial deformations are presented.It is found that the occurrence of the tubing regime is favored by increased viscosity of the dispersed phase or reduced cross-sectional aspect ratio,leading to the shrinkage of the flow rate range that could produce droplets.In order to reveal the physical mechanism,the force analysis is carried out based on the tunnel structure formed between the interface and channel side walls within the rectangular cross-section.The reshaping stage and pinch-off stage are mainly driven by the interfacial tension,leading to far larger neck thinning rate compared to the superficial velocity of either phase.The filling stage and squeezing stage are dominated by the pressure drop across the dispersed tip while the role of the shear force becomes more important with increasing tunnel width.The filling period is estimated as t2≈kHwn02/Qd with k=1.34 and the squeezing period is expressed as t3/Tc=0.3Cac−1.According to the force analysis,the critical tip velocity under dripping scales with three key parameters,which can be expressed as(utip/U)*~QcLtip/wtunnel3.

Classification of flow regimes in gas-liquid horizontal Couette-Taylor flow using dimensionless criteria

In this paper, the flow patterns observed in horizontal Couette-Taylor flow（CTF） were correlated using dimensionless numbers. The analysis of the results showed that the structure of the flow was an outcome of interaction between fluid inertia related to axial and rotational flows and gravitation. Therefore, the flow structures were correlated using axial and angular Reynolds numbers, and Archimedes number for the given value of gas-to-liquid flow ratio. Finally, the correlation for the prediction of the transition to the flow regime observed at high rotational speeds was proposed. The comparison with experiments carried out in the vertical CTF from the literature showed that this correlation can also be useful in the case of vertical flow.

THE GLOBAL EXISTENCE AND UNIQUENESS OF SMOOTH SOLUTIONS TO A FLUID-PARTICLE INTERACTION MODEL IN THE FLOWING REGIME

This paper is concerned with the Cauchy problem for a 3D fluid-particle interaction model in the so-called flowing regime inℝ3.Under the smallness assumption on both the external potential and the initial perturbation of the stationary solution in some Sobolev spaces,the existence and uniqueness of global smooth solutions in H3 of the system are established by using the careful energy method.

Experimental and numerical study on improvement performance by wave parallel flow field in a proton exchange membrane fuel cell

The performance and operation stability of proton exchange membrane fuel cells(PEMFCs)are closely related to the transportation of reactants and water management in the membrane electrode assembly(MEA)and flow field.In this paper,a new three-dimensional wave parallel flow field(WPFF)in cathode was designed and analyzed throughout simulation studies and an experimental method.The experimental results show that the performance of PEMFC with WPFF outperforms that of PEMFC with straight parallel flow field(SPFF).Specifically,the peak power density increased by 13.45%for the PEMFC with WPFF as opposed to PEMFC with SPFF.In addition,the flow field with area of 11.56 cm^(2) was formed by the assembly of transparent end plate used for cathode and the traditional graphite plate used for anode.To understand the mechanism of the novel flow field improving the performance of PEMFC,a model of PEMFC was proposed based on the geometry,operating conditions and MEA parameters.The thickness of gas diffusion layers(GDL),catalytic layers(CL)and proton exchange membrane were measured by scanning electron microscope.The simulation result shows that compared with SPFF,the WPFF based PEMFC promote the oxygen transfer from flow channel to the surface of CL through GDL,and it was beneficial to remove the liquid water in the flow channel and the MEA.

Design and Characterization of a Horizontal Double Impinging Jet Cell: Determination of Flow Modes at the Surface of a Flat Electrode

An electrochemical cell consisting of a double horizontal Impinging Jet Cell (IJC) has been conceived and characterized. The purpose of this system is the simultaneous electrodeposition of a composite metal/particle coating on both surfaces of a metal sheet. The silica particles imprint in the nickel matrix has allowed to distinguish four different flow areas onto the electrode namely the stagnation area, the radial flow area characterized by a higher flow speed, the return flow area that involves gravity effect, and the drainage area with a constant draining speed. Based on the limiting current evolution as a function of the Reynolds number, three flow modes were extracted: the Laminar Low Flow (LLF), the Laminar High Flow (LHF) and the Disturbance. The IJC investigated ensures a laminar flow for a large range of flow rate from a nozzle-to-sample distance of 19 mm and creates an laminar flow ovoid plan merged with the sample for the high flows.

Limitations of Lattice Boltzmann Modeling of Micro-Flows in Complex Nanopores

The multiscale transport mechanism of methane in unconventional reservoirs is dominated by slip and transition flows resulting from the ultra-low permeability of micro/nano-scale pores,which requires consideration of the microscale and rarefaction effects.Traditional continuum-based computational fluid dynamics(CFD)becomes problematic when modeling micro-gaseous flow in these multiscale pore networks because of its disadvantages in the treatment of cases with a complicated boundary.As an alternative,the lattice Boltzmann method(LBM),a special discrete form of the Boltzmann equation,has been widely applied to model the multi-scale and multi-mechanism flows in unconventional reservoirs,considering its mesoscopic nature and advantages in simulating gas flows in complex porous media.Consequently,numerous LBM models and slip boundary schemes have been proposed and reported in the literature.This study investigates the predominately reported LBM models and kinetic boundary schemes.The results of these LBM models systematically compare to existing experimental results,analytical solutions of Navier-Stokes,solutions of the Boltzmann equation,direct simulation of Monte Carlo(DSMC)and information-preservation DSMC(IP_DSMC)results,as well as the numerical results of the linearized Boltzmann equation by the discrete velocity method(DVM).The results point out the challenges and limitations of existing multiple-relaxation-times LBM models in predicting micro-gaseous flow in unconventional reservoirs.