Pressure Gradient Force Research Articles

Zonal Temperature Gradients in the Tropical Free Troposphere

Abstract The horizontal temperature gradients in the tropical free troposphere are generally assumed to be weak. We show with ERA5 data that substantial zonal virtual temperature (Tυ) gradients persist climatologically in the tropical free troposphere and investigate their causes. The gradients change seasonally: Tυ at 500 hPa over the equatorial western Pacific Ocean (EWP) is usually much warmer (up to 3 K) than that over the equatorial central Pacific Ocean (ECP) during December–February (DJF), while the temperature differences between EWP and ECP are much smaller during June–August (JJA). During DJF, Tυ gradients over the Pacific prevail throughout the entire free troposphere, especially in the upper troposphere near 300 hPa. We find that the associated hydrostatic pressure gradients are mainly balanced by the nonlinear terms in the momentum equation, in particular via zonal wind advection. Strong zonal winds occur near the equator in boreal winter, transporting zonal momentum so as to balance the pressure gradient force. The zonal winds are due to large-scale equatorial waves, excited by a heating pattern that is relatively symmetric about the equator. In boreal summer, the large-scale equatorial waves are less active in the Pacific region due to a more asymmetric temperature pattern, so the zonal momentum advection and Tυ gradients are both much weaker. The results point to an important role of the nonlinear terms in the tropical balanced dynamics, stressing the need for an improved theoretical understanding and modeling framework of the tropical atmosphere that includes these nonlinear terms, or their net effect.

Explaining Ionospheric Ion Upflow in the Subauroral Polarization Streams

Ionospheric ion upflow is an important process for magnetosphere-ionosphere coupling via O+ source for the magnetosphere. This process occurs frequently in the subauroral polarization stream (SAPS) region where the SAPS-enhanced ion-neutral frictional heating tends to push ions upward because of enhanced upward pressure gradient force. However, the SAPS-induced neutral wind transport by ion-neutral friction may also play an important role in triggering ion upflow, which has been rarely studied. In this work, the thermosphere-ionosphere-electrodynamics general circulation model (TIEGCM) with/without an empirical SAPS model has been employed to investigate the impacts of SAPS on ion upflow in the topside ionosphere. Our results separate different transport processes in the ion continuity equation, showing that SAPS can accelerate upward ambipolar diffusion along its channel because of ion-neutral frictional heating, but SAPS-induced horizontal neutral wind may have a comparable or even larger contribution to vertical ion drift when SAPS are fully developed. In addition, the neutral wind can induce both upward and downward ion drift in the SAPS region, depending on the direction of the neutral wind and the local geomagnetic declination and inclination.

Modelling of gas-liquid-solid distribution in the cocurrent three-phase moving bed

The three-phase moving bed reactors (TMBRs) can supply a potential solution for the multi-phase reactions with deactivating catalysts to realize Online Catalyst Replacement (OCR). In this work, computational fluid dynamics (CFD) simulations were employed to investigate the flow behavior of each phase in a cocurrent TMBR. The Euler-Euler multi-phase flow model and two different liquid-solid force models were employed to describe the dense-phase particle flow and liquid-solid interaction, respectively. The results revealed that the solid flow rate increased due to the gas-liquid flow, but radial solids distribution had not changed significantly. The effect of gas-liquid flow on the solid volume distribution was mainly reflected in the wall and inlet region, which led to lower solid volume fraction and higher granular temperature in the local area. Meanwhile, compared with trickle beds, with the increasing gas flow rate or decreasing liquid flow rate, both the liquid holdup and flow dead zone decreased in TMBRs. With the increase in liquid flow rate, the effect of liquid migration (from the wall to the center) on the liquid distribution was weakened. Besides, due to the competition between the pressure gradient force and gas-liquid drag force, the variations of volume and velocity of each phase depended on operating conditions, which were divided into three typical ranges. The gas-liquid-solid distribution could significantly advance the understanding of flow behaviors in TMBRs, based on which the reactor development could be further promoted.

An Analytical Solution of the Effective-Buoyancy Equation

Abstract The effective buoyancy per unit volume is the statically forced part of the local nonhydrostatic upward pressure-gradient force. It is important because it does not depend on the basic-state density defined with the anelastic approximation. Herein, an analytical solution is obtained for the effective buoyancy associated with an axisymmetric column of less dense air. In special cases where the radial profiles of density are step functions, the analytical solutions replicate qualitatively several features in a recently published numerical solution as follows. The effective buoyancy is positive within the column of lighter air and negative outside. It increases from the axis to the inner edge of the column, then jumps discontinuously to a negative value and thereafter increases until it reaches zero at radial infinity. As the column radius increases, the effective buoyancy on the axis decreases and the change in effective buoyancy between the axis and the inner edge increases, but the jump magnitude is unaltered. For continuous radial density distributions that resemble step functions, the solutions are similar except the cusps are rounded off and the jumps become smooth transition zones. Significance Statement In atmospheric convection, vertical accelerations are due to buoyancy forces and vertical perturbation pressure-gradient forces. Separately, these forces depend on the choice of a basic state. To avoid the ambiguity of an arbitrary reference atmosphere defining which parcels are buoyant, we define an effective-buoyancy force per unit volume that is independent of any basic state. It is the part of the vertical nonhydrostatic pressure-gradient force that depends solely on horizontal density variations. The remaining part of the vertical force is dynamical in origin; it depends only on inertial forces. An analytical solution demonstrates that, for an axisymmetric column of lighter air, effective buoyancy is greatest just inside the column edge and is most negative just outside the edge.

Investigation of the ΣO/N2 Depletion With Latitudinally Tilted Equatorward Boundary Observed by GOLD During the Geomagnetic Storm on April 20, 2020

AbstractA long‐lived (>10 hr) O/N2 column density ratio (∑O/N2) depletion at middle latitudes was observed by the Global‐scale Observations of the Limb and Disk (GOLD) during the 20 April 2020 geomagnetic storm. The observed ∑O/N2 depletion tilts latitudinally at equatorward boundary with the lowest latitude of ∼20°N at ∼75°W, and changes orientation near 75°W, with a north‐westward tilt to the west of ∼75W and a north‐eastward tilt to the east of ∼75W. The National Center for Atmospheric Research Thermosphere Ionosphere Electrodynamics General Circulation Model shows the similar ∑O/N2 depletion patterns and magnitudes, but the longitudes with the most equatorward were ∼100°W and moved westward from ∼100°W to ∼140°W during the storm recovery period. Horizontal winds play major role in forming this middle‐latitude ∑O/N2 depletion structure. The strongest equatorward winds in the longitude sector near the magnetic pole resulted in the most equatorward expansion of all longitudes, generating the depletion with latitudinally tilted equatorward boundary. In addition, the high‐latitude westward zonal wind and the middle‐latitude eastward zonal wind maintained the long existence of this depletion in the GOLD Field of View. The further analysis on neutral winds shows that storm‐time meridional winds at middle latitudes in the mid‐low thermosphere are mainly dominated by pressure gradient force, while zonal winds are determined primarily by horizontal momentum advection.

Theoretical framework bridging classical and quantum mechanics for the dynamics of cryogenic liquid helium-4 using smoothed-particle hydrodynamics

Our recent study suggested that a fully classical mechanical approximation of the two-fluid model of superfluid helium-4 based on smoothed-particle hydrodynamics (SPH) is equivalent to solving a many-body quantum mechanical equation under specific conditions. This study further verifies the existence of this equivalence. First, we derived the SPH form of the motion equation for the superfluid component of the two-fluid model, i.e., the motion equation driven by the chemical potential gradient obtained using the Gibbs–Duhem equation. We then derived the SPH form of the motion equation for condensates based on the Gross–Pitaevskii theory, i.e., the motion equation driven by the chemical potential gradient obtained from the Schrödinger equation of interacting bosons. Following this, we compared the two discretized equations. Consequently, we discovered that a condition maintaining zero internal energy for each fluid particle ensures the equivalence of the equations when the quantum pressure is negligible. Moreover, their equivalence holds even when the quantum pressure is non-negligible if the quantum pressure gradient force equals the mutual friction force. A zero internal energy indicates the thermodynamic ground state, which includes an elementary excitation state. Therefore, the condition can be sufficiently satisfied when the velocities of fluid particles do not exceed the Landau critical velocity, which is not a stringent condition for simulations with a characteristic velocity of a few cm·s−1 in a laboratory system. Based on the above, we performed a simulation of rotating liquid helium-4 and succeeded in generating a vortex lattice with quantized circulation, known as a quantum lattice.

Heat and mass transfer in a peristaltic rotating frame Jeffrey fluid via porous medium with chemical reaction and wall properties

ObjectiveThis paper provides a rudimentary insight into the influence of heat and mass transfer on the magneto-hydrodynamic (MHD) Jeffrey fluid peristaltic flow filling porous space in a symmetric inclined channel using a rotating frame with chemical reaction. In contrast to previous attempts, the flow formulation is based on the impact of a modified Darcy's law porous media on the Jeffrey fluid condition. MethodologyThe derived equations were solved analytically via the standard long wavelength and low Reynolds number assumptions to determine the pressure gradient, temperature, dimensionless velocity, pressure rise, and friction force. Otherwise, the concentration was numerically processed using the ND-Solve built-in command of Mathematica. Such a numerical technique is beneficial in minimizing error and reducing CPU time per evaluation. It chooses an appropriate algorithm for solving the problem. ResultsThe graph is used to physically interpret the numerical answers for the base flow profiles. For numerous parameters of interest that enter into the issues, graphical findings are developed and tested. The impacts of various involved parameters appearing in the solutions are carefully analyzed. The trapping phenomena are discussed for several parameters. Electromagnetic peristaltic micropumps, for example, are one application of the current study in biomedical engineering. It was claimed that our systematic approach may constitute a basis for accurately examining the impact of heat and mass transfer on the magneto-hydrodynamic (MHD) Jeffrey fluid peristaltic flow filling porous space in a symmetric inclined channel using a rotating frame with chemical reaction, useful for diverse medical applications such as gastric fluid flow through the small intestine.

Asymptotic behaviour of rotating convection-driven dynamos in the plane layer geometry

Dynamos driven by rotating convection in the plane layer geometry are investigated numerically for a range of Ekman number ( $E$ ), magnetic Prandtl number ( $Pm$ ) and Rayleigh number ( $Ra$ ). The primary purpose of the investigation is to compare results of the simulations with previously developed asymptotic theory that is applicable in the limit of rapid rotation. We find that all of the simulations are in the quasi-geostrophic regime in which the Coriolis and pressure gradient forces are approximately balanced at leading order, whereas all other forces, including the Lorentz force, act as perturbations. Agreement between simulation output and asymptotic scalings for the energetics, flow speeds, magnetic field amplitude and length scales is found. The transition from large-scale dynamos to small-scale dynamos is well described by the magnetic Reynolds number based on the small convective length scale, $\widetilde {Rm}$ , with large-scale dynamos preferred when $\widetilde {Rm} \lesssim O(1)$ . The magnitude of the large-scale magnetic field is observed to saturate and become approximately constant with increasing Rayleigh number. Energy spectra show that all length scales present in the flow field and the small-scale magnetic field are consistent with a scaling of $E^{1/3}$ , even in the turbulent regime. For a fixed value of $E$ , we find that the viscous dissipation length scale is approximately constant over a broad range of $Ra$ ; the ohmic dissipation length scale is approximately constant within the large-scale dynamo regime, but transitions to a $\widetilde {Rm}^{-1/2}$ scaling in the small-scale dynamo regime.

A Biological‐Parameter‐Optimized Modeling Study of Physical Drivers Controlling Seasonal Chlorophyll Blooms off the Southern Coast of Java Island

AbstractA physical‐biogeochemical model consists of many key parameters; theoretically, 10,000 or more numerical experiments are required to obtain a set of optimal biological parameters. The corresponding computing resources are too expensive when running a three‐dimensional and high‐resolution physical‐biogeochemical model. In this study, we improve the performance of a three‐dimensional physical‐biogeochemical model via the conditional nonlinear optimal perturbation method for southern Java Island, where chlorophyll blooms occur seasonally. Based on the improved model results, we calculated the mixed‐layer nutrient budget, thereby characterizing how each physical process transports nutrients into the surface oligotrophic layer and then stimulates the chlorophyll blooms during the southeast monsoon season. Nutrients that upwell along the submarine slope are found in narrow regions along the coast and spread into most of the study area by local wind‐induced offshore transport. The contribution of nonlinearity (advection) is essential to modulating the upslope movement of nutrients off the coast. If local winds are neglected in the model, onshore transport induced by the pressure gradient force in the zonal direction (alongshore) and subsequent downwelling would be dominant, and chlorophyll blooms would diminish in most regions. The role of the South Java Coastal Current varies under the joint influence of remote and local wind forcings. The Indonesian Throughflow from the Lombok Strait also contributes to surface phytoplankton growth along its path off the south of Java Island.

Winter–Summer Transition in the Southern South China Sea Western Boundary Current

Abstract The winter–summer transition in the southern South China Sea (SCS) western boundary current (WBC) is studied. Two categories have been identified. In case 1, the southern SCS WBC transition in the lower layer (below the thermocline) lags that in the upper layer (above the thermocline). In case 2, there is no transition lag at full depth. In both categories, the geostrophic balance dominates the transition. In case 1, the upper layer geostrophic balance is dominated by the sea surface height pressure gradient (SSHPG) and Coriolis forcing during southern SCS WBC transition. Therefore, there is no transition lag with depth in the upper layer. Below the thermocline layer, the competition between the SSHPG and the density pressure gradient (DPG) determines the transition. During the transition, the amplitudes of the SSHPG and DPG are basically equivalent. The SSHPG needs time to develop sufficiently larger than the DPG. Therefore, the transition in the deeper layer significantly lags that in the shallower layer. The reversal of the SSHPG is mainly attributed to the change in the basin-scale wind stress curl over the southern SCS. The change in the DPG is mainly associated with the cooling of the water along the western continental slope, which is induced by upwelling. In case 2, there is no cooling along the western continental slope, and then the amplitude of the DPG is always far smaller than that of the SSHPG. Responding to the change in the SSHPG, the southern SCS WBC transition behaves consistently at full depth. Significance Statement We have a comprehensive understanding of the South China Sea (SCS) circulation patterns in winter and summer. However, their seasonal transitions remain unclear, and a better understanding of them is potentially helpful for improving ocean circulation modeling and prediction. This paper focuses on the winter–summer transition in the SCS western boundary current (WBC). Above the thermocline (∼100 m), the transition behaves consistently in the vertical direction and is controlled by the conversion of the sea surface height–induced pressure gradient. Below the thermocline, the transition in the deeper layer of the WBC significantly lags that in the shallower layer of the WBC, which is associated with the competition between the SSH-induced pressure gradient and the density-induced pressure gradient at the sea surface.

Saltwater Intrusion‐Induced Flow Reversal in the Changjiang Estuary

AbstractSaltwater intrusion is a common feature in the Changjiang Estuary affected by river discharges and tidal flows. It leads to a two‐layer flow structure during the flood‐to‐ebb tidal transient period: the seaward tidal flow in the upper water column and onshore intruded salt flow in the lower column, even though the lower column water usually experiences an ebb flow eventually. Our recent measurements with a tripod deployed in a tidal channel of the North Branch in the East China Sea challenged this feature. We detected that the two‐layer flow structure disappeared in the ebb tide period during the neap cycle due to intense saltwater intrusion. A constant onshore flood‐like flow predominated the entire water column. The physical mechanism for the flow reversal was examined using the Finite Volume Community Ocean Model (FVCOM). The FVCOM was robust to capture the observed flow reversal in the tidal channel during the neap tidal cycle. The momentum balance analysis results suggest that the flow reversal occurred when the saltwater intrusion‐induced onshore baroclinic pressure gradient force and baroclinic tidal rectification overwhelmed the seaward barotropic pressure gradient force. A parameter‐driven criterion was derived theoretically to determine the potential occurrence of a stable ebb flow reversal in the tidal channel.

Numerical study of rising Taylor bubbles driven by buoyancy and additional pressure

The Taylor bubble driven by buoyancy and additional pressure is in a non-equilibrium state, which bubble and liquid flow have an accelerated tendency of rising, and the bubble behavior is significantly different with the Taylor bubble in stagnant liquid. In order to understand the dynamic properties of such bubbles, a numerical study was conducted using the coupled level-set and volume-of-fluid (CLSVOF) method combined with the stress-blended eddy simulation (SBES) model. The research results indicated that, due to the additional pressure, the difference between the bubble pressure head and the liquid column height is larger than zero, the pressure gradient force acting on the liquid column is greater than the force of gravity, this makes the bubble have an accelerating upward trend. The bubble shape and liquid film thickness are closely related to the relative bubble velocity, the correlation between dimensionless liquid film thickness and Reynolds number of relative bubble velocity was proposed. In addition, the article analyzed the influence mechanism of bubble shape, which is determined by the stress state of the fluid surrounding the bubble. Under the additional pressure, the axial stress on the bubble top increases significantly, while the radial stress remains almost invariable, which makes the bubble shape gradually become thinner.

Storm splitting process and the associated mechanisms for a long-lived hailstorm

Storm splitting poses a great challenge in storm tracking and forecasting. However, most of previous studies have focused on the effect of warm rain microphysics on storm splitting, that of ice microphysics, especially hail microphysics on hailstorm splitting remain unknown. The storm splitting and associated mechanisms for a long-lived severe hailstorm occurred on 19 June 2017 in Beijing are investigated in this study based on radar observations and simulated results from a three-dimensional cloud model with hail-bin microphysics. The results show that the hailstorm experienced twice splitting. Both right-moving and left-moving cells strengthened in the first splitting, while only the right-moving cell strengthened in the secondary splitting. It is found that the clockwise-curved hodograph environment initially creates asymmetric negative pressure perturbations at the low levels. With the development of the storm, the negative pressure perturbations are strengthened, lifted, and evolved as vertically clockwise- or anticlockwise-rotating low-pressure centers, which significantly enhance both upward and outward pressure gradient forces at the levels where the low-pressure centers are located, and selectively induce the updraft development on the flanks of the storm, resulting in the low-level upward-curved updraft splitting structure. In the mature and decaying stage of the storm, strong downward propagating gravity waves excited by high graupel/hail loading through buoyancy oscillations are found to have a critical role in the subsequent rapid updraft splitting prior to the graupel/hail-induced downdraft. Both the gravity waves and graupel/hail-induced downdraft have important roles in the hailstorm splitting rather than rain-induced downdraft as proposed in previous studies.

Modelling of tungsten impurity edge transport and screening for different divertor conditions in EAST

Tungsten (W) transport and screening in the edge plasma are investigated for EAST high dissipative divertor conditions. By combining the 1D impurity fluid model (1DImpFM) and the two-point model formatting (2PMF), W screening is proved to be enhanced for high upstream plasma density conditions, mainly because the impurity temperature gradient velocity decreases with the increase of the upstream plasma density. Based on dedicated EAST density ramp-up experiments, 2D simulations of W erosion and transport are carried out for different levels of dissipative divertor conditions by using the SOLPS-DIVIMP code package, and the modeling results are benchmarked with the 1DImpFM analytic model. The prompt-redeposition, the divertor screening, and the main SOL screening are quantitatively analyzed. For detached divertor conditions, the increase in the W ionization length reduces the prompt redeposition rate, but both the divertor screening and SOL screening are reinforced. The 1DImpFM can interpret well the W leakage in the near separatrix region; however, the 2D simulations suggest that the impurity pressure gradient force which is neglected by the 1DImpFM plays an important role, especially in the far-SOL region. With the divertor condition varied from the high-recycling regime to the deep detachment regime, the W source moves from the near strike point region to the far SOL, and thus makes the W transport in the far SOL more important. Therefore, the impurity pressure gradient force cannot be neglected for edge W transport analysis, especially for the detached divertor conditions.

Investigation of dust lifting by a moving shock wave based on compressible multiphase particle-in-cell method

A dust lifting process by shock waves performs high complexity and is of significance for industrial safety. To develop an in-depth understanding of an inherent physical mechanism of dust lifting, this study presents a detailed consideration regarding particle force models. First, a set of compressive force models of those that may affect lifting is distinguished, which afterwards is integrated into the original compressible multiphase particle-in-cell (CMP-PIC) method. Second, the value of the restitution coefficient is determined using the sensitivity analysis method. Good agreement of the dust lifting height is achieved between the numerical and different experimental results, which demonstrate the reliability of the CMP-PIC method. Then, the contributions of different kinds of forces to dust lifting are qualitatively and quantitatively analyzed. Flow field analysis shows that the shock-induced flow produces downward drag and pressure gradient forces on the particles to inhibit the rise of the particles, while the Magnus and Saffman forces perform a promoting role. Additionally, the compression wave and its reflected wave in the granular medium are clearly observed. Specially, when the reflected wave reaches the surface, huge collision forces on the particles and significantly promotes the initial lifting of particles. Moreover, the histories of forces acting on the particles at different layers of dust are discussed. The results show that different kinds of forces perform intense space-time dependent characteristics, and the dominant forces at different stages of dust lifting are identified. A dimensionless analysis of the force model qualitatively justifies the simulation results. The influence of the shock strength is also discussed.

Phase‐Resolved Modeling of Wave Interference and Its Effects on Nearshore Circulation in a Large Ebb Shoal‐Beach System

AbstractA time‐domain Boussinesq model was applied to modeling wave interference and its effects on nearshore circulation in San Francisco Bar and the adjacent Ocean Beach, CA. The model predicted the wave interference phenomena caused by the ebb shoal, with interference scales consistent with the radar observation and are persistent with nodal lines unchanged with time. Nearshore circulation predicted by the model shows small‐scale flow structures tied with the wave modulation patterns. However, the small‐scale modulation in the wave field seems not to generate alongshore variation in wave setup at similar scales. Therefore, in a large‐scale view, the alongshore currents predicted by the Boussinesq model still keep the general features shown in a wave‐averaged model, such as the flow divergence caused by the pressure gradient force associated with the alongshore variation of wave setup. The further analysis based on idealized short crest waves on a plane beach suggests that the alongshore pressure gradient is mainly balanced by the gradient of radiation stresses in the antinodal region, while by the flow advection in the nodal region. The rip current behavior is forced locally near breakers, rather than by gradients in wave setup close to shore. The time‐domain Boussinesq model predicted the spatial variability of wave‐induced processes. The alongshore‐varying wave breakers caused by wave interference are the source of the vorticity generation, inducing energetic vortex eddies nearshore.

Impacts of high-resolution atmospheric forcing and air-sea coupling on coastal ocean circulation off the Pearl River Estuary

We investigated the impacts of high-resolution atmospheric forcing and ocean-atmosphere coupling on the estuary-shelf ocean simulation off the Pearl River Estuary. We conducted process and dynamics analyses of the wind-driven coastal ocean circulation under atmospheric flux forcing from (1) global reanalysis data, (2) a high-resolution regional atmospheric model, and (3) an air-sea coupled model during an upwelling-favorable wind. The results revealed that the high-resolution atmospheric model significantly improved the representations of the near-surface wind field and air temperature. The air-sea coupled model outperformed the uncoupled model in simulating coastal currents, water temperature, and salinity. The high-resolution uncoupled model strengthened the surface wind stress and along-isobath pressure gradient force (PGF), resulting in an intensified cross-isobath transport. The improved wind forcing from the air-sea coupled model modulated the spatial variation of the net stress curl and vorticity advection and enhanced the along-isobath PGF for a stronger cross-isobath transport. The lower sea surface temperature (SST) in the air-sea coupled model reduced the air temperature and wind stress. Adjusting the SST in the air-sea coupled model improved the momentum fluxes and the associated ocean transport dynamics.

Mid-latitude neutral wind responses to sub-auroral polarization streams

Abstract. We investigate the response of the mid-latitude thermospheric neutral winds to a sub-auroral polarization stream (SAPS) event. Using red line (F region) airglow data from two Fabry–Pérot interferometers (FPIs), and F-region ionospheric flow velocities from four Super Dual Auroral Radar Network (SuperDARN) radars, the drivers behind changes seen in the neutral winds are explored within the context of the larger SAPS structure. Different, although strong, neutral wind responses to the SAPS are seen at the two FPI sites, even though they are relatively close geographically. We attribute the wind differences to the varying balance of pressure gradient, ion drag, and Coriolis forces, which ultimately depend on proximity to the SAPS. At the FPI site equatorward of the SAPS, pressure gradient and Coriolis forces drive the winds equatorward and then westward. At the FPI site co-located with the SAPS, the ion drag is strong and results in the winds surging westward before turning eastward when becoming influenced by dawnside sunward plasma convection drifts.

Performance analysis of the separator with inner channels by experiment and CFD-POST

ABSTRACT The separator with inner channels is designed to solve the re-entrainment phenomenon of particles, improving the separation efficiency. Firstly, experiments are established to compare the separation efficiency and pressure drop between ordinary separators and ones with inner channels. Secondly, the Reynolds Stress model and the Euler–Euler model are applied to simulate the turbulence and particle flow, respectively. Lastly, the Population Balance model (PBM) is used to define different distributions of particle diameter by initial moments. The research results demonstrate that the inner channels can improve separation efficiency significantly because they can restrain the re-entrainment phenomenon. The separation efficiency of the design and the conventional ones is 97% and 90%, respectively, but the pressure drop increases by 39 Pa in this structure. Simultaneously, this structure has a lower tangential velocity compared with the separator without inner channels, reducing particle collisions with the wall. Radial pressure differences are also declined in the structures with inner channels, leading to a decreased pressure gradient force. Furthermore, the sixth moment has a larger median particle size, while the particle size distribution at the outlet of the separator is similar to that at the inlet via the PBM. And the maximum separation efficiency of the design and ordinary ones is 99% and 80%, respectively. The characteristics listed above can help with efficient separator design.

Numerical Simulation and Analysis of Water and Suspended Sediment Transport in Hangzhou Bay, China

Hangzhou Bay is a large, high-turbidity shallow bay located on the southern side of the Changjiang Estuary, China. The process and dynamic mechanisms of water and sediment transport in the bay are not yet clear. An improved three-dimensional sediment numerical model that combined various dynamic factors was established to simulate and analyze these mechanisms. The residual current cannot properly represent the net water and sediment transport, and the residual unit width water flux (RUWF) and residual unit width sediment flux (RUSF) were used to explain the water and sediment transport. The results of numerical simulations indicate that in summer, the surface RUWF from the Changjiang Estuary near Nanhui Cape flows westward along the coast, in which the major part flows southward to the Zhenhai area, and the small part flows further westward along the north coast and then turns to the south coast and eastward, forming the water transport pattern of north-landward and south-seaward, which is stronger in the spring tide than in the neap tide. The bottom RUWF near Zhenhai flows northward to Nanhui Cape in the neap tide, which is larger in the neap tide than in the spring tide. In the middle and western parts of the bay, the RUWF has the same pattern as the surface water transport and is stronger in the spring tide than in the neap tide. The pattern of RUSF is roughly similar to the water flux transport. During the spring tide, the water and sediment transport fluxes near Nanhui Cape are from the Changjiang Estuary into Hangzhou Bay, but from Hangzhou Bay into the Changjiang Estuary during the neap tide. In the winter, the distributions of RUWF, RUSF, and suspended sediment concentration (SSC) are similar to those in the summer. In addition, the distance of surface water transport westward along the north coast is shorter than that in the summer, the magnitude of the bottom RUWF is smaller than that in the summer due to the weaker salinity gradient, and the bottom RUSF near Nanhui Cape is weaker than that in the summer during the neap tide. The net transect water flux (NTWF) and the net transect sediment flux (NTSF) near Nanhui Cape are from the Changjiang Estuary into Hangzhou Bay during the spring tide; during the neap tide, the NTWF is still from the Changjiang Estuary into Hangzhou Bay, but the NTSF is from Hangzhou Bay into the Changjiang Estuary because the SSC is much higher in the bottom layer than in the surface layer. The dynamic reason for the temporal and spatial variation in RUWF and RUSF is that the barotropic pressure gradient force is larger than the baroclinic pressure gradient force during the spring tide and is the opposite during the neap tide.