Horizontal Velocity Distribution Research Articles

Salinity mixing in a tidal multi-branched estuary with huge and variable runoff

The study of estuarine hydrodynamics within an isohaline framework has been well established in recent years. However, most studies of estuarine mixing and exchange flow using salinity coordinates have been conducted for idealized estuaries or realistic estuaries with simple bathymetry and constant runoff. In this study, a realistic numerical model is applied to the Changjiang River estuary, a complex multi-branched estuary with huge and variable runoff. The destruction of salinity variance is used to quantify salinity mixing, in which numerical mixing accounts for about one third of the total mixing. The results of total mixing per salinity class mS indicate that the universal law of estuarine mixing applies to realistic simulations under huge and variable runoff when averaged over two spring-neap cycles (28 days). During the flood season, volume integrated salinity mixing is approximately twice that of the dry season due to the double runoff. Salinity mixing at different channels displays distinct characteristics in both horizontal and vertical distributions. The patchy distribution of effective vertical diahaline velocity implies that the volume flux across an isohaline surface can exhibit significant spatial variability. The most vigorous salinity mixing occurs in the North Passage, where about 58 % of the freshwater enters the sea. We found that the estuarine mixing within different branches is linearly correlated with the corresponding water transport. Dikes fringing the navigational channel on both sides downstream of the North Passage significantly increase the length of saltwater intrusion in the North Passage, alter the distribution of horizontal and vertical flow velocities, and further cause significant changes in local mixing, especially near the mouth of the dikes.

Cattaneo-Christov heat and mass fluxes model of Casson fluid employing non-Fourier double diffusion theories with ion slip and Hall effects

It is vitally important to comprehend non-Newtonian fluids flow behaviour from an industrial perspective. Non-Newtonian fluids are needed for a number of industrial and technical processes, including the production of paper, photographic films, and polymer sheet extrusion. There are several industrial applications for heat and mass transfer. However, thermal and solute relaxation time phenomena can't be predicted by classical heat and mass transfer laws (Fourier and Fick laws). This work aims to apply the modified Ohm law to thermal and mass transfer which are based on Fick's and generalized Fourier principles, respectively. The current study examines the three-dimensional Darcy-Forchheimer flow of non-Newtonian fluid “Casson fluid” via porous medium with ion slip and Hall effects across a stretched sheet. Thermophoresis and Brownian motion aspects are also considered. The diffusion phenomena are modelled using the Boungrino model. The modified Buongiorno model (MBM) for nanofluids is used to investigate the enhancement of heat transport. Together with practical nanofluid properties, it covers the mechanics of thermo-migration and random motion of nanoparticles. By adding the appropriate similarity transformations, this collection of (PDEs) that reflect the mathematical model is transformed into an (ODEs) system, which it is subsequently resolved utilizing the Lobatto IIIA technique's powerful computing capabilities via Matlab software. Data visualisations and numerical examples are presented considering many physical restrictions affect the fluctuation of velocities, temperatures, concentration, dimensionless shear stress, Nusselt number, and Sherwood number. According to certain findings, the existence of Hall and ion slip effects, and other factors contribute to an increase in horizontal velocity distribution. Furthermore, Fourier's law produces a wider temperature distribution than the Cattaneo-Christov heat flux model.

Statistical Analysis of the Horizontal Phase Velocity Distribution of Atmospheric Gravity Waves and Medium‐Scale Traveling Ionospheric Disturbances in Airglow Images Over Sata (31.0°N, 130.7°E), Japan

AbstractAtmospheric gravity waves (AGWs) and medium‐scale traveling ionospheric disturbances (MSTIDs) in the upper atmosphere affect atmospheric circulation and radio‐wave transmission including satellite positioning and communications, and high‐frequency radio. The 3‐dimensional (3‐D) spectral analysis of airglow images makes it possible to extract wave parameters of AGWs and MSTIDs. Such spectral analysis of long‐term airglow images has not been performed in the southern part of Japan, which is a unique transition latitude from middle to equatorial region. In this study, we calculated the horizontal phase velocity distribution of AGWs in the mesosphere‐lower‐thermosphere (MLT), and MSTIDs in the F‐region ionosphere by applying the 3‐D spectral analysis method to the 557.7 and 630.0‐nm airglow images obtained at Sata (31.0°N, 130.7°E) in Japan over 20 years from 2000 to 2020. The spectra of AGWs in the MLT region in the 557.7‐nm airglow images show that the poleward (northward) power spectral density (PSD) is stronger in summer, suggesting that the tropospheric convection is a possible source of AGWs and the wave ducting propagation occurred. Westward propagation is also observed in winter, suggesting that wind filtering effect by mesospheric jets plays an important role. The PSD of MSTIDs in the 630‐nm airglow images increases during low solar activity periods, suggesting that MSTIDs are produced by ionospheric plasma instability. The westward PSD of MSTIDs is stronger in summer. These results are an important achievement in clarifying the statistical characteristics of AGWs and MSTIDs over Sata, Japan, based on long‐term airglow observations and 3‐D spectral analysis.

Greenwater due to plunging breaking wave impingement on a deck structure. Part 1: Experimental investigation on fluid kinematics

This study experimentally investigates the kinematics of greenwater resulting from plunging breaking wave impacts on a deck structure. Two impingement scenarios, characterized by different breaking points, were considered. The ensemble-averaged flow fields were obtained by applying both PIV (particle image velocimetry) and BIV (bubble image velocimetry) techniques to 50 repeated tests. The study examines flow patterns, velocity fields, and derived quantities from velocity data to identify differences in flow behaviors, variations in velocity magnitude, and potential distribution of peak impact pressures. The presented results provide useful information and indication for assessing concentrated loadings and enhancing our understanding of hydrodynamic behaviors. Additionally, the validity of applying Ritter dam break solutions to describe the horizontal velocity distribution of greenwater flows is examined, and prediction equations based on self-similar horizontal velocity distribution are derived.

Subgrid Model of Fluid Force Acting on Buildings for Three-Dimensional Flood Inundation Simulations

In recent years, large-scale heavy rainfall disasters have occurred frequently in several parts of the world. Therefore, a quantitative approach to understanding how buildings are damaged during floods is necessary to develop appropriate flood-resistant technologies. In flood inundation simulations for the quantitative evaluation of a building’s resistance to flooding, a subgrid model is necessary to appropriately evaluate the resistance of buildings smaller than the grid size at a medium grid resolution. In this study, a new subgrid (SG) 3D inundation model is constructed to evaluate the fluid force acting on buildings and assess the damage to individual buildings during flood inundation. The proposed method does not increase the computational load. The model is incorporated into a 2D and 3D hybrid model with high computational efficiency to construct a 3D river and inundation flow model. Its validity and effectiveness are evaluated through comparisons with field observations and the conventional equivalent roughness model. Considering horizontal and vertical velocity distributions, the proposed model showed statistically significant improvements in performance in terms of building loss indices such as velocity and fluid force. These results suggest that the SG model can effectively evaluate the fluid force acting on buildings, including the vertical distribution of flow velocities.

Green-Naghdi Theory, Part B: Green-Naghdi Equations for Deep Water Waves

“Green — Naghdi Theory, Part A: Green — Naghdi (GN) Equations for Shallow Water Waves” have investigated the linear dispersion relations of high-level GN equations in shallow water. In this study, the GN equations for deep water waves are investigated. In the traditional GN equations for deep water waves, the velocity distribution assumption involves only one representative wave number. Herein, a new velocity distribution shape function with multiple representative wave numbers is employed. Further, we have derived the three-dimensional GN equations and analyzed the linear dispersion relations of the GN-3 and GN-5 equations. In this study, the finite difference method is used to simulate focus waves in the time domain. Additionally, the GN-5 equations are used to validate the wave profile and horizontal velocity distribution along water depth for different focused waves.

Numerical investigations on fluid characteristics around the bottom-fixed aquacultural farm

Offshore aquacultural farms are world widely booming in recent years. The bottom-fixed aquacultural farm gains more and more attention because of the large volume and great strength. This study numerically investigates the fluid velocity distribution characteristic around the bottom-fixed aquacultural farm, which is of great importance for fish welfare and pollutant diffusion. The numerical model is developed based on the porous media model for the nets and the rigid walls for the fixed frame. The k-omega turbulence model and the finite volume method are employed to solve the Navier-Stokes equations. The flow velocity distributions around and inside the farm in the varied current velocity are analyzed. The vertical and horizontal flow velocity distributions in various current directions with different net solidities are investigated in detail. Results demonstrated that the configurations of trusses, vertical and horizontal columns of the farm and the interaction with the nets result in complex velocity distributions inside and around the farm. The velocity attenuations at different depths are quite different in uniform and non-uniform currents. The velocity distributions in different attack angles of the flow provide valuable suggestions on the arrangement and layout of the multiple farms.

Assessment of BSL kω Turbulence Model for Predicting Flow Characteristics in a Solitary Wave Motion

A deep understanding of boundary layer characteristics under wave motion, especially bottom shear stress on the seabed, is critical in sediment transport calculation and modeling. In this present study, boundary layer characteristics under solitary wave motion over the smooth bed are investigated through the Baseline (BSL) kω model. It will also consider the result of a laboratory experiment performed in a closed conduit generation system. The conclusion said that the BSL kω model can replicate well on horizontal and vertical velocity distribution at Reynolds number (Re) = 2.25 x 105. In addition, a turbulent spike which was occurred during decelerating phases of oscillatory motion can be predicted well also by the BSL kω model at Reynolds number (Re) = 6.06 x 105.

Parasitic Capillary Waves on Small-Amplitude Gravity Waves with a Linear Shear Current

This paper describes a numerical investigation of ripples generated on the front face of deep-water gravity waves progressing on a vertically sheared current with the linearly changing horizontal velocity distribution, namely parasitic capillary waves with a linear shear current. A method of fully nonlinear computation using conformal mapping of the flow domain onto the lower half of a complex plane enables us to obtain highly accurate solutions for this phenomenon with the wide range of parameters. Numerical examples demonstrated that, in the presence of a linear shear current, the curvature of surface of underlying gravity waves depends on the shear strength, the wave energy can be transferred from gravity waves to capillary waves and parasitic capillary waves can be generated even if the wave amplitude is very small. In addition, it is shown that an approximate model valid for small-amplitude gravity waves in a linear shear current can reasonably well reproduce the generation of parasitic capillary waves.

Shear Flow in Cylindrical Open Channel Under Precession

The study of forced oscillations in open cylindrical channel under precession is extended to include the shear effect, that is induced by inertial waves in such systems. The linear part of the problem led to two equations for stability one for the viscous part similar to Orr-Sommerfeld equation and one for the inviscid part similar to Rayleigh equation, the second was solved and discussed depending on the stream function observation. The linear part also led to relationship that connects between the stream velocity and the disturbance one is derived in a form similar to Burns conditions for open flows under normal conditions. Experimentally measuring the horizontal velocity distribution with depth showed that this distribution is sinusoidal one. Burns condition was solved based on this assumption. The nonlinear part of the problem led to a new version of Koteweg De-Vries (KdV) equation that is solved numerically by applying the leapfrog method for time discretization, Fourier transformation for the space one, and the trapezoidal rule for solving the integrals with depth, the results showed that the shear has no specific impact on the wave form which is similar to the classical results obtained by the theories under normal conditions.

Measurements of exhaled airflow velocity through human coughs using particle image velocimetry

The sudden outbreak of coronavirus (COVID-19) has infected over 100 million people and led to over two million deaths (data in January 2021), posing a significant threat to global human health. As a potential carrier of the novel coronavirus, the exhaled airflow of infected individuals through coughs is significant in virus transmission. The research of detailed airflow characteristics and velocity distributions is insufficient because most previous studies utilize particle image velocimetry (PIV) with low frequency. This study measured the airflow velocity of human coughs in a chamber using PIV with high frequency (interval: 1/2986 s) to provide a detailed validation database for droplet propagation CFD simulation. Sixty cough cases for ten young healthy nonsmoking volunteers (five males and five females) were analyzed. Ensemble-average operations were conducted to eliminate individual variations. Vertical and horizontal velocity distributions were measured around the mouth area. Overall cough characteristics such as cough duration time (CDT), peak velocity time (PVT), maximum velocities, and cough spread angle were obtained. The CDT of the cough airflow was 520–560 m s, while PVT was 20 m s. The male/female averaged maximum velocities were 15.2/13.1 m/s. The average vertical/horizontal cough spread angle was 15.3°/13.3° for males and 15.6°/14.2° for females. In addition, the spatial and temporal distributions of ensemble-averaged velocity profiles were obtained in the vertical and horizontal directions. The experimental data can provide a detailed validation database the basis for further study on the influence of cough airflow on virus transmission using computational fluid dynamic simulations.

Hydraulic design criteria of the modified meander C-type fishway using the combined experimental and CFD models

Fishways' structure has been developed to mitigate the harmful effects of human-made structures such as dams and weirs on the migratory fish process as an essential part of the environmental cycle. In this study, a Modified Meander C-type Fishway (MMCF) was designed and analyzed based on a fish species movement capability. The proposed fishways' structural design follows the key features of the vertical slot fishways (VSF) structure and consists of eleven successive cylindrical pools connected through vertical slots. In the present study, physical and computational fluid dynamics were used to investigate the flow characteristics inside the cylindrical pools with designed radius (R) and vertical slots as the system's connectors. Different geometry scenarios were applied to the model, such as the slots' various dimensionless opening ratios (s/R = 0.1, 0.2, 0.3) with varying bed slope scenarios (5%, 10%, and 20%). The obtained results illustrated the dimensionless hydraulic design diagrams based on the dimensionless discharge parameter (Q⁎) as a critical parameter for designing and operating the fishways. Horizontal and vertical flow velocity distribution graphs were presented, which could be used to estimate a potential low-velocity field for each specific fish species. As a geometrical improvement scenario, the pool's average-depth parameter (d) was increased for each scenario using the designed vertical baffles adjusted at the pools' opening gate with different vertical slot's height scenarios (hb/R = 0, 0.1, 0.2). Studying the radial and tangential fluctuations of the turbulent flow inside the proposed fishway demonstrated the structure's performance to make a more stable swimming path for the fishes toward the upstream movement.

A numerical and experimental investigation of wave generated by submerged landslides

The Weakly-Compressible Moving Particle Semi-implicit (WC-MPS) approach is applied to investigate the wave propagation and the flow fields induced by sliding blocks. Since there are already studies focusing on an inclination slope of 45°, two slope angles, 40° and 50°, are used to obtain the additional experimental results. Sliding blocks are released under water, where the top edges are parallel to the water surface. The simulation results are compared to the experimental measurements both on the water surface and the velocity distribution at specific locations. To analyze the flow fields, contour and vector plots illustrate the flow characteristics for the entire velocity distribution in the simulation domain along with the vortex movements from the sliding block. Two case scenarios are presented to investigate the velocity distribution of the sliding block. For the first case scenario, seven cross-sections, including the front edge, the top edge, and the back edge of the sliding block were selected to further identify the characteristics of the horizontal and vertical velocity distributions. The second case scenario has five specific locations at the front, top and back edge of the block. A good agreement was obtained between the WC-MPS simulated results to the experimental data.

Flow characteristics of three typical granular materials in near 2D moving beds

The granular materials involved in industrial moving beds vary widely, and the corresponding flow characteristics differ. This paper compares the flow characteristics of three kinds of typical granular materials, namely, glass beads, corundum beads, and coarse sand. The repose, internal friction, and particle-wall friction angles of these materials are measured, and the flow characteristics of these materials in near 2D silos, in moving beds with aligned pipes and staggered pipes are studied by particle image velocimetry (PIV). Detailed results regarding the vertical velocity distributions, horizontal velocity distributions, local velocity field surrounding pipes, and dimensionless tangential velocity distribution around pipes of the three granular materials are revealed and compared. The mass flow index of silos, the kinetic energy correction factor in certain cross sections and average dimensionless tangential velocities around pipes are calculated to reveal the similarities and differences of flow characteristics for different granular materials in moving beds.

Numerical simulation of two-phase flow within sudden expansion in horizontal channel pressure and velocity distribution

In this paper, we will study the flow of two immiscible fluids (air/water) through a sudden expansion in a horizontal channel. The first part of the paper will be a detailed bibliography study of sudden expansion problems followed by a mathematical and numerical study where detailed equations and numerical methods used for the numerical simulation are presented. The second part of the paper represents the numerical results obtained. First, we will validate our numerical model with the experimental results obtained by Chalfi and Ghiaasiaan (Int J Multiph Flow 34(1):2–12, 2008. https://doi.org/10.1016/j.ijmultiphaseflow.2007.09.004). The validation will be for the pressure distribution in the channel and the pressure jump over the sudden expansion. A comparison will be also done with the experimental results from Chalfi and Ghiaasiaan (2008) and the theoretical model from Armand-type void-quality expression for the pressure with different Reynolds numbers. After that, a numerical study will be done with a different ratio of the same geometry, pressure and velocity parameter will be studied and the jump over these variables is captured at the sudden expansion. The numerical part is done with the FEniCS platform which is a powerful finite-element computational open-source scientific platform.

A New Approach for Modeling Dissipation due to Breaking in Wind Wave Spectra

AbstractA robust spectral dissipation term for wind waves has long been a goal of detailed-balance spectral modeling and is represented by many different approximations in spectral models of random wave fields. A Monte Carlo approach is employed here to create a random-phase sea surface that is used to simulate the distribution of horizontal surface velocities at the sea surface and to relate these velocities to deep-water wind wave breaking. Results are consistent with many recent studies that show a kinematic-based breaking criterion can provide a consistent depiction of the onset of wave breaking. This criterion is combined with the calculated nonlinear flux rates to estimate a transition point within a spectrum at which a spectrum changes from an f−4 equilibrium-range form to an f−5 region dominated by dissipation, potentially an important factor within several air–sea interaction mechanisms, turbulence at the sea surface, and remote sensing applications. It also has the potential to improve operational modeling capabilities.

Experimental and numerical study of current-induced artificial upwelling

The aim of the current paper is to investigate hydrodynamic characteristics of the artificial upwelling induced by ocean currents. Experiments were performed in a flume at different density difference heads, horizontal current velocities and upwelling pipe diameters. A three-dimensional computational fluid dynamics (CFD) model was employed on wider range of parameters for further analysis. The performance of the numerical model has been confirmed by the experimental findings. The present results show that the volume flow rate of current-induced artificial upwelling is influenced by geometrical parameters and inclination angle of the pipe, the horizontal current velocity and vertical distribution of water density. In ideal two-layer density stratified water, the critical current velocity to generate upwelling linearly increases with the increase of the density difference, and the maximum rising height for upwelling is inversely proportional to the density difference. Feasibility analysis was taken by using current and density profiles of the East China Sea near Dongji Islands, which provides an useful reference for engineering practice.

An SPH wave-current flume using open boundary conditions

In this paper, a novel numerical wave-current flume is implemented based on the Smoothed Particle Hydrodynamics (SPH) method. The proposed flume is more stable and computationally efficient than conventional ones because it cancels wave paddles or sponge layers while using a non-reflective open boundary condition to simultaneously generate and absorb waves and currents. Numerical tests of nonlinear regular waves interacting with steady currents in the same/opposite directions indicate that the wave-current interactions mainly affect the horizontal velocity distributions in the water body, with little influence on the vertical movements. Water particle trajectories are stretched, and the mass transportation effects are enhanced when the waves and currents are in the same direction. When the directions are opposed, the trajectories, as well as the mass transportation, are compressed, suppressed and even reversed. The applications of solitary wave-current interaction over a submerged bump further show that the relative direction between the wave and the current has remarkable influence on the wave breaking pattern over an underwater obstacle.

Simulation of Influence of Mechanical Elements on Karman Vortex Street Parameters

This work presents the results of numerical modeling of Karman vortex street generation performed with ANSYS/FLUENT package application. The influence of the mechanical elements located downstream of the bluff body on the vortex frequency has been found during earlier laboratory investigations. Five various geometrical configurations have been tested. Considerable differences in pictures of distributions of pressure, horizontal and vertical velocities have appeared for various configurations. Qualitative as well as quantitative results are presented in the paper. They confirm the significant dependence of the Karman vortex street parameters on the meter configuration.

Influence of thermal stratification and slip conditions on stagnation point flow towards variable thicked Riga plate

Abstract This article addresses thermally stratified stagnation point flow of viscous fluid induced by a non-linear variable thicked Riga plate. Velocity and thermal slip effects are incorporated to disclose the flow analysis. Solar thermal radiation phenomenon is implemented to address the characteristics of heat transfer. Variations of different physical parameters on the horizontal velocity and temperature distributions are described through graphs. Graphical interpretations of skin friction coefficient (drag force at the surface) and Nusselt number (rate of heat transfer) are also addressed. Modified Hartman number and thermal stratification parameter result in reduction of temperature distribution.