Channel Velocity Research Articles

Model of surface roughness and material removal using abrasive flow machining of selective laser melted channels

PurposeInternal channels produced by selective laser melting (SLM) have rough surfaces that require post-processing. The purpose of this paper is to develop an empirical model for predicting the material removal and surface roughness (SR) of SLM-manufactured channels owing to abrasive flow machining (AFM).Design/methodology/approachA rheological model was developed to simulate the viscosity and power-law index of an AFM medium. To simulate the pressure distribution and velocity in the SLM channels, the fluid behavior and SR in the channels were simulated by using computational fluid dynamics. The results of this simulation were then applied to create an empirical model that can be used to predict the SR and material removal thickness. To verify this empirical model, it was applied to an actual part fabricated by SLM. The results were compared with the measurements of the SR and channel diameter subsequent to AFM.FindingsThe proposed model exhibits maximum deviation between the model and the measurement of −1.1% for the down-skin SR, −0.2% for the up-skin SR and −0.1% for material removal thickness.Practical implicationsThe results of this study show that the proposed model can avoid expensive iterative tests to determine whether a given channel design leads to the desired SR after smoothing by AFM. Therefore, this model helps to design an AFM-ready channel geometry.Originality/valueIn this paper, a quantitatively validated AFM model was proposed for complex SLM channels with varying orientation angles.

On the role of Tsallis entropy index for velocity modelling in open channels

Following the work on Shannon entropy together with the principle of maximum entropy, Luo and Singh (2010) and Singh and Luo (2011) explored the concept of non-extensive Tsallis entropy for modelling velocity in open channels. Later, the idea was extended by Cui and Singh (2012, 2013) by hypothesizing an accurate cumulative distribution function (CDF). However, these studies estimated the entropy index through a data-fitting procedure and the values of the index were different for different studies. The present study investigates the role of Tsallis entropy index for modelling velocity in open channels using the method of moments, based on conservation of mass and momentum. It is found that the entropy index depends on the normalized mean velocity and the momentum coefficient. In addition to the physical meaning of the index, it is also found that the modified velocity profile significantly improves for both wide and narrow channels, as shown by small predicted velocity errors. The proposed approach may be further employed for other open channel flow problems, such as sediment concentration, and shear stress distribution.

Propagation of tributary dam-break flows through a channel junction

For a channel with a constant discharge, the characteristics of the surge wave entering a junction are obtained from the classical Stoker solution, and then the effect of the junction is analysed by applying the momentum and mass conservation equations. Experimental cases involving different combinations of the tributary lake height and the main channel discharge were tested, and measurements show good agreement with the theoretical solution. The experiments showed that the initial lake height and initial velocity in the main channel influence the surge wave characteristics. The ratio between the Reynolds number in the lake and in the main channel can be used to predict time to peak and peak flow rate. Furthermore, power-law relations for surge wave height and velocity downstream of the junction were developed from the analytical solution.

Multivariate Jeffrey Fluid Flow past a Vertical Plate through Porous Medium

An analysis is suggested to study the impact of Hall currents in Jeffrey fluid which is chemically reactive through a porous medium limited by a semi-infinite vertical permeable plate within the existence of heat generation. An evenly distributed magnetic field turns vertically on the porous surface which absorbs the Jeffrey fluid with a changed suction velocity with time. The analytical expressions are solved by means of three terms harmonic and non-harmonic functions. Statistical calculations are carried out for the point of resultant outcomes which are shown graphically and the impacts of the parameters velocity, temperature and concentration are listed. In addition, the results of skin-friction coefficient (τ), Nusselt number (Nu) and Sherwood number (Sh) are taken in to consideration. It is revealed that the impact of the Hall parameter on the channel velocities and skin friction coefficient is subjected to the estimation of the wall suction parameter.

CFD-modeling of flow in confluence nodes of ventilation units of multi-storey buildings

This paper considers the flow characteristics in ventilation units, which are used in natural ventilation systems of multi-storey residential buildings. Three configurations of ventilation units were considered: standard with straight walls, with a beveled wall and with a guide insert. For each configuration, three sizes of bypass hole at the confluence of flows from the satellite channel and the collection channel were considered. The problem was solved numerically using the CFD Flow3d software package.It was established that for a ventilation unit with a straight wall in the satellite channel, the formation of separation zones that are significant in width and length at the confluence node is typical. The length and width of separation zones affecting the resistance of ventilation unit as a whole increases with the enlarging of the bypass hole size in the collection channel and decreases when using a beveled end wall, that directs the flow upstream of the exhaust air. For the considered geometries of confluence nodes of ventilation units, the relationships between local resistance coefficients and velocity (Reynolds number) in the collection channel are obtained.

Streamwise velocity profile in open-channel flow based on Tsallis relative entropy.

The present study derives the two-dimensional distribution of streamwise flow velocity in open channels using the Tsallis relative entropy, where the probability density function (PDF) based on the principle of maximum entropy (POME) is selected as the prior PDF. Here, we incorporate the moment constraints based on the normalization constraint, hydrodynamic transport of mass, and momentum through a cross section of an open channel for the formulation of the velocity profile. The minimization of the Tsallis relative entropy produces a nonlinear differential equation for velocity, which is solved using a non-perturbation approach along with the Padé approximation technique. We define two new parameters in terms of the Lagrange multipliers and the entropy index for assessing the velocity profile, which are calculated by solving a system of nonlinear equations using an optimization method. For different test cases of the flow in open channels, we consider a selected set of laboratory and river data for validating the proposed model. Besides, a comparison is made between the present model and the existing equation based on the Tsallis entropy. The study concludes that the inclusion of the POME-based prior significantly improves the velocity profile. Overall, the proposed work shows the potential of the Tsallis relative entropy in the context of application to open the channel flow velocity.

Subduction Dynamics and Mantle Pressure: 1. An Analytical Framework Relating Subduction Geometry, Plate Motion, and Asthenospheric Pressure

AbstractRecent work suggests that slab dip may be controlled by differences in dynamic pressure above and below the slab at mid‐asthenospheric depth, motivating exploration of how plate and slab motion are linked to dynamic pressure in the asthenosphere. This paper, the first of two companion papers, presents an analytical method for determining dynamic pressure and velocity in a thin asthenospheric channel, with linear viscosity, consistent with prescribed plate and slab kinematics. Slabs are explicitly incorporated as vertical barriers to asthenospheric flow. Dynamic pressure is expressed as sums of functions with two functional forms, Pedge and Pwall; the former generates discontinuities in velocity (but not pressure) at non‐slab boundaries, and the latter generates discontinuities in pressure (but not velocity) at boundaries with slabs. Application to simple rectangular plate systems demonstrates that asthenospheric velocities within about one trench length of slabs are insensitive to processes on the opposing side of the slab, that dynamic pressure scales linearly with trench length for a given plate aspect ratio and scales approximately linearly with the shortest plate dimension. Although dynamic pressure is quasisymmetrical across convergent plate boundaries that lack slabs, the presence of slabs creates discontinuity and asymmetry in dynamic pressure across subduction zones. When flux of asthenosphere into the lower mantle occurs adjacent to subducting slabs, dynamic pressure is decreased on the side of the slab where down‐flux occurs. This analytical method, applied to systems with multiple arbitrarily shaped plate boundaries, yields excellent results as benchmarked against 3‐D numerical solutions.

Advancing the Velocity Gradient Technique: Using Gradient Amplitudes and Handling Thermal Broadening

Abstract The recent development of the velocity gradient technique allows observers to map magnetic field orientations and magnetization using the direction of velocity gradients. Aside from the directions, amplitudes of velocity gradients also contain valuable information about the underlying properties of magnetohydrodynamic (MHD) turbulence. In this paper, we explore what physical information is contained in the amplitudes of velocity gradients and discuss how this information can be used to diagnose properties of turbulence in both diffuse and self-gravitating interstellar media. We identify the relations between amplitudes of both intensity and velocity centroid gradients and the sonic Mach number M s , and they are consistent with the theory’s predictions. We test the robustness of the method and discuss how to utilize the amplitudes of gradients into self-gravitating media. To extend the velocity gradient technique, we also discuss the usage of amplitude method to position–position–velocity space as a possible way to retrieve the velocity channel maps before the contamination of thermal broadening. We discuss that the velocity gradient technique with these advancements could potentially give a significantly more accurate statistical insight into the properties of magnetized turbulence.

Flow‐induced reconfiguration of aquatic plants, including the impact of leaf sheltering

AbstractMany aquatic plants are flexible and bend in response to current. This reconfiguration can reduce the drag on the plant, both by reducing the frontal area and by creating a more streamlined shape. Previous studies have considered how the buoyancy and rigidity of a plant impact the drag reduction. This study additionally considered how reconfiguration impacts the sheltering between leaves on a plant and how this, in turn, impacts the drag on the plant. The posture and drag of single‐stemmed, leaved plants were studied through a combination of laboratory experiments and theoretical modeling using both plastic Rotala bonsai and live Bacopa caroliniana. The laboratory experiments measured drag and posture on individual plants over a range of channel velocity. The theoretical model calculated plant posture and drag based on a force balance that included buoyancy, the restoring force due to stem stiffness, and leaf drag modified to account for sheltering between leaves. Leaf sheltering was characterized by a sheltering coefficient, Cs, which is a function of the plant posture, leaf angle, leaf spacing, and leaf width. Cs decreased from 1 to a minimum value, Cs0, associated with a fully deflected, horizontal stem posture. Once validated, the model was used to explore a range of leaf configurations, following examples found in real plants. The modeling and experiments revealed conditions for which drag increased with reconfiguration, and also that the drag reached a finite, limiting value for horizontal stem posture. Neither trend has been described in previous reconfiguration models.

Turbulence and Bed Load Transport in Channels With Randomly Distributed Emergent Patches of Model Vegetation

AbstractLaboratory experiments explored the impact of vegetation patchiness on channel‐averaged turbulence and sediment transport. Stems were clustered into 16 randomly distributed circular patches of decreasing diameter. For the same channel velocity, the sediment transport increased with total stem number but decreased as stems were clustered into smaller patch diameters, occupying a smaller fraction of the bed area. The channel‐averaged turbulence, which also declined with increased clustering, was shown to be a good predictor for sediment transport at the channel scale. Previous models for uniform vegetation were adapted to predict both the channel‐averaged turbulence and sediment transport as a function of the total number of stems and degree of clustering, represented by the fraction of bed covered by patches. This provides a way for numerical modelers to represent the impact of subgrid‐scale vegetation patchiness on sediment transport.

Producing synthetic maps of dust polarization using a velocity channel gradient technique

ABSTRACT In modern cosmology, many efforts have been made to detect the primordial B-mode of cosmic microwave background polarization from gravitational waves generated during inflation. Considering the foreground dust contamination of microwave polarization maps, it is essential to obtain a precise prediction for polarization in dust emission. In this work, we show a new method to produce synthetic maps of dust polarization in the magnetized turbulent interstellar medium from more abundant high-resolution H i data. By using the velocity channel gradient technique, we are able to predict both the direction and degree of dust polarization by investigating spectroscopic H i information in position–position–velocity space. We apply our approach to the Galactic Arecibo L-band Feed Array H i data, and find a good correspondence between synthesized maps and Planck’s polarization measurements at 353 GHz.

RESEARCH OF IMPACT OF THE VERTICAL FLOW ON THE DOWNSTREAM OF THE PIPE

The results of an experimental study of the factors influencing the velocity distribution in the trapezoidal outlet channel along a vertical shaft combined with a horizontal pipe are presented. Two schemes of construction were considered separately: scheme 1 with the location of the vertical shaft at a distance of less than 2/3 of the pipe length; schema 2 with the location of the shaft at the end of the main pipe. The model was studied the distribution of averaged, surface and bottom velocities in the outlet channel. The study confirmed the theoretical conclusion and found that the nature of the velocity distribution, both vertically and plan are functions of water depth in the channel and velocity in the outlet section of the pipe and are independent from the flow ratio in the horizontal pipe and the vertical shaft, except of the case placing the vertical tube on the end of the horizontal pipe.As a result of the mathematical processing of the experimental data, empirical equations of the lengths of the transformed sections of the bottom and surface averaged flow velocities were developed for different values of the dimensionless flow parameter depending on the water level of the outlet channel.

Modeling the longitudinal profiles of streamwise velocity in an open channel with a model patch of vegetation

This paper proposes a model for predicting the longitudinal profiles of streamwise velocities in an open channel with a model patch of vegetation. The governing equation was derived from the momentum equation and flow continuity equation. The model can estimate the longitudinal profiles of velocities both inside and outside a vegetation patch. Laboratory experiments indicate that the longitudinal profiles of velocities inside a patch and in the adjacent bare channel have the same adjustment distance in the longitudinal direction, but the profiles have different trends because the vegetation drag drives the flow from the patch to the adjacent bare channel. The model considers different dimensionless parameters in two flow adjustment regions upstream of and inside the patch. Sixteen sets of experimental data from different sources are used to verify the model. The model is capable of modeling the longitudinal profiles of velocities inside and outside patches of cylinders or cylinder-like plants. Compared to a previous model, the current model improves the modeling accuracy of longitudinal profiles of velocities.

High-energy proton irradiation effects on GaN hybrid-drain-embedded gate injection transistors

The characterization of commercial-grade power transistors upon high levels of particle irradiation is required to enable radiation tolerant LED power supplies for the new luminaires of CERN accelerator tunnels, which represent a harsh environment for semiconductor devices. This work describes the effects of 24 GeV/c proton irradiation on commercial GaN hybrid-drain-embedded gate injection transistors (HD-GITs) after a fluence of 5.9 × 1014 p/cm2. Measurements of drain leakage current, threshold voltage and Ids − Vds curves show that only a minor variation occurs in the electrical properties of GaN HD-GITs after the considered fluence; for example, an average increase of ≈11–13 mV is found in the threshold voltage upon irradiation. We also put forward a physical explanation of the observed degradation caused by proton irradiation; in particular, the electron drift velocity in the 2DEG channel at high electric fields appears to decrease due to a radiation-induced increase in phonon relaxation rate. Finally, an AC/DC LED power supply with current control using GaN HD-GITs is proposed for the new luminaires of CERN tunnels, meeting the requirements in terms of radiation hardness and light quality.

Resistance and wave characterizations of inland vessels in the fully-confined waterway

The resistance and ship-generated waves of two inland vessels in the fully-confined waterway are investigated based on numerical simulations. The simulation results are validated using towing tank experiments. The influences of the channel dimension, water depth, ship draught and velocity are studied. Specially, the ship resistance is characterized as a function of the blockage ratio and the theory of the linear ship wakes is corrected using the ship draught. These results are expected to predict the ship hydrodynamics in the restricted waterway and reveal the acting mechanism of the confinement effect on a certain level.

Flow field analyses of a porous membrane-separated, double-layered microfluidic chip for cell co-culture

Organs-on-chips composed of a porous membrane-separated, double-layered channels are used widely in elucidating the effects of cell co-culture and flow shear on biological functions. While the diversity of channel geometry and membrane permeability is applied, their quantitative correlation with flow features is still unclear. Immersed boundary methods (IBM) simulations and theoretical modelling were performed in this study. Numerical simulations showed that channel length, height and membrane permeability jointly regulated the flow features of flux, penetration velocity and wall shear stress (WSS). Increase of channel length, lower channel height or membrane permeability monotonically reduced the flow flux, velocity and WSS in upper channel before reaching a plateau. While the flow flux in lower channel monotonically increased with the increase of each factor, the WSS surprisingly exhibited a biphasic pattern with first increase and then decrease with increase of lower channel height. Moreover, the transition threshold of maximum WSS was sensitive to the channel length and membrane permeability. Theoretical modeling, integrating the transmembrane pressure difference and inlet flow flux with chip geometry and membrane permeability, was in good agreement with IBM simulations. These analyses provided theoretical bases for optimizing flow-specified chip design and evaluating flow microenvironments of in vivo tissue.

Correlating Interlayer Spacing and Separation Capability of Graphene Oxide Membranes in Organic Solvents.

Membranes synthesized by stacking two-dimensional graphene oxide (GO) hold great promise for applications in organic solvent nanofiltration. However, the performance of a layer-stacked GO membrane in organic solvent nanofiltration can be significantly affected by its swelling and interlayer spacing, which have not been systematically characterized. In this study, the interlayer spacing of the layer-stacked GO membrane in different organic solvents was experimentally characterized by liquid-phase ellipsometry. To understand the swelling mechanism, the solubility parameters of GO were experimentally determined and used to mathematically predict the Hansen solubility distance between GO and solvents, which is found to be a good predictor for GO swelling and interlayer spacing. Solvents with a small solubility distance (e.g., dimethylformamide, N-methyl-2-pyrrolidone) tend to cause significant GO swelling, resulting in an interlayer spacing of up to 2.7 nm. Solvents with a solubility distance larger than 9.5 (e.g., ethanol, acetone, hexane, and toluene) only cause minor swelling and are thus able to maintain an interlayer spacing of around 1 nm. Correspondingly, GO membranes in solvents with a large solubility distance exhibit good separation performance, for example, rejection of more than 90% of the small organic dye molecules (e.g., rhodamine B and methylene blue) in ethanol and acetone. Additionally, solvents with a large solubility distance result in a high slip velocity in GO channels and thus high solvent flux through the GO membrane. In summary, the GO membrane performs better in solvents that are unlike GO, i.e., solvents with large solubility distance.

Turbulence and Particle Deposition Under Steady Flow Along a Submerged Seagrass Meadow

AbstractSeagrass meadows can retain fine particles, improving water clarity and promoting carbon sequestration. Laboratory experiments were conducted to investigate the influence of velocity and meadow density on the retention of fine particles within a meadow. Vertical profiles of velocity and turbulent kinetic energy (TKE) were measured along a model meadow. The net deposition was measured using microscope slides positioned inside and outside the meadow. The deposition was correlated with the evolution of velocity along the meadow. At the leading edge, the net deposition decreased over a distance Lr, relative to the bare bed, which was associated with a region of vertical updraft and elevated TKE. Net deposition increased with the distance from the leading edge, associated with a decrease in vertical velocity and TKE. In some cases, a distinct peak in the deposition was observed at distance Lp from the leading edge, associated with a minimum in TKE. Both Lr and Lp decreased with increasing meadow density. Deposition in the fully developed region of the meadow decreased with decreasing stem density and increasing channel velocity, and for the lowest stem density and highest channel velocity the deposition in the meadow was less than that in the bare channel. Diminished deposition was linked to resuspension driven by stem‐generated turbulence. A model for canopy‐averaged TKE was validated and used to explore the range of field conditions for which TKE within a meadow would be reduced, relative to the bare bed, which would support the accumulation of fine organic material within the meadow.

Forecasting shear stress parameters in rectangular channels using new soft computing methods.

Shear stress comprises basic information for predicting the average depth velocity and discharge in channels. With knowledge of the percentage of shear force carried by walls (%SFw) it is possible to more accurately estimate shear stress values. The %SFw, non-dimension wall shear stress () and non-dimension bed shear stress () in smooth rectangular channels were predicted by a three methods, the Bayesian Regularized Neural Network (BRNN), the Radial Basis Function (RBF), and the Modified Structure-Radial Basis Function (MS-RBF). For this aim, eight data series of research experimental results in smooth rectangular channels were used. The results of the new method of MS-RBF were compared with those of a simple RBF and BRNN methods and the best model was selected for modeling each predicted parameters. The MS-RBF model with RMSE of 3.073, 0.0366 and 0.0354 for %SFw, and respectively, demonstrated better performance than those of the RBF and BRNN models. The results of MS-RBF model were compared with three other proposed equations by researchers for trapezoidal channels and rectangular ducts. The results showed that the MS-RBF model performance in estimating %SFw, and is superior than those of presented equations by researchers.

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.