Detailed Velocity Profiles Research Articles

Three-dimensional CFD modeling for hollow fiber gas separation membrane modules based on a dual porous media model

Mathematical modeling is crucial to optimizing the design of the hollow fiber membrane (HFM) module. A Computational Fluid Dynamics (CFD) model enables efficient three-dimensional (3D) simulations of HFM modules, which integrates a dual porous media approach, significantly reducing computational costs. Validation against alternative simulations and experimental data confirms its prediction capability (<7% deviation). Comparative analyses demonstrate the superior reliability of the 3D approach over one-dimensional simulations. Detailed velocity, pressure, and concentration profiles for the shell and tube sides reveal optimization opportunities such as dead zones within the module. Aerometric studies show significant pressure drops (>30%) for smaller fiber diameters (<100μm) on the permeate side. The model's adaptability suggests broader applications in membrane gas separation processes with modifications. This research highlights the efficacy of CFD modeling in enhancing the design and optimization of HFM modules, highlighting the cost savings of the dual porous media approximation.

Investigation of fluid flow during flow boiling inside a horizontal rectangular channel with single-sided heating using particle image velocimetry

Subcooled flow boiling is a highly efficient cooling systems for thermal management systems. This study explores the intricate dynamics of subcooled flow boiling within a horizontal channel, investigating the impact of vapor generation on liquid-phase velocity using Particle Image Velocimetry (PIV) and advanced image processing techniques. Four mass flow rates ranging from 5–20 g/s with subcooled inlet conditions are investigated in a rectangular channel with single-sided heating. Three regions of interest along the heated channel are investigated for instantaneous PIV analysis. The PIV system captures detailed velocity profiles, illustrating the impact of varying mass flow rates and heat flux levels on flow behavior. Vapor masking techniques are introduced to enhance the precision of PIV data by mitigating interference from the vapor phase. Results demonstrate the influence of vapor bubbles on flow resistance, revealing non-uniform velocity distributions and turbulence near the liquid–vapor interface. The study emphasizes the critical role of inertia and buoyancy forces in shaping the velocity profiles. Moreover, the investigation sheds light on the effects of flow rates on the interfacial behaviors, hinting at a transition point between 10 and 15 g/s. In summary, this research contributes valuable insights into the nuanced dynamics of flow boiling, laying the foundation for future studies on turbulence, heat transfer, and phase-change phenomena in two-phase thermal management systems.

A lower crust shear zone facilitates delamination and continental subduction under the Apennines

Physical properties and structure of the lithosphere are the first step to constrain the evolution of mountain belts. Here we show detailed shear wave velocity profiles of the lithosphere in the Apennines that clarify a controversial aspect of continental subduction: the intricate mechanism of crust delamination from the downgoing plate. From the analysis of complete and dense teleseismic Receiver Function data set, we find that the delamination of the continental lithosphere is favored by the development of a low seismic shear wave velocity zone in the middle-lower crust. We observe a double Moho below the external portions of the present mountain range, suggesting the progressive formation of the shallow interface. The delamination edge is located in the forearc, far eastward than expected, implying that the re-equilibration of the thermal unbalance, generated by the mantle substitution, may last 10-7 Myr.

In-situ material damping measurements using the crosshole seismic method

Crosshole seismic testing is commonly used to determine detailed and reliable wave velocity profiles. Material damping measurements can also be performed in crosshole seismic testing, but these measurements require a window function to maintain similar amplitude shapes over the frequency range of interest for the calculation. In-situ seismic testing, including downhole and seismic cone penetration testing (SCPT), also requires a window function for the material damping calculations. However, the length of the window function has the largest influence on the material damping calculation. Therefore, the half-power bandwidth method is introduced to determine the material damping ratio without the window function in crosshole testing by replicating the unconfined, free-free, resonant column (Fr-Fr) test. To demonstrate the influence in the length of the window function, the first cycle of the signal is used in the material damping calculation. The half- power bandwidth method is verified using synthetic signals and field data. Two sets of crosshole and downhole tests were performed, one at a backfill test pad and the second at a Hornsby Bend research site operated by the University of Texas at Austin. The in-situ material damping ratio calculated from these two sets of crosshole tests using the half-power bandwidth method are compare with the Spectral Ratio Slope (SRS) method applied to the downhole testing at these sites. The material damping calculated from the half-power bandwidth method using the full signal results in a reliable and precise damping value compared to the SRS method applied to the downhole data.

Validation of Pronghorn Pressure Drop Correlations Against Pebble Bed Experiments

The verification and validation of Pronghorn is imperative for predicting the fluid velocity, pressure, and temperature in advanced reactors, specifically high-temperature gas-cooled reactors. Pronghorn is a coarse-mesh, intermediate-fidelity, multidimensional thermal-hydraulic code developed by Idaho National Laboratory. The Pronghorn incompressible Navier-Stokes equations are validated by using the pressure drop measurements and axial velocity averaged from the particle image velocimetry data obtained at the engineering-scale pebble bed facility at Texas A&M University. Pronghorn and STAR-CCM+ porous media models using the Handley, Kerntechnischer Ausschuss, and Carman correlations comparably estimate the pressure drop better than other functions with a maximum 3.34% average relative difference compared to the experimental measurements. The precise average pebble bed porosity estimation has a large impact on the pressure drop. The implementation of the volume-averaged porosity in several sectors, with each sector’s thickness larger than the representative elementary length, has the potential to improve pressure drop modeling or provide more detailed velocity profiles in nuclear reactors with high aspect ratios. The wall effects can be considered using this approach, applying the relatively higher volume-averaged porosity near walls. In addition, the pressure gradients and volume- or surface-averaged axial velocities from the realizable two-layer and shear stress transport models are in good agreement with the porous media simulations and particle image velocimetry data.

Velocity Distribution in Channels with Submerged Vegetation

An experimental study is presented for investigating the effect of vegetation element geometry on the velocity distribution within and above the canopy. Three types of artificial submerged vegetation elements with common parts and different foliage are used, with two density patterns each. Detailed velocity profiles are obtained and compared at nine locations in the vegetation array. The velocity distribution above the canopy is found to closely follow a logarithmic law and its parameters, namely the shear velocity u*, zero-plane displacement height d and roughness height z0 are determined. These depend on the vegetation density and type of element, but also on the particular position in the array. A unified velocity distribution over the water column is found appropriate for the case of stems with no foliage and also for the cases of compound elements at certain positions in the vegetation array but not at those where locally minimum velocity values occur at the foliage level. Moreover, the logarithmic profile obtained for the upper layer is seen to also fit well the measured velocities to a certain extent below the top of the canopy.

How well can we predict earthquake site response so far? Machine learning vs physics-based modeling

In site-specific site-response assessments, observation-based site-specific approaches requiring a target–reference recording pair or a regional recording network cannot be implemented at many sites of interest. Thus, various estimation techniques have to be used. How effective are these techniques in predicting site-specific site responses (average over many earthquakes)? To address this question, we conduct a systematic comparison using a large data set which consists of detailed site metadata and Fourier outcrop linear site responses based on observations at 1725 K-NET and KiK-net sites. We first develop machine learning (i.e. random forest ( RF)) amplification models on a training data set (1580 sites). Then we test and compare their predictive powers at 145 independent testing sites with that of the one-dimensional (1D) ground response analysis (GRA). The standard deviation of residuals between observations and predictions, that is, between-site (site-to-site or inter-site) variability, is used as the benchmark. Results show that the machine learning model using a few predictor variables, surface roughness, peak frequency fP, HV, VS30, and depth Z2.5 achieves better performance than the physics-based modeling (GRA) using detailed 1D velocity profiles. This implies that machine learning can be more effective in using existing site information than 1D GRA which is inflicted by a high level of parametric and modeling uncertainties. This finding warrants the further exploration of machine learning in site effect characterization, especially on model transferability across different regions.

Velocity Structure and Cu-Au Mineralization of the Duobaoshan Ore District, NE China: Constrained by First-Arrival Seismic Tomography

The genesis of deeply buried deposits in the Duobaoshan ore district, the largest porphyry-related Cu-Mo-Au ore field in northeastern China, is not well understood and their exploration is lacking because the fine velocity structure of this region is not comprehensively understood. Herein, first-arrival seismic travel times were picked along a deep seismic reflection profile and inverted using the tomographic method to obtain a detailed velocity profile of the upper 2900 m of the crust beneath this region. The profile showed that the velocity varied from 1900 to 6100 m/s and that the crust was subdivided into five parts by two low-velocity (2500–4000 m/s) blocks. Based on previous studies, the boundaries between the high-speed and low-speed bodies were interpreted as hidden fractures, and the 5000–6100 m/s parts were interpreted as concealed granite bodies in these sections. Porphyry copper deposits in the Duobaoshan ore district were related to the occulted granite bodies, and epithermal Au deposits were associated with the occulted fracture zones. Comprehensive evaluation of hydrothermal activity, regional magnetic anomalies, and deposit distribution indicated that the hidden fractures served as channels for ore-related magmas. Combining previous research on the Duobaoshan ore district with our results of the high-velocity interface, we infer that the prospecting range of the Tongshan deposit is below the depth of 1000 m.

Study of the film boiling heat transfer and two-phase flow interface behavior using image processing

In the current study, based on a small-scale quench test facility, the two-phase flow interface behavior during quench transients is visualized and analyzed utilizing an image processing framework. The high-fidelity experimental results obtained for two-phase flow in the current framework can support various studies both in the time domain and in the frequency domain. In particular, visualization of the data obtained from different heating surfaces under different test conditions are used to perform a full-scale transient 2-D vapor film reconstruction. The liquid-vapor interface variations in various heat transfer regimes as well as at the initial film breakup point can be directly obtained through the processed data. Moreover, the temporal variation of the interfacial wave frequency approaching quench is investigated in detail. Based on the high-resolution data obtained for the liquid-vapor interface, the detailed phase velocity and temperature profiles are obtained through theoretic analysis, based on which the film boiling heat transfer coefficient (HTC) can be determined. In addition, an improved film boiling HTC model is developed considering the effects of wall superheat, liquid subcooling temperature, vapor film thickness as well as fluid properties. The model is found to predict film boiling HTC well within 15% error.

Computational Fluid Dynamic Analysis of Flow around Mangrove roots.

The objective of this paper is to study the flow patterns around mangrove roots to understand its significance in coastal risk reduction. A computational model of two-dimensional Pneumatophores mangrove roots is developed, and flow is simulated using ANSYS software with a predefined mathematical model and boundary conditions. Computational fluid dynamic analysis of a two-dimensional, viscous, incompressible, turbulent flow under steady and unsteady boundary condition is performed using the Finite volume method. Detailed velocity profiles, residual plots, pressure distributions, vectors of the velocity magnitude and pressure and velocity at different positions around the mangrove roots are presented to visualize the importance of mangroves in reducing the wave velocity. The simulation outcome confirms that the mangrove roots of mangrove species can reduce the initial velocity of water flow. The flow patterns and flow structures around the root in the mangrove forest establishes precious data in increasing the effectiveness of current breakwater model.

Using horizontal-to-vertical spectral ratios to construct shear-wave velocity profiles

Abstract. For seismic hazard assessment and earthquake hypocentre localization, detailed shear-wave velocity profiles are an important input parameter. Here, we present a method to construct a shear-wave velocity profiles for a deep unconsolidated sedimentary layer by using strong teleseismic phases and the ambient noise field. Gas extraction in the Groningen field, in the northern part of the Netherlands, is causing low-magnitude, induced seismic events. This region forms an excellent case study due to the presence of a permanent borehole network and detailed subsurface knowledge. Instead of conventional horizontal-to-vertical spectral ratios (H∕V ratios) from amplitude spectra, we calculate power spectral densities and use those as input for H∕V calculations. The strong teleseisms provide resonance recordings at low frequencies, where the seismic noise field is too weak to be recorded well with the employed geophones and accelerometers. The H∕V ratios of the ambient noise field are compared with several forward modelling approaches to quality check the teleseism-based shear-wave velocity profiles. Using the well-constrained depth of the sedimentary basin, we invert the H∕V ratios for velocity profiles. A close relationship is observed between the H∕V spectral ratios from the ambient noise field, shear-wave resonance frequencies and Rayleigh-wave ellipticity. By processing only five teleseismic events, we are able to derive shear-wave velocities for the deeper sedimentary sequence with a 7 % bias in comparison with the existing detailed velocity model for the Cenozoic sediments overlying the Groningen gas field. Furthermore, a relation between resonance frequency and unconsolidated sediment thickness is derived, to be used in other areas in the Netherlands, where detailed depth maps are not available.

Numerical investigation on erosion of hydrogen stratification by steam jet within a local compartment

During hypothetical severe accidents in nuclear power plants, a large amount of hydrogen is generated rapidly as a result of zirconium-water reaction and released into local compartments. Deflagration or detonation risk is probably caused by the uneven hydrogen distribution. Generally, buoyancy drives light combustible gas up to establish gas stratification. On the other hand, stratification may be destroyed by convection flow from steam injection due to coolant's discharge from the primary loop. The mechanism of erosion of stratification can be divided into buoyancy dominated and momentum dominated regimes, the priority of which depends on a nondimensional parameter, named of interaction Froude number. However, jet velocity and the diameter on the interface between steam and stratification are difficult to measure in experiments. Therefore, CFD method is adopted to capture a detailed velocity profile to solve this problem. In this article, a CFD model of single local compartment facility is built and helium distribution behavior within the local compartment is fully investigated, as a substitute of hydrogen, which is usually used in experiments. Prior to determining the interaction Froude number, four flow models, including laminar flow model, algebraic model, k-ε turbulence model and shear stress transport (SST) k-ω model are evaluated under three typical experimental stages, including light gas injection, the formation of stratification, and the erosion of stratification. Results show that SST k-ω model can predict much better under these specific conditions in the small-scaled configuration, compared to the experimental results. Next, with the setup of a helium stratification structure with homogeneous layer and gradient layer, the interaction between steam and gradient layer is analyzed in detail. The mechanisms of erosion of stratification can be divided into complete penetration, destruction from the bottom level to the top and soft dissolution without penetration, corresponding to the interaction Froude numbers of being greater than 1, close to 1, and far less than 1. The simulation results are consistent with relevant literature findings. The present work can help studying the complex hydrogen distribution process in local compartment and provide data for evaluation of postinerting strategy in severe accident management.

2D simulation of a microfluidic biosensor for CRP detection into a rotating micro-channel

Previously, pumping systems using centrifugal force has been regarded as an attractive control method for fluid flow interior microchannel. In this work, we propose a novel design of a biosensor for complex reactive protein detection in two-dimensional rotating microchannel using the finite element method. We have first developed the physical modeling of the centrifugal force driven, and detailed velocity profile and expended the pressure distribution. Several crucial factors that influence the equilibrium binding time are discussed, including the bulk analyte concentration and the biosensor length. The obtained analytical results reveal that the binding reaction is largely enhanced with the increase of the angular velocity. Hence, an appropriate choice of the angular velocity may enhance the microfluidic biosensor performance and reduce considerably the time response. This work can open new opportunity for further investigation in microflow injection experimental studies.

Experimental Investigations of Interactions between Sand Wave Movements, Flow Structure, and Individual Aquatic Plants in Natural Rivers: A Case Study of Potamogeton Pectinatus L.

Long-duration measurements were performed in two sandy bed rivers, and three-dimensional (3D) flow velocity and bottom elevation changes were measured in a vegetated area and in a clear region of a river. Detailed flow velocity profiles downstream and upstream of a single specimen of Potamogeton pectinatus L. were obtained and the bed morphology was assessed. Potamogeton plants gathered from each river were subjected to tensile and bending tests. The results show that the existence of the plants was influenced by both bottom and flow conditions, as the plants were located where water velocity was lower by 12% to 16% in comparison to clear region. The characteristics of the flow and sand forms depended on the cross-sectional arrangement of the river, e.g., dunes were approximately four times higher in the middle of the river than in vegetated regions near the bank. Furthermore, the studied hydrophytes were too sparse to affect water flow and had no discernible impact on the sand forms’ movements. The turbulent kinetic energy downstream of a single plant was reduced by approximately 25%. Additionally, the plants’ biomechanical characteristics and morphology were found to have adjusted to match the river conditions.

Mixing processes at an ice-covered river confluence

River confluences are characterized by a complex mixing zone with three-dimensional turbulent structures, which can be affected by the presence of an ice cover during the winter. The objective of this study is to characterize the flow structure in the mixing zone at a medium-size (~ 40 m) river confluence with and without an ice cover. Detailed velocity profiles were collected under the ice along the mixing plane with an Acoustic Doppler Velocimeter. For the ice-free conditions, drone imagery was used to characterize the mixing layer structures for various flow stages. Results indicate that during the ice-free conditions, very large Kelvin-Helmholtz (KH) coherent structures are visible due to turbidity differences, and occupy up to 50% of the width of the parent channel. During winter, the ice cover affects velocity profiles by moving the highest velocities towards the center of the profiles. Large turbulent structures are visible in both the streamwise and lateral velocity components. The strong correlation between these velocity components indicates that KH vortices are the dominating coherent structures in the mixing zone. A spatio-temporal conceptual model is presented to illustrate the main differences on the three-dimensional flow structure at the river confluence with and without the ice cover.

Computational Analysis of Flow Patterns during Inhalation and Exhalation of Carbon-monoxide

A computational model of human nasal cavity is developed from CT scan using MIMICS software. CFD analysis of flow patterns during inhalation and exhalation of carbon-monoxide is performed using Finite volume method. Detailed velocity profiles, pressure distribution, residual plots and streamline patterns during inhalation and exhalation are presented. The implications for olfaction are visualized.

Computational Fluid Dynamics Simulations of Gas-Phase Radial Dispersion in Fixed Beds with Wall Effects

The effective medium approach to radial fixed bed dispersion models, in which radial dispersion of mass is superimposed on axial plug flow, is based on a constant effective dispersion coefficient, DT. For packed beds of a small tube-to-particle diameter ratio (N), the experimentally-observed decrease in this parameter near the tube wall is accounted for by a lumped resistance located at the tube wall, the wall mass transfer coefficient km. This work presents validated computational fluid dynamics (CFD) simulations to obtain detailed radial velocity and concentration profiles for eight different computer-generated packed tubes of spheres in the range 5.04 ≤ N ≤ 9.3 and over a range of flow rates 87 ≤ Re ≤ 870 where Re is based on superficial velocity and the particle diameter dp. Initial runs with pure air gave axial velocity profiles vz(r) averaged over the length of the packing. Then, simulations with the tube wall coated with methane yielded radial concentration profiles. A model with only DT could not describe the radial concentration profiles. The two-parameter model with DT and km agreed better with the bed-center concentration profiles, but not with the sharp decreases in concentration close to the tube wall. A three-parameter model based on classical two-layer mixing length theory, with a wall-function for the decrease in transverse radial convective transport in the near-wall region, showed greatly improved ability to reproduce the near-wall concentration profiles.

On the error of the time–pulse method of measuring air consumption in mines

The derivation of a formula for the time during which a sound signal propagates between two given points A and B in a stationary gas flow is considered. It is shown that the gas flow changes the signal reception time by a quantity proportional to the consumption, regardless of the detailed velocity profile. The difference between the reception time of signals from point B to the point A and vice versa is proportional to air consumption with high accuracy. It is shown that the relative error of the obtained formula does not exceed the squared maximum Mach number in the gas flow. This allows measurement of the consumption of gas moving in a mine with an arbitrary stationary subsonic velocity field.

Stokes flow singularity at a corner joining solid and porous walls at arbitrary angle

Motivated by the internal flow geometry of spiral-wound membrane modules with ladder-type spacers, we consider the Stokes flow singularity at a corner that joins porous and solid walls at arbitrary wedge angle varTheta . Seepage flux through the porous wall is coupled to the pressure field by Darcy’s law; slip is described by a variant of the Beavers–Joseph boundary condition. On a macroscopic, outer length scale, the singularity appears like a jump discontinuity in the normal velocity, characterized by a non-integrable 1 / r divergence of the pressure. For arbitrary varTheta , we develop an algebraic criterion to determine the admissible radial exponent(s) in a leading, inner similarity solution—which represents a weaker, integrable singularity in the pressure. A complete map of exponent versus varTheta is provided for 0< varTheta < 2 pi : this has an intricate structure with infinitely many solution branches clustering around varTheta = pi and varTheta = 2 pi . By generalizing the similarity form with a (ln r) term and iterating on the slip and seepage conditions, we can carry the outer and inner power series to arbitrarily high order. Nevertheless, a numerical splice is required in between. For this purpose, we apply an iterative, numerical-asymptotic patching scheme described by Nitsche and Parthasarathi (J Fluid Mech 713:183–215, 2012). Detailed velocity and pressure profiles are calculated for three wedge angles (varTheta = 3pi /4, pi /2, pi /4) and two dimensionless slip lengths (sigma = 20, 40). The general trends for decreasing wedge angle are (i) weakening of the pressure singularity, (ii) increasing magnitude of the radial component of velocity, and (iii) movement of the inner–outer transition farther from the corner. Wedges with varTheta < pi are seen to differ fundamentally from the flat wedge (varTheta = pi ) previously considered by Nitsche and Parthasarathi (2012).

Detailed velocity profiles in close-coupled elbows—Measurements and computational fluid dynamics predictions (RP-1682)

This article presents a systematic study to measure detailed velocity profiles in close-coupled five-gore elbows having nominal diameters of 305 mm (12 in) and turning radii r/D = 1.5, and to, likewise, predict the velocity profiles using computational fluid dynamics. The purpose of the testing was to study the physics of the flow in complex geometries and to provide data that can be used to verify the accuracy of computational fluid dynamics modeling predictions. The close-coupled elbow combinations comprised either a Z-shape or a U-shape configuration. In every instance the duct length separating the center-points of the elbows was systematically varied. Detailed velocity profile measurements were performed at one traverse plane located one duct diameter upstream of the first elbow and at one duct diameter downstream of the second elbow, and at various axial locations in the straight section between the close-coupled elbows. Velocity profiles results are compared to computational fluid dynamics Reynolds Stress Model and Large Eddy Simulation predictions for the effect of separation distance of the elbows in Z-shape duct configurations. Reynolds Stress Model turbulence modeling predicted the velocity trends correctly with a maximum error of 15%. However, Large Eddy Simulation modeling failed to predict the trend and the magnitude of the velocities, thus Large Eddy Simulation approach is not suitable for this type of flow.