Inhomogeneous Flow Research Articles

Digital rock characterization and CO2 flow simulation of high-volatile bituminous coal: An application to carbon geosequestration

The permeability of CO2 sequestration is influenced by the characteristics of pore–fracture structures in coal, yet the flow simulation via the pore network model (PNM) and the controls of topology and morphology on permeability remain to be understood. First, the pore–fracture structure of high-volatile bituminous coal (HVBC) is characterized using micro-computed tomography, and the flow characteristics of single-phase CO2 in the connected pore–fracture network are simulated by the PNM. Second, the surface roughness of the connected pore–fracture is extracted by fractal characterization, and morphological algorithms are applied to accurately present the pore–fracture network structure. Finally, the implications of structural parameters (pore or throat diameter, coordination number, tortuosity, and sphericity) on CO2 transport are discussed, and the mechanism of pore–fracture structure response due to mineral dissolution in CO2 injection is analyzed. The results shows that the HVBC sample provides significant pore–fracture space (porosity of 10.87%) and flow path (connectivity of 66.50%) for hydrogen and carbon storage. CO2 flow simulation results demonstrate anisotropic flow, with higher CO2 permeability observed in the Z-axis direction (0.061 × 10−3 μm2) compared to the X- and Y-axis directions (0.044 × 10−3 μm2 and 0.059 × 10−3 μm2, respectively). Moreover, the fractures perpendicular to the coal bedding plane in the coal seam with a large tectonic dip strongly influence the flow of CO2 injection. Fractal analysis reveals a positive correlation between fractal dimension and porosity, indicating that structures with higher surface roughness are not convenient for CO2 transport. Significant pore angle characteristics (sphericity average of 0.58), high pore–throat connectivity (coordination number average of 4.31), and low capillary resistance (tortuosity average of 1.19) collectively affect the flow of CO2. Overall, the strongly anisotropic pore–fracture structure contributes to the inhomogeneous flow pattern in CO2 geosequestration. Changes in pore–fracture structure resulting from mineral dissolution during the early stage of CO2–coal matrix interaction in the HVBC reservoir can significantly enhance storage potential. This study contributes to the existing understanding of flow characteristics and provides insights for optimizing CO2 injection efficiency in carbon geosequestration.

T1rho and T2rho based myocardial tissue characterisation in small animals at high-field MRI

Abstract Introduction Cardiac tissue characterisation using T2-based MRI promises non-invasive diagnosis or monitoring of inflammatory heart disease, toxic heart damage after chemotherapy and myocardial infarction or post-infarction patients. T2 relaxation is also an indicator for the detection of myocardial oedema or intramyocardial haemorrhage [1]. However, accurate T2 quantification is challenging due to motion, blood flow and field inhomogeneities, especially in high-field MRI [2]. In this work, we present an alternative to T2 imaging that uses spin-locking (SL) to provide a robust measurement of T2ρ relaxation. It is known from relaxation theory that T2ρ has a sensitivity almost identical to T2 [3]. In the small animal study presented here, cardiac T2ρ quantification is tested for the first time using a newly developed pulse sequence and compared with established methods. Methods All measurements were performed on a preclinical 7T MRI. T2 contrast was prepared using a CPMG (Carr-Purcell-Meiboom-Gill) sequence. T2ρ contrast was conventionally generated by a balanced-SL (BSL) preparation [4]. Furthermore, a new approach for T2ρ was developed based on a MLEV sequence (Malcolm-Levitt, [2]). In contrast to [2], all pulse delays were minimised here, producing pure T2ρ contrast (Fig. 1). The new method was first validated in phantom experiments and then tested in three mice with radial image acquisition accelerated for cardio-MRI. Results The results of the phantom study are shown in figure 2. No significant differences were found between BSL and MLEV for T2ρ quantification (mean deviation 0.74%). In vivo, significant artefacts were observed for T2 (Fig. 3), while both T2ρ methods showed improved image quality. For the evaluation of relaxation times in the left ventricle, the mean across all animals was: T2=22.9±2.6ms (R2=0.979), BSL-T2ρ=51.4±5.4ms (R2=0.983) and MLEV-T2ρ=60.0±3.4ms (R2>0.99). Thus, the MLEV-T2ρ method achieves the most robust quantification with a mean R2>0.99 and provides relaxation time maps with diagnostic image quality. Discussion: In the present study, myocardial T2ρ mapping was tested at 7T. While no significant differences between BSL and MLEV appeared in phantom experiments, significant difference was found in vivo. Here, only the MLEV technique could achieve robust quantification. One reason for the improved performance is the continuous refocusing and minimisation of free dephasing of the transverse magnetisation. The results also show that MLEV-T2ρ has improved image quality and more robust quantification compared to CPMG-T2. Conclusion Cardiac T2ρ quantification is a robust alternative to established T2 imaging and can be applied under high-field conditions. A combined measurement of T1ρ and T2ρ relaxation time could be used for native detection of myocardial fibrosis and oedema.Figure 1)Comparison of image qualityFigure 2)Results in a knockout model

Study of plane strain compression of composite sheets

In the plane strain compression of multi-layers metal, each layer of metal shows a different degree of deformation due to the differences in material properties. Also, the deformation in different positions of a metal layer is always inhomogeneous. In this study, the effects of material ratios, friction between the metal layers and the amount of compression on the deformation behaviors of a bi-layer metal strip under plane strain compression are investigated. 2D plane strain finite element simulation models of AISI-1008/AL6061-T6 bi-layer metal strips are used. The results indicate that the strips show different deformation behaviors under different conditions, and non-smooth interfaces caused by the inhomogeneous material flow during the deformation process are detected in most cases.

Minimizing movements for anisotropic and inhomogeneous mean curvature flows

AbstractIn this paper we address anisotropic and inhomogeneous mean curvature flows with forcing and mobility, and show that the minimizing movements scheme converges to level set/viscosity solutions and to distributional solutions à la Luckhaus–Sturzenhecker to such flows, the latter result holding in low dimension and conditionally to the convergence of the energies. By doing so we generalize recent works concerning the evolution by mean curvature by removing the hypothesis of translation invariance, which in the classical theory allows one to simplify many arguments.

Solving the Hydrodynamical System of Equations of Inhomogeneous Fluid Flows with Thermal Diffusion: A Review

The present review analyzes classes of exact solutions for the convection and thermal diffusion equations in the Boussinesq approximation. The exact integration of the Oberbeck–Boussinesq equations for convection and thermal diffusion is more difficult than for the Navier–Stokes equations. It has been shown that the exact integration of the thermal diffusion equations is carried out in the Lin–Sidorov–Aristov class. This class of exact solutions is a generalization of the Ostroumov–Birikh family of exact solutions. The use of the class of exact solutions by Lin–Sidorov–Aristov makes it possible to take into account not only the inhomogeneity of the pressure field, the temperature field and the concentration field, but also the inhomogeneous velocity field. The present review shows that there is a class of exact solutions for describing the flows of incompressible fluids, taking into account the Soret and Dufour cross effects. Accurate solutions are important for modeling and simulating natural, technical and technological processes. They make it possible to find new physical mechanisms of momentum transfer for the design of new types of equipment.

Steady and Unsteady Flow Characteristics inside Short Jet Self-Priming Pump

Due to their great efficiency and minimal loss, self-priming jet pumps are frequently employed in a variety of sectors for sustainable development. A short jet self-priming pump’s steady and unsteady flow characteristics are investigated numerically in this study using a standard k-ε turbulence model. The precision and dependability of the numerical calculations used in this work are demonstrated by the less than 2% difference between the pump performance data from the numerical calculation and the external characteristics test results for each flow condition. It was found that due to the perpendicularity of the nozzle axis to the impeller axis, the high-flow velocity zone in the nozzle gradually deviates to the side away from the impeller under high-flow conditions. Backflow is generated on the side close to the impeller, where eccentric vortices are created. As time progresses, the asymmetry of the low-pressure zone within the impeller becomes more pronounced under high-flow conditions, and the fluid is unable to form a stable vortex structure at a specific location. This is an important cause of impeller vibration and noise. The nonlinear vibration at the impeller inlet is less periodic, while the increase in flow rate can make the nonlinear vibration generated within the impeller more regular and stable. This reflects the fact that the fluid flow at small flow rates is more likely to be affected by the blade configuration and the shape of the flow channel, which leads to fluid instability and discontinuity. For various flow rates, the main frequency of the pressure pulsation is higher at the impeller intake (W1) than it is in the impeller channel (W2~7). Additionally, the pressure pulsation is more frequent before 10 times the rotational frequency, with no significant regularity. This suggests that the impeller and injector rear chamber dynamic and static interference impacts may have some bearing on the pressure pulsation. The pressure pulsation coefficients (W2~7) in the impeller at different flow rates show an exponentially decreasing trend with the increase of multiples of five in the rotation frequency. The equations for the relationship between CP and 5NF were obtained, respectively: CP-Q1 = 0.07044 × exp(−0.2372NF), CP-Q3 = 0.06776 × exp(−0.2564 NF), CP-Q5 = 0.07005 × exp(−0.2884 NF). The findings of this study contribute to understanding the flow inhomogeneities inside the pump as well as the analysis of the internal pump vibration, enhancing the jet pump’s efficiency and lifespan.

Analysis of the inhomogeneous LPG-air flow field in a tube containing mixed obstructions

Based on numerical simulation, this paper further investigates the flow field structure near the obstacle during the premixed gas deflagration. In the deflagration flow field, the pressure gradient variation and vortex structure intensity in the upper surface region of the obstacle are larger, indicating that the pressure gradient has a stronger effect on the vortex structure. The changes in density gradients and pressure gradients induced by the combined rectangular, flat barrier configuration will be more pronounced than in the model with only flat barriers. This change in turn acts back on the combustion field, which in turn has a strong perturbative effect on the flame.

Numerical investigation on the effects of inhomogeneous gas diffusion layer and impact of interfacial contact resistance on the performance of polymer electrolyte fuel cells

In this study, a three-dimensional single channel is numerically modeled to simulate the polymer electrolyte fuel cell (PEFC) with a homogeneous and inhomogeneous gas diffusion layer (GDL). The influence of interfacial contact resistance (ICR) between GDL and current collector ribs (GDL|CC) is also studied. In the present study, GDL is considered as a single component (homogeneous) in one case and inhomogeneous with varying electrical and flow properties to illustrate the inhomogeneity in another case. The inhomogeneity in GDL is primarily caused by localized deformation due to non-uniform contact pressure during fuel cell assemblies. The consideration of ICR is observed to have a significant effect on both the ohmic and mass transport regions of the polarization curve. Inhomogeneous GDL with ICR, considered close to a practical scenario, shows a ∼7% drop in performance evaluation at 0.3V. The study reveals increased consumption of reactants at higher current loads when ICR is assumed negligible. This study examines the effects of homogeneous GDL, inhomogeneous GDL, and the impact of ICR on the distributions of reactant concentration, water concentration, temperature, current density, and polarization curve in PEFC. This study presents the practical aspects of PEFC considering inhomogeneous GDL electrical and flow properties.

Unsteady numerical investigations of the effect of guide vane openings on the hydrodynamic characteristics under stall conditions in a pump-turbine pump mode

The stall is extremely prone to surge of hydraulic loss, excessive pressure fluctuation and radial force of the pump-turbine in pump mode. These can pose a great threat to the safety operation of the unit. Current research focuses more on the manifestations and propagation mechanisms of the stall, which has limitations and effective methods for passive stall suppression cannot be directly identified. In this paper, unsteady simulations based on the SST-SAS turbulence model are conducted to discuss the effects of guide vane openings on the hydrodynamic characteristics under stall conditions of the pump-turbine from the perspectives of flow pattern, energy loss, pressure fluctuation and radial force. Firstly, the performance test results show that the positive slope of the flow-head curves is the largest at small guide vane openings and smallest at optimal guide vane openings. Then, energy loss analysis based on the energy balance equation indicates that the energy loss in the stay vane is most influenced by guide vane openings, with maximum turbulent kinetic energy production at large guide vane openings. Furthermore, the analysis of the stall characteristics in the impeller illustrates that at large guide vane openings, the axial meridional velocity in the impeller is negative under deep stall conditions, and the flow separation and vortex induce a great local pressure drop in the suction surface of impeller blades near the shroud. Subsequently, the stall characteristics analysis in the diffuser reveals that large-scale vortices in the vaneless regions and stay vane channels result in more severe flow blockage and higher energy loss at large guide vane openings. As the increased guide vane openings, the Rotor-stator interaction effect is weakened by the unstable flow pattern in the diffuser, and the low frequency and near blade frequency signals gradually become the dominant frequencies in the diffuser. Finally, the simulation results in the volute show that the unstable flow pattern in the diffuser provides poor inlet conditions for the volute, which significantly increases the energy loss and pressure fluctuations in the volute. The increase of guide vane openings can also make the flow inhomogeneity in the volute worse. The radial forces on the impeller and diffuser under deep stall conditions both increase with increasing guide vane openings due to the unstable flow patterns.

Mitral Annular Disjunction: A Scoping Review.

Mitral annular disjunction (MAD) is the atrial displacement of the mitral valve (MV) hinge point, especially along the posterior mitral leaflet, which leads to inhomogeneous blood flow into the left ventricle, causing chronic fibrotic changes, malignant arrhythmias, and even sudden cardiac arrest. Some studies suggest that MAD is a part of normal heart morphology; however, the origin is still controversial. MAD commonly occurs with MV prolapse and myxomatous degenerative MV disease. In almost 20% of cases, MAD can occur independently as well. The prevalence of MAD in normal hearts varies from 8.6% to 96%, depending on the imaging modality and the cutoff used to define MAD. Transthoracic echocardiography is often the initial screening test, but the low sensitivity of transthoracic echocardiography to identify MAD makes it easy to miss the diagnosis altogether. More advanced imaging, especially cardiac MRI, is the gold standard for diagnosing MAD and risk stratification. MAD is an independent predictor of malignant arrhythmia. Among patients with MAD, risk stratification is based on the age at diagnosis, previous syncopal attacks, premature ventricular contractions, papillary muscle fibrosis, and longitudinal disjunction distance. Most asymptomatic patients are managed conservatively; however, radiofrequency ablation should be considered in patients with high-risk or symptomatic MAD due to the risk of ventricular arrhythmias and sudden cardiac death.

FEATURES OF THE FLOW STRUCTURE IN A RECTANGULAR TRENCH

The study of features of the flow structure in rectangular trenches in a wide range of Reynolds numbers was carried out by means of direct numerical simulation of the flow in the channel and on а plate. Both isothermal and non-isothermal formulations of the problem were considered. Water and air were used as the investigated fluids. The flow structure inside and around the trench in the rectangular channel in the range of Reynolds numbers based on the trench length Re<=9000 was studied in a three-dimensional setting. In the Reynolds numbers range Re>=10000, unsteady flow around a plate with a trench was considered in two-dimensional formulation of the problem. Depending on the Reynolds number, the flow structure in the trench, the influence of geometric parameters on the vortices scales in the trench, their localization and intensity were analyzed. The scale of inhomogeneity of the trench flow in the transverse direction was obtained. The features of non-stationary behavior and interaction of vortex formations with each other and with the external flow at higher Reynolds numbers are considered, development of instability of the vortex structure in the trench and its influence on characteristics of the external flow are shown: from regular oscillations at certain frequency to gradual chaosization of the flow around the trench as the Reynolds number increases, when fractional and multiple frequencies appear. A comparison was made with the vortex structure obtained by other researchers for similar geometric parameters of the trench. The contributions of frictional drag and shape drag to the overall hydraulic drag of the trench, as well as the streamlined surface downstream the trench, are considered. Intensity of heat exchange processes inside the trench, localization of the maximum values of heat fluxes, dependence of heat transfer on the oncoming flow speed were evaluated.

Simulation of Mechanical Response in Machining of Ti-6Al-4V Based on Finite Element Model and Visco-Plastic Self-Consistent Model

The predictions of mechanical responses (stress–strain variations) in the machining of Ti-6Al-4V alloy are important to analyze the deformation conditions of machining to optimize the machining parameters and investigate the generation of a machined surface. The selection of a constitutive model is an essential factor that determines the deformation behavior in the machining simulation model. In this paper, two constitutive models of a modified Johnson–Cook (JC) equation and visco-plastic self-consistent (VPSC) model were used to investigate the stress–strain evolutions in the machining process of Ti-6Al-4V. A finite element (FE) machining model was established, considering the influences of grain refinement and deformation twins, based on a modified JC equation. The VPSC model was fitted based on the macro-strain rate sensitivity of the JC equation. The prediction results of the stress–strain curves of two models were compared, and their validities were further proved. The results show that flow stress hardening and inhomogeneities are caused by multi-scale grain refinement during the machining process of Ti-6Al-4V. Five slip deformation modes and one compressive twinning mode were activated in the VPSC model to be consistent with the macro-deformation behavior predicted with the FE model. The validations show the effectiveness of the modified JC equation, considering microstructural changes and the fitted VPSC model, in predicting dynamic behavior in the machining process of Ti-6Al-4V. The results provide two aspects of macro-deformation and polycrystal plasticity to elucidate the stress variations that occur during the machining of Ti-6Al-4V.

Lagrangian reduction and wave mean flow interaction

How does one derive models of dynamical feedback effects in multiscale, multiphysics systems such as wave mean flow interaction (WMFI)? We shall address this question for hybrid dynamical systems, defined as systems whose motion can be expressed as the composition of two or more Lie-group actions. Hybrid systems abound in fluid dynamics. Examples include: the dynamics of complex fluids such as liquid crystals; wind-driven waves propagating with the currents moving on the sea surface; turbulence modelling in fluids and plasmas; and classical–quantum hydrodynamic models in molecular chemistry. From among these examples, the motivating question here is: How do wind-driven waves produce ocean surface currents?The paper first summarises the geometric mechanics approach for deriving hybrid models of multiscale, multiphysics motions in ideal fluid dynamics. It then illustrates this approach for WMFI in the examples of 3D WKB waves and 2D wave amplitudes governed by the nonlinear Schrödinger (NLS) equation propagating in the frame of motion of an ideal incompressible inhomogeneous Euler fluid flow. The results for these examples tell us that the mean flow in WMFI does not create waves, although it does transport the waves. However, feedback in the opposite direction is possible, since the 3D WKB and 2D NLS wave dynamics discussed here do in fact create circulatory mean flow.

Simultaneously improved strength and ductility of low-cost Ti-Al-V-Fe alloy with TiB2 addition and thermomechanical processing

To obtain the low-cost titanium alloys with simultaneously improved strength and ductility by thermomechanical processing, 0.1 wt% of boron was added to the Ti-4Al-2.5V-1.5Fe alloy using titanium diboride (TiB2) as a boron source. The deformation mechanisms and microstructure evolution were systematically studied by comparative investigation of Ti-4Al-2.5V-1.5Fe alloys with and without boron. The results indicated that the addition of boride had a significant effect on the material parameters. Furthermore, TiB greatly improved the spheroidization and recrystallization of the alloy, and it can effectively limit grain growth during thermal exposure. Consequently, both high-temperature forging and further thermal deformation facilitated the generation and retention of the fine grain structure, dramatically improving the processibility of Ti alloys. For bare alloys, severe plastic deformation often leads to inhomogeneous microstructures and flow instability, which is harmful to mechanical integrity. In contrast, the addition of borides can significantly mitigate flow localization. In this study, boron-modified titanium alloys exhibited improved processibility and beneficial mechanical properties attributed to beneficial effects due to the addition of borides, which may enable new strategies for manufacturing high-strength titanium alloys in a more cost-effective way.

Large eddy simulations of inhomogeneous high-magnetic Reynolds number magnetohydrodynamic flows

Large eddy simulations of inhomogeneous high-magnetic Reynolds number magnetohydrodynamic flows

AGW spectrum filtering in a horizontally inhomogeneous atmospheric flow

AGW spectrum filtering in a horizontally inhomogeneous atmospheric flow

Design and construction of an LSTM-powered high sampling rate dual-beam gamma densitometer for real-time measurement of the two-phase flow void fraction

In this work, an intelligent gamma densitometer gauge for non-intrusive real-time measurement of the two-phase flow void fraction has been designed and constructed. It has been implemented in a horizontal pipe over a wide range of gas and liquid superficial velocities. Moreover, a Long Short-Term Memory (LSTM) neural network has been used for analyzing the data sequence from a dedicated high sampling rate dual-beam gamma densitometer. This approach considerably reduced the complexity of the data processing and regression operations while providing a high capability to identify and compensate for the errors caused by intermittent, and inhomogeneous flow regimes in a real-time mode. A comprehensive sensitivity analysis has been performed to adjust the network parameters for the most accurate void fraction prediction in all studied flow regimes including slug, plug, wavy, stratified, bubbly, and semi-annular. The experimental evaluations revealed that considering a sampling time of a few seconds, the optimized model approximated the actual data with an R-squared of 0.98, and almost all measurements were carried out with the maximum absolute error of 10%. The high accuracy and relatively fast response of the proposed method make it a reliable technique for developing a high-performance real-time multiphase flow meter.

Indirect noise from weakly reacting inhomogeneities

Indirect noise is a significant contributor to aircraft engine noise, which needs to be minimized in the design of aircraft engines. Indirect noise is caused by the acceleration of flow inhomogeneities through a nozzle. High-fidelity simulations showed that some flow inhomogeneities can be chemically reacting when they leave the combustor and enter the nozzle (Giusti et al., Trans. ASME J. Engng Gas Turbines Power, vol. 141, issue 1, 2019). The state-of-the-art models, however, are limited to chemically non-reacting (frozen) flows. In this work, first, we propose a low-order model to predict indirect noise in nozzle flows with reacting inhomogeneities. Second, we identify the physical sources of sound, which generate indirect noise via two physical mechanisms: (i) chemical reaction generates compositional perturbations, thereby adding to compositional noise; and (ii) exothermic reaction generates entropy perturbations. Third, we numerically compute the nozzle transfer functions for different frequency ranges (Helmholtz numbers) and reaction rates (Damköhler numbers) in subsonic flows with hydrogen and methane inhomogeneities. Fourth, we extend the model to supersonic flows. We find that hydrogen inhomogeneities have a larger impact on indirect noise than methane inhomogeneities. Both the Damköhler number and the Helmholtz number markedly influence the phase and magnitude of the transmitted and reflected waves, which affect sound generation and thermoacoustic stability. This work provides a physics-based low-order model which can open new opportunities for predicting noise emissions and instabilities in aeronautical gas turbines with multi-physics flows.

Identification of multi-regime detonation development for hydrocarbon fuels

Recently, a detonation response diagram with multiple nonmonotonic boundaries was identified for syngas/air mixtures (Pan et al., 2022), accounting for wide-ranging operation conditions with thermal inhomogeneities. In this work, we have identified the detonation response diagrams of various fuels, especially large hydrocarbons, initiated by temperature gradients under engine-relevant conditions, in both planar and spherical configurations. Results show significant differences in the multi-regime detonation development for different fuels due to reactivity sensitivities and thermophysical properties. Furthermore, the curvature effect in the spherical configuration can cause substantial degeneration of the detonation development, while cool flame partial oxidation of large hydrocarbons can greatly facilitate robust detonation development, suggesting the significance of the interaction between flow inhomogeneities and chemical kinetics.

Data-driven acoustic measurement of moisture content in flowing biomass

Measuring the moisture content in flowing biomass is critical to processes such as liquid biofuel conversion, such as biogasoline, biodiesel, bio jet kerosene, etc. However, biomass tends to flow in aggregates, which results in significant inhomogeneities in the amount of biomass flowing in front of a sensor at a given time, and there can be significant overlap in the material properties of dry vs wet biomass, leading to poor signal-to-noise ratio. We present a technique for identifying biomass moisture content using a series of acoustic pitch-catch measurements to quantify the sound speed and acoustic amplitude through the biomass, in conjunction with classical machine learning techniques, including Naive Bayes, Random Forest, and K-Nearest Neighbors classification. We amplify the differences between the acoustic measurements in different moisture levels by collecting a series of pulse-echo measurements, which we sort in order of ascending sound speed. We test the accuracy of the technique on experimentally-prepared batches of corn stover biomass with specified moisture levels, and measure the average error in the estimated moisture level as a function of the number of pitch-catch measurements used. We observe average estimation errors as low as 6.7% by increasing the number of measurements and optimizing the hyperparameters. This work presents a novel method determining moisture content in flowing biomass with inhomogeneous flow. Additionally, this technique has application in optimizing biomass conversion processes, as well as other fields including, paper production, natural fiber processing, and mineral extraction.