Qualitative Flow Patterns Research Articles

Local mass transfer and flow visualization around a cylinder in a liquid-solid fluidized bed

Adsorption method has been used for flow visualisation and determination of the local and average mass transfer coefficients around a horizontal cylinder in a liquid-solid fluidized bed. The obtained concentration fields on the adsorbent (silica-foils) represent a clear qualitative flow pattern around the cylinder. By comparison of the concentration fields around the cylinder in the single-phase flow and in the fluidized bed, a significant disturbance of the boundary layer by fluidized particles can be observed. Local mass transfer coefficients were shown to be dependent on the angular position around the cylinder with the maximum determined at the angle 140? (measured from the stagnant point 0?). Selected correlations were applied to predict the average mass transfer coefficients and the two best have shown deviations from the experimental data up to 5 %.

Спектр сверхзвукового обтекания вокруг летательного аппарата с управляющими тормозными щитками

The article presents the results of the study of the spatial flow pattern of the aircraft model, the study of the flow structure near the surface of the aircraft by experimental and numerical methods. Comparative materials for visualizing flows around a conical model with a stern control body – a flat end shield during supersonic flight in atmospheric pressure air are presented. The difference from the qualitative flow pattern according to experimental spectra at M≈4 and M≈5.5 lies in the presence, in addition to the formation of a breakaway flow zone in front of the shield, an oblique jump of the seal (from the point of separation of the flow) and a more intense direct jump of the seal, the possibility of the appearance of a flow separation zone induced by the shield on the side of the model surface opposite the shield, with the formation of an oblique jump of the seal. The efficiency of increasing the number of brake shields installed on the cylindrical-conical model is considered. The results of measurements of the dependence of the increments of the drag coefficient of the tested models on the area of the shields are presented.

Utilization of entire new dynamical system approach for peristalsis of Power law fluid with temperature-dependent viscosity

Peristalsis of non-Newtonian fluid with variable viscosity and viscous dissipation is considered in this paper. Modified Brinkman number highlighting both the variable viscosity and viscous dissipation is introduced. By utilizing the long wavelength and small Reynold number approximations, an analytical solution is obtained for stream function. The qualitative analysis is presented using the theory of dynamical system. The phase portraits representing topological structures like trapping, augmented flow and the backward flow are drawn. The change in qualitative flow patterns is discussed from the bifurcation diagrams. The exact size of the bolus is numerically determined. HIGHLIGHTS Analytical solution for Power law fluid with temperature-dependent viscosity. The theory of dynamical system is utilized for stability and bifurcation analysis. The topological structure of the flow is presented using bifurcation theory and phase plane analysis. The size of the bolus is calculated numerically.

Numerical Investigation of Flow Separation Control over Rotor Blades Using Plasma Actuator

The flow separation control over rotating rotor blades in hover using an alternating current dielectric barrier discharge (AC-DBD) plasma actuator is investigated through numerical simulation, possibly for the first time. Three-dimensional unsteady Reynolds-averaged Navier–Stokes calculation with a Reynolds stress turbulence model is adopted to resolve the airflow. The impact of the AC-DBD plasma discharge on the airflow is modeled by an empirical body force model. The objective of this work is to characterize the separated flow over the rotating blades, resolve the flow control procedure, reveal the flow control mechanism, and evaluate the control authority. Compared with the experiment, the numerical simulation can provide satisfactory predictions of the baseline flow over the rotor for the qualitative flow pattern and quantitative aerodynamic features. The good agreement between the simulation and experiment lends credibility to the observations made from the numerical result. It is found that in the baseline flow, the flow separation occurs in the vicinity of the blade tips and exhibits strong three-dimensional characteristics under the influence of centrifugal force. The plasma excitation can significantly inhibit the flow separation over the blades at large angles of attack (AOAs). The flow control is seen to be dominated by the spanwise vortices induced by the plasma discharges, for which the strong entrainment effect makes the separated flow fully or partially reattach to the blade surfaces. The resulting forced flow pattern is influenced by the AOA of the blades. At each high AOA under consideration, the controlled flow is a significant improvement over the baseline case, and the aerodynamic characteristics of the rotor blades are appreciably enhanced.

Hemoglobin Video Imaging Detects Differences in Aqueous Outflow Between Eyes With and Without Glaucoma During the Water Drinking Test.

Hemoglobin video imaging (HVI) demonstrates increased aqueous outflow (AO) in response to the water drinking test (WDT) in patients with and without glaucoma. In glaucomatous eyes, increased AO was not sustained, and characteristic flow patterns were seen. To observe how variations in intraocular pressure (IOP) correlate with the flow of aqueous in episcleral veins. Prospective observational cohort study. The WDT increased AO into the episcleral venous system in 30 eyes recruited from Sydney Eye Hospital. A comparison was made between glaucomatous (n=20) and nonglaucomatous eyes (n=10). Each patient had baseline IOP and HVI before drinking 10 mL/kg body weight of water. IOP and HVI were then repeated every 15 minutes for 1 hour. Aqueous column cross-sectional area (AqCA) of the most prominent nasal and temporal aqueous veins was used to semi-quantify conventional AO. Change in IOP and AqCA from baseline during the WDT. Aqueous flow characteristics were also observed. Peak IOP elevation above baseline was significantly higher in the glaucoma group, with an average IOP rise of 39.7% on 1.6 1.1 medications, compared with 22.9% in the control group ( P =0.04). AqCA significantly increased for glaucomatous and nonglaucomatous eyes in response to water ingestion ( P <0.05). AqCA fell by 50% in glaucomatous eyes ( P =0.003) and 33% in nonglaucomatous eyes ( P =0.08) at study completion compared with the peak measurement. IOP remained >30% elevated in 8 glaucomatous eyes (40%) after 60 minutes and no control eyes. Variations in qualitative aqueous flow patterns were observed in glaucomatous eyes but not in controls. AO volume, estimated by AqCA, increases in response to IOP elevation induced by an ingested water bolus in patients with and without glaucoma. The increase in aqueous drainage was not sustained in glaucomatous eyes and may have led to incomplete recovery of IOP. Using HVI in combination with the WDT may assist with clinical decision-making and facilitate the monitoring of responses to treatment.

Моделирование течения перед струйной преградой при вариации параметров набегающего потока

The results of numerical simulation of the problem of interaction of supersonic flow with a jet obstacle under variation of input flow parameters are considered. The problem is solved in the system of Navier-Stokes equations. Laminar flows are considered. The qualitative flow pattern has been studied under the variation of incoming flow velocity and boundary layer thickness in the incoming flow. The calculations were performed using the OpenFOAM software package.

The impact of heterogeneous pin based micro-structures on flow dynamics and heat transfer in micro-scale heat exchangers

Overheating is the most important limiting factor for efficient performance of miniature electronic devices. Porous microfluidic systems are recently introduced as a promising remedy to this problem. Increasing the heat removal using porous microfluidic systems comes at the cost of increased hydrodynamic friction in the device. In this study, we focus on the flow dynamics in microchannels with embedded heterogeneous porous structures to identify effective parameters to make porous patterns with less friction while maintaining a high heat transfer rate. The heterogeneous porous structures are defined using columns of pins with different pin sizes. We analyze the flow dynamics and heat transfer using quantitative and qualitative flow patterns, energy distribution, and particle tracking analyses. We find that the structure of the porous medium plays an important role in the hydrodynamic flow distribution and as a result on the overall heat transfer characteristics. While higher heat transfer rates in homogeneous porous media are proportional to higher friction, heterogeneous porous media revealed more complex flow dynamics. It was shown that an optimized distribution of the pins in the microchannel can lead to the systems where the heat transfer increases and, at the same time, the frictions decrease. We show that the columns at either end of the porous medium are the ones that affect flow dynamics and heat transfer the most.

A 4D flow MRI evaluation of the impact of shear-dependent fluid viscosity on in vitro Fontan circulation flow.

The Fontan procedure for univentricular heart defects creates a nonphysiologic circulation where systemic venous blood drains directly into the pulmonary arteries, leading to multiorgan dysfunction secondary to chronic low-shear nonpulsatile pulmonary blood flow and central venous hypertension. Although blood viscosity increases exponentially in this low-shear environment, the role of shear-dependent ("non-Newtonian") blood viscosity in this pathophysiology is unclear. We studied three-dimensional (3D)-printed Fontan models in an in vitro flow loop with a Philips 3-T magnetic resonance imaging (MRI) scanner. A 4D flow phase-contrast sequence was used to acquire a time-varying 3D velocity field for each experimental condition. On the basis of blood viscosity of a cohort of patients who had undergone the Fontan procedure, it was decided to use 0.04% xanthan gum as a non-Newtonian blood analog; 45% glycerol was used as a Newtonian control fluid. MRI data were analyzed using GTFlow and MATLAB software. The primary outcome, power loss, was significantly higher with the Newtonian fluid [14.8 (13.3, 16.4) vs. 8.1 (6.4, 9.8)%, medians with 95% confidence interval, P < 0.0001]. The Newtonian fluid also demonstrated marginally higher right pulmonary artery flow, marginally lower shear stress, and a trend toward higher caval flow mixing. Outcomes were modulated by Fontan model complexity, cardiac output, and caval flow ratio. Vortexes, helical flow, and stagnant flow were more prevalent with the non-Newtonian fluid. Our data demonstrate that shear-dependent viscosity significantly alters qualitative flow patterns, power loss, pulmonary flow distribution, shear stress, and caval flow mixing in synthetic models of the Fontan circulation. Potential clinical implications include effects on exercise capacity, ventilation-perfusion matching, risk of pulmonary arteriovenous malformations, and risk of thromboembolism.NEW & NOTEWORTHY Although blood viscosity increases exponentially in low-shear environments, the role of shear-dependent ("non-Newtonian") blood viscosity in the pathophysiology of the low-shear Fontan circulation is unclear. We demonstrate that shear-dependent viscosity significantly alters qualitative flow patterns, power loss, pulmonary flow distribution, shear stress, and caval flow mixing in synthetic models of the Fontan circulation. Potential clinical implications include effects on exercise capacity, ventilation-perfusion matching, risk of pulmonary arteriovenous malformations, and risk of thromboembolism.

Анализ моделей силового взаимодействия пара и жидкости в барботажном слое для двухскоростного описания пароводяной смеси

Тhe article analyzes the effect the interfacial force interaction models developed for different types of bubble flows have on the bubble layer description. The analysis is performed in the framework of a stationary 1D two-velocity mathematical model describing the flow of steam-water mixture with the liquid phase velocity assumed equal to zero. A conjecture was made based on the results from studying the qualitative flow pattern in the bubble layer that an emulsion flow mode takes place in it for practically important steam loads. The calculated values were compared with the typical actual values for horizontal steam generators used in nuclear steam supply systems built around VVER-type reactors. The calculated void fraction value in the bubble layer’s main part was found to be significantly higher than the experimental values. The same picture was also obtained for other values of reduced steam velocity and void fraction in the ranges obtained in these steam generators, which is attributed to the way in which the interfacial interaction force is simulated. It is shown that the use of the considered models leads either to a significant overestimation of the interfacial interaction force and, consequently, the void fraction in the bubble layer, or to lack of solution for the values of parameters characteristic for the horizontal steam generators of nuclear power plants equipped with VVER-type reactors. The correlations investigated in this study were derived proceeding from the flow friction coefficient of a single bubble as a function of the Reynolds number and introduction of the mixture viscosity that depends on the volume fraction of the dispersed phase. A steady flow of the two-phase mixture was considered under such conditions. Possibly, such a steady flow does not have enough time to be formed in steam generators. The steam entering from the bottom into the bubble layer through the submerged perforated sheet (SPS) holes initially ascends as a jet through the liquid layer. The steam-liquid interface separating the steam jet from the liquid may experience instability according to the Kelvin-Helmholtz mechanism. Estimates show that the time for which disturbances develop on the jet surface is essentially shorter than the time taken for the steam to pass through the bubble layer, a circumstance due to which perturbations may grow significantly up to reaching a nonlinear stage and appearance of complex two-phase structures.

The Effect of Valve-in-Valve Implantation Height on Sinus Flow.

Valve-in-valve transcatheter aortic valve replacement (VIV-TAVR) has proven to be a successful treatment for high risk patients with failing aortic surgical bioprostheses. However, thrombus formation on the leaflets of the valve has emerged as a major issue in such procedures, posing a risk of restenosis, thromboembolism, and reduced durability. In this work we attempted to understand the effect of deployment position of the transcatheter heart valve (THV) on the spatio-temporal flow field within the sinus in VIV-TAVR. Experiments were performed in an in vitro pulsatile left heart simulator using high-speed Particle Image Velocimetry (PIV) to measure the flow field in the sinus region. The time-resolved velocity data was used to understand the qualitative and quantitative flow patterns. In addition, a particle tracking technique was used to evaluate relative thrombosis risk via sinus washout. The velocity data demonstrate that implantation position directly affects sinus flow patterns, leading to increased flow stagnation with increasing deployment height. The particle tracking simulations showed that implantation position directly affected washout time, with the highest implantation resulting in the least washout. These results clearly demonstrate the flow pattern and flow stagnation in the sinus is sensitive to THV position. It is, therefore, important for the interventional cardiologist and cardiac surgeon to consider how deployment position could impact flow stagnation during VIV-TAVR.

Constraining OCT with Knowledge of Device Design Enables High Accuracy Hemodynamic Assessment of Endovascular Implants.

BackgroundStacking cross-sectional intravascular images permits three-dimensional rendering of endovascular implants, yet introduces between-frame uncertainties that limit characterization of device placement and the hemodynamic microenvironment. In a porcine coronary stent model, we demonstrate enhanced OCT reconstruction with preservation of between-frame features through fusion with angiography and a priori knowledge of stent design.Methods and ResultsStrut positions were extracted from sequential OCT frames. Reconstruction with standard interpolation generated discontinuous stent structures. By computationally constraining interpolation to known stent skeletons fitted to 3D ‘clouds’ of OCT-Angio-derived struts, implant anatomy was resolved, accurately rendering features from implant diameter and curvature (n = 1 vessels, r2 = 0.91, 0.90, respectively) to individual strut-wall configurations (average displacement error ~15 μm). This framework facilitated hemodynamic simulation (n = 1 vessel), showing the critical importance of accurate anatomic rendering in characterizing both quantitative and basic qualitative flow patterns. Discontinuities with standard approaches systematically introduced noise and bias, poorly capturing regional flow effects. In contrast, the enhanced method preserved multi-scale (local strut to regional stent) flow interactions, demonstrating the impact of regional contexts in defining the hemodynamic consequence of local deployment errors.ConclusionFusion of planar angiography and knowledge of device design permits enhanced OCT image analysis of in situ tissue-device interactions. Given emerging interests in simulation-derived hemodynamic assessment as surrogate measures of biological risk, such fused modalities offer a new window into patient-specific implant environments.

Computational fluid dynamics analysis and PIV validation of a bionic vortex flow pulsatile LVAD.

Hemocompatibility is highly affected by the flow field in Left Ventricular Assistant Devices (LVAD). An asymmetric inflow and outflow channel arrangement with a 45° intersection angle with respect to the blood chamber is proposed to approximate the vascular structure of the aorta and left atrium on the left ventricle. The structure is expected to develop uninterruptible vortex flow state which is similar to the flow state in human left ventricle. The Computational Fluid Dynamics (CFD) asymmetric model is simulated using ANSYS workbench. To validate the velocity field calculated by CFD, a Particle Image Velocimetry (PIV) experiment is conducted. The CFD results show that the proposed blood chamber could generate a shifting vortex flow that would be redirected to the aorta during ejection to form a persistent recirculating flow state, which is similar to the echocardiographic flow state in left ventricle. Both the PIV and the CFD results show the development of a persistent vortex during the pulsatile period. Comparison of the qualitative flow pattern and quantitative probed velocity histories in a pulsatile period shows a good agreement between the CFD and PIV data. The goal of developing persistent quasi intra-ventricle vortex flow state in LVAD is realized.

Towards highly accelerated Cartesian time-resolved 3D flow cardiovascular magnetic resonance in the clinical setting.

BackgroundThe clinical applicability of time-resolved 3D flow cardiovascular magnetic resonance (CMR) remains compromised by the long scan times associated with phase-contrast imaging. The present work demonstrates the applicability of 8-fold acceleration of Cartesian time-resolved 3D flow CMR in 10 volunteers and in 9 patients with different congenital heart diseases (CHD). It is demonstrated that accelerated 3D flow CMR data acquisition and image reconstruction using k-t PCA (principal component analysis) can be implemented into clinical workflow and results are sufficiently accurate relative to conventional 2D flow CMR to permit for comprehensive flow quantification in CHD patients.MethodsThe fidelity of k-t PCA was first investigated on retrospectively undersampled data for different acceleration factors and compared to k-t SENSE and fully sampled reference data. Subsequently, k-t PCA with 8-fold nominal undersampling was applied on 10 healthy volunteers and 9 CHD patients on a clinical 1.5 T MR scanner. Quantitative flow validation was performed in vessels of interest on the 3D flow datasets and compared to 2D through-plane flow acquisitions. Particle trace analysis was used to qualitatively visualise flow patterns in patients.ResultsAccelerated time-resolved 3D flow data were successfully acquired in all subjects with 8-fold nominal scan acceleration. Nominal scan times excluding navigator efficiency were on the order of 6 min and 7 min in patients and volunteers. Mean differences in stroke volume in selected vessels of interest were 2.5 ± 8.4 ml and 1.63 ± 4.8 ml in volunteers and patients, respectively. Qualitative flow pattern analysis in the time-resolved 3D dataset revealed valuable insights into hemodynamics including circular and helical patterns as well as flow distributions and origin in the Fontan circulation.ConclusionHighly accelerated time-resolved 3D flow using k-t PCA is readily applicable in clinical routine protocols of CHD patients. Nominal scan times of 6 min are well tolerated and allow for quantitative and qualitative flow assessment in all great vessels.

Multi-time-lag PIV analysis of steady and pulsatile flows in a sidewall aneurysm

The effect of inflow waveform on the hemodynamics of a real-size idealized sidewall intracranial aneurysm (IA) model was investigated using particle imaging velocimetry (PIV). For this purpose, we implemented an error analysis based on several PIV measurements with different time lags to ensure high precision of velocity fields measured in both the IA and the parent artery. The relative error measured in the main part of the circulating volume was <1 % despite the three orders of magnitude difference of parent artery and IA dome velocities. Moreover, important features involved in IA evolution were potentially emphasized from the qualitative and quantitative flow pattern comparison resulting from steady and unsteady inflows. In particular, the flow transfer in IA and the vortical structure were significantly modified when increasing the number of harmonics for a typical physiological flow, in comparison with quasi-steady conditions.

Исследование влияния длины улиц на течение воздуха в них

The paper compares the results of mathematical modeling of aerodynamics typical urban developments with different length of the streets. The calculations were performed using the redistributable package OpenFoam and remote console access to the control node computing cluster BL2x220 Cluster Console https://unihub.ru/resources/bl2x220cc Web-laboratory Unihub (www.unihub.ru) program "University cluster" (www.unicluster.ru). Consider a single street with houses of the same height at its sides, a single street with houses of different heights at its sides and two parallel streets located on a hillside. Comparison of simulation results in two-dimensional and three-dimensional approximation showed that the length of the street has a significant impact on the qualitative and quantitative flow pattern inside the streets and on buildings.

Preliminary Hydrodynamic Modeling of Fluidized Beds of Single Component and Binary Particle System in Compartmented Gasifier

In the present study, three-dimensional simulation using computational fluid dynamics (CFD, FLUENT 6.3.26) and experiments were conducted on a transparent cold-flow gas-solid bubbling compartmented fluidized bed gasifier (CFBG) model with identical diameter as the pilot-scaled CFBG. Using Eulerian-Eulerian granular model with closure laws according to the kinetic theory of granular flow that based on modified drag model simulations were conducted to model the hydrodynamics of CFBG in terms of gas-solid flow pattern, bed expansion ratio, bed pressure drop and bubble diameter. The model was resolved by semi-implicit method for pressure-linked equation (SIMPLE) algorithm in CFD. Different inerts like river sand, quartz sand, and alumina were used to examine the hydrodynamics behaviors both in single component and binary system where biomass, palm shell, was mixed with river sand. The modeling predictions compared reasonably well with experimental bed expansion ratio measurements and qualitative gas-solid flow patterns. Pressure drops predicted by the simulations were in relatively close agreement with experimental measurements. Furthermore, the simulated bubble diameters showed similarities with the Darton et al., bubble size equation.

Studies of Gas Velocity And Particles Size Effects on Fluidized Bed Hydrodynamics with Cfd Modeling and Experimental Investigation

AbstractWith applying Computational Fluid Dynamics (CFD) techniques, hydrodynamics of a twodimensional non-reactive gas-solid fluidized bed reactor was investigated. A multi fluid Eulerian model incorporating the kinetic theory for solid particles was applied to simulate the unsteady state behavior of this reactor and momentum exchange coefficients were calculated by using the Syamlal-O'Brien drag functions. A suitable numerical method that employed finite volume method applied to discritize the equations. Simulation results also indicated that small bubbles were produced at the bottom of the bed. These bubbles collided with each other as they moved upwards forming larger bubbles. Also, solid particles diameter and superficial gas velocity effect on hydrodynamics were studied. Simulation results were compared with the experimental data in order to validate the CFD model. Pressure drops and bed expansion ratio as well as the qualitative Gas-Solid flow patterns predicted by the simulations were in good agreement with experimental measurements at superficial gas velocities higher than the minimum fluidization velocity. Furthermore, this comparison showed that the model can predict hydrodynamicsbehavior of gas solid fluidized bed reasonably well.

On the particle paths in solitary water waves

We provide the qualitative flow pattern beneath a solitary water wave by describing the individual particle trajectories.

Flows near stagnation points in non-orthogonally colliding disperse viscous flows

Within the framework of a two-fluid dusty-gas model, a family of steady self-similar flows near a stagnation point formed by two different non-orthogonally colliding viscous incompressible streams, one of which contains solid inertial particles, is studied. The limiting case of non-orthogonal impingement of a viscous disperse medium on a rigid wall is considered separately. The possibility of the formation of multiple particle accumulation zones on the envelopes of particle trajectories and on the contact (in the limiting case, rigid) surface is demonstrated. The local structure of the particle velocity and concentration fields is studied. The threshold values of the governing parameters corresponding to qualitative flow pattern reconstruction are found.

DSC solution for flow in a staggered double lid driven cavity

AbstractA benchmark quality solution is presented for flow in a staggered double lid driven cavity obtained by using the wavelet‐based discrete singular convolution (DSC). The proposed wavelet based algorithm combines local methods' flexibility and global methods' accuracy, and hence, is a promising approach for achieving the high accuracy solution of the Navier–Stokes equations. Block structured grids with pseudo‐overlapping subdomains are employed in the present simulation. A third order Runge–Kutta scheme is used for the temporal discretization. Quantitative results are presented, apart from the qualitative fluid flow patterns. The prevalence of rich features of flow morphology, such as two primary vortex patterns, merged single primary vortex patterns, and secondary eddies, makes this problem very attractive and interesting. The problem is quite challenging for the possible existence of numerically induced asymmetric flow patterns and elliptic instability. Important computational issues like consistence, convergence and reliability of the numerical scheme are examined. The DSC algorithm is tested on the single lid driven cavity flow and the Taylor problem with a closed form solution. The double lid driven cavity simulations are cross‐validated with the standard second order finite volume method. Copyright © 2003 John Wiley &amp; Sons, Ltd.