Streamline Flow Research Articles

Effect of aspect ratio and nonuniform temperature on mixed convection in a double lid-driven cavity

The impact of aspect ratio and nonuniform temperature on mixed convection in an enclosure is examined numerically. The chosen shape is an enclosure with a sinusoidal temperature TH in its lower wall, while the upper wall is considered adiabatic. The sidewalls of the cavity move at a descending speed with a uniform temperature TC. The inspection is performed for different Richardson numbers and aspect ratios (AR) varying from 0.25 to 5, while the numbers of Prandtl (Pr = 0.71) and Grashof (Gr = 104) remain constant. The isothermal, streamline, and Nusselt numbers flow distributions inside the cavity are highlighted and discussed. Compared to uniform heating, significant changes in the flow rate are observed when receiving nonuniform heating on the lowest cavity surface. Two cells of flow rotating in opposing directions are formed inside the cavity when the cavity aspect ratio AR = 0.25. When the cavity aspect ratio becomes higher than the unity, these cells change with the development of Ri; they take an oval form and move to the heated side. The non-uniform heating yielded a sinusoidal localized thermal exchange rate with the lowest amounts at the edges and considerable amounts at the bottom center (Ri = 1 and 100).

Validation of time-resolved, automated peak trans-mitral velocity tracking: Two center four-dimensional flow cardiovascular magnetic resonance study

ObjectiveWe aim to validate four-dimensional flow cardiovascular magnetic resonance (4D flow CMR) peak velocity tracking methods for measuring the peak velocity of mitral inflow against Doppler echocardiography. MethodFifty patients were recruited who had 4D flow CMR and Doppler Echocardiography. After transvalvular flow segmentation using established valve tracking methods, peak velocity was automatically derived using three-dimensional streamlines of transvalvular flow. In addition, a static-planar method was used at the tip of mitral valve to mimic Doppler technique. ResultsPeak E-wave mitral inflow velocity was comparable between TTE and the novel 4D flow automated dynamic method (0.9 ± 0.5 vs 0.94 ± 0.6 m/s; p = 0.29) however there was a statistically significant difference when compared with the static planar method (0.85 ± 0.5 m/s; p = 0.01). Median A-wave peak velocity was also comparable across TTE and the automated dynamic streamline (0.77 ± 0.4 vs 0.76 ± 0.4 m/s; p = 0.77). A significant difference was seen with the static planar method (0.68 ± 0.5 m/s; p = 0.04). E/A ratio was comparable between TTE and both the automated dynamic and static planar method (1.1 ± 0.7 vs 1.15 ± 0.5 m/s; p = 0.74 and 1.15 ± 0.5 m/s; p = 0.5 respectively). Both novel 4D flow methods showed good correlation with TTE for E-wave (dynamic method; r = 0.70; P < 0.001 and static-planar method; r = 0.67; P < 0.001) and A-wave velocity measurements (dynamic method; r = 0.83; P < 0.001 and static method; r = 0.71; P < 0.001). The automated dynamic method demonstrated excellent intra/inter-observer reproducibility for all parameters. ConclusionAutomated dynamic peak velocity tracing method using 4D flow CMR is comparable to Doppler echocardiography for mitral inflow assessment and has excellent reproducibility for clinical use.

Washing Characterization of Compression Socks

Abstract Background Compression socks are highly recommended textile garments for the exertion of compression pressure (kPa) at the ankle. They work on the principle of the highest pressure at the ankle gradually decreasing from the ankle to the calf. Aim The aim of the current research is to analyze all of the compression sock samples (Class I, Class II, and Class III) simultaneously at various number of times of washing them. Method All of the sock samples were washed in a standard washing machine with standard methods (ISO 6330). For the measurement of the compression pressure, a Salzmann MST MKIV pressure measuring device was used according to the RAL-GZ 387/1 method. Results Results included the effect of multiple wearing and washing cycles (up to 20) on compression pressure, the effect of temperature (up to 100°C) on compression pressure (kPa); multiple wearing and washing cycles on the percentage of shrinkage and the effect of marking methodology on compression pressure (Kpa) were observed and are discussed in this article. The results suggest that washing is the most important factor to consider while compression socks are used for compression therapy because they directly influence the efficacy of streamline blood flow across the legs.

Long Term Vortex Flow Evolution around a Magnetic Island in Tokamaks.

We present a gyrokinetic analysis of the vortex flow evolution in a magnetic island in collisionless tokamak plasmas. In a short term ω[over ¯]_{D}t<1, where ω[over ¯]_{D} is the secular magnetic drift of the orbit center, initial monopolar vortex flow approaches to its residual level determined by the neoclassical enhancement of polarization shielding after collisionless relaxation. The residual level depends on the location inside an island and is higher than the Rosenbluth-Hinton level [M.N. Rosenbluth and F.L. Hinton, Phys. Rev. Lett. 80, 724 (1998)PRLTAO0031-900710.1103/PhysRevLett.80.724] due to finite island width. In a long term ω[over ¯]_{D}t>1, the residual vortex flow evolves to a dipolar zonal-vortex flow mixture due to toroidicity-induced breaking of a helical symmetry. The mixture forms localized flow shear layers near the island separatrix away from X points. The deviation of the streamlines of the mixture flows from magnetic surfaces allows turbulence advection across the island. We expect a small island w≲qρ_{Ti}/s[over ^] provides a favorable condition for this mixture flow formation, while the monopolar vortex flow persists for a larger island.

Investigation on the evolution characteristics of bed porous structure during iron ore sintering

To better understand the evolution characteristics of bed porous structure during iron ore sintering, X-ray computed tomography scanning technology was used to analyze the pore parameters in different areas of the sintering bed. A pore skeleton structure model was established to study the characteristics of the airflow channels in different zones. The absolute permeability of different areas was calculated through simulation, and the corresponding streamline and pressure drop distribution were analyzed. The results show that the porosity of raw material zone, high-temperature zone, and sintered zone increases gradually, which are 37.69%, 46.41%, and 55.57%, respectively. The absolute permeability calculation results of the raw material zone and sintered zones are 792.49 μm2 and 20560.80 μm2, while the tortuosity is 1.77 and 1.45, respectively. Compared with the raw material zone, the flow streamline in the sintered zone is thicker and denser, the airflow resistance and the pressure drop are minor.

Treatment of large and giant posterior communicating artery aneurysms with the Surpass streamline flow diverter: results from the SCENT trial

BackgroundThe Surpass flow diverter was developed to treat intracranial aneurysms not amenable to standard treatment. Indications for use allow placement in the internal carotid artery to the terminus, including the...

Shape evolution of long flexible fibers in viscous flows

The present work studies numerically the dynamics and shape evolution of long flexible fibers suspended in a Newtonian viscous cellular flow using a particle-level fiber simulation technique. The fiber is modeled as a chain of massless rigid cylindrical segments connected by ball and socket joints; one-way coupling between the fibers and the flow is considered while Brownian motion is neglected. The effect of stiffness, equilibrium shape, and aspect ratio of the fibers on the shape evolution of the fibers are analyzed. Moreover, the influence of fiber stiffness and their initial positions and orientations on fiber transport is investigated. For the conditions considered, the results show that the fiber curvature field resembles that of the flow streamline. It is found that the stiffer fibers experience not only a quicker relaxation phase, in which they transient from their initial shape to their “steady-state shape,” but they also regain their equilibrium shape to a larger extent. The findings also demonstrate that even a small deviation of fiber shape from perfectly straight impacts significantly the early-stage evolution of the fiber shape and their bending behavior. Increasing the fiber aspect ratio, when other parameters are kept fixed, leads the fiber to behave more flexible, and it consequently deforms to a larger extent to adjust to the shape of the flow streamlines. In agreement with the available experimental results, the fiber transport studies show that either the fiber becomes trapped within the vortices of the cellular array or it moves across the vortical arrays while exhibiting various complex shapes.

Influence of blade leading edge shape on hydraulic and suction performance of a mixed-flow pump

Abstract The shape of the blade leading edge (LE) is a design variable that cannot theoretically affect the inlet flow characteristics under the definition of the velocity triangle. However, the LE is the first to encounter the working fluid in terms of streamwise direction. Depending on its shape, not only the local flow characteristics but also the performance can be affected. In this study, a numerical analysis of the hydraulic and suction performance for a mixed-flow pump was performed with different shapes of the blade LE. The blade was prepared with four sets according to the ellipse ratio (ER), including a square (ER=0), round (1), elliptic (2), and parabolic (5) shape. As the shape of the blade LE was square, the flow streamline was immediately separated from the blade surface, showing a significant drop in the hydraulic performance. As the blade LE was designed in a round, elliptic, or parabolic shape instead of a square shape, the hydraulic performance did not show a noticeable difference. On the other hand, in the prediction of suction performance, the square LE obtained the best characteristics. As the LE shape gradually became a parabolic shape, the cavity blockage was reduced, and the suction performance was also improved.

Numerical and Experimental Study on the Opening Angle of the Double-Stage Flap Valves in Pumping Stations

Double-stage flap valves are widely used in new pumping stations. The different opening angles of the double-stage flap valves have a great influence on the outflow. To gain insight into this phenomenon, four commonly used operating conditions with opening angles were selected to perform three-dimensional simulation calculations and physical model studies on the flow pattern of the water behind the valves at different flow rates. The flow pattern of the water flow is analyzed by three indicators: the streamline of the water flow, the uniformity of the flow velocity, and the head loss in the culvert. The result shows that the coefficient of resistance loss along the way of the outlet culvert has a negative correlation with the opening angle. The larger the opening angle of the flap valve, the less the head loss of the water flow in the outlet culvert, and the flow pattern of the water flow in the culvert gradually becomes better.

Experimental and numerical investigation into effect of skirted caisson on local scour around the large-scale bridge foundation

Caisson foundation is widely used to support the long-span bridge, while the local scour is exacerbated due to the large volume of the caisson. A novel design, named “skirted caisson”, was proposed by reducing the upper size of the caisson and forming a skirt for preventing scour. This study conducted a series of experimental and numerical investigations into the local scour of the skirted caisson, including maximum scour depth, scour hole variation, flow streamline and vorticity field as a function of skirt width, skirt elevation, and skirt form, respectively. The following conclusions can be drawn, (1) the skirt caisson reduces the scour depth and the length and width of scour hole compared with the uniform caisson; (2) a wider skirt is helpful for scour prevention downward flow, while increases the accelerated flow intensity at two sides; (3) the increase of skirt elevation decreases the scour depth, but increases the length and width of scour hole within a specific range; and (4) the scour prevention is not sensitive to the skirt form. These findings provide insight into the design optimization of skirted caisson from scour prevention.

Use of Surpass Streamline Flow Diverter for the Endovascular Treatment of Craniocervical Aneurysms: A Single-Institution Experience

Flow diversion has revolutionized endovascular treatment for cerebral aneurysms. The Surpass Streamline flow diverter (SSFD) has shown promise for expanding flow diversion device options for aneurysm treatment. SSFD differs from earlier stents by maintaining high porosity with increased pore density to ensure appropriate flow disruption. Given the delivery system's increased dimension options and potential greater flow-diverting properties, SSFD is poised to extend the anatomic and pathologic reaches of flow diversion therapy. Data pertaining to SSFD-treated aneurysms were gathered retrospectively between 2019 and 2020, including aneurysm location, size, symptoms, complications, and occlusions rates at follow-up. Size was categorized as small (<10 mm), large (10-25 mm), and giant (>25 mm) according to SCENT (Surpass Intracranial Aneurysm Embolization System Pivotal Trial to Treat Large or Giant Wide Neck Aneurysms) criteria. Aneurysm occlusion on follow-up imaging was characterized by Simple Measurement of Aneurysm Residual after Treatment (SMART) grading with adequate occlusion defined as grades 3 and 4. Imaging was performed at time of treatment and 6-month and 1-year follow-up. There were 42 aneurysms treated with SSFD throughout the cerebrovascular system: 3 cervical, 4posterior, and 35 intracranial anterior circulation. Complete occlusion rates at 6 months and 1 year were 48% and 57% with adequate occlusion achieved in 89.6% and 85.7%, respectively. Rates of complete occlusion were higher for small (69%) compared with large (38%) aneurysms. Our data suggest comparable complete occlusion rates compared with SCENT (66.1% vs. 57% in our center) and adequate occlusion rates. Similar occlusion rates to prior studies despite broadened inclusion criteria and diversity of treated aneurysms demonstrate favorable generalizability of flow-diverting technology to a wide array of aneurysmal pathology.

Flow Diverter Reconstruction of Internal Carotid Artery (Loop) Dissections with or without Associated Pseudoaneurysms

Endovascular treatment of cervical internal carotid artery (ICA) loop dissections in acute stroke interventions can be challenging. Flow diverters can effectively reconstruct vessel loops and treat the injured vessel and provide a safe conduit for intracranial catheterization. We retrospectively reviewed our neurointerventional database and identified all patients with ICA loop dissections treated with flow diverters in the acute setting between August 2016 and September 2020. Patient demographics, procedural data, imaging follow-up results, and clinical outcome information were collected. Seven patients with a mean age of 62 years (range: 43-85 years) who underwent reconstruction of an ICA (loop) dissection with flow diverters were included. Four ICA dissections were treated with the Surpass Streamline flow diverter and 3 with the Pipeline embolization device. All cases were technically successful. All stroke cases achieved intracranial flow ≥thrombolysis in cerebral infarction 2B. Observed intracranial hemorrhages were all asymptomatic. All cases showed patent flow diverter(s) with or without (carotid) stent(s) on follow-up imaging. Semielectively treated patients did not show a change from baseline modified Rankin scale related to the procedure. Patients with acute stroke had a modified Rankin scale ≤2 in 4 of 5 cases (80%) at 3 months. Two patients died due to medical issues unrelated to the procedures. No patient showed new or recurrent symptoms. Use of flow diverters, in some cases in conjunction with (carotid) stents, is an effective treatment option for cervical carotid artery (loop) dissections.

MHD mixed convection and entropy generation of CNT-water nanofluid in a wavy lid-driven porous enclosure at different boundary conditions

In this study, Galerkin Finite Element Method or GFEM is used for the modeling of mixed convection with the entropy generation in wavy lid-driven porous enclosure filled by the CNT-water nanofluid under the magnetic field. Two different cases of boundary conditions for hot and cold walls are considered to study the fluid flow (streamlines) and heat transfer (local and average Nusselt numbers) as well as the entropy generation parameters. Richardson (Ri), Darcy (Da), Hartmann angle (γ), Amplitude (A), Number of peaks (N), Volume fraction (φ), Heat generation factor (λ), Hartmann number (Ha) and Reynolds number (Re) are studied parameters in this study which results indicated that at low Richardson numbers (< 1) increasing the inclined angle of magnetic field, decreases the Nu numbers, but at larger Richardson numbers (> 1) it improves the Nu numbers.

Computational Study of Abdominal Aortic Aneurysms with Severely Angulated Neck Based on Transient Hemodynamics Using an Idealized Model

An abdominal aortic aneurysm (AAA) is an enlargement of the abdominal aorta that can become a life-threatening disease. The pulsatile blood flow exhibits intricate laminar patterns in the abdominal portion of the human aorta under normal resting conditions, whereas secondary flows are caused by adjacent branches and abnormal vessel geometries. If a pathological disorder (e.g., aneurysm) alters the structural composition of the artery wall, the flow dynamics become more complex. In this study, we analyzed the hemodynamics of pulsatile blood flow in three-dimensional AAA models. Computational predictions of hemodynamic changes were performed considering idealized models for four severe proximal neck angulations of symmetric aneurysms assuming conditions of laminar flow and a rigid artery wall. The predictions were based on computational fluid dynamics throughout the cardiac cycle. Postprocessing was used to visualize the numerical findings. The hemodynamic changes in factors such as velocity, flow streamline, pressure, and wall shear stress were obtained and visualized. The resulting blood flow through the severely angulated proximal neck of the abdominal aorta caused strong turbulence and asymmetric flow inside the aneurysm sac, leading to blood recirculation, especially during diastole. The simulation results showed the formation of regions with high and low wall shear stress, turbulent flow, and recirculation in the aneurysm sac depending on the angulation, which could have led to aortic wall weakness.

Pipeline Embolization Device and Pipeline Flex Versus Surpass Streamline Flow Diversion in Intracranial Aneurysms: A Retrospective Propensity Score–Matched Study

To compare safety and efficacy profiles in aneurysms treated with Pipeline Embolization Device or Pipeline Flex versus Surpass Streamline flow diverters (FDs). Patients who underwent flow diversion for aneurysm treatment at 2 centers were included. Covariates comprised patient demographics, comorbidities, and aneurysm characteristics. Metrics included number of devices, adjuvant device use, case duration, and radiation exposure. Outcomes included periprocedural complications and radiographic results at follow-up. Propensity score-matched pairs were generated using demographic and aneurysm characteristics to verify the outcomes in equally sized groups. The majority of 141 flow diversion procedures performed on 126 patients were in the anterior circulation (96%) and unruptured (93%). Operators experienced more complications placing Surpass FDs compared with Pipelines (18.2% vs. 3.1%, P= 0.005) but used fewer Surpass devices per case (1 device in all Surpass cases and range for Pipeline cases 1-7; P < 0.001). Ballooning was more frequent for Surpass (29.5% vs. 2.1%, P < 0.001). There were no differences in mortality (2.1% vs. 0, P= 1.00), intracranial hemorrhage (3.1% vs. 0, P= 0.551), or stroke (4.2% vs. 6.8%, P= 0.680). Rates of aneurysm obliteration at follow-up were similar. Propensity-matched pairs had no differences in FD deployment complications or perioperative events, yet the significant differences remained for adjuvant balloon use and number of FDs deployed. While the devices demonstrated similar safety and efficacy profiles, deployment of the Surpass Streamline was more technically challenging than Pipeline Embolization Device or Pipeline Flex. Prospective cohort studies are needed to corroborate these findings.

Impact of velocity correlations on longitudinal dispersion in space-Lagrangian advective transport models

Space-Lagrangian random walk models conceptualize advective transport in heterogeneous media in terms of collections of particles undergoing fixed-length steps along flow streamlines. We study the impact of velocity correlation structure on longitudinal dispersion for different point velocity statistics. We find that asymptotic equivalence requires the step length of an uncorrelated continuous time random walk to be higher than the correlation length when velocity correlations decay exponentially with distance. We characterize the conditions for equivalence for broad classes of velocity distributions.

Analysis of Flow Characteristics of Different Shape Particles Chasing

in order to study the gas flow characteristics of particles with different shapes in the pursuit process, spherical, ellipsoidal and square particles are selected for numerical simulation by fluent. The results show that when the pursuit speed is the same, the streamline produced by square particles in the pursuit process is denser than that of spherical and ellipsoidal particles. Particle movement creates a certain vacuum on both sides and rear of the particle, causing the surrounding air flow to enter the areas on both sides of the particle, resulting in strong turbulence. After the rear particles catch up with the front particles, the changes of the surrounding flow field and streamline are similar to the inverse process before catching up, indicating that the particle motion has a certain regularity, and the square particles have the largest turbulent kinetic energy among the three particles.

Flow dynamics over a high, steep, erosional coastal dune slope

Flow dynamics over a high, unvegetated, and steep scarp slope that fronts a severely eroded relict transgressive dunefield were investigated at Salmon Hole (also known as Post Office Rock), a small headland-bay beach located near Beachport, south east South Australia. The ~15-metre-high steep dune at Salmon Hole provided the opportunity to conduct a wind flow experiment on a larger, higher and longer stoss slope than previously studied. The scarp slope is comprised of segments of varying slope that have a significant impact on flow dynamics over the dune. Percentage speed up and a decrease in turbulence were recorded up the stoss slope due to streamline convergence and flow compression. However, flow expansion at a change in gradient on the upper stoss slope caused a significant drop in wind speed and an increase in turbulence, contrary to what has previously been found in the literature where maximum percentage speed up is primarily recorded at the crest. Topographic steering typically seen in wind flow over scarps and foredunes was observed at Salmon Hole along with flow separation and the formation of a reversing vortex on the lee slope. This study also demonstrates how a lack of sediment delivery back to the beach and thence to the dune between storm events results in the inability for dune recovery or translation. However, the Salmon Hole study shows that blowouts can still develop and grow through dune cannibalization regardless of the lack of sediment supply from the beach and the recession of the shoreline.

Drawdown of urban drain trenches triggering 2-D transient seepage in soil massifs subject to managed aquifer discharge: sandbox experiments, analytical and HYDRUS2D modeling

ABSTRACT Managed Aquifer Discharge (MAD) through trenches lowers the water table of ‘shallow perched aquifers’ in urban areas (Muscat-Oman). Drawdown of the water table in periodic trenches or a single trench is experimentally studied in a sandbox, and modelled numerically (by HYDRUS2D) and analytically. Evaluation of transient flow fields of pore pressure and hydraulic gradients is necessary for assessing the stability of trench slopes to seepage-induced erosion. A controlled emptying of trench’s water level is examined. An analytical solution is obtained for an unconfined seepage at an early stage of drainage. Numerical simulations are conducted for early and late stages of seepage towards a partially filled trench in soils with capillarity. For a steady-state Darcian flow limit, comparisons of HYDRUS results with the Charny analytical formula for capillarity-free soils are done. The flow rates, isobars, isotachs and streamlines are determined, with assessment of zones of high hydraulic gradients susceptible to seepage erosion.

ПРИНЦИП НАИМЕНЬШЕГО ДЕЙСТВИЯ В РАСЧЕТЕ ВОДОСЛИВА С ШИРОКИМ ПОРОГОМ

Purpose: to apply the variation principle of least action to create a theory for calculating the broad-crested weir, to compare the results obtained with the data of various domestic and foreign researchers and to draw conclusions about the accuracy of the solution obtained. Materials and methods. The minimum flow depth on a broad-crested weir was determined by minimizing the Lagrangian liquid flow. This equation is used to close the equation of specific total flow energy. The verification of the obtained method in determining the minimum depth at the weir crest was carried out by a laboratory experiment and computer simulation of the flow movement through the weir, carried out in the ANSYS 17.0 software package. The results of determining weir capacity were compared with the experimental and theoretical data of domestic and foreign authors. Results. The comparison of the results of calculations of the broad-crested weir capacity with a wide threshold with the proposed method showed good agreement with the data of various authors, the difference did not exceed 3 %. The comparison of the results of depth calculations at the weir crest showed their agreement with the data of various authors, our own laboratory experiments and computer simulation. The adequacy of the obtained dependence was confirmed on the basis of determination coefficient and the Fisher variance ratio. Conclusions. A new theoretical method for hydraulic calculation of a broad-crested weir has been obtained, which made it possible to determine the liquid flow depth at the weir crest and its capacity. An analysis of the applicability of the method showed that the depth by the principle of least action is realized only in cases where the flow has no obstacles for free discharge. The limitation of the proposed method is the mandatory presence of a section with a relatively streamline flow and hydrostatic pressure distribution on the weir crest, as well as the absence of flooding of the structure.