Altered Flow Patterns Research Articles

Modulation of Residual Current on Impacts of Shoreline Changes in the Yangshan Deepwater Harbor

Abstract Coastal land reclamation projects significantly alter tidal wave propagation and residual flow structures. This study focuses on the Yangshan Deepwater Harbor (YDH) in China, aiming to scrutinize the effects of construction activities on residual flow patterns employing the Finite Volume Community Ocean Model (FVCOM). By calculating Lagrangian residual currents across different tidal periods, we analyzed alterations in flow patterns and velocity distribution pre- and post-construction. The research findings reveal that, although the residual flow direction in the harbor and the southern sea area remains largely unchanged from the pre-construction phase, the northern sea area has experienced a shift in residual flow direction. It is noteworthy that after the implementation of the project, the residual flow at the East Entrance was greatly weakened. This study underscores that coastal constructions can lead to remarkable influence on residual currents and emphasizes the necessity for thorough hydrodynamic assessments in the planning and implementation stages of coastal constructions.

Passive control of porous media on the aerodynamic forces and wake structures of wall-mounted short circular cylinders

This paper numerically investigates the aerodynamic forces and the three-dimensional wake characteristics of wall-mounted circular cylinders with and without porous media coatings using large eddy simulation at a Reynolds number of 3.2×104. Short cylinders with aspect ratios of 0.5, 1.0, and 3.0 are considered, with one end fixed to a bottom wall in the current work. The study focuses on aerodynamic coefficients, flow characteristics, and wake structures for cylinders both with and without porous coatings. The statistical results indicate that porous media significantly alter flow patterns behind the cylinders, suppress downwash flow from the free end, and reduce velocity fluctuations and turbulent kinetic energy within the wake. The porous coating enhances the leeward side's base pressure, leading to a reduction in drag on the cylinder surface. The analysis of flow structures reveals that the topology of the arch vortex behind solid cylinders is significantly dependent on the aspect ratio, whereas this dependency is negligible for porous cylinders. Porous coatings diminish the intensity of the tip and trailing vortices behind the cylinder. Finally, based on the time-averaged flow field, we proposed two conceptual models of topological correlation for wall-mounted short cylinders, both with and without porous coatings, which contributes to describing the geometric characteristics and interactions of vortex structures.

Assessing Zebra Mussels’ Impact on Fishway Efficiency: McNary Lock and Dam Case Study

The Columbia River Basin faces a threat from the potential invasion of zebra mussels (Dreissena polymorpha), notorious for their ability to attach to various substrates, including concrete, which is common in fishway construction. Extensive mussel colonization within fishways may affect fish passage by altering flow patterns or creating physical barriers, leading to increased travel times, or potentially preventing passage altogether. Many factors affect mussel habitat suitability including vectors of dispersal, water parameters, and various hydrodynamic quantities, such as water depth, velocity, and turbulence. The objective of this study is to assess the potential for zebra mussels to attach to fishway surfaces and form colonies in the McNary Lock and Dam Oregon-shore fishway and evaluate the potential impact of this infestation on the fishway’s efficiency. A computational fluid dynamics (CFD) model of the McNary Oregon-shore fishway was developed using the open-source code OpenFOAM, with the two-phase solver interFoam. Mesh quality is critical to obtain a reliable solution, so the numerical mesh was refined near the free surface and all solid surfaces to properly capture the complex flow patterns and free surface location. The simulation results for the 6-year average flow rate showed good agreement with the measured water column depth over each weir. Regions susceptible to mussel infestation were identified, and an analysis was performed to determine the mussel’s preference to colonize as a function of the depth-averaged velocity, water depth, and wall shear stress. Habitat suitability criteria were applied to the output of the hydraulic variables from the CFD solution and provided insight into the potential impact on the fishway efficiency. Details on the mesh construction, model setup, and numerical results are presented and discussed.

Influence of inertial and centrifugal forces on rate and flow patterns in natural fracture networks

Fluid production from fractured rock masses readily induces fracture flow velocities of meters per second. Yet, most discrete fracture flow models treat flow as laminar creeping flow or account for inertia effects only by single-fracture constitutive relationships.This numeric simulation study investigates water flow patterns and spatial velocity variations in a natural fracture network with mm-wide open fractures, studying the transition from laminar creeping to turbulent flow. After verification with a fracture intersection model, a Reynolds-time-averaged Navier Stokes solver serves to analyse flow regimes and velocity distribution. Our results show that for fracture flow velocities greater than ∼1-cm/s, fluid inertia begins to markedly alter flow patterns and the overall velocity distribution in the network. The pressure-gradient-flow relationship therefore becomes non-linear long before the flow in straight fractures enters the weak inertia regime. This prominence of inertia effects highlights the need to improve fracture network flow models.

How does the daily regulation hydropower station reduce the hydrological regime impact? A case study in upper Yellow River

ABSTRACT Human activities, particularly the regulation of hydropower stations, have profoundly altered river flow patterns. While studies have extensively assessed the impact of large or multi-year regulated hydropower stations on hydrological regimes using indicators of hydrological alteration (IHA) and range of variability approach (RVA), the impact of daily regulation hydropower stations has received comparatively less attention. This study aims to evaluate the influence of daily regulation hydropower stations on hydrological regime changes, focusing on the upper Yellow River region in China. Using daily runoff data from 1954 to 2020 at the Guide station, the study compares the impacts of multi-year regulated (Longyangxia) and daily regulation (Laxiwa and Nina) hydropower stations. The Mann-Kendall test showed that 27 out of 32 Indicators of Hydrological Alteration (IHAs) had significant trends under Longyangxia operation, which reduced to 18 IHAs with the inclusion of daily regulation stations. The Range of Variability Approach (RVA) revealed that only 46.87% of IHAs exhibited high alteration from the natural regime when daily regulation was considered, down from 75.00% with Longyangxia alone. This suggests that daily regulation can mitigate the negative impacts of multi-year regulation, potentially enhancing the river's eco-hydrological health.

Analysis of Intracranial Aneurysm Haemodynamics Altered by Wall Movement.

Computational fluid dynamics is intensively used to deepen our understanding of aneurysm growth and rupture in an attempt to support physicians during therapy planning. Numerous studies assumed fully rigid vessel walls in their simulations, whose sole haemodynamics may fail to provide a satisfactory criterion for rupture risk assessment. Moreover, direct in vivo observations of intracranial aneurysm pulsation were recently reported, encouraging the development of fluid-structure interaction for their modelling and for new assessments. In this work, we describe a new fluid-structure interaction functional setting for the careful evaluation of different aneurysm shapes. The configurations consist of three real aneurysm domes positioned on a toroidal channel. All geometric features, employed meshes, flow quantities, comparisons with the rigid wall model and corresponding plots are provided for the sake of reproducibility. The results emphasise the alteration of flow patterns and haemodynamic descriptors when wall deformations were taken into account compared with a standard rigid wall approach, thereby underlining the impact of fluid-structure interaction modelling.

Influence of Surface Waves on Liquid-to-Gas Mass Transfer in Molten Silicon

Abstract The paper focuses on the numerical analysis of the mass transfer of impurities from the wavy surface of molten silicon to the gas phase. The mathematical model is described herein, with the modelling of a wavy silicon melt surface being done with the moving mesh technique. The model employs assumptions about the mass transfer process on the surface, namely, that it can be modelled with effective diffusion across the interface. The assumption is verified against limited experimental data for a stationary melt surface, and reasonable agreement is obtained. Thereafter, numerical studies are undertaken for a wavy melt surface. The dependence of impurity removal rate on the wave amplitude, wavelength and frequency is analysed. It is shown that the waves on the surface of the liquid increase the mass transfer rate in a certain parameter range. Finally, results are analysed to find an explanation for this increase and to determine technological factors that impact it. Surface enlargement due to waves and altered flow patterns near the silicon melt are determined as potential reasons for the improved impurity removal rate. A dimensionless criterion for the minimal wave amplitude required to obtain improved impurity removal is found and discussed.

On the need for multi-dimensional models for the safety analysis of (fast-spectrum) Molten Salt Reactors

This paper aims at characterizing the impact of adopting numerical models with different dimensionalities on the predicted behavior of fast-spectrum Molten Salt Reactors (MSRs). The study encompasses 1-D, 2-D, and 3-D representations of thermal-hydraulics and precursor transport/diffusion, along with spatial and point kinetics models for neutronics. We evaluate the accuracy of each model based on steady-state results and on the reactor response to 2 different transient initiators. The findings emphasize the significance of utilizing a 3-D representation with accurate thermal-hydraulics modeling, and with either spatial kinetics or carefully calibrated point kinetics incorporating a spatial description of precursors transport. 2-D and 1-D models can reproduce main trends and remain valuable tools for e.g. reactor design, control-oriented studies or uncertainty quantification. However, proper calibration of these models is needed and the user should be aware that alterations in flow patterns could jeopardize model calibration and hide first-order local effects.

The effect of aortic valve replacement on 4D flow-measured flow displacement in patients with bicuspid and tri-leaflet aortic valves with severe aortic stenosis

Abstract Introduction Eccentric outflow jet direction in the ascending aorta is correlated with the altered haemodynamic flow patterns thought to contribute to bicuspid aortic valve (BAV)-associated aortopathy. Purpose We aimed to analyse the impact of surgical aortic valve replacement (AVR) on outflow jet displacement in the ascending aorta, and determine if differences exist between individuals with BAV and tri-leaflet aortic valves (TAV). Method Four-dimensional flow-cardiac magnetic resonance imaging (4D Flow) of the aorta was performed in prospectively recruited patients with BAV and TAV and severe symptomatic aortic stenosis (AS), before and 12 months after AVR. Healthy individuals with BAV and TAV morphology, but no significant valve disease, were also recruited as controls. Outflow direction was calculated from the in-plane, normalised flow displacement (NFD), defined as the distance between the centre of the aortic lumen (Clum) and the centre of velocity (Cvel) of the forward flow and normalised to the lumen diameter (Figure 1). Mean NFDs were evaluated at peak systole on planes perpendicular to 25 equidistant nodes along the centreline between the aortic root to the level of the pulmonary artery bifurcation in all subjects using custom Matlab code. Results 32 subjects with severe symptomatic AS (BAV n=11, TAV n=21; mean age 68±10 years) and 17 controls (BAV n=8, TAV n=9; mean age 57±7 years) were assessed (Table 1). In those with TAV, there were no differences in NFD between patients with severe AS pre-AVR compared to post-AVR, or compared to TAV controls. However, in BAV subjects, pre-AVR BAV patients with severe AS had a significantly higher mean NFD compared to BAV controls, and compared to pre-AVR TAV patients with severe AS. Post-AVR, there was no longer a significant difference in mean displacement between BAV vs TAV. Conclusion Our observations suggest that the BAV morphology plays a predominant role in the abnormal eccentric flow displacement in the ascending aorta, which may be normalised following bioprosthetic valve replacement. This may have implications for monitoring aortas post-AVR in BAV subjects.

Mixed convection of transient MHD stagnation point flow over a stretching sheet with quadratic convection and thermal radiation

AbstractThis study investigates the influence of quadratic (nonlinear) convection in transient magnetohydrodynamic (MHD) combined convection over a two‐dimensional stretching sheet. It explores the effects of thermal radiation, suction, and heat sources or sinks. The Crank–Nicholson implicit finite difference method is employed for numerical computations. The significance lies in considering secondary convection, which is crucial in understanding nonlinear convective effects affecting flow and heat transfer properties. The study aims to advance our comprehension of how secondary convection impacts the overall system behavior. Through numerical calculations validated against existing literature, strong agreement is demonstrated. The study evaluates secondary convection effects, magnetic, buoyancy, gravitational parameters, Prandtl number, and radiation parameters. Notably, strong quadratic convection alters flow patterns, affecting velocity and temperature profiles. Moreover, it is observed that when increasing the nonlinear (quadratic) convective factors, the temperature profile increases for and decreases for . The prevalence of nonlinear or second‐order convection highlights magnetic dominance. In essence, this research enhances our understanding of complex convection interactions in MHD flow, shedding light on the role of secondary convection in shaping system behavior.

The Use Of 4D Flow MRI in Predicting Clinical Outcomes in SAVR and TAVR

Four-dimensional (4D) flow magnetic resonance imaging (MRI) is a novel imaging technique capable of assessing aortic blood flow and quantifying aortic haemodynamics. Previous studies have reported alterations in aortic wall shear stress distribution and flow eccentricity after both transcatheter aortic valve replacement (TAVR) and surgical aortic valve replacement (SAVR); however, sample size was small, and follow-up limited. Previous studies have demonstrated that changes in the geometry of the AV, such as bicuspid valves, or AVR result in altered blood flow patterns and parameters. Transcatheter aortic valve implantation and AVR with a stented bioprosthesis lead to altered blood flow characteristics in the ascending aorta compared with healthy controls, with more intense flow eccentricity and regional elevation of wall shear stress.

Influence of operating conditions on in-tube vapour condensation heat transfer characteristics in the presence of noncondensable gases at high pressure

The in-tube vapour condensation heat characteristics in the presence of noncondensable gas at high pressures are experimentally validated with an error of 20%. Numerical simulations are then conducted to explore heat transfer characteristics at different operating pressures, wall surface temperatures and mass flow rates. The flow and heat transfer characteristics are thoroughly discussed and the buoyancy effects induce a secondary circulation altering flow patterns, changing the water film and heat transfer coefficient distribution. In addition, increasing operating pressures is found to reduce the wall heat transfer rate. Even though the flow pattern is significantly different caused by the increased gas mixture density, the total condensate flow rate is approximately the same at different operating pressures due to the same inlet conditions and temperature difference. The difference in the wall heat transfer rate is attributed to the change of latent heat of vapourisation and falling film at different pressures and is evident at high pressures. At the high temperature difference, a nonuniform film height towards the bottom is emerged, sweeping the condensate upward. Similarly, increasing the mass flow rate can also increase the total wall heat transfer rate and total condensate flow rate.

Hydro‐Thermodynamic Processes at a Large Confluence Under Reservoir Regulation

AbstractConfluences are ubiquitous and important components in river systems, and their hydrodynamic complexity attracts increasing attention. The flow pattern in a confluence is influenced by the planform geometry, momentum, discharge ratio and bed concordance/discordance. In recent years, flow density is found to be a significant factor in natural confluence flow patterns, while the generated hydrodynamic processes that affects mixing within confluences are not fully known, especially in large rivers under heavy human activities. In this study, we investigate the hydro‐thermodynamic processes at a major confluence in the Yangtze River using a three‐dimensional numerical model. The water level in the confluence zone is regulated seasonally by the Three Gorges Reservoir, that is, the zone is within the reservoir's fluctuating backwater reach. The results show that reservoir regulation alters flow patterns in the confluence zone significantly in both horizontal and vertical planes, including shrinking re‐circulation, complicated cross‐sectional vortexes, as well as weakened riverine mixing capacity. The density difference leads to changes in the hydro‐thermodynamic processes, especially in combination with the reservoir regulation. When the tributary water temperature is high, the generated buoyancy strengthens the secondary flow in the mainstream, which further enhances the lateral transport capacity and accelerates the water mixing. More importantly, it is found that the combined effect of reservoir regulation and thermal buoyancy alters the flow structure considerably in the confluence zone, and modifies the water transport mode in the mainstream. Thus, a dimensionless number S is defined to represent the lateral water transport capacity.

Effect of fillets on a blade/vane of wave energy harvesting impulse turbine

Fillets on leading edges (LE) of turbine blades alter flow patterns and change the loss profile. A bidirectional flow impulse turbine utilized for harnessing wave energy is introduced and computational fluid dynamics (CFD) was used to perform various analysis. In the present work, fillets of different radii on the leading and trailing edges of both the rotor blade (RB) and guide vane (GV) are modified to study the change in overall performance. After an appropriate gird convergence study, ANSYS-CFX 16.0 solver is used for solving the Reynolds averaged Navier-Stokes (RANS) equations incorporating the k-ω-SST turbulence closure model. The numerical investigations were performed using the high-resolution scheme with the convergence criteria of 10−6 to produce unwavering results. The results show that the boundary layer near the endwall creates flow blockage and losses. Also, the increase in pressure drop due to the thickening of the boundary layers (BLs) across the blade/vane leads to a depletion in the overall performance of the turbine. The rotor and guide vane filleted turbine experience higher losses than the base model due to the radial pressure gradient that is explained with post-processed figures. The concept of fillet shapes has been applied to gas turbines and which improves the performance of the turbine due to a reduction in the secondary flow losses occurring inside the turbine and the same concept has been applied to wave energy air turbine to check its performance based on the losses present across the turbine passage.

The role of 4-dimensional flow in the assessment of bicuspid aortic valve and its valvulo-aortopathies.

Bicuspid aortic valve is the most common congenital cardiac malformation and the leading cause of aortopathy and aortic stenosis in younger patients. Aortic wall remodelling secondary to altered haemodynamic flow patterns, changes in peak velocity, and wall shear stress may be implicated in the development of aortopathy in the presence of bicuspid aortic valve and dysfunction. Assessment of these parameters as potential predictors of disease severity and progression is thus desirable. The anatomic and functional information acquired from 4D flow MRI can allow simultaneous visualisation and quantification of the pathological geometric and haemodynamic changes of the aorta. We review the current clinical utility of haemodynamic quantities including velocity, wall sheer stress and energy losses, as well as visual descriptors such as vorticity and helicity, and flow direction in assessing the aortic valve and associated aortopathies.

Altered cerebral blood flow patterns in ankylosing spondylitis: A three-dimensional pseudo-continuous arterial spin labeling study.

ObjectiveThis study aimed to detect the cerebral blood flow (CBF) values changes in patients with ankylosing spondylitis (AS) and to evaluate the correlation between the CBF values and the specific clinical characteristics.Materials and methodsForty-eight patients with AS (43 male and 5 female) and 42 healthy controls (HCs) (38 male and 4 female) were recruited. Three-dimensional pseudo-continuous arterial spin labeling (3D-pCASL) was performed on a 3.0T magnetic resonance imaging (MRI). CBF values were obtained on the Philips post-processing workstation based on arterial spin labeling (ASL) data. The two-sample t-test was used to compare CBF differences. The correlation between CBF values and specific clinical characteristics of AS was evaluated.ResultsThe AS group showed increased CBF values in the right precentral gyrus, the left inferior frontal gyrus, and the left temporal pole compared with HCs the AS group also showed decreased CBF values in the left precuneus and the left superior occipital gyrus compared with HCs. There were no significant correlations between the CBF values and the clinical characteristics including total back pain (TBP), erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP).ConclusionPatients with AS displayed CBF changes compared with HCs using 3D-PCASL. These results may enhance our understanding of the neural substrates of AS and provide evidence of AS-related neurological impairment.

Aortic Viscous Energy Loss for Assessment of Valve-related Hemodynamics in Asymptomatic Severe Aortic Stenosis

Purpose To investigate whether functional assessment of aberrant flow patterns by viscous energy loss (E′L) using four-dimensional (4D) flow MRI could determine aortic stenosis (AS) severity in accordance with transvalvular energy loss and aid in surgical decision-making in asymptomatic patients with severe AS. Materials and Methods In this prospective, single-center study, E′L was measured in the thoracic aorta of 74 consecutive asymptomatic patients with severe AS and preserved left ventricular ejection fraction who presented between January 2015 and December 2017, and 23 healthy volunteers using 4D flow MRI. Transvalvular energy loss was assessed based on the energy loss index (ELI) measured using Doppler echocardiography. The association between E′L and AS-related events including aortic valve replacement was evaluated by receiver operating characteristic curve analysis, Kaplan-Meier analysis, and multivariable Cox regression analysis. Results Among 74 asymptomatic patients with severe AS (mean age, 60 years ± 9 [SD]; 43 men; 56 with bicuspid aortic valve), 33 experienced AS-related events during a median follow-up of 42 months (IQR, 30–53 months). Altered flow patterns in severe AS resulted in a sevenfold increase in peak systolic E′L in the ascending aorta compared with controls (13.9 mW ± 3.4 vs 1.80 mW ± 0.44; P < .001). Peak systolic E′L in the ascending aorta was independently associated with the ELI (standardized β, −0.52; P < .001) and showed better discrimination for AS-related events (area under the curve, 0.83; 95% CI: 0.74, 0.93; P < .001) than conventional echocardiographic parameters. After adjustment for confounding variables, peak systolic E′L in the ascending aorta was associated with a significant increase in AS-related events (P < .001 for adjusted hazard ratio). Conclusion Changes in AS-mediated poststenotic three-dimensional outflow patterns can be quantified by 4D flow MRI-derived energetic markers to aid in the risk stratification and clinical management of asymptomatic patients with severe AS. Keywords: Aortic Stenosis, 4D Flow MRI, Flow Energetics, Vascular, Aorta, Aortic Valve, MR Angiography Supplemental material is available for this article. © RSNA, 2022

479 Commissural Misalignment Is An Independent Predictor Of Leaflet Thrombosis After Transcatheter Aortic Valve Implantation

Introduction: Hypo-attenuated leaflet thickening (HALT) - a marker of subclinical leaflet thrombosis commonly detected by cardiac computed tomography (CT) after transcatheter aortic valve implantation (TAVI) - may influence valve durability and function. We hypothesize that altered flow patterns in the aortic root as a consequence of commissural misalignment may contribute to the occurrence of HALT. Therefore, the purpose of this project was to compare the commissural alignment of the native and prosthetic aortic valves in cardiac CT in subjects with and without HALT and thereby identify potential predictors for subclinical leaflet thrombosis after TAVI.

Solid-liquid phase change subjected to unipolar charge injection from a circular wire electrode

A numerical investigation of isothermal melting of a dielectric phase change material in a square cavity subjected to unipolar charge injection from a circular wire electrode is reported. Governing equations for the solid-liquid phase change under the influence of an electric field include the Navier–Stokes equations for fluid flow, energy equation for thermal transport, Poisson equation for electric potential, and the Nernst-Planck equation for charge conservation. An enthalpy source-term based fixed grid approach is adopted to model the melting process. The governing equations that consider the coupled interactions between flow, thermal and electric fields are solved using the finite volume framework of OpenFOAM®. Time evolution of the melting rate, maximum flow velocity, mean Nusselt number, and mean Coulomb force in the electrohydrodynamic flow assisted melting process is mapped. The mechanism and role of electrohydrodynamic forces on influencing the net flow and melt interface morphology is studied. The competing viscous, buoyancy, and electric forces result in an altered flow pattern that aids the melting process. The enhancement in the rate of melting at different strengths of buoyancy and electrostatic forces is quantified. Furthermore, the effects of the radius of the circular wire electrode in relation to the cavity size are highlighted. A maximum of 63% enhancement in melting rate is observed within the considered parameter space.

Right Ventricular Flow Vorticity Relationships With Biventricular Shape in Adult Tetralogy of Fallot.

Remodeling in adults with repaired tetralogy of Fallot (rToF) may occur due to chronic pulmonary regurgitation, but may also be related to altered flow patterns, including vortices. We aimed to correlate and quantify relationships between vorticity and ventricular shape derived from atlas-based analysis of biventricular shape. Adult rToF (n = 12) patients underwent 4D flow and cine MRI imaging. Vorticity in the RV was computed after noise reduction using a neural network. A biventricular shape atlas built from 95 rToF patients was used to derive principal component modes, which were associated with vorticity and pulmonary regurgitant volume (PRV) using univariate and multivariate linear regression. Univariate analysis showed that indexed PRV correlated with 3 modes (r = −0.55,−0.50, and 0.6, all p < 0.05) associated with RV dilatation and an increase in basal bulging, apical bulging and tricuspid annulus tilting with more severe regurgitation, as well as a smaller LV and paradoxical movement of the septum. RV outflow and inflow vorticity were also correlated with these modes. However, total vorticity over the whole RV was correlated with two different modes (r = −0.62,−0.69, both p < 0.05). Higher vorticity was associated with both RV and LV shape changes including longer ventricular length, a larger bulge beside the tricuspid valve, and distinct tricuspid tilting. RV flow vorticity was associated with changes in biventricular geometry, distinct from associations with PRV. Flow vorticity may provide additional mechanistic information in rToF remodeling. Both LV and RV shapes are important in rToF RV flow patterns.