scholarly journals Intraventricular Flow Simulations in Singular Right Ventricles Reveal Deteriorated Washout and Low Vortex Formation

2021 ◽  
Author(s):  
Anna Grünwald ◽  
Jana Korte ◽  
Nadja Wilmanns ◽  
Christian Winkler ◽  
Katharina Linden ◽  
...  
Keyword(s):  
Vortex Formation ◽  
Three Dimensional ◽  
Patient Specific ◽  
Univentricular Heart ◽  
Cfd Simulations ◽  
Vortex Formation Time ◽  
Intraventricular Flow ◽  
Cardiac Lesions ◽  
Health And Disease ◽  
Echocardiographic Images

Abstract Purpose Patients with a functionally univentricular heart represent one of the most common severe cardiac lesions with a prevalence of 3 per 10,000 live births. Hemodynamics of the singular ventricle is a major research topic in cardiology and there exists a relationship between fluid dynamical features and cardiac behavior in health and disease. The aim of the present work was to compare intraventricular flow in single right ventricle (SRV) patients and subjects with healthy left hearts (LV) through patient-specific CFD simulations. Methods Three-dimensional real-time echocardiographic images were obtained for five SRV patients and two healthy subjects and CFD simulations with a moving mesh methodology were performed. Intraventricular vortex formation and vortex formation time (VFT) as well as the turbulent kinetic energy (TKE) and ventricular washout were evaluated. Results The results show significantly lower values for the VFT and the TKE in SRV patients compared with healthy LV subjects. Furthermore, vortex formation does not progress to the apex in SRV patients. These findings were confirmed by a significantly lower washout in SRV patients. Conclusions The study pinpoints the intriguing role of intraventricular flows to characterize performance of SRVs that goes beyond standard clinical metrics such as ejection fraction.

scholarly journals Intraventricular hemodynamics in pediatric patients with single right ventricles reveal deteriorated washout and low vortex for-mation times: An in silico study

2020 ◽  
Author(s):  
Anna Gruenwald ◽  
Jana Korte ◽  
Nadja Wilmanns ◽  
Christian Winkler ◽  
Katharina Linden ◽  
...  
Keyword(s):  
Right Ventricle ◽  
Cfd Simulation ◽  
Fontan Procedure ◽  
Vortex Formation ◽  
Three Dimensional ◽  
Flow Simulation ◽  
Patient Specific ◽  
Univentricular Heart ◽  
Numerical Comparison ◽  
Vortex Formation Time

The congenital heart disease univentricular heart (UVH) occurs with an incidence of 0.04-0.5% in newborns and is often treated with the Fontan procedure. In this intervention, the cardiac circulation is transformed into a singular circulation with only one ventricular chamber pumping. Hemodynamics the singular ventricle is a major research topic in cardiology and there exists a rela-tionship between fluid dynamical features and cardiac behavior in health and disease. By visualizing the flow using Computational Fluid Dynamics (CFD) models, an option is created to investigate the flow in patient-specific geometries. CFD simulation of the pathological single right ventricle in contrast to the healthy left ventricle is the research object of the present work. The aim is the numerical comparison of the intraventricular flow within the ventricles. Based on this, flow formation in different anatomies of the ventricles is investi-gated. Patient-specific measurements of ventricles from three-dimensional real-time echocardiographic im-ages served as the basis for the simulations with five single right ventricle (SRV) patients and two sub-jects with healthy left hearts (LV) investigated. Interpolation of these data reproduced the shape and continuous motion of the heart during a cardiac cycle. This motion was implemented into a CFD mod-el with a moving mesh methodology. For comparison of the ventricles, the vortex formation as well as the occurring turbulent kinetic energy (TKE) and washout were evaluated. Vortex formation was as-sessed using the dimensionless vortex formation time (VFT). The results show significantly lower values for the VFT and the TKE in SRV patients than for the compared LV Patients. Furthermore, vortex formation does not progress to the apex in SRV patients. These findings were confirmed by a significantly lower washout in SRV patients. Flow simulation within the moving ventricle provides the possibility of more detailed analysis of the ventricular function. Simulation results show altered vortex formation and reduced washout of SRV in comparison to healthy LV. This information could provide important information for the planning and treatment of Fontan patients.

Vortex Generation in Two Intracranial Aneurysms

2014 ◽  
Author(s):  
Hafez Asgharzadeh ◽  
Iman Borazjani ◽  
Jianping Xiang ◽  
Hui Meng
Keyword(s):  
Immersed Boundary Method ◽  
Time Scale ◽  
Vortex Formation ◽  
Three Dimensional ◽  
Immersed Boundary ◽  
Parent Artery ◽  
Aneurysm Neck ◽  
Vortex Formation Time ◽  
Previous Hypothesis ◽  
Aneurysm Shape

Three-dimensional numerical simulations, using the sharp-interface immersed boundary method, are carried out to investigate the effect of aneurysm shape on the hemodynamics of intracranial aneurysm. In our previous work [1] only a single geometry of an aneurysm was tested, but here two three-dimensional geometries are tested by reconstruction from three-dimensional rotational angiography of a human subject [2]. The results support our previous hypothesis [1], i.e., when the vortex formation time scale at the parent artery is smaller than the transportation time scale across the aneurysm neck, the flow aneurysm dome is dominated by a dynamic, unsteady vortex formation.

A scaling for vortex formation on swept and unswept pitching wings

2017 ◽  
Vol 832 ◽  
pp. 697-720 ◽  
Author(s):  
Kyohei Onoue ◽  
Kenneth S. Breuer
Keyword(s):  
Control Volume ◽  
Vortex Formation ◽  
Fluid Motion ◽  
Three Dimensional ◽  
Leading Edge ◽  
Sweep Angle ◽  
Reduced Frequency ◽  
Vortex Formation Time ◽  
The Stability ◽  
Vorticity Transport

We examine the dynamics of the leading-edge vortex (LEV) on a rapidly pitching plate with the aim of elucidating the underlying flow physics that dictates the stability and circulation of the LEV. A wide variety of flow conditions is considered in the present study by systematically varying the leading-edge sweep angle ($\unicode[STIX]{x1D6EC}=0^{\circ }$, $11.3^{\circ }$, $16.7^{\circ }$) and the reduced frequency ($f^{\ast }=0.064{-}0.151$), while keeping the pitching amplitude and the Reynolds number fixed. Tomographic particle image velocimetry is used to characterise the three-dimensional fluid motion inside the vortex core and its relation to the LEV stability and growth. A series of control volume analyses are performed to quantify the relative importance of the vorticity transport phenomena taking place inside the LEV to the overall vortex development. We show that, near the wing apex where tip effects can be neglected, the vortex develops in a nominally two-dimensional manner, despite the presence of inherently three-dimensional vortex dynamics such as vortex stretching and compression. Furthermore, we demonstrate that the vortex formation time and circulation growth are well-described by the principles of optimal vortex formation number, and that the occurrence of vortex shedding is dictated by the relative energetics of the feeding shear layer and the resulting vortex.

scholarly journals Validation of CFD Simulations of Cerebral Aneurysms With Implication of Geometric Variations

2006 ◽  
Vol 128 (6) ◽  
pp. 844-851 ◽  
Author(s):  
Yiemeng Hoi ◽  
Scott H. Woodward ◽  
Minsuok Kim ◽  
Dale B. Taulbee ◽  
Hui Meng
Keyword(s):  
Flow Field ◽  
Cfd Simulation ◽  
Three Dimensional ◽  
Cerebral Aneurysms ◽  
Patient Specific ◽  
Hemodynamic Parameters ◽  
Cfd Simulations ◽  
Piv Measurements ◽  
Cfd Method ◽  
Aneurysm Model

Background. Computational fluid dynamics (CFD) simulations using medical-image-based anatomical vascular geometry are now gaining clinical relevance. This study aimed at validating the CFD methodology for studying cerebral aneurysms by using particle image velocimetry (PIV) measurements, with a focus on the effects of small geometric variations in aneurysm models on the flow dynamics obtained with CFD. Method of Approach. An experimental phantom was fabricated out of silicone elastomer to best mimic a spherical aneurysm model. PIV measurements were obtained from the phantom and compared with the CFD results from an ideal spherical aneurysm model (S1). These measurements were also compared with CFD results, based on the geometry reconstructed from three-dimensional images of the experimental phantom. We further performed CFD analysis on two geometric variations, S2 and S3, of the phantom to investigate the effects of small geometric variations on the aneurysmal flow field. Results. We found poor agreement between the CFD results from the ideal spherical aneurysm model and the PIV measurements from the phantom, including inconsistent secondary flow patterns. The CFD results based on the actual phantom geometry, however, matched well with the PIV measurements. CFD of models S2 and S3 produced qualitatively similar flow fields to that of the phantom but quantitatively significant changes in key hemodynamic parameters such as vorticity, positive circulation, and wall shear stress. Conclusion. CFD simulation results can closely match experimental measurements as long as both are performed on the same model geometry. Small geometric variations on the aneurysm model can significantly alter the flow-field and key hemodynamic parameters. Since medical images are subjected to geometric uncertainties, image-based patient-specific CFD results must be carefully scrutinized before providing clinical feedback.

CFD and PTV Steady Flow Investigation in an Anatomically Accurate Abdominal Aortic Aneurysm

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Evangelos Boutsianis ◽  
Michele Guala ◽  
Ufuk Olgac ◽  
Simon Wildermuth ◽  
Klaus Hoyer ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Three Dimensional ◽  
Numerical Data ◽  
Aortic Aneurysms ◽  
Patient Specific ◽  
Velocity Measurements ◽  
Cfd Simulations ◽  
Aneurysm Neck ◽  
Hexahedral Elements ◽  
Abdominal Aortic

There is considerable interest in computational and experimental flow investigations within abdominal aortic aneurysms (AAAs). This task stipulates advanced grid generation techniques and cross-validation because of the anatomical complexity. The purpose of this study is to examine the feasibility of velocity measurements by particle tracking velocimetry (PTV) in realistic AAA models. Computed tomography and rapid prototyping were combined to digitize and construct a silicone replica of a patient-specific AAA. Three-dimensional velocity measurements were acquired using PTV under steady averaged resting boundary conditions. Computational fluid dynamics (CFD) simulations were subsequently carried out with identical boundary conditions. The computational grid was created by splitting the luminal volume into manifold and nonmanifold subsections. They were filled with tetrahedral and hexahedral elements, respectively. Grid independency was tested on three successively refined meshes. Velocity differences of about 1% in all three directions existed mainly within the AAA sack. Pressure revealed similar variations, with the sparser mesh predicting larger values. PTV velocity measurements were taken along the abdominal aorta and showed good agreement with the numerical data. The results within the aneurysm neck and sack showed average velocity variations of about 5% of the mean inlet velocity. The corresponding average differences increased for all velocity components downstream the iliac bifurcation to as much as 15%. The two domains differed slightly due to flow-induced forces acting on the silicone model. Velocity quantification through narrow branches was problematic due to decreased signal to noise ratio at the larger local velocities. Computational wall pressure and shear fields are also presented. The agreement between CFD simulations and the PTV experimental data was confirmed by three-dimensional velocity comparisons at several locations within the investigated AAA anatomy indicating the feasibility of this approach.

scholarly journals Three-dimensional printing of atrial septal defect from echocardiographic images: feasibility, fidelity and potential applications

2021 ◽  
Author(s):  
Dan'e Mei ◽  
jinling chen ◽  
Qing Zhou ◽  
Sheng Cao ◽  
Zhiyu Zhao ◽  
...  
Keyword(s):  
Atrial Septal Defect ◽  
Septal Defect ◽  
Three Dimensional ◽  
Absolute Difference ◽  
Patient Specific ◽  
Three Dimensional Printing ◽  
Maximal Diameter ◽  
Potential Applications ◽  
3D Printed ◽  
Echocardiographic Images

Objectives —We sought to investigate the technical feasibility, fidelity and the potential applications of three-dimensional(3D) printed atrial septal defect (ASD) models based on three-dimensional transesophageal echocardiography (3D-TEE) images preliminarily. Methods—We retrospectively collected 40 ASD patients’ 3D-TEE images. The 3D-TEE data were imported into post-processing software to create printable 3D digital models, the patient-specific models were then printed by the 3D printer. Fidelity of the 3D printed models were quantitatively evaluated by comparing the measurements from 3D ASD models and echocardiographic data. Results —Ultrasound-derived 3D ASD models were acquired in all the forty cases successfully. There was good consistency and no significant differences in ASD size parameters among 3D printed models, 2D-TEE images and 3D-TEE images（all P>0.05）. Also, it showed small difference among 3D printed models, 2D-TEE images and 3D-TEE images in the absolute difference value of ASD size parameters. There’s a highly significant correlation between the ASD parameters including the maximal diameter, the minimal diameter and circumference measured by 3D ASD printed models and the corresponding parameters of ASD occluders applied in actual surgical procedure. Simulation exercises in the 3D ASD printed models had an impressive effect based on the comprehensive assessment of the ASD parameters. Conclusions—It is feasible to use 3D-TEE images as the data source of ASD 3D printed models. Ultrasound-derived ASD 3D printed models show highly fidelity, which contributes to provide evidence for the clinical application of 3D printing technology in decision of ASD occlusion.

scholarly journals Particulate Deposition in a Patient With Tracheal Stenosis

2017 ◽  
Vol 1 (1) ◽  
Author(s):  
S. Taherian ◽  
H. R. Rahai ◽  
J. Bonifacio ◽  
B. Z. Gomez ◽  
Thomas Waddington
Keyword(s):  
Tracheal Stenosis ◽  
Air Flow ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Ct Images ◽  
Patient Specific ◽  
Post Intervention ◽  
Cfd Simulations ◽  
Layer Manufacturing ◽  
Computational Fluid Dynamics Cfd

The presence of obstructions such as tracheal stenosis has important effects on respiratory functions. Tracheal stenosis impacts the therapeutic efficacy of inhaled medications as a result of alterations in particle transport and deposition pattern. This study explores the effects of the presence and absence of stenosis/obstruction in the trachea on air flow characteristics and particle depositions. Computational fluid dynamics (CFD) simulations were performed on three-dimensional (3D) patient-specific models created from computed tomography (CT) images. The analyzed model was generated from a subject with tracheal stenosis and includes the airway tree up to eight generations. CT scans of expiratory and inspiratory phases were used for patient-specific boundary conditions. Pre- and post-intervention CFD simulations' comparison reveals the effect of the stenosis on the characteristics of air flow, transport, and depositions of particles with diameters of 1, 2.5, 4, 6, 8, and 10 μm. Results indicate that the existence of the stenosis inflicts a major pressure force on the flow of inhaled air, leading to an increased deposition of particles both above and below the stenosis. Comparisons of the decrease in pressure in each generation between pre- and post-tracheal stenosis intervention demonstrated a significant reduction in pressure following the stenosis, which was maintained in all downstream generations. Good agreements were found using experimental validation of CFD findings with a model of the control subject up to the third generation, constructed via additive layer manufacturing from CT images.

Performance enhancement of Savonius wind turbine by blade shape and twisted angle modifications

2021 ◽  
pp. 095765092098794
Author(s):  
Ahmed M Nagib Elmekawy ◽  
Hassan A Hassan Saeed ◽  
Sadek Z Kassab
Keyword(s):  
Wind Turbine ◽  
Performance Enhancement ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Vertical Axis ◽  
Cfd Simulations ◽  
Sliding Mesh ◽  
Blade Shape ◽  
Rotor Shape ◽  
Twisting Angle

Three-dimensional CFD simulations are carried out to study the increase of power generated from Savonius vertical axis wind turbines by modifying the blade shape and blade angel of twist. Twisting angle of the classical blade are varied and several proposed novel blade shapes are introduced to enhance the performance of the wind turbine. CFD simulations have been performed using sliding mesh technique of ANSYS software. Four turbulence models; realizable k -[Formula: see text], standard k - [Formula: see text], SST transition and SST k -[Formula: see text] are utilized in the simulations. The blade twisting angle has been modified for the proposed dimensions and wind speed. The introduced novel blade increased the power generated compared to the classical shapes. The two proposed novel blades achieved better power coefficients. One of the proposed models achieved an increase of 31% and the other one achieved 32.2% when compared to the classical rotor shape. The optimum twist angel for the two proposed models achieved 5.66% and 5.69% when compared with zero angle of twist.

scholarly journals Radial Turbine Design for Solar Chimney Power Plants

Energies ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 674
Author(s):  
Paul Caicedo ◽  
David Wood ◽  
Craig Johansen
Keyword(s):  
Power Plants ◽  
Reference Frames ◽  
Three Dimensional ◽  
Discrete Ordinates ◽  
Large Area ◽  
Solar Chimney ◽  
Cfd Simulations ◽  
Radial Turbine ◽  
Design Changes ◽  
Turbine Design

Solar chimney power plants (SCPPs) collect air heated over a large area on the ground and exhaust it through a turbine or turbines located near the base of a tall chimney to produce renewable electricity. SCPP design in practice is likely to be specific to the site and of variable size, both of which require a purpose-built turbine. If SCPP turbines cannot be mass produced, unlike wind turbines, for example, they should be as cheap as possible to manufacture as their design changes. It is argued that a radial inflow turbine with blades made from metal sheets, or similar material, is likely to achieve this objective. This turbine type has not previously been considered for SCPPs. This article presents the design of a radial turbine to be placed hypothetically at the bottom of the Manzanares SCPP, the only large prototype to be built. Three-dimensional computational fluid dynamics (CFD) simulations were used to assess the turbine’s performance when installed in the SCPP. Multiple reference frames with the renormalization group k-ε turbulence model, and a discrete ordinates non-gray radiation model were used in the CFD simulations. Three radial turbines were designed and simulated. The largest power output was 77.7 kW at a shaft speed of 15 rpm for a solar radiation of 850 W/m2 which exceeds by more than 40 kW the original axial turbine used in Manzanares. Further, the efficiency of this turbine matches the highest efficiency of competing turbine designs in the literature.

scholarly journals Numerical computation of blood flow for a patient-specific hemodialysis shunt model

2021 ◽  
Author(s):  
Surabhi Rathore ◽  
Tomoki Uda ◽  
Viet Q. H. Huynh ◽  
Hiroshi Suito ◽  
Toshitaka Watanabe ◽  
...  
Keyword(s):  
Stokes Equations ◽  
Three Dimensional ◽  
Arteriovenous Shunt ◽  
Navier Stokes ◽  
Patient Specific ◽  
Stabilized Finite Element ◽  
Computed Tomography Scanning ◽  
Outflow Boundary ◽  
Stage Renal Disease ◽  
End Stage

AbstractHemodialysis procedure is usually advisable for end-stage renal disease patients. This study is aimed at computational investigation of hemodynamical characteristics in three-dimensional arteriovenous shunt for hemodialysis, for which computed tomography scanning and phase-contrast magnetic resonance imaging are used. Several hemodynamical characteristics are presented and discussed depending on the patient-specific morphology and flow conditions including regurgitating flow from the distal artery caused by the construction of the arteriovenous shunt. A simple backflow prevention technique at an outflow boundary is presented, with stabilized finite element approaches for incompressible Navier–Stokes equations.

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