Wall Shear Stress Decrease Research Articles

Discrete particle behavior in solid-liquid concave-wall jet

The aim of this paper is to reveal the solid-liquid separation mechanism in concave-wall jet. The discrete particle experiments and numerical simulations were performed to study the large particle behavior near concave-wall. The results show that the particle behavior is divided into two stages by the first collision point of particle-to-wall and the wall shear stress at the collision point quickly changes from zero to peak. The iterative formulae for particle position coordinates are used and 27.88° is obtained as the maximum of circumferential collision position when the jet width is 20 mm. Before the first collision, the particle tangential velocity is constant and the wall shear stress is 0. After the first collision, the wall shear stress and tangential velocity decrease with time. The distance of particle-to-wall is within 0.1 times of jet width. Low-frequency contact of particle-to-wall is the collision and the particle Reynolds number often exceeds 400. The large particle behavior is affected by the shape of jet inlet cross-section. Comparing to the square inlet cross-section, the particle cumulative probability of rectangle inlet cross-section is lower at the same residence time, the local maximum of turbulent kinetic energy and wall shear stress decrease 5.3 % and 5.9 %, respectively.

Numerical Simulation of Non-Newtonian Blood Flow through a Tapered Stenosed Artery using the Cross Model

A Non-Newtonian model is used to examine the effect of tapering on the flow of blood along a stenosed artery which is caused by the pulsating nature the heart. The constitutive equation of the Cross model is used to capture the rheology of the streaming blood which accounts for the shear thinning behaviour of blood. The flow is considered to be laminar, incompressible, and axisymmetric. The finite- difference scheme was adopted to solve the non-linear equations describing the fluid motion in an unsteady two-dimensional case. The computation is presented in terms of the axial and radial velocities, volumetric flow rate, resistance to flow and the wall shear stress. The result from the numerical simulation clearly indicates that vessel tapering has considerable effect on the flow pattern of blood: as the tapering angle increases the flow rate and the axial velocity increases proportionately while the radial velocity, wall shear stress decreases and resistance to flow.

Evaluation of personalized right ventricle to pulmonary artery conduits using in silico design and computational analysis of flow.

ObjectivesRight ventricle to pulmonary artery (RV-PA) conduits are required for the surgical management of pulmonary atresia with ventricular septal defect and truncus arteriosus. Bioengineered RV-PA connections may address some of the shortcomings of homografts and xenografts, such as lack of growth potential and structural deterioration and may be manufactured to accommodate patient-specific anatomy. The aim of this study was to develop a methodology for in silico patient-specific design and analysis of RV-PA conduits.MethodsCross-sectional imaging was obtained from patients with truncus arteriosus (n = 5) and pulmonary atresia with ventricular septal defect (n = 5) who underwent complete repair with a RV-PA conduit. Three-dimensional models of the heart were constructed by segmentation of the right ventricle, existing conduit, branch pulmonary arteries, and surrounding structures. A customized conduit design for each patient was proposed. Computational fluid dynamics analysis was performed and outputs, including wall shear stress and energy loss, were used to compare the performance of the existing conduits and the customized geometries.ResultsIn this study, a methodology for patient-specific analysis of RV-PA conduit in silico was developed. The results of simulations for 10 patients showed between 23% and 56% decrease in the average wall shear stress and between 24% and 87% reduction in average power requirements in customized designs compared with the stenosed conduits, translating into better hemodynamic performance.ConclusionsCreation of an optimal conduit for an individual patient can be achieved using surgeon-guided design and computational fluid dynamics analysis. Manufacture of personalized RV-PA conduits may obviate the need for surgical customization to accommodate existing materials and provide superior long-term outcomes.

Abnormal Flow Dynamics Result in Low Wall Shear Stress and High Oscillatory Shear Index in Abdominal Aortic Dilatation: Initial in vivo Assessment with 4D-flow MRI.

Purpose:To characterize the non-laminar flow dynamics and resultant decreased wall shear stress (WSS) and high oscillatory shear index (OSI) of the infrarenal abdominal aortic dilatation, cardiac phase-resolved 3D phase-contrast MRI (4D-flow MRI) was performed.Methods:The prospective single-arm study was approved by the Institutional Review Board and included 18 subjects (median 67.5 years) with the dilated infrarenal aorta (median diameter 35 mm). 4D-flow MRI was conducted on a 1.5T MRI system. On 3D streamline images, laminar and non-laminar (i.e., vortex or helical) flow patterns were visually assessed both for the dilated aorta and for the undilated upstream aorta. Cardiac phase-resolved flow velocities, WSS and OSI, were also measured for the dilated aorta and the upstream undilated aorta.Results:Non-laminar flow represented by vortex or helical flow was more frequent and overt in the dilated aorta than in the undilated upstream aorta (P < 0.0156) with a very good interobserver agreement (weighted kappa: 0.82–1.0). The WSS was lower, and the OSI was higher on the dilated aortic wall compared with the proximal undilated segments. In mid-systole, mean spatially-averaged WSS was 0.20 ± 0.016 Pa for the dilated aorta vs. 0.68 ± 0.071 Pa for undilated upstream aorta (P < 0.0001), and OSI on the dilated aortic wall was 0.093 ± 0.010 vs. 0.041 ± 0.0089 (P = 0.013). The maximum values and the amplitudes of the WSS at the dilated aorta were inversely proportional to the ratio of dilated/undilated aortic diameter (r = −0.694, P = 0.0014).Conclusion:4D-flow can characterize abnormal non-laminar flow dynamics within the dilated aorta in vivo. The wall of the infrarenal aortic dilatation is continuously and increasingly affected by atherogenic stimuli due to the flow disturbances represented by vortex or helical flow, which is reflected by lower WSS and higher OSI.

Effect of sex differences in treatment response to angioplasty in a murine arteriovenous fistula model.

Failure to mature and venous neointimal hyperplasia formation are the two major causes of hemodialysis arteriovenous fistula (AVF) vascular access failure. Percutaneous transluminal angioplasty (PTA) is the firstline treatment for both of these conditions, but, clinically, women have decreased patency rates compared with men. The hypothesis to be tested in the present study was that female mice after PTA of venous areas of higher intimal thickening have increased gene expression of transforming growth factor-β1 (TGF-β1) and TGF-β receptor 1 (TGFβ-R1) accompanied with histological changes of fibrosis compared with male mice. Seventeen male and eighteen female C57BL/6J mice were used in this study. Chronic kidney disease was induced by partial nephrectomy, and, 28 days later, an AVF was created to connect the left carotid artery to the right jugular vein. Two weeks later, the higher intimal thickening area was treated with PTA, and mice were euthanized 3 days later for gene expression analysis or 14 days later for histopathological analysis. Doppler ultrasound was performed weekly after AVF creation. At day 3, female AVF had significantly higher average gene expression of TGF-β1 and TGFβ-R1 compared with male AVF. At day 14, female outflow veins had a smaller venous diameter, lumen vessel area, decreased wall shear stress, lower average peak systolic velocity, and an increased neointima area-to-media area ratio. Moreover, female outflow veins showed a significant increase in α-smooth muscle actin and fibroblast-specific protein-1. There was a decrease in M1/M2 with an increase in CD68.

Numerical studies of hemodynamic alterations in pre- and post-stenting cerebral aneurysms using a multiscale modeling.

The aim of this work was to use a multiscale modeling to study the influence of stent deployment, with generic stents, on flow distributions within the vascular network and the hemodynamic alterations within the cerebral aneurysms pre- and post-stenting. To achieve this goal, two image-based anatomical cerebral aneurysm models were reconstructed along with the respective aneurysms post-stenting models after deploying a 16- or 24-wire stent. The investigation results revealed that the stent may increase the local pressure resistance resulting in flow alterations. The hemodynamic parameters demonstrated stent placement can reduce the intra-aneurysmal pressure, decrease wall shear stress (WSS) at the neck region, and increase blood turnover time for aneurysm case I (sidewall aneurysm). These findings are consistent with the trends of hemodynamic changes reported previously. However, aneurysm case II (bifurcation aneurysm) showed gradually increased intra-aneurysmal pressure and the pressure at the neck region, decreased WSS over the sac surface, and enhanced flow vortices within the aneurysm. When simulating the hemodynamics of pre- and post-stenting aneurysms for a patient using measured flow waveforms, the flow alteration induced by the stent deployment may affect the hemodynamic predictions for the post-stenting aneurysm. Thus, the remeasurement of boundary conditions once the morphology of the aneurysm is deformed is needed in follow-up studies with a focus on aneurysm growth and stent deployment.

Numerical analysis of the blood flow in the left ventricle with internal structures: Effect of trabeculae carneae models and atrial fibrillation

Internal structures of the inner wall of the left ventricle (LV), such as trabeculae carneae (TC) and papillary muscles, may reduce the blood flow velocity, resulting in thrombus formation in the LV of a healthy heart or a heart with atrial fibrillation. The purpose of the present study was to numerically clarify the effects of simplified TC models around the LV wall and atrial fibrillation on the blood flow field as a fundamental study. The LV model was constructed from magnetic resonance images, and the model considering atrial fibrillation was constructed based on the volume change data of a healthy subject from which volume increase with atrial contraction was removed. Numerical analysis was performed considering eight simplified TC models around the LV wall. The numerical results revealed that the oscillatory shear index and relative residence time (RRT) at the apex in the LV model with internal structures were larger than those in the LV model without internal structures, which indicates that the blood flow tends to stagnate. On the other hand, as a result of the LV model considering the atrial fibrillation, the time-averaged wall shear stress decreases and the RRT increases at valley points of the internal structures.

A four-layered model for flow of non-Newtonian fluid in an artery with mild stenosis

The present article deals with a four-layered mathematical model for blood flow through an artery with mild stenosis. The four-layered model comprises a cell-rich core of suspension of all the erythrocytes described as a non-Newtonian (Jeffrey) fluid, a peripheral zone of cell-free plasma (Newtonian fluid) and the stenosed artery with porous wall consisting of a thin transition (Brinkman) layer followed by Darcy region. Analytical expressions have been obtained for velocity profiles in all the four regions, total volumetric flow rate, wall shear stress and flow impedance. MATLAB software is employed to compute numerical values of the pressure gradient. The influences of different parameters such as variable core fluid viscosity, hematocrit, thickness of the plasma layer, Brinkman and Darcy layer thickness, Darcy number, Jeffrey fluid parameter, and size and shape parameters of stenosis on the physiologically vital flow characteristics, specifically velocity profile, volume flow rate, wall shear stress and flow impedance, have been examined. It is observed that the wall shear stress and resistive impedance decrease with the increase of plasma layer thickness, Jeffrey fluid parameter, Darcy number and Darcy slip parameter, and increase with the rise of hematocrit. The results in the case of variable core viscosity and constant core viscosity are compared to investigate the impact of variable core viscosity in managing the flow of blood.

Morphology and Hemodynamics in Isolated Common Iliac Artery Aneurysms Impacts Proximal Aortic Remodeling.

Objective- Isolated common iliac artery aneurysms (CIAA) are rare. Their prognosis and influence on aortoiliac blood flow and remodeling are unclear. We evaluated the hypotheses that morphology at and distal to the aortic bifurcation, together with the associated hemodynamic changes, influence both the natural history of CIAA and proximal aortic remodeling. Approach and Results- Twenty-five isolated CIAAs (15 intact, 10 ruptured), in 23 patients were reconstructed and analyzed with computational fluid dynamics: all showed abnormal flow. Then we studied a series of 24 hypothetical aortoiliac geometries in silico with varying abdominal aortic deflection and aortic bifurcation angles: key findings were assessed in an independent validation cohort of 162 patients. Wall shear stress in isolated unilateral CIAAs was lower than the contralateral common iliac artery, 0.38±0.33 Pa versus 0.61±0.24 Pa, inversely associated with CIAA diameter ( P<0.001) and morphology (high shear stress in variants distal to a sharp kink). Rupture usually occurred in regions of elevated low and oscillatory shear with a wide aortic bifurcation angle. Abdominal aortas deflected towards the CIAA for most unilateral isolated CIAAs (14/21). In silico, wider bifurcation angles created high focal regions of low and oscillatory shear in the common iliac artery. The associations of unilateral CIAA with aortic deflection and common iliac artery diameter with bifurcation angle were confirmed in the validation cohort. Conclusions- Decreasing wall shear stress is strongly associated with CIAA progression (larger aneurysms and rupture), whereas abnormal blood flow in the CIAA seems to promote proximal aortic remodeling, with adaptive lateral deflection of the abdominal aorta towards the aneurysmal side.

Decreased wall shear stress at high-pressure areas predicts the rupture point in ruptured intracranial aneurysms.

Degenerative cerebral aneurysm walls are associated with aneurysm rupture and subarachnoid hemorrhage. Thin-walled regions (TWRs) represent fragile areas that may eventually lead to aneurysm rupture. Previous computational fluid dynamics (CFD) studies reported the correlation of maximum pressure (Pmax) areas and TWRs; however, the correlation with aneurysm rupture has not been established. This study aims to investigate this hemodynamic correlation. The aneurysmal wall surface at the Pmax areas was intraoperatively evaluated using a fluid flow formula under pulsatile blood flow conditions in 23 patients with 23 saccular middle cerebral artery (MCA) bifurcation aneurysms (16 unruptured and 7 ruptured). The pressure difference (Pd) at the Pmax areas was calculated by subtracting the average pressure (Pave) from the Pmax and normalized by dividing this by the dynamic pressure at the aneurysm inlet side. The wall shear stress (WSS) was also calculated at the Pmax areas, aneurysm dome, and parent artery. These hemodynamic parameters were used to validate the correlation with TWRs in unruptured MCA aneurysms. The characteristic hemodynamic parameters at the rupture points in ruptured MCA aneurysms were then determined. In 13 of 16 unruptured aneurysms (81.2%), Pmax areas were identified that corresponded to TWRs. In 5 of the 7 ruptured cerebral aneurysms, the Pmax areas coincided with the rupture point. At these areas, the Pd values were not higher than those of the TWRs in unruptured cerebral aneurysms; however, minimum WSS, time-averaged WSS, and normalized WSS at the rupture point were significantly lower than those of the TWRs in unruptured aneurysms (p < 0.01). At the Pmax area of TWRs, decreased WSS appears to be the crucial hemodynamic parameter that indicates the risk of aneurysm rupture.

Classification of wall shear stress of human common carotid artery and ascending aorta on the basis of age

Wall shear stress is one of the major factors responsible for increase in cardiovascular disease. The present work calculate the level of wall shear stress in the common carotid artery (CCA) and aorta to see which artery has more chance of having cardiovascular diseases and at which age. Wall shear stress (WSS) is determined in the CCA and aorta of presumed healthy volunteers, having age between 10 and 60 years. A real 2D model of both aorta and common carotid artery is constructed for different age groups using computational fluid dynamics (CFD). WSS of both the arteries is calculated and compared for different age groups. It is found that with increase in diameter of common carotid artery and ascending aorta with advancing age wall shear stress decreases. WSS of aorta is found less than common carotid artery.

Computational Fluid Dynamics Modeling of Respiratory Airflow in Tracheobronchial Airways of Infant, Child, and Adult.

During human growth and development from infancy to adulthood, dramatic changes occur in the respiratory system. It is important to understand respiratory airflow in different age groups in age-specific treatment of respiratory disorders. This study numerically investigated the age-related effects on inspiratory and expiratory airflow dynamics in four-generation lung airway models under normal breathing conditions. Tracheobronchial airway models of infant (6 month old), child (5 years old), and adult (25 years old) from sixth to ninth generations were constructed for the study. Computational fluid dynamics (CFD) was used to solve the equations governing the airflow. Results of this study indicate that as age increases, airflow velocity, pressure, and wall shear stress decrease for both inspiration and expiration in this particular subregion of the respiratory tract. During inspiration, the splitting of velocity streamlines at bifurcations increases with age. The opposite situation merging happens during expiration, and it also increases with age. The level of splitting and merging of streamlines here reflects the influence of respiratory mechanics in the age groups. The computational models provide new information on characteristics and patterns of age-dependent respiratory airflow in the sixth to ninth generations of tracheobronchial airways and can be applied in other generations.

Construction of a bilayered vascular graft with smooth internal surface for improved hemocompatibility and endothelial cell monolayer formation

Formation of a continuous endothelial cell (EC) monolayer inside the luminal surface with enhanced hemocompatibility, is a promising solution for improving performance and overall patency of small-diameter vascular grafts. There has been much debate regarding the ideal substrate surface topography to achieve this. Here, we investigated different polycaprolactone (PCL)-derived substrate surfaces fabricated from nanofibers, microfibers, or with smooth surfaces, and evaluated their effect on hemocompatibility and EC behavior. Our results demonstrated that, compared with the other two substrates, smooth surfaces inhibited platelet adhesion and activation, suppressed fibrinogen adsorption, and enhanced EC monolayer formation. In addition, smooth surfaces increased EC nitric oxide (NO) production and acetylated low-density lipoprotein (Ac-LDL) uptake. Thus, we designed and fabricated a bi-layered vascular graft composed of a smooth ultrathin internal layer and a microfibrous external layer, which were capable of preventing spiral-flow and decreasing wall-shear stress. Arterio-venous shunt models revealed that bi-layered grafts avoided bleeding and inhibited both protein absorption and platelet adhesion. Overall, these findings indicated that the prepared bi-layered grafts could perform better for in vivo implantation. Furthermore, this approach doesn't require chemical or biological modifications, and therefore can be easily applied to the fabrication of other implantable tubular grafts using various materials.

Release of endothelial microparticles in patients with arterial hypertension, hypertensive emergencies and catheter-related injury

Background and aimsCirculating endothelial microparticles (EMPs) are increased in arterial hypertension. The role of physicomechanical factors that may induce EMP release in vivo is still unknown. We studied the relationship of EMPs and physicomechanical factors in stable arterial hypertension and hypertensive emergencies, and investigated the pattern of EMP release after mechanical endothelial injury. MethodsIn a pilot study, 41 subjects (50% hypertensives) were recruited. EMPs were discriminated by flow-cytometry (CD31+/41-, CD62e+, CD144+). Besides blood pressure measurements, pulse-wave-analysis was performed. Flow-mediated dilation (FMD), nitroglycerin-mediated dilation (NMD), and wall-shear-stress (WSS) were measured ultrasonographically in the brachial artery; microvascular perfusion by laser-Doppler (Clinicaltrials.gov: NCT02795377). We studied patients with hypertensive emergencies before and 4 h after BP lowering by urapidil (n = 12) and studied the release of EMPs due to mechanical endothelial injury after coronary angiography (n = 10). ResultsHypertensives exhibited increased EMPs (CD31+/41-, CD144+, CD62e+) as compared to normotensives and EMPs univariately correlated with systolic BP (SBP), augmentation index, and pulse wave velocity and inversely with FMD. CD31+/41--EMPs correlated with diameter and inversely with WSS and NMD. CD62e+ and CD144+-EMPs inversely correlated with microvascular function. During hypertensive emergency, only CD62e+ and CD144+-EMPs were further elevated and FMD was decreased compared to stable hypertensives. Blood pressure lowering decreased CD62e+ and CD144+-EMPs and increased FMD. CD31+/41—EMPs, diameter, and WSS remained unaffected. Similar to hypertensive emergency, catheter-related endothelial injury increased only CD144+ and CD62e+-EMPs. ConclusionsEMP release in hypertension is complex and may involve both physicomechanical endothelial injury and activation (CD144+, CD62e+) and decreased wall shear stress (CD31+/41-).

On the fluid dynamics of unsteady separated stagnation-point flow of a power-law fluid on the surface of a moving flat plate

The transformation group theoretic approach is applied to perform an analysis of the unsteady separated stagnation-point (USSP) flow over a moving flat plate immersed in a non-Newtonian power-law fluid. This unsteady two-dimensional laminar boundary layer flow of a power-law fluid is governed by the classical Ostwald–de Waele power-law model. The system of governing partial differential equations reduces to an autonomous third order nonlinear ordinary differential equation via two-parameter group theoretic method. By using an efficient shooting method, we have established the existence of two different kinds of solutions, namely: (i) attached flow solution (AFS) and (ii) reverse flow solution (RFS) of this USSP flow problem under a definite negative value of the unsteadiness parameter β with a given value of the acceleration parameter a and for all values of the power-law index n considered in the present study. We have also found a unique AFS solution that is irrespective of n when β≥0. Dual solutions of the governing boundary layer equation are found for all kinds of fluids with the fixed values of a=1 and β=−1. The role of the rheological index n on the displacement thickness, skin-friction coefficient and velocity boundary layer are explored numerically. The results of this analysis reveal that the wall shear stress is always positive for AFS flow and negative for RFS flow for the above values of a and β with any given value of n. A novel result that emerges from this analysis is that the magnitude of the wall shear stress decreases and finally it approaches asymptotically to a constant value with the increase in the non-Newtonian behavior (n>1) of the fluids for both the cases of AFS and RFS.

An efficient parallel simulation of unsteady blood flows in patient-specific pulmonary artery.

Simulation of blood flows in the pulmonary artery provides some insight into certain diseases by examining the relationship between some continuum metrics, eg, the wall shear stress acting on the vascular endothelium, which responds to flow-induced mechanical forces by releasing vasodilators/constrictors. V. Kheyfets, in his previous work, studies numerically a patient-specific pulmonary circulation to show that decreasing wall shear stress is correlated with increasing pulmonary vascular impedance. In this paper, we develop a scalable parallel algorithm based on domain decomposition methods to investigate an unsteady model with patient-specific pulsatile waveforms as the inlet boundary condition. The unsteady model offers tremendously more information about the dynamic behavior of the flow field, but computationally speaking, the simulation is a lot more expensive since a problem which is similar to the steady-state problem has to be solved many times, and therefore, the traditional sequential approach is not suitable anymore. We show computationally that simulations using the proposed parallel approach with up to 10 000 processor cores can be obtained with much reduced compute time. This makes the technology potentially usable for the routine study of the dynamic behavior of blood flows in the pulmonary artery, in particular, the changes of the blood flows and the wall shear stress in the spatial and temporal dimensions.

Influence of Iliac Stenotic Lesions on Blood Flow Patterns Near a Covered Endovascular Reconstruction of the Aortic Bifurcation (CERAB) Stent Configuration

Purpose: To investigate the effect of distal stenotic lesions on flow patterns near a covered endovascular reconstruction of the aortic bifurcation (CERAB) configuration used in the treatment of aortoiliac occlusive disease. Method: Laser particle image velocimetry measurements were performed using in vitro models of the aortic bifurcation with and without a CERAB configuration in place. A hemodynamically nonsignificant stenosis (ΔP: 9 mm Hg), a hemodynamically significant (ΔP: 26 mm Hg) stenosis, and a total occlusion were simulated in the left iliac arteries. Velocity fields and time-averaged wall shear stress (TAWSS) were calculated. Results: Hemodynamically significant distal lesions did not influence the inflow patterns or TAWSS (0.5–0.6 Pa) in either model. However, hemodynamically significant distal stenotic lesions caused a 2-fold decrease in peak outflow velocities (control: 106 vs 56 cm/s, CERAB: 96 vs 54 cm/s) and a 3-fold decrease in TAWSS (control: 1.34 vs 0.44 Pa, CERAB: 0.75 vs 0.21 Pa). There was a 2-fold decrease in wall shear stress in the CERAB outflow compared with the control, independent of lesion severity. Conclusion: In the CERAB technique, adequate distal runoff is identified as an important parameter to ensure patency. This in vitro study showed that distal stenotic lesions influence aortic bifurcation outflow patterns and TAWSS more extensively in the CERAB configuration. Distal stenotic lesions could therefore increase the risk of disease progression and loss of stent patency. In vivo studies are necessary to confirm these observations.

Finite element analysis of mechanical behavior, permeability and fluid induced wall shear stress of high porosity scaffolds with gyroid and lattice-based architectures

Scaffold design necessitates the consideration of mechanical properties and fluid flow dynamics as the main factors in the development of such materials. The mechanical behavior of bone scaffolds is characterized by properties such as elastic modulus and compressive strength. In terms of fluid flow dynamics, within bone scaffolds, permeability is an important parameter that affects cells' biological activities, and flow-induced shear stress is used as a mechanical stimulant of cell growth. In this study, two scaffold architectures with gyroid and lattice-based rectangular unit cells were designed to analysis the effective elastic moduli, compressive strength, permeability and fluid flow-induced wall shear stress as functions of porosity. Six levels of porosity (65%, 70%, 75%, 80%, 85% and 90%) were assigned to the scaffold architectures, and 12 models were developed. Scaffold deformation under static loading, compressive strength based on von Mises criteria, pressure drop, and fluid flow-induced wall shear stress in the scaffolds were then determined by finite element analysis. In both the scaffold types, models with higher porosity exhibited lower mechanical properties. Under the same porosity, the lattice-based scaffolds exhibited a Young's modulus and a compressive strength higher than those achieved by the gyroid scaffolds. With reference to geometrical parameters and the derived pressure drop from the computational fluid dynamics (CFD) analysis, scaffolds permeability was calculated using Darcy's law. In both the scaffold architectures, high porosity increased permeability and decreased wall shear stress. In the same porosity, the lattice-based models exhibited higher permeability and lower wall shear stress than did the gyroid models. On the basis of the results on elastic modulus and permeability, the models that most effectively mimic the properties of cancellous bones were identified.

Numerical analysis of cavitation erosion and particle erosion in butterfly valve

Abstract The investigation of butterfly valve applied in the circulation water filtration system (CWF) of one pressurized water reactor (PWR) nuclear power station is performed in the paper. A coupling computational fluid dynamics model combined multiphase, cavitation and discrete phase model has been built to simulate the cavitation erosion and particle erosion. The validity and rationality of the coupling model is sufficiently verified with the experiment of flow coefficient and effects of different factors including inlet pressure and valve opening angle are discussed in detail. The results reveal that the erosion of butterfly valve mainly occurs at the forward and backward part of valve disc. With the increase of inlet pressure, max velocity, mass flow rate, wall shear stress, turbulent intensity and particle erosion would increase. Mass flow rate, wall shear stress, turbulent intensity and particle erosion decrease with the decrease of valve opening angle. The simulation results are well consistent with the failure feature of butterfly valve applied in actual operation. The numerical analysis is expected to improve the erosion condition and reliability of butterfly valve.

Computational Investigation of the Thermal-Hydraulic Performance for Twisted Tape Enabled High Heat Flux Components

High heat flux thermal management is an important challenge for upcoming nuclear fusion and plasma physics experiments. The plasma facing components (PFCs) in devices such as ITER or Wendelstein 7-X (W7-X) will be subjected to extreme heat loads on the order of 10–20 MW/m2 in the divertor region. The heat dissipation issue will become critical in this next generation of experiments, and active cooling will be necessary. The current state-of-the-art water cooled technologies can accommodate extreme heat fluxes and often utilize passive heat transfer enhancement techniques, such as swirl flow, to decrease the thermal loading on PFCs. Swirling flow is commonly induced with a twisted tape that is inserted into a circular tube. Twisted tape devices are planned for use in both W7-X and ITER. Computational modeling was performed to investigate the thermal-hydraulic performance for single-phase, turbulent flow of water through a twisted tape device. This study exploited the advantage of computational simulations by analyzing local flow information. It was shown that points of low wall shear stress corresponded to locations of low heat transfer coefficient and high surface temperatures. Thus, decreased wall shear stress could be an indicator for early burnout in twisted tape geometries. This analysis was the first step towards informing the design of twisted tape devices utilized in PFCs.