Increase In Wall Shear Stress Research Articles

Electromagnetohydrodynamic flow and thermal performance in a rotating rough surface microchannel

Rough surfaces in microchannels effectively enhance liquid mixing, thermal performance, and chemical reactions in electrically actuated microfluidic devices. Rotation of the microchannel with surface roughness intensifies this enhancement. We investigate the combined effects of electromagnetohydrodynamics and surface roughness on transient rotating flow in microchannels. We present a mathematical model considering the variable zeta potential, heat transfer characteristics, and entropy generation within the microchannel. We obtain analytical solutions using the separation of variables method and Fourier series expansion. The surface roughness of the microchannel, when combined with rotation, impacts the temperature enhancement. Higher rotation rates result in the formation of multiple vortices. The secondary flow pushes the primary velocity toward the boundary layer, which affects the flow pattern. Surface roughness and electroosmotic flow significantly affect secondary flow, resulting in complex flow patterns and reversals. The interaction between centrifugal and viscous forces results in maximum velocities at the boundary layers. Higher roughness and electromagnetic effects enhance temperature by intensifying fluid-solid friction and joule heating. Surface roughness causes an increase in wall shear stress and friction factor, resulting in a higher Poiseuille number. Moreover, surface roughness increases entropy production by enhancing fluid mixing and internal friction despite improved heat transfer. Higher rotation also elevates entropy generation due to additional vortices induced by secondary flow.

Numerical simulation and in vitro experimental study of the hemodynamic performance of vena cava filters with helical forms

Inferior vena cava filter (IVCF) implantation is a common method of thrombus capture. By implanting a filter in the inferior vena cava (IVC), microemboli can be effectively blocked from entering the pulmonary circulation, thereby avoiding acute pulmonary embolism (PE). Inspired by the helical flow effect in the human arterial system, we propose a helical retrievable IVCF, which, due to the presence of a helical structure inducing a helical flow pattern of blood in the region near the IVCF, can effectively avoid the deposition of microemboli in the vicinity of the IVCF while promoting the cleavage of the captured thrombus clot. It also reduces the risk of IVCF dislodging and slipping in the vessel because its shape expands in the radial direction, allowing its distal end to fit closely to the IVC wall, and because its contact structure with the inner IVC wall is curved, increasing the contact area and reducing the risk of the vessel wall being punctured by the IVCF support structure. We used ANSYS 2023 software to conduct unidirectional fluid–structure coupling simulation of four different forms of IVCF, combined with microthrombus capture experiments in vitro, to explore the impact of these four forms of IVCF on blood flow patterns and to evaluate the risk of IVCF perforation and IVCF dislocation. It can be seen from the numerical simulation results that the helical structure does have the function of inducing blood flow to undergo helical flow dynamics, and the increase in wall shear stress (WSS) brought about by this function can improve the situation of thrombosis accumulation to a certain extent. Meanwhile, the placement of IVCF will change the flow state of blood flow and lead to the deformation of blood vessels. In in vitro experiments, we found that the density of the helical support rod is a key factor affecting the thrombus trapping efficiency, and in addition, the contact area between the IVCF and the vessel wall has a major influence on the risk of IVCF displacement.

Influence of Double-Ducted Serpentine Nozzle Configurations on the Interaction Characteristics between the External and Nozzle Flow of Aircraft

To clarify the influence of the serpentine nozzle configurations on the flow characteristics and aerodynamic performance of aircraft, the flow features and aerodynamic performances of the double-ducted serpentine nozzles with different aspect ratios (AR), length–diameter ratios (LDR) and shielding ratios (SR) are numerically investigated. The results show that the asymmetric nozzle flow occurs due to the curved profile of serpentine nozzles, and a local accelerating effect exists at the S-bend, causing the increase in wall shear stress. The unilateral unsymmetrical expansion of the tail jet in the upward direction interacts with the separated external flow of the afterbody, forming an obvious cross-shock wave and shear layer structure. The surface pressure of the afterbody increases along the external flow direction, and decreases sharply in the separation point of the boundary layer. With the increase in AR and LDR, the local accelerating effect of the nozzle flow weakens, while with the increase in SR, the accelerating effect increases. The total pressure recovery coefficient, flow coefficient and axial thrust coefficient all decrease with the increase in AR, LDR, and SR. The thrust vector angle decreases with the increase in AR but is less affected by LDR and SR.

Characterization of nasal aerodynamics and air conditioning ability using CFD and its application to improve the empty nose syndrome (ENS) submucosal floor implant surgery–Part II virtual surgery

BackgroundInformative virtual surgeries provide useful insights for surgical options to patients. In the case of evaluating surgical treatments for the empty nose syndrome (ENS), reliable CFD virtual surgery is a predictive tool for symptom improvement. MethodsFive submucosal implant surgeries with two different implant volumes and three different implant sites were performed on the diseased side of an ENS patient. In each case, a post-surgery nasal cavity was created based on ENS patient's computed tomography images. The airflow and air-conditioning abilities of these nasal surgery models were computed to examine the effects of implant size and site on the surgical outcomes. Significant findingsThe largest improvements were achieved with the larger submucosal implant size at the lateral site. Airflow was redistributed into the inferior and superior meatuses, enhancing air interactions with the nasal mucus. The increased wall shear stress enhanced mucus secretion and sensation of airflow. The reduced vortex size alleviated the paradoxical nasal obstruction feeling. The results suggested that larger implant sizes and the lateral implant site would be advisable for submucosal implant surgeries on ENS patients. Inferior implant with a smaller size being a second advisable approach in terms of heating and humidification efficiencies.

The impact of choledochal cysts on bile fluid dynamics: A perspective using computational fluid dynamics and surface mapping technique

Choledochal cysts (CCs) are an important risk factor for cholangiocarcinoma, though their etiology remains debated. Given the vital role of bile fluid in digestive processes within the biliary system, examining such mechanisms from the perspective of bile fluid dynamics may offer additional insights for clinical use. This study utilized magnetic resonance imaging (MRI)-based patient-specific scans for detailed reconstruction and further employed the computational fluid dynamic method to assess the physiological functions of each system, including refilling and emptying processes. The impact of bile rheological property was also examined. Key biomechanical parameters—pressure and wall shear stress (WSS)—were displayed on a two-dimensional plane via surface mapping for enhanced visualization and comparative analysis. Outcomes demonstrated a significant reduction in bile flow velocity in CCs patients due to common bile duct's anatomical features and bile's shear-thinning, non-Newtonian nature, with a notable increase in pressure drop observed. In healthy biliary systems, WSS variations were minimal; however, in CCs patients, extreme WSS differences were found, with the highest WSS in the segmental bile duct and the lowest in the dilatation area, presenting a magnitude difference of approximately 1000. CCs one showed WSS levels 100–250 times higher than healthy ones in the common bile duct. Bile rheological properties substantially affect pressure and WSS patterns, particularly WSS, where pathological bile caused a tenfold increase in WSS compared to healthy bile. The findings aimed to enhance the understanding of biliary fluid mechanics in CCs and offer insights into selected fluidic variables for future microfluidic chip experiments.

Hemodynamics in nutcracker syndrome: implications for diagnosis.

Nutcracker syndrome is a disease characterized by complex symptoms, making its diagnosis challenging and often delayed, often resulting in a painful experience for the patients. This study aimed to investigate the pathogenesis of nutcracker syndrome through the perspective of hemodynamics by simulating blood flow with varying compression degrees of the left renal vein. 3D patient-specific vascular models of the abdominal aorta, superior mesenteric artery and left renal vein were constructed based on CT images of patients suspected of having nutcracker syndrome. A hemodynamic simulation was then conducted using computational fluid dynamics to identify the correlation between alterations in hemodynamic parameters and varying degrees of compression. The study indicated the presence of anevident gradient in velocity distribution over the left renal vein with relatively high degrees of stenosis (α ≤ 50°), with maximum velocity in the central region of the stenosis. Additionally, when the compression degree of the left renal vein increases, the pressure distribution of the left renal vein presents an increasing number of gradient layers. Furthermore, the wall shear stress shows a correlation with the variation of blood flow velocity, i.e., the increase of wall shear stress correlates with the acceleration of the blood flow velocity. Using computational fluid dynamics as a non-invasive instrument to obtain the hemodynamic characteristics of nutcracker syndrome is feasible and could provide insights into the pathological mechanisms of thenutcracker syndrome supporting clinicians in diagnosis.

Study of the mechanism of action of sand therapy on atherosclerosis based on the two-phase flow-Casson model.

Sand therapy is a non-pharmacological physiotherapy method that uses the natural environment and resources of Xinjiang to treat through the heat transfer and magnetic effects of sand. Employing the two-phase flow-Casson blood flow model, we investigate the mechanism of atherosclerosis prevention via sand therapy, offering a biomechanical theoretical rationale for the prevention of atherosclerosis through sand therapy via the prism of computational fluid dynamics (CFD). Sand therapy experiments were conducted to obtain popliteal artery blood flow velocity, and blood was considered as a two-phase flow composed of plasma and red blood cells, and CFD method was applied to analyze the hemodynamic effects of Casson's blood viscosity model before and after sand therapy. (1) The blood flow velocity increased by 0.24 m/s and 0.04 m/s at peak systolic and diastolic phases, respectively, after sand therapy; the axial velocity of blood vessels increased by 28.56% after sand therapy. (2) The average red blood cell viscosity decreased by 0.00014 Pa ⋅ s after sand therapy. (3) The low wall shear stress increased by 1.09Pa and the high wall shear stress reached 41.47Pa after sand therapy. (4) The time-averaged wall shear stress, shear oscillation index and relative retention time were reduced after sand therapy. The increase of blood flow velocity after sand therapy can reduce the excessive deposition of cholesterol and other substances, the decrease of erythrocyte viscosity is beneficial to the migration of erythrocytes to the vascular center, the increase of low wall shear stress has a positive effect on the prevention of atherosclerosis, and the decrease of time-averaged wall shear stress, shear oscillation index and relative retention time can reduce the occurrence of thrombosis.

A modeling study of position and orientation of hemodialysis needles and the impact on vascular access

Patients with chronic kidney disease (CKD) need renal replacement therapy (RRT) and the favored method is hemodialysis (HD). An arteriovenous fistula is the preferred choice of vascular access, with two metal needles used to transfer the blood with waste to the dialysis machine and return the blood without waste from the dialysis machine to the patient’s body. However, wounds on the veins can cause blood clots which if left untreated could be life threatening. The hemodialysis needles can cause vascular wall abnormalities. The position and orientation of these needles might cause intimal hyperplasia (IH) and finally lead to blood clots. This study aims to analyze the hemodynamic effects on the vascular endothelium in AVF vascular access. A 15G needle was placed inside a vein at angles of 20°, 40°, and 90° with normal insertion and flipped needle in an idealized cephalic vein with the bore of the needle centrally located, conforming to standard cannulation practice. The 3D model created by SolidWorks consists of shaft, back eye, bevel, and vein only; the vein and 15G needle were assembled together. The mathematical model of blood rheology in this paper used Carreau’s law in the fluid domain. It was imported into Ansys CFX for calculation, a finite volume based software, which was implemented to solve the governing equations of the blood flow. The result showed that if the venous needle was not towards the venous return, a vortex appeared at the vein both upstream and downstream due to the venous needle, resulting in wall shear stress at the vein increasing significantly, and the flipped bevel seems to cause higher wall shear stress. For antegrade positioning of the vein vascular access return in the model when normally inserted, it was found that only 1% of the flow out of the back eye and vortex occurred downstream of the vein. Needles placed at a higher angle can increase wall shear stress and pressure on the vein. The flipped bevel is not significant in terms of either pressure or wall shear stress. However, when the needle is placed at a greater angle, wall shear stress and pressure on the vein were also increased. The flipped bevel caused higher wall shear stress and pressure when increasing the needle angle. Jetting from the venous needle causing intimal hyperplasia (IH) leads to blood clots, pain on the vein, and ultimately arm pain. Thus, the best cannulation procedure is for the venous needle to be toward the venous return, at a lower angle, and with the tip of the needle on the middle of the vein. Furthermore, the back eye should not be used for the venous needle but should be used for the arterial needle.

Impact of nasal septal perforation on the airflow and air-conditioning characteristics of the nasal cavity

We investigated (1) how nasal septal perforations (NSPs) modify nasal airflow and air-conditioning characteristics and (2) how the modifications of nasal airflow are influenced by the size and location of the NSP. Computed tomography scans of 14 subjects with NSPs were used to generate nasal cavity models. Virtual repair of NSPs was conducted to examine the sole effect of NSPs on airflow. The computational fluid dynamics technique was used to assess geometric and airflow parameters around the NSPs and in the nasopharynx. The net crossover airflow rate, the increased wall shear stress (WSS) and the surface water–vapor flux on the posterior surface of the NSPs were not correlated with the size of the perforation. After the virtual closure of the NSPs, the levels in relative humidity (RH), air temperature (AT) and nasal resistance did not improve significantly both in the choanae and nasopharynx. A geometric parameter associated with turbinate volume, the surface area-to-volume ratio (SAVR), was shown to be an important factor in the determination of the RH and AT, even in the presence of NSPs. The levels of RH and AT in the choanae and nasopharynx were more influenced by SAVR than the size and location of the NSPs.

Regional aortic wall shear stress increases over time in patients with a bicuspid aortic valve

BackgroundAortic wall shear stress (WSS) is a known predictor of ascending aortic growth in patients with a bicuspid aortic valve (BAV). The aim of this study was to study regional WSS and changes over time in BAV patients. MethodsBAV patients and age-matched healthy controls underwent 4D flow CMR. Regional, peak systolic ascending aortic WSS, aortic valve function, aortic stiffness measures and aortic dimensions were assessed. In BAV patients, 4D flow CMR was repeated after three years follow-up and both at baseline and follow-up computed tomography angiography (CTA) was acquired. Aortic growth (volume increase of ≥5%) was measured on CTA. Regional WSS differences within patients’ aorta and WSS changes over time were analysed using linear mixed-effect models and were associated with clinical parameters. ResultsThirty BAV patients (aged 34 years [IQR 25-41]) were included in the follow-up analysis. Additionally, another 16 BAV patients and 32 healthy controls (aged 33 years [IQR 28-48]) were included for other regional analyses. Magnitude, axial, and circumferential WSS increased over time (all p<0.001) irrespective of aortic growth. The percentage of regions exposed to a magnitude WSS >95th percentile of healthy controls increased from 21% (baseline 506/2400 regions) to 31% (follow-up 734/2400 regions) (p<0.001). WSS angle, a measure of helicity near the aortic wall, decreased during follow-up. Magnitude WSS changes over time were associated with systolic blood pressure, peak aortic valve velocity, aortic valve regurgitation fraction, aortic stiffness indexes, and normalized flow displacement (all p<0.05). ConclusionsAn increase of regional WSS over time was observed in BAV patients, irrespective of aortic growth. The increasing WSSs comprising a larger area of the aorta warrants further research to investigate the possible predictive value for aortic dissection.

Patient-specific computational flow simulation reveals significant differences in paravisceral aortic hemodynamics between fenestrated and branched endovascular aneurysm repair

BackgroundEndovascular aneurysm repair with four-vessel fenestrated endovascular aneurysm repair (fEVAR) or branched endovascular aneurysm repair (bEVAR) currently represent the forefront of minimally invasive complex aortic aneurysm repair. This study sought to use patient-specific computational flow simulation (CFS) to assess differences in postoperative hemodynamic effects associated with fEVAR vs bEVAR. MethodsPatients from two institutions who underwent four-vessel fEVAR with the Cook Zenith Fenestrated platform and bEVAR with the Jotec E-xtra Design platform were retrospectively selected. Patients in both cohorts were treated for paravisceral and extent II, II, and V thoracoabdominal aortic aneurysms. Three-dimensional finite element volume meshes were created from preoperative and postoperative computed tomography scans. Boundary conditions were adjusted for body surface area, heart rate, and blood pressure. Pulsatile flow simulations were performed with equivalent boundary conditions between preoperative and postoperative states. Postoperative changes in hemodynamic parameters were compared between the fEVAR and bEVAR groups. ResultsPatient-specific CFS was performed on 20 patients (10 bEVAR, 10 fEVAR) with a total of 80 target vessels (40 renal, 20 celiac, 20 superior mesenteric artery stents). bEVAR was associated with a decrease in renal artery peak flow rate (−5.2% vs +2.0%; P < .0001) and peak pressure (−3.4 vs +0.1%; P < .0001) compared with fEVAR. Almost all renal arteries treated with bEVAR had a reduction in renal artery perfusion (n = 19 [95%]), compared with 35% (n = 7) treated with fEVAR. There were no significant differences in celiac or superior mesenteric artery perfusion metrics (P = .10-.27) between groups. Time-averaged wall shear stress in the paravisceral aorta and branches also varied significantly depending on endograft configuration, with bEVAR associated with large postoperative increases in renal artery (+47.5 vs +13.5%; P = .002) and aortic time-averaged wall shear stress (+200.1% vs −31.3%; P = .001) compared with fEVAR. Streamline analysis revealed areas of hemodynamic abnormalities associated with branched renal grafts which adopt a U-shaped geometry, which may explain the observed differences in postoperative changes in renal perfusion between bEVAR and fEVAR. ConclusionsbEVAR may be associated with subtle decreases in renal perfusion and a large increase in aortic wall shear stress compared with fEVAR. CFS is a novel tool for quantifying and visualizing the unique patient-specific hemodynamic effect of different complex EVAR strategies. Clinical RelevanceThis study used patient-specific CFS to compare postoperative hemodynamic effects of four-vessel fenestrated endovascular aneurysm repair (fEVAR) and branched endovascular aneurysm repair (bEVAR) in patients with complex aortic aneurysms. The findings indicate that bEVAR may result in subtle reductions in renal artery perfusion and a significant increase in aortic wall shear stress compared with fEVAR. These differences are clinically relevant, providing insights for clinicians choosing between these approaches. Understanding the patient-specific hemodynamic effects of complex EVAR strategies, as revealed by CFS, can aid in future personalized treatment decisions, and potentially reduce postoperative complications in aortic aneurysm repair.

Evaluation of Femoropopliteal In-Stent Restenosis Characteristics Stratified by Stent Design

Purpose: To evaluate the potential differences in characteristics of femoropopliteal in-stent restenosis (ISR) stratified by stent design with a focus on the swirling flow-inducing BioMimics 3D helical centerline stent. Methods: Patients with ISR of the superficial femoral and popliteal arteries undergoing reintervention were included in this study. The primary endpoint was the angiographic localization and extent of restenosis or reocclusion with the following five different stent systems: SMART Control stent, Supera peripheral stent, GORE® VIABAHN® endoprosthesis, BioMimics 3D stent, and Zilver® PTX® stent. Results: 414 ISR lesions were analyzed, affecting 236 Supera stents, 67 BioMimics 3D stents, 48 Zilver® PTX® stents, 38 SMART Control stents, and 25 VIABAHN® endoprostheses. The mean stent diameter and length were 5.7 ± 0.77 mm and 121.4 ± 94.8 mm, respectively. ISR included 310 (74.9%) lesions with 1 stent, 89 (21.5%) lesions with 2 stents, 14 (3.4%) lesions with 3 stents, and 1 lesion (0.2%) with 4 stents. Most lesions presented as reocclusions (67.4%) rather than focal (13.3%) or diffuse restenoses (19.3%). No significant differences in ISR lesion morphology were found. By trend, BioMimics 3D stent lesion extension was more focal (16.4% versus 12.7%, p = 0.258), with the highest proportion of lesions in which only the proximal stent third was affected (9.0% versus 5.8%, p = 0.230), as compared to the average of the other four devices. The occlusion rate was the second lowest for the BioMimics 3D stent (64.2 vs. 68.0%, p = 0.316). Risk factors for restenosis or occlusion were active smoking, pre-interventional occlusion, and popliteal intervention. Conclusion: Our results suggest that the helical centerline stent design of the BioMimics 3D stent, which results in a swirling flow with increased wall shear stress, may offer protective properties over straight stent designs, including DES and endoprosthesis, regarding localization and extension of restenosis. Prospective, randomized studies are warranted.

Impact of Cross-Limb Stent-Graft Configuration on Hemodynamics in Abdominal Aortic Aneurysm Interventional Therapy.

The cross-limb (CL) technique is a commonly used endovascular treatment for addressing unfavorable anatomical features in patients with abdominal aortic aneurysm (AAA). The configuration of CL stent-graft plays a critical role in determining the postoperative hemodynamic properties and physiological behaviors, which ultimately impact the efficacy and safety of endovascular AAA treatment. This study aims to investigate the relationship between hemodynamics and CL stent-graft configuration from a hemodynamic perspective. Five distinct geometric models of cross-limb (CL) stent-graft configurations were constructed by optimizing the real clinical computed tomography angiography (CTA) data. These models varied in main body lengths and cross angles and were used to perform numerical simulations to analyze various hemodynamic parameters. Flow pattern, distribution of wall shear stress (WSS)-related parameters, localized normalized helicity (LNH), pressure drop, and the displacement force of all models were examined in this paper. In patient-specific cases, helical flow and WSS increase with the main body. However, it also generated secondary flow in localized areas, leading to increased oscillation in the WSS direction. Notably, increasing the stent graft's main body length or decreasing the cross angle reduced the displacement force exerted on the stent-graft. Reducing the cross angle did not significantly alter the hemodynamic characteristics. In the clinical practice of CL deployment, it is crucial to carefully consider the stent-graft configuration and the patient specific to achieve optimal postoperative outcomes. This study provides valuable insights for guiding stent selection and treatment planning in patients with abdominal aortic aneurysm undergoing CL techniques, from a hemodynamic perspective.

Assessing turbulent effects in ascending aorta in presence of bicuspid aortic valve

Aortic valves with bicuspids have two rather than three leaflets, which is a congenital heart condition. About 0.5–2% of people have a bicuspid aortic valve. Blood flow through the aorta is commonly believed to be laminar, although aortic valve disorders can cause turbulent transitions. Understanding the impact of turbulence is crucial for foreseeing how the disease will progress. The study’s objective was use large eddy simulation to provide a thorough analysis of the turbulence in bicuspid aortic valve dysfunction. Using a large eddy simulation, the blood flow patterns of the bicuspid and tricuspid aortic valves were compared, and significant discrepancies were found. The velocity field in flow in bicuspid configurations was asymmetrically distributed toward the ascending aorta. In tricuspid aortic valve (TAV) the flow, on the other hand, was symmetrical within the same aortic segment. Moreover, we looked into standard deviation, Q-criterion, viscosity ratio and wall shear stresses for each cases to understand transition to turbulence. Our findings indicate that in the bicuspid aortic valve (BAV) case, the fluid-dynamic abnormalities increase. The global turbulent kinetic energy and time-averaged wall shear stress for the TAV and BAV scenarios were also examined. We discovered that the global turbulent kinetic energy was higher in the BAV case compared to TAV, in addition to the increased wall shear stress induced by the BAV in the ascending aorta.

Uncovering the mystery of the vortex dynamics in a micropolar fluid with multiple magnetic field strips: A novel case study

From transportation to energy production, environmental protection, and medical advancements, vortices are known to influence everything. Therefore, a remarkable aspect of engineering and scientific research in these areas is the prediction, control, and optimization of such vortices. Motivated by these potential applications, we numerically study ‘how confined magnetic fields may give rise to new vortices in the micropolar flow inside a square cavity, by employing the Alternating Direction Implicit approach. Unlike most of the previous studies, we do not assume a uniform magnetic field throughout the flow domain, which is more realistic. Instead, we introduce several confined magnetic fields in the form of multiple horizontal and vertical strips. Further, we have applied the theory of micropolar fluids proposed by Eringen to model the micropolar fluid and visualize the flow patterns around the magnetic strips in the flow regime. Using our self-developed MATLAB codes, we examine how various parameters, such as the magnetic field strength, the number and position of the strips, and the micropolar parameter affect the flow and thermal properties of the micropolar fluid. The findings of this study will contribute to a better understanding of the vortex generation and heat transfer enhancement of micropolar fluids in lid-driven cavities under localized magnetic fields. The study reveals that both the Nusselt number (Nu) and skin friction (CfRe) coefficient decrease by 45% and 1% respectively with a magnetic number (Mn) for a fixed Reynolds number (Re). However, increasing the Reynolds number at a fixed magnetic number increases the Nusselt number (909%) and skin friction coefficient (7%). This means that the higher flow velocity translates into increased wall shear stress and heat transfer, which destabilizes the flow and may cause turbulence. This knowledge can be used to develop new and improved micropolar fluid-based technologies for a variety of applications, such as energy production, medical devices, and microfluidics.

Wall shear stress and pressure patterns in aortic stenosis patients with and without aortic dilation captured by high-performance image-based computational fluid dynamics.

Spatial patterns of elevated wall shear stress and pressure due to blood flow past aortic stenosis (AS) are studied using GPU-accelerated patient-specific computational fluid dynamics. Three cases of moderate to severe AS, one with a dilated ascending aorta and two within the normal range (root diameter less than 4cm) are simulated for physiological waveforms obtained from echocardiography. The computational framework is built based on sharp-interface Immersed Boundary Method, where aortic geometries segmented from CT angiograms are integrated into a high-order incompressible Navier-Stokes solver. The key question addressed here is, given the presence of turbulence due to AS which increases wall shear stress (WSS) levels, why some AS patients undergo much less aortic dilation. Recent case studies of AS have linked the existence of an elevated WSS hotspot (due to impingement of AS on the aortic wall) to the dilation process. Herein we further investigate the WSS distribution for cases with and without dilation to understand the possible hemodynamics which may impact the dilation process. We show that the spatial distribution of elevated WSS is significantly more focused for the case with dilation than those without dilation. We further show that this focal area accommodates a persistent pocket of high pressure, which may have contributed to the dilation process through an increased wall-normal forcing. The cases without dilation, on the contrary, showed a rather oscillatory pressure behaviour, with no persistent pressure "buildup" effect. We further argue that a more proximal branching of the aortic arch could explain the lack of a focal area of elevated WSS and pressure, because it interferes with the impingement process due to fluid suction effects. These phenomena are further illustrated using an idealized aortic geometry. We finally show that a restored inflow eliminates the focal area of elevated WSS and pressure zone from the ascending aorta.

Effect of Blood Viscosity Variation on the Flow of Blood in an Artery Having Time Dependent Stenosis

The aim of this paper is to examine the impact of blood viscosity variation on the flow of blood in a diseased artery having time-dependent stenosis. The viscosity of blood is axial co-ordinate dependent so that the viscosity of the blood increases up to the highest point of stenosis in the whole artery after which it decreases. Analytical methods have been used to explore the problem. The equations of volumetric rate of flow, resistance to flow, wall shear stress, and axial velocity have been obtained. It is noticed that as stenosis height increases, the resistance to flow and the wall shear stress increases. Also, investigation has been done to investigate how the wall sheer stress and flow resistance vary with different time-related parameters and varying viscosity index values.

Analysis of pulsatile flow of Rabinowitsch fluid in the multi-stenosed inclined artery under the influence of external body acceleration

The stenosis builds up and its progression in the artery causes serious damages, which may lead to death. This research aims to investigate the non-Newtonian properties of the pulsatile blood flow through the multi-stenotic inclined artery. The effect of external body acceleration is considered, and blood is taken as Rabinowitsch fluid in this work. The mathematical model representing the proposed problem is transformed into a dimensionless form by applying the assumption for mild stenosis. The dimensionless mathematical equations are solved using the perturbation method. The solutions of mathematical equations are investigated graphically to analyze the impacts of various physical constraints. We find that strong non-Newtonian effects lead to an increase in flow velocity and wall shear stress. The stenosis’s presence and progression in the artery reduces the flow velocity. The stenotic artery (diseased artery) is found to have less flow rate than the healthy artery. It is noted that the vertically held conduit effectively has a larger flow velocity and wall shear stress than the horizontal one. External body acceleration is noted to have an impact that raises velocity and wall shear stress.

Large-Eddy Simulation for Slowly Oscillating Turbulent Flow Using Harmonic Balance Approach

Herein, harmonic balanced large-eddy simulation (HB-LES) is proposed for the efficient high-fidelity simulation of slowly oscillating turbulent flows such as cascade flutter in turbomachinery or transonic airfoil buffet. The harmonic balance method for unsteady Reynolds-averaged Navier–Stokes simulation is introduced to large-eddy simulation (LES), utilizing the difference in timescales between the periodic flow and the turbulent fluctuations. Considering their nonlinear mutual interaction, periodic flow and turbulent fluctuations are computed by iterating short-time LES and the harmonic balance method. The HB-LES is applied to the analysis of a Stokes boundary-layer problem at the Reynolds number based on the Stokes boundary-layer thickness of 1790. The characteristics and evolution of the turbulent structures near the wall are consistent with those observed in the results of conventional LES. Both the phase-averaged periodic component and the turbulence statistics show good quantitative agreement with the experimental results and conventional LES. Furthermore, nonlinearity of the periodic component caused by the mutual interaction between turbulent fluctuations and the periodic component is reproduced as a rapid increase in wall-shear stress. The proposed HB-LES demonstrated approximately a 10-fold improvement in computational efficiency.

Computational investigation of homogeneous-heterogeneous reactions in fluid with transport mechanisms: A finite element simulations approach

There are numerous applications in engineering and industry for homogeneous and heterogeneous chemical reactions in fluid regimes under the influence of nanoparticles and hybrid nanoparticles. This article models homogeneous and heterogeneous chemical reactions in the flow of polymer liquid (glycerin) containing Cu-Al2O3 in the presence of heat and mass transfer. The finite element method is used to quantitatively solve these models. A 76% increase in wall shear stress for the case of simultaneous dispersion of Cu and Al2O3 in comparison of only dispersion of Cu is noticed. Similarly, 44% increase in wall heat flux in noticed due to dispersion Cu and Al2O3 in comparison of dispersion of Cu only. The vortex parameter is responsible for a significant increase in the macro-motion of the fluid particles. Macro-motion gets more influence of micro motion than the influence of micro-motion on the macro-motion of Cu-Al2O3- polymer. To control momentum boundary layer thickness, reduce the diameter of the circular pipe. Magnetic force has the opposite direction of flow. Therefore, fluid motion is a decreasing function of magnetic field intensity. Further, the Lorentz force (magnetic force) for the case of Cu-Al2O3 - polymer is stronger than that for the case of Cu- polymer. Additionally, it can be seen that Cu-Al2O3- polymer experiences more Joule heating than Cu- polymer does. The micromotion is compromised when the curvature parameter is increased. As a result, convective transport slows down and the temperature of Cu- polymer and Cu-Al2O3 - polymers decreases. The result, the rate of conversion of electrical energy into heat speeds up intensity of magnetic field increase as and therefore, fluid temperature increases.