Fluid Dynamic Factors Research Articles

Experimental Investigation of the Effect of Heart Rate on Flow in the Left Ventricle in Health and Disease-Aortic Valve Regurgitation.

There is much debate in the literature surrounding the effects of heart rate on aortic regurgitation (AR). Despite the contradictory information, it is still widely believed that an increase in heart rate is beneficial due to the disproportionate shortening of the duration of diastole relative to systole, permitting less time for the left ventricle to fill from regurgitation. This in vitro work investigates how a change in heart rate affects the left ventricular fluid dynamics in the absence and presence of acute AR. The experiments are performed on a novel double-activation left heart simulator previously used for the study of chronic AR. The intraventricular velocity fields are acquired via time-resolved planar particle image velocimetry (PIV) in a clinically relevant plane. Considering fluid dynamic factors, an increase in heart rate was observed to have a limited benefit in the case of mild AR and a detrimental effect for more severe AR. With increasing heart rate, mild AR was associated with a decrease in regurgitant volume, a negligible change in regurgitant volume per diastolic second, and a limited reduction in the fraction of retained regurgitant inflow. More severe AR was accompanied by an increase in both regurgitant volume and the fraction of retained regurgitant inflow, implying a less effective pumping efficiency and a longer relative residence time of blood in the ventricle. Globally, the left ventricle's capacity to compensate for the increase in energy dissipation associated with an increase in heart rate diminishes considerably with severity, a phenomenon which may be exploited further as a method of noninvasive assessment of the severity of AR. These findings may affect the clinical belief that tachycardia is preferred in acute AR and should be investigated further in the clinical setting.

Computational Fluid Dynamics Analysis of Lateral Striate Arteries in Acute Ischemic Stroke Using 7T High-resolution Magnetic Resonance Angiography

Background: Infarcts in the lateral striate artery (LSA) territory can be caused by several pathological changes, including lipohyalinosis and microatheroma. However, fluid dynamic effects on these changes remain unknown. Thus, we investigated whether the fluid dynamic metrics of the LSAs were altered in patients with acute ischemic stroke using computational fluid dynamics (CFD) analysis. Methods: Fifty-one patients with acute ischemic stroke confined in the basal ganglia and/or corona radiata underwent high-resolution magnetic resonance angiography (HR-MRA) at 7T. We performed CFD analyses to obtain indices including the wall shear stress (WSS), WSS gradient (WSSG), and flow velocity (FV) and compared these values between the ipsilesional and contralesional sides in the patients with infarcts in the LSA or non-LSA territories. Results: In patients with LSA-territory infarcts, the WSS, WSSG, and FV values were significantly lower in the ipsilesional LSAs than in the contralesional LSAs (P = .01-.03), while these values in the proximal middle cerebral arteries showed no significant lateralities. In contrast, in patients with non-LSA-territory infarcts, there were no significant lateralities in the metrics between the ipsilesional and contralesional sides. Conclusions: The CFD analyses using HR-MRA revealed significantly low WSS and WSSG values of the ipsilesional LSAs compared with that of the contralesional side in patients with LSA-territory infarcts, suggesting that fluid dynamic factors of LSAs can be one of the risk factors for LSA-territory infarctions.

Detailed heat transfer and fluid flow investigation in a rectangular duct with truncated prismatic ribs

The paper presents an experimental study of detailed heat transfer and flow field characteristics in a rectangular duct having different types of truncated prismatic ribs on the bottom surface. The truncated prismatic ribs are manufactured by tapering the square rib from both the sides up to the center to provide rib height at the ends of 0, 2, 4, 6 and 8 mm. Experimental heat transfer results using transient liquid crystal thermography (LCT) are reported along with the mean flow field results using particle image velocimetry (PIV) at a rib pitch-to-height ratio of 10. The heat transfer effectiveness of proposed rib configurations is evaluated by examining the surface- and spanwise-averaged Nusselt number distribution. The effect of rib configurations on the flow parameters as well as on the heat transfer augmentation, with an emphasis to overall averaged augmentation Nusselt number, friction factor ratio, and performance index factors, are studied over a wide range of Reynolds number (9400–58,850). Most of the truncated prismatic ribs provide higher augmentation Nusselt number (about 25.15%) and lower pressure penalty (about 54.65%) than those with the square ribs. The truncated prismatic ribs provide better thermohydraulic performance than the square rib, however, these values are about 25–53% higher respectively at the lowest and the highest Reynolds number. Further, the aero-thermal characteristics are studied and documented in order to enhance the understanding and to correlate the flow dynamic mechanisms with the heat transfer augmentation from the fundamental perspective for all proposed rib configurations at a fixed Reynolds number of 42,500. The combined analysis of aerothermal characteristics puts in evidence the role of fluid dynamic factors i.e. flow features, mean velocities, and the turbulence intensity in the heat transfer augmentation.

(997) - Experimental and Numerical Analysis of Dye Washout in Ventricular Assist Devices

PurposeVentricular Assist Devices (VADs) are associated with complications due to the damage done to the blood. This damage relates to shear stress and exposure time. Designing VADs to minimise exposure time, in addition to reducing stress, should then reduce damage. The aim of this work was to use washout of a dye to investigate local and overall residence times in VADs.MethodsA flow rig was developed such that initially dyed glycerol circulated and a three way tap was used to switch to a transparent solution. A camera was focused on the transparent VAD outlet tube, and the colour change in the images calibrated to dye concentration. The concentration change at the outlet, ‘dye washout curve’, was used as an indicator of the residence times in the VAD. Dye washout curves were measured for VADs both in development and commercially available.Computational Fluid Dynamics (CFD) was used to calculate dye washout curves. An established flow field was first obtained with a transient simulation. A scalar variable was introduced to represent the dye, and a transport equation was used to model its convection. Simulated dye washout curves were compared with experiment, and simulations were used to understand fluid dynamic factors determining the different curves.ResultsDifferences in experimental washout were clearest at a flow rate of 1 l/min. The time taken for the concentration to drop from 100 to 20 %, T20, was an initial indicator of residence time. T20 was 2.1 s in the CentriMag (magnetic suspension) and just 0.9 s in the HeartMate II (axial & contact bearings). This difference may be explained by the larger volume of the CentriMag. Despite a similar internal volume to the HeartMate II, the Calon MiniVAD (centrifugal & magnetic suspension) had T20 of 1.4 s. The difference is likely due to the secondary flow in the MiniVAD which is required for suspension.ConclusionThe secondary flow path plays a critical role in determining blood residence time in the VAD. Ongoing work is focussed on investigating the importance of secondary flow path parameters.

Areas of Bacterial Communities of Aquatic Mud Volcanic Depositions in Lake Baikal Region

In the Lake Baikal region, freshwater Baikal mega area and six spatially isolated areas of bacterial communities, localized in water reservoirs of mineralized waters of mud volcanic origin, have been identified. The fluid-dynamic factors of areal formation have been considered, and analysis has been conducted regarding the characteristics of prevailing and specific functional groups and the genera of microorganisms, representing bacterial communities. KeywordsAreas; Bacteria; Seismicity; Heat Flow; Geo-fluid-dynamic Mode; Thermal Spring

Optimum Design of Shell and Tube Heat Exchanger Using Response Surface Methodology

The design process of shell and tube heat exchanger is difficult due to the complex geometric parameters with thermodynamic and fluid dynamic factors, which consume more time and minimum possibility for an optimum result in the case of conventional design. The optimum design of shell and tube heat exchanger was determined to predict optimum heat transfer coefficient with the effect of geometrical parameters such as number of baffles (NB), Shell diameter (Ds), Tube pitch (Pt) and Baffle spacing (LB). The analytical calculations were done using Response Surface Methodology on four factors, three level, central composite face centered design matrix with full replications technique by 95% confidence level. The results indicate that the geometrical parameters with optimum design.

DIAGNOSTIC AND THERAPEUTIC TREATMENTS OF PLAQUES IN THE CAROTID BIFURCATION — STUDIES IN MODELS WITH STENTS AND FILTERS

Fluid dynamics, especially forces and velocity distribution, influence the development of plaques. Flow parameters: pulsatility, the non-Newtonian flow behavior of blood and wall elasticity are considered. Flow visualization techniques (dyes and birefringent solution with a photo-elasticity apparatus) and LDA measurements demonstrate the importance of the flow. Accurate in vivo velocity measurements are necessary to calculate shear stresses. Different bifurcation angles and flow rate ratios were tested in true to life artery models. The most important fluid dynamic factors at bifurcations are the flow rate ratio and the geometry which create flow separation regions which are responsible for platelet aggregation and intima damage. It is necessary to measure all three velocity components to calculate the velocity vector. The highest shear stresses in a healthy carotid artery are 16 Pa and are found just at the apex. In artery models with 90% stenosis, shear stresses up to 250 Pa were found. Distally, vortices were created where particles remained over several pulse cycles. Measurements show that stents must be selected carefully and placed precisely. Filters must be closed during the systolic phase before removal, so that no trapped particles can escape.

Cavitation research from an intetrnational perspective

This paper reviews some current research at the Saint Anthony Falls Laboratory from the perspective of the experience gained from cooperative research in other laboratories that the author has had the opportunity to participate in for several decades. Examples are drawn from the author's experience with collaborative efforts in China, Germany, Japan, Netherlands, Norway, and the US. Emphasis is placed on the progress in our understanding of the physics of cavitation as influenced by water quality, i.e. the strength of the water as influenced by the concentration of free and dissolved gas and complex fluid dynamic factors such as turbulence. The shift from experimental research to studies involving an integrated experimental/numerical approach is also underscored. Examples are drawn from early studies of inception and acoustics, vortex cavitation and more recent research on sheet/cloud cavitation and supercavitation. Some thoughts on new directions are also presented.

Caracterización del flujo pulsante vascular mediante observaciones in vitro en modelos biológico y mecánico

The evidence accumulated on the use of pulsatile and non-pulsatile flow-dependent devices raises a controversy concerning the effects of the flow type on the Circulatory system. This paper proposes to characterize the properties of pulsatile flow in elastic conduits in order to determine how the pulse affects the system and to determine the specific details of the flow in the vascular bed. The biomechanical properties of pulsatile flow were measured on flexible (calf venous vessel), and rigid (plastic pipe) conduits in which the flow was implemented using a pneumatic elastic sack-like pumping device. The experimental data and the biomechanical analysis of the pulsing flow was used to determine the flow pattern in order to develop a mechanical model explaining the effects of the pulse on the vascular system. The resulting model includes the flow's general condition (mechanical component) and its effects on the vascular system (biological/physiological component). The model proposed here allows determining the relationship between the flow conditions and the reaction on the wall; it also allows unifying the interpretation of fluid-dynamic factors affecting these phenomena and represents a warning system about the effects of flow changes on the operation of circulatory assistance devices.

Reservoir compartmentalization: an introduction

Reservoir Compartmentalization – the segregation of a petroleum accumulation into a number of individual fluid/pressure compartments – occurs when flow is prevented across ‘sealed’ boundaries in the reservoir. These boundaries are caused by a variety of geological and fluid dynamic factors, but there are two basic types: ‘static seals’ that are completely sealed and capable of withholding (trapping) petroleum columns over geological time; and ‘dynamic seals’ that are low to very low permeability flow baffles that reduce petroleum crossflow to infinitesimally slow rates. The latter allow fluids and pressures to equilibrate across a boundary over geological time-scales, but act as seals over production time-scales, because they prevent crossflow at normal production rates – such that fluid contacts, saturations and pressures progressively segregate into ‘dynamic’ compartments. Thus, reservoir compartmentalization impacts the volume of moveable (produceable) oil or gas that might be connected to any given well drilled in a field, which restricts the volume of reserves that can be ‘booked’ for that field. Booking of reserves is tightly regulated by government authorities because it is a key measure used by stock analysts and investors to value an oil company. This places reservoir compartmentalization studies, and the predictive science and technology applied to them, at the heart of company valuation. Unexpected compartmentalization can also seriously impact the profitability of a field: with more data acquisition, more study, more wells, more time being required to produce less oil and gas than was originally anticipated. In extreme cases, this might even lead to early field abandonment. However, unexpected or misunderstood reservoir compartmentalization has been an industrywide experience for over 30 years, and it is clear that there is great value in learning from past, often expensive mistakes (e.g. Smith 2008). This learning process has often driven developments in geoscience, engineering and related technology – enabling operating companies to identify and predict ‘new’ untapped volumes in old fields, make general improvements to field management (e.g. Gainski et al.; Wonham et al.), and apply this knowledge to other similar, but lessmature fields in their portfolio. Reservoir compartmentalization is therefore a major uncertainty that should be accurately assessed during the appraisal of petroleum reservoirs, in order to avoid unexpected compartmentalization at the production stage. In the past few decades, there have been major advances in data, detection and surveillance methods, and our geoscience and reservoir engineering approaches. However, reservoir compartmentalization can still be underestimated during field appraisal, and can still give surprises that force a re-think of the field development and production plan (e.g. Smith 2008). This is not necessarily a defect in the science or technology – but, rather, it may also be a result of ineffectual data appraisal or discipline integration within subsurface workflows. Thus, it is not unusual for subsurface teams to place too much emphasis on one aspect of the evidence, or to make early assumptions that bias data acquisition, analyses and interpretations later on. For example, Fisher & Jolley (2007) point out that non-existent faults or improbable fault seal capacities might be invoked to explain variable petroleum contacts and dynamic fluid/pressure behaviour – when an alternative or combination of factors, or other unrelated explanations might be more appropriate for the data (e.g. hydrodynamic tilting of petroleum contacts, Tozer & Borthwick). Research initiatives and collaborations between oil companies, service groups and academic institutions vary considerably in scope and content, and there is often a creative tension between the competitive advantages, motivations and knowledge gaps perceived by the sponsoring companies and their research partners. In addition to this, the scientific insights that can be gained from the

Impact of In Vivo Ranges of the Variances in the Flow Velocity Waveforms and Flow Split Ratio on the Hemodynamic Effects of the Anastomotic Cuff at Distal End-to-Side Anastomosis

The blood flow inside distal end-to-side anastomoses may be affected by inlet flow velocity profiles and outlet blood distribution ratios. This study investigated the in vivo range of these variables and their impact on the hemodynamic effects of an anastomotic cuff using a computational fluid dynamics approach. Predesigned expanded polytetrafluoroethylene cuffed grafts were used in 22 femoropopliteal bypasses and straight grafts were used for 10 cases. The flow distribution was examined by angiographic techniques and the inlet flow velocity was determined by a spectral Doppler method. The caudal outflow distribution ratio was 95.6% +/- 7.2% (75%-100%). The positive peak flow velocity was 1.66 +/- 0.25 m/s. The ratio of the absolute value of the negative to positive peak velocity was 0.32 +/- 0.12. The cuff increased wall shear stress along the artery floor regardless of the flow velocity profiles at 100% of the caudal distribution ratio but not at 75%. The hemodynamics inside the anastomosis were thus found to be affected by these flow variables. The proper indications for the cuff should therefore not be decided based simply on the location of the anastomosis without taking the fluid dynamic factors in the vicinity of the anastomosis into full consideration.

The endotelial and vein wall reaction on pulsatile flow and shear stress from arterial ‘jets’ originating from arterioVenous anastomoses (AVAs) studied by scanning electron microscopy (SEM)

Cardiovascular disease is the primary cause of morbidity and mortality in the western world. Complex hemodynamics play a critical role in the development of atherosclerosis and the processes of aging, as well as many other disease processes. Biofluid mechanics play a major role in the cardiovascular system and it is important to understand the forces and movement of blood cells and whole blood as well as the interaction between blood cells and the vessel wall. Fundamental fluid mechanical, which are important for the understanding of the blood flow in the cardiovascular circulatory system of the human body aspects are presented. Measurement techniques for model studies such as LDA, ultrasound, and MRI studies will be discussed. Viscosity and flow behavior changes specifically the creation of vortices and flow disturbances can be used to show how medication can influence flow behavior. Experiments have shown that hemodynamics may have a strong influence on the creation of aneurysms and varicose veins. Other factors such as vessel wall structure are also important. In preliminary studies, it has been demonstrated that geometry and elasticity of vessel walls help determine flow behavior. High velocity fluctuations indicate flow disturbances that should be avoided. Health care practitioners must understand fluid dynamic factors such as flow rate ratio, pressure and velocity gradients, and flow behavior, velocity distribution, shear stress on the wall and on blood cells. These mechanical factors are largely responsible for the deposit of blood cells and lipids, a leading cause of atherosclerosis. The interaction between blood cells and of the cells with the vessel, leads to the formation of plaques and agglomerations. These deposits are found predominantly at arterial bends and bifurcations where blood flow is disturbed, where a secondary flow is created, and where flow separation regions are found. Experiments on hemodynamic effects in elastic silicon rubber models of the cardiovascular system with flow wire, stents, or patches for vessel surgery will be discussed. These studies can be important in improving diagnostics and therapeutic applications.

The effect of velocity on the suspension feeding and growth of the marine mussels Mytilus trossulus and M. californianus: implications for niche separation

The role of fluid dynamic factors on the feeding and growth of two sympatric blue mussels was examined in a laboratory flow chamber and in a dockside flow-through chamber. The experiments involved the blue mussels Mytilus trossulus and Mytilus californianus of two size categories (∼1 and ∼2 cm shell length) and water from the Bamfield Inlet. Larger mussels cleared more water of seston than smaller ones, and the clearance rate (CR) of M. trossulus increased with velocity (1–18 cm s −1), whereas M. californianus exhibited a somewhat continuous unimodal functional response that peaked at ∼12 cm s −1. Although growth decreased with velocity in all experiments over the range of 1–40 cm s −1, the growth rates of M. californianus were consistently higher than M. trossulus, and this difference extended to the highest velocity. It is evident that M. californianus has a fluid dynamically mediated growth advantage over M. trossulus, which would explain its dominance in wave-exposed habitats. Given this finding, we conclude that fluid dynamics are important to the evolutionary ecology of blue mussels.

PULSATILE FLOW FIELDS IN A MODEL OF ABDOMINAL AORTA WITH ITS PERIPHERAL BRANCHES

In a previous study by the authors, steady flow fields in a model of abdominal aorta with its seven peripheral branches were reported. In the present study, the some aorta model was simulated numerically with a pulsatile inlet waves for both the resting and exercise conditions. The baseline pulsatile flow field was presented in terms of velocity vectors and iso-velocity contours as well as the wall shear stress (WSS) distribution and the recirculation zones. The time-averaged behavior of the flow field represented by the fluid dynamic factors was discussed. The results were consistent with those obtained experimentally and numerically by other investigators. It was also found that under the present conditions, the steady flow behavior could adequately describe the time-averaged behavior of its corresponding pulsatile case, particularly in the regions where convective flow dominated. The present computer code may provide a platform for clinical simulations.

Flow in the early embryonic human heart: a numerical study.

Computational fluid dynamic (CFD) experimentation provides a unique medium for detailed examination of flow through complex embryonic heart structures. The purpose of this investigation was to demonstrate that streaming blood flow patterns exist in the early embryonic heart and that fluid surface stresses change significantly with anomalous alterations in fetal heart lumen shape. Stages 10 and 11 early human embryo hearts were digitized as calibrated two-dimensional (2D) cross-sectional sequential images. A 3D surface was constructed from the stacking of these 2D images. CFD flow solutions were obtained (steady and pulsatile flow). Particle traces were placed in the inlet and outlet portions of these two stages. Sections of the embryonic heart were artificially reshaped. CFD flow solutions were obtained and surface stress changes analyzed. Streaming was shown to exist, with particles released on one or the other side of the cardiac lumen tending not to cross over and mix with particles released from the opposite side of the cardiac lumen. Shear stress changes (stage 10) occur in the altered lumens. Streaming exists in steady and pulsatile flow scenarios in the embryonic heart models. There are differences in local shear stress distributions with surface shape anomalies of the fetal heart lumen. These observations may help shed light on the potential role of fluid dynamic factors in determining patterns of abnormal heart development.

Rotating Effect on Fluid Flow in Two Smooth Ducts Connected by a 180-Degree Bend

Laser Doppler velocimetry (LDV) measurements are presented of turbulent flow in a two-pass square-sectioned smooth duct simulating the coolant passages employed in gas turbine blades under rotating and nonrotating conditions. For all cases studied, the Reynolds number characterized by duct hydraulic diameter and bulk mean velocity was fixed at 1×104. The rotation number Ro was varied from 0 to 0.2. It is found that as Ro is increased, both the skewness (SK) of streamwise mean velocity and magnitude of secondary-flow velocity increase linearly, SK=2.3 Ro and U2+V2¯/Uh=2.3 Ro+0.4, and the magnitude of turbulence intensity level increases exponentially. As Ro is increased, the curvature induced symmetric Dean vortices in the turn for Ro=0 is gradually dominated by a single vortex most of which impinges directly on the outer part of leading wall. The high turbulent kinetic energy is closely related to the dominant vortex prevailing inside the 180-deg sharp turn. The size of separation bubble immediately after the turn is found to diminish to null as Ro is increased from 0 to 0.2. A simple correlation is developed between the bubble size and Ro. A critical range of Ro responsible for the switch of faster moving flow from near the outer wall to the inner wall is identified. For both rotating and nonrotating cases, the direction and strength of the secondary flow with respect to the wall are the most important fluid dynamic factors affecting local the heat transfer distributions inside a 180-deg sharp turn. The role of the turbulent kinetic energy in the overall enhancement of heat transfer is well addressed.

Interaction of fluid dynamic factors in the migration and accumulation of natural gas

The migration of fluid petroleum gas, described as fluid potential, depends only on gravity, fluid pressure controlled by depression and capillary force during tectonically stable period; but on tectonic stress during the tectonically active period with severe compression. This method is applied in the Junggar Basin, showing that the migration of Jurassic gas during Cretaceous and Eocene and the migration of Permian gas from Jurassic till the present are determined by capillary force and fluid pressure (including overpressure) which is controlled by depression; the migration of Jurassic gas from Eocene till the present and the migration of Permian gas during Triassic are controlled by tectonic stress.

Interaction of fluid dynamic factors in the migration and accumulation of natural gas

Interaction of fluid dynamic factors in the migration and accumulation of natural gas

An introduction to biofluid mechanics—basic models and applications

Cardiovascular disease is the primary cause of morbidity and mortality in the western world. Complex hemodynamics play a critical role in the development of atherosclerosis and the processes of aging, as well as many other disease processes. Biofluid mechanics play a major role in the cardiovascular system and it is important to understand the forces and movement of blood cells and whole blood as well as the interaction between blood cells and the vessel wall. Fundamental fluid mechanical, which are important for the understanding of the blood flow in the cardiovascular circulatory system of the human body aspects are presented. Measurement techniques for model studies such as LDA, ultrasound, and MRI studies will be discussed. Viscosity and flow behavior changes specifically the creation of vortices and flow disturbances can be used to show how medication can influence flow behavior. Experiments have shown that hemodynamics may have a strong influence on the creation of aneurysms and varicose veins. Other factors such as vessel wall structure are also important. In preliminary studies, it has been demonstrated that geometry and elasticity of vessel walls help determine flow behavior. High velocity fluctuations indicate flow disturbances that should be avoided. Health care practitioners must understand fluid dynamic factors such as flow rate ratio, pressure and velocity gradients, and flow behavior, velocity distribution, shear stress on the wall and on blood cells. These mechanical factors are largely responsible for the deposit of blood cells and lipids, a leading cause of atherosclerosis. The interaction between blood cells and of the cells with the vessel, leads to the formation of plaques and agglomerations. These deposits are found predominantly at arterial bends and bifurcations where blood flow is disturbed, where a secondary flow is created, and where flow separation regions are found. Experiments on hemodynamic effects in elastic silicon rubber models of the cardiovascular system with flow wire, stents, or patches for vessel surgery will be discussed. These studies can be important in improving diagnostics and therapeutic applications.

Non-intrusive measurements of near-wall fluid flow and surface heat transfer in a serpentine passage

Flow visualization using a transient liquid crystal method is presented to study the effect of divider thickness on the local heat transfer distributions around a sharp 180-deg turn of a two-pass smooth square duct. Detailed local Nusselt number distributions on the bottom, blade-tip, and side walls are given for three divider thicknesses, W ∗ d =0.10 , 0.25, and 0.50, at a Reynolds number of 1.2×10 4. Complementary pressure loss measurements are presented in terms of variation of friction factor with W ∗ d . The thermal performance investigation shows that W ∗ d =0.25 provides the highest total averaged Nusselt number ratios, both at constant flow rate and at constant pumping power conditions, and a moderate friction factor. Near-wall laser-Doppler velocimetry measurements are further performed to explain the liquid crystal measured surface heat transfer distributions. The results show that the direction and strength of the secondary flow with respect to the wall are most important fluid dynamic factors affecting the heat transfer distributions, followed by the convective mean velocity, and then the turbulent kinetic energy.