Induced Flow Changes Research Articles

Erosion Induced Flow Changes in Pelton Bucket: A Numerical Approach

Abstract The hydro-turbines working in sediment-laden conditions often experience some material loss from their surface, which modifies the surface design. This material loss alters the mechanical strength of the turbine component as well as the corresponding flow phenomenon. These changes in the flow pattern can lead to efficiency losses, but they can also be exploited to determine the actual condition of the component in real time. In fact, if detected, they can be useful for developing maintenance strategies to predict the turbine conditions in real time. To compare the flow parameters, a numerical simulation has been performed for a 2D stationary Pelton bucket under both eroded and uneroded scenarios considering clean water as the working fluid. The 2D middle section of a reference Pelton bucket has been considered in two configurations: the uneroded bucket case and eroded, whose uneven surface patterns were created taking inspiration from real erosion patterns inside Pelton buckets observed in sediment-laden power plants. The CFD simulations have been carried out using OpenFOAM multiphase solver interFoam. The two cases were then compared based on several flow parameters such as water film thickness, velocity, and exit flow angle. The result analysis confirmed flow disturbances due to erosion causes the decrement in the overall flow velocity and the increment in water film thickness. The velocity reduction effect, as well as the water film thickness increment effect, strengthens approaching the outlet of the bucket. The results also showed a significant alteration of exit flow angle due to erosion. Specifically, for the erosion pattern considered in this study, the exit flow angle was observed to be larger compared to the uneroded bucket case.

P.09 Differential Low Flow Mediated Constriction (LFMC) Responses in Radial and Brachial Arteries of Healthy Humans are Attributed to Occlusion Induced Flow Changes

BackgroundLiterature describes differences in Low flow mediated constriction (LFMC) of radial versus brachial artery [1,2]. We investigated whether differences in occlusion induced changes in luminal flow and shear rates could explain the observed radial vs brachial differences in LFMC responses.MethodsTwenty Healthy volunteers (Age 23.50 ± 2.06 years) underwent examination of Brachial and radial arteries of both the arms. Arteries were visualized in Pulsed wave doppler in duplex mode (Vivid-e; GE Healthcare) using a 12 MHz probe at baseline and during low flow state produced using an occluding cuff placed around the forearm (for brachial artery) and over the wrist joint (for radial artery) inflated to supra-systolic pressures.ResultsLFMC in Radial artery was significantly higher than that of Brachial artery [delta LFMC of –0.58 mm (–0.24––0.76) in radial artery vs 0.03 mm (0.21––0.13) in brachial artery; p < 0.0001). Occlusion induced reduction in anterograde shear rate was comparatively higher in radial artery than brachial artery [–67.9% (–43––77) in radial vs –56.7% (–40.9––65.4) in brachial; p = 0.0098] whereas, the rise in retrograde shear rate and changes in oscillatory shear index were comparable between both. Percentage changes in anterograde shear rate and anterograde flow velocities emerged as independent predictors in the regression model that explained 86% of the variance in LFMC responses of brachial artery.ConclusionDiscrepancies in the LFMC responses of radial vs brachial artery could be attributed to the occlusion induced differences in the anterograde shear rate and anterograde flow velocities.

Effect of Induced Flow Changes by DBD Plasma Actuaotr on Suppressed Flow on a NACA0012 Airfoil

Effect of Induced Flow Changes by DBD Plasma Actuaotr on Suppressed Flow on a NACA0012 Airfoil

Evaluation of Perfusion Quantification Methods with Ultrasound Contrast Agents in a Machine-Perfused PigLiver.

To evaluate dynamic contrast-enhanced ultrasound (DCEUS) as a tool for measuring blood flow in the macro- and microcirculation of an ex-vivo machine-perfused pig liver and to confirm the ability of DCEUS to accurately detect induced flow rate changes so that it could then be used clinically for monitoring flow changes in liver tumors. Bolus injections of contrast agents in the hepatic artery (HA) and portal vein (PV) were administered to 3 machine-perfused pig livers. Flow changes were induced by the pump of the machine perfusion system. Theinduced flow rates were of clinical relevance (150 - 400 ml/min for HA and 400 - 1400 ml/min for PV). Quantification parameters from time-intensity curves [rise time (RT), mean transit time (MTT), area under the curve (AUC) andpeak intensity (PI)] were extracted in order to evaluate whether the induced flow changes were reflected in these parameters. A linear relationship between the image intensity and the microbubble concentration was confirmed first, while time parameters (RT and MMT) were found to be independent of concentration. The induced flow changes which propagated from the larger vessels to the parenchyma were reflected in the quantification parameters. Specifically, RT, MTT and AUC correlated with flow rate changes. Machine-perfused pig liver is an excellent test bed for DCEUS quantification approaches for the study of the hepatic vascular networks. DCEUS quantification parameters (RT, MTT, and AUC) can measure relative flow changes of about 20 % and above in the liver vasculature. DCEUS quantification is a promising tool for real-time monitoring of the vascular network of tumors.

Comparison of pulsed and pseudocontinuous arterial spin‐labeling for measuring CO2‐induced cerebrovascular reactivity

To compare the performance of pulsed and pseudocontinuous arterial spin-labeling (PASL and pCASL) methods in measuring CO(2) -induced cerebrovascular reactivity (CVR). Subjects were scanned using both ASL sequences during a controlled hypercapnia procedure and visual stimulation. CVR was computed as the percent CO(2) -induced increase in cerebral blood flow (Δ%CBF) per mmHg increase in end-tidal PCO(2) . Visually evoked responses were expressed as Δ%CBF. Resting CBF and temporal signal-to-noise ratio were also computed. Regionally averaged values for the different quantities were compared in gray matter (GM) and visual cortex (VC) using t-tests. Both PASL and pCASL yielded comparable respective values for resting CBF (56 ± 3 and 56 ± 4 mL/min/100g) and visually evoked responses (75 ± 5% and 81 ± 4%). Values of CVR determined using pCASL (GM 4.4 ± 0.2, VC 8 ± 1 Δ%CBF/mmHg), however, were significantly higher than those measured using PASL (GM 3.0 ± 0.6, VC 5 ± 1 Δ%CBF/mmHg) in both GM and VC. The percentage of GM voxels in which statistically significant hypercapnia responses were detected was also higher for pCASL (27 ± 5% vs. 16 ± 3% for PASL). pCASL may be less prone to underestimation of CO(2) -induced flow changes due to improved label timing control.

Simulation study of brain blood flow regulation by intra-cortical arterioles in an anatomically accurate large human vascular network. Part II: Flow variations induced by global or localized modifications of arteriolar diameters

In a companion paper (Lorthois et al., Neuroimage, in press), we perform the first simulations of blood flow in an anatomically accurate large human intra-cortical vascular network (~10000 segments), using a 1D non-linear model taking into account the complex rheological properties of blood flow in microcirculation. This model predicts blood pressure, blood flow and hematocrit distributions, volumes of functional vascular territories, regional flow at voxel and network scales, etc. Using the same approach, we study flow reorganizations induced by global arteriolar vasodilations (an isometabolic global increase in cerebral blood flow). For small to moderate global vasodilations, the relationship between changes in volume and changes in flow is in close agreement with Grubb's law, providing a quantitative tool for studying the variations of its exponent with underlying vascular architecture. A significant correlation between blood flow and vascular structure at the voxel scale, practically unchanged with respect to baseline, is demonstrated. Furthermore, the effects of localized arteriolar vasodilations, representative of a local increase in metabolic demand, are analyzed. In particular, localized vasodilations induce flow changes, including vascular steal, in the neighboring arteriolar trunks at small distances (<300μm), while their influence in the neighboring veins is much larger (about 1mm), which provides an estimate of the vascular point spread function. More generally, for the first time, the hemodynamic component of various functional neuroimaging techniques has been isolated from metabolic and neuronal components, and a direct relationship with several known characteristics of the BOLD signal has been demonstrated.

Convection in directionally solidifying alloys under inclined rotation

In an experiment on binary alloys directionally solidifying from below, Sample &amp; Hellawell (1984) showed that the plume convection can be successfully prohibited by rotating the cooling tank around an inclined axis. In the present paper we interpret their experimental observation by an analytical approach. Results show that there is a flow induced by the inclination. The induced flow in the fluid layer is a parallel shear flow consisting of three parts: the thermal boundary-layer flow, the solute boundary- layer flow, and the Ekman-layer flow. In the mush, the induced flow is also a parallel flow but of much smaller velocity, consisting of two flows of opposite directions. The induced velocity in the fluid layer increases with inclination angle and decreases with the effective Taylor number Te. The induced velocity in the mush also increases with inclination angle but remains virtually the same on varying the speed of rotation. The linear stability analysis of the mushy layer shows that, due mostly to the reduction of buoyancy, the mush becomes more stable as the inclination angle increases. In the precession-only case, the most-unstable mode of instability is the longitudinal mode, which propagates in a direction perpendicular to the induced flow. In the spin (with or without precession) case, the instability modes propagating in different directions are of equal stability. Because the induced flow changes direction with a frequency equal to the spin angular velocity, the flow scans over all the directions of the system and stabilizes equally the modes in different directions. We conclude on the basis of the present results and from the practical point of view that spin-only rotation is more effective than the precession-only rotation in stabilizing the convection during solidification.

Changes of renal resistive index in response to hydration and diuretic administration in normal subjects and in patients with small ureteral stone.

The renal resistive index has been measured before and after hydration and administration of diuretics in persons with normal kidneys and in kidneys with small ureteral stone, either obstructing or nonobstructing, to assess induced flow changes and to identify features differentiating obstructing from nonobstructing stones. In normal kidneys the resistive index was normal (mean, 0.62+/-0.03); no changes in the resistive index occurred within 15 to 60 min after hydration alone, whereas the resistive index rose within 15 min after hydration plus administration of diuretics and then returned to initial values within 30 min. In both cases the resistive index decreased below basal values after 75 to 90 min. Similar changes were observed in kidneys with a nonobstructing ureteral stone. In kidneys with an obstructing ureteral stone the resistive index was higher than in normal subjects (mean, 0.73+/-0.02, P<0.01), increased further within 15 min after hydration and administration of diuretics (P<0.01), and remained higher than basal values during the following 90 min. In conclusion, different resistive index changes have been observed in response to hydration and diuretics in normal and obstructed kidneys. Duplex Doppler sonography and diuresis duplex Doppler sonography seem promising diagnostic tools to identify obstructing stones.

Estrogen-induced increases in coronary blood flow are antagonized by inhibitors of nitric oxide synthesis

Objective: Estrogen receptors have been found in coronary arterial endothelial and vascular smooth muscle cells. Therefore the present study was designed to determine if estradiol-17β can increase coronary blood flow and if so whether the changes are mediated by nitric oxide. Study design: Five oophorectomized non-pregnant sheep were chronically instrumented to measure blood pressure, heart rate, cardiac output, left circumflex coronary blood flow and central venous pressure. Animals received estradiol-17β (1.0 μg/kg) and cardiovascular responses were followed for 135 min. Results: Estradiol-17β (1.0 μg/kg) increased left circumflex (coronary) blood flow 28±3%, cardiac output 15±1% and heart rate by 13±3% Coronary vascular resistance decreased 23±5%, systemic vascular resistance decreased by 12±2% while blood pressure did not change significantly. Administration of the nitric oxide synthetase inhibitor l-nitroarginine methylester ( l-NAME), had no effect on basal coronary blood flow but completely reversed estradiol-17β induced increases in coronary blood flow. Conclusion: These results demonstrate that estrogen increases coronary blood flow in the non-pregnant sheep and that l-NAME, an inhibitor of nitric oxide, is able to reverse the estrogen induced flow changes.

Cerebrovascular response during and following severe insulin-induced hypoglycemia: CO2-sensitivity, autoregulation, and influence of prostaglandin synthesis inhibition.

The objective of the present experiments was to study mechanisms governing cerebrovascular responses during severe hypoglycemia, and in the posthypoglycemic recovery period. To that end, lightly anesthetized (70% N2O) and artificially ventilated rats were injected with insulin so as to abolish spontaneous EEG activity for 15 or 30 min ("coma"). In separate animals, recovery was induced by glucose administration. Previous experiments have shown that in normo- or moderately hypertensive animals hypoglycemic coma is accompanied by a relatively marked increase in cerebral blood flow (CBF), and that a delayed hypoperfusion develops in the recovery period. The present results demonstrate that oxygen supply is in excess of the demands during coma, and falls below control during recovery. During hypoglycemic coma, the CO2 response of the circulation was retained but autoregulation was lost. In the recovery period, both CO2 response and autoregulation were lost. Pretreatment with indomethacin was introduced in order to evaluate the possible influence of fatty acid cyclo-oxygenase products on the pattern of CBF changes. Measurements of local cerebral blood flow (1-CBF) showed that, in the majority of structures analysed, indomethacin failed to modulate the changes in CBF. It is concluded that alterations in cerebrovascular tone and loss of autoregulation induce flow changes that may influence substrate and oxygen availability during hypoglycemia. The pronounced decrease in CBF and the loss of autoregulation and CO2-response in the post-hypoglycemic period may influence functional, metabolic and morphological recovery. The 1-CBF findings indicate that neither the increase in CBF during hypoglycemia nor the reduction in flow in the posthypoglycemic period are mediated by mechanisms related to prostaglandin metabolism.