Direct Flow Measurements Research Articles

Direct aeroacoustic simulations and measurements of flow and acoustic fields around a recorder with tone holes

Direct aeroacoustic simulations and experiments were performed regarding the flow and acoustic fields around a recorder, which is one of air-reed instruments. The present simulations reproduced the jet oscillations and acoustic radiation around the recorder with tone holes. The effects of conditions of the tone holes and the jet velocity on the flow and acoustic fields are discussed.

On the evolution and form of coherent flow structures over a gravel bed: Insights from whole flow field visualization and measurement

AbstractThe microtopography of a gravel bed river has been shown to generate turbulent flow structures that originate from shear flow generated in the near‐bed region. Although field and laboratory measurements have shown that such flows contain a range of coherent flow structures (CFS), the origin, evolution, and characteristics of the turbulent structures are poorly understood. Here we apply a combined experimental methodology using planar laser‐induced fluorescence and particle imaging velocimetry (LIF‐PIV) to measure simultaneously the geometric, kinematic, and dynamic characteristics of these CFS. The flow structures were analyzed by applying standard Reynolds decomposition and Lagrangian vortex detection methods to understand their evolution, propagation, and growth in the boundary layer and characterize their internal dynamical complexity. The LIF results identify large, individual, fluid packets that are initiated at the bed through shear that generate a bursting mechanism. When these large individual fluid packets are analyzed through direct flow measurement, they are found to contain several smaller scales of fluid motion within the one larger individual fluid parcel. Flow measurements demonstrate that near‐bed shear controls the initiation and evolution of these CFS through merging with vortex chains that originate at the bed. The vortex chains show both the coalescence in the formation of the larger structures and also the shedding of vortices from the edges of these packets, which may influence the life span and mixing of CFS in open channels. The life span and geometric characteristics of such CFS are critical in influencing the duration and intensity of near‐bed stresses that are responsible for the entrainment of sediment.

Cardiovascular Adaptation in Response to Chronic Hypoxia in Awake Rats.

To examine how cardiovascular adaptation to chronic hypoxia might evolve, the responses to blood pressure (Pt) and hematocrit (Ht) during long-term systemic exposure to hypoxia were observed in awake rats. Furthermore, the total peripheral vascular resistance (TPR) was estimated using direct measurements of systemic blood pressure (Ps) and blood flow (Qs) in carotid artery based on Darcy's law (TPR=Ps/Qs) to evaluate the remodeling procedure in the microcirculation. BP and Ht under normoxic conditions were kept almost constant, while hypoxic exposure immediately increased Ht to 58% and, thereafter, it remained stable. The TPR values showed no significant differences between hypoxic and normoxic conditions. These results suggest that effects of high viscosity caused by increasing Ht on peripheral vascular resistance can be compensated by inducing microvascular remodeling with the arteriolar dilation and capillary angiogenesis.

Measuring fluid flow and heat output in seafloor hydrothermal environments

AbstractWe review techniques for measuring fluid flow and advective heat output from seafloor hydrothermal systems and describe new anemometer and turbine flowmeter devices we have designed, built, calibrated, and tested. These devices allow measuring fluid velocity at high‐ and low‐temperature focused and diffuse discharge sites at oceanic spreading centers. The devices perform at ocean floor depths and black smoker temperatures and can be used to measure flow rates ranging over 2 orders of magnitude. Flow velocity is determined from the rotation rate of the rotor blades or paddle assembly. These devices have an open bearing design that eliminates clogging by particles or chemical precipitates as the fluid passes by the rotors. The devices are compact and lightweight enough for deployment from either an occupied or remotely operated submersible. The measured flow rates can be used in conjunction with vent temperature or geochemical measurements to obtain heat outputs or geochemical fluxes from both vent chimneys and diffuse flow regions. The devices have been tested on 30 Alvin dives on the Juan de Fuca Ridge and 3 Jason dives on the East Pacific Rise (EPR). We measured an anomalously low entrainment coefficient (0.064) and report 104 new measurements over a wide range of discharge temperatures (5°–363°C), velocities (2–199 cm/s), and depths (1517–2511 m). These include the first advective heat output measurements at the High Rise vent field and the first direct fluid flow measurement at Middle Valley. Our data suggest that black smoker heat output at the Main Endeavour vent field may have declined since 1994 and that after the 2005–2006 eruption, the high‐temperature advective flow at the EPR 9°50′N field may have become more channelized, predominately discharging through the Bio 9 structure. We also report 16 measurements on 10 Alvin dives and 2 Jason dives with flow meters that predate devices described in this work and were used in the process of their development. This includes the first advective measurements in the Lau Basin and at the EPR 9°39.5′N. We discuss potential error sources and how they may affect the accuracy of measurements by our devices and other devices. In particular, we use the turbulent plume theory to evaluate the effect of entrainment of ambient seawater.

Direct measurement of internal material flow in a bench scale wet low-intensity magnetic separator

In this work an ultrasound-based measurement method is used for monitoring suspension velocity and build-up of magnetic material inside a wet low-intensity magnetic separator, a process used e.g. in beneficiation of magnetite ores. Today the only available option is to monitor material transport between unit operations; i.e. flow rate, solids concentration, and particle size distribution of suspension flow in pipes are measured online using standard equipment.An acoustic backscatter system is fitted to the tank of a separator, and used to monitor the internal flow. A method called ultrasonic velocity profiling is used to capture internal velocity profiles. Simultaneously, the backscatter signal intensity is used to get indications about local solids concentration of the flow, and build-up of magnetic material. The methods are evaluated in realistic conditions, where the effect of varying factors relevant to machine performance is investigated. The included factors are; the slurry feed rate, the slurry solids concentration, the magnet assembly angle, and the drum rotational speed.The presented method gives useful information about the internal material flow inside the separator. The velocity measurements capture the, sometimes complex, internal flow patterns, for example the presence and velocity of a recirculating flow in the dewatering zone. Additionally, keeping a balanced material loading in the concentrate dewatering zone is important to separator performance. Using the signal backscatter intensity it is possible to qualitatively monitor this material loading. Generally these direct measurements can aid in improvements to machine design, process optimization, and process control.

Multidirectional plasma flow measurement by Gundestrup Probe in scrape-off layer of ADITYA tokamak

Multidirectional plasma flow measurements by using Gundestrup Probe in the scrape-off layer of ADITYA tokamak are presented. The ADITYA Gundestrup Probe-head consists of eight plates arranged around the ceramic rod and three pins normal to side plates. Plates are used to measure both parallel and perpendicular flows simultaneously and pins are used to measure plasma density and floating potential. A comparison of direct perpendicular flow measurement and by two other plates of Gundestrup Probe is presented. Possible causes of perpendicular flows are identified and compared with the measured flows. It is observed that the mechanism of the parallel flow and the perpendicular flow is different only at high parallel Mach number. A puff of the working gas is used to study its effect on the perpendicular flows and its reversal with the gas puff is observed.

PCB Food Web Dynamics Quantify Nutrient and Energy Flow in Aquatic Ecosystems.

Measuring in situ nutrient and energy flows in spatially and temporally complex aquatic ecosystems represents a major ecological challenge. Food web structure, energy and nutrient budgets are difficult to measure, and it is becoming more important to quantify both energy and nutrient flow to determine how food web processes and structure are being modified by multiple stressors. We propose that polychlorinated biphenyl (PCB) congeners represent an ideal tracer to quantify in situ energy and nutrient flow between trophic levels. Here, we demonstrate how an understanding of PCB congener bioaccumulation dynamics provides multiple direct measurements of energy and nutrient flow in aquatic food webs. To demonstrate this novel approach, we quantified nitrogen (N), phosphorus (P) and caloric turnover rates for Lake Huron lake trout, and reveal how these processes are regulated by both growth rate and fish life history. Although minimal nutrient recycling was observed in young growing fish, slow growing, older lake trout (>5 yr) recycled an average of 482 Tonnes·yr(-1) of N, 45 Tonnes·yr(-1) of P and assimilated 22 TJ yr(-1) of energy. Compared to total P loading rates of 590 Tonnes·yr(-1), the recycling of primarily bioavailable nutrients by fish plays an important role regulating the nutrient states of oligotrophic lakes.

Arterial spin labeling in clinical pediatric imaging.

Arterial spin labeling (ASL) perfusion-weighted magnetic resonance imaging is the only approach that enables direct and non-invasive quantitative measurement of cerebral blood flow in the brain regions without administration of contrast material and without radiation. ASL is thus a promising perfusion imaging method for assessing cerebral blood flow in the pediatric population. Concerning newborns, there are current limitations because of their smaller brain size and lower brain perfusion. This article reviews and illustrates the use of ASL in pediatric clinical practice and discusses emerging cerebral perfusion imaging applications for children due to the highly convenient implementation of the ASL sequence.

Quantification of methane emissions at abandoned gas wells in the Central North Sea

As a result of extensive hydrocarbon exploration, the North Sea hosts several thousand abandoned wells; many believed to be leaking methane. However, how much of this greenhouse gas is emitted into the water column and ultimately reaches the atmosphere is not known. Here, we investigate three abandoned wells at 81–93 m water depth in the Norwegian sector of the North Sea, all of which show gas seepage into the bottom water. The isotopic signature of the emanating gas points towards a biogenic origin and hence to gas pockets in the sedimentary overburden above the gas reservoirs that the wells were drilled into. Video-analysis of the seeping gas bubbles and direct gas flow measurements resolved initial bubble sizes ranging between 3.2 and 7.4 mm in diameter with a total seabed gas flow between 1 and 19 tons of CH4 per year per well. Estimated total annual seabed emissions from all three wells of ∼24 tons are similar to the natural seepage rates at Tommeliten, suggesting that leaky abandoned wells represent a significant source of methane into North Sea bottom waters. However, the bubble-driven direct methane transport into the atmosphere was found to be negligible (<2%) due to the small bubble sizes and the water depth at which they are released.

Aerodynamics of dynamic wing flexion in translating wings

We conducted a systematic experimental study to investigate the aerodynamic effects of active trailing-edge flexion on a high-aspect-ratio wing translating from rest at a high angle of attack. We varied the timing and speed of the trailing-edge flexion and measured the resulting aerodynamic effects using a combination of direct force measurements and two-dimensional PIV flow measurements. The results indicated that the force and flow characteristics depend strongly on the timing of flexion, but relatively weakly on its speed. This is because the force and vortical flow structure are more sensitive to the timing of flexion relative to the shedding of starting vortex and leading-edge vortex. When the trailing-edge flexion occurred slightly before the starting vortex was shed, the lift production was greatly improved with the instantaneous peak lift increased by 54 % and averaged lift increased by 21 % compared with the pre-flexed case where the trailing-edge flexed before wing translation. However, when the trailing-edge flexed during or slightly after the leading-edge vortex shedding, the lift was significantly reduced by the disturbed development of leading-edge vortex. The force measurement results also imply that the trailing-edge flexion prior to wing translation does not augment lift but increases drag, thus resulting in a lower lift–drag ratio as compared to the case of flat wing.

Assessment of PIV-based analysis of water entry problems through synthetic numerical datasets

The phenomenon of hull-slamming, that is, the sudden impact of a solid body on the water surface, is critical in the design of naval structures. Thus, the development and validation of schemes to predict the slamming load and elucidate energy exchange during water entry are of fundamental importance in a wide range of engineering applications. Recent studies have demonstrated the possibility of using direct flow measurements from particle image velocimetry (PIV) to investigate the kinetics of water entry. Specifically, these efforts have contributed a first characterization of the hydrodynamic loading on impacting wedges and of the energy imparted to the water pile-up and the spray jets. Here, we seek to provide a thorough assessment of such a PIV-based approach through synthetic datasets, in which PIV parameters, such as the camera acquisition rate and the size of the interrogation area, are systematically varied, without experimental confounds. We implement a direct computational framework to study the two-dimensional flow physics generated during the water entry of a rigid wedge. Water and air are treated as immiscible phases and their relative motion is utilized to track the free surface dynamics. Our results show that the PIV-based methodology allows for an accurate reconstruction of the pressure field from the measured velocity field, except for early stages of the impact and for a small region close to the free surface. We also demonstrate that the reconstruction is only marginally affected by the spatial resolution, while a sufficiently high acquisition frequency is required to correctly predict the pressure field in the pile-up region. The proposed computational framework can also find application in the analysis of less studied aspects of water entry problems, such as cycling loading, flow transitions and separation, and formation of spray jets.

The mathematical model of the radial artery blood pressure waveform through monitoring of the age-related changes

Age-related changes in blood vessels affect the pulse wave propagation. These changes may cause an increase in wave reflection which leads to amplification of pulse pressure. The pulse pressure changes are associated with certain vascular diseases. Here we present a mathematical model of blood pressure for different age groups. The model is based on one-dimensional wave propagation theory and assumes that the pressure waveform is a superposition of forward propagating wave and backward waves from many reflection sites. The model is based on experimental data obtained by direct measurement of radial artery blood flow. The model clearly shows age-related changes in blood pressure waveform. The results of mathematical model correlate with the radial pressure waveform data. The model can be used in cases where it is not possible to measure the pressure due to movement of subject. Application of model to the direct blood flow measurements data allows the real-time pressure waveform monitoring. Furthermore, this approach enables monitoring of changes in pressure waveform due to the effects of medications.

Ethylene Polymerization via Metallocenes: An Experimental Study

ABSTRACTAn experimental study oriented to gather kinetic modelling data in the ethylene polymerization via metallocenes is reported. Also is illustrated the employment of two methods for determination of kinetic behavior and the instantaneous activity of Ziegler-Natta catalysts in the slurry polymerization of ethylene. The theoretical basis for both methods is described as well as the required instrumentation for its implantation at a laboratory level. An experimental program of polymerization with two different metallocenic systems was executed, showing that the direct (measurement of ethylene flow) as well as the calorimetric method (based on energy balances) give equivalent high quality information on the kinetic performance of the catalyst.

Direct Blood Flow Measurements in a Free RPE-Choroid Graft with Phase-Resolved Doppler OCT.

We directly demonstrated the revascularization in a free retinal pigment epithelium (RPE)-choroid graft with direct blood flow detection by experimental phase-resolved Doppler optical coherence tomography (PRD-OCT). Seven patients with age-related macular degeneration underwent an RPE-choroid graft translocation in a prospective institutional cohort study. Spectral domain optical coherence tomography (SD-OCT) was used to measure the revascularization stage. With PRD-OCT the presence of flow was imaged postoperatively. The PRD-OCT confirmed flow in three patients when SD-OCT indicated the afferent vessel ingrowth stage, and in all seven patients when the SD-OCT indicated the efferent vessel ingrowth stage. The PRD-OCT study was able to detect the presence of blood flow in a free RPE-choroid graft. The PRD-OCT findings directly confirmed the revascularization that was otherwise based on the more circumstantial evidence provided by SD-OCT images and angiography. The use of both techniques to monitor the revascularization process in a free graft in patients are an interesting example of replacing more invasive by noninvasive techniques. There is potential future use of PRD-OCT for the visualization of vascularization patterns in other pathologies.

A novel dementia diagnosis strategy on arterial spin labeling magnetic resonance images via pixel-wise partial volume correction and ranking

Arterial Spin Labeling (ASL) is an emerging magnetic resonance imaging technique attracting increasing attention in dementia diagnosis only beginning from recent years. ASL is capable to provide direct and quantitative measurement of cerebral blood flow (CBF) of scanned patients, so that brain atrophy of demented patients could be revealed by measured low CBF within certain brain regions through ASL. However, partial volume effects (PVE) mainly caused by signal cross-contamination due to pixel heterogeneity and limited spatial resolution of ASL, often prevents CBF from being precisely measured. Inaccurate CBF is prone to mislead and even deteriorate dementia disease diagnosis results, thereafter. In this paper, a novel dementia disease diagnosis strategy based on ASL is proposed for the first time. The diagnosis strategy is composed of two steps: 1) to conduct pixel-wise PVE correction on original ASL images and 2) to predict dementia disease severities based on corrected ASL images via ranking. Extensive experiments and comprehensive statistical analysis are carried out to demonstrate the superiority of the new strategy with comparison to several existing ones. Promising results are reported from the statistical point of view.

Reproductive strategies and isolation-by-demography in a marine clonal plant along an eutrophication gradient.

Genetic diversity in clonal organisms includes two distinct components, (i) the diversity of genotypes or clones (i.e. genotypic richness) in a population and (ii) that of the alleles (i.e. allelic and gene diversity within populations, and differentiation between populations). We investigated how population differentiation and genotypic components are associated across a gradient of eutrophication in a clonal marine plant. To that end, we combined direct measurements of sexual allocation (i.e. flower and seed counts) and genotypic analyses, which are used as an estimator of effective sexual reproduction across multiple generations. Genetic differentiation across sites was also modelled according to a hypothesis here defined as isolation-by-demography, in which we use population-specific factors, genotypic richness and eutrophication that are hypothesized to affect the source-sink dynamics and thus influence the genetic differentiation between a pair of populations. Eutrophic populations exhibited lower genotypic richness, in agreement with lower direct measurements of sexual allocation and contemporaneous gene flow. Genetic differentiation, while not explained by distance, was best predicted by genotypic richness and habitat quality. A multiple regression model using these two predictors was considered the best model (R(2) = 0.43). In this study, the relationship between environment and effective sexual-asexual balance is not simply (linearly) predicted by direct measurements of sexual allocation. Our results indicate that population-specific factors and the isolation-by-demography model should be used more often to understand genetic differentiation.

Numerical evaluation of ventilation performance in children day care centres

Modelling of ventilation is strongly dependent on the physical characteristics of the building of which precise evaluation is a complex and time consuming task. In the frame of a research project, two children day care centres (CDCC) have been selected in order to measure the envelope air permeability, the flow rate of mechanical ventilation systems and indoor and outdoor temperature. The data obtained was used as input to the computer code CONTAM for ventilation simulations. The results obtained were compared with direct measurements of ventilation flow from short term measurements with CO2 tracer gas and medium term measurements with perfluorocarbon tracer (PFT) gas decay method. After validation, in order to analyse the main parameters that affect ventilation, the model was used to predict the ventilation rates for a wide range of conditions. The purpose of this assessment was to find the best practices to improve natural ventilation. A simple analytical method to predict the ventilation flow rate of rooms is also presented. The method is based on the estimation of wind effect on the room through the evaluation of an average factor \(\sqrt {2(\Delta P/\rho _\infty )^* }\) and on the assessment of relevant cross section of gaps and openings combined in series or in parallel. It is shown that it may be applied with acceptable accuracy for this type of buildings when ventilation is due essentially to wind action.

Qinghai spruce (Picea crassifolia) forest transpiration and canopy conductance in the upper Heihe River Basin of arid northwestern China

Tree transpiration plays a determining role in the water balance of forest stands and in water yields from forested catchments, especially in arid regions. This study describes direct measurements of tree sap flow by heat pulse velocity method, and calculations of stand transpiration and canopy conductance, during the 2011 and 2012 growing seasons, in an 80- to 120-year-old Picea crassifolia stand in a natural forest. The experiment was carried out on Qilianshan Mountain, located in the upper Heihe River Basin, in the arid region of Northwest China. It was found that stand transpiration (Ec) ranged from 1.0mmd−1 to 2.4mmd−1, and from 1.2mmd−1 to 2.4mmd−1, during the 2011 and 2012 growing seasons, respectively. Total Ec was 195.2mm, 219.6mm during the 2011 and 2012 growing seasons, respectively. And total Ec during the 2012 growing season was 12.5% higher than during the 2011 growing season. Based on the half-hourly temporal scale, canopy conductance was between 0.3mms−1 and 51.3mms−1, and between 1.2 and 57.0mms−1, during the 2011 and 2012 growing seasons, respectively. Canopy conductance was sensitive to variations in climatic variables such as vapor pressure deficit (D), air temperature (T), wind speed (W) and global short-wave radiation (R). It is also evident that an exponential decay function, including D and T, accounted for 81% and 19% of the variations in canopy conductance, respectively. These results was not only providing the basis for more detailed analyses of water physiology and growth of Qinghai spruce trees for the later application of a climate-driven process model, but also might have implications for forest management in Qilianshan Mountains.

Utility of Pre and Post-Transplant Renal Resistance (RR) Index to Evaluate Organ Viability.

INTRODUCTION: Extended Criteria Donors (ECD) after Brain Death and uncontrolled Donors after Cardiac Death (DCD) have higher risk of Primary Nonfunction (PNF) and Acute Tubular Necrosis (ATN) and have become > 60% of our current deceased donors. Utility of Pre and Post-transplant Renal Resistance (RR) Index to Evaluate Organ Viability is described. METHODS: Retrospective analysis of 42 uncontrolled DCD and 24 ECD kidneys transplanted from 2009 through 2012, all preserved with RMP. Grafts with clinical criteria and biopsy proven ATN were analyzed. Correlation between RR obtained after 6 hours preservation with RMP and RR measured with Doppler Ultrasound (DU) 24 hours post-grafting was assessed. RESULTS: ECD kidneys had a lower RR with RPM than DCD kidneys (0.22 v 0.29 mmHg/mL/min; p=0.02). However, no differences were found among these groups regarding RR with US (0.78 v 0.73; p=0.12). ATN was more frequent in DCD vs EDC (77% vs 31%: p<0.001) with 86% of biopsy proven ATN in DCD. PNF due to venous thrombosis was present in 2 DCD kidneys. Simple linear regression failed to prove a significant degree of correlation between pre and post-transplant RR (p=0.76). CONCLUSIONS: RR is used to evaluate the renal hemodynamics and decide pre transplant organ suitability and orientate organ functionality after transplantation, however they are neither correlated nor able to predict ATN specially in DCD. RR obtained with RMP, as a calculation from direct measurement of renal flow and pressure, would produce a selection bias, considering that only kidneys with low RR (<0.4) are deemed acceptable rejecting those with higher RR and perhaps more risk of ATN. Additionally, in vivo assessment of RR with US can be affected by many clinical variables and only periodic follow-up of US morphology and blood flow can suggest ATN. Perhaps other markers of isquemic damage can be more efficient to predict ATN than hemodynamic approach. The different environments in which these measures are taken may be accountable for these result.

ANNUAL ASSESSMENT OF HIGHWAY TRAFFIC NOISE USING TWO CHANNEL SHORT-TERM MEASUREMENTS

Research has shown that for residential area nearby (up to 50 m) exurbia roads, there are cases where the evaluation of noise impact needs more than using the calculation methods alone. Thus, in order to confirm (or not) the implementation of designed measures for noise abatement procedures in these areas, some direct acoustical measurements of traffic flow are required. The present paper deals with the development of new approach to the methodology that allows truly estimate the annual Lden value using the one short-term (till 1 h) time interval measurement. The method is based on the original extrapolation procedure that allows to adapt results obtained in representative shortterm time interval to the annual average rating time periods of day (12 h), evening (4 h) and night (8 h), for which the Lden value is assessed. The procedure is based on the statistical processing of Sound Exposure Levels (SEL) distribution histogram of all vehicles passing by and registered on the reference microphone. The sound propagation correction is evaluated by applying simultaneous measured sound levels registration on two microphones, placed in reference point and in receiver point, considering living environment. This method allows to extend results of extrapolation obtained in the reference point into desired environment point, where such extrapolation to the annual noise levels can not be done.