Doppler Velocimeter Research Articles

Application of K008 camera in diagnostics of shock and detonation waves

Results of tests of the K008 camera to determine its resistance to the action of factors that accompany gaseodynamic experiments, such as powerful electromagnetic, acoustic, and optical interference, and its application as a component of laser Doppler velocity meters of objects thrown by an explosion are presented.

OS2-10 リボン型風車の性能評価(OS2 自然エネルギー,循環型社会における動力エネルギー技術)

The performance of the ribbon type wind turbine was investigated in wind tunnel experimentally. The test was performed with changing the rotational speed of rotor for several wind velocity. Moreover, the velocity field around rotor was measured by an laser Doppler velocity meter (LDV). The areas for velocity measurement are both circumference of maximum diameter of blades and around wind turbine. The flow was visualized by using the measured velocity. As a result of velocity measurement around maximum diameter, it turned out that vortex was observed in the point of maximum diameter of blades. Furthermore, the stream tube around ribbon type rotor is shown and the velocity distribution in the rotor wake is shown.

Quantifying flow structure in vortex chamber using fractal dimension

The flow in a vortex chamber consists of a series of vortices with a variety of different length scales. In the present study, an effort was made to scale and quantify flow structure inside the vortex chamber. To understand the structure of flow in a vortex chamber, three dimensions of flow velocity were measured using acoustic Doppler velocity meter (ADV). The velocity of the flow was measured in a fine grid from the bed to the water surface at sections 45°, 90°, 135° and 180° in the radius of the chamber. To scale the eddies of the flow, a fractal interpolation function algorithm was used to compute fractal dimension of tangential velocity, vertical velocity and Reynolds shear stress. The variation of the fractal dimension for tangential velocity, vertical velocity and Reynolds shear stress at the depth of flow and at the distance from the center of the chamber is investigated in this study. The results indicated that no significant variation for the fractal dimension of vertical velocity fluctuation and Reynolds shear stress was found for the depth in all sections. However, the fractal dimension of tangential velocity fluctuates significantly over the depth and in the distance from the center. As a result, the averaged value of fractal dimension for tangential velocity is lower than the value of fractal dimension for vertical velocity and Reynolds shear stress. The average fractal dimensions of tangential velocity are 1.63, 1.64, 1.64 and 1.63 for the sections of 45°, 90°, 135° and 180°, respectively.

Mixing of confined coaxial flows

The paper presents experimental results on the mixing process in a coaxial jet mixer in two mixing regimes. In the first mixing regime, a recirculation zone develops just behind a nozzle near mixer walls, while in the second regime a jet is mixed with the co-flow without developing a recirculation zone. In the both regimes, the mixing process is studied at Re d = 10 000. Behind the nozzle over the range 0.1 < x/ D < 9.1, a velocity field in mixer cross-sections is measured by a one-component laser Doppler velocity meter and a scalar field is detected by the laser image fluorescence (LIF) method. A transverse autocorrelation function, integral length scales and probability density functions (PDF) are calculated using instantaneous distributions of a scalar and its fluctuations. It is shown that the scalar field acquires a homogeneous state faster than the velocity one. A quasi-uniform scalar distribution over the mixer cross-section is completed at the distance x/ D = 5.1 in the first mixing regime, while this distribution has not been yet attained in the second. Analysis of the turbulent statistical moments and the autocorrelation function reveals how unsteady vortex structures exert a dramatic influence on the mixing. When the recirculation zone has developed, long-period antiphase oscillations exist near the mixer walls.

Hydrologic measurements and implications for tree island formation within Everglades National Park

Tree islands in the Shark River Slough of the Everglades National Park (ENP), in the southern state of Florida in the United States, are part of a wetland system of densely vegetated ridges interspersed within relatively open sloughs. Human alteration of this system has had dramatic negative effects on the landscape of the region and restoration efforts will require adjusting the hydrology of the region to assure the preservation of these important ecologic features. The primary objectives of this study were to document the hydrology in the vicinity of tree islands in ENP by measuring velocities in time and space and by characterizing suspended sediments. The results of such measurements were interpreted with respect to factors that may limit tree island growth. The measurements were conducted in the vicinity of three tree islands known as Black Hammock (BH), Gumbo Limbo (GL), and an unnamed island that was named for this study as Satin Leaf (SL). Acoustical Doppler Velocity (ADV) meters were used for measuring the low velocities of the Everglades water flow. Properties of suspended sediments were characterized through measurements of particle size distribution, turbidity, concentration and particle density. Mean velocities observed at each of the tree islands varied from 0.9 to 1.4 cm/s. Slightly higher mean velocities were observed during the wet season (1.2–1.6 cm/s) versus the dry season (0.8–1.3 cm/s). Maximum velocities of more than 4 cm/s were measured in areas of Cladium jamaicense die-off and at the hardwood hammock (head) of the islands. At the island’s head, water is channelized around obstructions such as tree trunks in relatively rapid flow, which may limit the lateral extent of tree island growth. Channelization is facilitated by shade from the tree canopy, which limits the growth of underwater vegetation thereby minimizing the resistance to flow and limiting sediment deposition. Suspended sediment concentrations were low (0.5–1.5 mg/L) at all study sites and were primarily of organic origin. The mean particle size of the suspended sediments was 3 μm with a distribution that was exponential. Critical velocities needed to cause re-suspension of these particles were estimated to be above the actual velocities observed. Sediment transport within the water column appears to be at a near steady state during the conditions evaluated with low rates of sediment loss balanced by presumably the release of equivalent quantities of particles of organic origin. Existing hydrologic conditions do not appear to transport sufficient suspended sediments to result in the formation of tree islands. Of interest would be to collect hydrologic and sediment transport data during extreme hydrologic events to determine if enough sediment is transported under these conditions to promote sufficient sediment accumulations.

Three-dimensional fractal scaling of bursting events and their transition probability near the bed of vortex chamber

Abstract The structure of flow inside the vortex chamber is complicated and fully three-dimensional particularly near the bed of the chamber. The secondary currents inside the vortex chamber play the main role in sediment extraction. In this study, fractal dimension of 3-D bursting process was used to define the turbulent coherent structure of the flow at the bed of the vortex chamber. It is very important for the entrainment of sediment particles from the bed and moving them towards the flushing orifice. The 3-D bursting process were categorized into eight different cubic zones according to sign of 3-D velocity fluctuations. The turbulent data was measured at 48 points near the bed of chamber using three-dimensional acoustic Doppler velocity meter (ADV). A fractal interpolation function (FIF) algorithm was used to simulate more than 300,000 time series data including time series of v′, u′, ω′, v′u′ and v′ω′ for each particular cubic zone. It was found that the fractal dimensions of 3-D velocity fluctuations and tangential and radial Reynolds shear stress for eight cubic zone of 3-D bursting process are very different. The fractal dimensions of Df(v′ω′) in cubic zone of 1, 2, 3, 4, 5, 6, 7 and 8 was found to be 1.639, 1.630, 1.609, 1.586, 1.636, 1.618, 1.623, and 1.641, respectively. With the application of 1st order Markov process, transition probabilities of 64 movements were found for the measured data along the radius and at the bed of the chamber. Additionally fractal dimension of the bursting events computed for eight particular stable organizations with the transition probability of the events. The mean fractal dimension of tangential velocity fluctuation u′ for eight movements was found to be 1.667, 1.704, 1.700, 1.695, 1.709, 1.693, 1.697 and 1.689, respectively.

Monitoring the impact of urbanisation on the Glinscica stream

Stream flow regimes are determined by watershed characteristics: climate, geology, topography, soil, vegetation and human activities. In the process of urbanisation, natural land surfaces are replaced by man made artificial coverage, such as paved roads, parking lots and roofs, which usually also implies vegetation clearing and soil compaction. Gutters, drains and storm sewers are built to accelerate the conveyance of runoff to stream channels, thus affecting the drainage system. The impact of urbanisation is complex and affects different elements of the hydrological cycle. The commonly observed hydrological responses of the watershed to urbanization are increased volume and peak of floodwaters. Concerning the ecological status of stream water, the intensified rainfall runoff induces increased pollution risks and diminishes the value of the stream water body as a habitat, especially during dry periods. In order to improve the flood safety, the regulations of the stream channel have further devaluated the ecological role of the urban streams. The magnitude of the impact is usually enlarged with the decrease in the stream size. The present paper aims at presenting the results of a two-year study monitoring the impacts of the urban environment on the watershed of the Glinscica stream situated in the central part of Slovenia. The study area of 19.3 km 2 represents a great complexity in terms of the land use pattern. The watershed was equipped with three rainfall stations, a Doppler velocity meter and a water quality multiprobe. In a short period of time more than 10 thunderstorm events were recorded and analyzed. The hydrological response of the watershed was analyzed and, interestingly, it did not show the “typical” urban impact on the runoff processes. The main water quality parameters such as temperature, pH, TDS, ORP, conductivity, dissolved oxygen and especially the concentrations of nitrate and ammonium, were measured to obtain an insight into seasonal and short time dynamics of the water quality. The results show substantial seasonal and along-the-channel variations of concentration of dissolved oxygen, nitrate and ammonium content due to biochemical processes in the channeled stream. The continuous tracing of nitrate and ammonium showed significant influence of stream regulation works on short time variations of the measured water quality parameters.

Fractal-Markovian scaling of turbulent bursting process in open channel flow

Abstract The turbulent coherent structure of flow in open channel is a chaotic and stochastic process in nature. The coherence structure of the flow or bursting process consists of a series of eddies with a variety of different length scales and it is very important for the entrainment of sediment particles from the bed. In this study, a fractal-Markovian process is applied to the measured turbulent data in open channel. The turbulent data was measured in an experimental flume using three-dimensional acoustic Doppler velocity meter (ADV). A fractal interpolation function (FIF) algorithm was used to simulate more than 500,000 time series data of measured instantaneous velocity fluctuations and Reynolds shear stress. The fractal interpolation functions (FIF) enables to simulate and construct time series of u ′, v ′, and u ′ v ′ for any particular movement and state in the Markov process. The fractal dimension of the bursting events is calculated for 16 particular movements with the transition probability of the events based on 1st order Markov process. It was found that the average fractal dimensions of the streamwise flow velocity ( u ′) are; 1.73, 1.74, 1.71 and 1.74 with the transition probability of 60.82%, 63.77%, 59.23% and 62.09% for the 1–1, 2–2, 3–3 and 4–4 movements, respectively. It was also found that the fractal dimensions of Reynold stress u ′ v ′ for quadrants 1, 2, 3 and 4 are 1.623, 1.623, 1.625 and 1.618, respectively.

Epinephrine Affects Hemodynamics of Noninnervated Normal and All-Trans Retinoic Acid-Treated Embryonic Chick Hearts

Objective: To study the acute effect of epinephrine on hemodynamics of noninnervated normal and retinoic-acid-treated embryos. Design: Prospective interventional study design. Methods: A total of 190 stage 15 (50–55 h of incubation) chick embryos were randomly treated with 1 µg all-trans retinoic acid and reincubated. At stage 20 (day 3) and stage 24 (day 4), dorsal aortic flow velocities were measured with a 20-MHz pulsed Doppler velocity meter, in normal and retinoic-acid-treated embryos. Flow velocity waveforms were assessed both before and after the administration of epinephrine (5 or 10 µg). Results: Epinephrine caused a significant increase (p < 0.05) in heart rate, peak and mean velocities, peak acceleration, peak and mean blood flows, stroke volume and dorsal aortic area of both stage 20 and stage 24 normal and retinoic-acid-treated chick embryos. However, before epinephrine administration, stage 24 retinoic-acid-treated embryos displayed a significantly lesser increase in all outcome variables with the exception of dorsal aortic area. This was even observed after epinephrine administration. The effect of retinoic acid on cardiac output could not be compensated by epinephrine application. Conclusion: Epinephrine affects hemodynamics in both normal embryos and retinoic-acid-treated embryos prior to sympathetic innervation. A significant difference in hemodynamics exists between stage 24 normal and retinoic-acid-treated embryos. The underlying mechanism for the observed hemodynamic changes will need to be investigated.

The distribution of creep activation energies in oriented polyethylene films

The “flow” creep in oriented polyethylene was studied using a Doppler velocity meter. The activation energy of the creep process was evaluated and it was established that there are three activation barriers for creep in the material studied. The most probable values, the scatter, and the relative concentration of these barriers in polyethylene samples were determined.

Field Measurements and Flow Modeling of Overbank Flows in River Severn, U.K.

Field measurements of velocity and turbulence have been carried out in a study reach of the River Severn (U.K.) during overbank flows. Directional current (DCM) and acoustic Doppler Velocity (ADV) meters have been used for the field measurements of velocity and turbulence particularly in the interface region between main channel and floodplain. The values of local shear velocity and roughness length for the reach under study were calculated using measured velocity data. The distributions of turbulent intensities, and the Reynolds stresses are also presented. A two-dimensional depth averaged numerical model is used to investigate how accurately the field measurements are reproduced. A fully 3D model of the river reach is also constructed using CFX and the results are presented.

人工リーフ開口部の鉛直断面流速分布に関する実験的研究

Artificial reefs have been constructed for protecting coast form erosion and for replacing detached breakwaters. The constrictions cause topographical change around them. Main sediment transport around an opening is bed load, but suspended sediment cannot be ignored. So the experiment using 3-ADV (Acoustic Doppler Velocity Meter) was carried out to measure the vertical mean velocity distribution at a center of opening.The result of experiment shows that the return flows direction was upward at onshore, and downward at an opening. The return flows turn alternately up and down. The amplitude of mean horizontal velocity was the maximum at the bottom. Closing to water surface, the amplitudes of velocity were getting to small.

An Attempt to Realize Experimental Isotropic Turbulence at Low Reynolds Number

This paper presents an attempt to realize experimental isotropicturbulence at low Reynolds number. For this aim an experimentalapparatus, a turbulence chamber “Box”, was designed and built togenerate a turbulent flow field in the center of the chamber. Theturbulent airflow field was generated by eight electrical fans placedsymmetrically at the eight internal corners of the externally cubicchamber. The turbulence intensity was controlled by the fans speed.Laser Doppler velocimeter (LDV) in single and two-point velocitymeasurements was used to fully characterize the turbulent field insidethe chamber. The main results indicate that the turbulence ishomogeneous and isotropic with a quasi-zero mean velocity within aspherical region of 20 mm radius from the center of the chamber. Themeasured turbulent integral length scale was found to be constant andindependent of the turbulence intensity (or fans speed). Furthermore, anoticeable spectral inertial subrange as prescribed by the Kolmogorovtheory has not been observed at the range of Reynolds number exploredhere, where Reλ < 100. But rather a scaling region characterized by anexponent that is lower than the Kolmogorov value, −5/3, has beenidentified. Moreover, the value of this exponent showed no definedtrend, while the width of the inertial scaling region expands as themicroscale Reynolds number increases.

Anomalías hemodinámicas cerebrales en gestantes con preeclampsia

Transcranial Doppler (TCD) is being used more and more frequently in the study of brain haemodynamics in pre-eclampsia/eclampsia. It has received less attention in the puerperium of these patients. The aim of our study was to compare pre-eclamptic (PE) and normotensive (NT) patients at the end of gestation, using a Doppler velocimeter, and also to compare the results from PE women in two consecutive periods of time: at the end of gestation and in early puerperium (EP). TCD was performed with bilateral evaluation of the anterior, middle and posterior cerebral arteries (ACA, MCA and PCA, respectively). Average speed (AS) and the pulsatility index (PI) were used as Doppler parameters. Arterial blood pressure (BP) and haematocrit were also measured. The AS, PI, average BP (ABP) and haematocrit were used as variables in the statistical analysis. At the end of gestation (33 weeks to full term) we compared the average values of these variables in PE (n=38) against those of NT (n=44). We also compared the results obtained for PE (n=30) in two consecutive periods: at the end of gestation and EP (the first five days following childbirth). At the end of gestation, AS were significantly higher in the PE than in the NT in all the arteries that were examined. The ABP was higher in the first group but there was no significant correlation between ABP and AS. PI were lower in the first group, with statistical signification in four of the six arteries. The AS rose significantly in the EP of the PE women, in spite of the existence of a drop in the ABP. Conversely, the PI remained unaltered. A pattern of high AS and low PI was found in PE women at the end of gestation and may be due to a primary failure of the brain's capacity to regulate itself. Anomalies in the TCD increased in the EP, despite a drop in the ABP, and this could account for the predominance of the neurological symptoms that are reported in the later forms of the syndrome.

Velocity and Turbulence Measurements for Two Overbank Flow Events in River Severn

Field measurements of velocity and turbulence have been carried out in a study reach of the River Severn at Lower Farm near Shrewsbury during overbank flow. Acoustic Doppler velocity meters have been used for the field measurements of velocity and turbulence, particularly in the interface region between river channel and floodplain. The values of local shear velocity and roughness length for the reach under study were calculated using measured velocity data. The distributions of turbulent intensities, and the Reynolds stresses are also presented. The variation of horizontal shear stress in the vertical direction deviates from linear for the main channel/floodplain interaction region due to the existence of a lateral shear and momentum transfer from the floodplain towards the main channel. Comparisons are made between the field data and previous experimental data from the Flood Channel Facility.

Flow Velocity Measurements in Vegetated Channels

Understanding of the hydraulics of flow over vegetation is very important to support the management of fluvial processes. In this paper the flow over flexible bottom vegetation is experimentally studied. A two-dimensional-acoustic doppler velocimeter is used to measure the local flow velocities for different vegetation concentrations, discharges, and flume slopes. The influence of vegetation concentration and the depth/vegetation height ratio on the measured velocity profiles is analyzed. All measured velocity distributions are S-shaped and exhibit a three-zone profile. The relationship between the velocity distribution and the turbulence intensity distribution is also analyzed. The characteristics ~inflection point, maximum value, asymptotes ! of the measured velocity distributions and the results of the previous investigators are used to select an analytical expression for the shape of the velocity profile. A theoretical velocity profile is deduced using the classical Prandtl's mixing length approach with a new expression for the mixing length. The deduced four-coefficient profile allows description of the flow both inside and above the vegetation. The physical and geometrical meaning of the four coefficients are also shown. DOI: 10.1061/~ASCE!0733-9429~2002!128:7~664! CE Database keywords: Velocity profile; Vegetation; Channel flow.

STUDY IN BOTTOM VELOCITY DISTRIBUTION AROUND OPENING OF IMPERMEABLE ARTIFICAL REEFS

Artificial reefs have been constructed for protecting coast from erosion and for replacing detached breakwaters. The construction causes topographical change around them. Bottom flow and water surface variation and others caused topographical change. So the experiment using 3-ADV (Acoustic Doppler Velocity Meter) to measure the bottom velocity profile around opening was carried out. And the topographical change by movable bed was investigated.This study shows the result of the distribution of bottom velocity around opening. The result shows that the mean velocity of flow at offshore side of reef was different from that at shore side reef. The former region has cyclic current field. And the change of topographical flux was nearly equals to the calculation results that using the Brown's theory and incident wave conditions.

Doppler tomography of mass-transfer processes in condensed media induced by femtosecond laser pulses

A femtosecond laser scheme for studying laser-induced mass transfer is proposed. A Doppler velocity meter using a femtosecond Ti: sapphire laser is created. A thermal capillary convection initiated by this laser in paraffin is investigated (with a spatial resolution of 15 μm).

Reliability and uncertainty in flow measurement techniques - some current thinking

Improvements in the quality and availability of flow measurement equipment are undoubtedly capable of enhancing the reliability and accuracy of the hydrometric data that we require. However much of the UK's hydrometric data is acquired by the tried and trusted methods that have remained the mainstay of flow monitoring for many years. Should the results provided by these established techniques always be so readily accepted given the range of assumptions on which they are based?Current meter gauging is the principle technique used for the establishment of stage discharge relationships in the UK. Either directly for the establishment of stage-discharge relationships in open channels, indirectly for calibration of flow measurement equipment (e.g. ultrasonic Doppler velocity meters) or as a means of verification of existing flow measurement structures. Recent projects involving current meter gauging techniques have provoked much thought as to the validity of established techniques and in particular the assumptions on which they are based.The chosen case studies highlight a number of projects where there have been questions regarding the reliability and uncertainty of the flow measurement techniques employed. The alternative approaches required to deal with such problems are also discussed.

Modulation of platelet aggregation after percutaneous transluminal angioplasty of the iliac artery for atherosclerosis obliterans

Background: Platelet aggregation is modulated by blood flow. We investigated whether platelet function is altered during percutaneous transluminal balloon angioplasty in patients with atherosclerosis obliterans. Methods: Blood samples were obtained from the iliac artery in 9 lower limbs of 7 patients undergoing percutaneous balloon angioplasty of the iliac artery. An agonists-induced platelet aggregation test was performed with an aggregometer. Femoral blood flow was measured with a Doppler velocimeter before and after the procedure. Results: Before dilatation, the maximum platelet aggregation rates (± SEM) induced by adenosine phosphate, epinephrine, and arachidonic acid were 54.7% ± 5.8%, 64.8% ± 4.3%, and 60.5% ± 6.1%, respectively. After angioplasty, these values reduced to 36.7% ± 4.1%, 36.1% ± 8.6%, and 40.1% ± 5.0%, respectively (P <.05). The pre-procedural ankle-brachial pressure index, mean flow rate, mean velocity, and shear stress variation were 0.63 ± 0.1, 218.1 ± 32.1 mL/min, 9.4 ± 1.1 cm/sec, and 60.6 ± 17.7 dyne/cm2, respectively. The mean velocity at the stenotic lesion was 215.1 ± 83.9 cm/sec, which was significantly greater than those of the distal artery or after angioplasty (P <.01). Both ankle-brachial pressure index and shear stress variation increased after angioplasty to 0.99 ± 0.07 (P <.05) and 139.8 ± 17.0 (P <.05) dyne/cm2, but the mean flow rate and the mean velocity (198.3 ± 24.5 mL/min and 8.8 ± 1.2 cm/sec after angioplasty) did not change significantly. Conclusions: These results indicate that activated platelet function at a stenosed artery was decreased after angioplasty, possibly because of normalized blood flow with reduction of stenotic lesion.(Surgery 2000;127:87-91)