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Publisher: Springer-Verlag   (Total: 2209 journals)

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Dynamic Games and Applications     Hybrid Journal   (Followers: 2)
Dysphagia     Hybrid Journal   (Followers: 144, SJR: 0.684, h-index: 46)
e & i Elektrotechnik und Informationstechnik     Hybrid Journal   (Followers: 7, SJR: 0.146, h-index: 8)
e-Neuroforum     Hybrid Journal  
Early Childhood Education J.     Hybrid Journal   (Followers: 11, SJR: 0.367, h-index: 12)
Earth Science Informatics     Hybrid Journal   (Followers: 3, SJR: 0.245, h-index: 5)
Earth, Moon, and Planets     Hybrid Journal   (Followers: 3, SJR: 0.436, h-index: 28)
Earthquake Engineering and Engineering Vibration     Hybrid Journal   (Followers: 7, SJR: 0.433, h-index: 17)
Earthquake Science     Hybrid Journal   (Followers: 9, SJR: 0.486, h-index: 7)
East Asia     Hybrid Journal   (Followers: 6, SJR: 0.165, h-index: 9)
Eating and Weight Disorders - Studies on Anorexia, Bulimia and Obesity     Hybrid Journal   (Followers: 6, SJR: 0.289, h-index: 23)
EcoHealth     Hybrid Journal   (Followers: 1, SJR: 0.651, h-index: 22)
Ecological Research     Hybrid Journal   (Followers: 7, SJR: 0.698, h-index: 38)
Economic Botany     Hybrid Journal   (Followers: 8, SJR: 0.666, h-index: 40)
Economic Bulletin     Hybrid Journal   (Followers: 3)
Economic Change and Restructuring     Hybrid Journal   (Followers: 1, SJR: 0.263, h-index: 6)
Economic Theory     Hybrid Journal   (Followers: 5, SJR: 1.857, h-index: 31)
Economic Theory Bulletin     Hybrid Journal  
Economics of Governance     Hybrid Journal   (Followers: 2, SJR: 0.367, h-index: 12)
Ecosystems     Hybrid Journal   (Followers: 18, SJR: 1.793, h-index: 83)
Ecotoxicology     Hybrid Journal   (Followers: 10, SJR: 1.041, h-index: 53)
Education and Information Technologies     Hybrid Journal   (Followers: 129, SJR: 0.207, h-index: 15)
Educational Assessment, Evaluation and Accountability     Hybrid Journal   (Followers: 11, SJR: 0.519, h-index: 14)
Educational Psychology Review     Hybrid Journal   (Followers: 13, SJR: 1.781, h-index: 52)
Educational Research for Policy and Practice     Hybrid Journal   (Followers: 6, SJR: 0.211, h-index: 8)
Educational Studies in Mathematics     Hybrid Journal   (Followers: 7, SJR: 0.946, h-index: 27)
Educational Technology Research and Development     Partially Free   (Followers: 132, SJR: 1.124, h-index: 45)
Electrical Engineering     Hybrid Journal   (Followers: 8, SJR: 0.352, h-index: 17)
Electrocatalysis     Hybrid Journal   (SJR: 0.542, h-index: 7)
Electronic Commerce Research     Hybrid Journal   (Followers: 3, SJR: 0.636, h-index: 14)
Electronic Markets     Hybrid Journal   (Followers: 5, SJR: 0.326, h-index: 5)
Electronic Materials Letters     Hybrid Journal   (Followers: 2, SJR: 0.566, h-index: 11)
Elemente der Mathematik     Hybrid Journal  
Emergency Radiology     Hybrid Journal   (Followers: 4, SJR: 0.446, h-index: 22)
Empirica     Hybrid Journal   (Followers: 3, SJR: 0.185, h-index: 12)
Empirical Economics     Hybrid Journal   (Followers: 7, SJR: 0.5, h-index: 29)
Empirical Software Engineering     Hybrid Journal   (Followers: 4, SJR: 2.319, h-index: 33)
Employee Responsibilities and Rights J.     Hybrid Journal   (Followers: 2, SJR: 0.21, h-index: 13)
Endocrine     Hybrid Journal   (Followers: 4, SJR: 0.659, h-index: 55)
Endocrine Pathology     Hybrid Journal   (Followers: 2, SJR: 0.555, h-index: 27)
Energy Efficiency     Hybrid Journal   (Followers: 9, SJR: 1.056, h-index: 10)
Energy Systems     Hybrid Journal   (Followers: 8, SJR: 0.589, h-index: 5)
Engineering With Computers     Hybrid Journal   (Followers: 5, SJR: 0.497, h-index: 26)
Entomological Review     Hybrid Journal   (Followers: 3, SJR: 0.128, h-index: 5)
Environment Systems & Decisions     Hybrid Journal   (Followers: 2)
Environment, Development and Sustainability     Hybrid Journal   (Followers: 25, SJR: 0.319, h-index: 26)
Environmental and Ecological Statistics     Hybrid Journal   (Followers: 5, SJR: 0.389, h-index: 29)
Environmental and Resource Economics     Hybrid Journal   (Followers: 16, SJR: 1.651, h-index: 46)
Environmental Biology of Fishes     Hybrid Journal   (Followers: 3, SJR: 0.486, h-index: 53)
Environmental Chemistry Letters     Hybrid Journal   (Followers: 3, SJR: 0.664, h-index: 22)
Environmental Earth Sciences     Hybrid Journal   (Followers: 10, SJR: 0.601, h-index: 55)
Environmental Economics and Policy Studies     Hybrid Journal   (Followers: 5, SJR: 0.35, h-index: 3)
Environmental Evidence     Open Access  
Environmental Fluid Mechanics     Hybrid Journal   (Followers: 2, SJR: 0.732, h-index: 23)
Environmental Geochemistry and Health     Hybrid Journal   (Followers: 2, SJR: 0.909, h-index: 32)
Environmental Geology     Hybrid Journal   (Followers: 11)
Environmental Health and Preventive Medicine     Hybrid Journal   (Followers: 2, SJR: 0.388, h-index: 14)
Environmental Management     Hybrid Journal   (Followers: 29, SJR: 0.773, h-index: 60)
Environmental Modeling & Assessment     Hybrid Journal   (Followers: 11, SJR: 0.413, h-index: 27)
Environmental Monitoring and Assessment     Hybrid Journal   (Followers: 9, SJR: 0.671, h-index: 46)
Environmental Science and Pollution Research     Hybrid Journal   (Followers: 11, SJR: 0.878, h-index: 42)
Epidemiologic Perspectives & Innovations     Open Access   (Followers: 1, SJR: 1.002, h-index: 14)
Epileptic Disorders     Hybrid Journal   (Followers: 1, SJR: 0.669, h-index: 34)
EPJ A - Hadrons and Nuclei     Hybrid Journal   (Followers: 1, SJR: 1.435, h-index: 58)
EPJ B - Condensed Matter and Complex Systems     Hybrid Journal   (Followers: 3, SJR: 0.749, h-index: 85)
EPJ direct     Hybrid Journal  
EPJ E - Soft Matter and Biological Physics     Hybrid Journal   (Followers: 1, SJR: 0.661, h-index: 57)
EPMA J.     Open Access   (SJR: 0.161, h-index: 4)
ERA-Forum     Hybrid Journal   (Followers: 1, SJR: 0.13, h-index: 2)
Erkenntnis     Hybrid Journal   (Followers: 11, SJR: 0.62, h-index: 14)
Erwerbs-Obstbau     Hybrid Journal   (SJR: 0.173, h-index: 8)
Esophagus     Hybrid Journal   (SJR: 0.268, h-index: 9)
Estuaries and Coasts     Hybrid Journal   (Followers: 3, SJR: 1.111, h-index: 61)
Ethical Theory and Moral Practice     Hybrid Journal   (Followers: 7, SJR: 0.278, h-index: 8)
Ethics and Information Technology     Hybrid Journal   (Followers: 151, SJR: 0.363, h-index: 20)
Ethik in der Medizin     Hybrid Journal   (SJR: 0.204, h-index: 6)
Euphytica     Hybrid Journal   (Followers: 7, SJR: 0.709, h-index: 57)
Eurasian Soil Science     Hybrid Journal   (Followers: 2, SJR: 0.271, h-index: 10)
EURO J. of Transportation and Logistics     Hybrid Journal   (Followers: 4)
EURO J. on Computational Optimization     Hybrid Journal  
EURO J. on Decision Processes     Hybrid Journal  
Europaisches J. fur Minderheitenfragen     Hybrid Journal  
European Actuarial J.     Hybrid Journal   (Followers: 2)
European Archives of Oto-Rhino-Laryngology     Hybrid Journal   (Followers: 3, SJR: 0.737, h-index: 37)
European Archives of Paediatric Dentistry     Hybrid Journal   (Followers: 1, SJR: 0.446, h-index: 12)
European Archives of Psychiatry and Clinical Neuroscience     Hybrid Journal   (Followers: 2, SJR: 1.334, h-index: 62)
European Biophysics J.     Hybrid Journal   (Followers: 4, SJR: 0.979, h-index: 53)
European Child & Adolescent Psychiatry     Hybrid Journal   (Followers: 4, SJR: 1.269, h-index: 51)
European Clinics in Obstetrics and Gynaecology     Hybrid Journal   (Followers: 4)
European Food Research and Technology     Hybrid Journal   (Followers: 8, SJR: 0.773, h-index: 49)
European J. for Education Law and Policy     Hybrid Journal   (Followers: 5)
European J. for Philosophy of Science     Partially Free   (Followers: 4, SJR: 0.165, h-index: 2)
European J. of Ageing     Hybrid Journal   (Followers: 8, SJR: 0.49, h-index: 17)
European J. of Applied Physiology     Hybrid Journal   (Followers: 7, SJR: 1.044, h-index: 74)
European J. of Clinical Microbiology & Infectious Diseases     Hybrid Journal   (Followers: 9, SJR: 0.958, h-index: 74)
European J. of Clinical Pharmacology     Hybrid Journal   (Followers: 9, SJR: 0.916, h-index: 69)
European J. of Dermatology     Hybrid Journal   (Followers: 7)
European J. of Drug Metabolism and Pharmacokinetics     Hybrid Journal   (Followers: 6, SJR: 0.24, h-index: 25)
European J. of Epidemiology     Hybrid Journal   (Followers: 17, SJR: 1.946, h-index: 60)
European J. of Forest Research     Hybrid Journal   (Followers: 3, SJR: 0.864, h-index: 25)

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Journal Cover Experiments in Fluids
   [6 followers]  Follow    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
     ISSN (Print) 1432-1114 - ISSN (Online) 0723-4864
     Published by Springer-Verlag Homepage  [2209 journals]   [SJR: 1.033]   [H-I: 62]
  • Turbulent swirling flow in a dynamic model of a uniflow-scavenged
           two-stroke engine
    • Abstract: Abstract It is desirable to use computational fluid dynamics for optimization of the in-cylinder processes in low-speed two-stroke uniflow-scavenged marine diesel engines. However, the complex nature of the turbulent swirling in-cylinder flow necessitates experimental data for validation of the used turbulence models. In the present work, the flow in a dynamic scale model of a uniflow-scavenged cylinder is investigated experimentally. The model has a transparent cylinder and a moving piston driven by a linear motor. The flow is investigated using phase-locked stereoscopic particle image velocimetry (PIV) and time-resolved laser Doppler anemometry (LDA). Radial profiles of the phase-locked mean and rms velocities are computed from the velocity fields recorded with PIV, and the accuracy of the obtained profiles is demonstrated by comparison with reference LDA measurements. Measurements are carried out at five axial positions for 15 different times during the engine cycle and show the temporal and spatial development of the swirling in-cylinder flow. The tangential velocity profiles in the bottom of the cylinder near the end of the scavenge process are characterized by a concentrated swirl resulting in wake-like axial velocity profiles and the occurrence of a vortex breakdown. After scavenge port closing, the axial velocity profiles indicate that large transient swirl-induced structures exist in the cylinder. Comparison with profiles obtained under steady-flow conditions shows that the scavenge flow cannot be assumed to be quasi-steady. The temporal development of the swirl strength is investigated by computing the angular momentum. The swirl strength shows an exponential decay from scavenge port closing to scavenge port opening corresponding to a reduction of 34 %, which is in good agreement with theoretical predictions.
      PubDate: 2014-05-22
       
  • Multi-time-lag PIV analysis of steady and pulsatile flows in a sidewall
           aneurysm
    • Abstract: Abstract The effect of inflow waveform on the hemodynamics of a real-size idealized sidewall intracranial aneurysm (IA) model was investigated using particle imaging velocimetry (PIV). For this purpose, we implemented an error analysis based on several PIV measurements with different time lags to ensure high precision of velocity fields measured in both the IA and the parent artery. The relative error measured in the main part of the circulating volume was <1 % despite the three orders of magnitude difference of parent artery and IA dome velocities. Moreover, important features involved in IA evolution were potentially emphasized from the qualitative and quantitative flow pattern comparison resulting from steady and unsteady inflows. In particular, the flow transfer in IA and the vortical structure were significantly modified when increasing the number of harmonics for a typical physiological flow, in comparison with quasi-steady conditions.
      PubDate: 2014-05-22
       
  • Corrections for one- and two-point statistics measured with
           coarse-resolution particle image velocimetry
    • Abstract: Abstract A theoretical model to determine the effect of the size of the interrogation window in particle image velocimetry measurements of turbulent flows is presented. The error introduced by the window size in two-point velocity statistics, including velocity autocovariance and structure functions, is derived for flows that are homogeneous within a 2D plane or 3D volume. This error model is more general than those previously discussed in the literature and provides a more direct method of correcting biases in experimental data. Within this model framework, simple polynomial approximations are proposed to provide a quick estimation of the effect of the averaging on these statistics. The error model and its polynomial approximation are validated using statistics of homogeneous isotropic turbulence obtained in a physical experiment and in a direct numerical simulation. The results demonstrate that the present formulation is able to correctly estimate the turbulence statistics, even in the case of strong smoothing due to a large interrogation window. We discuss how to use these results to correct experimental data and to aid the comparison of numerical results with laboratory data.
      PubDate: 2014-05-22
       
  • Inertial migration of spherical elastic phytoplankton in pipe flow
    • Abstract: Abstract Inertial migration of spherical elastic phytoplankton in a microscale pipe was investigated in Reynolds number range of 10–100. Three-dimensional position of migrating cells was obtained using digital in-line holographic microscopy. Characteristics of inertial migration were studied by analyzing the spatial distribution of cells. As Reynolds number increases, Segre–Silberberg annulus clearly appeared at the same measurement location. The effect of elastic shell compliance was experimentally investigated by comparing the probability density function of normal and hardened cells. As Re increases, the equilibrium positions of both normal and hardened cells drift toward the tube wall as the result of balanced lifts. The degree of inertial-migration development of elastic cells is slower than that of hardened cells. These results will be useful for better understanding of dynamic behaviors of phytoplankton, especially inertial migration in pipe flow.
      PubDate: 2014-05-20
       
  • Drag reduction of square cylinders with cut-corners at the front edges
    • Abstract: Abstract Flow around square cylinders with cut-corners at the front edges is investigated using particle image velocimetry. It is found that drag reduction can be achieved for the tested cut-corner dimensions. The mechanism for the drag reduction is explored on the statistical and structural aspects of the flow. After cutting the corners, the fluctuation intensity of the wake is weakened, the length of the recirculation region behind the square cylinder is increased, while the width of the wake decreases. It is found that the drag coefficient is proportional to the minimum wake width, and the Strouhal number St is inversely proportional to the minimum wake width. It is revealed that the reduced wake width is due to the suppressed separation over the side surfaces for the cylinders with cut-corners at the front edges. On the structural aspect, the phase-averaged flow field and the modes from proper orthogonal decomposition both indicate a decrease in the wake vortex size. A statistical analysis of instantaneous vortices based on Oseen vortex fit reveals that not only the size of the vortex is reduced, but also the strength is weakened.
      PubDate: 2014-05-18
       
  • Meandering jets in shallow rectangular reservoirs: POD analysis and
           identification of coherent structures
    • Abstract: Abstract The effect of the shallowness on meandering jets in a shallow rectangular reservoir is investigated. Four meandering flows were investigated in an experimental shallow rectangular reservoir. Their boundary conditions were chosen to cover a large range of friction numbers (defined with the sudden expansion width). Due to the unsteady characteristics of the flows, a proper orthogonal decomposition (POD) of the fluctuating part of the surface velocity fields measured using Large-Scale Particle Image Velocity was used for discriminating the flow structures responsible for the meandering of the jet. Less than 1 % of the calculated POD modes significantly contribute to the meandering of the jet, and two types of instability are in competition in such a flow configuration. The sinuous mode is the dominant mode in the flow, and it induces the meandering of the flow, while the varicose mode is a source of local mixing and weakly participates to the flow. The fluctuating velocity fields were then reconstructed using the POD modes corresponding to 80 % of the total mean fluctuating kinetic energy, and the coherent structures were identified using the residual vorticity, their centres being localised using a topology algorithm. The trajectories of the structures centres emphasise that at high friction number the coherent structures are small and laterally paired in the near, middle and far fields of the jet, while with decreasing friction number, the structures merge into large horizontal vortices in the far field of the jet, their trajectories showing more variability in space and time. The analysis of the stability regime finally reveals that the sinuous mode is convectively unstable and may become absolutely unstable at the end of the reservoir when the friction number is small.
      PubDate: 2014-05-18
       
  • Effect of metachronal phasing on the pumping efficiency of oscillating
           plate arrays
    • Abstract: Abstract A programmable oscillating plate array was constructed in order to study the detailed hydrodynamics of external pumping by a series of oscillating plates at Reynolds numbers on the order of 10. The array was modeled after the geometry and kinematics found in the nymphal mayfly (Ephemeroptera) Centroptilum triangulifer, and consisted of five plates, each of which could be actuated independently for stroke and pitch. Scaled tests were performed at a Reynolds number, Re = fL g 2 /ν = 18, with a single stroke kinematic pattern modeled after the living animal. In mayflies, and in many other oscillating plate systems, an antiplectic metachronal wave is used with a phase delay of approximately 90°, which corresponds to a travelling wave that moves from posterior to anterior with a wavelength of approximately four plates. In order to better understand possible reasons for why the animal system might favor the observed phase lag, ensemble-correlation stereo PIV measurements were made to reconstruct the unsteady three-dimensional phase averaged flow field at a resolution that allowed a uniform and converged estimate of the net pumped flux and the total energy dissipation within and around the vicinity of the gill array. The results indicate that the baseline case offered an optimal spot in the mass flux of fluid pumped through the array per unit energy expended, while also providing a great deal of flexibility in modifying the stroke amplitude without interference effects from adjacent gills.
      PubDate: 2014-05-16
       
  • Gas-dynamic disturbances created by surface dielectric barrier discharge
           in the constricted mode
    • Abstract: Abstract Three-dimensional structure of the gas-dynamic disturbances, created by surface dielectric barrier discharge in a constricted (saturated) mode, was analyzed simultaneously with the discharge morphology. Discharge was created in the still air under normal conditions. Flow visualization was performed by shadowgraphy and stereo-PIV technique. The wall-normal jets with the origins located in between the positions of the constricted filaments are found. Velocity magnitude in the wall-normal direction is comparable with the tangential component. Flow structure is similar to the one created by the serpentine actuator.
      PubDate: 2014-05-16
       
  • Characterizing the lower log region of the atmospheric surface layer via
           large-scale particle tracking velocimetry
    • Abstract: Abstract As a first step toward characterizing coherent structures within the atmospheric surface layer (ASL), measurements obtained via a large-scale particle tracking velocimetry (LS-PTV) system were validated against wind-measurement station data as well as canonical turbulent boundary layer studies. The LS-PTV system resolves three-dimensional, Lagrangian tracks over a 16 m3 volume. Mean-velocity measurements, as well as vertical and shear Reynolds-stress measurements, generally agreed with wind-measurement station data and Reynolds-stress profiles referenced from literature. The probability distributions for streamwise, spanwise and vertical velocity-fluctuation components appear normally distributed about zero. Furthermore, the probability distributions for all three components of Lagrangian acceleration were exponential and followed the parametrization curve from LaPorta et al. (Lett Nat 409:1017–1019, 2001). Lastly, the vorticity probability distributions were exponential and symmetric about zero, which matches findings from Balint et al. (Fluid Mech 228:53–86, 1991). The vorticity intensity measured by the LS-PTV system was less than values from Priyadarshana et al. (Fluid Mech 570:307–346, 2007), which is attributed to the low spatial resolution. However, the average spacing of 0.5 m between tracer particles is deemed sufficient for the future characterization of vortical structures within the ASL.
      PubDate: 2014-05-13
       
  • UV-mediated coalescence and mixing of inkjet printed drops
    • Abstract: Abstract In this study, we experimentally investigated the material flows of coloured dyes in coalescing small inkjet printed droplets of different volume ratios. With two differently coloured dyes, one in each droplet, we were able to distinguish the time-resolved contributions in dye transport across the coalescence bridge due to convection and diffusion. Droplets with differently coloured dyes were inkjet printed onto a glass substrate at a sufficiently large pitch such that they do not touch each other. Under UV exposure, the wetting of the substrate improves, causing the droplets to coalesce. Filmed at 50 fps, the coalescence and mixing of the droplets of volume ratios 1:1, 2:1 and 4:1 was followed. For equally sized drops, the mixing of the dyes shows good agreement with a 1D approximation of Fick’s second law along the central axes of the coalescing droplets with a diffusion coefficient D = 2 × 10−9 m2 s−1. For unequally sized droplets, convective flows from the small to the large droplet were demonstrated. The convective flows increase in size with increasing volume ratio, but only enter the droplet over a small distance. Complete mixing of the dyes in the unequally sized droplets is only reached after a long period and is diffusion controlled. At the initial moment of coalescence of unequally sized droplets, a small convective flow is observed from the large into the small droplets. Further investigation in this phenomenon is recommended.
      PubDate: 2014-05-13
       
  • Active flow control on a 1:4 car model
    • Abstract: Abstract Lift and drag of a passenger car are strongly influenced by the flow field around its rear end. The bluff body geometry produces a detached, transient flow which induces fluctuating forces on the body, affecting the rear axle, which may distress dynamic stability and comfort significantly. The investigations presented here deal with a 1:4 scale model of a simplified test car geometry that produces fluctuating lift and drag due to its strongly rounded rear geometry. To examine the influence of active flow control on this behavior, steady air jets were realized to exhaust from thin slots across the rear in three different configurations. Investigations were performed at $Re = 2.1 \times 10^{6}$ and included the capturing of effective integral lift and drag, velocity measurements in the surrounding flow field with Laser Doppler Anemometry, surface pressure measurements and surface oil flow visualization on the rear. The flow field was found to be dominated by two longitudinal vortices, developing from the detachment of the flow at the upper C-pillar positions, and a recirculating, transverse vortex above the rear window. With an air jet emerging from a slot across the surface right below the rear window section, tangentially directed upstream toward the roof section, total lift could be reduced by more than 7 %, with rear axle lift reduction of about 5 % and negligible drag affection ( $<$ 1 %).
      PubDate: 2014-05-10
       
  • Measurement of atmospheric boundary layer based on super-large-scale
           particle image velocimetry using natural snowfall
    • Abstract: Abstract We present an implementation of super-large-scale particle image velocimetry (SLPIV) to characterize spatially the turbulent atmospheric boundary layer using natural snowfall as flow tracers. The SLPIV technique achieves a measurement area of ~22 m × 52 m, up to 56 m above the ground, with a spatial resolution of ~0.34 m. The traceability of snow particles is estimated based on their settling velocity obtained from the wall-normal component of SLPIV velocity measurements. The results are validated using coincident measurements from sonic anemometers on a meteorological tower situated in close proximity to the SLPIV sampling area. A contrast of the mean velocity and the streamwise Reynolds stress component obtained from the two techniques shows less than 3 and 12 % difference, respectively. Additionally, the turbulent energy spectra measured by SLPIV show a similar inertial subrange and trends when compared to those measured by the sonic anemometers.
      PubDate: 2014-05-10
       
  • Experimental investigation of interactions of three co-planar and
           converging jets
    • Abstract: Abstract This experimental study focused on the structures of the flow produced by a novel configuration of three co-planar circular and neutrally buoyant pipe jets. The configuration presented in this paper was symmetrical about the central jet, with both side jets set at an inclined angle of 30° towards the central jet. These three jets discharged into a tank of still receiving water. The flow fields were captured using a particle image velocimetry system, and the complex flow patterns on two orthogonal planes (in-plane and normal to the central jet flow direction) were analysed and characterised in terms of velocity and vorticity distributions. Based on the findings of the study, it was deduced that the centreline velocity of the combined jet exhibited a preserved core before a longitudinal distance of 12D (D is the jet diameter) from the pipe exit and then decayed linearly until 17D. After 17D, the in-plane velocity profile followed a Gaussian distribution, while the profile in the normal plane portrayed a double-peak distribution. Finally, the dynamic interactions among the three converging jets were illustrated through a time series of instantaneous flow fields.
      PubDate: 2014-05-06
       
  • Evaluation of hot-wire spatial filtering corrections for wall turbulence
           and correction for end-conduction effects
    • Abstract: Abstract Several recent spatial filtering corrections for Reynolds stress measured by single component hot-wire probes were assessed using turbulent channel flow data measured over a moderate Reynolds number range. Using measurements with a variety of hot-wire lengths and aspect ratios, the current work determines the impact of these corrections on the actual magnitude and Reynolds number dependence of the near-wall turbulent peak in Reynolds stress and compares it to results from prior direct numerical simulations of turbulent channel flow. Comparison of the results following application of previously published correction schemes were found to produce similar results, with some limitations observed for each technique. Comparison to direct numerical simulation results suggested that additional corrections were needed to correct for end conduction effects. An additional modification for these effects was devised which improved agreement between probes of different lengths and aspect ratios and improved agreement between the measured and direct numerical simulation results .
      PubDate: 2014-05-06
       
  • Measuring void fraction and velocity fields of a stepped spillway for
           skimming flow using non-intrusive methods
    • Abstract: Abstract Stepped spillways have higher energy dissipation than smoother hydraulic structures used to divert flood discharges. The inception point related to air entrainment is, however, located further upstream causing an undesired bulking of the flow depth. For large discharge rates and for straight stepped spillways, the skimming flow regime may be assumed two dimensional; this is an attractive feature for the application of non-intrusive flow visualization techniques because these methods measure the flow characteristics in the vicinity of the sidewalls which are likely to correlate with the flow at the centre of the flume. This paper tests the hypothesis that such techniques can be used to measure the flow inside the flume. The hypothesis is tested against measurements taken with an intrusive probe. Void fraction contour lines and velocity fields are obtained in 12 different stepped spillway configurations using the image processing procedure and the bubble image velocimetry, respectively. The void fraction and velocity results are overall consistent with the probe measurements. The velocity fields show a persistent underestimation of the probe measurements which can at least be partially explained by sidewall effects and possible probe’s overestimation.
      PubDate: 2014-05-06
       
  • The potential of on-line optical flow measurement in the control and
           monitoring of pilot-scale oxy-coal flames
    • Abstract: Abstract Digital image processing techniques offer a wide array of tools capable of extracting apparent displacement or velocity information from sequences of images of moving objects. Optical flow algorithms have been widely used in areas such as traffic monitoring and surveillance. The knowledge of instantaneous apparent flame velocities (however, they are defined) may prove to be valuable during the operation and control of industrial-scale burners. Optical diagnostics techniques, coupled with on-line image processing, have been applied in the optimization of coal-fired power plants; however, regardless of the available technology, the current methods do not apply optical flow measurement. Some optical flow algorithms have the potential of real-time applicability and are thus possible candidates for on-line apparent flame velocity extraction. In this paper, the potential of optical flow measurement in on-line flame monitoring and control is explored.
      PubDate: 2014-05-04
       
  • Development of a wall-shear-stress sensor and measurements in
           mini-channels with partial blockages
    • Abstract: Abstract The design, construction, operation and validation of a wall-shear-stress sensor, and measurements obtained using this sensor in air flows downstream of partial blockages in a mini-channel are presented. The sensor consisted of a hot wire mounted over a small rectangular slot and operated using a constant-temperature anemometer. It was used to investigate flows similar to those within the mini-channels inside notebook computers. The overall goal of the present work was to develop a sensor suitable for measurements of the wall-shear stress in such flows, which can be used to validate corresponding numerical simulations, as the latter are known to be often surprisingly inaccurate. To this end, measurements of the wall-shear stress, and the corresponding statistical moments and power spectral densities, were obtained at different distances downstream of the partial blockage, with blockage ratios of 39.7, 59.2, and 76.3 %. The Reynolds number (based on average velocity and hydraulic diameter) ranged from 100 to 900. The results confirmed the presence of unsteadiness, separation, reattachment, and laminar-turbulent transition in the ostensibly laminar flow of air in mini-channels with partial blockages. The present results demonstrate why accurate numerical predictions of cooling air flows in laptop and notebook computers remain a challenging task.
      PubDate: 2014-05-03
       
  • Dynamics of a small number of droplets in microfluidic Hele–Shaw
           cells
    • Abstract: Abstract We investigate the dynamics of a small number of droplets (N = 1, 2, 3) in microfluidic Hele–Shaw cells. We study the cases N = 1, 2, and 3 droplets and analyze the influence of the side walls. In the course of the study, we observe spontaneous alignment of droplet pairs, pair exchanges, droplet escape, multiple reflections between walls, i.e., a number of phenomena that have not been reported yet. As a whole, using pairwise far-field dipolar interactions between droplets, along with treating the walls as mirrors, allows to reproduce the observations, even though limitations in the predictability of the model are pointed out in a few cases. From a more practical prospective, the work shows that the behavior of elementary droplet assemblies can be put under acceptable experimental control in a wide variety of situations, a feature potentially interesting for self-assembly, mixing, or transport of particles in microfluidic environments.
      PubDate: 2014-05-01
       
  • A device to achieve low Reynolds numbers in an open surface water channel
    • Abstract: Abstract When investigating flow structures, and especially flow transitions, research projects often seek to increase insight using complementary numerical and physical experiments. Obtaining exact Reynolds number correspondence can frequently be difficult in experiments, particularly when relatively low values are required. Often, available test facilities were designed and optimised for a specific velocity range, meaning they have restrictions on the minimum flow velocity. This study describes a device to reduce the flow velocity locally in an open surface water channel. The underlying idea is to divert a controlled fraction of the incoming flow from the working section by increasing the pressure there, resulting in reduced velocity. This idea is realised using a ‘sub-channel’ that can be inserted into the main test chamber, with a variable porosity perforated screen at its downstream end. This study assesses and optimises the flow quality inside this structure, such as usable test section length, uniformity of the velocity profiles and turbulence intensity. The results demonstrate that the device creates high quality low Reynolds number flows, which is exemplified with the canonical circular cylinder in cross-flow.
      PubDate: 2014-05-01
       
  • Internal jet interactions in a fluidic oscillator at low flow rate
    • Abstract: Abstract This study focuses on the internal jet interactions and the oscillation mechanism of the feedback-free fluidic oscillator at low flow rate, corresponding to a Reynolds number of 1,350 (based on exit nozzle width and average exit velocity). Particle image velocimetry (PIV) was used in this study with a refractive index-matched fluid to minimize reflections that would otherwise occur at the fluid-acrylic interface in the test setup. A simple microphone-tube sensor configuration generated a reference signal, with a phase-averaging method based on each quarter period for velocity time history reconstruction. PIV results revealed the existence of a vortex of fluctuating size, shape, and strength on each side of the oscillator; and two transient vortices that are formed in the dome region of the oscillator by each of the jets once per period. The dome vortices periodically bifurcate each of the jets and transfer some of the kinetic energy of that jet to the opposing jet. This kinetic energy transfer mechanism dictates the dominance of either jet at the exit, and this mechanism repeats itself to sustain the oscillations created by the fluidic oscillator. At this flow rate, the two jets form a continuous mutual collision, and the jets are never completely cut off from the exit. The oscillatory behavior at this flow rate is due to a complex combination of jet interactions and bifurcations, vortex–shear layer interactions, vortex–wall interactions, and saddle point formations.
      PubDate: 2014-05-01
       
 
 
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