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Publisher: Springer-Verlag   (Total: 2210 journals)

 Dysphagia       (Followers: 193, SJR: 0.684, h-index: 46) e & i Elektrotechnik und Informationstechnik       (Followers: 8, SJR: 0.146, h-index: 8) e-Neuroforum Early Childhood Education J.       (Followers: 12, SJR: 0.367, h-index: 12) Earth Science Informatics       (Followers: 3, SJR: 0.245, h-index: 5) Earth, Moon, and Planets       (Followers: 5, SJR: 0.436, h-index: 28) Earthquake Engineering and Engineering Vibration       (Followers: 7, SJR: 0.433, h-index: 17) Earthquake Science       (Followers: 9, SJR: 0.486, h-index: 7) East Asia       (Followers: 7, SJR: 0.165, h-index: 9) Eating and Weight Disorders - Studies on Anorexia, Bulimia and Obesity       (Followers: 7, SJR: 0.289, h-index: 23) EcoHealth       (Followers: 1, SJR: 0.651, h-index: 22) Ecological Research       (Followers: 8, SJR: 0.698, h-index: 38) Economic Botany       (Followers: 8, SJR: 0.666, h-index: 40) Economic Bulletin       (Followers: 4) Economic Change and Restructuring       (Followers: 1, SJR: 0.263, h-index: 6) Economic Theory       (Followers: 8, SJR: 1.857, h-index: 31) Economic Theory Bulletin       (Followers: 1) Economics of Governance       (Followers: 2, SJR: 0.367, h-index: 12) Ecosystems       (Followers: 19, SJR: 1.793, h-index: 83) Ecotoxicology       (Followers: 10, SJR: 1.041, h-index: 53) Education and Information Technologies       (Followers: 174, SJR: 0.207, h-index: 15) Educational Assessment, Evaluation and Accountability       (Followers: 14, SJR: 0.519, h-index: 14) Educational Psychology Review       (Followers: 14, SJR: 1.781, h-index: 52) Educational Research for Policy and Practice       (Followers: 6, SJR: 0.211, h-index: 8) Educational Studies in Mathematics       (Followers: 9, SJR: 0.946, h-index: 27) Educational Technology Research and Development       (Followers: 181, SJR: 1.124, h-index: 45) Electrical Engineering       (Followers: 12, SJR: 0.352, h-index: 17) Electrocatalysis       (SJR: 0.542, h-index: 7) Electronic Commerce Research       (Followers: 2, SJR: 0.636, h-index: 14) Electronic Markets       (Followers: 5, SJR: 0.326, h-index: 5) Electronic Materials Letters       (Followers: 3, SJR: 0.566, h-index: 11) Elemente der Mathematik       (Followers: 1) Emergency Radiology       (Followers: 4, SJR: 0.446, h-index: 22) Empirica       (Followers: 3, SJR: 0.185, h-index: 12) Empirical Economics       (Followers: 8, SJR: 0.5, h-index: 29) Empirical Software Engineering       (Followers: 4, SJR: 2.319, h-index: 33) Employee Responsibilities and Rights J.       (Followers: 2, SJR: 0.21, h-index: 13) Endocrine       (Followers: 5, SJR: 0.659, h-index: 55) Endocrine Pathology       (Followers: 2, SJR: 0.555, h-index: 27) Energy Efficiency       (Followers: 11, SJR: 1.056, h-index: 10) Energy Systems       (Followers: 10, SJR: 0.589, h-index: 5) Engineering With Computers       (Followers: 5, SJR: 0.497, h-index: 26) Entomological Review       (Followers: 3, SJR: 0.128, h-index: 5) Environment Systems & Decisions       (Followers: 2) Environment, Development and Sustainability       (Followers: 28, SJR: 0.319, h-index: 26) Environmental and Ecological Statistics       (Followers: 5, SJR: 0.389, h-index: 29) Environmental and Resource Economics       (Followers: 17, SJR: 1.651, h-index: 46) Environmental Biology of Fishes       (Followers: 4, SJR: 0.486, h-index: 53) Environmental Chemistry Letters       (Followers: 3, SJR: 0.664, h-index: 22) Environmental Earth Sciences       (Followers: 10, SJR: 0.601, h-index: 55) Environmental Economics and Policy Studies       (Followers: 6, SJR: 0.35, h-index: 3) Environmental Evidence Environmental Fluid Mechanics       (Followers: 2, SJR: 0.732, h-index: 23) Environmental Geochemistry and Health       (Followers: 2, SJR: 0.909, h-index: 32) Environmental Geology       (Followers: 11) Environmental Health and Preventive Medicine       (Followers: 2, SJR: 0.388, h-index: 14) Environmental Management       (Followers: 32, SJR: 0.773, h-index: 60) Environmental Modeling & Assessment       (Followers: 11, SJR: 0.413, h-index: 27) Environmental Monitoring and Assessment       (Followers: 9, SJR: 0.671, h-index: 46) Environmental Science and Pollution Research       (Followers: 11, SJR: 0.878, h-index: 42) Epidemiologic Perspectives & Innovations       (Followers: 1, SJR: 1.002, h-index: 14) Epileptic Disorders       (Followers: 1, SJR: 0.669, h-index: 34) EPJ A - Hadrons and Nuclei       (Followers: 1, SJR: 1.435, h-index: 58) EPJ B - Condensed Matter and Complex Systems       (Followers: 3, SJR: 0.749, h-index: 85) EPJ direct EPJ E - Soft Matter and Biological Physics       (Followers: 1, SJR: 0.661, h-index: 57) EPMA J.       (SJR: 0.161, h-index: 4) ERA-Forum       (Followers: 2, SJR: 0.13, h-index: 2) Erkenntnis       (Followers: 11, SJR: 0.62, h-index: 14) Erwerbs-Obstbau       (SJR: 0.173, h-index: 8) Esophagus       (SJR: 0.268, h-index: 9) Estuaries and Coasts       (Followers: 3, SJR: 1.111, h-index: 61) Ethical Theory and Moral Practice       (Followers: 7, SJR: 0.278, h-index: 8) Ethics and Information Technology       (Followers: 183, SJR: 0.363, h-index: 20) Ethik in der Medizin       (SJR: 0.204, h-index: 6) Euphytica       (Followers: 7, SJR: 0.709, h-index: 57) Eurasian Soil Science       (Followers: 2, SJR: 0.271, h-index: 10) EURO J. of Transportation and Logistics       (Followers: 4) EURO J. on Computational Optimization EURO J. on Decision Processes Europaisches J. fur Minderheitenfragen European Actuarial J.       (Followers: 3) European Archives of Oto-Rhino-Laryngology       (Followers: 4, SJR: 0.737, h-index: 37) European Archives of Paediatric Dentistry       (Followers: 1, SJR: 0.446, h-index: 12) European Archives of Psychiatry and Clinical Neuroscience       (Followers: 2, SJR: 1.334, h-index: 62) European Biophysics J.       (Followers: 4, SJR: 0.979, h-index: 53) European Child & Adolescent Psychiatry       (Followers: 5, SJR: 1.269, h-index: 51) European Clinics in Obstetrics and Gynaecology       (Followers: 5) European Food Research and Technology       (Followers: 8, SJR: 0.773, h-index: 49) European J. for Education Law and Policy       (Followers: 5) European J. for Philosophy of Science       (Followers: 4, SJR: 0.165, h-index: 2) European J. of Ageing       (Followers: 10, SJR: 0.49, h-index: 17) European J. of Applied Physiology       (Followers: 8, SJR: 1.044, h-index: 74) European J. of Clinical Microbiology & Infectious Diseases       (Followers: 11, SJR: 0.958, h-index: 74) European J. of Clinical Pharmacology       (Followers: 9, SJR: 0.916, h-index: 69) European J. of Dermatology       (Followers: 7) European J. of Drug Metabolism and Pharmacokinetics       (Followers: 6, SJR: 0.24, h-index: 25) European J. of Epidemiology       (Followers: 17, SJR: 1.946, h-index: 60) European J. of Forest Research       (Followers: 3, SJR: 0.864, h-index: 25) European J. of Health Economics       (Followers: 11, SJR: 0.67, h-index: 25)
 Experiments in Fluids    [8 followers]  Follow        Hybrid journal (It can contain Open Access articles)      ISSN (Print) 1432-1114 - ISSN (Online) 0723-4864      Published by Springer-Verlag  [2210 journals]   [SJR: 1.033]   [H-I: 62]
• A new experiment to measure shocked particle drag using multi-pulse
particle image velocimetry and particle tracking
• Abstract: Abstract We demonstrate the measurement capabilities for a new horizontal shock tube facility designed to measure the displacements, velocities and accelerations of shock-accelerated particles just after shock passage. Eight-frame particle image accelerometry and particle tracking velocimetry accelerometry diagnostics are implemented, along with a shadowgraphy system for measuring the shock location during experiments. We demonstrate the driving conditions of the facility using a unique membraneless pneumatic driver and particle seeding system that can accommodate both solid and liquid particles in the carrier phase. Measurements of two types of solid particles show unsteady drag forces higher than those for steady drag.
PubDate: 2014-11-22

• On the use of refractive-index-matched hydrogel for fluid velocity
measurement within and around geometrically complex solid obstructions
• Abstract: Abstract Laboratory-based particle image velocimetry (PIV) was used to measure current-driven hydrodynamics within and around a collection of complex obstacles. These obstacles were fabricated using a specialty superabsorbent hydrogel produced through the free-radical copolymerization of sodium acrylate and acrylamide. The optical properties of this gel were found to be nearly identical to those of liquid water. Because of refractive index matching (RIM) of both the fluid and solid media, PIV laser light sheets passed through the obstructions without significant degradation or modification. As a result, all tracer particles suspended in the flow were uniformly illuminated, regardless of their position or proximity relative to individual obstacle features. PIV light sheets were also successfully imaged through the hydrogel, enabling accurate velocity measurement in regions that would otherwise be optically inaccessible. These outcomes were reached without reliance on unconventional fluids or specialized flow facilities. For many experimenters interested in fluid–solid interactions, hydrogel-based RIM may thus be less costly and more adaptable than methods that rely on the existing suite of techniques.
PubDate: 2014-11-21

• Unsteadiness of the internal flow in an effervescent atomizer nozzle
• Abstract: Abstract In order to better understand the mechanisms that effect spray unsteadiness of effervescent atomizers and therefore to efficiently eliminate it, the two-phase flow pattern within the nozzle has been studied by pressure measurement and flow visualization. We found that the speed of sound in the two-phase flow can be predicted by the model suggested by Nguyen et al. (Int J Multiphase Flow 7:311–320, 1981) using an averaged void fraction value. Dominant peak frequencies of pressure fluctuations both inside and outside the mixing chamber become synchronized in the slug flow regime. We show that the slug passage frequency is linearly proportional to the speed of sound and almost equal to the fundamental frequency of the mixing chamber. At a constant liquid flow rate and as the gas flow rate is increased, pressure fluctuations reach a maximum value with the appearance of a synchronized peak frequency. The amplitude of pressure fluctuation is then insensitive to further increases in the gas flow rate. For a constant gas flow rate, the pressure fluctuation increases with the increment of the liquid flow rate, reaching the maximum value at the moment of transition from slug flow to the bubbly flow.
PubDate: 2014-11-19

• A scanning PIV method for fine-scale turbulence measurements
• Abstract: Abstract A hybrid technique is presented that combines scanning PIV with tomographic reconstruction to make spatially and temporally resolved measurements of the fine-scale motions in turbulent flows. The technique uses one or two high-speed cameras to record particle images as a laser sheet is rapidly traversed across a measurement volume. This is combined with a fast method for tomographic reconstruction of the particle field for use in conjunction with PIV cross-correlation. The method was tested numerically using DNS data and with experiments in a large mixing tank that produces axisymmetric homogeneous turbulence at $$R_\lambda \simeq 219$$ . A parametric investigation identifies the important parameters for a scanning PIV set-up and provides guidance to the interested experimentalist in achieving the best accuracy. Optimal sheet spacings and thicknesses are reported, and it was found that accurate results could be obtained at quite low scanning speeds. The two-camera method is the most robust to noise, permitting accurate measurements of the velocity gradients and direct determination of the dissipation rate.
PubDate: 2014-11-19

• Multi-layer film flow down an inclined plane: experimental investigation
• Abstract: Abstract We report the results from an experimental study of the flow of a film down an inclined plane where the film itself is comprised of up to three layers of different liquids. By measuring the total film thickness for a broad range of parameters including flow rates and liquid physical properties, we provide a thorough and systematic test of the single-layer approximation for multi-layer films for Reynolds numbers $$Re = \rho Q/\mu \approx 0.03 - 60$$ . In addition, we also measure the change in film thickness of individual layers as a function of flow rates for a variety of experimental configurations. With the aid of high-speed particle tracking, we derive the velocity fields and free-surface velocities to compare to the single-layer approximation. Furthermore, we provide experimental evidence of small capillary ridge formations close to the point where two layers merge and compare our experimental parameter range for the occurrence of this phenomenon to those previously reported.
PubDate: 2014-11-19

• SparkJet characterizations in quiescent and supersonic flowfields
• Abstract: Abstract The aerodynamic community has studied active flow control actuators for some time, and developments have led to a wide variety of devices with various features and operating mechanisms. The design requirements for a practical actuator used for active flow control include reliable operation, requisite frequency and amplitude modulation capabilities, and a reasonable lifespan while maintaining minimal cost and design complexity. An active flow control device called the SparkJet actuator has been developed for high-speed flight control and incorporates no mechanical/moving parts, zero net mass flux capabilities and the ability to tune the operating frequency and momentum throughput. This actuator utilizes electrical power to deliver high-momentum flow with a very fast response time. The SparkJet actuator was characterized on the benchtop using a laser-based microschlieren visualization technique and maximum blast wave and jet front velocities of ~400 and ~310 m/s were, respectively, measured in the flowfield. An increase in jet front velocity from 240 to 310 m/s during subatmospheric (60 kPa) testing reveals that the actuator may have greater control authority at lower ambient pressures, which correspond to high-altitude flight conditions for air vehicles. A SparkJet array was integrated into a flat plate and tested in a Mach 1.5 crossflow. Phase-conditioned shadowgraph results revealed a maximum flow deflection angle of 5° created by the SparkJet 275 µs after the actuator was triggered in single-shot mode. Burst mode operation of frequencies up to 700 Hz revealed similar results during wind tunnel testing. Following these tests, the actuator trigger mechanism was improved and the ability of the actuator to be discharged in burst mode at a frequency of 1 kHz was achieved.
PubDate: 2014-11-19

• Advantageous swirling flow in 45° end-to-side anastomosis
• Abstract: Abstract The effects of swirling flow on the flow field in 45° end-to-side anastomosis are experimentally investigated using a particle image velocimetry technique to reveal fluid dynamic advantages of swirling flow in the vascular graft. Non-swirling Poiseuille inlet flow unnecessarily induces pathological hemodynamic features, such as high wall shear stress (WSS) at the ‘bed’ side and large flow separation at the ‘toe’ side. The introduction of swirling flow is found to equalize the asymmetric WSS distribution and reduces the peak magnitude of WSS. In particular, the intermediate swirling intensity of S = 0.45 induces the most uniform axial velocity and WSS distributions compared with weaker or stronger swirling flows, which addresses the importance of proper selection of swirling intensity in the vascular graft to obtain optimum flow fields at the host vessel. In addition, swirling flow reduces the size of flow separation because it disturbs the formation of Dean-type vortices in secondary flow and inhibits secondary flow collision. The beneficial fluid dynamic features of swirling flow obtained in this study are helpful for designing better vascular graft suppressing pathological hemodynamic features in the recipient host vessel.
PubDate: 2014-11-19

• Size distribution measurement for densely binding bubbles via image
analysis
• Abstract: Abstract For densely binding bubble clusters, conventional image analysis methods are unable to provide an accurate measurement of the bubble size distribution because of the difficulties with clearly identifying the outline edges of individual bubbles. In contrast, the bright centroids of individual bubbles can be distinctly defined and thus accurately measured. By taking this advantage, we developed a new measurement method based on a linear relationship between the bubble radius and the radius of its bright centroid so to avoid the need to identify the bubble outline edges. The linear relationship and method were thoroughly tested for 2D bubble clusters in a highly binding condition and found to be effective and robust for measuring the bubble sizes.
PubDate: 2014-11-19

• Measurement of liquid sheet using laser tagging method by photochromic dye
• Abstract: Abstract Liquid atomization system has been extensively applied as the most significant process in many industrial fields. In the internal combustion engine, the combustion phenomenon is strongly influenced by the spray characteristics of the fuel given by the atomization process. In order to completely understand the whole atomization process, a detail investigation of relations between the liquid jet characteristics and the breakup phenomenon is required. In this study, a non-intrusive method called as laser tagging method by photochromic dye has been developed with aim to study the breakup process of liquid sheet in detail, covering from the behavior in film until disintegrated into ligament and droplets. The laser tagging method by photochromic dye is based on a shift in the absorption spectrum of photochromic dye molecules tagged by ultraviolet laser. The shift results a color change at the tagged region of liquid containing the dye. In this study, the motions of the dye traces were analyzed as the liquid surface velocity. As a result, liquid sheet was found to keep its velocity constantly in film before suddenly increase around broken point. However, it then decreased after broken into droplets. By forming a set of four points of dye traces on the liquid sheet, the change of relative position of the set enabled the measurement of deformation and rotational motion of the liquid sheet. As a result, the normal strain of the liquid sheet parallel to the flow direction depended on the flow behavior of ligament formation.
PubDate: 2014-11-18

• Flow field studies on a micro-air-vehicle-scale cycloidal rotor in forward
flight
PubDate: 2014-11-13

• Reconstructing the 3D shapes of droplets in glass microchannels with
application to Bretherton’s problem
• Abstract: Abstract The outstanding potential of absorbance imaging for the 3D shape analysis of dynamic scenes in multiphase flows is demonstrated and experimentally confirmed. The experimental procedures and workflows have been extended and applied to the 3D shape analysis of droplets moving in microchannels. Using this technique, the problem of measuring the thickness of the lubrication layer and the droplet geometry with sub- $$\upmu$$ m resolution could be solved. The obtained data generally conform to models based on Bretherton’s theory and allow its extension even for non-circular microchannel geometries.
PubDate: 2014-11-08

• Statistical axisymmetry of the turbulent sphere wake
• Abstract: Abstract The turbulent sphere wake is studied experimentally at $${Re}=1.9\,10^4$$ using an axisymmetric support that holds the body from upstream. This setup allows the axisymmetry of the mean wake and preserves the global mode activity at $${St}=0.19$$ . The analysis of the PIV snapshots in a cross-flow plane indicates that this axisymmetry is due to an equal exploration of all the azimuths by the instantaneous wake. Using conditional averaging techniques, we extract the flow topology associated with one azimuthal direction; the obtained wake shows strong similarities with the unsteady planar symmetric flow reported in the laminar regime. In addition, the use of perturbations of the axisymmetry leads to modifications of the azimuthal statistics: The periodicity of the perturbation is recovered in the wake since one or several preferred orientations are identified. Hence, such statistics pave the way to multi-stable behaviors in three-dimensional wakes.
PubDate: 2014-11-06

• Three-dimensional reconstruction of cardiac flows based on multi-planar
velocity fields
• Abstract: Abstract Measurement of the three-dimensional flow field inside the cardiac chambers has proven to be a challenging task. This is mainly due to the fact that generalized full-volume velocimetry techniques cannot be easily implemented to the heart chambers. In addition, the rapid pace of the events in the heart does not allow for accurate real-time flow measurements in 3D using imaging modalities such as magnetic resonance imaging, which neglects the transient variations of the flow due to averaging of the flow over multiple heartbeats. In order to overcome these current limitations, we introduce a multi-planar velocity reconstruction approach that can characterize 3D incompressible flows based on the reconstruction of 2D velocity fields. Here, two-dimensional, two-component velocity fields acquired on multiple perpendicular planes are reconstructed into a 3D velocity field through Kriging interpolation and by imposing the incompressibility constraint. Subsequently, the scattered experimental data are projected into a divergence-free vector field space using a fractional step approach. We validate the method in exemplary 3D flows, including the Hill’s spherical vortex and a numerically simulated flow downstream of a 3D orifice. During the process of validation, different signal-to-noise ratios are introduced to the flow field, and the method’s performance is assessed accordingly. The results show that as the signal-to-noise ratio decreases, the corrected velocity field significantly improves. The method is also applied to the experimental flow inside a mock model of the heart’s right ventricle. Taking advantage of the periodicity of the flow, multiple 2D velocity fields in multiple perpendicular planes at different locations of the mock model are measured while being phase-locked for the 3D reconstruction. The results suggest the metamorphosis of the original transvalvular vortex, which forms downstream of the inlet valve during the early filling phase of the right ventricular model, into a streamline single-leg vortex extending toward the outlet.
PubDate: 2014-11-05

• Total pressure fluctuations and two-phase flow turbulence in hydraulic
jumps
• Abstract: Abstract The large-scale turbulence and high air content in a hydraulic jump restrict the application of many traditional flow measurement techniques. This paper presents a physical modelling of hydraulic jump, where the total pressure and air–water flow properties were measured simultaneously with intrusive probes, namely a miniature pressure transducer and a dual-tip phase-detection probe, in the jump roller. The total pressure data were compared to theoretical values calculated based upon void fraction, water depth and flow velocity measured by the phase-detection probe. The successful comparison showed valid pressure measurement results in the turbulent shear region with constant flow direction. The roller region was characterised by hydrostatic pressure distributions, taking into account the void fraction distributions. The total pressure fluctuations were related to both velocity fluctuations in the air–water flow and free-surface dynamics above the roller, though the time scales of these motions differed substantially.
PubDate: 2014-11-05

• Electrical and mechanical characteristics of surface AC dielectric barrier
discharge plasma actuators applied to airflow control
• Abstract: Abstract The present paper is a wide review on AC surface dielectric barrier discharge (DBD) actuators applied to airflow control. Both electrical and mechanical characteristics of surface DBD are presented and discussed. The first half of the present paper gives the last results concerning typical single plate-to-plate surface DBDs supplied by a sine high voltage. The discharge current, the plasma extension and its morphology are firstly analyzed. Then, time-averaged and time-resolved measurements of the produced electrohydrodynamic force and of the resulting electric wind are commented. The second half of the paper concerns a partial list of approaches having demonstrated a significant modification in the discharge behavior and an increasing of its mechanical performances. Typically, single DBDs can produce mean force and electric wind velocity up to 1 mN/W and 7 m/s, respectively. With multi-DBD designs, velocity up to 11 m/s has been measured and force up to 350 mN/m.
PubDate: 2014-11-05

• Mind the gap: a new insight into the tip leakage vortex using stereo-PIV
• Abstract: Abstract The tip leakage vortex (TLV), which develops in the clearance between the rotor and the stator of axial hydro turbines, has been studied for decades. Yet, many associated phenomena are still not understood. For instance, it remains unclear how the clearance size is related to the occurrence of cavitation in the vortex, which can lead to severe erosion. Experiments are here carried out on the influence of the clearance size on the tip vortex structure in a simplified case study. A NACA0009 hydrofoil is used as a generic blade in a water tunnel while the clearance between the blade tip and the wall is varied. The 3D velocity fields are measured using Stereo Particle Image Velocimetry (SPIV) in three planes located downstream of the hydrofoil for different values of the upstream velocity, the incidence angle and a large number of tip clearances. The influence of the flow conditions on the structure of the TLV is described through changes in the vortex intensity, core axial flow, vortex center position and wandering motion amplitude. Moreover, high-speed visualizations are used to highlight the vortex core trajectory and clearance flow alteration, turning into a wall jet as the tip clearance is reduced. The measurements clearly reveal the existence of a specific tip clearance for which the vortex strength is maximum and most prone to generating cavitation.
PubDate: 2014-11-05

• Tomographic PIV investigation of roughness-induced transition in a
hypersonic boundary layer
• Abstract: Abstract The disturbance generated by roughness elements in a hypersonic laminar boundary layer is investigated, with attention to its three-dimensional properties. The transition of the boundary layer is inspected with tomographic particle image velocimetry that is applied for the first time at Mach 7.5 inside a short duration hypersonic wind tunnel. A low aspect ratio cylindrical roughness element is installed on a flat plate, and experiments are conducted downstream of the element describing the mean velocity field and the turbulent fluctuations. Details of the experimental procedure needed to realize these measurements are discussed, along with the fluid dynamic behaviour of the perturbed hypersonic boundary layer.
PubDate: 2014-11-05

• Irregular particle sizing using speckle pattern for continuous wave laser
applications
• Abstract: Abstract A technique to retrieve the size of irregular particles using the speckle pattern produced from the scattering of laser light is presented. A sizing algorithm based on the maximum curvature peak detection of the Fourier transform of the speckle pattern is introduced, and its application to sand particles with and without motion is studied, using a continuous wave laser. The sizes obtained with this algorithm are in good agreement with the sizes resulting from shadowgraph measurements. It was also observed that the properties of the speckle pattern are independent on the scattering angle. When using a continuous wave laser, special attention is paid to the exposure time while recording the speckle pattern. This special care avoids the images to be blurred as a consequence of the speckle pattern displacement and reshaping due to particle rotation. Finally, further recommendations to define the setup parameters are given in order to apply the technique, focusing on a continuous wave application.
PubDate: 2014-11-05

• Cluster-based analysis of cycle-to-cycle variations: application to
internal combustion engines
• Abstract: Abstract We define and illustrate a cluster-based analysis of cycle-to-cycle variations (CCV). The methodology is applied to engine flow but can clearly be valuable for any periodically driven fluid flow at large Reynolds numbers. High-speed particle image velocimetry data acquired during the compression stroke for 161 consecutive engine cycles are used. Clustering is applied to the velocity fields normalised by their kinetic energy. From a phase-averaged analysis of the statistics of cluster content and inter-cluster transitions, we show that CCV can be associated with different sets of trajectories during the second half of the compression phase. Conditional statistics are computed for flow data of each cluster. In particular, we identify a particular subset associated with a loss of large-scale coherence, a very low kinetic energy of the mean flow and a higher fluctuating kinetic energy. This is interpreted as a good indicator of the breakdown of the large-scale coherent tumbling motion. For this particular subset, the cluster analysis confirms the idea of a gradual destabilisation of the in-cylinder flow during the final phase of the compression. Moreover, inter-cycle statistics show that the flow states near TDC and in the measurement zone are statistically independent for consecutive engine cycles. It is important to point out that this approach is generally applicable to very large sets of data, e.g. generated by PIV or LES, and independent of the considered type of information (velocity, concentration, etc.).
PubDate: 2014-11-04

• Determination of secondary flow morphologies by wavelet analysis in a
curved artery model with physiological inflow
• Abstract: Abstract Secondary flow vortical patterns in arterial curvatures have the potential to affect several cardiovascular phenomena, e.g., progression of atherosclerosis by altering wall shear stresses, carotid atheromatous disease, thoracic aortic aneurysms and Marfan’s syndrome. Temporal characteristics of secondary flow structures vis-à-vis physiological (pulsatile) inflow waveform were explored by continuous wavelet transform (CWT) analysis of phase-locked, two-component, two-dimensional particle image velocimeter data. Measurements were made in a 180° curved artery test section upstream of the curvature and at the 90° cross-sectional plane. Streamwise, upstream flow rate measurements were analyzed using a one-dimensional antisymmetric wavelet. Cross-stream measurements at the 90° location of the curved artery revealed interesting multi-scale, multi-strength coherent secondary flow structures. An automated process for coherent structure detection and vortical feature quantification was applied to large ensembles of PIV data. Metrics such as the number of secondary flow structures, their sizes and strengths were generated at every discrete time instance of the physiological inflow waveform. An autonomous data post-processing method incorporating two-dimensional CWT for coherent structure detection was implemented. Loss of coherence in secondary flow structures during the systolic deceleration phase is observed in accordance with previous research. The algorithmic approach presented herein further elucidated the sensitivity and dependence of morphological changes in secondary flow structures on quasiperiodicity and magnitude of temporal gradients in physiological inflow conditions.
PubDate: 2014-11-04

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