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Publisher: Springer-Verlag   (Total: 2210 journals)

 Dynamic Games and Applications       (Followers: 2) Dysphagia       (Followers: 200, 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: 8, 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: 191, 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: 7, SJR: 0.211, h-index: 8) Educational Studies in Mathematics       (Followers: 10, SJR: 0.946, h-index: 27) Educational Technology Research and Development       (Followers: 190, 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: 4, 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: 33, 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: 2, 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: 191, 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: 9, 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: 7, 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)
 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]
• Experimental analysis and semicontinuous simulation of low-temperature
droplet evaporation of multicomponent fuels
• Abstract: Abstract Low-pollutant and efficient combustion not only in internal combustion engines requires a balanced gaseous mixture of fuel and oxidizer. As fuels may contain several hundred different chemical species with different physicochemical properties as well as defined amounts of biogenic additives, e.g., ethanol, a thorough understanding of liquid fuel droplet evaporation processes is necessary to allow further engine optimization. We have studied the evaporation of fuel droplets at low ambient temperature. A non-uniform temperature distribution inside the droplet was already considered by including a finite thermal conductivity in a one-dimensional radial evaporation model (Rivard and Brüggemann in Chem Eng Sci 65(18):5137–5145, 2010). For a detailed analysis of droplet evaporation, two non-laser-based experimental setups have been developed. They allow a fast and relatively simple but yet precise measurement of diameter decrease and composition change. The first method is based on collecting droplets in a diameter range from 70 to 150 µm by a high-precision scale. A simultaneous evaluation of mass increase is employed for an accurate average diameter value determination. Subsequently, a gas chromatographic analysis of the collected droplets was conducted. In the second experiment, evaporation of even smaller droplets was optically analyzed by a high-speed shadowgraphy/schlieren microscope setup. A detailed analysis of evaporating E85 (ethanol/gasoline in a mass ratio of 85 %/15 %) and surrogate fuel droplets over a wide range of initial droplet diameters and ambient temperatures was conducted. The comparison of experimental and numerical results shows the applicability of the developed model over a large range of diameters and temperatures.
PubDate: 2014-12-09

• Three-dimensional reconstruction of helicopter blade–tip vortices
using a multi-camera BOS system
• Abstract: Abstract Noise and structural vibrations in rotorcraft are strongly influenced by interactions between blade–tip vortices and the structural components of a helicopter. As a result, knowing the three-dimensional location of vortices is highly desirable, especially for the case of full-scale helicopters under realistic flight conditions. In the current study, we present results from a flight test with a full-scale BO 105 in an open-pit mine. A background-oriented schlieren measurement system consisting of ten cameras with a natural background was used to visualize the vortices of the helicopter during maneuvering flight. Vortex filaments could be visualized and extracted up to a vortex age of 360°. Vortex instability effects were found for several flight conditions. For the camera calibration, an iterative approach using points on the helicopter fuselage was applied. Point correspondence between vortex curves in the evaluated images was established by means of epipolar geometry. A three-dimensional reconstruction of the main part of the vortex system was carried out for the first time using stereophotogrammetry. The reconstructed vortex system had good qualitative agreement with the result of an unsteady free-wake panel method simulation. A quantitative evaluation of the 3D vortex system was carried out, demonstrating the potential of the multi-camera background-oriented schlieren measurement technique for the analysis of blade–vortex interaction effects on rotorcraft.
PubDate: 2014-12-09

• Fast-response temperature-sensitive-paint measurements on a hypersonic
transition cone
• Abstract: Abstract Experiments are performed using a fast-response temperature-sensitive-paint (TSP) technique to measure the heat-flux distribution on a slender cone in a hypersonic shock tunnel under both laminar and transitional conditions. The millisecond-order test duration together with the self-luminosity of shock layers place stringent conditions on the choice of TSP luminophore and the TSP-layer thickness that can be employed. The luminosity and dimming from particulates in the free-stream cause additional problems in interpreting the obtained intensity profiles. Nevertheless, favorable agreement with thermocouple-based measurements show that it is possible to derive quantitatively accurate heat-flux distributions with the TSP technique for temperature rises of up to approximately 40 K above room temperature. The technique accuracy is adversely affected at higher temperatures, which is thought to result from non-constant thermal properties of the insulating base layer. At high unit Reynolds number conditions, time-resolved heat-flux distributions show large-scale unsteadiness in the boundary-layer transition location and reveal transient streamwise streaks developing in the transitional region.
PubDate: 2014-12-07

• Estimating the effective viscosity of bubble suspensions in oscillatory
shear flows by means of ultrasonic spinning rheometry
• Abstract: Abstract We have proposed a novel methodology using ultrasonic velocity profiling to estimate the effective viscosity of bubble suspensions that are accompanied by non-equilibrium bubble deformations in periodic shear flows. The methodology was termed “ultrasonic spinning rheometry” and validated on measurement of the effective viscosity of particle suspensions that has a semi-empirical formula giving good estimation of the actual viscosity. The results indicated that the proposed technique is valid for particle volume fractions below 3.0 %. Applying this to bubble suspensions suggested that the effective value of temporal variations in the capillary number, $$\hbox{Ca}_{\rm rms}$$ , is an important indicator to distinguish regimes in estimating the effective viscosity: Unsteady flows having larger $$\hbox{Ca}_{\rm rms}$$ number than the critical capillary number for the deformation of bubbles are categorized into Regime 2 that includes both highly unsteady conditions and large steady deformation of bubbles.
PubDate: 2014-12-05

• Quantitative exploitation of PFG NMR and MRI velocimetry data for the
rheological study of yield stress fluid flows at macro- and micro-scales
in complex geometries
• Abstract: Abstract We explore the use of magnetic resonance imaging (MRI) velocimetry and pulsed field gradient nuclear magnetic resonance (PFG NMR) data for studying the flow characteristics of yield stress fluids through model pores (a succession of ducts of different diameters) or real porous media (bead packings). We propose different methods for the quantitative analysis of the velocity field, aimed at getting a deep understanding of the different flow regimes (solid and liquid) which typically take place in such fluids and at seeing how the transition from one to the other occurs in space or in time. Our approach exemplifies interdependences between PFG NMR data and local flow features and how the statistical velocity distribution function obtained by this way can be used and/or processed for extracting quantitative information concerning critical flow characteristics at a local scale. This provides a solid framework of analysis of flows through porous media with pores much smaller than the resolution of MR velocimetry.
PubDate: 2014-12-05

• Control of vortex on a non-slender delta wing by a nanosecond pulse
surface dielectric barrier discharge
• Abstract: Abstract Wind tunnel experiments are conducted for improving the aerodynamic performance of delta wing using a leading-edge pulsed nanosecond dielectric barrier discharge (NS-DBD). The whole effects of pulsed NS-DBD on the aerodynamic performance of the delta wing are studied by balanced force measurements. Pressure measurements and particle image velocimetry (PIV) measurements are conducted to investigate the formation of leading-edge vortices affected by the pulsed NS-DBD, compared to completely stalled flow without actuation. Various pulsed actuation frequencies of the plasma actuator are examined with the freestream velocity up to 50 m/s. Stall has been delayed substantially and significant shifts in the aerodynamic forces can be achieved at the post-stall regions when the actuator works at the optimum reduced frequency of F + = 2. The upper surface pressure measurements show that the largest change of static pressure occurs at the forward part of the wing at the stall region. The time-averaged flow pattern obtained from the PIV measurement shows that flow reattachment is promoted with excitation, and a vortex flow pattern develops. The time-averaged locations of the secondary separation line and the center of the vortical region both move outboard with excitation.
PubDate: 2014-12-05

• 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

• 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

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