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Publisher: Springer-Verlag   (Total: 2335 journals)

 Showing 1201 - 1400 of 2335 Journals sorted alphabetically J. of Communications Technology and Electronics       (Followers: 1, SJR: 0.267, h-index: 14) J. of Community Genetics       (Followers: 1, SJR: 0.699, h-index: 8) J. of Community Health       (Followers: 8, SJR: 0.676, h-index: 39) J. of Comparative Physiology A: Neuroethology, Sensory, Neural, and Behavioral Physiology       (Followers: 7, SJR: 0.98, h-index: 63) J. of Comparative Physiology B : Biochemical, Systemic, and Environmental Physiology       (Followers: 3, SJR: 0.981, h-index: 50) J. of Compassionate Health Care       (Followers: 1) J. of Computational Analysis and Applications       (SJR: 0.284, h-index: 16) J. of Computational Electronics       (Followers: 3, SJR: 0.457, h-index: 17) J. of Computational Neuroscience       (Followers: 19, SJR: 1.419, h-index: 54) J. of Computer and Systems Sciences Intl.       (SJR: 0.252, h-index: 11) J. of Computer Science and Technology       (Followers: 4, SJR: 0.342, h-index: 26) J. of Computer Virology and Hacking Techniques       (Followers: 5) J. of Computer-Aided Molecular Design       (Followers: 4, SJR: 0.951, h-index: 70) J. of Computers in Education       (Followers: 5) J. of Computing in Higher Education       (Followers: 12, SJR: 0.725, h-index: 16) J. of Consumer Policy       (Followers: 3, SJR: 0.44, h-index: 23) J. of Contemporary Mathematical Analysis       (SJR: 0.115, h-index: 4) J. of Contemporary Physics (Armenian Academy of Sciences)       (Followers: 1, SJR: 0.174, h-index: 4) J. of Contemporary Psychotherapy       (Followers: 3, SJR: 0.441, h-index: 16) J. of Control Theory and Applications       (Followers: 2, SJR: 0.406, h-index: 13) J. of Control, Automation and Electrical Systems       (Followers: 6, SJR: 0.168, h-index: 8) J. of Crop Science and Biotechnology       (Followers: 7) J. of Cross-Cultural Gerontology       (Followers: 3, SJR: 0.412, h-index: 23) J. of Cryptographic Engineering       (Followers: 5, SJR: 0.757, h-index: 6) J. of Cryptology       (Followers: 2, SJR: 1.598, h-index: 49) J. of Cultural Economics       (Followers: 2, SJR: 0.445, h-index: 24) J. of Database Marketing & Customer Strategy Management       (Followers: 8, SJR: 0.183, h-index: 5) J. of Derivatives & Hedge Funds       (Followers: 8, SJR: 0.207, h-index: 3) J. of Developmental and Physical Disabilities       (Followers: 8, SJR: 0.615, h-index: 23) J. of Digital Imaging       (Followers: 8, SJR: 0.535, h-index: 29) J. of Direct Data and Digital Marketing Practice       (Followers: 6, SJR: 0.296, h-index: 3) J. of Dynamical and Control Systems       (Followers: 2, SJR: 0.556, h-index: 22) J. of Dynamics and Differential Equations       (SJR: 1.33, h-index: 29) J. of Earth Science       (Followers: 6, SJR: 0.299, h-index: 11) J. of Earth System Science       (Followers: 27, SJR: 0.466, h-index: 27) J. of East Asian Linguistics       (Followers: 5, SJR: 0.669, h-index: 15) J. of Echocardiography       (Followers: 3, SJR: 0.136, h-index: 3) J. of Economic Growth       (Followers: 25, SJR: 5.251, h-index: 54) J. of Economic Interaction and Coordination       (SJR: 0.231, h-index: 11) J. of Economics       (Followers: 9, SJR: 0.463, h-index: 20) J. of Economics and Finance       (Followers: 7, SJR: 0.238, h-index: 15) J. of Educational Change       (Followers: 7, SJR: 0.694, h-index: 14) J. of Elasticity       (Followers: 4, SJR: 0.821, h-index: 38) J. of Electroceramics       (SJR: 0.566, h-index: 49) J. of Electronic Materials       (Followers: 2, SJR: 0.752, h-index: 68) J. of Electronic Testing       (Followers: 2, SJR: 0.241, h-index: 24) J. of Electronics (China)       (Followers: 3, SJR: 0.127, h-index: 7) J. of Elementary Science Education       (Followers: 8) J. of Engineering Mathematics       (SJR: 0.707, h-index: 32) J. of Engineering Physics and Thermophysics       (Followers: 1, SJR: 0.132, h-index: 8) J. of Engineering Research J. of Engineering Thermophysics       (Followers: 1, SJR: 0.294, h-index: 7) J. of Environmental Studies and Sciences       (Followers: 2) J. of Ethology       (Followers: 2, SJR: 0.484, h-index: 21) J. of Evolution Equations       (SJR: 1.312, h-index: 22) J. of Evolutionary Biochemistry and Physiology       (SJR: 0.127, h-index: 9) J. of Evolutionary Economics       (Followers: 8, SJR: 0.878, h-index: 42) J. of Experimental and Theoretical Physics       (Followers: 2, SJR: 0.565, h-index: 34) J. of Experimental Criminology       (Followers: 26, SJR: 1.587, h-index: 22) J. of Failure Analysis and Prevention       (Followers: 5, SJR: 0.256, h-index: 12) J. of Family and Economic Issues       (Followers: 6, SJR: 0.532, h-index: 27) J. of Family Violence       (Followers: 15, SJR: 0.552, h-index: 45) J. of Financial Services Marketing       (Followers: 3, SJR: 0.241, h-index: 6) J. of Financial Services Research       (Followers: 16, SJR: 1.196, h-index: 29) J. of Fixed Point Theory and Applications       (SJR: 0.467, h-index: 10) J. of Fluorescence       (Followers: 4, SJR: 0.553, h-index: 47) J. of Food Measurement and Characterization       (SJR: 0.104, h-index: 1) J. of Food Science and Technology       (Followers: 5, SJR: 0.839, h-index: 21) J. of Forest Research       (Followers: 3, SJR: 0.578, h-index: 22) J. of Forestry Research       (Followers: 6, SJR: 0.271, h-index: 10) J. of Fourier Analysis and Applications       (Followers: 1, SJR: 1.248, h-index: 36) J. of Friction and Wear       (Followers: 6, SJR: 0.263, h-index: 6) J. of Fusion Energy       (Followers: 3, SJR: 0.389, h-index: 16) J. of Gambling Studies       (Followers: 3, SJR: 1.122, h-index: 50) J. of Gastroenterology       (Followers: 13, SJR: 1.724, h-index: 73) J. of Gastrointestinal Cancer       (Followers: 3, SJR: 0.371, h-index: 36) J. of Gastrointestinal Surgery       (Followers: 5, SJR: 1.632, h-index: 87) J. of General Internal Medicine       (Followers: 13, SJR: 2.379, h-index: 115) J. of General Plant Pathology       (SJR: 0.357, h-index: 17) J. of Genetic Counseling       (Followers: 4, SJR: 0.535, h-index: 32) J. of Genetics       (Followers: 4, SJR: 0.42, h-index: 24) J. of Geodesy       (Followers: 8, SJR: 4.049, h-index: 48) J. of Geographical Sciences       (Followers: 1, SJR: 0.58, h-index: 14) J. of Geographical Systems       (Followers: 2, SJR: 0.839, h-index: 32) J. of Geometric Analysis       (SJR: 1.496, h-index: 23) J. of Geometry       (Followers: 1, SJR: 0.349, h-index: 13) J. of Global Optimization       (Followers: 3, SJR: 0.919, h-index: 51) J. of Global Policy and Governance       (Followers: 8) J. of Grid Computing       (SJR: 0.727, h-index: 32) J. of Hand and Microsurgery       (Followers: 1) J. of Happiness Studies       (Followers: 14, SJR: 0.785, h-index: 30) J. of Hematopathology       (Followers: 3, SJR: 0.194, h-index: 11) J. of Heuristics       (Followers: 5, SJR: 1.718, h-index: 43) J. of High Energy Physics       (Followers: 4, SJR: 1.027, h-index: 139) J. of Homotopy and Related Structures       (SJR: 0.102, h-index: 1) J. of Housing and the Built Environment       (Followers: 6, SJR: 0.553, h-index: 21) J. of Huazhong University of Science and Technology [Medical Sciences]       (SJR: 0.317, h-index: 15) J. of Ichthyology       (Followers: 4, SJR: 0.28, h-index: 7) J. of Immigrant and Minority Health       (Followers: 8, SJR: 0.573, h-index: 29) J. of Inclusion Phenomena and Macrocyclic Chemistry       (Followers: 1, SJR: 0.459, h-index: 41) J. of Indian Philosophy       (Followers: 10, SJR: 0.179, h-index: 7) J. of Indian Prosthodontic Society       (SJR: 0.165, h-index: 5) J. of Industrial Microbiology and Biotechnology       (Followers: 10, SJR: 1.064, h-index: 68) J. of Industry, Competition and Trade       (Followers: 7, SJR: 0.411, h-index: 11) J. of Infection and Chemotherapy       (Followers: 1, SJR: 0.65, h-index: 39) J. of Information Technology       (Followers: 45, SJR: 1.659, h-index: 43) J. of Information Technology Teaching Cases       (Followers: 5) J. of Infrared, Millimeter and Terahertz Waves       (Followers: 1, SJR: 0.902, h-index: 31) J. of Inherited Metabolic Disease       (Followers: 2, SJR: 1.182, h-index: 66) J. of Inorganic and Organometallic Polymers and Materials       (Followers: 6, SJR: 0.316, h-index: 27) J. of Insect Behavior       (Followers: 8, SJR: 0.537, h-index: 36) J. of Insect Conservation       (Followers: 9, SJR: 0.775, h-index: 36) J. of Intelligent and Robotic Systems       (Followers: 2, SJR: 0.501, h-index: 36) J. of Intelligent Information Systems       (Followers: 1, SJR: 0.427, h-index: 39) J. of Intelligent Manufacturing       (Followers: 4, SJR: 1.095, h-index: 44) J. of Interventional Cardiac Electrophysiology       (SJR: 1.073, h-index: 38) J. of Intl. Business Studies       (Followers: 25, SJR: 4.835, h-index: 108) J. of Intl. Entrepreneurship       (Followers: 8, SJR: 0.489, h-index: 16) J. of Intl. Migration and Integration / Revue de l integration et de la migration internationale       (Followers: 12, SJR: 0.385, h-index: 9) J. of Intl. 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1.042, h-index: 14) J. of Maxillofacial and Oral Surgery       (Followers: 2) J. of Mechanical Science and Technology       (Followers: 4, SJR: 0.589, h-index: 20) J. of Medical and Biological Engineering       (SJR: 0.434, h-index: 13) J. of Medical Humanities       (Followers: 18, SJR: 0.251, h-index: 13) J. of Medical Systems       (Followers: 2, SJR: 0.604, h-index: 32) J. of Medical Toxicology       (Followers: 6, SJR: 0.765, h-index: 21) J. of Medical Ultrasonics       (Followers: 2, SJR: 0.209, h-index: 11) J. of Medicine and the Person J. of Membrane Biology       (Followers: 1, SJR: 0.971, h-index: 75) J. of Micro-Bio Robotics J. of Microbiology       (Followers: 7, SJR: 0.641, h-index: 35) J. of Mining Science       (Followers: 5, SJR: 0.296, h-index: 11) J. of Molecular Evolution       (Followers: 11, SJR: 1.07, h-index: 99) J. of Molecular Histology       (Followers: 2, SJR: 0.791, h-index: 43) J. of Molecular Medicine       (Followers: 15, SJR: 2.452, h-index: 100) J. of 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21) J. of Orofacial Orthopedics / Fortschritte der Kieferorthopädie       (SJR: 0.667, h-index: 27) J. of Orthopaedic Science       (Followers: 5, SJR: 0.684, h-index: 42) J. of Paleolimnology       (Followers: 5, SJR: 1.284, h-index: 58) J. of Parasitic Diseases       (Followers: 2, SJR: 0.272, h-index: 5) J. of Pediatric Neuropsychology J. of Pest Science       (Followers: 2, SJR: 1.002, h-index: 21) J. of Pharmaceutical Health Care and Sciences J. of Pharmaceutical Innovation       (Followers: 8, SJR: 0.617, h-index: 14) J. of Pharmaceutical Investigation       (Followers: 1, SJR: 0.16, h-index: 2) J. of Pharmacokinetics and Pharmacodynamics       (Followers: 22, SJR: 0.567, h-index: 41) J. of Phase Equilibria and Diffusion       (Followers: 19, SJR: 0.367, h-index: 31)
 Experiments in Fluids   [SJR: 1.596]   [H-I: 69]   [7 followers]  Follow         Hybrid journal (It can contain Open Access articles)    ISSN (Print) 1432-1114 - ISSN (Online) 0723-4864    Published by Springer-Verlag  [2335 journals]
• Retraction Note to: A robust vector field correction method via a mixture
statistical model of PIV signal
• PubDate: 2016-06-23

• 3D conformation of a flexible fiber in a turbulent flow
• Abstract: Abstract A growing number of studies is devoted to anisotropic particles in turbulent flows. In most cases, the particles are assumed to be rigid and their deformations are neglected. We present an adaptation of classical computer vision tools to reconstruct from two different images the 3D conformation of a fiber distorted by the turbulent fluctuations in a von Kármán flow. This technique allows us notably to characterize the fiber deformation by computing the correlation function of the orientation of the tangent vector. This function allows us to tackle the analogy between polymers and flexible fibers proposed by Brouzet et al. (Phys Rev Lett 112(7):074501, 2014). We show that this function depends on an elastic length $$\ell _\mathrm{e}$$ which characterizes the particle flexibility, as is the case for polymers, but also on the fiber length L, contrary to polymers.
PubDate: 2016-06-23

• Temperature field measurements in liquids using ZnO thermographic phosphor
tracer particles
• Abstract: Abstract Temperature field measurements in liquids are demonstrated using zinc oxide (ZnO) thermographic phosphor particles. The particles are added to the liquid as a tracer. Following laser excitation, the temperature-dependent luminescence emission of the particles is imaged and the temperature is determined using a two-colour intensity ratio method. The particle size requirements for accurate temperature tracing in turbulent flows are calculated using a numerical heat transfer model. Particle–water mixtures were prepared using ultrasonic dispersion and characterised using scanning electron microscope imaging and laser diffraction particle-sizing, indicating that the particle size is 1–2  $$\upmu$$ m. The particle luminescence properties were characterised using spectroscopic and particle luminescence imaging techniques. Using 355 nm laser excitation, the luminescence signal is the same in water and in air. However, 266 nm excitation is used to avoid spectral overlap between Raman scattering from water and the detected ZnO luminescence emission. It is shown that 266 nm excitation can be used for temperature measurements in water using mass loads as low as 1–5 mg L $$^{-1}$$ , corresponding to measured particle number densities 0.5–2.5  $$\times \,10^{12}$$ particles  $$\hbox {m}^{-3}$$ . In this range, the measured intensity ratio is independent of the mass load. The dependence of the intensity ratio on the laser fluence is less pronounced using excitation at 266 nm compared to 355 nm. A single-shot, single-pixel temperature precision of ±2–3  $$^{\circ }\hbox {C}\,(1\sigma )$$ can be achieved over a temperature range spanning $$50\,^{\circ }\hbox {C}$$ . The technique was applied to a convection experiment to measure the temperature fields in a buoyant thermal plume, demonstrating the suitability of these imaging diagnostics for the investigation of thermal convection and heat transfer.
PubDate: 2016-06-22

• Comparison of a separated flow response to localized and global-type
disturbances
• Abstract: Abstract The flow structure and lift response of a separated flow over an airfoil that is subjected to an impulsive type of pitching motion are compared to the response produced by a localized pulse disturbance at the leading edge of an airfoil. Time-resolved PIV data are used to obtain the velocity field on the suction side of the airfoil. POD analysis shows that the majority of energy is contained within the first four modes. Strong similarities in the shapes of the POD basis functions are found, especially for the second mode, irrespective of the type of actuation (global or local). The time-varying coefficient of this second POD mode tracks the negative of the lift coefficient or circulation in each case. Basis functions from the localized actuation data were projected on the velocity field of the globally actuated flow to obtain a hybrid set of coefficients. The hybrid coefficients matched reasonably well with the coefficients obtained from the original POD analysis for the globally excited flow. Both types of actuation were found to generate very similar Lagrangian flow structures. The results suggest a certain degree of universality in the POD modes/flow structures for the separated flow over an airfoil, irrespective of the type of excitation.
PubDate: 2016-06-21

• Experimental research on thermocapillary migration of drops by using
digital holographic interferometry
• Abstract: Abstract The thermocapillary migration of drops in a rectangular cell, with a heated top wall and a cooled bottom wall, was investigated experimentally on the ground. The rectangular test cell was 70 mm high, with a horizontal cross section of 40 mm × 40 mm. In the present experiment, 30 cSt silicon oil was used as the continuous phase, and a water–ethanol mixture was used as the drop phase, respectively. The drops ranged in size from 1.87 to 6.94 mm in diameter and were injected into the continuous phase, where the temperature gradients ranged from 0.193 to 0.484 °C mm−1. In order to measure the temperature distribution of the liquid, a digital holographic interferometry was used, which was non-contact, full-field, and in-situ. The holograms were recorded, and then the corresponding wrapped phase distributions images were numerically reconstructed. The temperature distribution of the continuous phase liquid in the cell had been obtained following the unwrapping. Also, through an algebra layer analysis, the temperature distribution around the drop during the thermocapillary migration was obtained. As a result, the drop was colder than the continuous phase liquid, and a thermal wake existed behind the drop. The influence of convective transport on the drop migration was also investigated for the Marangoni number in the range of 7–174. With the increasing of the Marangoni number, the dimensionless interface temperature difference decreased, which was caused by the convective transport enhanced results in the drop thermocapillary migration velocity becoming decreased. The data were compared with previous space experiments to explain the phenomena of the drop migration. Finally, with the increasing Marangoni numbers, the length of the thermal wake region increased, and the thermal wake region became extended.
PubDate: 2016-06-20

• Characterization of zebrafish larvae suction feeding flow using μPIV
and optical coherence tomography
• Abstract: Abstract The hydrodynamics of suction feeding is critical for the survival of fish larvae; failure to capture food during the onset of autonomous feeding can rapidly lead to starvation and mortality. Fluid mechanics experiments that investigate the suction feeding of suspended particles are limited to adult fishes, which operate at large Reynolds numbers. This manuscript presents the first literature results in which the external velocity fields generated during suction feeding of early zebrafish larvae (2500–20,000 μm total length) are reported using time-resolved microscopic particle image velocimetry. For the larval stages studied, the maximum peak suction velocity of the inflow bolus is measured at a finite distance from the mouth tip and ranges from 1 to 8 mm/s. The average pressure gradient and the velocity profile proximal to the buccal (mouth) cavity are calculated, and two distinct trends are identified. External recirculation regions and reverse flow feeding cycles are also observed and quantified. One of the unresolved questions in fish suction feeding is the shape and dynamics of the buccal cavity during suction feeding; optical coherence tomography imaging is found to be useful for reconstructing the mouth kinematics. The projected area of the mouth cavity during the feeding cycle varies up to 160 and 22 % for the transverse and mid-sagittal planes, respectively. These findings can inspire novel hydrodynamically efficient biomedical and microfluidic devices.
PubDate: 2016-06-16

• Towards local isotropy of higher-order statistics in the intermediate wake
• Abstract: Abstract In this paper, we assess the local isotropy of higher-order statistics in the intermediate wake region. We focus on normalized odd moments of the transverse velocity derivatives, $${M_{2n + 1}}(\partial u/\partial z) = {{\overline{{{(\partial u/\partial z)}^{2n + 1}}} }}/{{{{\overline{{{(\partial u/\partial z)}^2}} }^{(2n + 1)/2}}}}$$ and $${N_{2n + 1}}(\partial u/\partial y) = {{\overline{{{(\partial u/\partial y)}^{2n + 1}}} }}/{{{{\overline{{{(\partial u/\partial y)}^2}} }^{(2n + 1)/2}}}}$$ , which should be zero if local isotropy is satisfied (n is a positive integer). It is found that the relation $$M_{2n+1}(\partial u/\partial z) \sim R_\lambda ^{-1}$$ is supported reasonably well by hot-wire data up to the seventh order ( $$n=3$$ ) on the wake centreline, although it is also dependent on the initial conditions. The present relation $$N_{3}(\partial u/\partial y) \sim R_\lambda ^{-1}$$ is obtained more rigorously than that proposed by Lumley (Phys Fluids 10:855–858, 1967) via dimensional arguments. The effect of the mean shear at locations away from the wake centreline on $$M_{2n+1}(\partial u/\partial z)$$ and $$N_{2n+1}(\partial u/\partial y)$$ is addressed and reveals that, although the non-dimensional shear parameter is much smaller in wakes than in a homogeneous shear flow, it has a significant effect on the evolution of $$N_{2n+1}(\partial u/\partial y)$$ in the direction of the mean shear; its effect on $$M_{2n+1}(\partial u/\partial z)$$ (in the non-shear direction) is negligible.
PubDate: 2016-06-14

• A biomimetic bi-leaflet mitral prosthesis with enhanced physiological left
ventricular swirl restorative capability
• Abstract: Abstract Mechanical heart valve prostheses are often implanted in young patients due to their durability and long-term reliability. However, existing designs are known to induce elevated levels of blood damage and blood platelet activation. As a result, there is a need for patients to undergo chronic anti-coagulation treatment to prevent thrombosis, often resulting in bleeding complications. Furthermore, recent studies have suggested that the implantation of a mechanical prosthetic valve at the mitral position results in a significant alteration of the left ventricular flow field which may contribute to flow turbulence. This study proposes a bi-leaflet mechanical heart valve design (Bio-MHV) that mimics the geometry of a human mitral valve, with the aim of reducing turbulence levels in the left ventricle by replicating physiological flow patterns. An in vitro three-dimensional particle velocimetry imaging experiment was carried out to compare the hemodynamic performance of the Bio-MHV with that of the clinically established ATS valve. The Bio-MHV was found to replicate physiological left ventricular flow patterns and produced lower turbulence levels.
PubDate: 2016-06-13

• Some observations on vortex-ring collisions upon inclined surfaces
• Abstract: Abstract This paper reports upon a laser-induced fluorescence visualization and time-resolved particle image velocimetry study to resolve the detailed dynamics associated with Re = 2000 and 4000 circular vortex rings colliding with 30°–75° inclined surfaces. Two-dimensional visualization results show that larger inclination angles lead to increasingly rapid size reduction in the primary vortex-ring core closer to the surface, faster formation of the secondary vortex-ring core, and subsequent ingestion by the former. In contrast, primary vortex-ring core further away from the surface becomes physically larger and incoherent more rapidly, with slower formation and entrainment of the secondary vortex-ring core. Interestingly, a vortex dipole and small vortex-ring-like structure are produced for the largest inclination angle of 75°, possibly due to vortex disconnection and reconnection processes. Results taken along the non-inclined plane show significant bulging of the primary vortex-ring cores when the inclination angle increases from 30° onwards. More importantly, additional vortex cores are observed to entwine with the primary vortex-ring core and provide strong direct evidence for the bi-helical vortex line flow mechanism put forward by Lim (Exp Fluids 7:453–463, 1989). Lastly, the behaviour of the primary and secondary vortex-ring cores further away from the surface is highly sensitive towards the state of the bi-helical lines compressed at that region. Strong compression driven by circumferential flows due to large inclination angles may explain the unique flow structures and behaviour observed for 75° inclination angle here.
PubDate: 2016-06-13

• Flow visualization by mobile phone cameras
• Abstract: Abstract Mobile smart phones were completely changing people’s communication within the last ten years. However, these devices do not only offer communication through different channels but also devices and applications for fun and recreation. In this respect, mobile phone cameras include now relatively fast (up to 240 Hz) cameras to capture high-speed videos of sport events or other fast processes. The article therefore explores the possibility to make use of this development and the wide spread availability of these cameras in the terms of velocity measurements for industrial or technical applications and fluid dynamics education in high schools and at universities. The requirements for a simplistic PIV (particle image velocimetry) system are discussed. A model experiment of a free water jet was used to prove the concept and shed some light on the achievable quality and determine bottle necks by comparing the results obtained with a mobile phone camera with data taken by a high-speed camera suited for scientific experiments.
PubDate: 2016-06-09

• Closed-loop enhancement of jet mixing with extremum-seeking and
physics-based strategies
• Abstract: Abstract The closed-loop control of a turbulent round air jet is experimentally investigated based on two unsteady minijets, with a view to enhancing jet mixing. The two minijets are placed at diametrically opposite locations upstream of the nozzle exit. The open-loop control experiments are first performed. Given the mass flow rate ratio C m of the minijets to that of the main jet, the decay rate $$\overline{K}$$ of jet centerline mean velocity exhibits a maximum at the frequency ratio f e/f 0 ≈ 1.0, where f e and f 0 are the excitation frequency of minijets and the preferred mode frequency of the natural main jet, respectively. An extremum-seeking feedback control has been developed to achieve autonomously the optimal control performance. It has been found that, given C m, this closed-loop control technique may obtain automatically and rapidly the optimal value of f e and the desired or maximum $$\overline{K}$$ , as achieved in the open-loop control. This control technique is robust and adaptable when the Reynolds number and initial excitation frequency are changed separately. A flow-physics-based feedback control strategy has also been investigated, which could achieve the optimal control performance automatically with a shorter convergence time than the extremum-seeking control, not robust though.
PubDate: 2016-06-08

• On a PLIF quantification methodology in a nonlinear dye response regime
• Abstract: Abstract A new technique of planar laser-induced fluorescence calibration is presented in this work. It accounts for a nonlinear dye response at high concentrations, an illumination light attenuation and a secondary fluorescence’s influence in particular. An analytical approximation of a generic solution of the Beer–Lambert law is provided and utilized for effective concentration evaluation. These features make the technique particularly well suited for high concentration measurements, or those with a large range of concentration values, c, present (i.e. a high dynamic range of c). The method is applied to data gathered in a water flume experiment where a stream of a fluorescent dye (rhodamine 6G) was released into a grid-generated turbulent flow. Based on these results, it is shown that the illumination attenuation and the secondary fluorescence introduce a significant error into the data quantification (up to 15 and 80 %, respectively, for the case considered in this work) unless properly accounted for.
PubDate: 2016-06-03

• High-speed OH-PLIF imaging of deflagration-to-detonation transition in H 2
–air mixtures
• Abstract: Abstract Planar laser-induced fluorescence (PLIF) is considered a standard experimental technique in combustion diagnostics. However, it has only been occasionally applied to explosion experiments with fast combustion regimes. It has been shown that single-shot OH-PLIF with high pulse energies yields clear fluorescence images of fast deflagrations and also detonations. This paper presents the first application of high-speed OH-PLIF at 20 kHz repetition rate to a deflagration-to-detonation transition experiment. Hydrogen–air mixtures at initial atmospheric pressure and ambient temperature are investigated. Satisfactory results are obtained for flame speeds up to about 500 m/s. Flame instabilities and turbulence–flame interactions are observed. Two factors limit the applicability of HS OH-PLIF toward higher flame speeds: excessive flame luminescence masking the HS OH-PLIF signal and strong absorption of laser light by the flame. The variation in OH-PLIF signal-to-background ratio across a DDT process is studied using a 1D laminar premixed flame simulation extended by spectroscopic models.
PubDate: 2016-06-02

• An irrotation correction on pressure gradient and orthogonal-path
integration for PIV-based pressure reconstruction
• Abstract: Abstract Particle image velocimetry (PIV)-based pressure reconstruction has become a popular technique in experimental fluid mechanics. Noise or errors in raw velocity field would significantly affect the quality of pressure reconstruction in PIV measurement. To reduce experimental errors in pressure gradient and improve the precision of reconstructed pressure field, a minimal 2-norm criteria-based new technique called irrotation correction (IC) with orthogonal decomposition is developed. The pressure reconstruction is therefore composed of three steps: calculation of pressure gradient from time-resolved velocity fields of PIV, an irrotation correction on the pressure gradient field, and finally a simple orthogonal-path integration (OPI) for pressure. Systematic assessments of IC algorithm are performed on synthetic solid-body rotation flow, direct numerical simulations of a channel flow and an isotropic turbulent flow. The results show that IC is a robust algorithm which can significantly improve the accuracy of pressure reconstruction primarily in the low wave number domain. After irrotation correction, noisy pressure gradient field ideally becomes an irrotational field on which the pressure integration is independent of integrating paths. Therefore, an OPI algorithm is proposed to perform the pressure integration in an efficient way with very few integration paths. This makes the new technique to be a doable method on three-dimensional pressure reconstruction with acceptable computational cost.
PubDate: 2016-06-01

• Pressure-field extraction from Lagrangian flow measurements: first
experiences with 4D-PTV data
• Abstract: Abstract As a follow-up to a previous proof-of-principle study, a novel Lagrangian pressure-extraction technique is analytically evaluated, and experimentally validated using dense 4D-PTV data. The technique is analytically evaluated using the semi-three-dimensional Taylor–Green vortex, and it is found that the Lagrangian technique out-performs the standard Eulerian technique when Dirichlet boundary conditions are enforced. However, the Lagrangian technique produces worse estimates of the pressure field when Neumann boundary conditions are enforced on boundaries with strong pressure gradients. The technique is experimentally validated using flow data obtained for the case of a free-falling, index-matched sphere at $$Re=2100$$ . The experimental data were collected using a four-camera particle tracking velocimetry measurement system, and processed using 4D-PTV. The pressure field is then extracted using both the Eulerian and Lagrangian techniques, and the resulting pressure fields are compared. Qualitatively, the pressure fields agree; however, quantitative differences are found with respect to the magnitude of the pressure minima on the side of the sphere. Finally, the pressure-drag coefficient is estimated using each technique, and the two techniques are found to be in very close agreement. A comparison to a reference value from literature confirms that the drag coefficient estimates are reasonable, demonstrating the validity of the technique.
PubDate: 2016-06-01

• A digital holography set-up for 3D vortex flow dynamics
• Abstract: Abstract In the present paper, a digital in-line holography (DIH) set-up, with a converging beam, is used to take three-dimensional (3D) velocity measurements of vortices. The vortices are formed periodically at the edges of a submerged horizontal plate submitted to regular waves. They take the form of vortex filaments that extend from side to side of the channel. They undergo strongly three-dimensional instability mechanisms that remain very complicated to characterize experimentally. The experiments are performed in a 10 × 0.3 × 0.3 m3 wave flume. The DIH set-up is performed using a modulated laser diode emitting at the wavelength of 640 nm and a lensless CCD camera. The beam crosses the channel side to side. To reveal the flow dynamics, 30-μm hydrogen bubbles are generated at the edge of the plate to serve as tracers. Their locations are recorded on the holograms multiple times to access the dynamics of the flow. This method leads to an accuracy in the order of 100 μm on the axial location. Those measurements have been validated with stereo-PIV measurements. A very good agreement is found on time-averaged velocity fields between the two techniques.
PubDate: 2016-06-01

• Time-resolved and time-averaged stereo-PIV measurements of a unit-ratio
cavity
• Abstract: Abstract An experimental setup was developed to perform wind tunnel measurements on a unit-ratio, 2D open cavity under perpendicular incident flow. The open cavity is characterized by a mixing layer at the cavity top, that divides the flow field into a boundary layer flow and a cavity flow. Instead of precisely replicating a specific type of inflow, such as a turbulent flat plate boundary layer or an atmospheric boundary layer, the setup is capable of simulating a wide range of inflow profiles. This is achieved by using triangular spires as upstream turbulence generators, which can modify the otherwise laminar inflow boundary layer to be moderately turbulent and stationary, or heavily turbulent and intermittent. Measurements were performed by means of time-resolved stereo PIV. The cavity shear layer is analyzed in detail using flow statistics, spectral analysis, and space–time plots. The ability of the setup to generate typical cavity flow cases is demonstrated for characteristic inflow boundary layers, laminar and turbulent. Each case is associated with a distinct shear layer flow phenomena, self-sustained oscillations for the former and Kelvin–Helmholtz instabilities for the latter. Additionally, large spires generate a highly turbulent wake flow, resulting in a significantly different cavity flow. Large turbulent sweep and ejection events in the wake flow suppress the typical shear layer and sporadic near wall sweep events generate coherent vortices at the upstream edge.
PubDate: 2016-05-31

• Evolution of vortical structures in a curved artery model with
non-Newtonian blood-analog fluid under pulsatile inflow conditions
• Abstract: Abstract Steady flow and physiological pulsatile flow in a rigid 180° curved tube are investigated using particle image velocimetry. A non-Newtonian blood-analog fluid is used, and in-plane primary and secondary velocity fields are measured. A vortex detection scheme (d 2-method) is applied to distinguish vortical structures. In the pulsatile flow case, four different vortex types are observed in secondary flow: deformed-Dean, Dean, Wall and Lyne vortices. Investigation of secondary flow in multiple cross sections suggests the existence of vortex tubes. These structures split and merge over time during the deceleration phase and in space as flow progresses along the 180° curved tube. The primary velocity data for steady flow conditions reveal additional vortices rotating in a direction opposite to Dean vortices—similar to structures observed in pulsatile flow—if the Dean number is sufficiently high.
PubDate: 2016-05-31

• Evaporation dynamics and sedimentation pattern of a sessile particle laden
water droplet
• Abstract: Abstract The dynamics of the flow inside an evaporating sessile droplet of water with polystyrene micro-spheres of 1.0 μm in diameter in suspension is described. The initial volume of the droplets is in the range from 0.6 to 1.0 μl, and observations were made in the last stages before total evaporation. The flow was recorded in a sequence of images that were analyzed with a micro-PIV system to extract quantitative information. Also, using image analysis techniques we determined the dynamics of the retreating liquid film once unpinned from the original contact line. Additionally, we have explored its correlation to the formation of the sediment pattern which is organized in elongated mounds roughly deposited in azimuthal and radial orientations. It is found that the aggregation dynamics of micro-spheres in the segments of the two orientations is different. This might have a substantial influence on the final arrangement of micro-spheres in the sediments.
PubDate: 2016-05-25

• 3D flow visualization and tomographic particle image velocimetry for
vortex breakdown over a non-slender delta wing
• Abstract: Abstract Volumetric measurement for the leading-edge vortex (LEV) breakdown of a delta wing has been conducted by three-dimensional (3D) flow visualization and tomographic particle image velocimetry (TPIV). The 3D flow visualization is employed to show the vortex structures, which was recorded by four cameras with high resolution. 3D dye streaklines of the visualization are reconstructed using a similar way of particle reconstruction in TPIV. Tomographic PIV is carried out at the same time using same cameras with the dye visualization. Q criterion is employed to identify the LEV. Results of tomographic PIV agree well with the reconstructed 3D dye streaklines, which proves the validity of the measurements. The time-averaged flow field based on TPIV is shown and described by sections of velocity and streamwise vorticity. Combining the two measurement methods sheds light on the complex structures of both bubble type and spiral type of breakdown. The breakdown position is recognized by investigating both the streaklines and TPIV velocity fields. Proper orthogonal decomposition is applied to extract a pair of conjugated helical instability modes from TPIV data. Therefore, the dominant frequency of the instability modes is obtained from the corresponding POD coefficients of the modes based on wavelet transform analysis.
PubDate: 2016-05-24

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