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Publisher: Springer-Verlag   (Total: 2336 journals)

 Showing 1201 - 1400 of 2336 Journals sorted alphabetically J. of Community Genetics       (Followers: 1, SJR: 0.727, h-index: 14) J. of Community Health       (Followers: 8, SJR: 0.921, h-index: 44) J. of Comparative Physiology A: Neuroethology, Sensory, Neural, and Behavioral Physiology       (Followers: 7, SJR: 1.087, h-index: 74) J. of Comparative Physiology B : Biochemical, Systemic, and Environmental Physiology       (Followers: 4, SJR: 1.126, h-index: 59) J. of Compassionate Health Care       (Followers: 1) J. of Computational Analysis and Applications       (SJR: 0.291, h-index: 19) J. of Computational Electronics       (Followers: 3, SJR: 0.511, h-index: 20) J. of Computational Neuroscience       (Followers: 19, SJR: 1.068, h-index: 60) J. of Computer and Systems Sciences Intl.       (SJR: 0.27, h-index: 13) J. of Computer Science and Technology       (Followers: 5, SJR: 0.437, h-index: 31) J. of Computer Virology and Hacking Techniques       (Followers: 7, SJR: 0.151, h-index: 2) J. of Computer-Aided Molecular Design       (Followers: 4, SJR: 0.995, h-index: 78) J. of Computers in Education       (Followers: 8) J. of Computing in Higher Education       (Followers: 12, SJR: 0.363, h-index: 21) J. of Consumer Policy       (Followers: 5, SJR: 0.704, h-index: 30) J. of Contemporary Mathematical Analysis       (SJR: 0.237, h-index: 5) J. of Contemporary Physics (Armenian Academy of Sciences)       (Followers: 2, SJR: 0.197, h-index: 6) J. of Contemporary Psychotherapy       (Followers: 5, SJR: 0.397, h-index: 23) J. of Control Theory and Applications       (Followers: 2, SJR: 0.359, h-index: 19) J. of Control, Automation and Electrical Systems       (Followers: 7, SJR: 0.231, h-index: 9) J. of Crop Science and Biotechnology       (Followers: 7) J. of Cross-Cultural Gerontology       (Followers: 3, SJR: 0.631, h-index: 29) J. of Cryptographic Engineering       (Followers: 5, SJR: 0.989, h-index: 11) J. of Cryptology       (Followers: 2, SJR: 1.443, h-index: 55) J. of Cultural Economics       (Followers: 2, SJR: 0.539, h-index: 29) J. of Database Marketing & Customer Strategy Management       (Followers: 8, SJR: 0.149, h-index: 8) J. of Derivatives & Hedge Funds       (Followers: 7, SJR: 0.114, h-index: 5) J. of Developmental and Physical Disabilities       (Followers: 8, SJR: 0.574, h-index: 29) J. of Digital Imaging       (Followers: 8, SJR: 0.578, h-index: 35) J. of Direct Data and Digital Marketing Practice       (Followers: 8, SJR: 0.154, h-index: 6) J. of Dynamical and Control Systems       (Followers: 2, SJR: 0.4, h-index: 26) J. of Dynamics and Differential Equations       (SJR: 1.418, h-index: 31) J. of Earth Science       (Followers: 8, SJR: 0.483, h-index: 16) J. of Earth System Science       (Followers: 41, SJR: 0.448, h-index: 32) J. of East Asian Linguistics       (Followers: 5, SJR: 0.537, h-index: 20) J. of Echocardiography       (Followers: 4, SJR: 0.22, h-index: 3) J. of Economic Growth       (Followers: 23, SJR: 3.273, h-index: 63) J. of Economic Interaction and Coordination       (SJR: 0.263, h-index: 12) J. of Economics       (Followers: 9, SJR: 0.418, h-index: 23) J. of Economics and Finance       (Followers: 6, SJR: 0.272, h-index: 19) J. of Educational Change       (Followers: 7, SJR: 0.961, h-index: 21) J. of Elasticity       (Followers: 5, SJR: 0.851, h-index: 45) J. of Electroceramics       (SJR: 0.577, h-index: 57) J. of Electronic Materials       (Followers: 3, SJR: 0.609, h-index: 75) J. of Electronic Testing       (Followers: 2, SJR: 0.372, h-index: 27) J. of Electronics (China)       (Followers: 4, SJR: 0.112, h-index: 9) J. of Elementary Science Education       (Followers: 9) J. of Engineering Mathematics       (SJR: 0.347, h-index: 37) J. of Engineering Physics and Thermophysics       (Followers: 1, SJR: 0.288, h-index: 11) J. of Engineering Research       (SJR: 0.145, h-index: 5) J. of Engineering Thermophysics       (Followers: 2, SJR: 0.763, h-index: 9) J. of Environmental 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0.465, h-index: 56) J. of Food Measurement and Characterization       (SJR: 0.307, h-index: 4) J. of Food Science and Technology       (Followers: 5, SJR: 0.441, h-index: 29) J. of Forest Research       (Followers: 3, SJR: 0.495, h-index: 27) J. of Forestry Research       (Followers: 6, SJR: 0.304, h-index: 14) J. of Fourier Analysis and Applications       (Followers: 1, SJR: 1.18, h-index: 42) J. of Friction and Wear       (Followers: 6, SJR: 0.373, h-index: 7) J. of Fusion Energy       (Followers: 3, SJR: 0.387, h-index: 19) J. of Gambling Studies       (Followers: 4, SJR: 1.171, h-index: 57) J. of Gastroenterology       (Followers: 12, SJR: 1.651, h-index: 88) J. of Gastrointestinal Cancer       (Followers: 3, SJR: 0.304, h-index: 39) J. of Gastrointestinal Surgery       (Followers: 5, SJR: 1.64, h-index: 99) J. of General Internal Medicine       (Followers: 13, SJR: 1.804, h-index: 134) J. of General Plant Pathology       (SJR: 0.554, h-index: 22) J. of Genetic Counseling       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of Housing and the Built Environment       (Followers: 6, SJR: 0.648, h-index: 28) J. of Huazhong University of Science and Technology [Medical Sciences]       (SJR: 0.344, h-index: 19) J. of Ichthyology       (Followers: 3, SJR: 0.304, h-index: 10) J. of Immigrant and Minority Health       (Followers: 8, SJR: 0.759, h-index: 37) J. of Inclusion Phenomena and Macrocyclic Chemistry       (Followers: 1, SJR: 0.331, h-index: 46) J. of Indian Philosophy       (Followers: 11, SJR: 0.127, h-index: 12) J. of Indian Prosthodontic Society       (SJR: 0.164, h-index: 7) J. of Industrial Microbiology and Biotechnology       (Followers: 13, SJR: 0.966, h-index: 80) J. of Industry, Competition and Trade       (Followers: 6, SJR: 0.327, h-index: 15) J. of Infection and Chemotherapy       (Followers: 1, SJR: 0.673, h-index: 46) J. of Information Technology       (Followers: 49, SJR: 1.474, h-index: 55) J. of Information Technology Teaching Cases       (Followers: 7) J. of Infrared, Millimeter and Terahertz Waves       (Followers: 1, SJR: 1.25, h-index: 36) J. of Inherited Metabolic Disease       (Followers: 2, SJR: 1.389, h-index: 77) J. of Inorganic and Organometallic Polymers and Materials       (Followers: 7, SJR: 0.338, h-index: 33) J. of Insect Behavior       (Followers: 9, SJR: 0.569, h-index: 39) J. of Insect Conservation       (Followers: 10, SJR: 0.872, h-index: 43) J. of Intelligent and Robotic Systems       (Followers: 2, SJR: 0.629, h-index: 43) J. of Intelligent Information Systems       (Followers: 1, SJR: 0.691, h-index: 43) J. of Intelligent Manufacturing       (Followers: 4, SJR: 1.397, h-index: 54) J. of Interventional Cardiac Electrophysiology       (SJR: 0.93, h-index: 43) J. of Intl. 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and Oral Surgery       (Followers: 1) J. of Mechanical Science and Technology       (Followers: 5, SJR: 0.589, h-index: 26) J. of Medical and Biological Engineering       (Followers: 1, SJR: 0.387, h-index: 18) J. of Medical Humanities       (Followers: 19, SJR: 0.299, h-index: 18) J. of Medical Systems       (Followers: 1, SJR: 0.717, h-index: 44) J. of Medical Toxicology       (Followers: 4, SJR: 0.874, h-index: 28) J. of Medical Ultrasonics       (Followers: 2, SJR: 0.18, h-index: 13) J. of Medicine and the Person J. of Membrane Biology       (Followers: 1, SJR: 0.738, h-index: 82) J. of Micro-Bio Robotics       (SJR: 0.28, h-index: 3) J. of Microbiology       (Followers: 7, SJR: 0.741, h-index: 43) J. of Mining Science       (Followers: 5, SJR: 0.317, h-index: 16) J. of Molecular Evolution       (Followers: 9, SJR: 0.952, h-index: 108) J. of Molecular Histology       (Followers: 2, SJR: 0.755, h-index: 48) J. of Molecular Medicine       (Followers: 15, SJR: 2.165, h-index: 113) J. 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65) J. of Ornithology       (Followers: 21) J. of Orofacial Orthopedics / Fortschritte der Kieferorthopädie       (SJR: 0.574, h-index: 33) J. of Orthopaedic Science       (Followers: 5, SJR: 0.708, h-index: 48) J. of Paleolimnology       (Followers: 5, SJR: 0.984, h-index: 64) J. of Parasitic Diseases       (Followers: 2, SJR: 0.298, h-index: 9) J. of Pediatric Neuropsychology       (Followers: 2) J. of Pest Science       (Followers: 2, SJR: 1.341, h-index: 28) J. of Pharmaceutical Health Care and Sciences J. of Pharmaceutical Innovation       (Followers: 8, SJR: 0.524, h-index: 17) J. of Pharmaceutical Investigation       (Followers: 1, SJR: 0.331, h-index: 6) J. of Pharmacokinetics and Pharmacodynamics       (Followers: 21, SJR: 0.708, h-index: 46) J. of Phase Equilibria and Diffusion       (Followers: 19, SJR: 0.433, h-index: 36) J. of Philosophical Logic       (Followers: 8, SJR: 0.704, h-index: 26)
 Experiments in Fluids   [SJR: 1.088]   [H-I: 82]   [10 followers]  Follow         Hybrid journal (It can contain Open Access articles)    ISSN (Print) 1432-1114 - ISSN (Online) 0723-4864    Published by Springer-Verlag  [2336 journals]
• Direct measurement of wall slip and slip layer thickness of non-Brownian
hard-sphere suspensions in rectangular channel flows
• Authors: Steffen Jesinghausen; Rene Weiffen; Hans-Joachim Schmid
Abstract: Wall slip is a long-known phenomenon in the field of rheology. Nevertheless, the origin and the evolution are not completely clear yet. Regarding suspensions, the effect becomes even more complicated, because different mechanisms like pure slip or slip due to particle migration have to be taken into account. Furthermore, suspensions themselves show many flow anomalies and the isolation of slip is complicated. In order to develop working physical models, further insight is necessary. In this work, we measured experimentally the wall slip velocities of different highly filled suspensions in a rectangular slit die directly with respect to the particle concentration and the particle size. The slip velocities were obtained using a particle image velocimetry (PIV) system. The suspensions consisting of a castor oil–cinnamon oil blend and PMMA particles were matched in terms of refractive indexes to appear transparent. Hereby, possible optical path lengths larger than 15 mm were achieved. The slip velocities were found to be in a quadratic relation to the wall shear stress. Furthermore, the overall flow rate as well as the particle concentration has a direct influence on the slip. Concerning the shear stress, there seem to be two regions of slip with different physical characteristics. Furthermore, we estimated the slip layer thickness directly from the velocity profiles and propose a new interpretation. The PIV technique is used to investigate the viscosity and implicit the concentration profile in the slit die. It is shown that the particle migration process is quite fast.
PubDate: 2016-09-12
DOI: 10.1007/s00348-016-2241-6
Issue No: Vol. 57, No. 9 (2016)

• Design and testing of temperature tunable de Laval nozzles for
applications in gas-phase reaction kinetics
• Authors: A. Canosa; A. J. Ocaña; M. Antiñolo; B. Ballesteros; E. Jiménez; J. Albaladejo
Abstract: A series of three de Laval nozzles initially designed to generate uniform supersonic flows in helium at 23 and 36 K and in argon at 50 K have been used with either pure nitrogen or mixtures of nitrogen with helium or argon in order to make a sequence of pulsed supersonic flows working at different temperatures. For this, a computer homemade program has been used to design de Laval nozzles contours for gas mixtures in order to determine the theoretical pressure P and temperature T in these supersonic flows. Spatial evolution of T along the flow axis downstream of the nozzle exit has been characterized with a fast response Pitot tube instrument newly developed. Twenty-eight different gas mixture conditions have been tested, indicating a very good agreement with the corresponding calculated flow conditions. The length of uniformity ΔL of the supersonic flows have been found to be >30 cm in more than 80 % of the situations and >50 cm for more than 50 % of the tested conditions. Fine temperature tunability was achieved in the range 22–107 K with very small fluctuations of the mean temperature along ΔL. Advantages and limits of these new developments for studies of gas-phase reaction kinetics are discussed.
PubDate: 2016-09-07
DOI: 10.1007/s00348-016-2238-1
Issue No: Vol. 57, No. 9 (2016)

• FFT integration of instantaneous 3D pressure gradient fields measured by
Lagrangian particle tracking in turbulent flows
• Authors: F. Huhn; D. Schanz; S. Gesemann; A. Schröder
Abstract: Pressure gradient fields in unsteady flows can be estimated through flow measurements of the material acceleration in the fluid and the assumption of the governing momentum equation. In order to derive pressure from its gradient, almost exclusively two numerical methods have been used to spatially integrate the pressure gradient until now: first, direct path integration in the spatial domain, and second, the solution of the Poisson equation for pressure. Instead, we propose an alternative third method that integrates the pressure gradient field in Fourier space. Using a FFT function, the method is fast and easy to implement in programming languages for scientific computing. We demonstrate the accuracy of the integration scheme on a synthetic pressure field and apply it to an experimental example based on time-resolved material acceleration data from high-resolution Lagrangian particle tracking with the Shake-The-Box method.
PubDate: 2016-09-02
DOI: 10.1007/s00348-016-2236-3
Issue No: Vol. 57, No. 9 (2016)

• An experimental study on the aeromechanics and wake characteristics of a
novel twin-rotor wind turbine in a turbulent boundary layer flow
• Authors: Zhenyu Wang; Wei Tian; Ahmet Ozbay; Anupam Sharma; Hui Hu
Abstract: The aeromechanic performance and wake characteristics of a novel twin-rotor wind turbine (TRWT) design, which has an extra set of smaller, auxiliary rotor blades appended in front of the main rotor, was evaluated experimentally, in comparison with those of a conventional single-rotor wind turbine (SRWT) design. The comparative study was performed in a large-scale wind tunnel with scaled TRWT and SRWT models mounted in the same incoming turbulent boundary layer flow. In addition to quantifying power outputs and the dynamic wind loadings acting on the model turbines, the wake characteristics behind the model turbines were also measured by using a particle image velocimetry system and a Cobra anemometry probe. The measurement results reveal that, while the TRWT design is capable of harnessing more wind energy from the same incoming airflow by reducing the roots losses incurred in the region near the roots of the main rotor blades, it also cause much greater dynamic wind loadings acting on the TRWT model and higher velocity deficits in the near wake behind the TRWT model, in comparison with those of the SRWT case. Due to the existence of the auxiliary rotor, more complex vortex structures were found to be generated in the wake behind the TRWT model, which greatly enhanced the turbulent mixing in the turbine wake, and caused a much faster recovery of the velocity deficits in the turbine far wake. As a result, the TRWT design was also found to enable the same downstream turbine to generate more power when sited in the wake behind the TRWT model than that in the SRWT wake, i.e., by mitigating wake losses in typical wind farm settings.
PubDate: 2016-09-02
DOI: 10.1007/s00348-016-2233-6
Issue No: Vol. 57, No. 9 (2016)

• A new method of dynamic and static stall detection using infrared
thermography
• Authors: A. D. Gardner; C. C. Wolf; M. Raffel
Abstract: A new method of detecting flow separation for static and pitching airfoils is described, with application to the generation of stall maps for helicopter rotors. An airfoil is heated using a lamp, and a high-speed infrared camera monitors the surface temperature. Subtracting consecutive images and performing a spatial standard deviation over a region of interest yields a single $$\sigma \hbox {DIT}$$ value which is used to detect boundary layer separation on the airfoil. The data can be analysed to identify attached flow (low values of $$\sigma \hbox {DIT}$$ ) and separated flow (high values of $$\sigma \hbox {DIT}$$ ). Although appropriate filtering can significantly improve the signal-to-noise ratio, the method is robust regarding the exact method of analysis and the unfiltered data are sufficiently clear to be analysed without additional processing. For the test airfoil used, stall was measured up to a pitching frequency of 5 Hz, and signal-to-noise ratios indicate that it should be possible to measure stall for a pitching frequency of 20 Hz for a carbon-fibre surface with the thermal properties used.
PubDate: 2016-09-01
DOI: 10.1007/s00348-016-2235-4
Issue No: Vol. 57, No. 9 (2016)

• Influence of short rear end tapers on the wake of a simplified square-back
vehicle: wake topology and rear drag
• Authors: Anna-Kristina Perry; Giancarlo Pavia; Martin Passmore
Abstract: As vehicle manufacturers work to reduce energy consumption of all types of vehicles, external vehicle aerodynamics has become increasingly important. Whilst production vehicle shape optimisation methods are well developed, the need to make further advances requires deeper understanding of the highly three-dimensional flow around bluff bodies. In this paper, the wake flow of a generic bluff body, the Windsor body, based on a square-back car geometry, was investigated by means of balance measurements, surface pressure measurements and 2D particle image velocimetry planes. Changes in the wake topology are triggered by the application of short tapers (4 % of the model length) to the top and bottom edges of the base, representing a shape optimisation that is realistic for many modern production vehicles. The base drag is calculated and correlated with the aerodynamic drag data. The results not only show the effectiveness of such small devices in modifying the time average topology of the wake but also shed some light on the effects produced by different levels of upwash and downwash on the bi-stable nature of the wake itself.
PubDate: 2016-10-18
DOI: 10.1007/s00348-016-2260-3
Issue No: Vol. 57, No. 11 (2016)

• LDV survey of cavitation and resonance effect on the precessing vortex
rope dynamics in the draft tube of Francis turbines
• Authors: A. Favrel; A. Müller; C. Landry; K. Yamamoto; F. Avellan
Abstract: The large-scale penetration of the electrical grid by intermittent renewable energy sources requires a continuous operating range extension of hydropower plants. This causes the formation of unfavourable flow patterns in the draft tube of turbines and pump-turbines. At partial load operation, a precessing cavitation vortex rope is formed at the Francis turbine runner outlet, acting as an excitation source for the hydraulic system. In case of resonance, the resulting high-amplitude pressure pulsations can put at risk the stability of the machine and of the electrical grid to which it is connected. It is therefore crucial to understand and accurately simulate the underlying physical mechanisms in such conditions. However, the exact impact of cavitation and hydro-acoustic resonance on the flow velocity fluctuations in the draft tube remains to be established. The flow discharge pulsations expected to occur in the draft tube in resonance conditions have for instance never been verified experimentally. In this study, two-component Laser Doppler Velocimetry is used to investigate the axial and tangential velocity fluctuations at the runner outlet of a reduced scale physical model of a Francis turbine. The investigation is performed for a discharge equal to 64 % of the nominal value and three different pressure levels in the draft tube, including resonance and cavitation-free conditions. Based on the convective pressure fluctuations induced by the vortex precession, the periodical velocity fluctuations over one typical precession period are recovered by phase averaging. The impact of cavitation and hydro-acoustic resonance on both axial and tangential velocity fluctuations in terms of amplitude and phase shift is highlighted for the first time. It is shown that the occurrence of resonance does not have significant effects on the draft tube velocity fields, suggesting that the synchronous axial velocity fluctuations are surprisingly negligible compared to the velocity fluctuations induced by the vortex precession.
PubDate: 2016-10-17
DOI: 10.1007/s00348-016-2257-y
Issue No: Vol. 57, No. 11 (2016)

• Wavelet analysis of transonic buffet on a two-dimensional airfoil with
vortex generators
• Authors: Toshinori Kouchi; Shingo Yamaguchi; Shunske Koike; Tsutomu Nakajima; Mamoru Sato; Hiroshi Kanda; Shinichiro Yanase
Abstract: We visualized the shock buffets on a two-dimensional transonic airfoil with and without vortex generators (VGs) by using a fast-framing focusing schlieren imaging. The focusing schlieren visualization showed that the flow three-dimensionality around the airfoil became remarkable with installing the VGs. This implies that narrow depth of focus of imaging systems was a key to accurately capture the characteristics of the shock oscillation due to the buffet for the cases with VGs. The time-resolved imaging also revealed that non-periodic components were included in the shock oscillation due to the buffet for the cases with VGs. This prevented Fourier analysis from being applied. We used wavelet analysis to extract the characteristic of the shock oscillation for the cases with VGs. The wavelet spectrograms revealed that the low-frequency oscillation having the buffet frequency was still included intermittently in the shock oscillation even when VG controlled the buffet. The rate of appearing the low-frequency oscillation increased with increasing both the interval between VGs and the angle of attack.
PubDate: 2016-10-14
DOI: 10.1007/s00348-016-2261-2
Issue No: Vol. 57, No. 11 (2016)

• 3D analysis of vortical structures in an abdominal aortic aneurysm by
stereoscopic PIV
• Authors: Valérie Deplano; Carine Guivier-Curien; Eric Bertrand
Abstract: The present work presents an experimental in vitro three-dimensional analysis of the flow dynamics in an abdominal aortic aneurysm (AAA) through stereoscopic particle image velocimetry (SPIV) measurements. The experimental set-up mimics the pathophysiological context involving a shear thinning blood analogue fluid, compliant AAA and aorto-iliac bifurcation walls and controlled inlet and outlet flow rate and pressure waveforms as well as working fluid temperature. SPIV was carefully calibrated and conducted to assess the three velocity components in the AAA volume. For the first time in the literature, the 3D vortex ring genesis, propagation, and vanishing in the AAA bulge are experimentally described and quantified. In comparison with classical 2-component PIV measurements (2C PIV), the third component of the velocity vector was shown to be of importance in such a geometry, especially, during the deceleration phase of the flow rate. The 3D velocity magnitude reached up more than 20 % of the 2D one showing that 2C PIV are definitively not accurate enough to provide a complete description of flow behaviour in an AAA. In addition to potential clinical implications of a full 3D vortex ring description in AAA evolution, the 3D in vitro experimental quantification of the flow dynamics carried out in the present study offers an interesting tool for the validation of fluid–structure interaction numerical studies dealing with AAA.
PubDate: 2016-10-14
DOI: 10.1007/s00348-016-2263-0
Issue No: Vol. 57, No. 11 (2016)

• Measurement of flow structures and heat transfer behind a wall-proximity
square rib using TSP, PIV and split-fiber film
• Authors: Chuangxin He; Yingzheng Liu; Di Peng; Savas Yavuzkurt
Abstract: In the present study, complementary measurement techniques—temperature sensitive paint (TSP), planar particle image velocimetry (planar PIV) and a split-fiber film probe—were used to investigate the effects of a “wall-proximity square rib” on flow structure and surface heat transfer augmentation. TSP was used to measure the time-averaged wall temperature field at three different Reynolds numbers ( $$Re_{d}$$  = 3800, 7600 and 11,400) based on the rib height d and the mainstream velocity $$U_{o}$$ , and wall-proximity configurations with four different gap ratios (gap size $$G$$ over rib height d), G/d = 0, 0.25, 0.50 and 0.75. The two-dimensional distribution of the normalized Nusselt number convincingly demonstrated the existence of a hot spot immediately behind the rib in the attached rib configuration (G/d = 0) and surface heat transfer augmentation in the reattachment zone. Among the three wall-proximity configurations, G/d = 0.25 resulted in maximum heat transfer augmentation immediately behind the rib and overall improvement in surface heat removal. However, no distinctly different spatial patterns of the normalized Nusselt number distribution were found at the three different Reynolds numbers. A subsequent experiment examined the flow pattern and flow structures at $$Re_{d}$$  = 7600 and three wall-proximity configurations (G/d = 0, 0.25 and 0.50). Velocity field measurements using PIV, along with complementary measurements using split-fiber film, gave a clear view of the flow pattern behind the rib; a very slender separation bubble with highly unsteady flow reversal was found close to the surface when G/d = 0.25. For configurations with G/d = 0.25 and 0.50, the high-speed jet issuing from the gap had a complicated influence on the interaction between the upper free shear layer and lower strong shear layer, resulting in slanted movement of the coupled wake flow. Proper orthogonal decomposition was used to identify the spatial characteristics of the superimposed flow structures. In the configuration G/d = 0.25, coherent structures were found throughout most of the wake region, beginning roughly 1.2d behind the rib. Fluid flow in the region near the wall was strongly influenced by the dominant coherent structures, which were evidently the main mechanism for surface heat removal. In the configuration with G/d = 0.50, the area with large velocity fluctuation intensity shifted away from the wall toward the mainstream due to rapid expansion of the wall jet. This, in combination with large-scale coherent structures from the surface, meant a much reduced influence on the fluid near the wall and a corresponding deterioration of surface heat transfer beyond the station x/d = 4 (x being the downstream distance from the rib’s trailing edge).
PubDate: 2016-10-13
DOI: 10.1007/s00348-016-2262-1
Issue No: Vol. 57, No. 11 (2016)

• Large-scale volumetric pressure from tomographic PTV with HFSB tracers
• Authors: Jan F. G. Schneiders; Giuseppe C. A. Caridi; Andrea Sciacchitano; Fulvio Scarano
Abstract: The instantaneous volumetric pressure in the near-wake of a truncated cylinder is measured by use of tomographic particle tracking velocimetry (PTV) using helium-filled soap bubbles (HFSB) as tracers. The measurement volume is several orders of magnitude larger than that reported in tomographic experiments dealing with pressure from particle image velocimetry (PIV). The near-wake of a truncated cylinder installed on a flat plate (Re D  = 3.5 × 104) features both wall-bounded turbulence and large-scale unsteady flow separation. The instantaneous pressure is calculated from the time-resolved 3D velocity distribution by invoking the momentum equation. The experiments are conducted simultaneously with surface pressure measurements intended for validation of the technique. The study shows that time-averaged pressure and root-mean-squared pressure fluctuations can be accurately measured both in the fluid domain and at the solid surface by large-scale tomographic PTV with HFSB as tracers, with significant reduction in manufacturing complexity for the wind-tunnel model and circumventing the need to install pressure taps or transducers. The measurement over a large volume eases the extension toward the free-stream regime, providing a reliable boundary condition for the solution of the Poisson equation for pressure. The work demonstrates, in the case of the flow past a truncated cylinder, the use of HFSB tracer particles for pressure measurement in air flows in a measurement volume that is two orders of magnitude larger than that of conventional tomographic PIV.
PubDate: 2016-10-13
DOI: 10.1007/s00348-016-2258-x
Issue No: Vol. 57, No. 11 (2016)

• Surface topography measurements of the bouncing droplet experiment
• Authors: Adam P. Damiano; P.-T. Brun; Daniel M. Harris; Carlos A. Galeano-Rios; John W. M. Bush
Abstract: A free-surface synthetic Schlieren (Moisy et al. in Exp Fluids 46:1021–1036, 2009; Eddi et al. in J Fluid Mech 674:433–463, 2011) technique has been implemented in order to measure the surface topography generated by a droplet bouncing on a vibrating fluid bath. This method was used to capture the wave fields of bouncers, walkers, and walkers interacting with boundaries. These wave profiles are compared with existing theoretical models and simulations and will prove valuable in guiding their future development. Specifically, the method provides insight into what type of boundary conditions apply to the wave field when a bouncing droplet approaches a submerged obstacle.
PubDate: 2016-10-11
DOI: 10.1007/s00348-016-2251-4
Issue No: Vol. 57, No. 10 (2016)

• Topology of vortex–wing interaction
• Authors: C. McKenna; D. Rockwell
Abstract: A trailing vortex incident upon a wing can generate different modes of vortex–wing interaction. These modes, which may involve either enhancement or suppression of the vortex generated at the tip of the wing, are classified on the basis of the present experiments together with computations at the Air Force Research Laboratory. Occurrence of a given mode of interaction is predominantly determined by the dimensionless location of the incident vortex relative to the tip of the wing and is relatively insensitive to the Reynolds number and dimensionless circulation of the incident vortex. The genesis of the basic interaction modes is clarified using streamline topology with associated critical points that show compatibility between complex streamline patterns in the vicinity of the tip of the wing. Whereas formation of an enhanced tip vortex involves a region of large upwash in conjunction with localized flow separation, complete suppression of the tip vortex is associated with a small-scale separation–reattachment bubble bounded by downwash at the wing tip.
PubDate: 2016-09-26
DOI: 10.1007/s00348-016-2244-3
Issue No: Vol. 57, No. 10 (2016)

• In-flight active wave cancelation with delayed-x-LMS control algorithm in
a laminar boundary layer
• Authors: Bernhard Simon; Nicolò Fabbiane; Timotheus Nemitz; Shervin Bagheri; Dan S. Henningson; Sven Grundmann
Abstract: This manuscript demonstrates the first successful application of the delayed-x-LMS (dxLMS) control algorithm for TS-wave cancelation. Active wave cancelation of two-dimensional broadband Tollmien–Schlichting (TS) disturbances is performed with a single DBD plasma actuator. The experiments are conducted in flight on the pressure side of a laminar flow wing glove, mounted on a manned glider. The stability properties of the controller are investigated in detail with experimental flight data, DNS and stability analysis of the boundary layer. Finally, a model-free approach for dxLMS operation is introduced to operate the controller as a ‘black-box’ system, which automatically adjusts the controller settings based on a group speed measurement of the disturbance wave packets. The modified dxLMS controller is operated without a model and is able to adapt to varying conditions that may occur during flight in atmosphere.
PubDate: 2016-09-25
DOI: 10.1007/s00348-016-2242-5
Issue No: Vol. 57, No. 10 (2016)

• Feedback control of bimodal wake dynamics
• Authors: Ruiying Li; Diogo Barros; Jacques Borée; Olivier Cadot; Bernd R. Noack; Laurent Cordier
Abstract: Feedback control is applied to symmetrize the bimodal dynamics of a turbulent blunt body wake. The flow is actuated with two lateral slit jets and monitored with pressure sensors at the rear surface. The physics-based controller is inferred from preliminary open-loop tests and is capable of symmetrizing the wake. A slight pressure recovery is achieved due to the net balance between the favourable effect of wake symmetrization and adverse effect of shear-layer mixing and vortex shedding amplification.
PubDate: 2016-09-22
DOI: 10.1007/s00348-016-2245-2
Issue No: Vol. 57, No. 10 (2016)

• Image processing using proper orthogonal and dynamic mode decompositions
for the study of cavitation developing on a NACA0015 foil
• Authors: Sebastien Prothin; Jean-Yves Billard; Henda Djeridi
Abstract: The purpose of the present study is to get a better understanding of the hydrodynamic instabilities of sheet cavities which develop along solid walls. The main objective is to highlight the spatial and temporal behavior of such a cavity when it develops on a NACA0015 foil at high Reynolds number. Experimental results show a quasi-steady, periodic, bifurcation domain, with aperiodic cavity behavior corresponding to σ/2α values of 5.75, 5, 4.3 and 3.58. Robust mathematical methods of signal postprocessing (proper orthogonal decomposition and dynamic mode decomposition) were applied in order to emphasize the spatio-temporal nature of the flow. These new techniques put in evidence the 3D effects due to the reentrant jet instabilities or due to propagating shock wave mechanism at the origin of the shedding process of the cavitation cloud.
PubDate: 2016-09-21
DOI: 10.1007/s00348-016-2246-1
Issue No: Vol. 57, No. 10 (2016)

• Reconstructing three-dimensional wake topology based on planar PIV
measurements and pattern recognition analysis
• Authors: C. Morton; S. Yarusevych
Abstract: The present study presents a new technique for reconstructing the salient aspects of three-dimensional wake topology based on time-resolved, planar, two-component particle image velocimetry data collected in multiple orthogonal planes. The technique produces conditionally averaged flow field reconstructions based on a pattern recognition analysis of velocity fields. It is validated on the wake of a low-aspect ratio dual step cylinder geometry, consisting of a large diameter cylinder (D) with small aspect ratio (L/D) attached to the mid-span of a small diameter cylinder (d). For a dual step cylinders with D/d = 2, and L/D = 1, numerical and experimental data are considered for ReD = 150 (laminar wake) and for ReD = 2100 (turbulent wake). The results show that the proposed technique successfully reconstructs the dominant periodic wake vortex interactions and can be extended to a wide range of turbulent flows.
PubDate: 2016-09-17
DOI: 10.1007/s00348-016-2240-7
Issue No: Vol. 57, No. 10 (2016)

• Measurement and characterization of fully transient diesel fuel jet
processes in an optical engine with production injectors
• Authors: Nicholas Neal; David Rothamer
Abstract: The effects of transient rate-of-injection profiles on high-pressure diesel fuel jets have been studied in an optically accessible internal combustion engine. High-speed optical imaging measurements were applied over a range of ambient conditions, fuel types, and injection parameters. This paper demonstrates that during the early part of the injection, while the liquid core is disintegrating, the penetration is functionally linked to the inviscid orifice exit velocity up until a downstream distance hypothesized to be the jet breakup length. The jets then transitioned to a mixing dominated penetration behavior afterward. Therefore, for cases that exhibit transient rate-of-injection profiles, quasi-steady penetration analytical solutions for penetration have poor agreement with the empirical data. The development of an adaptive edgefinding algorithm for accurately detecting jets in engines is detailed. These findings indicate that empirical correlations widely used throughout the engine community for estimating jet penetration do not accurately represent actual injection parameters under transient conditions.
PubDate: 2016-09-14
DOI: 10.1007/s00348-016-2239-0
Issue No: Vol. 57, No. 10 (2016)

• Velocity field measurements in the wake of a propeller model
• Authors: R. Mukund; A. Chandan Kumar
Abstract: Turboprop configurations are being revisited for the modern-day regional transport aircrafts for their fuel efficiency. The use of laminar flow wings is an effort in this direction. One way to further improve their efficiency is by optimizing the flow over the wing in the propeller wake. Previous studies have focused on improving the gross aerodynamic characteristics of the wing. It is known that the propeller slipstream causes early transition of the boundary layer on the wing. However, an optimized design of the propeller and wing combination could delay this transition and decrease the skin friction drag. Such a wing design would require the detailed knowledge of the development of the slipstream in isolated conditions. There are very few studies in the literature addressing the requirements of transport aircraft having six-bladed propeller and cruising at a high propeller advance ratio. Low-speed wind tunnel experiments have been conducted on a powered propeller model in isolated conditions, measuring the velocity field in the vertical plane behind the propeller using two-component hot-wire anemometry. The data obtained clearly resolved the mean velocity, the turbulence, the ensemble phase averages and the structure and development of the tip vortex. The turbulence in the slipstream showed that transition could be close to the leading edge of the wing, making it a fine case for optimization. The development of the wake with distance shows some interesting flow features, and the data are valuable for flow computation and optimization.
PubDate: 2016-09-14
DOI: 10.1007/s00348-016-2237-2
Issue No: Vol. 57, No. 10 (2016)

• X-ray fluorescence measurements of dissolved gas and cavitation
• Abstract: The dynamics of dissolved gas and cavitation are strongly coupled, yet these phenomena are difficult to measure in-situ. Both create voids in the fluid that can be difficult to distinguish. We present an application of X-ray fluorescence in which liquid density and total noncondensible gas concentration (both dissolved and nucleated) are simultaneously measured. The liquid phase is doped with 400 ppm of a bromine tracer, and dissolved air is removed and substituted with krypton. Fluorescent emission at X-ray wavelengths is simultaneously excited from the Br and Kr with a focused monochromatic X-ray beam from a synchrotron source. We measure the flow in a cavitating nozzle 0.5 mm in diameter. From Br fluorescence, total displacement of the liquid is measured. From Kr fluorescence, the mass fraction of both dissolved and nucleated gas is measured. Volumetric displacement of liquid due to both cavitation and gas precipitation can be separated through estimation of the local equilibrium dissolved mass fraction. The uncertainty in the line of sight projected densities of the liquid and gas phases is 4–6 %. The high fluorescence yields and energies of Br and Kr allow small mass fractions of gas to be measured, down to 10−5, with an uncertainty of 8 %. These quantitative measurements complement existing optical diagnostic techniques and provide new insight into the diffusion of gas into cavitation bubbles, which can increase their internal density, pressure and lifetimes by orders of magnitude.
PubDate: 2016-09-28
DOI: 10.1007/s00348-016-2250-5

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