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Donald Rockwell - One of the best experts on this subject based on the ideXlab platform.
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Flow structure on a three-dimensional wing subjected to small amplitude perturbations
Experiments in Fluids, 2009Co-Authors: T. O. Yilmaz, Donald RockwellAbstract:Small amplitude angular perturbations, of the order of one-half degree, can substantially modify the flow structure along a three-dimensional wing configuration, which is quantitatively characterized using a technique of high-image-Density Particle image velocimetry. Excitation at either the fundamental or the first subharmonic of the spanwise-averaged instability frequency of the separating shear layer from the stationary wing nearly eliminates the large-scale separation zone along the wing at high angle of attack. The physics of the flow is interpreted in terms of time-mean streamlines, vorticity and Reynolds stress, in conjunction with phase-averaged patterns of instantaneous vorticity. Distinctive vorticity patterns occur along the leading edge when the time-averaged separation zone is minimized.
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Interaction of a deep-water wave with a vertical cylinder: flow structure and loading
Journal of Fluid Mechanics, 2004Co-Authors: Y. Yang, Donald RockwellAbstract:Interaction of a deep-water wave with a vertical cylinder is characterized using techniques of high-image-Density Particle image velocimetry, in conjunction with measurement of the transverse and in-line loading coefficients. Phase-locked patterns of locally two-dimensional vortex formation are attainable only for sufficiently high values of the Keulegan-Carpenter number KC, e.g. KC ≥ 12. Even in these cases, such patterns are interrupted by non-phase-locked patterns that, nevertheless, show basic forms, including mode inversion or switching of the initially formed vortex from the cylinder, along with patterns of symmetrical vortex formation, all represented by patterns of instantaneous vorticity
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Flow Structure in a Radial Flow Pumping System Using High-Image-Density Particle Image Velocimetry
Journal of Fluids Engineering, 1994Co-Authors: O. Akin, Donald RockwellAbstract:Use of high-image-Density Particle image velocimetry (PIV) allows characterization of the instantaneous structure of wake and wake-blade interactions in a simulated rotating machine. The distribution of vorticity over an entire plane within the pumping system is related to the instantaneous pressure source terms in the wake of the impeller. Comparison of instantaneous and ensemble-averaged vorticity contours shows that limited ensemble-averaging can produce a substantial reduction in vorticity levels associated with the instantaneous pressure source terms. When the wake from the impeller interacts with a stationary diffuser blade, the instantaneous processes of flow separation and reattachment can be effectively characterized using combinations of instantaneous streamline patterns and contours of constant vorticity. Moreover, active control of the inflow into the pumping system allows substantial modification of these vorticity distributions.
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Cinematographic system for high-image-Density Particle image velocimetry
Experiments in Fluids, 1994Co-Authors: J.-c. Lin, Donald RockwellAbstract:A cinematographic system, which integrates the concepts of high-image-Density PIV, laser scanning, and framing photography, allows temporal resolution of the order of one percent of the time scale of the largest vortical structures in the turbulent wake from a cylinder at a Reynolds number of 10,000. With this resolution in time, it is possible to track, in a continuous fashion, the patterns of streamwise vorticity in the near-wake.
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Quantitative interpretation of complex unsteady flows via high-image-Density Particle image velocimetry
Optical Diagnostics in Fluid and Thermal Flow, 1993Co-Authors: Donald Rockwell, J.-c. LinAbstract:Representative classes of unsteady separated flows are interpreted using high-image-Density Particle image velocimetry,l which allows determination of the instantaneous, sectional streamline patterns and distributions of vorticity. Comparison of these instantaneous realizations in two orthogonal planes reveals fundamental mechanisms of distortion of the vorticity concentrations. Furthermore, by acquiring successive images closely spaced in time, it is possible to construct 3D volume representations of iso-vorticity. These quantitative approaches reveal limitations of interpreting patterns of instantaneous and ensemble-averaged flow structure.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
C H Ataide - One of the best experts on this subject based on the ideXlab platform.
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physical characterization of sweet sorghum bagasse tobacco residue soy hull and fiber sorghum bagasse Particles Density Particle size and shape distributions
Powder Technology, 2013Co-Authors: Cassia Regina Cardoso, Tiago Jose Pires De Oliveira, J A Santana, C H AtaideAbstract:Abstract Biomass offers an alternative to meet the increasing interest in renewable energy. For thermal conversion processes such as fast pyrolysis, which often involve fluidization, spherical Particles are considered unsuitable for materials such as biomass. An investigation was made of relevant physical properties of four types of biomass: sweet sorghum bagasse, tobacco waste, soybean hulls and fiber sorghum bagasse. Three samples of each biomass with different granulometries were analyzed. Density values were determined. Particle shape and size distributions were evaluated by digital image analysis. It was observed that the moisture content affected the materials' true Density and for dried biomass the smaller the Particle sizes the higher the true Density. The results indicated that sweet sorghum bagasse Particles of different sizes have similar shapes; that the Particle roundness of the four types of biomass is a property more closely related with the characteristic shape of the material than with its granulometric classification; and that the granulometric classification of tobacco waste, soybean hull and fiber sorghum bagasse Particles can effectively influence the obtainment of Particles with higher or lower roundness. The average roundness varied from 0.45 to 0.70 and the aspect ratio from 1.90 to 2.60. The results obtained in this study are useful for numerical simulations of the fluid dynamics of pyrolysis, combustion and gasification processes and also for studies about the optimal operating conditions of mixture fluidization.
D Rockwell - One of the best experts on this subject based on the ideXlab platform.
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flow structure on diamond and lambda planforms trailing edge region
AIAA Journal, 2005Co-Authors: B Yaniktepe, D RockwellAbstract:The instantaneous and averaged flow structure on diamond and lambda planforms is characterized by using a technique of high-image-Density Particle image velocimetry. Emphasis is on the structure in the trailing-edge region, over a range of angle of attack. Elongated layers of vorticity in the crossflow plane exhibit well-defined mean (time-averaged) and instantaneous concentrations of vorticity. These features are interpreted in conjunction with patterns of streamline topology, as well as images of rms velocity fluctuation and velocity spectra obtained from space-time imaging.
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interaction of a deep water wave with a vertical cylinder at low keulegan carpenter number transition from phase locked modes of vortex formation
Physics of Fluids, 2004Co-Authors: M Ozgoren, D RockwellAbstract:Vortex formation from a cylinder in a deep-water wave is characterized using a technique of high-image-Density Particle image velocimetry for small values of wave amplitude, which corresponds to low magnitudes of the Keulegan–Carpenter (KC) number. Despite the fact that the deep-water wave involves Particle trajectories in the form of circular orbits, whose axes are normal to the axis of the cylinder, it is possible to attain modes of vortex formation that are phase locked to the wave motion at lower values of KC. At a critical value of KC, however, the onset of non-phase-locked modes occurs. These modes, which are defined in terms of patterns of instantaneous vorticity, take three basic forms. Furthermore, when the cylinder undergoes self-excited vibrations at the critical value of KC, it is possible to identify the same basic modes as for the stationary cylinder.
Y. Yang - One of the best experts on this subject based on the ideXlab platform.
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Interaction of a deep-water wave with a vertical cylinder: flow structure and loading
Journal of Fluid Mechanics, 2004Co-Authors: Y. Yang, Donald RockwellAbstract:Interaction of a deep-water wave with a vertical cylinder is characterized using techniques of high-image-Density Particle image velocimetry, in conjunction with measurement of the transverse and in-line loading coefficients. Phase-locked patterns of locally two-dimensional vortex formation are attainable only for sufficiently high values of the Keulegan-Carpenter number KC, e.g. KC ≥ 12. Even in these cases, such patterns are interrupted by non-phase-locked patterns that, nevertheless, show basic forms, including mode inversion or switching of the initially formed vortex from the cylinder, along with patterns of symmetrical vortex formation, all represented by patterns of instantaneous vorticity
Cassia Regina Cardoso - One of the best experts on this subject based on the ideXlab platform.
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physical characterization of sweet sorghum bagasse tobacco residue soy hull and fiber sorghum bagasse Particles Density Particle size and shape distributions
Powder Technology, 2013Co-Authors: Cassia Regina Cardoso, Tiago Jose Pires De Oliveira, J A Santana, C H AtaideAbstract:Abstract Biomass offers an alternative to meet the increasing interest in renewable energy. For thermal conversion processes such as fast pyrolysis, which often involve fluidization, spherical Particles are considered unsuitable for materials such as biomass. An investigation was made of relevant physical properties of four types of biomass: sweet sorghum bagasse, tobacco waste, soybean hulls and fiber sorghum bagasse. Three samples of each biomass with different granulometries were analyzed. Density values were determined. Particle shape and size distributions were evaluated by digital image analysis. It was observed that the moisture content affected the materials' true Density and for dried biomass the smaller the Particle sizes the higher the true Density. The results indicated that sweet sorghum bagasse Particles of different sizes have similar shapes; that the Particle roundness of the four types of biomass is a property more closely related with the characteristic shape of the material than with its granulometric classification; and that the granulometric classification of tobacco waste, soybean hull and fiber sorghum bagasse Particles can effectively influence the obtainment of Particles with higher or lower roundness. The average roundness varied from 0.45 to 0.70 and the aspect ratio from 1.90 to 2.60. The results obtained in this study are useful for numerical simulations of the fluid dynamics of pyrolysis, combustion and gasification processes and also for studies about the optimal operating conditions of mixture fluidization.