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  • 1
    Electronic Resource
    Electronic Resource
    The investigation of an unstable convective flow using optical methods (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 10 (1998), S. 2995-3008 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The convective flow field in a vessel is investigated by laser Doppler Anemometry (LDA) and Particle Image Velocimetry (PIV, namely Particle Tracking Velocimetry—PTV). The vessel is heated from below along a linear element at a temperature higher than that of the fluid. Hot fluid raises up and generates two counterrotating vortices. For a given aspect ratio, the two vortices become unstable and start to oscillate on a vertical plane (orthogonal to the heating element). This regime is investigated for increasing Rayleigh numbers to analyze the transition from regular to irregular conditions. The main transition mechanism is observed to be mostly connected to type II intermittency, a mechanism not frequently observed in experiments. However, at some Rayleigh numbers the present data does not definitely rule out type III intermittency. The phenomenon is analyzed by looking at the main frequencies in the spectrum of the horizontal velocity component and their changes with the Rayleigh number at a point above the heating element. Modifications in the local energy spectrum are analyzed by using the Wavelet Transform (WT) tool. Data obtained by PTV measurements make it possible to point out the spatial configuration of the flow and to determine the two velocity components on the measurement plane. These data are used to clarify the fundamental mechanisms of the transition. Instabilities are observed as sudden changes between two regimes of oscillations of the two counterrotating vortices: the first is characterized by oscillations centered on the vertical axis and the second by nonsymmetrical oscillations. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.869819
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  • 2
    Electronic Resource
    Electronic Resource
    Analysis of two-point velocity measurements in near-wall flows (1995)
    Springer
    Experiments in fluids 20 (1995), S. 68-83 
    Details
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Two-point measurements of the streamwise velocity in a turbulent channel flow are performed using laser-Doppler anemometry. High spatial and temporal resolutions (about 1 Kolmogorov microscale in space and time) are achieved. Data are obtained at several distances from the wall forRe δ in the range 1500–5000. Results from correlation functions are compared with the hypotheses of Taylor and Tennekes: they reproduce the experimental data even at low Reynolds numbers and small distances from the wall, providing that convection rather than mean velocity is used. Convection velocities are computed from transfer function phase diagrams: the ratio of convection to mean flow velocity is found to decrease with increasing Reynolds number and distance from the wall. Large flow structures are convected with the local mean velocity rather than the test section mean velocity; data at small Reynolds and close to the wall exhibit convection velocities lying between the two. The good agreement between the time evolution of the envelope of space-time-correlation function with the corresponding Lagrangian correlation over one integral time scale confirms the existence of a strict relation between the Eulerian and Lagrangian descriptions of turbulence.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01061584
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  • 3
    Electronic Resource
    Electronic Resource
    Evaluation of LDA temporal and spatial velocity structure functions in a low Reynolds number turbulent channel flow (1999)
    Springer
    Experiments in fluids 27 (1999), S. 368-377 
    Details
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  Measurements have been made using Laser Doppler Anemometry (LDA) in a fully developed turbulent channel flow with the aim of determining second-order and third-order temporal and spatial structure functions of the longitudinal velocity fluctuation. A reliable determination of these moments requires the data to be corrected for the effect of noise. Correction procedures are outlined, based on the behaviour of temporal or spatial correlation functions in the limit of small time intervals or small separations. No a priori assumptions about the nature of the noise are made so that the procedure should be quite general. The corrected LDA data indicate that, especially for spatial separations, the effect of noise can be felt even within the inertial range. The corrected structure functions should allow an unambiguous assessment to be made of Taylor’s hypothesis and of the extended self-similarity (ESS) method; examples are given in each case. Temporal structure functions obtained by hot wire anemometry (HWA) are much less affected by noise than the LDA data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003480050361
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  • 4
    Electronic Resource
    Electronic Resource
    Investigation of the near wake of a propeller using particle image velocimetry (2000)
    Springer
    Experiments in fluids 29 (2000), S. S227 
    Details
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The investigation of a propeller wake is carried out in a cavitation tunnel using particle image velocimetry. To achieve high spatial resolution, a multigrid adaptive cross-correlation algorithm is used for image analysis. The contributions of the viscous wake, originated by the boundary layer on the blades of the trailing vortex sheets, as well as of the vorticity distribution are resolved and discussed for different angular positions of the blade. The near wake flow is characterised by strong deformations, due to the bending of the blade wake sheets, to the contraction of the slipstream and to the trajectory of the tip vortex. The turbulent diffusion and the viscous dissipation rapidly lead to broadening and decay of the trailing edge wake. Furthermore, secondary tip vortex structures are also pointed out.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003480070025
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  • 5
    Electronic Resource
    Electronic Resource
    Experimental testing of Taylor's hypothesis by L.D.A. in highly turbulent flow (1991)
    Springer
    Experiments in fluids 11 (1991), S. 351-358 
    Details
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A new configuration for the transmitting optics of a laser Doppler anemometer has been developed in order to measure the velocity at two different points at the same time. From the simultaneous measurements at two points along the mean flow direction it is possible to evaluate the spatial correlations and to compare them with the temporal correlation to verify the validity limits of Taylor's hypothesis also known as the frozen turbulence hypothesis. The transfer function between the velocity signals at two different points has been introduced to better explain the differences between Taylor's hypothesis and non frozen flow. The analysis is carried out in a flow with high turbulence levels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00211789
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  • 6
    Electronic Resource
    Electronic Resource
    Analysis of two-point velocity measurements in near-wall flows (1995)
    Springer
    Experiments in fluids 20 (1995), S. 68-83 
    Details
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Two-point measurements of the streamwise velocity in a turbulent channel flow are performed using laser-Doppler anemometry. High spatial and temporal resolutions (about 1 Kolmogorov microscale in space and time) are achieved. Data are obtained at several distances from the wall for Re δ in the range 1500–5000. Results from correlation functions are compared with the hypotheses of Taylor and Tennekes: they reproduce the experimental data even at low Reynolds numbers and small distances from the wall, providing that convection rather than mean velocity is used. Convection velocities are computed from transfer function phase diagrams: the ratio of convection to mean flow velocity is found to decrease with increasing Reynolds number and distance from the wall. Large flow structures are convected with the local mean velocity rather than the test section mean velocity; data at small Reynolds and close to the wall exhibit convection velocities lying between the two. The good agreement between the time evolution of the envelope of space-time-correlation function with the corresponding Lagrangian correlation over one integral time scale confirms the existence of a strict relation between the Eulerian and Lagrangian descriptions of turbulence.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00189296
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  • 7
    Electronic Resource
    Electronic Resource
    A comment on the “linear” law of the wall for fully developed turbulent channel flow (1998)
    Springer
    Experiments in fluids 25 (1998), S. 165-170 
    Details
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  In fully developed turbulent channel or pipe flows, the validity of a viscous sublayer with a quadratic mean velocity profile strictly requires the gradient of the Reynolds shear stress to be negligible compared to the gradient of the viscous shear stress. Direct numerical simulations suggest that this requirement is satisfied only in the limit y +→0. The use of a quartic, instead of quadratic, profile represents the available numerical and experimental mean velocity data satisfactorily in the region y +〈10.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003480050221
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  • 8
    Electronic Resource
    Electronic Resource
    Investigation on time scales in a low Reynolds number jet flow using particle-tracking velocimetry (1996)
    Springer
    Flow, turbulence and combustion 56 (1996), S. 209-220 
    Details
    ISSN: 1573-1987
    Keywords: jet ; image analysis ; Lagrangian statistics ; time scales
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The near flow field of an axisymmetric water jet at Reynolds numbers between 2000 and 5000 is investigated using Particle-Tracking Velocimetry. Measurements are taken in the longitudinal section (along the mean flow) and in cross-sections (orthogonal to the mean flow). From the former, correlation coefficients of the two in-plane velocity components in a Lagrangian framework are obtained: thus Lagrangian integral scales can be computed. Those of the streamwise velocity (axial) component increase on moving away from the centreline, whereas the opposite happens for the vertical velocity (radial) component: integral time scales of the two components are almost equal at the interface between jet and ambient fluids. On the other hand, integral scales are almost constant or increase slightly with the axial direction. In cross-sections, fluid ejection and injection from the jet centreline are observed to be connected to counter-rotating vortices (“mushroom”): their number and size change with Reynolds number in agreement with results from other authors. The maximum ejection velocity (orthogonal to the mean jet flow), at 3 nozzle diameters downstream of the outlet, is found to be one half of the mean outlet velocity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02249382
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  • 9
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    Aeroacoustics and aerodynamics of impinging supersonic jets: Analysis of the screech tones (2013)
    American Institute of Physics
    Details
    Publication Date: 2013-08-01
    Print ISSN: 1070-6631
    Electronic ISSN: 1089-7666
    Topics: Physics
    Published by American Institute of Physics
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  • 10
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    Investigation on time scales in a low Reynolds number jet flow using particle-tracking velocimetry (1996)
    Springer
    Details
    Publication Date: 1996-06-01
    Print ISSN: 1386-6184
    Electronic ISSN: 1573-1987
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Springer
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