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  • 1
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    Measurements in a subsonic turbulent jet using a quantitative schlieren technique (1971)
    Cambridge University Press
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    Publication Date: 1971-04-27
    Description: The development of optical methods for the quantitative study of the fluctuating properties of turbulent flows can provide a supplement to conventional hot-body anemometry techniques. In particular, the study of high-speed flows by hot-wire or hot-film anemometry is often difficult owing to the presence of temperature and velocity fluctuations in the flow, thereby complicating the correct interpretation of measured signals. In addition, restrictions are placed on the application of such anemometers by their physical strength, frequency-response characteristics and the introduction of disturbances by the measuring probes into the flow. The operation of an optical detection system depends primarily on the mechanism by which the detected radiation intensity is modulated by the flow. Methods which have been used successfully include scattering or absorption of incident light by tracer constituents or particles, the absorption or emission of infra-red radiation by the flow and quantitative adaptations of the schlieren and interferometer systems which are sensitive to the flow density structure. All these systems detect a summation of signals from different parts of the flow and in consequence it is necessary to consider in detail the relation of the integrated signal to the local properties of the flow. This paper deals in particular with the application of the schlieren principle to an axisymmetric turbulent jet. © 1971, Cambridge University Press. All rights reserved.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 2
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    Shear fluctuations in a turbulent jet shear layer (1979)
    Cambridge University Press
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    Publication Date: 1979-07-01
    Description: The initial development of turbulence in the shear layer of a circular jet is observed to show disturbances of increasing scale at discrete frequencies in an approximate 4:2:1 sequence. These are completely confined within the laminar shear layer and convect at 0·59 of the jet velocity. Such relatively regular behaviour was not observed once the disturbances became larger in transverse dimension than the laminar shear layer. In the development of the subsequent turbulent shear layer it was found that the fluctuating turbulent shear did not scale with local mean shear, but rather scaled more closely with the minus half power of distance from the apparent origin of the laminar shear layer emanating from the nozzle. The scale of the shear fluctuations departed from growth in proportion to shear layer thickness, remaining almost constant. In these aspects it appears that the turbulent shear layer is not well described by a similar growth with axial distance. The shear fluctuations convected at a speed closer to the local mean velocity than do velocity fluctuations and showed a relatively more patchy distribution with a distinct rotational sense and no reversal of skewness across the layer. Velocity fluctuations showed phase lags approaching [formula ommited] relative to shear fluctuations suggesting that dominant velocity disturbances are those associated with entrainment behind concentrations of rotation. © 1979, Cambridge University Press. All rights reserved.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 3
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    Quantitative schlieren measurements in a supersonic turbulent jet (1972)
    Cambridge University Press
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    Publication Date: 1972-02-08
    Description: This paper describes the results of a series of measurements made using a single beam schlieren system to investigate the density fluctuations present in the initial region of a supersonic axisymmetric turbulent jet with a Mach number of 1-82 in the flow a t the nozzle exit. A preheater was used to reduce the difference between the jet static temperature and that of the surrounding air to a relatively low level. The results show that significant density fluctuations are present in the potential core of the jet and that the distribution of fluctuating intensity across the shear layer differs from that obtained with a subsonic jet without preheating. © 1972, Cambridge University Press. All rights reserved.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 4
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    Structural development of gas-liquid mixture flows (1976)
    Cambridge University Press
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    Publication Date: 1976-01-13
    Description: The paper describes an experimental study of the structure of air-water mixtures flowing vertically. Resistivity probe techniques were applied to measurements of local void properties, including void fraction, gas-phase convection velocity, bubble size distributions and space-time correlation functions. The axial development of flows for six different air-water mixing conditions were examined. Measurements up to 108 diameters from inlet indicated that, while flow patterns for the different mixers may be significantly different initially, the flows tend to develop towards a common structure determined only by the flux rates of the two phases. This was evidenced by the convergence of the void and velocity profiles, and particularly the bubble size distributions, as the flow developed. Estimates of bubble sizes for these more developed conditions, based on a balance of energy between the interfacial structure and the turbulent structure, gave values of diameters which were on average 13% above experimental values. The void distributions obtained for bubbly flow conditions, after an adequate settling length, appear to be characterized by a local minimum at the centre of the pipe. © 1976, Cambridge University Press. All rights reserved.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 5
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    Coherence between large-scale jet-mixing structure and its pressure field (1982)
    Cambridge University Press
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    Publication Date: 1982-03-01
    Description: A schlieren system has been arranged to sense the total fluctuation over a cross-section of the flow and thus becomes very sensitive to large-scale azimuthally coherent structures in the flow. For a natural unexcited jet it is found that there is a concentration of the large-scale structure at a characteristic Strouhal number which is not sensitive to the beam thickness and which reduces progressively with distance from the nozzle. This large-scale structure exhibits a coherence of over 70 % with the near-field pressure and convects at between 75 % and 95 % of the jet velocity. The coherence between the potential core-pressure field and the large-scale structure downstream increases rapidly with distance from the nozzle exit plane, rather limited coherence being found at the exit plane for these observations at a jet-exit Mach number M¡ = 0.7. Movement of a central microphone from x = 0 to x = 2D introduced a solid centre body over the first 2.5 diameters of flow and gave rise to a set of discrete components in the flow structure in the range 0.6 〈S〈1.4. With harmonic excitation at S = 1.12 a subharmonic at S = 0.55 occurs at x/D = 3 and a second at 8 = 0.26, x/D = 6. The flow cross-sectional-average sensing thus appears to show up the vortex-pairing mechanism at greater distances from the nozzle than is easily detectable by other means. Under strong impulse excitation a set of discrete components was observed in a transient response extending over times of 400D/U¡. These had a strongest component which decreases more rapidly in Strouhal number with distance than that associated with natural or harmonically excited conditions. © 1982, Cambridge University Press. All rights reserved.
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    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 6
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    Intensity, scale and convection of turbulent density fluctuations (1975)
    Cambridge University Press
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    Publication Date: 1975-08-12
    Description: This paper extends the quantitative schlieren technique to the separate determination of the local scales and intensity of turbulent density fluctuations. Measurements in an unheated supersonic jet are also extended to positions substantially further away from the jet than those reported hitherto, and show that high levels close to the nozzle reduce to levels comparable to subsonic velocity fluctuations beyond 18 diameters from the nozzle exit. Trends for the integral scales are similar to those based on subsonic jet velocity fluctuations. Separated-beam measurements show reflexion of disturbances on the jet centre-line just beyond the potential core. Spectra show a more peaked form close to the jet, and exhibit a rapid decrease in level with wavenumber. © 1975, Cambridge University Press. All rights reserved.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 7
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    Jet diffusion from a circular nozzle above a solid plane (1980)
    Cambridge University Press
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    Publication Date: 1980-11-13
    Description: The decay of a jet discharging from a circular nozzle parallel to and displaced from a solid surface is investigated under conditions where the transitional process from circular-jet flow to oblate wall-jet flow begins in the initial, transition or self-preserving regions of the original jet. The influence of displacement of the nozzle from the plane on the developed three-dimensional wall jet downstream is demonstrated and it is found that the transitional interaction with the plane is more extended when the plane interacts first in the initial zone of the circular jet. Measurements of turbulence and Reynolds stress show the transverse mixing parallel to the plane to exceed that perpendicular to the plane, and are generally consistent with the spreading rates in these two directions, the ratio of which approaches 8·5 at large distances from the nozzle. It is shown that the interaction between the plane and jet involves a relatively large-scale coherent motion in which components of velocity directed towards or away from the surface are associated with outflow or inflow along the surface. This motion is more extended in the direction parallel to the surface and provides a mechanism for the increases in mixing rate in the direction parallel to the plane. © 1980, Cambridge University Press. All rights reserved.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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