WAKE BOUNDARY LAYER INTERACTION IN TURBOMACHINERY.
Item
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Title
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WAKE BOUNDARY LAYER INTERACTION IN TURBOMACHINERY.
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Identifier
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AAI8120764
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identifier
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8120764
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Creator
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PAL, SATYA.
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Contributor
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Chan M. Tchen
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Date
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1981
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Language
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English
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Publisher
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City University of New York.
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Subject
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Engineering, Mechanical
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Abstract
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The wake developed from the trailing edge of a thin and smooth flat plate including the effect of free stream turbulence was studied analytically as well as experimentally. The experimental measurements were taken in a low speed wind tunnel using cross-wire anemometry for three levels of free stream turbulence. Two levels of free stream turbulence were obtained at the leading edge of the flat plate using grids with square bars (T (TURN) 5.23%) and circular rods (T (TURN) 7.23%). The third level of free stream turbulence was obtained in the absence of the grid (T (TURN) 0.4%) because the wind tunnel had turbulence of the order of 0.4%. The grids were kept at a distance of 273 mm from the leading edge of the flat plate. Experimental results are presented on mean velocity profile, wake center line velocity, half wake width, displacement thickness, momentum thickness, energy thickness, shape factor, components of turbulence intensity and Reynolds stress. It is shown that the free stream turbulence increases the wake recovery and growth rates. The semi-empirical correlations are developed to predict the foregoing behavior. The analytical investigation also lead to the establishment of two turbulence parameters. These parameters simulate the effect of free stream turbulence on the wake velocity (U(,0)) and length (L(,0)) scales. Free stream turbulence increases the turbulence intensity and Reynolds stress in the wake. Correlations are developed to predict the decay behavior of turbulence quantities. These correlations depend upon the trailing edge conditions, free stream turbulence level, drag coefficient and distance downstream from the trailing edge. A self-preservation of wake has been taken as the basis for obtaining the correlations for turbulence quantities.;The wake boundary layer interacted flow was treated as three-dimensional. The order of magnitude analysis, and similarity considerations were used in the theoretical study. Decay laws for the mean velocity and growth laws for length scale were obtained. Theoretical study also lead to the development of three-dimensional turbulence interaction parameters. The wake developed from the trailing edge of a thin and smooth flat plate in the x-z plane interacted with the boundary layer developed on an artifically roughened flat plate in the x-y plane was studied experimentally for three axial spacings between the two plates. Experimental measurements were taken in a low speed wind tunnel using a triple sensor hot-wire probe. Experimental results are presented on three components of mean velocity, turbulence intensity, Reynolds stress and on wake width. The effect of spacing on the mean and turbulence quantities is also presented. Spectral measurements were taken in the inner region of the wake interacted boundary layer. Frequency energy spectra for three spacings were also measured with the help of a spectrum analyzer. The results on energy spectra are compared with available data on other types of flows. Axial, lateral and normal components of mean velocity defect decrease towards the inner region as well as with increase in spacing due to wake boundary layer interaction. Length scale increases towards the wall, with the increase in downstream distance and with the increase in spacing. Three components of turbulence intensity and Reynolds stress increase towards the wall, decrease towards the outer edge of the wake and with the increase in spacing in the interacting region. Correlation coefficient increases towards the inner region and decreases with the increase in downstream distance and with the increase in spacing.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
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Program
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Engineering
