A study of turbulent wakes with and without the presence of free stream turbulence.
Item
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Title
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A study of turbulent wakes with and without the presence of free stream turbulence.
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Identifier
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AAI9325065
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identifier
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9325065
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Creator
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Ardebili, Mahmoud Khosro.
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Contributor
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Adviser: Rishi Raj
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Date
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1993
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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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Physics, Fluid and Plasma | Engineering, Mechanical | Engineering, Aerospace
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Abstract
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The objective was to investigate symmetric and asymmetric turbulent wakes subjected to free stream turbulence. The wake environment was generated experimentally by using a modified airfoil. Symmetric wake was simulated by merging of two similar boundary layers on two sides of the model into wake. Asymmetric wake was simulated by merging of dissimilar boundary layers on the two sides of the model. Free stream turbulence was generated by placing grids upstream of the model. The mean velocity was obtained with the aid of pressure measurement, and the turbulence quantities were obtained by using hot-wire anemometry.;In order to assess the ability of K-{dollar}\varepsilon{dollar} and Reynolds stress models to predict turbulent wake under varying free stream conditions, the wake governing equations for the closure models were numerically solved by a second order accurate, parabolic, forward marching finite difference method.;The mean velocity and its flow properties of symmetric and asymmetric wakes were affected by the presence of free stream turbulence. The recovery rate increased while shape factor decreased with higher level and larger length scale of the free stream turbulence. The displacement thickness and half-wake width became larger under moderate free stream turbulence, and decreased with higher free stream turbulence.;The free stream turbulence affected the turbulence structure of the wake. Increase in the level and length scale of the free stream turbulence increased the level of turbulence quantities in the wake. It affected outer layer of wake, while the inner core of the wake essentially remained unaffected.;The K-{dollar}\varepsilon{dollar} model and Reynolds stress model of turbulence closure resulted in acceptable prediction of mean velocity throughout the wake. However in far wake the turbulence quantities predicted with the K-{dollar}\varepsilon{dollar} model are closer to the experimental data than predictions with Reynolds Stress model. The turbulence quantities of wake were predicted with maximum average deviation of 23% in asymmetric wake, and 24% in symmetric wake from the experimental data.;The mean velocity of asymmetric wake under free stream turbulence was predicted successfully with Reynolds stress model, with maximum average deviation of 2% from the experimental data. The maximum average deviation of turbulence quantities from the experimental data was 23%. These deviations increased with increases in the free stream turbulence.;There was too much uncertainty in the estimate of dissipation rate used as initial condition in the wakes for the closure models to be tested with certainty.
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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.
