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Title:  Velocity moment analysis on oscillatory flow above selfformed vortex ripples 
Author(s):  Wu, Heng 
Advisor(s):  Garcia, Marcelo H. 
Department / Program:  Mechanical Sci & Engineering 
Discipline:  Mechanical Engineering 
Degree Granting Institution:  University of Illinois at UrbanaChampaign 
Degree:  M.S. 
Genre:  Thesis 
Subject(s):  Oscillatory flow
Velocity moments 
Abstract:  This thesis investigated the flow characteristics of oscillatory flow above selfformed vortex ripples. Using the data collected by Admiraal et al. (2006), phaseaveraged and timeaveraged mean velocities, rootmeansquare speeds, turbulent kinetic energy, Reynolds shear stress, and higher order velocity moments including skewness factors, flatness factors, and turbulent diffusion factors were studied for nine different Reynolds numbers. The study on phaseaveraged skewness factors indicated that the area of skewed streamwise velocity oscillated around the ripple. The wallnormal velocity is skewed to the negative near the ripple and positive away from it. The contours of streamwise and transverse turbulent diffusion factors are similar due to the comparable magnitude of rootmeansquare velocities in the two directions. All the nonzero regions of phaseaveraged velocity moments oscillated with the flow, suggesting that turbulence was transported by the oscillatory flow. There are no significant effects of Reynolds number among the nine experiments. For the timeaveraged variables, the asymmetry phenomenon (MusalemJara, 2006) is observed for streamwise mean velocity, Reynolds shear stress, streamwise skewness factor, streamwise flatness factor, streamwise and transverse turbulent diffusion factors. The timeaveraged turbulent kinetic energy was dominated by streamwise rootmeansquare velocity. In addition, from the skewness and flatness factors, it can be found that the timeaveraged streamwise velocity is close to a Gaussian distribution in the area above the ripple crest and deviates from it on either side of the ripple crest. The degree of deviation from Gaussian distribution of the timeaveraged wallnormal velocity increases with the wallnormal velocity. A band where the transverse velocity is closest to Gaussian distribution is near the crest of the ripple. 
Issue Date:  20140916 
URI:  http://hdl.handle.net/2142/50465 
Rights Information:  Copyright 2014 Heng Wu 
Date Available in IDEALS:  20140916 20160922 
Date Deposited:  201408 
This item appears in the following Collection(s)

Dissertations and Theses  Mechanical Science and Engineering

Graduate Dissertations and Theses at Illinois
Graduate Theses and Dissertations at Illinois