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Title:On the modulation of low-order roughnesses on the flow over low-order topographies
Author(s):Colombo Baeza, Matias
Advisor(s):Chamorro, Leonardo
Department / Program:Mechanical Sci & Engineering
Discipline:Mechanical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):low-order topographies, wavy walls, sinusoidal waves, roughness, POD, quadrant analysis
Abstract:The impact of low-order roughness on low-order topographies was experimentally explored using high-resolution particle image velocimetry in a refractive-index-matching channel at Reynolds numbers Re = 40,000, based on the channel half height and the bulk velocity. The topographies consisted on 2D and 3D sinusoidal waves, which spanned most of the test section. The roughnesses also consisted on the same waveforms but one order of magnitude smaller than the topographies. We focused on 2D-2D and 3D-3D roughness-topography configurations. The flow statistics are compared with hydrodynamically smooth wavy topographies to get insight on the effects of the 2D and 3D roughnesses. Inspection of the flow statistics reveal that the low-order roughness induced changes in the velocity fluctuations near the wall; mean flow was not substantially modified. In particular, the Reynolds stress decomposition via quadrant analysis revealed that the 2D roughness reduced the sweeps and ejections in the 2D topography; however, negligible changes occurred in the 3D case. Inspection of the flow fluctuations with Proper orthogonal decomposition at various spatial regions revealed that the 3D roughness increased the complexity of the flow, attributed possibly to the generation of small-scale motions located within the troughs.
Issue Date:2019-04-25
Rights Information:Copyright 2019 Matias Colombo Baeza
Date Available in IDEALS:2019-08-23
Date Deposited:2019-05

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