On the modulation of low-order roughnesses on the flow over low-order topographies

Colombo Baeza, Matias

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https://hdl.handle.net/2142/105260 Copy

Description

Title

On the modulation of low-order roughnesses on the flow over low-order topographies

Author(s)

Colombo Baeza, Matias

Issue Date

2019-04-25

Director of Research (if dissertation) or Advisor (if thesis)

Chamorro, Leonardo

Department of Study

Mechanical Sci & Engineering

Discipline

Mechanical Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(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.

Graduation Semester

2019-05

Type of Resource

text

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http://hdl.handle.net/2142/105260

Copyright and License Information

Copyright 2019 Matias Colombo Baeza

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