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

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.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Mechanical Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2019

Author dc:creator

• Colombo Baeza, Matias

Contributors dc:contributor

• Chamorro, Leonardo

• low-order topographies, wavy walls, sinusoidal waves, roughness, POD, quadrant analysis

Statement dc:rights

• Copyright 2019 Matias Colombo Baeza

Language dc:language

en

Handle dc:identifier

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

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/105260