Flow over large-scale low-order topographies: impact of heterogeneities
type: CreativeWork
description: A systematic experimental investigation was carried out to provide phenomenological and quantitative insight on the flow over large-scale topographies characterized by few dominant modes. Particle image velocimetry (PIV) was used in a refractive-index-matching (RIM) channel to study the dynamics of the flow over a series of topographies consisting of (i) 2D and 3D wavy walls and (ii) homogeneous and heterogeneous canopies. The focus of these experiments is to characterize and quantify the impact of specified heterogeneities on the mean flow field and turbulence quantities. In the first set of experiments, the surface heterogeneity is given by a single spanwise sinusoidal mode superimposed on a 2D wavy wall; this allowed to uncover the impact of topography three-dimensionality on the flow field. In the second set of experiments, the flow over an array of rigid elements with uniform height, i.e. homogeneous canopy, was compared to that over a heterogeneous canopy composed of elements with varied heights. The impact of three-dimensionality on the flow field over the wavy walls was investigated in multiple regimes, including developed and developing turbulent flows as well as the transition to turbulence. The results show that, within the developed region, the 3D wall induces distinctive spanwise flows within the topography that lead to drag and turbulence reduction compared with the 2D counterpart. In the developing regime, the turbulent boundary layer is highly sensitive to the large-scale topography. The integral parameters such as displacement and momentum thicknesses are significantly more modulated by the topography in the 2D case due to relatively larger pressure variations in the streamwise direction. The three-dimensionality of the topography also impacts the mechanisms by which the boundary layer transitions to turbulence. This phenomenon over the 2D topography occurs due to an inflection point in the velocity profile resulting from flow separation within the …
abstract: A systematic experimental investigation was carried out to provide phenomenological and quantitative insight on the flow over large-scale topographies characterized by few dominant modes. Particle image velocimetry (PIV) was used in a refractive-index-matching (RIM) channel to study the dynamics of the flow over a series of topographies consisting of (i) 2D and 3D wavy walls and (ii) homogeneous and heterogeneous canopies. The focus of these experiments is to characterize and quantify the impact of specified heterogeneities on the mean flow field and turbulence quantities. In the first set of experiments, the surface heterogeneity is given by a single spanwise sinusoidal mode superimposed on a 2D wavy wall; this allowed to uncover the impact of topography three-dimensionality on the flow field. In the second set of experiments, the flow over an array of rigid elements with uniform height, i.e. homogeneous canopy, was compared to that over a heterogeneous canopy composed of elements with varied heights. The impact of three-dimensionality on the flow field over the wavy walls was investigated in multiple regimes, including developed and developing turbulent flows as well as the transition to turbulence. The results show that, within the developed region, the 3D wall induces distinctive spanwise flows within the topography that lead to drag and turbulence reduction compared with the 2D counterpart. In the developing regime, the turbulent boundary layer is highly sensitive to the large-scale topography. The integral parameters such as displacement and momentum thicknesses are significantly more modulated by the topography in the 2D case due to relatively larger pressure variations in the streamwise direction. The three-dimensionality of the topography also impacts the mechanisms by which the boundary layer transitions to turbulence. This phenomenon over the 2D topography occurs due to an inflection point in the velocity profile resulting from flow separation within the …
author: Hamed, Ali Mohamed Mohamed
language: en
keywords: Turbulence, Boundary layer, Topography, Canopy flows, Environmental flows
date published: 2017-09-29T16:39:03Z
date modified: 2026-07-22T22:24:35Z
provider: University of Illinois - Urbana-Champaign
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Illinois at Urbana-Champaign

PropertyValue
property ID: Handle
value: http://hdl.handle.net/2142/98218