The effect of the slope of irregularly distributed roughness elements on turbulent wall-bounded flows

Enrico Napoli, Armenio, Mauro De Marchis

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85 Citazioni (Scopus)

Abstract

Wall roughness produces a downward shift of the mean streamwise velocity profile in the log region, known as the roughness function. The dependence of the roughness function on the height and arrangement of roughness elements has been confirmed in several studies where regular rough walls were analysed; less attention has been paid to non-regular rough walls. Here, a numerical analysis of turbulent flows over irregularly shaped rough walls is performed, clearly identifying the importance of a parameter, called the effective slope (ES) of the wall corrugations, in characterizing the geometry of non-smooth irregular walls. The effective slope proves to be one of the fundamental geometric parameters for scaling the roughness function. Specifically, for a moderate range of roughness heights, both in the transitionally and in the fully rough regime, ES appears to scale the roughness function for a wide range of irregular rough geometric configurations. The effective slope determines the relative importance of friction drag and pressure drag. For ES similar to 0.15 we find that the friction contribution to the total wall stress is nearly in balance with the pressure-drag contribution. This value separates the region where the roughness function Delta U+ = f(ES) is linear from that where a smooth nonlinear behaviour is observed. In the cases investigated, value ES similar to 0.15 also separates the transitionally rough regime from the fully rough regime.
Lingua originaleEnglish
Numero di pagine10
RivistaDefault journal
Volume2008
Stato di pubblicazionePublished - 2008

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wall flow
Wall flow
roughness
Surface roughness
slopes
pressure drag
Drag
friction drag
Friction
Delta functions
delta function
turbulent flow
Turbulent flow
drag
numerical analysis
Numerical analysis
friction
velocity distribution
scaling
Geometry

All Science Journal Classification (ASJC) codes

  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

Cita questo

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title = "The effect of the slope of irregularly distributed roughness elements on turbulent wall-bounded flows",
abstract = "Wall roughness produces a downward shift of the mean streamwise velocity profile in the log region, known as the roughness function. The dependence of the roughness function on the height and arrangement of roughness elements has been confirmed in several studies where regular rough walls were analysed; less attention has been paid to non-regular rough walls. Here, a numerical analysis of turbulent flows over irregularly shaped rough walls is performed, clearly identifying the importance of a parameter, called the effective slope (ES) of the wall corrugations, in characterizing the geometry of non-smooth irregular walls. The effective slope proves to be one of the fundamental geometric parameters for scaling the roughness function. Specifically, for a moderate range of roughness heights, both in the transitionally and in the fully rough regime, ES appears to scale the roughness function for a wide range of irregular rough geometric configurations. The effective slope determines the relative importance of friction drag and pressure drag. For ES similar to 0.15 we find that the friction contribution to the total wall stress is nearly in balance with the pressure-drag contribution. This value separates the region where the roughness function Delta U+ = f(ES) is linear from that where a smooth nonlinear behaviour is observed. In the cases investigated, value ES similar to 0.15 also separates the transitionally rough regime from the fully rough regime.",
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TY - JOUR

T1 - The effect of the slope of irregularly distributed roughness elements on turbulent wall-bounded flows

AU - Napoli, Enrico

AU - Armenio, null

AU - De Marchis, Mauro

PY - 2008

Y1 - 2008

N2 - Wall roughness produces a downward shift of the mean streamwise velocity profile in the log region, known as the roughness function. The dependence of the roughness function on the height and arrangement of roughness elements has been confirmed in several studies where regular rough walls were analysed; less attention has been paid to non-regular rough walls. Here, a numerical analysis of turbulent flows over irregularly shaped rough walls is performed, clearly identifying the importance of a parameter, called the effective slope (ES) of the wall corrugations, in characterizing the geometry of non-smooth irregular walls. The effective slope proves to be one of the fundamental geometric parameters for scaling the roughness function. Specifically, for a moderate range of roughness heights, both in the transitionally and in the fully rough regime, ES appears to scale the roughness function for a wide range of irregular rough geometric configurations. The effective slope determines the relative importance of friction drag and pressure drag. For ES similar to 0.15 we find that the friction contribution to the total wall stress is nearly in balance with the pressure-drag contribution. This value separates the region where the roughness function Delta U+ = f(ES) is linear from that where a smooth nonlinear behaviour is observed. In the cases investigated, value ES similar to 0.15 also separates the transitionally rough regime from the fully rough regime.

AB - Wall roughness produces a downward shift of the mean streamwise velocity profile in the log region, known as the roughness function. The dependence of the roughness function on the height and arrangement of roughness elements has been confirmed in several studies where regular rough walls were analysed; less attention has been paid to non-regular rough walls. Here, a numerical analysis of turbulent flows over irregularly shaped rough walls is performed, clearly identifying the importance of a parameter, called the effective slope (ES) of the wall corrugations, in characterizing the geometry of non-smooth irregular walls. The effective slope proves to be one of the fundamental geometric parameters for scaling the roughness function. Specifically, for a moderate range of roughness heights, both in the transitionally and in the fully rough regime, ES appears to scale the roughness function for a wide range of irregular rough geometric configurations. The effective slope determines the relative importance of friction drag and pressure drag. For ES similar to 0.15 we find that the friction contribution to the total wall stress is nearly in balance with the pressure-drag contribution. This value separates the region where the roughness function Delta U+ = f(ES) is linear from that where a smooth nonlinear behaviour is observed. In the cases investigated, value ES similar to 0.15 also separates the transitionally rough regime from the fully rough regime.

KW - LES

KW - Rough-wall

KW - turbulent flow

UR - http://hdl.handle.net/10447/36207

M3 - Article

VL - 2008

JO - Default journal

JF - Default journal

ER -