Turbulence in Open Channel Flows

Hiroji Nakagawa, Iehisa Nezu, Hiroji Nakagawa

• Publisher: Routledge
• Year: 2017
• Print ISBN: 9789054101185
• eBook ISBN: 9781351406604
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

A review of open channel turbulence, focusing especially on certain features stemming from the presence of the free surface and the bed of a river. Part one presents the statistical theory of turbulence; Part two addresses the coherent structures in open-channel flows and boundary layers.

PART 1

Statistical structures of turbulence

CHAPTER 1

Introduction

1.1 INTRODUCTORY REMARKS

Real flows are usually classified into the two categories of laminar flow and turbulent flow. Because almost all geophysical flows are turbulent, one of the most important topics in hydraulics and fluid mechanics is a clarification of the structure of turbulence and the associated transport of momentum, heat and mass. A general theoretical solution for turbulent flows has not been obtained because the governing equations of turbulence, the Navier-Stokes equations, have both non-linear and chaotic features.

In concrete terms, geophysical turbulent flows in nature occur in rivers, lakes, estuaries and oceans. Almost all of flows in man-made hydraulic structures, such as spillways, weirs, conveyance channels, irrigation networks, water supply systems, sewers, harbors and fluvial works, are turbulent. Therefore, it is indispensable in hydraulic engineering to investigate structures of ‘Open-channel turbulence’ in order to evaluate friction laws, to control turbulent flows and to design hydraulic structures properly; they are also needed to solve the associated transport phenomena for sediment, various waste waters and in other polluting processes.

Comparable needs exist for air flows in mechanical and aerodynamic engineering and atmospheric environmental science. Intensive research on the dynamics of wall turbulence in boundary layers, pipes and closed channels for air flows has been performed by many investigators in the last forty years, i.e., since the 1950’s, a much longer time than for open-channel turbulence in flowing water. Thus, enormous corpus of literature resulting from theoretical and experimental investigations on solid-wall turbulence in air tunnels is now available. Summaries and reviews of this literature are given in the well-known monographs written by Monin & Yaglom (1971, 1975), Tennekes & Lumley (1972), Rotta (1972), Hinze (1975), Townsend (1976), Bradshaw (1976), Schlichting (1979), Tani (1980, 1984), Tatsumi (1986), Landahl & Mollo-Christensen (1986) and others.

In contrast, turbulence measurements in water flows were begun only twenty years ago, with the development of hot-film anemometers and flow visualization techniques like the hydrogen-bubble method. In the 1980’s, much more accurate measurements of water flows became feasible with the laser-Doppler anemometer. Consequently, standard data for open-channel turbulence that can be compared with standard data of boundary layers and closed channels, is just becoming available. Thus, physical explanation and understanding of open-channel turbulence are now being made quantitatively, as well as in a qualitative sense, although many unknown features remain to be clarified.

This monograph is a review of the findings of open-channel turbulence obtained in the last twenty years. To explain why this research has not progressed further, in spite of the importance of turbulence research in open-channel flows, the authors first present a brief history of turbulence research, including air turbulence. The following section gives the purpose and scope of this monograph.

1.2 BRIEF HISTORY OF TURBULENCE RESEARCH

Many huge and marvelous hydraulic works such as dams, weirs, fluvial works, irrigation networks and water supply systems, had been already constructed before the Renaissance, the age that opens with Leonardo da Vinci (1452–1519) and ends with Galileo (1564–1642) and Castelli (1577–1644), according to Rouse & Ince (1957) and Fasso (1987). Many water supply systems were constructed in the old Roman age; an outstanding example is the stone bridge for water supply, the Pont du Gard, in the southern France, a famous monument even now. In China, the flood control of the Yellow River was the most important civil project. Since the construction of waterways was closely related to the regulation of rivers, the connection of the water c...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• FOREWORD
• PREFACE
• PART 1: STATISTICAL STRUCTURES OF TURBULENCE
• PART 2: COHERENT STRUCTURES IN OPEN-CHANNEL FLOWS
• REFERENCES
• SUBJECT INDEX