Introduction to Convective Heat Transfer

9Foundations of Turbulent Flow

9.1 Introduction

Turbulent flow is very important in engineering applications. It involves in a large majority of fluid flow and heat transfer problems encountered engineering. Velocity, temperature, and pressure along with other properties change in time at every point in flow field. The governing equations of mass, momentum, and energy developed for laminar flows are also valid for turbulent flow; however, all three components of the velocity vector will be nonzero functions of the spatial coordinates and time. Velocity, temperature, and pressure along with other properties are instantaneous values in the equations. This makes the problem very complicated in turbulent flows. Turbulent flows are characterized by highly irregular fluctuations in velocity, temperature, pressure, and other properties. At each point, these properties fluctuate around a mean value. For this reason, mean and fluctuating components of velocity, temperature, pressure, and other properties are defined to simplify the problem. Turbulence is a very difficult topic to tackle; although it has been under study for more than a century, there is no single universal solution to problems encountered in turbulent flows.

On the other hand, direct numerical simulation (DNS) is very expensive, and at present, it is possible to use only in simple flow configurations. Key tools to study the turbulence are the time‐averaged equations of motion, continuity, and energy and experimental ...