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Abstract

Most flows encountered in engineering practice are turbulent and therefore require different treatment. Turbulent flows are characterized by the following properties:

  • Turbulent flows are highly unsteady. A plot of the velocity as a function of time at most points in the flow would appear random to an observer unfamiliar with these flows. The word ‘chaotic’ could be used but it has been given another definition in recent years.

  • They are three-dimensional. The time-averaged velocity may be a function of only two coordinates, but the instantaneous field fluctuates rapidly in all three spatial dimensions.

  • They contain a great deal of vorticity. Indeed, vortex stretching is one of the principal mechanisms by which the intensity of turbulence is increased.

  • Turbulence increases the rate at which conserved quantities are stirred. Stirring is a process in which parcels of fluid with differing concentrations of at least one of the conserved properties are brought into contact. The actual mixing is accomplished by diffusion. Nonetheless, this process is often called turbulent diffusion.

  • By means of the processes just mentioned, turbulence brings fluids of differing momentum content into contact. The reduction of the velocity gradients due to the action of viscosity reduces the kinetic energy of the flow; in other words, mixing is a dissipative process. The lost energy is irreversibly converted into internal energy of the fluid.

  • It has been shown in recent years that turbulent flows contain coherent structures-repeatable and essentially deterministic events that are responsible for a large part of the mixing. However, the random component of turbulent flows causes these events to differ from each other in size, strength, and time interval between occurrences, making study of them very difficult.

  • Turbulent flows fluctuate on a broad range of length and time scales. This property makes direct numerical simulation of turbulent flows very difficult. (See below.)

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© 2002 Springer-Verlag Berlin Heidelberg

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Ferziger, J.H., Perić, M. (2002). Turbulent Flows. In: Computational Methods for Fluid Dynamics. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-56026-2_9

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  • DOI: https://doi.org/10.1007/978-3-642-56026-2_9

  • Publisher Name: Springer, Berlin, Heidelberg

  • Print ISBN: 978-3-540-42074-3

  • Online ISBN: 978-3-642-56026-2

  • eBook Packages: Springer Book Archive

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