29. Features of turbulent flows and approaches to their simulation

This lecture starts with a brief introduction to the main properties of turbulent flows: unsteadiness, three-dimensionality, vorticity, stirring, dissipation, coherent structures, broad range of length and time scales, and Reynolds-number dependence.
Next, the phenomena associated with the transition from laminar to turbulent flow regime are described: natural, bypass, and separation-induced transition. Examples from experiments and simulations are used to highlight the main features.
In engineering applications turbulence is sometimes desired (e.g., to improve mixing or heat transfer), but sometimes we try to avoid it, or at least to control it (e.g., to reduce noise or vibrations). Practical examples are used to emphasize the main points.
Finally, the main approaches to studying turbulence are described: empirical correlations, measurement techniques, and numerical simulations.
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