Chapt06

The changeover is called transition to turbulence in

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Unformatted text preview: r is called transition to turbulence. In Fig. 5.3a we saw that transition on the cylinder and sphere occurred at about Re 3 105, where the sharp drop in the drag coefficient appeared. Transition depends upon many effects, e.g., wall roughness (Fig. 5.3b) or fluctuations in the inlet stream, but the primary parameter is the Reynolds number. There are a great many data on transition but only a small amount of theory [1 to 3]. Turbulence can be detected from a measurement by a small, sensitive instrument such as a hot-wire anemometer (Fig. 6.29e) or a piezoelectric pressure transducer. The | v v 325 | e-Text Main Menu | Textbook Table of Contents | Study Guide 326 Chapter 6 Viscous Flow in Ducts u u Small natural disturbances damp quickly Fig. 6.1 The three regimes of viscous flow: (a) laminar flow at low Re; (b) transition at intermediate Re; (c) turbulent flow at high Re. u Continuous turbulence Intermittent bursts of turbulence t (a) t t (b) (c) flow will appear steady on average but will reveal rapid, random fluctuations if turbulence is present, as sketched in Fig. 6.1. If the flow is laminar, there...
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