The turbulent stresses are unknown a priori and must

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Unformatted text preview: ontents | Study Guide 6.3 Semiempirical Turbulent Shear Correlations 335 y y y = δ (x) U(x) Outer turbulent layer τ (x, y) τ turb u (x, y) Overlap layer τ lam Viscous wall layer Fig. 6.8 Typical velocity and shear distributions in turbulent flow near a wall: (a) shear; (b) velocity. τ w(x) 0 (a) (b) geometry and flow conditions, as detailed in Refs. 1 to 3. Fortunately, in duct and boundary-layer flow, the stress u associated with direction y normal to the wall is dominant, and we can approximate with excellent accuracy a simpler streamwise momentum equation du dt u y where p x gx u (6.15) y lam turb (6.16) Figure 6.8 shows the distribution of lam and turb from typical measurements across a turbulent-shear layer near a wall. Laminar shear is dominant near the wall (the wall layer), and turbulent shear dominates in the outer layer. There is an intermediate region, called the overlap layer, where both laminar and turbulent shear are important. These three regions are labeled in Fig. 6.8. In the outer layer turb is two or three orders of magnitude greater than lam, and vice vers...
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This note was uploaded on 10/27/2009 for the course MAE 101a taught by Professor Sakar during the Spring '08 term at UCSD.

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