Flow in a stream can be described as either laminar or turbulent Laminar flow in
ID: 116595 • Letter: F
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Flow in a stream can be described as either laminar or turbulent Laminar flow involves streamlined flow of water particles along parallel paths, with streamlines remaining distinct and with no mixing between streamlines. Strictly speaking, perfectly lamina flow flow occurring in erratic paths at varying speed. Flow in streams is almost always turbulent. is never found in streams. Turbulent flow involves complex mixing of water, with The onset of distinctly turbulent flow from relatively laminar flow can be roughly predicted for a is a dimensionless parameter (and one of the most important parameters in the discipline of fluid dynamics) that is given by the following equation Rn (R vel)/v where Rn Reynolds number; R hydraulic radius (A/P-) (given in m), vel mean flow velocity (m/s), and v (ie., nu)-kinematic viscosity (m2/s) (note: there are different types of viscosity and thus different forms of the Reynolds equation, kinematic viscosity -v- / (that is, kinematic viscosity equals the dynamic viscosity (mu) in Pascal seconds divided by density in kg per m)). For streams with non-turbid aqueous conditions, the v value varies only slightly with temperature and can be treated as a constant (vw.ter-1 * 1o-m?/s-0.000001 /s; vaa to'o.-1 . 103 m-0.001 /s). Hydraulic radius (R) is sometimes replaced by stream depth (h) to simplify Rn calculations, although in this lab exercise we'll use R The Reynolds number (Rn) can be used to distinguish flow of approximately laminar character from flow of turbulent character (with transitional flow taking place between the two extremes) using the following rules of thumb: Values typical of relatively laminar flow: Values typical of turbulent flow: Rn 1200 Note that natural streams typically have Reynolds numbers far above 1200 (i.e, values of millions); low values are only associated with certain types of sheet flow or environments such as wetlands. Note also that the Reynolds number about which the transition between laminar and turbulent flow takes place -the "critical Rn"- is difficult to predict precisely and thus must normally be determined experimentally for a given system. Laminar flow Turbulent flow Figure 6 Dye injected into flowing fluid characterized by both laminar (left) and turbulent (right) flow (W.H. Freeman and CompanyExplanation / Answer
6. A) Depth = 2m = R
Vel = 3 m/s
v = 0.0000001 m2/s
Rn = (R * Vel)/ v = 6 /10-6 = 6,000,000
B) Rn = 500
Vel = 3 m/s and R= 2 m
Rn = (R * Vel)/ v
v = (3 * 2)/500 = 0.012 m2/s
C) Caster bean 0.001 m2/s
Honey = 0.01 m2/s
Calculcated v = 0.012 m2/s
The calculated viscosity is similar to honey and much higher than the caster bean viscosity.
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