turbulent Reynolds number
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It is well known that the laminar Reynolds number is below 2000. The turbulent Reynolds number can be over 4000 in some cases, but it can also be 10^4 in other cases. Can someone explain why there are two different values?
Japan allows marriage at the age of 18, while China requires women to be at least 20, based on the perceived level of maturity. After the Reynolds number exceeds 20, there is also an issue related to the development of turbulence; a low Re value indicates that the development is not sufficient. A value greater than 10,000 is generally considered to indicate fully developed turbulence.
1. Re〈2000 is the laminar flow region； 2. 2000 < Re < 4000 is the transition zone ； 3. Re > 4000 is the turbulent region.
A value greater than 10,000 generally indicates fully turbulent flow; in such cases, the friction coefficient of the pipe can be considered independent of the Reynolds number and dependent only on the relative roughness. In heat and mass transfer calculations, the application conditions of many formulas require a Reynolds number greater than 10,000; therefore, such a requirement is justified.
Reply to 2# Regular of the Drunken Land: Brother, your analogy is truly vivid, apt, concise, clear, and to the point!
Great question! The numerical criterion for laminar-to-turbulent transition is merely a matter of experience, or rather it is determined by experiments. For Re4000, turbulence generally occurs in flow within the pipe, but when calculating the convective heat transfer coefficient, a value of Re>10000 is specified; this is determined primarily based on the applicable range of the fitting formula (or rather, the experimental range of the researchers).