Is Reynolds number ρvD/μ or ρvR/μ?

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Homework Statement


https://en.wikipedia.org/wiki/Reynolds_number#Flow_in_a_pipe

In this link , i was told that Reynold number = ρvD / μ ,

However in the notes below , i was told that Reynold number = ρvR / μ .

Homework Equations

The Attempt at a Solution


I think Reynold number = ρvR / μ is wrong , because i learned that Reynold number = ρvD / μ in fluid mechanics , however , in the hydraulics notes , i was told that that Reynold number = ρvR / μ . I'm very confused now
 

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I agree. The characteristic length is the hydraulic diameter and it is confusing to use the term "hydraulic radius".
 
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fonseh said:

Homework Statement


https://en.wikipedia.org/wiki/Reynolds_number#Flow_in_a_pipe

In this link , i was told that Reynold number = ρvD / μ ,

However in the notes below , i was told that Reynold number = ρvR / μ .

Homework Equations

The Attempt at a Solution


I think Reynold number = ρvR / μ is wrong , because i learned that Reynold number = ρvD / μ in fluid mechanics , however , in the hydraulics notes , i was told that that Reynold number = ρvR / μ . I'm very confused now
It doesn't really matter, as long as the meaning is established within the context of the system being analyzed. Anyway, it's Reynolds number, not Reynold number.
 
BvU said:
I agree. The characteristic length is the hydraulic diameter and it is confusing to use the term "hydraulic radius".
So , which is correct ? ρvD / μ or ρvR / μ ??
 
BvU said:
I agree. The characteristic length is the hydraulic diameter and it is confusing to use the term "hydraulic radius".
So , do you mean ρvD / μ is correct ? and ρvR / μ is wrong ?
 
fonseh said:
So , do you mean ρvD / μ is correct ? and ρvR / μ is wrong ?
Both are correct, depending on how it is used.
 
Chestermiller said:
Both are correct, depending on how it is used.
Can you explain further when we need to use ρvD / μ or ρvR / μ ?
 
fonseh said:
Can you explain further when we need to use ρvD / μ or ρvR / μ ?
In a given problem, you just need to specify which definition is being used. For example, the laminar-turbulent transition occurs at ##\rho v D/\mu=2100## for flow in a pipe, but it also occurs at ##\rho v R/\mu=1050##. So you have to tell which definition of the Re you are using.