In internal flow, when a fluid flows inside a circular pipe, the most practical value of critical Reynolds number is taken as 2300. I was wondering if this number is also the same for non circular ducts? Does the critical Reynolds number of a duct will also be around 2300 for most practical cases?
$\begingroup$ The transition range is normally taken as 1700 to 2300 but laminar flow has been found outside these values under controlled conditions. $\endgroup$– Solar MikeAug 7, 2021 at 14:11
$\begingroup$ There are relatively simple scaling laws for arbitrary polygon shapes. Here's a paper: researchgate.net/publication/… $\endgroup$– Pete WAug 7, 2021 at 15:34
To my understanding, if a flow has a different geometry, such as flow in a square duct, or over a turbine blade, transition will occur at different values of Re.
Additionally another very important point is that in circular tube:
- if the flow is undisturbed (i.e. very smooth pipe walls) then the transition to transient flow is at much greater Re numbers
- if Re is less than 2000, then the flow will always be laminar even when it is disturbed.