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?
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.