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How to calculate Reynolds number in Fluent or cfx

- March 4, 2025 at 4:36 am
  
  rahul_kv
  Subscriber
  
  I want to calculate Reynolds number in the geometry attached below, but I am confused about how to calculate the Reynolds number using Fluent?
  As Re=(fluid density*fluid velocity*characteristic length)/dynamic viscosity, should i consider the characteristic length as inlet dia of flow (i.e., Dia of outer pipe - dia of small circular pipe) or it should be different ?
- March 4, 2025 at 3:43 pm
  
  V.P
  Ansys Employee
  
  Hi Rahul,
  In ANSYS Fluent and CFX, the Reynolds number (𝑅𝑒) is not always directly available, but you can calculate it using the standard formula.
  Regarding the annulus flow, I think the formula you have is correct.
- March 4, 2025 at 4:45 pm
  
  rahul_kv
  Subscriber
  
  Thanks for reply, but I got confused as fluent show us turbulent reynolds number, should I rely on that or not, And moreover in fluent I can see molecular viscosity, turbulent viscosity, effective viscosity . Which one should I consider as dynamic viscosity for analytically calculating reynolds number ?

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