# I Reynolds number of washing machine like object

1. Feb 9, 2017

### fahraynk

What would the reynolds number be for a closed pipe spinning like a washing machine? would the characteristic length be the diameter... if so why. Everything I have read is so vauge on this. How can I determine it for strange situations?

Can I skip it and figure out if flow is laminar or turbulent some other way?

2. Feb 9, 2017

### Staff: Mentor

Depends. Agitator or Spin cycle? Whites, Permanent Press, or Delicates?

3. Feb 9, 2017

The diameter would be one length scale you could pick. It really depends on the physics you hope to study, though. Choosing the length scale for calculating the Reynolds number is all about choosing one that is appropriate to the physics you are trying to describe.

4. Feb 9, 2017

### fahraynk

Well, sort of like a couette flow with a outer and inner cylinder but just remove the inner cylinder...
What would be the difference in this case between choosing the radius (since the velocity should be 0 in the center?) and choosing the diameter?

I was thinking it would be similar to a couette flow with 2 moving plates going in opposite directions?
Can you recommend something that will help me learn what I should consider when choosing a characteristic length? How did you get the hang of it?

I guess the only reason I need this is to know if I should do a sim in turbulent or laminar flow... I could just try it in both and see. .. but id rather learn how to choose. Plus a simulation could take all day. I tried running a simulation for regular 2d couette flow and once I went over 20 meters/sec the time to solve went up from 10 seconds to 3 hours and growing so fast...