Determining Turbulent or Laminar Flow in Regions with Varying Reynolds Numbers

lbj007 · September 24, 2023, 05:10

I encountered an issue while setting up the fluid model in Fluent. Suppose a pipeline has an inlet velocity satisfying a Reynolds number less than 2300. However, in certain corners within this region, the velocity corresponds to Reynolds numbers exceeding 2300. Should the model for this region rely solely on the inlet velocity to classify it as laminar flow, or should it be classified as turbulent flow because there are locations within the region where the velocity exceeds a Reynolds number of 2300?

LuckyTran · September 24, 2023, 12:24

The flow is turbulent or laminar by its own nature. No magic formula changes it.

Some parts of the universe maybe laminar and other parts may be turbulent. If you suspect certain regions to be turbulent then use a turbulence model there and use a laminar model in regions that are laminar. One model might not work for both cases, they rarely do.

lbj007 · September 24, 2023, 23:15

Thanks for the reply. I still wonder how to suspect certain regions to be turbulent. Is there a standard to determine whether a certain area is turbulent or is it based on experience? Alternatively, could I initially employ a laminar model to compute and examine the velocity vector map to see if there are any vortex regions as a means of identifying turbulence?

September 24, 2023, 05:10	Determining Turbulent or Laminar Flow in Regions with Varying Reynolds Numbers	#1
lbj007 Senior Member Join Date: Feb 2020 Posts: 114 Rep Power: 6	I encountered an issue while setting up the fluid model in Fluent. Suppose a pipeline has an inlet velocity satisfying a Reynolds number less than 2300. However, in certain corners within this region, the velocity corresponds to Reynolds numbers exceeding 2300. Should the model for this region rely solely on the inlet velocity to classify it as laminar flow, or should it be classified as turbulent flow because there are locations within the region where the velocity exceeds a Reynolds number of 2300?

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September 24, 2023, 12:24		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,672 Rep Power: 65	The flow is turbulent or laminar by its own nature. No magic formula changes it. Some parts of the universe maybe laminar and other parts may be turbulent. If you suspect certain regions to be turbulent then use a turbulence model there and use a laminar model in regions that are laminar. One model might not work for both cases, they rarely do.

September 24, 2023, 23:15		#3
lbj007 Senior Member Join Date: Feb 2020 Posts: 114 Rep Power: 6	Thanks for the reply. I still wonder how to suspect certain regions to be turbulent. Is there a standard to determine whether a certain area is turbulent or is it based on experience? Alternatively, could I initially employ a laminar model to compute and examine the velocity vector map to see if there are any vortex regions as a means of identifying turbulence?