# Conceptual doubt about laminar/turbulent flows

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 March 14, 2011, 03:14 Conceptual doubt about laminar/turbulent flows #1 Senior Member   Raashid Baig Join Date: Mar 2010 Location: Bangalore, India Posts: 136 Rep Power: 9 Sponsored Links I have a very basic conceptual doubt about how we runa laminar or turbulent simulations. 1. Is there a definite way by which we can say a flow is laminar/turbulent or in transition ? Is it not dependent heavily on the geometry shape and it is more difficult to define weather a flow is laminar or turbulent for bodies with complicated geometry (like flow over a terrain or flow over an oil rig where there is no single fixed reference length). 2. If we know for sure that a flow is laminar but we run it as a turbulent simulation, will not the artificial numerical turbulence die on it's own ? In other words what are the pits falls of our choice. Thanks in advance to anyone who enlighten me with these doubts. Raashid

 March 16, 2011, 06:25 #2 New Member   Vic Join Date: Feb 2011 Posts: 5 Rep Power: 8 Hi Raashid, I have the same question with you and I would like to just present my own thinking, (1). Generally in macroscale, the difference between laminar and turbulence flow is Re around 2300. But during CFD analysis, we usually encounter problems with various Re or special geometries where no Re could be calculated. At this time i tend to use turbulence. (2). I was told by someone that using turbulence model in a laminar flow problem only increases the calculation time. Yes there are much possibilities of numerical diffussion, but as long as the result converge.. Of couse, we should test with calculating both models in the same boundary. Victor

 March 16, 2011, 10:19 how to create turbulent flow #3 New Member   muhammad ridhwan Join Date: Sep 2010 Posts: 3 Rep Power: 8 hi.. i'm new to cfd..therefore,i'm having a problem to define the variable to run turbulent flow.. it is very appreciate to those can help me with this.. tq

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