Typically, eddy viscosity ratio of more than 100 to 1000 indicates turbulent flow. So it sounds reasonable too use this ratio as a measure of turbulence. And if the ratio = 1 the flow is transitional? Of course I may be wrong (I suspect I am!) and I am happy to be corrected!Īre there any papers or books that you can recommend that'll lead me to the correct path?įrom first principle, it would be fair to say that while any laminar flow would have shear stress owing to its viscosity and velocity gradients, the reason of "turbulence" is the additional shear stresses (Reynolds stresses) that arise due to random fluctuating velocity components, which are realized through the definition of turbulent viscosity.Įssentially, the ratio of turbulent to molecular viscosity gives an indication about how strong the Reynolds stresses are, as compared to molecular stresses. My guess is that if the ratio is 1 eddy viscosity dominates and the flow is turbulent. So I guess what I'm asking is: is the ratio of eddy viscosity to molecular viscosity a good indicator of laminar or turbulent flow? Is it a simple case of going into CFD Post and checking the ratio between these two viscosities?
But how can this be true for laminar flow as laminar flow won't have an eddy viscosity? I've read somewhere (I can't recall where!) that the ratio between eddy viscosity to molecular viscosity will truly tell me if my flow is laminar or turbulent. When I switch to a turbulence model (SST) the Reynolds number indicates the flow may be laminar. Using a laminar model when I post process the Reynolds number it indicates the flow may be turbulent. I've tried laminar and turbulent models but I'm not getting the results I expect. I'm modelling a differently heated cavity, which induces density variations and causes the fluid to recirculate. I'm stuck between a rock and a hard place. Ratio of eddy viscosity to molecular viscosity : Laminar or turbulent flow? - CFD Online Discussion Forums
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