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Optimize for laminar flow, assume it valid for turbulent flow? |
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October 21, 2011, 21:15 |
Optimize for laminar flow, assume it valid for turbulent flow?
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#1 |
Senior Member
Join Date: Oct 2010
Location: Zurich
Posts: 176
Rep Power: 16 |
Hi,
I want to optimize a design for convective heat transfer and pressure drop. I have four designs..design 1 ,2,3 and 4. I want to judge how these designs compare at different inlet Re numbers. The Re numbers are in laminar region at lowest level and sweep through transition range on the higher side. I am finding it difficult to get convergence at higher Re both with or without using turbulence models. However i am able to get converged results at low Re i.e. in the laminar flow regime. I analyse through CFD and rank the available designs in terms of their performance at low Re i.e. in the laminar flow regime and get a ranking say 2>3>1>4 in terms of their performance for pressure drop and conjugate heat transfer. Now how safe will it be to assume that the same ranking of designs will also hold at higher Re i.e. in the transition and turbulent flow regimes ( and thus avoid CFD analysis at higher Re)? |
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October 22, 2011, 06:43 |
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#2 |
Senior Member
cfdnewbie
Join Date: Mar 2010
Posts: 557
Rep Power: 20 |
Hello,
I would consider that very dangerous. Turbulent flows can behave significantly different from laminar ones, and extrapolating things like heat or momentum transfer usually goes awfully wrong: that's why Airbus and Boeing are not relying on laminar simulations to build their big birds. My advice: do the turbulent simulations, maybe you will need to increase your grid resolution, but do not extrapolate laminar results! |
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October 24, 2011, 08:43 |
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#3 |
Senior Member
Join Date: Oct 2010
Location: Zurich
Posts: 176
Rep Power: 16 |
Thanks cfdnewbie for your advice!
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