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Iflation layer and Y+ questions

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Old   April 21, 2015, 14:44
Default Iflation layer and Y+ questions
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Hi all,

I am pretty new to Fluent and recently I bumped into a turbulenece model / meshing conflict.
The company I work for manufactures small products (ranges from 30-200 mm in diameter) with reletively low flows (around 50 m/s, and up t0 200 m/s in very thin regions). These conditions dictates the following to my understanding:

When using k-e model the Y+ should be >30, and this means first layer thickness of about 1mm in my products. I have alot of models with very thin flow regions (going down to the area of 0.1mm thickness) which means I have to mesh the inflation layer with Y+ in the area of 1 (I cannot put big cells there, only small in the order of 0.01mm, or else I will have space for only 1 elements layer)

The main results that I am interested in the solution are bulk, meaning I need the total pressure drop on the system, sum of flow through the inlets / outlets etc.

I can use the k-w model, but with this I have two othr issues / questions:

1. this model requires finer mesh and from what I see needs more time to compute.
2. For the problems I tried, the same model gives better convergence using k-e

And what I am asking myself is - do I really need turbulence modeling? or maybe I can stay with laminar model? if not and if the boundary layer effects the quantities that I am looking for (which are in the bulk as I stated)
is there a workaround that can enable the use of the k-e model with very small cells at the wall?

Thanks for your time.
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