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Turbulence intensity too high on the inlet

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Old   November 5, 2013, 11:07
Default Turbulence intensity too high on the inlet
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Laszlo A.
Join Date: Oct 2013
Location: Bristol, UK
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I am a beginner (or more like a restarter) of CFD.
I am modelling atmospheric boundary layer flow, trying to simulate the flow around wind turbines. I set an inlet boundary condition with incoming flow velocity of 10m/s and turbulence intensity of 10%. The model is a 2D top view. The turbines are large (107m diameter), the flow domain is 1500x3000m, the mesh has roughly 70,000 elements (refined around the turbines). The turbines are modelled in this very simple first try as fans with a pressure drop determined from a thrust coefficient of 0.7 on the turbines (or for those familiar with the actuator disk concept an axial induction factor of ~0.3). I am using a k-epsilon model with the standard parameters in Fluent.

The problem I am facing is that even though I set the inlet turbulence intensity between 10-15%, the solution converges, but a contour plot of turbulence intensity shows TI values between 60% and 200% across the simulation domain, including the inlet.

I may be missing something here, but I do not understand where these high TI values are coming from? Must be something with the definition of the k-epsilon model and/or the definition of turbulence intensity and turbulent length scale on the inlet. The length scale I am choosing is anywhere between 10m to 340.2m, I tried several scenarios but in each case the TI is very high.

Any help is appreciated.
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fan boundary condition, k-epsilon model, length scale, turbulence intensity

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