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Turbulent Heat Flux Extraction

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Old   April 4, 2020, 06:18
Arrow Turbulent Heat Flux Extraction
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Hi all,

Hope everyone is well. Can anyone please guide me on extracting turbulent heat flux <u'T'> from k-w SST and LES?

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Old   April 6, 2020, 07:09
Default Turbulent Heat Flux
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Do you want this at a boundary or at interior faces of the mesh?
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Old   April 6, 2020, 18:02
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Quote:
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Do you want this at a boundary or at interior faces of the mesh?
Hi Vinerm,

Actually both as I want turbulent heat fluxes along a line normal to the wall.

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Old   April 7, 2020, 16:42
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For LES, this definition makes sense but k-\omega has neither of these fields available. So, you have to define it either using k or subtract heat flux due to molecular diffusion from total to fetch turbulent heat flux.
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Old   April 11, 2020, 12:37
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Quote:
Originally Posted by vinerm View Post
For LES, this definition makes sense but k-\omega has neither of these fields available. So, you have to define it either using k or subtract heat flux due to molecular diffusion from total to fetch turbulent heat flux.
Sorry for replying a bit late. I think that'd a bit tricky and unreliable to reconstruct turbulent heat fluxes from turbulent kinetic energy so I'll probably stick to unsteady simulations. For LES or URANS, should I directly multiply RMS u and RMS T to get <u't'>? or is there any alternative way to do so?

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Old   April 11, 2020, 13:12
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For RANS, you can determine u' using k,

u' = \sqrt\frac{2k}{3}

Whether LES or RANS, turbulent heat flux is product of u' with mean T and not T'. Another method of determining turbulent heat flux in RANS is via \alpha_t and mean temperature gradient. You can use this for LES as well, however, for LES, you directly have u'. I am not sure but Fluent may directly have turbulent heat flux field available.
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Old   April 12, 2020, 12:37
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Quote:
Originally Posted by vinerm View Post
For RANS, you can determine u' using k,

u' = \sqrt\frac{2k}{3}

Whether LES or RANS, turbulent heat flux is product of u' with mean T and not T'. Another method of determining turbulent heat flux in RANS is via \alpha_t and mean temperature gradient. You can use this for LES as well, however, for LES, you directly have u'. I am not sure but Fluent may directly have turbulent heat flux field available.
I've further looked into the definition of turbulent heat fluxes but I'm actually a bit confused with your comment as I think it must be T' -fluctuating temperature. Can you please refer me a book or paper where it says it is mean T rather than T'?

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Old   April 12, 2020, 16:28
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You are correct, in similarity with Reynolds stress, turbulent heat flux uses temperature fluctuation and not it's mean. It's only if turbulent diffusivity is used that the gradient of mean makes sense for turbulent heat flux determination.
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