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Forced convection and active temperature?

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Old   July 19, 2023, 06:41
Question Forced convection and active temperature?
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Hi all,

Is the use of the temperature as an active scalar relevant when performing a forced convection RANS or LES computation (Ri<0.01), Ri being the Richardson number? If yes, could you explain me why, since forced convection is defined as a state where the fluid motion is not controled by the temperature variations of the fluid?

Thanks for your answer
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Old   July 19, 2023, 08:33
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You still need to solve a temperature equation if you want to know what is the temperature field looking like or if you want to know what is the heat transfer rate.

The energy (i.e. temperature) transport equation has an advection term that is a div(U*T), UT is nonlinear.

Forced convection means U is more related to dP than dT, it doesn't mean U is constant or that T is constant.
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Old   July 19, 2023, 10:32
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Thanks for your answer, but I do not see in what it answers my question. Maybe it is because I misunderstood something.



Could you confirm or correct the following points:



* Temperature equation is solved in both active and passive temperature.

* passive temperature -> no buoyancy effect -> density is constant -> no effect on the dynamic of the flow
* active temperature -> buoyancy effect -> density depends on the temperature -> dynamic of the flow is altered



So in forced convection, the buoyancy effects being negligible, why active temperature should be considered?
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Old   July 19, 2023, 14:07
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Because p=rho*R*T for an ideal gas means that the temperature change, affects the density, affects the flow. And the flow obviously affects the energy transport equation. Temperature also affects other transport properties like thermal conductivity, viscosity, etc.


Passive temperature can only be used in forced convection for the limiting case with all constant properties (constant density, constant conductivity, constant viscosity, constant everything).
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