[leasken]

Hi! I am a bit confused on how CFX calculates heat flux at the wall. Trying to model heat transfer in a smooth duct, steady state, SST, velocity and temperature inlet, pressure outlet, fixed temperature on the walls, Air Ideal Gas. In the theory guide, Modelling Flow Near the Wall 2.8.1, it is stated that

qw =( rho cp u* (Tw-Tf) )/ T+

where T+ = 2.12 ln (y*) + B for Scalable Wall Function, SWF
and T+ = Pr y* e^(-gamma) + [2.12 ln (y*) + B]e^(-1/gamma) for Automatic Wall Treatment/Function, AWT/AWF,

where gamma and B are functions of Pr and y*.

What is u* for AWF/AWT? What is y* for AWF/AWT? If the mesh is refined, y+<1, is CFX really using AWF/AWT? If CFX is not using AWF/AWT, how is then qw calculated?

[Antanas]

Originally Posted by leasken

Hi! I am a bit confused on how CFX calculates heat flux at the wall. Trying to model heat transfer in a smooth duct, steady state, SST, velocity and temperature inlet, pressure outlet, fixed temperature on the walls, Air Ideal Gas. In the theory guide, Modelling Flow Near the Wall 2.8.1, it is stated that

qw =( rho cp u* (Tw-Tf) )/ T+

where T+ = 2.12 ln (y*) + B for Scalable Wall Function, SWF
and T+ = Pr y* e^(-gamma) + [2.12 ln (y*) + B]e^(-1/gamma) for Automatic Wall Treatment/Function, AWT/AWF,

where gamma and B are functions of Pr and y*.

What is u* for AWF/AWT? What is y* for AWF/AWT? If the mesh is refined, y+<1, is CFX really using AWF/AWT? If CFX is not using AWF/AWT, how is then qw calculated?

CFX always use AWT at least for eddy viscosity turbulence models. If model is not able to integrate directly to wall (like k-e) then Wall Functions is always used, in opposite case it depends on mesh (local y+) what approach will be used in particular point to obtain near wall velocity and temperature.