About Heat Flux Equation in StarCCM+ manual

jshu004 · March 25, 2020, 15:37

Hello Star-CCM+ users,

I am doing a turbulent heat transfer simulation and going through a difficulty understanding the heat flux equation (eqn. 257) shown in User Manual.

In OpenFoam, the heat flux is calculated using:

$q"=\frac{k_{eff}}{C_{p}}\frac{\partial(C_{p}T)}{\partial y}$

evaluated at y=0.

Why these equations are different? I do understand the equation in OpenFOAM.

When I simulate a simple turbulent heat transfer using both StarCCM+ and OpenFOAM, the heat flux obtained from StarCCM+ is little different from OpenFOAM.

Anyone teach me about the heat flux equation used in StarCCM+?
My detail questions are:
1) why the ustar is used in equation?
2) does the parenthesis mean a function of a variable?
e.g.) $\rho_f(y_{c})$ is a density as a function of y_{c}?
3) what does the denominator mean?

Thank you in advance.

Best Wishes,
Jung Shu

fluid23 · March 26, 2020, 09:40

Are you working in an old version or something? I tried to pull up these help files and found a slightly different description that what you show. Long story short, it looks like the the open foam equation is in differential form while the star-ccm equation is worked out a little more fully.

Capture.jpg

Basically, all that non-sense in front of the (Ts-Tc) term is the local heat transfer coefficient, whereas (I suspect, but I don't know for sure) that keff in openfoam is a global value and that the actual deployment of the equation looks much closer to Star-CCM.

Capture2.jpg

To answer your questions:

1) u* appears in the numerator to cancel out the u* inside the prandtl number (see no. 3) to give local heat transfer coefficient.

2) yes, density, specific heat capacity and non-dimensional temperature can (and are allowed to) vary with wall distance. These are describing functions of wall distance.

3) the denomentator is only T+ (dimensionless temperature = Prantdl No * y+ which is a function of u* and y). They are simply stating that T+ varies with wall distance.

March 25, 2020, 15:37	About Heat Flux Equation in StarCCM+ manual	#1
jshu004 New Member Jung Il Shu Join Date: Apr 2017 Posts: 1 Rep Power: 0	Hello Star-CCM+ users, I am doing a turbulent heat transfer simulation and going through a difficulty understanding the heat flux equation (eqn. 257) shown in User Manual. In OpenFoam, the heat flux is calculated using: $q"=\frac{k_{eff}}{C_{p}}\frac{\partial(C_{p}T)}{\partial y}$ evaluated at y=0. Why these equations are different? I do understand the equation in OpenFOAM. When I simulate a simple turbulent heat transfer using both StarCCM+ and OpenFOAM, the heat flux obtained from StarCCM+ is little different from OpenFOAM. Anyone teach me about the heat flux equation used in StarCCM+? My detail questions are: 1) why the ustar is used in equation? 2) does the parenthesis mean a function of a variable? e.g.) $\rho_f(y_{c})$ is a density as a function of y_{c}? 3) what does the denominator mean? Thank you in advance. Best Wishes, Jung Shu

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March 26, 2020, 09:40		#2
fluid23 Senior Member Matt Join Date: Aug 2014 Posts: 947 Rep Power: 17	Are you working in an old version or something? I tried to pull up these help files and found a slightly different description that what you show. Long story short, it looks like the the open foam equation is in differential form while the star-ccm equation is worked out a little more fully. Capture.jpg Basically, all that non-sense in front of the (Ts-Tc) term is the local heat transfer coefficient, whereas (I suspect, but I don't know for sure) that keff in openfoam is a global value and that the actual deployment of the equation looks much closer to Star-CCM. Capture2.jpg To answer your questions: 1) u* appears in the numerator to cancel out the u* inside the prandtl number (see no. 3) to give local heat transfer coefficient. 2) yes, density, specific heat capacity and non-dimensional temperature can (and are allowed to) vary with wall distance. These are describing functions of wall distance. 3) the denomentator is only T+ (dimensionless temperature = Prantdl No * y+ which is a function of u* and y). They are simply stating that T+ varies with wall distance.