Page 386 - TransAT_Tutorial_Manual

TransAT Tutorial Manual 9.2. Forced Convection in an Isothermal Pipe

// Function executed at end of simulation
void crossflow_output::operator ()(){
// Write profiles in crossflow direction in crossflow_output.dat
output->write_file("crossflow_output.dat");
...
}

Comments on output generation in the streamwise direction

In this case, the output in the streamwise direction consist of the bulk temperature and Nussselt
number distribution. The line output feature cannot be used as both the bulk temperature and the
Nusselt number must be computed. To do so, the streamwise output function has been created.

Theoretical basis of the streamwise output function The streamwise output function
proceeds to compute the bulk temperature and the Nusselt number then writes them to a file.

The bulk temperature is obtained by computing the following integral in the cross-sections along
the pipe:
R
ρuTdΣ
Σ
T bulk = R (9.2)
ρudΣ
Σ
with Σ the cross-section and the Nusselt number definition reads:

2Rq00
Nu = (9.3)
λ (T w − T bulk )

with q00 the heat flux through the pipe, R = 0.1m the radius of the pipe, λ the conductivity of
air and T w the pipe temperature.

Given that the domain is axisymmetric and that air is modelled as an incompressible fluid,
Eq. 9.2 simplifies as follows
y=R
R
uTdy
y=0
T bulk = (9.4)
y=R
R
udy
y=0
with R = 0.1m the radius of the pipe.

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Ascomp AG Switzerland 376 Version 5.7