Numerical Simulation of the Dynamics of Turbulent Swirling Flames

5.6 Influence of Combustor Confinement on the Flame Transfer Function
Figure 5.38: Turbulent kinetic energy profiles with low and high confinement
combustors at various positions of the middle cross plane shown
in Fig. 5.2.
should be the same between cases. Results show that the low-confinement
case has a longer flame than the high-confinement case with a low level of
reaction close to the burner exit. The flame lengths, computed as the position
of the maximum heat release, are 45 and 75 mm, for the high- and lowconfinement
cases, respectively.
5.6.2 Comparison of Flame Transfer Functions
The low-confinement simulation is excited using the same signal indicated on
section 5.4.3 with an amplitude of 9.5% of the mean inlet velocity for 350 ms
in real time (2.8 million iterations). The identified FTF is compared with the
one obtained with high confinement at nonadiabatic conditions and shown
in Fig. 5.41. For the low confinement case, the amplitude shows similar behavior
to the high-confinement, but with the maximum amplitude slightly
higher and at a lower frequency. The time lag response is larger which is represented
by the higher steepness in the phase. This is in agreement with
the differences in flame length shown in Fig. 5.40. Comparing the dynamic
behavior of the flames, the high-confinement case shows strong interaction
between the flame and the wall, being elongated along the walls as shown
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