Numerical Simulation of the Dynamics of Turbulent Swirling Flames

5 Identification of Flame Transfer
Functions using LES/SI
In this chapter, the flame dynamics of an axial swirl burner is investigated by
the determination of its Flame Transfer Function with the LES/SI method. The
experimental set-up is introduced at the beginning, followed by the validation
of the method with experiments. The case of a nonadiabatic combustor with
30 kW is used as reference for the validation. After that, the geometrical and
operating conditions in the combustor and burner are varied by changing the
thermal conditions at the combustor walls, increasing combustor cross section
area, changing the position of the swirler and increasing the power rating,
to study the impact of these variations on the flame dynamics. All experimental
data was carried out and provided by T. Komarek [104].
5.1 Experimental Set-up of the BRS Burner
The BRS (Beschaufelter RingSpalt) burner is a swirl-stabilized burner with an
axial swirl generator developed by Komarek and Polifke [103] in the framework
of the KW 21 project GV 6 Premixed Flame Dynamics. A scheme of the
experimental set-up is shown in Fig. 5.1. The burner is operated in “perfectly
premixed” mode with a completely homogeneous mixture of natural gas and
air to eliminate any equivalence ratio fluctuations. The experimental set-up
consists of a cylindrical plenum followed by the burner with the axial swirl
generator of 30 mm length mounted on a central bluff body. The burner exit
has an annular section with an inner and outer diameter of 16 and 40 mm, respectively.
A combustor of quadratic cross section of 90×90 mm and a length
of 300 mm follows the burner. With this combustor length, the test conditions
were stable to perform OH chemiluminescence, flow field and FTF measure-
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