Disturbance Field Characteristics of a Transversely Excited Annular Jet

Abstract

This paper describes an investigation of transverse acoustic instabilities in premixed, swirl-stabilized flames. Additional measurements, beyond the scope of the current work, are described in O’Connor et al. [1]. Transverse excitation of swirling flow involves complex interactions between acoustic waves and fluid mechanic instabilities. The flame’s response to transverse acoustic excitation is a superposition of both acoustic and vortical disturbances that fluctuate in both the longitudinal and transverse direction. In the nozzle near field region, the disturbance field is a complex superposition of convecting vortical disturbances, as well as longer wavelength transverse and longitudinal acoustic disturbances. Farther downstream, the disturbance field is dominated by the transverse acoustic field. The phasing between the disturbances on the inside and outside of the burner annulus, as well as the left and right sides of the burner annulus is a strong function of the transverse disturbance field characteristics. For cases where the burner centerline is an approximate pressure node and velocity anti-node, the mass flow out of the left and right sides of the burner actually oscillates out-of-phase with respect to each other. In contrast, for cases where the centerline is a pressure anti-node, the burner responds symmetrically about the burner and annulus centerlines. These results show that the burner response characteristics strongly depend upon their location in the acoustic mode shape.

Experimental and Numerical Investigation of Thermoacoustic Sources Related to High-Frequency Instabilities

“…of eqn (14) vanishes. Using this equation for the calculation of the Rayleigh index therefore leads to:…”

“…The experimental characterization of transversely excited swirled jets has been presented earlier by O'Connor and co-workers [14][15][16], Hauser et al [17], and Worth and Dawson [18,19] for the low-frequency range. High-frequency instabilities in swirlstabilised flames were observed in the numerical works of Huang et al [20,21] and Huang and Yang [22], who gave a detailed description of the flame dynamics using proper orthogonal decomposition (POD) methods.…”

Acoustic and Large Eddy Simulation studies of azimuthal modes in annular combustion chambers

“…Even for modes where burners can be assumed to respond in a one-dimensional manner to acoustic perturbations, determining their FTFs remains difficult [24,25,26]. FTFs are the key elements of acoustic solvers for combustion stability as these solvers require the flame response to the acoustic field as an input data [11,10] pilot flames, etc) so that an accurate description of FTF is often not available [27,28,7].…”

Response of an Annular Burner Nozzle to Transverse Acoustic Excitation

“…Within the flame sheet approximation, the response of the flame to flow excitation is largely controlled by flame kinematics, i.e., the propagation of the flame normal to itself into an oscillatory flow field. This is mathematically described by the so-called G-equation [54]: (1) In this equation, the flame position is described by the parametric equation whose local normal vector is given by . Also, and S L denote the flow field just upstream of the flame and laminar burning velocity, respectively.…”

“…HE objective of this study is to improve understanding of transverse combustion instabilities in premixed combustors. It is a companion study to work presented in O'Connor et al [1]. Combustion dynamics is a problem that has plagued numerous rocket and air-breathing engine development programs.…”