60285 - Optimum Multi-Nozzle Configuration for Minimizing the Rayleigh Integral During High-Frequency Transverse Instabilities 

Recent work by the authors has modeled the response of premixed flames to excitation by natural high-frequency transverse modes in a can combustor, and simultaneous excitation by induced axial fluctuations. The stability of these acoustically non-compact flames was assessed using the Rayleigh Integral (RI). Several key control parameters were studied, namely – flame angle, swirling strength, nozzle location. An important result from these studies showed that nozzle location strongly affected the resulting Rayleigh integral indicating that for fixed flame parameters, different nozzles experienced different amplification factors for a given transverse mode. For non-axisymmetric modes such as the commonly occurring 1-T mode, both radial and azimuthal offsets of the nozzle location affected stability. In this study, we consider a N-around-1 configuration such as typically used in a multi-nozzle can system and study the overall stability of this system for different natural transverse modes. Typically, such nozzles are distributed in a uniformly circular manner for which we study the overall RI and for cases where RI>0, we optimize the nozzle distribution that can reduce and minimize RI. For a fixed geometry such a circular configuration, the analysis shows how the flame’s parameters must vary across the different nozzles, to result in a relatively stable system. Additionally, for a fixed set of flame parameters, the analysis also indicates the non-circular distribution of the N nozzles that minimizes RI. Overall, the analysis aims to provide insights on designing nozzle locations around the center nozzle for minimal amplification of a given transverse mode.