FDF-based Analysis for Thermoacoustic Instability and Acoustic Stabilization Effects

FDF-based Analysis for Thermoacoustic Instability and Acoustic Stabilization Effects
Seungtaek Oh
Yongmo Kim
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The present study has been mainly motivated to analyze thermoacoustic instability in terms of the prediction and stabilization. In order to analyze thermoacoustic instability by utilizing numerical approaches, there are largely classified by the self-excited mode strategy and the hybrid method. In this thesis, these two approaches are both employed. First, it has been researched how to efficiently and effectively predict thermoacoustic instability in combustors. With the hybrid method, the FDF-based combustion instability analysis together with the Helmholtz solver has been made for the wide range of velocity perturbation in the lab-scale combustors
EM2C combustor and multiple flame combustor. In this hybrid method, it is suggested that FDF can be refined by neural network methods (RBFNN and GRNN). This allows to reduce the cost to model FDF and show the potential to increase the input variables of FDF. In addition, for the multiple flame combustor, the new nonlinear behavior of thermoacoustic instability has been discovered here from the detail analysis. In the present thesis, it has been researched that how to develop the hybrid method via improved FDF and how to better utilize it. With the self-excited mode strategy, LES with the DTF has been utilized to simulate thermoacoustic instability realistically. For PRECCINSTA combustor, it has been tried to catch up with the numerical results from the reference research groups. After then, in order to surpass them, heat loss via combustor walls are considered to realistically simulate the temperature field in PRECCINSTA combustor. From doing that, reasonable results can be obtained, and it can be available to observe the development of thermoacoustic instability up to the limit cycle. Second, it has been researched that how to effectively stabilize thermoacoustic instability by utilizing passive dampers. For a passive damper, various kinds of concepts and optimization methods are discussed here. First of all, a perforated plate has been suggested for a passive damper, and it has been shown how to optimize this to obtain max damping performance at target frequency. After then, a slotted plate has been introduced instead of the perforated plate to reduce the cost and analyzed in terms of the damping performance. After then, it has been shown that passive dampers can be optimized in a given frequency range thanks to SA algorithm. In addition, in order to increase the damping performance more and more, the dual-plate methodology and multi-cavity concept have been also suggested. Finally, the MIU concept has been compared with the perforated plates and slotted plates during finding a better concept of passive dampers. With the passive dampers discussed above, it has been shown that thermoacoustic instability can be effectively stabilized with the hybrid method. From all the mentioned numerical approaches and results in this thesis, it can be confirmed that some improvements have been made in both prediction part and stabilization part of thermoacoustic instability.
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