Session: Student Poster Competition

Submission Number: 187016

Study on Acoustic Mode Prediction Based on Non-Uniform Distribution of Flame Transfer Function in a Multi-Nozzle Combustor 

The interaction between nozzles in a multi-nozzle combustor leads to complex and variable global flame dynamics. However, the global flame transfer function fails to capture the local flame dynamics information of individual nozzles, thereby hindering an in-depth understanding of the thermoacoustic instability mechanisms in multi-nozzle combustors. In this study, the dual-microphone method was employed to measure the velocity perturbations at the nozzle inlets, with a perturbation amplitude of 10% and frequencies ranging from 45 Hz to 240 Hz. The flame OH* zonal measurement method was used to obtain the flame transfer functions of the central flame, outer flame, and global flame in a can-type multi-nozzle combustor. Based on the n-τ model, a study on the acoustic mode prediction of the multi-nozzle combustor was conducted. The results show that by arranging dual microphones at the inlets of the central and outer nozzles, it was observed that under the same excitation condition, the amplitude and phase of the acoustic pressure measured by the microphones at the central and outer nozzles differ. Due to the reflection of incident acoustic waves generated by the speakers mounted on the wall of the intake duct, standing wave patterns formed by the interference between the incident and reflected waves change as the excitation frequency varies. This leads to variations in the amplitude and phase difference of velocity perturbations between the central and outer nozzles, indicating non-uniform spatial distribution of inlet velocity perturbations.

Based on the inlet velocity perturbations of the same nozzle, differences exist between the measured local flame transfer functions and the global flame transfer function. Moreover, the gain and phase characteristics of the global flame transfer function are jointly determined by the local flame transfer functions of the central and outer nozzles. The gain peaks and troughs of the local flame transfer functions differ between the central and outer nozzles, and the flame response delay time τ of the central nozzle is shorter than that of the outer nozzle, reflecting the non-uniform distribution characteristics of the local flame transfer functions.

Using the non-uniformly distributed local and global flame transfer functions to analyze the characteristic frequencies of the system acoustic modes, the prediction errors compared with experimental results were all within 10%. However, the local flame transfer function of the central nozzle provided more accurate predictions of the characteristic frequencies. Predictions of the axial distribution of sound pressure level based on the flame transfer functions measured by the dual microphones at the outer nozzle were generally consistent. Based on the flame transfer functions measured by the dual microphones at the central nozzle, the axial position of the maximum sound pressure level predicted by the local flame transfer function of the central nozzle was closer to the downstream region.

Presenting Author: Ming Jin Shanghai Jiao Tong University

Presenting Author Biography: My name is Ming Jin from Shanghai Jiaotong university. My major is the mechanism and suppression of multi-nozzle combustion instability.

Authors:

Ming Jin Shanghai Jiao Tong University
Mingmin Chen Shanghai Electric Gas Turbine Co. Ltd.
Wei Yan Shanghai Electric Gas Turbine Co. Ltd.
Bing Ge Shanghai Jiao Tong University