The relative importance of direct and indirect combustion noise in a realistic gas-turbine combustor is investigated. While temperature fluctuations are commonly recognized as the primary source of indirect combustion noise, recent theoretical analysis has shown that mixture inhomogeneities and associated variations in the Gibbs free energy represent another indirect noise-source contribution that is further investigated in this study. To this end, a hybrid model is developed that combines large-eddy simulations for predicting the unsteady turbulent reacting flow field in the combustor with a linearized Euler solver to describe the transmission and generation of noise through the downstream nozzle. By considering an operating point near the lean blow-out limit at cruise conditions, it is shown that indirect noise has an appreciable contribution to the overall noise emission at low frequencies, and direct noise arising from a tonal instability in the combustor dominates at higher frequencies. At this operating point, indirect noise contributing from compositional inhomogeneities was found to be comparable in magnitude to entropy noise from temperature inhomogeneities. A modal analysis of the indirect noise sources showed that the entropy and compositional noise are shifted in phase, resulting in a cancellation of the indirect noise. Effects of Mach number and modal shape of the combustor-exit perturbations on the noise generation are investigated, demonstrating the importance of spatial inhomogeneities to the core-noise contribution.

研究了实际燃气轮机燃烧器中直接和间接燃烧噪声的相对重要性。虽然温度波动通常被认为是间接燃烧噪声的主要来源，但最近的理论分析表明，混合物的不均匀性和吉布斯自由能的相关变化代表了本研究中进一步研究的另一个间接噪声源贡献。为此，开发了一种混合模型，该模型将用于预测燃烧器中非定常湍流反应流场的大涡模拟与线性欧拉求解器相结合，以描述通过下游喷嘴的噪声传递和产生。通过考虑巡航条件下接近稀薄井喷极限的操作点，结果表明，在低频下，间接噪声对整体噪声排放有显着贡献，而由燃烧器中音调不稳定性引起的直接噪声在高频下占主导地位。在这个操作点，发现由成分不均匀性引起的间接噪声在幅度上与温度不均匀性引起的熵噪声相当。对间接噪声源的模态分析表明，熵和成分噪声发生了相位偏移，从而抵消了间接噪声。研究了马赫数和燃烧室出口扰动的模态形状对噪声产生的影响，证明了空间不均匀性对核心噪声贡献的重要性。由燃烧器中音调不稳定性引起的直接噪声在较高频率处占主导地位。在这个操作点，发现由成分不均匀性引起的间接噪声在幅度上与温度不均匀性引起的熵噪声相当。对间接噪声源的模态分析表明，熵和成分噪声发生了相位偏移，从而抵消了间接噪声。研究了马赫数和燃烧室出口扰动的模态形状对噪声产生的影响，证明了空间不均匀性对核心噪声贡献的重要性。由燃烧器中音调不稳定性引起的直接噪声在较高频率处占主导地位。在这个操作点，发现由成分不均匀性引起的间接噪声在幅度上与温度不均匀性引起的熵噪声相当。对间接噪声源的模态分析表明，熵和成分噪声发生了相位偏移，从而抵消了间接噪声。研究了马赫数和燃烧室出口扰动的模态形状对噪声产生的影响，证明了空间不均匀性对核心噪声贡献的重要性。发现由成分不均匀性引起的间接噪声在幅度上与温度不均匀性引起的熵噪声相当。对间接噪声源的模态分析表明，熵和成分噪声发生了相位偏移，从而抵消了间接噪声。研究了马赫数和燃烧室出口扰动的模态形状对噪声产生的影响，证明了空间不均匀性对核心噪声贡献的重要性。发现由成分不均匀性引起的间接噪声在幅度上与温度不均匀性引起的熵噪声相当。对间接噪声源的模态分析表明，熵和成分噪声发生了相位偏移，从而抵消了间接噪声。研究了马赫数和燃烧室出口扰动的模态形状对噪声产生的影响，证明了空间不均匀性对核心噪声贡献的重要性。