Entropy (temperature) fluctuations produced by turbulent flames generate noise when they are accelerated by the flow. This so-called entropy noise is an important contributor to core noise in modern aeroengines and several semi-analytical models exist in the literature for its prediction. All these models assume the flow to be inviscid. In the present paper, contribution of viscosity on entropy noise generation and scattering through a nozzle is investigated numerically with URANS simulations and analytically through the extension of the 2D inviscid model of Emmanuelli et al. (2020). Simulations indicate noise generation and scattering is slightly reduced in the medium-frequency range in the presence of viscosity with variations below 3 dB in comparison to reference inviscid data. This noise variation is qualitatively well reproduced by the low-order model. The major effect of viscosity on noise generation and propagation lies in the presence of boundary layers. Viscous entropy noise sources and viscous diffusion of acoustic perturbations have a negligible impact on noise. Discrepancies between simulations and analytical solutions are found to come from the radial evolution of the acoustic waves in thick boundary layers, not accounted for in the model, and which impact noise scattering.

湍流火焰产生的熵（温度）波动在被流动加速时会产生噪音。这种所谓的熵噪声是现代航空发动机核心噪声的重要贡献者，文献中存在几种用于其预测的半解析模型。所有这些模型都假设流动是无粘性的。在本文中，粘度对熵噪声生成和通过喷嘴散射的贡献通过 URANS 模拟进行了数值研究，并通过 Emmanuelli 等人的 2D 无粘性模型的扩展进行了分析。(2020)。模拟表明，与参考无粘性数据相比，在存在粘度且变化低于 3 dB 的情况下，噪声产生和散射在中频范围内略有减少。低阶模型很好地再现了这种噪声变化。粘度对噪声产生和传播的主要影响在于边界层的存在。粘性熵噪声源和声扰动的粘性扩散对噪声的影响可以忽略不计。发现模拟和解析解之间的差异来自厚边界层中声波的径向演化，模型中没有考虑，这会影响噪声散射。