In this paper, a novel open-source framework is presented for the evaluation of noise emissions produced by aerodynamic bodies exhibiting dominant motion at specific frequencies. This behavior is frequently encountered in propellers used for urban air mobility applications. The reduced order model called harmonic balance is employed to compute the unsteady flow solution, reducing the computational cost. The approach tackles K different frequencies by capturing the flow solution at N discrete time instances within a single period, where N is defined as 2K+1. The time history of the conservative variables on the solid surfaces is reconstructed through a Fourier interpolation. The Kirchhoff Ffowcs Williams Hawkings integral formulation, integrated into SU2, is used to compute the sound pressure level perceived by farfield observers. The integral formulation propagates the acoustic solution with a computational cost independent of observer distance. The noise emission of a pitching wing and a propeller is computed with the proposed framework. Regarding a small, isolated propeller operating at low Reynolds numbers in forward flight, we conducted a comparison of the aerodynamic and aeroacoustic results between a fully time-accurate solution and a steady-state Reynolds Averaged Navier-Stokes solution within a rotating reference frame. The harmonic balance results demonstrated improved agreement with the fully unsteady solution across the first three blade-pass frequencies and exhibited this consistency over a broader range of propagation angles.

中文翻译：

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基于谐波平衡解的螺旋桨气动声学计算


在本文中，提出了一种新的开源框架，用于评估在特定频率下表现出主导运动的空气动力学物体产生的噪声发射。这种行为在用于城市空中交通应用的螺旋桨中经常遇到。采用称为谐波平衡的降阶模型来计算非定常流解，从而降低了计算成本。该方法通过在单个周期内捕获 N 个离散时间实例的流动解来处理 K 个不同的频率，其中 N 定义为 2K+1。实体表面上守恒变量的时间历史是通过傅里叶插值来重建的。集成到 SU2 中的 Kirchhoff Ffowcs Williams Hawkings 积分公式用于计算远场观测器感知到的声压级。积分公式以独立于观察者距离的计算成本传播声学解。使用所提出的框架计算了俯仰翼和螺旋桨的噪声发射。对于在向前飞行中以低雷诺数运行的小型孤立螺旋桨，我们在旋转参考系内对完全时间精确解和稳态雷诺平均纳维-斯托克斯解的空气动力学和气动声学结果进行了比较。谐波平衡结果表明，在前三个 blade-pass 频率上与完全非稳态解的一致性更高，并且在更广泛的传播角度范围内表现出这种一致性。