Purpose

The purpose of this paper is to investigate airfoil’s tonal noise reduction mechanism when deploying surface irregularities, such as surface waviness by means of spatial stability analyses.

Design/methodology/approach

Flow field calculations over smooth and wavy-surface NACA 0012 airfoils at 2° angle of attack and at Reynolds number of 200,000 are performed using the large eddy simulation (LES) approach. Three geometrical configurations are considered: a smooth NACA 0012 airfoil, wavy surface on the suction side (SS) and wavy surface on the pressure side (PS). The spatial stability analyses using the LES-generated flow fields are conducted and validated against the Orr-Sommerfeld stability analysis for the smooth airfoil configuration.

Findings

The spatial stability analyses show that inclusion of the wavy-type modification on the SS of the airfoil does not lead to altering of the acoustic feedback loop mechanism, with respect to the mechanism observed for the smooth airfoil configuration. In contrast, applying the surface modifications to the airfoil PS leads to a significant reduction of the amplification range of disturbances in the vicinity of the trailing edge for the frequency of the acoustic feedback loop mechanism.

Practical implications

The spatial analyses using, for example, LES-generated flow fields can be widely used to determine acoustic sources and associated distributions of amplifications for a wide range of applications in the aeroacoustics.

Originality/value

The spatial stability analysis approach based on flow fields computed a priori using the LES method has been introduced, validated and used to determine behaviour of the acoustic feedback loop when accurate reconstruction of geometry effects is required.

中文翻译：

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波浪形表面对翼型边界层不稳定性的影响

目的

本文的目的是通过空间稳定性分析研究翼型在部署表面不规则（例如表面波纹）时的音调降噪机制。

设计/方法/方法

使用大涡模拟 (LES) 方法在 2° 迎角和 200,000 雷诺数下对光滑和波浪形表面 NACA 0012 翼型进行流场计算。考虑了三种几何配置：光滑的 NACA 0012 翼型、吸力侧 (SS) 的波浪形表面和压力侧 (PS) 的波浪形表面。使用 LES 生成的流场进行空间稳定性分析，并根据 Orr-Sommerfeld 稳定性分析对平滑翼型进行验证。

发现

空间稳定性分析表明，相对于观察到的光滑翼型结构的机制，在翼型的 SS 上包含波浪型修改不会导致声反馈回路机制的改变。相比之下，对翼型 PS 应用表面修改导致后缘附近对于声反馈回路机制的频率扰动的放大范围显着减小。

实际影响

使用例如 LES 生成的流场的空间分析可广泛用于确定声源和相关的放大分布，以用于气动声学中的广泛应用。

原创性/价值

已经引入、验证了基于流场的空间稳定性分析方法，该方法使用 LES 方法先验计算，并用于在需要精确重建几何效应时确定声反馈回路的行为。