Noise from Boundary Layer Flow over Fabric Covered Perforate Panels
Noise from Boundary Layer Flow over Fabric Covered Perforate Panels
复制标题
织物覆盖的穿孔面板上的边界层流产生的噪声
DOI：
10.2514/6.2014-2908
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发表时间：
2014
期刊：
影响因子：
2.5
通讯作者：
W. Devenport
中科院分区：
文献类型：
--
作者：
W. N. Alexander;W. Devenport
航空声学风洞通常采用织物覆盖物来降低仪器的自噪声或通过抑制气流来改善设备的背景噪声。为了研究这些织物覆盖物的影响，从开放的和织物覆盖的3.2 mm直径的隔音板测量声学谱。织物覆盖物在较低频率下降低了来自隔音板的噪声，但引入了额外的高频噪声。从织物覆盖的表面的声学频谱有两个最大值，其缩放不同的速度。低频最大值归因于椭圆几何形状，并与速度的六次方成比例。高频最大值被推测为织物覆盖的结果，并且与速度的十一次方成比例。覆盖物的增加也影响了噪声的流向方向性。开放的平行四边形几何结构对称地向上游和下游辐射噪声，在平行四边形样品中心正上方产生的噪声最小。织物覆盖的表面产生了不同的流向频谱方向性图案，该图案被投射到上游并且随着下游接收角单调地减小。由具有固体背衬的织物表面产生的噪声相比于具有开放式背衬的光谱减少了超过20 dB，这表明由织物产生的噪声可能是孔隙率、弹性和/或与底层几何形状的耦合的复杂函数。
Aeroacoustic wind tunnels often employ fabric coverings to reduce instrumentation selfnoise or to improve the background noise of a facility by containing the flow. To investigate the impact of these fabric coverings, acoustic spectra were measured from open and fabric covered 3.2 mm diameter perforate panels. Noise from the perforate panels was reduced at lower frequencies by the fabric coverings, but additional high frequency noise was introduced. The acoustic spectra from the fabric covered surfaces had two maxima which scaled differently with velocity. The low frequency maximum was attributed to the perforate geometry and scaled with the sixth power of velocity. The high frequency maximum is speculated to be a result of the fabric covering and scales with the eleventh power of velocity. The addition of the coverings also affected the streamwise directivity of the noise. The open perforate geometry radiated noise symmetrically upstream and downstream about a minimum produced directly above the center of the perforate sample. The fabric covered surfaces produced a different streamwise spectral directivity pattern which was projected upstream and decreased monotonically with downstream receiving angle. The noise produced by a fabric surface with a solid backing was reduced by more than 20dB compared to spectra with an open perforate backing indicating that the noise produced by the fabric may be a complex function of porosity, elasticity, and/or a coupling with the underlying geometry.