Mach Number Effects on Jet Noise Sources and Radiation to Shallow Angles
Mach Number Effects on Jet Noise Sources and Radiation to Shallow Angles
复制标题
马赫数对射流噪声源和浅角辐射的影响
DOI：
10.2514/1.19959
复制
发表时间：
2006
期刊：
影响因子：
2.5
通讯作者：
M. Samimy
中科院分区：
文献类型：
--
作者：
J. Hileman;M. Samimy
LL射流由于湍流混合而产生噪声;这种混合导致了Lighthill声学类比中的源项--雷诺应力的产生[1]。除此之外，具有相干、大尺度结构且以超过当地声速的速度传播的射流将发射马赫波辐射，这是一种高效的噪声产生机制。喷流噪声的幅值与喷流面积和出射速度成一个角度相关的幂n，但对n的取值存在分歧，基于量纲分析，Lighthill[1]发现n = 8.在对喷流噪声定标的广泛研究中，Viswanathan [2]观察到，对于测量位置（30 °）和环境温度与总温度的比值，n为9：8。Venkatesh等人[3]提出了一套广泛的亚音速喷流噪声测量，表明最大噪声产生区域与均匀无旋转喷流核心的崩溃相一致。本技术说明研究了马赫数对喷流噪声产生机制、喷流噪声定标和最大噪声产生区域的影响。它是通过检查马赫数为0.9的、理想情况下扩展马赫数为1.3和2.0的浅角喷流噪声的时域和频域特性来实现这一点的。最近的一组实验表明，马赫数为1.3的喷流在时域数据中具有大振幅的声峰，这些声峰可以用来将辐射声场的产生与混合层的演变联系起来[4-7]。这些声学峰值在本技术说明中被检查以表征三个射流的噪声产生机制和源区域。对于所研究的所有马赫数，大振幅声峰都起源于一个椭圆形区域，该区域的中心超过了势线的末端，并且随着马赫数的增加，横向流中的噪声源区域变窄。与马赫数为0.9和1.3时不同，马赫数为2.0时的声峰具有时间不对称性，这与噪声产生机制从马赫数混合到马赫数波发射的变化有关。
LL jets have noise generation due to turbulent mixing; suchmixingleadstotheproductionofReynoldsstresses,thesourceterm within the Lighthill acoustic analogy [1]. In addition to thissource,ajetthatpossessescoherent,large-scalestructuresthattravelwith velocities exceeding the local speed of sound will emit Machwave radiation, a highly efficient noise production mechanism. Theamplitudeofjetnoisescaleswiththejetareaandtheexitvelocitytoanangle-dependentpowern.Thereisdisagreement,however,inthevalueofn.Basedondimensionalanalysis,Lighthill[1]foundntobe8. In anextensive examination of jet noise scaling, Viswanathan [2]observed that n 9:8 for the measurement location (30 deg) andambient to total temperature ratio of unity examined in this work.Venkatesh et al. [3] presented an extensive set of subsonic jet noisemeasurements that show the region of maximum noise generationcoincides withthecollapseoftheuniform, irrotationaljetcore.Thistechnical note examines the impact of Mach number on themechanism of jet noise generation, the scaling of jet noise, and theregion of maximum noise generation. It does this throughexamination of the time and frequency domain properties of theshallow angle jet noise from Mach 0.9, and ideally expandedMach 1.3 and 2.0 jets.A recent set of experiments showed that a Mach 1.3 jet possesseslarge amplitude acoustic peaks within the time-domain data andthesepeakscouldbeusedtorelatethegenerationoffarfieldradiatedsound to the evolution of the mixing layer [4–7]. These acousticpeaks are examined in this technical note to characterize the noisegeneration mechanism and source region of the three jets. For allMachnumbersstudied,thelargeamplitudeacousticpeaksoriginatefrom an ellipsoid-shaped region that is centered past the end of thepotentialcoreandthenoisesourceregionnarrowsinthecross-streamwith increasing Mach numbers. Unlike at Mach 0.9 and 1.3, theMach2.0acousticpeakshavetemporalasymmetry,whichisrelatedtothechangeinnoisegenerationmechanismfromturbulencemixingto Mach wave emission.