题目

英语翻译
Fig.6 shows the completed open jet wind tunnel inside the
ISVR’s anechoic chamber (control valve and primary silencer are
in the roof space of the chamber and are not shown in the figure).
Also shown is the new coordinate system (x,y,z) employed for the
cross section of the nozzle exit plane.We now present the overall
facility background noise characteristics for the entire rig as a function
of exit jet velocity.The flow uniformity and turbulence intensity
variation over the jet nozzle of the jet were also measured and
are also presented below.Note that both the acoustic and aerodynamic
measurement results are plotted using the new coordinate
system (x,y,z) as defined in Fig.6.
4.1.Analysis of background noise levels
A microphone was placed at (x,y,z) = (0,0.5,0),i.e.0.5 m vertically
above the centre of the cross-sectional nozzle exit plane to
measure the background noise level inside the anechoic chamber
at different

提问时间：2020-10-30

答案

八
Fig.6 shows the completed open jet wind tunnel inside the ISVR’s anechoic chamber (control valve and primary silencer are in the roof space of the chamber and are not shown in the figure).图6示出了在英国南安普顿大学声与振动研究所（ISVR）消声室（控制阀和主消声器是在消声室的屋顶空间,在图中没有显示）内的完整的开放式风洞.Also shown is the new coordinate system (x,y,z) employed for the cross section of the nozzle exit plane.示出的还有用于喷嘴出口平面横截面的新坐标系统（x,y,z）.We now present the overall facility background noise characteristics for the entire rig as a function of exit jet velocity.现在我们介绍整个装置（rig）总的设施背景噪声特性与出口射流速度的函数关系.The flow uniformity and turbulence intensity variation over the jet nozzle of the jet were also measured and
are also presented below.在射流喷嘴范围的流动均匀性和湍流强度变化也进行了测量,并在下面加以介绍.Note that both the acoustic and aerodynamic measurement results are plotted using the new coordinate system (x,y,z) as defined in Fig.6.请注意,声学和空气动力学的测量结果都用新的坐标系统（x,y,z）绘制,入图6所示.
4.1.Analysis of background noise levels
背景噪声水平的分析
A microphone was placed at (x,y,z) = (0,0.5,0),i.e.0.5 m vertically above the centre of the cross-sectional nozzle exit plane to measure the background noise level inside the anechoic chamber
at different exit jet velocities.在（x,y,z）＝(0,0.5,0)处,即在横截面的喷嘴出口平面中心正上方0.5m处放置一个麦克风,以测量不同出口射流速度下消声室内的背景噪声水平.This corresponds to a polar angle,h = 90 ,where h is the angle from the jet axis,as shown in Fig.1.这相当于h＝90度的极角,这里,h为离开射流轴线的角度,入图1所示.In addition,another microphone was placed at h = 45 (0.35,0.35,0) to assess the noise directivity of the exit jet.此外,在h＝45度（0.35,0.35,0）处放置另一个麦克风,以评估出口射流的噪声方向性.Fig.7a and b show the narrowband (spectral density) sound pressure level at h = 45 and 90 ,respectively pertaining to the open jet wind tunnel over a range of jet velocities between 33.1 and 99.6 ms 图7a和b分别示出了在h＝45度和90度时,关于射流速度在33.1和99.6m/s之间范围时开放式风洞的窄带（谱密度）声压水平.1.These figures are plotted in the form of power spectral density with a 1 Hz bandwidth and a frequency resolution,Df of 6.25 Hz.这些图是以1Hz带宽的功率谱密度和Df为6.25Hz的频率分辨率的形式绘制的.The spectra are smoothly varying and decay slowly with frequency.该谱平滑变化,并随频率缓慢衰落.It is also insightful to examine how the sound pressure level varies with jet velocity as the function of frequency.研究声压水平作为频率的函数如何随射流速度变化也是很有见识的.Fig.8 shows the dependence of sound pressure level on jet velocity,p2 / VN for h = 45 and 90 .图8示出了,声压水平与射流速度的依存关系,在h＝45度和90度下p2
/VN.For h = 45 ,the sound pressure level is observed to scale as V7.5–V8 in the frequency range between 400 Hz and 10 kHz.在h＝45度时,在400Hz和10kHz之间的频率范围,观察到的声压水平标度为V7.5－V8.This power law is classically associated with quadrupole jet mixing noise.For h = 90 ,a power law of V6.5 in the frequency range 100 Hz–2 kHz is observed.这一幂率经典来说与四极射流混合噪声相关联.在h＝90度时,在100Hz－2kHz的频率范围观察到了V6.5的幂率.This velocity dependence implies that dipole aerodynamic noise sources are dominant at this measurement angle.这一速度依存关系表明了,双极空气动力学噪声源在这一测量角度时是主导性的.One possible dipole noise source is due to the boundary layer being scattered at the nozzle lip.Another possible dipole noise contributor at this frequency range could be due to the noise breakout from inside of the rig.一个可能的双极噪声源是由于边界层在喷嘴唇部被散射而引起的.在这一频率范围,另一个可能的双极噪声贡献源可能是由于在装置（rig）内部的噪声爆发而引起的.From 2 kHz and above,the从2kHz及以上,……