英语翻译A further undesirable consequence of introducing the 90\2-curved diffuser is that its critically unfavourable geometry isprone to generating pressure fluctuations in the flow,whichcan then be transmitted to distance along the wind tunnel.

英语翻译A further undesirable consequence of introducing the 90\2-curved diffuser is that its critically unfavourable geometry isprone to generating pressure fluctuations in the flow,whichcan then be transmitted to distance along the wind tunnel.
英语翻译
A further undesirable consequence of introducing the 90\2-
curved diffuser is that its critically unfavourable geometry is
prone to generating pressure fluctuations in the flow,which
can then be transmitted to distance along the wind tunnel.Furthermore,
the addition of flow splitters inside the 90\2-curved diffuser
may also generate extraneous noise as a result of flow
impingement and boundary layer growth.The settling chamber
was therefore acoustically lined to attenuate the noise sources
located downstream of the valve.The theory of Kurze [19] was
used to predict the transmission loss for different combinations
of lined-splitter numbers and thicknesses.In the final design,
the acoustical liners consist of five parallel absorptive-line splitter
plates and two lined-sideliners.The splitter plates are
1800 mm in length and 110 mm in thickness; whereas the sideliners
are 40 mm in thickness.Super-elliptical leading edge and
tapered trailing edge shapes were included to ensure that
smooth and attached flows exist on the splitter walls.The overall
pressure drop caused by the growth of the boundary layer displacement
thickness on the splitter walls was estimated to be
of negligibly small at 90 Pa.The transmission loss of this silencer
was predicted to be about 35 dB at 2 kHz,falling to about 15 dB
at higher frequencies.
3.5.Nozzle
The flow is accelerated rapidly in the nozzle resulting in large
streamwise strain.The choice of large contraction ratio,such as
in the present design (25:1CR),which is directly proportional to
the strain in the streamwise direction,is useful for minimizing
flow non-uniformity and streamwise velocity fluctuations.However,
the use of a large CR nozzle carries the risk of causing flow
separation near the nozzle exit.In general,the radius of curvature
at the ends can be kept small to avoid separation but this will result
in a longer contraction length and an increase in exit boundary
layer thickness.In addition,the nozzle consists of concave (at upstream)
and convex (at downstream) parts so the inflection point
should be designed such that the first and second derivatives of
the nozzle profiles are as small as possible.
The present nozzle is designed as a three-dimensional,25:1 CR
nozzle.The inlet of the nozzle is a square section measuring
1.3 m \2 1.3 m and the outlet is rectangular shape measuring
0.15 m \2 0.45 m.The axial length of the nozzle is 1.35 m.An isometric
view of the nozzle is presented in Fig.5a.The nozzle performance
has been investigated numerically from a steady RANS
calculation incorporating a k–e turbulence model.As shown in
the velocity contours of Fig.5b,no flow separation is predicted inside
the nozzle.

英语翻译A further undesirable consequence of introducing the 90\2-curved diffuser is that its critically unfavourable geometry isprone to generating pressure fluctuations in the flow,whichcan then be transmitted to distance along the wind tunnel.
A further undesirable consequence of introducing the 90 - curved diffuser is that its critically unfavourable geometry is prone to generating pressure fluctuations in the flow,which can then be transmitted to distance along the wind tunnel.引入90度曲线扩压器的进一步不希望有的结果是,它的受到批评的不利的几何形状,有在流动中产生压力波动的倾向,于是它可能沿风洞传递到远处.Furthermore,the addition of flow splitters inside the 90 -curved diffuser may also generate extraneous noise as a result of flow impingement and boundary layer growth.而且,在90地曲线扩压器中加一个分流器,也可能因为流动冲击和边界层生长而产生外来的噪声.The settling chamber was therefore acoustically lined to attenuate the noise sources located downstream of the valve.因此沉降室从声学上衬里,以衰减位于阀门下游的噪声源.The theory of Kurze [19] was used to predict the transmission loss for different combinations of lined-splitter numbers and thicknesses.Kurze的理论【19】被用来预测不同衬里分流器数和厚度组合下的传递损耗.In the final design,the acoustical liners consist of five parallel absorptive-line splitter plates and two lined-sideliners.在最后设计中,声学衬里包括5块平行的吸收线分流板和2个衬里的侧面衬里（sideliner）.The splitter plates are 1800 mm in length and 110 mm in thickness; whereas the sideliners are 40 mm in thickness.分流板长1800mm,厚110mm；而侧面衬里厚度为40mm.Super-elliptical leading edge and tapered trailing edge shapes were included to ensure that smooth and attached flows exist on the splitter walls.超椭圆的前缘和锥形的拖尾边缘被包括,以确保在分流器壁上存在平滑部分和联系在一起的流动.The overall pressure drop caused by the growth of the boundary layer displacement thickness on the splitter walls was estimated to be of negligibly small at 90 Pa.在分流器壁上由边界层位移厚度的生长引起的总的压力降,估计小的可以忽略,在90Pa.The transmission loss of this silencer was predicted to be about 35 dB at 2 kHz,falling to about 15 dB at higher frequencies.这种消声器的传递损耗,在2 kHz时预测约35dB,在更高频率下降到15dB左右.
3.5.Nozzle
3.5 喷嘴
The flow is accelerated rapidly in the nozzle resulting in large streamwise strain.在喷嘴中,气流被迅速加速,导致很大的流向应变.The choice of large contraction ratio,such as in the present design (25:1CR),which is directly proportional to the strain in the streamwise direction,is useful for minimizing flow non-uniformity and streamwise velocity fluctuations.选择大的收缩比（例如在本设计中25：1CR）对于尽量减小流动的不均匀性和流向速度波动是很有用的,此收缩比与流向方向的应变成正比.However,the use of a large CR nozzle carries the risk of causing flow separation near the nozzle exit.不过,采用大收缩比的喷嘴也带来了风险,那就是引起气流在靠近喷嘴出口处分离.In general,the radius of curvature at the ends can be kept small to avoid separation but this will result in a longer contraction length and an increase in exit boundary layer thickness.总的来说,在末端处的曲率半径可以保持得很小,以避免分离,但这会导致较长的收缩长度和出口边界层厚度的增加.In addition,the nozzle consists of concave (at upstream) and convex (at downstream) parts so the inflection point should be designed such that the first and second derivatives of the nozzle profiles are as small as possible.此外,喷嘴包括凹的（在上游）和凸的（在下游）部分,因此拐点的设计应该是,喷嘴剖面的一次和二次导数要尽可能小.The present nozzle is designed as a three-dimensional,25:1 CR nozzle.本喷嘴设计成一种三维的25：1CR喷嘴.The inlet of the nozzle is a square section measuring 1.3 m 1.3 m and the outlet is rectangular shape measuring 0.15 m 0.45 m.喷嘴的入口是1.3m×1.3m的方形截面,出口则是0.15×0.45m的矩形截面.The axial length of the nozzle is 1.35 m.喷嘴的轴向长度为1.35m.An isometric view of the nozzle is presented in Fig.5a.喷嘴的等轴视图示于图5a.The nozzle performance has been investigated numerically from a steady RANS calculation incorporating a k–e turbulence model.喷嘴的性能已在数值上做了研究,采用的是结合了k－e湍流模型的RANS计算.As shown in the velocity contours of Fig.5b,no flow separation is predicted inside the nozzle.如在图5b的速度轮廓中显示的那样,在喷嘴中没有预测到气流分离.