问题描述：
英语翻译
Fig.11a shows the velocity profiles of the plane parallel to the
jet axis (x–y plane) at z = 0 between streamwise distance,x of 0.1
and 1.3 m with an increment of every 0.1 m.Fig.11a shows the
evolution of the jet velocity profile and its development downstream.
It begins as a ‘top-hat’ profile close to the jet nozzle,eventually
forming a fully-developed profile further downstream.This
variation characterizes the spreading of the momentum-deficit
shear layers that were shed from the top and bottom nozzle edges
by entrainment as the flow progresses downstream.The end of the
jet’s potential core is clearly seen to be situated between x = 0.8
and 0.9 m,or 3.6–4Dh,where Dh,is the hydraulic diameter of the
nozzle.It is expected that this length is relatively constant over
the range of Reynolds numbers proposed here.The distribution
of the velocity profiles averaged across the y-axis at different spanwise
location of the nozzle exit plane at x = 0.05 m is shown in
Fig.11b.From the figure,apart from the left and right edges where
mixing layers exist,the velocity profile across the nozzle exit plane
is found to be uniform with an average jet velocity of 21.6 m/s in
this example.Flow uniformity was demonstrated by the small error
bars corresponding to the maximum and minimum velocity
deviations inside the potential core.The results in Fig.11a and b
provide a clear indication of the extent and profile of the potential
core in which the airfoil must be completely located to perform the
trailing edge self-noise study to avoid the noise contribution from
interaction with extraneous turbulence.
The turbulence intensity in the exit jet was measured using a
TSI 1210-T1.5 miniature hot wire probe with 3.8 lm diameter.
The same computer-controlled traverse system was used to measure
at several points from the nozzle edge to the centre in a single
run.Fig.12 shows the distribution of the turbulence intensity
along the z-axis of the free jet at 60 m/s from the nozzle edge
(z = 0.225 m) to the centre (z = 0).This measurement was performed
at a streamwise distance,x = 0.1 m away from the nozzle
exit.Apart from the first point near the edge that is located within
the shear layer,the potential core of the free jet has a typical turbulence
intensity of about 0.1%.This value is well below the initial
target of 0.5%.With such low disturbance level in the free flow,
extraneous noise caused by the interaction of the jet turbulence
with the airfoil leading edge is likely to be insignificant.
Fig.11a shows the velocity profiles of the plane parallel to the
jet axis (x–y plane) at z = 0 between streamwise distance,x of 0.1
and 1.3 m with an increment of every 0.1 m.Fig.11a shows the
evolution of the jet velocity profile and its development downstream.
It begins as a ‘top-hat’ profile close to the jet nozzle,eventually
forming a fully-developed profile further downstream.This
variation characterizes the spreading of the momentum-deficit
shear layers that were shed from the top and bottom nozzle edges
by entrainment as the flow progresses downstream.The end of the
jet’s potential core is clearly seen to be situated between x = 0.8
and 0.9 m,or 3.6–4Dh,where Dh,is the hydraulic diameter of the
nozzle.It is expected that this length is relatively constant over
the range of Reynolds numbers proposed here.The distribution
of the velocity profiles averaged across the y-axis at different spanwise
location of the nozzle exit plane at x = 0.05 m is shown in
Fig.11b.From the figure,apart from the left and right edges where
mixing layers exist,the velocity profile across the nozzle exit plane
is found to be uniform with an average jet velocity of 21.6 m/s in
this example.Flow uniformity was demonstrated by the small error
bars corresponding to the maximum and minimum velocity
deviations inside the potential core.The results in Fig.11a and b
provide a clear indication of the extent and profile of the potential
core in which the airfoil must be completely located to perform the
trailing edge self-noise study to avoid the noise contribution from
interaction with extraneous turbulence.
The turbulence intensity in the exit jet was measured using a
TSI 1210-T1.5 miniature hot wire probe with 3.8 lm diameter.
The same computer-controlled traverse system was used to measure
at several points from the nozzle edge to the centre in a single
run.Fig.12 shows the distribution of the turbulence intensity
along the z-axis of the free jet at 60 m/s from the nozzle edge
(z = 0.225 m) to the centre (z = 0).This measurement was performed
at a streamwise distance,x = 0.1 m away from the nozzle
exit.Apart from the first point near the edge that is located within
the shear layer,the potential core of the free jet has a typical turbulence
intensity of about 0.1%.This value is well below the initial
target of 0.5%.With such low disturbance level in the free flow,
extraneous noise caused by the interaction of the jet turbulence
with the airfoil leading edge is likely to be insignificant.
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