Quantcast Section 9: Augmented Exit Velocity

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Section 9:
Exit Velocity Limits.  Augmenter exit velocity measurements were
taken in the postconstruction checkout tests reported in References [1, 3, and
8] and in model tests reported in References [3, 13 and 14].  Velocities were
derived from measurements of augmenter exit total pressure and total
temperature assuming that the static pressure across the augmenter exit plane
was uniform and equal to ambient (barometric) pressure.  Augmenter exit
velocity is important because the flow leaving the augmenter is an important
noise source.  For all of the facilities (which were designed to meet an 85
dBA noise limit at 250 ft (76.2 m) from the engine exhaust plane), the intent
was that the "self-noise" caused by flow leaving the augmenter exit shall not
contribute more than 2 dBA to the maximum noise level at the 250-ft distance.
This implied limiting the peak velocity in the flow which leaves the augmenter
to less than 500 f/s (152.4 m/s).  A much lower exit velocity, 350 f/s (106.7
m/s), will be required to meet a noise limit of 75 dBA at 250 ft with a lined
augmenter plus a ramp-type sound suppressor.
Exit Velocity Test Results.  All of the full-scale augmenter exit
velocity distributions measured are presented in Figures 23 and 24.  Figure 23
contains data from the checkouts of the Miramar No. 2 and El Toro hush-houses.
Figure 24 contains data taken with a J-79 in the NAS Dallas test cell.  Figure
24 shows the effect of throttling (reducing augmentation) on the augmenter
exit velocity.  This would normally have resulted in a lower maximum noise
level at 250 ft, but the throttle ring generated noise so the total noise
level increased.


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