| Tweet |
Custom Search
|
|
|
||
 Section 6:
AUGMENTER MASS FLOW RATE
6.1
Augmenter Mass Flow Correlations. Figures 6, 7 and 8 contain the
augmenter mass flow (pumping) correlation based upon all of the
postconstruction facility checkout data. In this correlation, the total inlet
air mass flow to engine flow rate ratio is plotted versus the ratio of
augmenter duct area to engine flow rate. This form of correlation suggested
itself after the first Miramar checkout where it was noted that total inlet
flow rate remained constant during excursions from military thrust to maximum
afterburning thrust (engine mass flow rate remaining constant). This form of
correlation is fairly accurate as long as the augmenter duct area, AA, is
larger than the engine nozzle throat area (A+A, > 10A+NT(8),) and the total
pressure rise in the pumped flow is lower than the engine nozzle total
pressure (P+TFlow, 0.005 P+TN(8),). Augmenter pumping then becomes primarily
the functions of relative augmenter duct area (increased pumping with
increased duct area) and the location and orientation of the exhaust nozzle
centerlines with respect to the augmenter duct boundaries (maximum pumping
with engine exhaust centered and aligned in augmenter).
6.1.1
Exhaust Data from Augmenter Center. Figure 6 presents data for
aircraft/engine situations where the engine exhaust was centered in the
augmenter. Model test results are included for reference. These data
represent the maximum pumping performance with an essentially constant area
augmenter duct. Model test data reported in [3] show that significant
increases in pumping can be obtained by incorporating a subsonic diffuser on
the augmenter. For the facilities covered herein, however, the constant
section augmenter duct provided adequate pumping of cooling air and the
constant section duct is less expensive to build. Moreover, increasing total
air flow above the minimum needed for cooling can require a bigger, more
costly, air inlet. In the case of the NAS Dallas test cell, a throat section
was included at the upstream end to limit pumping to only cooling. This made
it possible to reduce the air inlet net area and to limit the cell velocity to
less than 50 f/s (15.2 m/s) without a secondary air inlet.
6.1.2
Correlation for Bare J-79 Engines and F-79 Powered F-14. Figure 7
contains the augmenter mass flow correlation for bare J-79 engines and the
J-79 powered F-4. This correlation involves centered and nearly-centered and
aligned engines. Thus, the pumping is close to maximum. In Figure 7 the
effect of a throttle ring (in addition to the throat) in the N.A.S. Dallas
test cell is shown.
6.1.3
Effect of Engine Centerline Offset. Figure 8 shows the effect of
significant engine centerline offset and misalignment on augmenter pumping.
In the case of the F-14, the nozzle centerlines are 9 ft (2.74 m) apart and
splayed outward 1 deg. with an augmenter of 19 ft (5.79 m) width. The exhaust
centerlines for the S-3A are 16 ft (4.88 m) apart and necessitate an enlarged
flow pickup upstream of the 19 ft wide augmenter duct. Figure 8 contains
model test data from Reference [11] for comparison.
6.1.4
Augmenter Length Selection. The augmenter length for the various
dry-cooled facilities was chosen in every case on the basis of required noise
suppression, since the augmenter with its absorptive liner is an important
exterior noise reduction component. Pumping data suggest that adequate
20
|
 
|
|
|
||
