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 Section 7:
ENCLOSURE INTERIOR FLOW CONDITIONS
7.1
Enclosure Interior Conditions.
Enclosure interior conditions of
interest include:
a)
interior pressure (cell depression)
b)
velocity approaching aircraft/engine inside of enclosure -
V+int,
c)
enclosure interior flow patterns
hush-house/test cell designs are based on providing acceptable
interior conditions from the standpoint of the enclosure structure, engine
operation and personnel comfort and safety. Thus, it is typical to limit cell
depression to 2 in. (50.76 mm) H+2,O, interior velocity to 50 f/s (15.24 m),
and to avoid significant recirculation of exhaust gases within the enclosure.
7.1.1
Interior Pressure. Interior pressure (cell depression) data are
presented in Table 5 and in Figures 9 and 10. It is apparent from a
comparison of Figures 9 and 10 that hush-house cell depression data group best
when plotted versus the specific flow rate through the primary between the
baffles net area (W+1,/A+1net,). The Patuxent River hush-house primary
exhibits a higher loss because of the inclusion of demisting elements. The
N.A.S. Dallas test cell exhibits lower loss because the vaned turn from
vertical to horizontal does not involve flow deceleration. Note that the cell
depression varies roughly as the square of the specific flow rate or, i.e., as
the dynamic pressure in the minimum net area A+1net,.
7.1.2
Interior Velocity. Table 5 and Figures 11, 12 and 13 present
enclosure interior velocity, V+int, data. A comparison between Figures 11, 12
and 13 indicates that the best correlation occurs with specific mass flow rate
based upon the effective flow area within the enclosure. (A+door, in the case
of a hush-house and total cell cross-section in the case of the N.A.S. Dallas
test cell.) The velocity measurements used in Figures 11 through 13 were
taken 15 ft (4.57 m) from the hush-house door outlet and about 10 ft (3.05 m)
into the constant height test cell in the case of N.A.S. Dallas.
7.1.3
Interior Flow Patterns. Enclosure flow patterns are of interest
because of concerns about exhaust recirculation in the hush-houses and, in the
case of the A/E 32T-15 Pegasus dedicated test cell at MCAS Cherry Point,
concerns about bad compressor face distortion arising from ingestion of low
energy flow. Figures 14 and 15 show enclosure interior flow patterns with the
A-6 at El Toro and with the S-3A at Patuxent River respectively. The A-6 and
S-3A represent the most difficult hush-house flow capture problem. In both
cases, the degree of recirculation appears to be acceptable (in the case of
the S-3A, this is true because most of the recirculation involves relatively
cool air from the fan exhaust). Figure 16 shows A/E 32-T15 interior flow
patterns during F-402 Pegasus runup. A recommendation was made that the cell
flow rate be increased to minimize low energy air ingestion, even though the
problem being addressed did not result from the flow distribution.
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