Investigation at Transonic Speeds of the Effects of Inlet Lip Stagger on the Internal-Flow Characteristics of an Unswept Semielliptical Air Inlet Page: 3 of 33
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NACA RM L56C22
The results of many investigations of scoop-type air intakes with-
out boundary-layer control devices have indicated that in general the
inlet total-pressure recovery tends to decrease as the inlet mass-flow
ratio is reduced. (For example, see refs. 1 and 2.) This trend is
attributed to the effect of the adverse pressure rise on the growth or
separation of the boundary layer ahead of the inlet which becomes more
severe as the inlet flow rate is reduced. At supersonic speeds, addi-
tional boundary-layer losses are effected by the interaction of the
inlet shock with the boundary layer.
The results of a more recent invest-gation (ref. 5) of the internal-
flow characteristics of an unswept scoop inlet which had a lip stagger of
300 have indicated an unusual trend of increasing total-pressure recovery
with decreasing inlet mass-flow ratio. Inasmuch as the configuration did
not have a fixed boundary-layer control device, this trend was attributed
to a "natural" bypassing of some of the fuselage-boundary-layer air around
and outside of the downstream lip as a result of the superstream static
pressure field immediately ahead of the inlet. The static pressure near
the inlet would increase wTith a decrease in mass-flow ratio for any inlet
configuration, but in this case the lip stagger apparently permitted the
thickened or separated boundary layer to be diverted around the inlet to
the lower pressure field of the fuselage.
A survey of existing data on scoop-type inlets without boundary-layer
control devices indicates that these inlets either have little or no lip
stagger. (For example, see ref. 1.) For the cases where lip stagger was
employed, the inlets were swept. (For example, see ref. 2.) None of
these configurations without boundary-layer control had the unusual trend
of increasing pressure recovery with decreasing mass-flow ratio obtained
in reference 3. Upon consideration of these results along with those of
reference 3, it seemed apparent that inlet lip stagger and sweep were
important factors affecting the internal-flow characteristics of a scoop-
The present investigation was undertaken in the Langley transonic
blowdown tunnel to study some of the effects of stagger and sweep on the
internal-flow characteristics of a scoop-type inlet. The results of the
lip-stagger portion of the investigation are reported in this paper.
For the present tests, the inlet lip stagger was varied from 0 to
600 in increments of 15c. These tests were conducted at Mach numbers of
1.0, 1.2, and 1.4 through a range of mass-flow ratio from about 0.3 to
0.9 at an angle of attack of 00.
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Bingham, Gene J. & Trescot, Charles D., Jr. Investigation at Transonic Speeds of the Effects of Inlet Lip Stagger on the Internal-Flow Characteristics of an Unswept Semielliptical Air Inlet, report, May 1, 1956; (digital.library.unt.edu/ark:/67531/metadc62240/m1/3/: accessed January 21, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.