Investigation of the air-flow-regulation characteristics of a translating-spike inlet with two oblique shocks from Mach 1.6 to 2.0 Page: 4 of 16
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NACA RM E56D23b
RESULTS AND DISCUSSION
The variation of pressure recovery with equivalent air flow is pre-
sented in figure 3 for various Mach numbers and spike positions. Equiv-
alent air flow was based on the cowl capture area and is related to the
mass-flow ratio by the expression
w~-2JAi 2 = 49.4(A/A0)(m2mo )P
Contours of the mass-flow ratio, m2/m0 are shown for reference in fig-
ure 3. Spike position is given as MD, which is the Mach number at which
the shock from the 150 half-angle cone would intersect the cowl lip with
a particular spike position. The variation in MD from 1.87 to 2.15 for
a 150 cone is equivalent on a linear translation basis to a variation in
MD from 1.8 to 2.2 for a 250 cone.
The method used for determining the juncture between the 150 and
250 cones did not fully compensate for the curvature of the second shock.
As a consequence, when operating at Mg = 2.0 with the spike at its
design position MD = 2, the shock fell from the second conical surface
H inside the cowl lip. Observation of the schlieren indicated that it was
necessary to extend the spike to a position of MD = 2.09 in order to
make the second shock intersect the cowl lip. For this spike position
the air flow was 96 percent of theoretical maximum at the critical point,
and the pressure recovery was 90 percent.
In general, the pressure-recovery performance of the two-shock con-
figuration was the same as that of the single shock. The greatest sig-
nificant difference occurred for the forward spike position at a Mach
number of 2.0, where the peak pressure recovery was 0.91, which compares
with 0.895 for the 250 cone. Separation of the flow across the spike
juncture did not occur on this model.
Operation of the inlet at an angle of attack of 50 and at a Mach
number of 2.0 indicated a small decrease in both the critical air flow
and pressure recovery and virtually no subcritical stability range. An
approximate calculation indicates that the 50 angle of attack was suf-
ficient to cause shock-induced separation on the upper surface of the
second cone according to the criteria of reference 6. This separation
may account for the loss of stable flow range.
The performance of the inlet at a Mach number of 0.6 is presented
in figure 4 for the limit of spike travel in the fore and aft directions.
This performance was essentially the same as that for the 250 spike in-
let of reference 2. Extrapolation of the performance to air flows higher
than the tested values was made by the methods of reference 7.
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Nettles, J. C. Investigation of the air-flow-regulation characteristics of a translating-spike inlet with two oblique shocks from Mach 1.6 to 2.0, report, July 24, 1956; (digital.library.unt.edu/ark:/67531/metadc53048/m1/4/: accessed February 17, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.