Scramjet intake usually employs shock waves to reduce the flow velocity and
increases the static pressure of the flow. However, this causes flow
separation and multiple reflections of shock waves, which result in total
pressure loss for the flow. This research investigates the performance
enhancement of scramjet intake through the implementation of a concavity
along the ramp surface, cowl surface, ramp & cowl surfaces. The baseline
intake model [B] used here is the same as that reported in Emami *et al.*
(1995) Three models namely [R1, R2 & R3] with the concavities of depth 0.05
in., 0.1 in. and 0.15 in. respectively on the ramp inner surface are
numerically simulated at Mach number 4.03, and compared with the baseline
model. Similarly four models namely [C1, C2, C3 & C4] with concavities of
depth 0.05 in. and 0.1 in on the cowl inner surface are numerically
simulated and compared with baseline model [B]. Then the best model R2
based on total pressure recovery is selected and combined with concavity on
cowl surfaces namely [R2C1, R2C2, R2C3 and R2C4] are simulated and compared
with baseline model [B]. A combination of ramp surface inclination and
change in throat position is also considered as a means to enhance the
performance of scramjet air intake. Ramp surface angle is initially 11° in
the baseline model. This angle is reduced by 3° after 1 in. flat length
from ramp leading edge. This inclined surface is extended up to 4.92 in.
and then connected to the throat with 4 different locations and four models
are formed namely [TS1, TS2, TS3 & TS4]. An improvement in the performance
is investigated in terms of total pressure recovery, mass flow rate and
flow separation. Present study shows that all the above modified models
except TS1, reduce the flow separation on the ramp wall and increase the
total pressure recovery when compared to the baseline case. This is
achieved by expansion fans produced at the beginning of the concavity.
These expansion fans weaken both the ramp leading edge shock and the cowl
lip shock and suppress the separation size. Further, it turns the shock
waves along the flow, decreasing the number of shock wave reflections in
the isolator. Thus, increase in total pressure at the exit of the isolator
and improved back pressure sustainability are observed. It is found that
there is a marginal increase in Mach number in all the modified models.
Increase in mass flow rate is also observed in the modified models except
[C1, C2, C3 & C4]. Thus, this study demonstrates the scope of overall
improvement in scramjet engine intake performance by implementing concavity along the ramp surface, cowl surface, both ramp & cowl surfaces and ramp surface inclination & throat shift.