  This work investigates the unsteady behavior of unstart phenomena within a
scramjet inlet using advanced computational techniques. Scramjets and ramjets,
with their reliance on inlet compression, offer promising airbreathing
propulsion for hypersonic regimes. This research focuses on understanding and
modeling the onset of unstart phenomena in supersonic inlets, a critical step
towards developing mitigation strategies. These strategies have the potential
to improve engine efficiency, range, and maneuverability of hypersonic
vehicles. To achieve this, the state-of-the-art compressible flow solver,
Eilmer, is used to simulate shockwave behavior within the inlet/isolator of a
planar scramjet characterized experimentally at North Carolina State University
(NCSU). Baseline comparisons are presented with the wind tunnel experiments via
the shock structures present within the isolator section conducted at Mach 3.9
on a 3D scramjet inlet model. Simulations are then carried out at varying
angles of attack (0 to 10 deg) and multiple pitch rates (10 deg/sec and 100
deg/sec) to demonstrate the shock train inertial response and to characterize
unstart onset. In both cases the timing of inlet unstart is observed to
correlate well with the rapid surge in exit pressure as well as shock
detachment at the lower leading edge region. Lastly, exit pressures are
significantly higher in the 10 deg/s case than in that of the 100 deg/s case at
the same angle of attack. These observations suggest that unstart is not only
dependent on angle of attack but also on AoA pitch rate. The findings provide
valuable insights into the unsteady flow behavior during hypersonic inlet
unstart, with potential applications for unstart detection at high angles of
attack.
