High fidelity simulations of unstart phenomena in a scramjet inlet due to angle of attack

TL;DR

This study uses advanced simulations to analyze unstart phenomena in a scramjet inlet caused by angle of attack, revealing how unstart timing depends on attack angle and pitch rate, which is crucial for hypersonic vehicle design.

Contribution

It provides high-fidelity computational insights into unstart behavior at various angles of attack and pitch rates, advancing understanding of unsteady flow dynamics in scramjet inlets.

Findings

Unstart timing correlates with rapid surge in exit pressure and shock detachment.

Higher exit pressures observed at 10 deg/s pitch rate compared to 100 deg/s.

Unstart depends on both angle of attack and pitch rate.

Abstract

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.