Numerical Study of Hysteresis related to the Unstart/Restart Cycle in Scramjet Engines

Author(s)	Dr. Jayahar Sivasubramanian, Mr. Vishesh V, Mr. Zaid M
Country	India
Abstract	A Turbine Based Combined Cycle (TBCC) with a dual mode scramjet is a key candidate for future end-to-end hypersonic flight. The design of scramjet inlets is critical for the overall performance of the engine. With a variable supersonic inlet, the throat area decreases to alter the aerodynamic losses, but extreme constriction seen in terms of Internal Contraction Ratio (ICR) increases the chances of unstart. Two-dimensional unsteady numerical simulations are conducted to study the features of the flow and the process of start, unstart, and restart states in scramjet engines. Hysteresis of the flow is observed in the results obtained and it is concluded that a restart is found after increasing the aerodynamic throat area. It is found that separation ahead of the inlet held in place by the separation shock affects the hysteresis and the ability of the engine to return to its original operating condition. The option of utilizing bleed to delay unstart and to bring stability to the flow is also explored.
Keywords	Unstart, TBCC, Scramjet, Flow Separation, SBLI
Field	Engineering
Published In	Volume 8, Issue 2, March-April 2026
Published On	2026-04-15
DOI	https://doi.org/10.36948/ijfmr.2026.v08i02.74866

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