Low-Order Model for Buzz Oscillations in the Intake of a Ramjet Engine

Abstract

Buzz refers to the self-sustained oscillations of the terminal shock in a mixed-compression supersonic intake where it is periodically sucked into the intake duct and then forced out. Correspondingly, the air mass flow rate entering the intake and the intake backpressure (combustion chamber pressure) fluctuate. The related phenomenon where the terminal shock emerges and establishes itself outside the intake duct in a relatively steady manner is usually called unstart. Buzz oscillations have plagued every type of supersonic intake ever since the phenomenon was discovered by Oswatitsch, and ramjets are no exception. There is a heightened risk of intake unstart or buzz for ramjet-powered vehicles during maneuvers such as accelerated climb where the fuel injection rate has to be delicately balanced between the increased thrust requirement and the decreasing air mass flow rate with altitude. Besides, atmospheric disturbances which may trigger buzz/unstart are the most severe at low altitudes, typical at the start of an accelerated climb segment. Hence, there is a need to actively control the position of the terminal shock in the intake duct, usually by prescribing a certain unstart/buzz margin or, ∗Ph. D. Student, Division of Aerospace Engineering, KAIST, 373-1 Guseong-dong, Yuseong-gu, Daejeon 305-701, South Korea; ispak@fdcl.kaist.ac.kr †Research Professor, Division of Aerospace Engineering, KAIST, 373-1 Guseong-dong, Yuseong-gu, Daejeon 305-701, South Korea; drakn19@kaist.ac.kr ‡Professor, Division of Aerospace Engineering, KAIST, 373-1 Guseong-dong, Yuseong-gu, Daejeon 305-701, South Korea; mjtahk@fdcl.kaist.ac.kr §Associate, IDeA Research & Development (P) Ltd, Magarpatta City, Hadapsar, Pune 411013, India; vineeth@idearesearch.in ¶CEO, IDeA Research & Development (P) Ltd, Magarpatta City, Hadapsar, Pune 411013, India; nitin@idearesearch.in