Unstart phenomena induced by flow choking in scramjet inlet-isolators

Seong kyun Im, Hyungrok Do

Research output: Contribution to journalReview articlepeer-review

77 Citations (Scopus)


A review of recent research outcomes in downstream flow choking-driven unstart is presented. Unstart is a flow phenomenon at the inlet that severely reduces the air mass flow rate through the engine, causing a loss of thrust and considerable transient mechanical loading. Therefore, unstart in a scramjet engine crucially affects the design and the operation range of hypersonic vehicles. Downstream flow choking is known to be one of the major mechanisms inducing inlet unstart, as confirmed by recent scramjet-powered flight tests. The current paper examines recent research progress in identifying flow choking mechanisms that trigger unstart. Three different flow choking mechanisms are discussed: flow blockage, mass addition, and heat release from combustion reactions. Current research outcomes on the characteristic of unstarting flows, such as transient and quasi-steady motions, are reviewed for each flow choking mechanism. The characteristics of unstarted flows are described including Buzzing phenomena and oscillatory motions of unstarted shockwaves. Then, the state-of-the-art methods to predict, detect, and control unstart are presented. The review suggests that further investigations with high-enthalpy ground facilities will aid understanding of heat release-driven unstart.

Original languageEnglish
Pages (from-to)1-21
Number of pages21
JournalProgress in Aerospace Sciences
Publication statusPublished - 2018 Feb
Externally publishedYes


  • Flow choking
  • Flow control
  • Hypersonic propulsion
  • Scramjet inlet-isolator
  • Shockwave-boundary layer interaction
  • Unstart

ASJC Scopus subject areas

  • Aerospace Engineering
  • Mechanics of Materials
  • Mechanical Engineering


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