Intrinsic Instability of Compressible Reacting Flows and Its Role in Scramjet Unstart and Transition
Abstract
Approved for Public ReleaseBackground # The transition of a scramjet to thermal-throat operation is accompanied by theformation of a shock train in the isolator. The position of the shock train depends sensitively on theamount of heat release generated by turbulent flames in the combustor. Turbulent flame can enterthe regime when it propagates upstream, which in turn pushes the shock train upstream resultingin the engine unstart. This process is inherently transient, and it critically relies on the delicateinterplay between the supersonic flow and the combustion process in the engine.Objectives # Traditional thinking about the causes of this phenomenon has focused on the onsetof thermal choking due to heat addition in a duct in a classical Rayleigh flow framework. This canbe viewed effectively as a global effect tied to the overall geometry of the system as well as theproperties of the reacting flow in it. Here, we propose to investigate the following questions: i) Canthe flame itselfserve as a source of pressure increase, which can trigger an unstart? ii) Is there anintrinsic instability in the flow or incoming boundary layer turbulence, which can produce local,ratherthan global, choking?Method # The scientific objective of the proposed work is to explore the fundamental mechanismof the intrinsicinstability of super-CJ premixed and non-premixed turbulent flames in the contextof scramjet unstart. The research program will investigate the instability mechanism, throughwhich turbulence can induce local choking producing strong shocks capable of unstarting the engine.Proposed work will examine the effects of fast turbulence and mixture composition on adual-mode scramjet turbulent flame using high-fidelity experiments and DNS with particular focuson realistic system configurations and operating conditions.Significance#The obtained unique data will be used to develop and validate the detailed predictivemodel for scramjet unstart. The investigation will target advanced naval propulsion systems.Insights obtained in the course of this work will significantly advance the high-speedpropulsionresearch and modeling development at engine-relevant conditions. Furthermore, it is expected thatnew strategies will emerge for turbulent combustion control in practical scramjet designs.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- May 15, 2023
- Source ID
- N000142312461
Entities
People
- Alexei Poludnenko
Organizations
- Office of Naval Research
- United States Navy
- University of Connecticut