A Rocket-Like Coaxial Injector in an Acoustic Field Under Sub- and Supercritical Conditions

Abstract

An experimental investigation was undertaken under non-reacting condition to gain a physical understanding of the interaction of acoustic waves and a coaxial-jet injector similar to those used in cryogenic liquid rockets. Liquid nitrogen (the round inner jet) and gaseous nitrogen (the annular outer jet) were used under subcritical, near critical, and supercritical chamber pressures, with and without presence of an external acoustic field. High-speed imaging provided information on the dynamic behavior of the jet under a variety of conditions. It is found that when the jet is at the pressure node, an externally-imposed acoustic field excites the dark-core of the jet to a wavy-shaped structure consistent with the field's characteristics. Mean and root mean square (RMS) values of the dark-core length fluctuations were measured from images. It is found that when the outer-to-inner-jet velocity ratio increases, the RMS of the dark-core length fluctuations decreases both with and without the existence of the acoustic field. A connection to the rocket instability may be established from these data through examination of the RMS values. It is possible that decreases in the fluctuation levels, observed at higher velocity ratios, could weaken a key feedback mechanism for the self-excitation process that could be driving combustion instability in rocket engines. This can offer a possible explanation of the combustion stability improvements experienced in engines when a transition to higher values of the outer-to-inner-jet velocity ratio is made. Finally, after a careful review of relevant data taken here and elsewhere, there appears to be a good correlation between the dark-core length and the momentum flux ratio.

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Document Details

Document Type
Technical Report
Publication Date
Jul 03, 2006
Accession Number
ADA456610

Entities

People

  • Bruce Chehroudi
  • D. W. Davis
  • Douglas G. Talley

Organizations

  • Air Force Research Laboratory

Tags

Communities of Interest

  • Materials and Manufacturing Processes
  • Weapons Technologies

DTIC Thesaurus Topics

  • Acoustic Fields
  • Acoustic Waves
  • Air Force Research Laboratories
  • Combustion
  • Combustion Stability
  • Engines
  • Flow Rate
  • Fluid Flow
  • Fluid Mechanics
  • Injectors
  • Instability
  • Liquid Oxygen
  • Measurement
  • Mechanical Engineering
  • Propulsion Systems
  • Rocket Engines
  • Waves

Fields of Study

  • Physics

Readers

  • Atmospheric Science / Meteorology, specifically Wind Wave Turbulence.
  • Combustion and Flow Dynamics.