Receptivity of a Cryogenic Coaxial Gas-Liquid Jet to Acoustic Disturbances
[report]
Jeffrey L. Wegener, David J. Forliti, Ivett A. Leyva, Douglas G. Talley
2014
unpublished
Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services,
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... torate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. An experimental study has been conducted at the Air Force Research Laboratory at Edwards Air Force Base to explore the receptivity of cryogenic coaxial jet flows to transverse acoustic disturbances. The shear coaxial jet flow employed liquid nitrogen in the inner jet and cooled helium in the outer annular jet to represent the nominal fluid dynamical conditions of an oxygen/hydrogen liquid rocket engine injector. The injector flow is submerged in a chamber that experiences a monotonic transverse acoustic resonance characteristic of a rocket chamber in the presence of combustion instability. The coaxial jet is exposed to a variety of acoustic conditions including different frequencies, amplitudes, and locations within the resonant mode shape. High-speed back-lit images were captured to record the behavior of the natural (unforced) and forced coaxial jets. Proper orthogonal decomposition and spectral analysis were used to extract natural and forced modes. Convective modes are extracted, and a new Strouhal number is used to characterize the dominant natural convective mode that is analogous to the preferred mode in free jets. The threshold of receptivity was found for a number of different injector flows and acoustic forcing conditions. The results indicate that the dimensionless frequency plays an important role, and there exists a finite forcing amplitude at which the threshold of receptivity occurs. The receptivity threshold and post receptivity response provides useful insight on the suitability of a given injector design for specific rocket combustion chamber conditions. 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT 18. NUMBER OF PAGES 19a. NAME OF RESPONSIBLE PERSON Doug Talley a. REPORT Unclassified b. ABSTRACT Unclassified c. THIS PAGE Unclassified SAR 14 19b. TELEPHONE NO (include area code) 661-275-6174 Standard Form 298 (Rev. 8-98) An experimental study has been conducted at the Air Force Research Laboratory at Edwards Air Force Base to explore the receptivity of cryogenic coaxial jet flows to transverse acoustic disturbances. The shear coaxial jet flow employed liquid nitrogen in the inner jet and cooled helium in the outer annular jet to represent the nominal fluid dynamical conditions of an oxygen/hydrogen liquid rocket engine injector. The injector flow is submerged in a chamber that experiences a monotonic transverse acoustic resonance characteristic of a rocket chamber in the presence of combustion instability. The coaxial jet is exposed to a variety of acoustic conditions including different frequencies, amplitudes, and locations within the resonant mode shape. High-speed back-lit images were captured to record the behavior of the natural (unforced) and forced coaxial jets. Proper orthogonal decomposition and spectral analysis were used to extract natural and forced modes. Convective modes are extracted, and a new Strouhal number is used to characterize the dominant natural convective mode that is analogous to the preferred mode in free jets. The threshold of receptivity was found for a number of different injector flows and acoustic forcing conditions. The results indicate that the dimensionless frequency plays an important role, and there exists a finite forcing amplitude at which the threshold of receptivity occurs.
doi:10.21236/ada611404
fatcat:nqagwnjcvbaqlb4f6fupjeu5ze