Hostname: page-component-7b7567c8c-jswmv Total loading time: 0 Render date: 2026-11-15T22:16:38.148Z Has data issue: false hasContentIssue false
  • English
  • Français

Low-frequency pressure oscillations in a model ramjet combustor

Published online by Cambridge University Press:  26 April 2006

Ken H. Yu,
Arnaud Trouvé and
John W. Daily
Ken H. Yu
Affiliation:
Department of Mechanical Engineering, University of California, Berkeley, CA 94720, USAPresent address: Research Department, Naval Weapons Center, China Lake, CA 93555, USA.
Arnaud Trouvé
Affiliation:
Center for Turbulence Research, Stanford University, Stanford, CA 94305, USA
John W. Daily
Affiliation:
Department of Mechanical Engineering, University of Colorado, Boulder, CO 80309, USA
Get accessRights & Permissions [Opens in a new window]

Abstract

Low-frequency combustion instabilities are studied in a model ramjet combustor facility. The facility is two-dimensional, and is comprised of a long inlet duct, a dump combustor cavity with variable size capability, and an exhaust nozzle. The flame is observed to be unstable over a wide range of operating conditions. Acoustic pressure and velocity measurements are made at various locations in the system. They show that the inlet duct acts as a long-wavelength acoustic resonator. However, the instability frequency does not lock to any particular value. This result suggests that the instability mechanism is not purely acoustic in nature. Schlieren imaging reveals that the instability is associated with large-scale flame-front motions which are driven by periodic vortex shedding at the instability frequency. Vortices are generated at the dump in phase with the acoustic velocity fluctuations in the inlet duct. The unsteady heat addition process closely follows the vortex history: the vortices form, grow in size, convect through the combustor cavity, impinge on the exhaust nozzle, break down to small scales and burn. C2 and CH radical spectroscopy is used to determine the phase relation between heat release and pressure in the reaction zone. Rayleigh's criterion is thereby shown to be satisfied. Next, the crucial question of how the oscillation frequency is determined is addressed. Inlet velocity and combustor length are systematically varied to assess the role of vortices by modification of their characteristic lifetime. The influence of the acoustic feedback time is also studied by shortening the inlet duct. The results show that the instability frequency is controlled by both vortex kinetics in the combustor and acoustic response of the inlet section. Therefore, the instability may be considered as a mixed acoustic-convective mode. Finally, combining Rayleigh's criterion with a global feedback loop equation, it is found that the resonant frequencies are selected according to the restriction\[\frac{1}{4N-1} < \frac{\tau_{\rm v}}{\tau_{\rm f}} < \frac{3}{4N-3},\]where N is the mode of oscillation and τv is the time for vortices to be convected from inlet to exhaust with τf being the feedback time taken for a pressure disturbance to travel up the inlet system and back.

Information

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 232 , November 1991, pp. 47 - 72
Copyright
© 1991 Cambridge University Press

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

Article purchase

Temporarily unavailable

References

Abouseif, G. E., Keklak, J. A. & Toong, T. Y. 1984 Ramjet rumble: the low frequency instability mechanism in coaxial dump combustors. Combust. Sci. Tech. 36, 83–108.Google Scholar
Bradley, D. & Mitcheson, A. 1978 The venting of gaseous explosions in spherical vessels. I-theory. Combust. Flame 32, 221–236.Google Scholar
Chu, B. T. 1956 On the energy transfer to small disturbances in a viscous compressible heat conductive medium. AFOSR Contractor Rep., Johns Hopkins University.
Crump, J. E., Schadow, K. C., Yang, V. & Culick, F. E. C. 1986 Longitudinal combustion instabilities in ramjet engines: identification of acoustic modes. J. Propulsion Power 2, 105–109.Google Scholar
Eaton, J. K. & Johnston, J. P. 1980 Turbulent flow reattachment: an experimental study of the flow and structure behind a backward-facing step. Rep. MD-39. Stanford University.
Hegde, U. G., Reuter, D., Zinn, B. T. & Daniel, B. R. 1987 Fluid mechanically coupled combustion instabilities in ramjet combustors. 25th Aerospace Sciences Meeting, Reno, NV, Paper 0216.
Ho, C. M. & Nosseir, N. S. 1981 Dynamics of an impinging jet. Part 1. the feedback phenomenon. J. Fluid Mech. 105, 119–142.Google Scholar
Humphrey, J. W. & Culick, F. E. C. 1987 Linear and nonlinear stability of acoustics with nonuniform entropy in chambers with mean flow. 19th Fluid Dynamics, Plasma Dynamics and Lasers Conf., Honolulu, HW, Paper 1417.
Jou, W. H. & Menon, S. 1986 Numerical simulation of the vortex-acoustic wave interaction in a dump combustor. 24th Aerospace Sciences Meeting, Reno, NV, Paper 0002.
Jou, W. H. & Menon, S. 1987 Simulations of ramjet combustor flow fields. Part II. origin of pressure oscillations. 19th Fluid Dynamics, Plasma Dynamics and Lasers Conf. Honolulu, HW, Paper 1422.
Langhorne, P. J. 1988 Reheat buzz: an acoustically coupled combustion instability. Part 1. experiment. J. Fluid Mech. 193, 417–443.Google Scholar
Marble, F. E. & Candel, S. M. 1977 Acoustic disturbance from gas non-uniformities convected through a nozzle. J. Sound Vib. 55, 225–243.Google Scholar
Martin, R. M., Brooks, T. F. & Hoad, T. R. 1985 Reduction of background noise induced by wind tunnel jet exit vanes. AIAA J. 23, 1631–1632.Google Scholar
Morse, P. M. & Ingard, K. U. 1968 Theoretical Acoustics. McGraw-Hill.
Pitz, R. W. & Daily, J. W. 1983 Combustion in a turbulent mixing layer formed at a rearward-facing step. AIAA J. 21, 1565–1570.Google Scholar
Poinsot, T., Trouvé, A., Veynante, D., Candel, S. M. & Esposito, E. 1987 Vortex driven acoustically coupled combustion instability. J. Fluid Mech. 177, 265–292.Google Scholar
Putnam, A. A. 1971 Combustion Driven Oscillations in Industry. Elsevier.
Rayleigh Lord 1878 The explanation of certain acoustic phenomena. R. Inst. Proc. 8, 536–542.Google Scholar
Rayleigh Lord 1945 The Theory of Sound, p. 227. Dover.
Rockwell, D. 1983 Oscillations of impinging shear layers. AIAA J. 21, 645–664.Google Scholar
Rogers, D. E. & Marble, F. E. 1956 A mechanism for high frequency oscillations in ramjet combustors and afterburners. Jet Propulsion 26, 456–462.Google Scholar
Schlichting, H. 1979 Boundary Layer Theory, pp. 436–438. McGraw Hill.
Smith, D. A. 1985 An experimental study of acoustically excited, vortex driven, combustion instability within a rearward facing step combustor. PhD thesis, California Institute of Technology.
Smith, D. A. & Zukoski, E. E. 1985 Combustion instability sustained by unsteady vortex combustion. 21st Joint Propulsion Conf., Monterey, CA, Paper 1248.
Sterling, J. D. & Zukoski, E. E. 1987 Longitudinal mode combustion instabilities in a dump combustor. 25th Aerospace Sciences Meeting, Reno, NV, Paper 0220.
Trouvé, A., Candel, S. M. & Daily, J. W. 1988 Linear stability of the inlet jet in a ramjet dump combustor. 26th Aerospace Sciences Meeting, Reno, NV, Paper 0149.
Trouvé, A., Yu, K. & Daily, J. W. 1987 Phase sensitive schlieren system for studying periodic combustion phenomena. Joint Meeting of the Western States Section of the Combustion Institute, Honolulu, HW.