Identification of longitudinal acoustic modes associated with pressure oscillations in ramjets

1986 ◽  
Vol 2 (3) ◽  
pp. 199-205 ◽  
Author(s):  
W. H. Clark ◽  
J. W. Humphrey
Keyword(s):  
Pressure Oscillations ◽  
Longitudinal Acoustic ◽  
Acoustic Modes

Coupling Between Internal Vortex Shedding and the Axial Acoustic Modes in a Choked Duct Flow: New Experiments

2000 ◽  
Author(s):  
Eric L. Petersen ◽  
John W. Murdock
Keyword(s):  
Reynolds Number ◽  
Vortex Shedding ◽  
Longitudinal Mode ◽  
Flow Chamber ◽  
Acoustic Mode ◽  
Duct Flow ◽  
Pressure Oscillations ◽  
Longitudinal Acoustic ◽  
Acoustic Modes ◽  
Plate Spacing

Abstract Experiments on vortex shedding within a choked duct and its coupling with the duct’s longitudinal acoustic modes are reported. The vortex shedding and impingement mechanism was produced by a pair of concentric orifice plates placed within the duct. The results of the experiments demonstrate that the frequencies and strengths of the measured acoustic tones depend on the flow velocity, Reynolds number, orifice size, and orifice spacing. A standing wave was produced when the orifice-pair tone was near a longitudinal acoustic mode of the chamber. The oscillation frequency increased slightly with increasing Reynolds number but usually remained within 2-3% of a chamber longitudinal mode. Dual tones and abrupt frequency shifts in singular tones were observed for changes in Reynolds number and/or plate-to-plate spacing. The results of these experiments are part of an ongoing study to better understand the fundamental mechanisms of vortex-induced pressure oscillations within a flow chamber.

The mechanics of vibrating flames in tubes

1977 ◽  
Vol 353 (1675) ◽  
pp. 459-473 ◽  
Keyword(s):  
Experimental Determination ◽  
Wave Motion ◽  
Pressure Oscillations ◽  
Acoustic Modes ◽  
Closed Tube ◽  
Modes Of Vibration ◽  
Dynamical Properties ◽  
Narrow Section ◽  
Derivatives Of

A mechanism of flame vibration is proposed which depends upon the instability of a reacting gas with respect to wave motion. A flame, steadily advancing down a tube, is represented by a narrow section of reacting gas bounded on either side by non-reacting gases at appropriate temperatures. By matching the derivatives of the velocity potentials of the reacting gas and the non-reacting gases at the two interfaces the dynamical properties of the flame are investigated. Relative values of the intensities of the possible acoustic modes, as well as their frequencies, are calculated and are shown to be in general agreement with observations. The pressure oscillations at the end of a closed tube in the unburnt gases are investigated and it is shown how such measurements can provide an experimental determination of the rate of growth of the amplitudes of the permissible modes of vibration.

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