Research Summary on the AEDC ASTF C-2 Aeroacoustic Resonance Phenomenon

Sebourn, Charles L.; Shope, Frederick L.

doi:10.2514/6.2005-2932

Cited by 7 publications

(13 citation statements)

References 9 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In worst cases, there may be a 'locked-in' resonance accompanied by a howl that can involve high unsteady aerodynamic loads raising structural concerns. Such phenomena have been encountered historically in different facilities, e.g., at the Arnold Engineering Development Center (AEDC) in the early nineties (see, [1,2]) as well as in the Propulsion System Laboratory (PSL) at NASA Glenn Research Center (GRC) on various occasions. Reference [1] also cites similar experiences in a few other facilities in the past.…”

Section: Introductionmentioning

confidence: 99%

Noise from a Jet Discharged into a Duct and its Suppression

Zaman

Clem

Fagan

2013

International Journal of Aeroacoustics

View full text Add to dashboard Cite

This study addresses unwanted high intensity noise sometimes encountered in engine test facilities. Model-scale experiments are conducted for a round jet discharged into a cylindrical duct. In most cases, the unwanted noise is found to be due to longitudinal resonance modes of the duct excited by the random turbulence of the jet. When the 'preferred mode' frequency of the jet matches a duct resonant frequency there can be a locked-in 'super-resonance' accompanied by a high intensity tone or 'howl'. Various techniques are explored for suppression of the unwanted noise. Tabs placed on the ends of the duct are found ineffective; so are longitudinal fins placed inside the duct. A rod inserted perpendicular to the flow ('howl stick') is also found generally ineffective; however, it is effective when there is a super-resonance. By far the most effective suppression is achieved by a wire-mesh screen placed at the end of the duct. The screen not only eliminates the superresonance but also the duct mode spectral peaks. Apparently the screen works by dampening the velocity fluctuations at the pressure node and thereby weakening the resonant condition.

show abstract

Section: Introductionmentioning

confidence: 99%

Noise from a Jet Discharged into a Duct and its Suppression

Zaman

Clem

Fagan

2013

International Journal of Aeroacoustics

View full text Add to dashboard Cite

show abstract

“…In actual situations, however, the wavelength of the sound in the resonance modes is usually comparable to the shroud length, which in turn is comparable to its diameter (e.g. Jones & Lazalier 1992;Sebourn & Shope 2005). It is well known that for open-exit configurations, reflections of outgoing acoustic waves are significantly reduced when these lengths are comparable (e.g.…”

Section: Introductionmentioning

confidence: 99%

Finite-wavelength scattering of incident vorticity and acoustic waves at a shrouded-jet exit

Samanta

Freund

2008

J. Fluid Mech.

View full text Add to dashboard Cite

As the vortical disturbances of a shrouded jet pass the sharp edge of the shroud exit some of the energy is scattered into acoustic waves. Scattering into upstream-propagating acoustic modes is a potential mechanism for closing the resonance loop in the ‘howling’ resonances that have been observed in various shrouded jet configurations over the years. A model is developed for this interaction at the shroud exit. The jet is represented as a uniform flow separated by a cylindrical vortex sheet from a concentric co-flow within the cylindrical shroud. A second vortex sheet separates the co-flow from an ambient flow outside the shroud, downstream of its exit. The Wiener–Hopf technique is used to compute reflectivities at the shroud exit. For some conditions it appears that the reflection of finite-wavelength hydrodynamic vorticity modes on the vortex sheet defining the jet could be sufficient to reinforce the shroud acoustic modes to facilitate resonance. The analysis also gives the reflectivities for the shroud acoustic modes, which would also be important in establishing resonance conditions. Interestingly, it is also predicted that the shroud exit can be ‘transparent’ for ranges of Mach numbers, with no reflection into any upstream-propagating acoustic mode. This is phenomenologically consistent with observations that indicate a peculiar sensitivity of resonances of this kind to, say, jet Mach number.

show abstract

“…The acoustic normal mode (0, 2) of the duct has a pressure node at y H=4. Similarly, the normal mode (2, 0) has pressure nodes at x L=5 and 3L=5, the normal mode (1,4) has pressure nodes at y H=8 and 3H=8 and x L=3, and the normal mode (3, 2) has pressure nodes at y H=3 and x L=7, 3L=7, and 5L=7. Such pressure nodes can be observed at approximately those positions in Fig.…”

Section: A Hydrodynamic Instability and Mechanisms Of Resonancementioning

confidence: 99%

“…It has been reported in several studies [1][2][3][4], that under certain testing conditions high-intensity pressure fluctuations are observed in such facilities. The intensity of the fluctuations in the exhaust system reach, in some cases, nearly 170 dB, which is beyond the acceptable limit for the installations, and so the tests are stopped to prevent structural damage.…”

mentioning

confidence: 99%

“…There is to date no means to predict whether or not this highamplitude resonance will occur for a given set of testing conditions, or to anticipate the intensity under resonance [4]. So far, these resonances have been suppressed by trial-and-error procedures, either by changing the flow testing conditions (e.g., changing the amount of water spray injected to cool the diffuser walls or the amount of coflow) or the facility configuration (e.g., adding Helmholtz resonators to the diffuser, tuned to the frequency of the excited normal mode) [3].…”

mentioning

confidence: 99%

See 1 more Smart Citation