Experiments on the transmission of sound through jets

Bechert, D. W.; Michel, U.; Pfizenmaier, E.

doi:10.2514/6.1977-1278

Cited by 30 publications

(17 citation statements)

References 9 publications

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“…The lower value range is chosen to investigate the effect of sound absorption by vortex shedding, which is known to be strongest for the lower Helmholtz numbers [17,18]. The formula is an approximation of Munt's full analytical solution [7] and for the jet (MR = M ) known to be in very good agreement (in the lower k-range) both with Munt's solution and with the experiments of Bechert, Michel and Pfizenmaier [17]. From the figures the same good agreement is seen in the case of uniform flow (and h =O).…”

Section: Computed Resultsmentioning

confidence: 99%

Acoustic radiation from a semi-infinite annular duct in a uniform subsonic mean flow

Rienstra

1984

Journal of Sound and Vibration

130

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By using a Wiener-Hopf approach, an analytical description is derived of the scattered field of a harmonic sound wave coming out of an open ended annular duct (a semi-infinite cylinder inside of which, coaxially, is a doubly infinite hub), submerged in a subsonic, coaxial, uniform mean flow. The possibility of vortex shedding from the pipe exit edge is included. Explicit expressions are given for the acoustic power inside the pipe, in the acoustic far field and, in the presence of vortex shedding, in the hydrodynamic far field, and of the power absorbed by the vortex sheet. The formulae are evaluated numerically with the aid of asymptotic expansions, and a method in which complex contour deformation is used, which is more convenient than those usually employed for this type of diffraction problem. The equality of power appeared to be an important check on the calculations. A numerical survey is made of the behaviour of the acoustic power loss, due to vortex shedding from the trailing edge, at frequencies near cut-off, as a function of Mach number, mode number of the incident wave, and hub radius. The power loss appears to increase with increasing Mach number, increasing hub radius and with decreasing frequency. Only in the case of the plane wave (where k + 0) does the ratio of radiated and transmitted power become zero; for the other modes (at their cut-off frequencies) this ratio tends to a finite value. Son~ewhat surprising is that, in comparison with the jet, the power loss in a uniform flow is much higher. As a typical example for higher frequencies, the far field radiation pattern of a k = 50, m = 4 wave is considered as a function of the Kutta condition and hub radius.

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Section: Computed Resultsmentioning

confidence: 99%

Acoustic radiation from a semi-infinite annular duct in a uniform subsonic mean flow

Rienstra

1984

Journal of Sound and Vibration

130

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“…According to experiments of Crow (1972) and of Gerend, Kumasaka & Roundhill (1 973), upstream-generated sound is significantly amplified by passage through the jet a t subsonic velocities, the additional radiation being attributed to the excitation of instability waves of the jet. This conclusion has been challenged by Moore (1 977) and by Bechert, Michel & Pfizenmaier (1977), who pointed out that it was based on measurements of the acoustic intensity a t a single far-field location. I n a series of carefully conducted experiments Moore demonstrated that, over a wide frequency range and for jet Mach numbers lying between 0.1 and 0.9, there is no significant overall radiation from the instability mode a t the excitation frequency.…”

Section: Introductionmentioning

confidence: 99%

“…This question was investigated by Bechert et al (1977) using an acoustic tone generated within the jet pipe by means of a system of matched loudspeakers. Although their experiment was confined to the case of a cold subsonic jet, which precluded a strict comparison with the earlier work, the absence of amplification a t the tonal frequency was confirmed.…”

Section: Introductionmentioning

confidence: 99%

Attenuation of sound in a low Mach Number nozzle flow

Howe¹

1979

J. Fluid Mech.

151

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This paper examines the energy conversion mechanisms which govern the emission of low frequency sound from an axisymmetric jet pipe of arbitrary nozzle contraction ratio in the case of low Mach number nozzle flow. The incident acoustic energy which escapes from the nozzle is partitioned between two distinct disturbances in the exterior fluid. The first of these is the free-space radiation, whose directivity is equivalent to that produced by monopole and dipole sources. Second, essentially incompressible vortex waves are excited by the shedding of vorticity from the nozzle lip, and may be associated with the large-scale instabilities of the jet. Two linearized theoretical models are discussed. One of these is an exact linear theory in which the boundary of the jet is treated as an unstable vortex sheet. The second assumes that the finite width of the mean shear layer of the real jet cannot be neglected. The analytical results are shown to compare favourably with recent attenuation measurements.

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“…Taken one by one the effect of high acoustic excitation levels, bias flow and grazing flow are reasonably well understood. The nonlinear effect of high level acoustic excitation has for instance been studied in [1][2][3][4][5][6][7][8][9][10][11] . It is well known from this literature that perforates can become non-linear at fairly low acoustic excitation levels.…”

Section: Introductionmentioning

confidence: 99%

The effect of combined high level acoustic excitation and bias flow on the acoustic properties of an in-duct orifice

Zhou

Bodén

2013

19th AIAA/CEAS Aeroacoustics Conference

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This paper investigates the acoustic properties of an orifice with bias flow under medium and high sound level excitation. Orifices with two different edge configurations were tested experimentally.The study includes a wide range of bias flow velocities, various acoustic excitation levels and different frequencies. The so-called Cummings equation was the starting point for the theoretical modelling. It was modified and a novel orifce acoustic discharge coefficient model was developed both for cases with and without bias flow. The model was experimentally validated. With this model the acoustic resistance is obtained by the harmonic balance method, and the results agree fairly well with the experimental results for low frequencies. Experimental results also show that bias flow makes the acoustic properties much more complex compared to the no bias flow case, especially when the velocity ratio between acoustic particle velocity and mean flow velocity is near unity. Nomenclature C C = Orifice time varying discharge coefficient C CA = Acoustic flow discharge coefficient C CA0 = Acoustic flow discharge coefficient under low acoustic excitation C CAmin = Minimum acoustic flow discharge coefficient under high acoustic excitation C CAi = Acoustic flow discharge coefficient for different regions, i=1,2,3,4 C CM = Mean flow discharge coefficient l = Effective orifice thickness l = Average effective orifice thickness l 0 = End correction on one side of orifices ≈ (π/4)· r l W = Orifice thickness L J = Orifice jet length U = Mean flow velocity V = Fluctuating acoustic velocity V ˆ = Peak velocity for acoustic flow V rms = Root mean square velocity value for acoustic flow r = Orifice radius Re rms = Reynolds number for acoustic flow Sr rms = Strouhal number for acoustic flow T ω f = Acoustic period time, angular frequency=2π/T, and frequency=1/T ρ 0 = Air density σ = Porosity of orifice plate p = Fluctuating pressure difference P = Steady pressure drop P R P I = Real and imaginary part of acoustic pressure difference ν = Air kinetic viscosity (1.55×10-5 Pa· s)

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Experiments on the transmission of sound through jets

Cited by 30 publications

References 9 publications

Acoustic radiation from a semi-infinite annular duct in a uniform subsonic mean flow

Acoustic radiation from a semi-infinite annular duct in a uniform subsonic mean flow

Attenuation of sound in a low Mach Number nozzle flow

The effect of combined high level acoustic excitation and bias flow on the acoustic properties of an in-duct orifice

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