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Nov 1988

Volume 84, Issue S1, pp. S2-S224

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back to top Session LL. Structural Acoustics and Vibration IV: Flow‐Induced Sound and Vibration
Invited Papers
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The basics of flow noise (A)

Eugen J. Skudrzyk

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S116-S116 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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The flow noise nearfield that is recorded by a flush‐mounted hydrophone is generated by a “Bernoulli” effect. Because the pressure within the eddies is less than that in the fluid outside, fluid is injected into the eddies and thrown against the wall. The kinetic pressure is then recorded as nearfield noise. The nearfield sensitivity of a hydrophone seems to depend greatly on its shape and size. But a closer investigation shows that its sensitivity is inversely proportional to its extension in the direction of the flow and is approximately independent of its width. At high frequencies, the radiation field dominates over the nearfield. The radiation field is described by the Lighthill equation. Its left‐hand side is identical with the wave equation for an inviscid fluid; on the right, turbulence‐generating effects are accounted for by a known “forcing function.” For a point force, the solution is an image source supplemented by a thin layer of evanescent shear waves along the boundary. A similar solution is obtained for multipoles and for turbulence. There is no layer of sound‐radiating dipoles nor a resonance board effect, as is proved by performing the computation in terms of the Fourier amplitudes.
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Generation of discrete frequency noise due to periodic vortex shedding from a streamlined body (A)

Tohru Fukano

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S116-S116 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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The mechanism of discrete frequency noise generated from a flat plate with a sharp trailing edge immersed in a uniform oncoming flow was investigated experimentally. The results show that discrete frequency noise is caused by the periodic shedding of Karman vortices, and the necessary conditions of its generation are summarized as follows: (1) There must be a dead flow region with a definite area of a sufficiently large scale. (2) The shear layers starting from the two separation points near the trailing edge of the body must be very strong on either or both sides of the plate. A flow model was introduced to estimate the sound‐pressure level theoretically and was verified experimentally as useful. The characteristics of Karman vortex shedding from a rotating blade were also examined.
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Control of Karman‐vortex sound by two crossing cylinders (A)

Yoshiyuki Maruta and Shoji Suzuki

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S116-S117 (1988); (2 pages)

Online Publication Date: 13 Aug 2005

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The pure tone generated from a cylinder's wake with a Karman vortex in the airflow is the basic phenomenon of aerodynamic sound and is also the sound that is often generated by flows of wind around constructions and the inner flow of turbomachinery. By putting another crossing cylinder into contact with the first, the Karman‐vortex sound becomes quieter than for a single cylinder [Maruta et al., Proc. Internoise 87, 481–484 (1987)]. This phenomenon was investigated experimentally by changing the diameters, space, and crossing angle between the two cylinders. For cylinders with the same diameter, normal crossing was more effective for this sound reduction. For the ones with different diameters, inclined crossing was more effective with space less than 1.5 times the upstream cylinder's diameter. The sound reduction results from the fact that the spanwise coherence of the Karman vortex from the upstream cylinder is prevented by crossing with other cylinders. The Karman‐vortex sound can be controlled by the optimum condition of two crossing cylinders.
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The response of plates to TBL excitation: High versus low wavenumber effects (A)

Nathan C. Martin

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S117-S117 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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Structural response to turbulent boundary layer (TBL) wall pressure fluctuations has been recognized as an important consideration in the design of aircraft and ships for many years. Unlike most sources of structural response, the TBL generates fluctuating pressure components over a wide range of spatial (i.e., wavenumber) as well as temporal (i.e., frequency) scales. In the frequency range of interest for many applications, the dominant spatial components of TBL excitation lie at relatively high wavenumbers compared to the major acceptance regions of resonant structural modes. Chandiramani [J. Acoust. Soc. Am. 61, 1460 (1977)] has shown that the low wavenumber components of TBL excitation dominate the response of plates with simply supported boundary conditions when certain assumptions are made about the relative levels of TBL high and low wavenumber content. The purpose of this paper is to re‐examine the subject of the relative importance of high and low wavenumber contributions to TBL‐excited plate response as influenced by potential variables such as the various models of TBL wavenumber content and the nature of the plate boundary conditions.
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Design considerations for reducing propeller cavitation noise (A)

Tetsuji Hoshino, Takao Sasajima, and Akira Oshima

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S117-S117 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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In designing naval or oceanographic ships, the reduction of underwater noise radiated from the ship is of primary importance to secure the reliable operation of acoustic instruments. Among various hydrodynamic and mechanical noise sources, propeller cavitation is considered to be most harmful for acoustic survey operation. A design for low‐noise propellers and design examples for oceanographic research ships are presented. The cavitation patterns and radiated noise characteristics of the propellers thus designed were investigated by model tests in a cavitation tunnel. It was shown that the radiated noise level from the propeller was sufficiently low in the model scale. This was further confirmed by radiated noise measurements on the propeller at full scale. The comparison of the full‐scale noise data with those estimated from the model scale noise data showed that the noise measurements in a cavitation tunnel are useful in evaluating the design of a low‐noise propeller.
Contributed Papers
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Laser Doppler vibrometer technique for measuring surface waves produced on submerged elastomeric layers (A)

Timothy E. McDevitt and Alan D. Stuart

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S117-S117 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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A dual‐channel, combination vibrometer/velocimeter laser Doppler system has been developed to measure the surface waves produced on a submerged elastomeric layer excited mechanically or by a fluid flow. This nonintrusive laser system permits velocity measurements to be made both normal and in the plane of the layer's surface without distorting its vibratory field. Since two laser systems are employed, measurements can be made simultaneously in two locations: permitting the spatial coherence of the surface disturbance to be assessed and transfer functions between source and response to be determined. This paper will present the results obtained for a long sample of elastomeric material submerged in water, and driven both longitudinally and in flexure to simulate typical in‐plane and transverse motion of its surface. [Work supported by ONR.]
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Acoustic concepts in nonuniform, steady potential flows (A)

L. M. B. C. Campos

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S117-S118 (1988); (2 pages)

Online Publication Date: 13 Aug 2005

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The concepts of Doppler factor, local Doppler‐shifted frequency, Blikhintsev wave invariant, and group velocity, which are well known for sound in a uniformly moving medium, and in the ray approximation to the acoustics of nonuniform flows, are generalized to waves of arbitrary frequency in a steady, nonuniform potential flow of arbitrary Mach number. The generalized concepts coincide with the usual Doppler factor, local frequency, wave invariant, and group velocity, in the ray approximation, and their definition is made unique by the requirement that, outside the ray approximation, the following relations remain valid: (i) The generalized wave invariant remains an adiabatic invariant, in the sense that it equals the total (kinetic plus compression) energy divided by local frequency; (ii) the latter is related to the wave frequency through the generalized Doppler factor; (iii) the energy velocity is the ratio of energy flux to energy density. All these concepts depend on convection and energy partition factors, which reduce to unity in the ray limit. These concepts are introduced on the basis of the acoustic energy equation, which can be derived from a variational principle, which also yields wave equations.
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Tip vortex sound (A)

Jonathan L. Gershfeld and Edward J. Skiko

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S118-S118 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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The aerodynamic sound generated by the convection of a tip vortex past a trailing edge is examined. For angles of attack greater than ± 5 deg, a vortex is generated that produces a high‐frequency fluctuating pressure field several hundred hertz in bandwidth, and as much as 5 dB above the boundary layer wall pressure field, centered at roughly twice the frequency of vortex shedding due to Helmholtz wake instabilities. Sound is generated as the vortex‐induced pressure field is scattered by the trailing edge. The increase in the acoustic source level, quantified by fluctuating boundary layer surface pressure statistics both near the trailing edge of the foil and under the tip vortex, corresponds in level and frequency to the increase in measured radiated noise. The wall pressure field due to tip vortex flow is superimposed on the boundary layer pressure field and apparently does not alter the wall pressure field at other frequencies. The directivity of the radiated tip vortex sound shows a reduction in the sound in the plane of the foil around the tip. This suggests that a quarter plane Green's function is required to describe the radiated noise. [Work supported by O.N.R.]
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Wall pressure fluctuations in the transition region (A)

Thomas A. Galib

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S118-S118 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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Wall pressure fluctuations on an axisymmetric body of revolution were measured with piezoelectric pressure transducers. Spectral analysis of the data showed discrete frequency bands of the pressure fluctuations corresponding to predicted Tollmien‐Schlichting disturbance frequencies in the transitional boundary layer. Nondimensional power spectra showed that the peaks of the disturbance frequencies (for three free‐stream velocities) collapsed to a single Strouhal number. Further manipulation of this result yielded an expression for the Tollmien‐Schlichting frequencies in terms of a constant and the displacement thickness Reynolds number. These results were for a near‐zero pressure gradient. They were later reproduced in an adverse pressure gradient for a variety of Reynold's numbers.
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Vibroacoustic analysis of a space shuttle payload (A)

Y. Albert Lee

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S118-S118 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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A Vibroacoustic payload environment prediction system (VAPEPS) has been developed to perform statistical energy analysis of spacecraft under acoustic excitation. VAPEPS was employed to analyze the random vibration response of the NASA Office of Space Science‐1 (USS‐1 Payload in the space shuttle cargo bay acoustic environment. The OSS‐1 payload consists of various experimental hardwares mounted on a pallet. The pallet is constructed of a framework covered with face panels that is responsive to the acoustic pressure field. The entire pallet structure was modeled as an equivalent plate with the same dimension, stiffness, surface mass density, and longitudinal wavespeed. Detailed models were also constructed of the individual panels of honeycomb construction, which make up the overall face panels. The predicted acceleration power spectral density in third octave bands was compared with experimental data measured at system level acoustic test in a reverberant chamber. The agreement is good.
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Noise radiation from a jet impinging on a flat plate (A)

Jianping Shen and William C. Meecham

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S118-S118 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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In this study, a search is made for high‐noise‐source regions for a jet impinging on a large flat plate. By using cross‐correlation techniques for the pressure fluctuation on the plate and the farfield acoustic radiation, the location of the noise source using time delays (phase shifts) can be determined. Different jet speeds (up to Mach number 0.4), jet‐to‐plate distances (5 to 10 jet diameters), and impinging angles (0° to 80° from the jet axis) were used in an experiment in the UCLA Aeroacoustics Laboratory anechoic room. A full digitization treatment was used in analysis. The results show that the source is located on or near the plate in a circular region centered on the jet center, with a radius of approximately one jet diameter. The directivity pattern of the radiation will also be discussed. Standard theory indicates that there should be little surface, dipole sound from a large flat plate. The question will be discussed.
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Structural resonance influences on flow‐induced acoustic amplification (A)

Alison Flatau

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S118-S118 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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An experimental investigation of the influence of structural resonance on the acoustic response to vortex shedding is presented. Flow‐induced amplification of acoustic energy is of interest in the field of combustion instability in solid rocket motors. Baffles located at the junction of motor segments can cause generation of flow vortices and amplification of acoustic energy. This investigation examines the hypothesis that an additional amplifier of acoustic energy is provided by the vibratory response of these baffles. Flow through a cylindrical cavity is interrupted by annular baffles that extend radially inward from the cylinder walls. Baffle configurations are controlled to induce various frequencies of vortex shedding. Acoustic pressure and baffle vibratory responses for various combinations of baffle resonance and vortex shedding frequency are recorded using a modal analysis technique. This provides the database used to quantify the influence of vortex shedding frequencies and structural resonance on acoustic pressure amplitudes. A theoretical model of the interactions of different baffle configurations with chamber acoustics is presented and shown to be in general agreement with the acoustic pressure amplitudes measured in the test section. [Work supported by Morton Thiokol, Inc.]
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On sound radiated by inhomogeneities convected through a space‐varying flow (A)

Alan Powell

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S118-S118 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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It was pointed out in Powell [J. Acoust. Soc. Am. 36, 1032 (1964)] that inhomogeneities in composition, entropy, or vorticity give rise to sound radiation when convected through a steady space‐varying flow as in a nozzle or past a curved surface. The one‐dimensional case was extended by Cuadra [J. Acoust. Soc. Am. 42, 725–732 (1967)] and more completely by Ffowes‐Williams and Howe (1975), but the initial “scattering approach” presented appears to have been published only qualitatively, e.g., Powell [Noise Control Eng. J. 8, 108–119 (1977)]; but note related developments by Crighton and Leppington (1971), and Morfey (1973). This is simply Rayleigh scattering with an axis change so that the inhomogeneities sense time‐varying changes as they are swept supersonically through weak oblique standing waves springing from a fixed sinusoidal wall. The physical arguments carry over for evanescent waves (complex wavenumber), the corresponding steady flow being subsonic. It is readily inferred, e.g., that for subsonic and supersonic flows (away from M ≃ 1), the sound power depends on the sixth power of the velocity.
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Turbulent boundary layer simulation setup on a sonar dome (A)

Jean Audet, Michel Lagier, Pierre Marin‐Curtoud, and Thierry Rohan

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S118-S119 (1988); (2 pages)

Online Publication Date: 13 Aug 2005

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An experimental‐analytical technique was developed to evaluate the noise produced inside various types of sonar domes under the effect of a turbulent flow, in a frequency range where the structure has a high modal density. The transfer functions between a punctual external force applied to the dome and the acoustic pressure at a point inside the cavity was measured on a scale model. This measure was made using a reciprocity technique with emitting hydrophones within the cavity and with accelerometers all over the dome's external surface. The noise level at a point inside the cavity is calculated from these experimental transfer functions and a turbulent boundary layer wall pressure model. The wave vector frequency spectrum model used is Chase's model [D. M. Chase, J. Sound Vib. 70, 29–67 (1980)], adjusted according to the local parameters of the flow. The results obtained with this method agree with experimental results. In order to test various types of structure, this technique on a scale model has considerable advantages compared with experimentations on a real structure: limited expense, experimental ease, and reliability.
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Wall pressure fluctuations beneath a transitional boundary layer (A)

J. Audet and Ph. Dufoureq

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S119-S119 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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Up to now, different models have been developed to describe wall pressure fluctuations beneath a fully developed turbulent boundary layer [G. M. Corcos, J. Acoust. Soc. Am. 35, 192 (1963); D. M. Chase, J. Sound Vib. 70, (1)]. Recent]y, the total field pressure in the transition zone was described in different papers [G. C. Lauchle, J. Acoust. Soc. Am. 67, 158–168 (1980); M. Laglet and D. Sornette, Acustica 61, 116–124]. These works show that intermittent processes induce monopole sources whose radiation could be dominant. The present paper is devoted to the development and numerical analysis of a formulation based on these new models and fitted to wall pressure fluctuations calculation (local field). In this case, the wall pressure fluctuation is the sum of two terms: one associated with the turbulent content of intermittent spots and the other associated with the spot boundaries (monopole radiation). The relative contribution of each kind of sources to the transitional boundary layer wall pressure fluctuation can be investigated. Successful comparisons wth experimental results [Ph. Dufoureq, these Docteur Ingénieur, Ecole Centrale de Lyon (1984)] prove, in many cases, the dominance of monopole sources induced by intermittency. Noise generated by the transition region could be dominant at low frequency and could even disturb the upstream laminar flow.
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Radiated sound‐pressure levels and sound source locations on the German ICE high‐speed train (A)

E. Pfizenmaier, W. F. King, III, H. Lettmann, and B. Barsikow

J. Acoust. Soc. Am. Volume 84, Issue S1, pp. S119-S119 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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The German ICE high‐speed train demonstrated on 1 May 1988 that speeds up to 406 km/h can be attained using conventional wheel/rail technology. High‐speed railway vehicles such as the ICE generate strong aerodynamic sound sources that overwhelm the noise contribution produced by wheel/rail interaction, particularly when the wheels have been acoustically treated. If radiated noise levels are to be held to a minimum, the aerodynamic characteristics of such vehicles have to be optimized. The ICE has been designed in this way. Sound‐source location measurements were carried out using a line array of 15 microphones positioned along the wayside. The first results of this study will be discussed in the present paper for train speeds up to 300 km/h. Wayside noise measurements made during the record‐breaking run on 1 May 1988, when a speed of 406.9 km/h was attained, are also presented. The aerodynamic component of radiated noise is separated from that due to wheel/rail interactions, and the resulting analysis is shown to be also applicable to maglev vehicles. Also at Technische Universität Berlin, Inst. füt Techn. Akustik.
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