scholarly journals Latent spatial resonances at thin‐walled structure vibration and acoustic radiation in convecting field of random pressure fluctuations

1994 ◽  
Vol 95 (5) ◽  
pp. 2996-2996
Author(s):  
B. M. Efimtsov
Keyword(s):  
Acoustic Radiation ◽  
Pressure Fluctuations ◽  
Structure Vibration ◽  
Thin Walled

Acoustical Radiation Characteristics Test of Magnesium Alloy Sheets with Element Method

2014 ◽  
Vol 926-930 ◽  
pp. 375-378
Author(s):  
Ting Jin ◽  
Zheng Yin Ding
Keyword(s):  
Magnesium Alloy ◽  
Acoustic Radiation ◽  
Radiation Characteristics ◽  
Paper Advance ◽  
Structure Vibration ◽  
Connection Type ◽  
Thin Walled ◽  
Element Method

Structure vibration is one of the main causes of noise. Thin-walled workpiece has a smaller stiffness,it will easily produce vibrations at work ,and become a source of noice. It is very necessary to study acoustic radiation characteristics of plat,so can we effectively control the structure and connection type of panel structure to change acoustical radiation characteristics.This paper advance a element method to test acoustical radiation characteristics of plat,and take experiment with magnesium alloy sheets.

Radial pulsations of a fluid sphere in a sound wave

1999 ◽  
Vol 380 ◽  
pp. 1-38 ◽  
Author(s):  
S. TEMKIN
Keyword(s):  
Sound Wave ◽  
Acoustic Radiation ◽  
Pressure Fluctuations ◽  
Resonant Peak ◽  
Attenuation Coefficients ◽  
Near Resonance ◽  
Dissipation Mechanism ◽  
Dilute Suspensions ◽  
Temperature And Pressure ◽  
Radial Pulsations

This paper presents analytical results for the temperature and pressure fluctuations in a droplet or bubble pulsating in a sound wave, the related damping coefficients, as well as the corresponding sound attenuation coefficients for dilute suspensions. The study is limited to small-amplitude motions but includes the effects of compressibility and heat conduction in the fluid outside the particle. Results are obtained for both average and surface values of the particle's temperature and pressure fluctuations that are applicable to droplets in gases and liquids, and to gas bubbles in liquids. In the latter instance, it is found that the bubble's response exhibits a clear resonant peak at the isothermal natural frequency, that acoustic radiation is the dominant dissipation mechanism near resonance, and that the disturbances produced by the bubble in the liquid significantly reduce the thermal damping at most frequencies. Similar conclusions apply for droplets in liquids, except that the effects of resonance are significantly diminished.

Acoustic Radiation From Separated Boundary-Layer Flow Over a Rearward-Facing Step on a Flat Panel

2003 ◽  
Author(s):  
Walter A. Kargus ◽  
Gerald C. Lauchle
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Acoustic Radiation ◽  
Fluid Dynamic ◽  
Pressure Fluctuations ◽  
Wall Pressure ◽  
Wall Jet ◽  
Measured Velocity ◽  
Wall Pressure Fluctuations ◽  
Layer Flow

The acoustic radiation from a turbulent boundary layer that occurs downstream of a rearward facing step discontinuity and reattaches to a flat plat is considred experimentally. The step is exposed ot a zero incidence, uniform subsonic flow. a quiet wall jet facility situated in an anechoic chamber is used for the studies. The “point” wall pressure spectra are measured by small, “pinhole” microphones located at various locations under the layer, including a point directly in the 90° corner of the step. The wall pressure fluctuations measured at the various locations are correlated with the signal detected by a far-field microphone. The measured cross-spectral densities are thus used to identify the relative contributions of the various flow regimes to the direct radiation. It is shown that the separation of the flow over the corner of the step is a dominant acoustic source, which is supported not only by the measured cross spectra, but also by the favorable comparison of the measured velocity power law to the theoretical value. Measurements made where the flow reattaches and at the turbulent boundary layer are less conclusive. This is because the pinhole tube attached to the microphone produced a sound due to a fluid-dynamic oscillation, which contaminated the measurement of the aeroacoustic sources.

scholarly journals Selection of a Suitable Wall Pressure Spectrum Model for Estimating Flow-Induced Noise in Sonar Applications

1995 ◽  
Vol 2 (5) ◽  
pp. 403-412 ◽  
Author(s):  
V. Bhujanga Rao
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
High Speed ◽  
Acoustic Radiation ◽  
Pressure Fluctuations ◽  
Theoretical Data ◽  
Wall Pressure ◽  
Wave Number ◽  
Wall Structure ◽  
Structural Noise

Flow-induced structural noise of a sonar dome in which the sonar transducer is housed, constitutes a major source of self-noise above a certain speed of the vessel. Excitation of the sonar dome structure by random pressure fluctuations in turbulent boundary layer flow leads to acoustic radiation into the interior of the dome. This acoustic radiation is termed flow-induced structural noise. Such noise contributes significantly to sonar self-noise of submerged vessels cruising at high speed and plays an important role in surface ships, torpedos, and towed sonars as well. Various turbulent boundary layer wall pressure models published were analyzed and the most suitable analytical model for the sonar dome application selected while taking into account high frequency, fluid loading, low wave number contribution, and pressure gradient effects. These investigations included type of coupling that exists between turbulent boundary layer pressure fluctuations and dome wall structure of a typical sonar dome. Comparison of theoretical data with measured data onboard a ship are also reported.

Numerical study of acoustic radiation due to a supersonic turbulent boundary layer

2014 ◽  
Vol 746 ◽  
pp. 165-192 ◽  
Author(s):  
Lian Duan ◽  
Meelan M. Choudhari ◽  
Minwei Wu
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Numerical Simulations ◽  
Surface Pressure ◽  
Free Stream ◽  
Acoustic Radiation ◽  
Numerical Study ◽  
Near Field ◽  
Pressure Fluctuations ◽  
Spatial Coherence

AbstractDirect numerical simulations are used to examine the pressure fluctuations generated by fully developed turbulence in a Mach 2.5 turbulent boundary layer, with an emphasis on the acoustic fluctuations radiated into the free stream. Single- and multi-point statistics of computed surface pressure fluctuations show good agreement with measurements and numerical simulations at similar flow conditions. Consistent with spark shadowgraphs obtained in free flight, the quasi-homogeneous acoustic near field in the free-stream region consists of randomly spaced wavepackets with a finite spatial coherence. The free-stream pressure fluctuations exhibit important differences from the surface pressure fluctuations in amplitude, frequency content and convection speeds. Such information can be applied towards improved modelling of boundary layer receptivity in conventional supersonic facilities and, hence, enable a better utilization of transition data acquired in such wind tunnels. The predicted acoustic characteristics are compared with the limited available measurements. Finally, the numerical database is used to understand the acoustic source mechanisms, with the finding that the supersonically convecting eddies that can directly radiate to the free stream are confined to the buffer zone within the boundary layer.

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