An investigation of the sound field above the audience in large lecture halls with a scale model

1986 ◽  
Vol 80 (3) ◽  
pp. 815-827
Author(s):  
David W. Kahn ◽  
Jiri Tichy
Keyword(s):  
Sound Field ◽  
Scale Model ◽  
Large Lecture

Active control of fan noise from high-bypass ratio aeroengines: a numerical study

2001 ◽  
Vol 105 (1053) ◽  
pp. 627-631
Author(s):  
P. Traub ◽  
F. Kennepohl ◽  
K. Heinig
Keyword(s):  
Active Control ◽  
Numerical Study ◽  
Active Noise Control ◽  
Sound Field ◽  
Primary Objective ◽  
Scale Model ◽  
Research Centre ◽  
Infinite Length ◽  
Circular Duct ◽  
Bypass Ratio

Abstract Under the national research project, dubbed Turbotech II, in which MTU Aero Engines, DLR Institute of Propulsion Technology and EADS Corporate Research Centre participate, active noise control (ANC) has been tested with a scale model fan of one metre diameter for a high bypass ratio aeroengine. MTU’s task in this project was to develop a computer code to predict the sound field in the intake duct of the fan-rig by the use of active control. The primary objective of the numerical study was to specify numbers of actuators (loudspeakers) and error sensors (microphones) and their positioning to control the harmonic sound power, radiated upstream to the duct intake. The computer model is based on the geometry of an annular or circular duct of rigid walls and infinite length, containing a subsonic axial uniform flow. The modal amplitudes of the primary sound field are input data. The actuators are modelled by acoustic monopoles. Two control algorithms have been used for achieving the control objective. The first consists simply in the reduction of the in-duct mean squared pressures. The second, so called modal control, is designed to cancel dominant modes selectively. Numerical results are presented using a typical configuration of wall mounted actuators and error sensors in the form of a number of rings uniformly distributed along the length of the intake duct. Guidelines have also been derived to design a favourable configuration of actuators and sensors. The findings of the numerical study are compared with the results of the ANC tests.

Prediction of subjective properties of a sound field in a concert hall with tenth‐scale model

1999 ◽  
Vol 105 (2) ◽  
pp. 1197-1197
Author(s):  
Koji Ishida ◽  
Kiyoshi Sugino ◽  
Hideki Tachibana
Keyword(s):  
Sound Field ◽  
Scale Model ◽  
Concert Hall

scholarly journals Sound Scattering Properties of Surfaces with Diffusers

2020 ◽  
Vol 320 ◽  
pp. 00024
Author(s):  
Marina Lavrova ◽  
Nikolay Kanev
Keyword(s):  
Model Experiment ◽  
Decay Curve ◽  
Sound Field ◽  
Characteristic Size ◽  
Scattering Coefficient ◽  
Scale Model ◽  
Rigid Surface ◽  
Sound Scattering ◽  
The Third ◽  
Applied Method

This article compares the values of the normal scattering coefficient measured in a model experiment for two types of diffusers placed on a rigid surface. Wooden diffusers of cubic and pyramidal shapes were tested in a scale model of a room with dimensions of 0.7x0.4x0.4 m. Sound decay curves were measured at frequencies of 4kHz and 8kHz. Two large walls were covered with a porous absorber, on the third, in certain combinations, the investigated diffusers with a characteristic size of 3.5 cm were placed, the number of which varied from 0 to 29. The idea of the applied method is that the sound decay curve in a room with a non-diffuse sound field depends significantly from the scattering properties of surfaces. The decay curve was measured with different numbers of the diffusers on the test wall, which made it possible to determine the influence of the shape of the diffusers and their number on the value of the normal scattering coefficient. According to the results of the measurements a high scattering ability of cubic elements was revealed in comparison with pyramidal ones.

A High-Resolution Continuous-Scan Acoustic Measurement Method for Turbofan Engine Applications

2015 ◽  
Vol 137 (12) ◽  
Author(s):  
Parthiv N. Shah ◽  
Håvard Vold ◽  
Dan Hensley ◽  
Edmane Envia ◽  
David Stephens
Keyword(s):  
Spatial Resolution ◽  
Sound Field ◽  
Rotational Frequency ◽  
Scale Model ◽  
Acquisition Time ◽  
Time Signal ◽  
Noise Sources ◽  
Turbofan Engine ◽  
Complex Envelope ◽  
The Time Domain

Detailed mapping of the sound field produced by a modern turbofan engine, with its multitude of overlapping noise sources, often requires a large number of microphones to properly resolve the directivity patterns of the constituent tonal and broadband components. This is especially true at high frequencies where the acoustic wavelength is short, or when shielding, scattering, and reflection of the sound field may be present due to installation effects. This paper presents a novel method for measuring the harmonic and broadband content of complex noncompact noise sources using continuously moving (referred to here as continuous-scan (CS)) microphones in conjunction with a state-of-the-art phase-referencing technique. Because the microphones are moving through the sound field produced by the noise sources, they effectively provide infinite spatial resolution of the sound directivity over the scan path. In this method, harmonic (i.e., shaft-coherent) content at the integer multiples of the instantaneous shaft rotational frequency is first extracted from the time signal using a tachometer signal and the Vold-Kalman (VK) filter. The residual broadband signal is then filtered in the time domain in fractional octave bands. The broadband spectra of the signals from the moving microphones are then computed at arbitrary positions along their scan paths using weighted averages (based on Chebyshev polynomial zero-crossings) and the assumption of a complex envelope that varies slowly over a spatial scale whose lower bound is set by the acoustic wavenumber. A benefit of this method is that the decomposition of the total measured sound field into a stochastic superposition of components preserves a meaningful phase definition for each “partial field” associated with a given shaft order (SO). This preservation of phase data enables the forward or backward projection of each of these partial fields using acoustical holography (AH). The benefits of the CS method are demonstrated using acoustic data acquired for a 22-in. scale-model fan stage run at the NASA Glenn Research Center's 9-foot by 15-foot wind tunnel. Two key outcomes of the work include (1) significant improvement in the spatial resolution of the measured sound field and (2) reduction in the overall data acquisition time. Additionally, the methods described here lead to new opportunities for noise source diagnostics and visualization.

Development of BWR Steam Dryer Loading Evaluation Methods Through Scale Model Tests Under Actual Steam Conditions

2013 ◽  
Author(s):  
Shiro Takahashi ◽  
Keita Okuyama ◽  
Akinori Tamura ◽  
Yasuhiro Mabuchi ◽  
Teppei Kubota ◽  
...  
Keyword(s):  
Dynamic Pressure ◽  
Sound Field ◽  
Acoustic Resonance ◽  
Steam Pressure ◽  
Evaluation Methods ◽  
Test Methods ◽  
Normal Operation ◽  
Scale Model ◽  
Fluctuating Pressure ◽  
Main Steam

It has been demonstrated that intense fluctuating pressures acted on the steam dryer in a boiling water reactor (BWR) at higher velocity flows than in normal operation through actual BWR plant tests [1] and scale model air tests [2]. The cause of the dryer loading was considered as flow-induced acoustic resonance at the stub pipes of safety relief valves (SRVs) in the main steam lines (MSLs). Acoustic resonance was considered to be generated by interaction between the sound field and an unstable shear layer across the closed side branches of the SRV stub pipes. We have started a research program on BWR dryers to develop their loading evaluation methods. Some air scale tests were conducted and those are useful for evaluation of occurrence of acoustic resonance in SRV stub pipes and characteristics of fluctuating pressure in MSLs. However, it is a possibility that differences in pressure conditions and fluid proprieties caused the dryer loading to be underestimated. In the present study, we conducted scale tests under actual steam conditions to evaluate the scale model test methods for BWR dryer loading estimation. The Hitachi Utility Steam Test Leading facility (HUSTLE) was used for the scale model steam tests of MSLs and a steam dryer. Steam which was at the same pressure and temperature conditions as an actual BWR was used in the tests. The test apparatus consisted of the steam dryer, steam dome and 4 MSLs with 20 SRV stub pipes. We demonstrated that acoustic resonance occurred in the SRV stub pipes and fluctuating pressure which propagated from the SRVs to the dryer caused fluctuating stress on the steam dryer at the SRV resonance frequency. The increasing of fluctuating pressure due to the double vortex mode which occurred at a Strouhal number (St) from 0.8 to 0.9 could be clearly seen in the scale model steam tests unlike in the air tests. It was possible that self excited acoustic resonance was affected by the low pressure conditions and different fluid proprieties for the scale model air tests. However, no significant influence from steam pressure was seen at more than 3MPa. Normalized fluctuating pressure was almost the same regardless of pressure. We verified that normalization by dynamic pressure in the main pipe was a reasonable approach for evaluation of fluctuating pressure in the SRV stub pipes. Increasing of fluctuating pressure due to the double vortex mode was clearly distinguished for SRV stub pipes but became smaller for MS pipes and had insignificant impact on the dryer loading.

Comparison of sound field measurements and predictions in coupled volumes between numerical methods and scale model measurements

2013 ◽  
Vol 133 (5) ◽  
pp. 3530-3530
Author(s):  
Paul Luizard ◽  
Makoto Otani ◽  
Jonathan Botts ◽  
Lauri Savioja ◽  
Brian F. Katz
Keyword(s):  
Numerical Methods ◽  
Sound Field ◽  
Field Measurements ◽  
Scale Model

Basic study on three-dimensional sound field auralization using a scale model

2018 ◽  
Vol 144 (3) ◽  
pp. 1919-1919
Author(s):  
Kazunori Suzuki ◽  
Yoshinari Yamada ◽  
Shinichiro Koyanagi ◽  
Takayuki Hidaka
Keyword(s):  
Three Dimensional ◽  
Sound Field ◽  
Scale Model ◽  
Basic Study
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