Measurements of spoiler aerodynamic noise, generated in a low velocity flow duct and radiated from an open exhaust termination, have been made in the form of sound power spectra. The individual 1/3 octave power measurements are satisfactorily collapsed with the aid of derived theoretical scaling laws. Non-dimensional spectra are presented which permit generalized predictions of flow noise for bluff bodies, including splitter attenuators, mounted in low speed flow ducts.
On the basis of a method devised by Nelson and Morfey, measured sound power levels generated by a variety of induct spoiler configurations have been collapsed. A method of determining the duct clear area ratio and magnitude of the characteristic dimension coefficient from the measurement of the pressure loss has been devised. The non-dimensional spectra produced have been used to predict the sound power levels generated by single-vane dampers. The predicted levels are in good agreement with measured levels.
In this paper, some of the more fundamental notions of the phenomena classified as "subsonic aerodynamic noise" are prsented. In light of these, the authors wish to discuss the mechanisms of noise generation responsible for the self-noise of sound-traps, dampers, diffusers and other duct-located flow discontinuities. Then they suggest on the basis of some recent experimental studies, that the intensity and frequency spectrum of self-noise in ventilation systems can be predicted in a general sense. Tentative formulae are presented to this effect.
Recent work on the prediction of airflow generated noise in ducts based upon pressure loss characteristics is applied to a range of in duct components including bends and branch take-offs. An excellent collapse of measured data onto a single characteristic curve is reported for each component based upon standard values of pressure loss coefficients. It is shown that these characteristic curves can be used as the basis for a practical prediction method.
This paper presents a prediction model of the blade trailing-edge noise and its validation from tests carried out on a fixed flat plate at different angles of attack in an anechoic wind tunnel. The comparison between the measured and predicted far-field sound spectra is very good, which confirms the validity of the model. The same approach has been recently applied to a single rotating blade without casing. The paper presents the first experimental results obtained and the work to be done to check the validity of the model in this case.
The authors have experimentally studied on the relation between the periodic velocity fluctuation in the near wake of a rotating blade and the generated broad band noise. Typical periodic velocity fluctuation was clearly caused by Karman vortex shedding and produced a discrete frequency noise. The frequency of the velocity fluctuation increased toward the blade tip. Then the spectrum of noise generated from the whole span of the blade becomes broadband. In addition we have proposed a theory to predict the spectrum of the broadband noise.
Commercial buildings in North America are generally inadequately constructed and are therefore quite leaky. Uncontrolled air leakage increases the heating and cooling energy consumption (up to 40 %).. The author demonstrates the importance of commissioning the air barrier system in the design and construction of buildings for them to be healthful, durable and energy efficient.
The author has conducted an indoor/outdoor air quality study in Delaware before and after the enactment of Delaware 's clean indoor air law that banned smoking in all restaurants, bars and casinos. He demonstrates that it is impossible for ventilation technology to achieve acceptable indoor air quality in the presence of smoking. For him smoking bans are the only alternative.
The standard 62.1 prescribes new minimum breathing zone ventilation rates . It also clarifies the calculation procedures required by standard 62. That standard with the dual-path system equation presented in appendix A becomes an important tool for designers.
In this article, the description of of results of a different monitoring technique that consists in a continuous, unobtrusive monitoring of air-quality at 20 second intervals in 85 rooms of eight different Minnesota schools. The data are transmitted over the internet to a central project server where the data are translated into graphs and charts
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