Journal of Environmental Engineering and Landscape ManagementPublication details, including instructions for authors and subscription information:Abstract. Now, it is normally agreed that noise barriers -shields with appropriate devices on the top edge -limit the diffraction of sound waves more effectively than the usual shields of the equal or in some cases even greater height. These barriers are referred to as "edge-modified" noise shields. The article describes acoustic field researches that estimate the impact of the slope of the upper edge of the noise barrier on the effectiveness of shielding from environmental noise. The article was drafted on the basis of methodical recommendations presented in the standard ISO 11821: 1997 "Acoustics -Measurement of the in situ sound attenuation of a removable screen". While altering the slope angle, respectively to 90°, 120°, 150°, 180°, different noise barriers were formed: "L90" (slope angle 90°), "J120", "J150" (slope angles 120° and 150°), and the usual "straight type" (slope angle 180°). The impact made by the form of the noise barrier on the spread of noise in the noise suppression area was observed at the areas of low (100-315 Hz) and high (2000-5000 Hz) frequency. The most effective form of a barrier in reducing the diffraction of low frequency sound waves was "J120", whereas high frequency sound waves were most effectively reduced using a usual straight noise barrier.
The Environmental Protection Laboratory of Vilnius Gediminas Technical University has developed and installed a one-level 8-channel cyclone with different internal structure, which is used for separation of particulate matter from air streams. Airflow velocity was measured in five points of each channel: at the end and the beginning of the channel, in the middle of the channel and in points arranged at 45° angle from the channel's end and beginning. The highest airflow velocity determined in 8-channel device by regulating volumes of peripheral and transit airflows with curvilinear semi-rings was in cyclone's channel 1, while the lowest – in channel 2. Contrary to the above, the highest airflow velocity in 8-channel cyclone by using quarter-rings without holes and with 5° opening angle of plates in holes was recorded in channel 2. Tests on aerodynamic resistance were carried out in airflow inlet and outlet ducts. In all cases analysed the highest aerodynamic resistance in 8-channel cyclone was determined when airflow distribution was regulated at 75/25 ratio with semi-rings. When quarter-rings without holes and with 5° opening angle of plates in holes were used, higher aerodynamic resistance in the system was created by using quarter-rings without holes, i.e. 0° opening of plates.
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