This paper presents results of Computational Fluid Dynamics (CFD)results for flows around propellers and compares their aerodynamic performance as well as their acoustics. After some validation of the employed CFD method, using wind tunnel experiments, a modern propeller design was assessed. Using the same baseline blade, different propellers were put together by adding stagger at the blade hub and small variations of the inter-blade angle. The employed method produced results showing differences in the propeller acoustics regarding the frequency spectrum produced by each design and the level of the acoustic tones. The effect of chancing the hub was to generate frequencies in-between the tones of the baseline design while keeping the overall propeller performance the same. The effect of the employed hub changes was to generate tones in-between the harmonics of the fundamental blade passing frequency that dominated the baseline design. Installed and un-installed blades were compared and the results show that the wing, nacelle and fuselage around the blades, influence the obtained level of noise but not the frequency content. Computations for a climbing case also show the strong effect of the flight conditions on the acoustic results.
The herbicide thiobencarb is suspected of causing delayed phytotoxicity syndrome (DPS) in rice plants. While the ultimate agent appears to be its dechlorinated product (deschlorothiobencarb), the influence of organic carbon on the formation of deschlorothiobencarb in California rice field soils has not been investigated. Thus, two different soils were compared for their ability to reductively dechlorinate thiobencarb with carbon augmentation: one from the eastern Sacramento Valley, which has historically displayed DPS, and one from the western Sacramento Valley, which has not. Rice straw was homogenized into samples of each soil to produce 0, 0.33 or 2% organic carbon augmentation. During 90-days of anoxic incubation, substantial deschlorothiobencarb production was measured in both soil types. However, only the thiobencarb degradation rate in the eastern valley soil was positively correlated with carbon content. Thus, other characteristics of DPS-resistant soils may limit deschlorothiobencarb formation.
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