Analysis of model rotor blade pressures during parallel interaction with twin vortices

This paper presents and provides analysis of unsteady surface pressures measured on a model rotor blade as the blade experienced near parallel blade vortex interaction with a twin vortex system. To provide a basis for analysis, the vortex system was characterized by hot-wire measurements made in the interaction plane but in the absence of the rotor. The unsteady pressure response resulting from a single vortex interaction is then presented to provide a frame of reference for the twin vortex results. A series of twin vortex interaction cases are then presented and analyzed. It is shown that the unsteady blade pressures and forces are very sensitive to the inclination angle and separation distance of the vortex pair. When the vortex cores lie almost parallel to the blade chord, the interaction is characterized by a two-stage response associated with the sequential passage of the two cores. Conversely, when the cores lie on a plane that is almost perpendicular to the blade chord, the response is similar to that of a single vortex interaction. In all cases, the normal force response is consistent with the distribution of vertical velocity in the flow field of the vortex system. The pitching moment response, on the other hand, depends on the localized suction associated with the vortex cores as they traverse the blade chord

Transmission of pangola stunt virus by Sogatella kolophon

A fijivirus causing minor enations, stunting, leaf notching, seed head deformity and excess tillering of Digitaria spp. was transmitted from naturally infected Digitaria ciliaris to D. ciliaris, D. decumbens and Urochloa panicoides by the planthopper Sogatella kolophon; 40–70% of insects transmitted after an incubation period of 15–21 days, and continued to transmit for up to 30 more days until death. Symptoms developed in test plants 30–50 days after inoculation. Sogatella longifurcifera failed to transmit the virus under similar conditions. Virus particles were present in roots, stems and leaves of infected plants, and particles were found in regular arrays and random aggregates in fat body cells of transmitting insects. Viroplasm and tubular structures were associated with these particles. Extracts from infective insects contained 10‐segment dsRNA when analysed by polyacrylamide gel electrophoresis. Virus survives over winter in planthoppers and D. ciliaris seedlings in frost‐free areas of coastal Queensland, but infected plants have debilitated root systems and compete poorly with healthy plants. Copyrigh

Initial infection processes by Colletotrichum gloeosporioides on avocado fruit

Infection of avocado fruit by Colletotrichum gloeospioroides was studied using light and transmission electron microscopy. In unripe fruit C gloeosporoides produced an appressorium and an infection peg which ceased growth in the cuticle. In field-inoculated avocado fruit sampled up to 4 d after inoculation, most infection pegs had penetrated the fruit cuticle to a depth of less than 1.5 mum. In fruit inoculated after harvest, however, the majority of infection pegs had grown down to the subcuticular region of the fruit peel within 48 h of inoculation. There was no further development of these infection pegs until the climacteric rise in respiration when fruit produced amounts of CO2 in excess of 50 ml CO2 kg-1 h-1. When the fungus resumed growth, infection pegs enlarged either within the walls or within the lumen of epidermal cells. Subsequent intracellular and intercellular development of the fungus resulted in the rapid degradation of cell wall and membrane structural integrity, although cells were not killed in advance of invasion during these early stages of colonization

Reduction of Helicopter BVI Noise Using Active Flow Control; The Case Of Vortex Street Interactions

A novel technique regarding the reduction of helicopter blade-vortex interaction noise is proposed. The proposed technique is based on the idea of injecting air at the leading edge of the blade to alter the vortex characteristics (strength and core size). The numerical investigations are performed using the large-eddy simulation (LES) approach. The simulations were performed for a Reynolds number, Re = 1.3 x 106, based on the NACA0012 airfoil chord and free-stream velocity. The present study shows that by injecting air at the leading edge of the blade, the influence of blade-vortex interaction on the aerodynamic coefficients and aeroacoustic noise is significantly reduced. © 2012 by Marcel Ilie