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This paper presents a computational fluid–structure interaction analysis for free movements with a flapping wing in a quiescent fluid. We demonstrated the moving velocity of a flapping wing according to the phase difference between the angle of attack and the positional angle in the case of a fruit fly with a Reynolds number of 136. If we considered the moving velocity of the flapping wing, the physics were different from that of hovering flight of previous studies, which did not consider the propulsive velocity and presented the advanced rotation of the angle of attack as the best mechanism for propulsion force, as compared to symmetric rotation and delayed rotation. We found that symmetric rotation produced a better propulsion velocity with less fluctuation in other direction than the advanced rotation. The hairpin vortex generated at the end of a stroke did not clearly contribute to the enhancement of propulsion; the wake capture is considered to be one of the main enhancements of the advanced rotation in a previous studies. We studied the effects of the angle of attack to determine why the fruit fly uses a large angle of attack during a constant angle of attack period. Larger angles of attack produced greater propulsion velocities. Further, larger angles of attack did not generate greater peak force during the rotation of the angle of attack at the reversal of stroke, but they produced less fluctuation at the reversal of the stroke and greater force during the constant angle of attack period. [ABSTRACT FROM AUTHOR]

This paper presents a computational fluid–structure interaction analysis for a flexible plate in a free-stream to investigate the effects of flexibility and angle of attack on force generation. A Lattice Boltzmann Method with an immersed boundary technique using a direct forcing scheme model of the fluid is coupled to a finite element model with rectangular bending elements. We investigated the effects of various angles of attack of a flexible plate fixed at one of the end edges in a free-stream at a Reynolds number of 5000, which represents the wing flapping condition of insects and small birds in nature. The lift of the flexible plate is maintained at the large angle of attack, whereas the rigid plate shows the largest lift at angles of attack around 30–40° and then drastic reductions in the lift at the large angle of attack. If we consider the efficiency as the lift divided by the drag, the flexible plate shows better efficiency at angles of attack greater than 30° compared to the rigid plate. The better performance of the flexible plate at large angles of attack comes from the deformation of the plate, which produces an interaction between the trailing edge vortex and the short edge vortex. The horseshoe-shaped vortex produced by a large vortex interaction at the trailing edge side has an important role in increasing the lift, and the small projection area due to the deformation reduces the drag. Furthermore, we investigate the role of flexibility on the lift and the drag force of the rectangular plate in a free-stream as the Reynolds number increases. Whenever a large vortex interaction at the trailing edge side is shown, the efficiency of the rectangular plate is improved. Especially, the flexible plate shows better efficiency as the Reynolds number increases regardless of the angle of attack. [ABSTRACT FROM AUTHOR]

For renewable electricity production, biomass can fully displace coal in an existing power plant with some equipment modifications. Recently, a 125 MWe power plant burning mainly anthracite in Korea was retrofitted for dedicated wood pellet combustion with a change of boiler configuration from arch firing to wall firing. However, this boiler suffers from operational problems caused by high unburned carbon (UBC) contents in the bottom ash. This study comprises an investigation of some methods to reduce the UBC release while achieving lower NOx emissions. The computational fluid dynamics approach was established and validated for typical operating data. Subsequently, it was applied to elucidate the particle combustion and flow characteristics leading to the high UBC content and to evaluate the operating variables for improving the boiler performance. It was found that the high UBC content in the bottom ash was a combined effect of the poor fuel grindability and low gas velocity in the wide burner zone originating from the arch-firing boiler. This prevented the operation with deeper air staging for lower NOx emissions. Reducing the particle size to <1.5 mm by modifying mills or pretreating the fuel using torrefaction was the only effective way of lowering the UBC and NOx emissions with deeper air staging while increasing the boiler efficiency. [ABSTRACT FROM AUTHOR]