The objective of this study is to develop a new CFD solver by combining the structured and unstructured grid methods so that the tip vortices can be predicted accurately for the realistic geometry of a helicopter. Flow around a helicopter has unique features caused by the rotor and a variety of equipment on the helicopter fuselage surface such as hoist crane and landing gear. There are difficulties in CFD analysis for rotorcraft, particularly in accurately capturing of rotor tip vortices and solving flow around a complicated geometry. Generally, structured grid method is suitable for capturing tip vortices, while unstructured grid method can solve flow around complicated geometry. In this study, two validations are conducted to show effectiveness of this coupled CFD solver. The first validation is related to a steady flow around ROBIN fuselage (Mach # 0.062). Computational results are compared with both experimental data and existing CFD results. The results show that the coupled CFD solver can predict surface pressure distributions in good agreement with experimental data and existing CFD results. The second validation is related to an unsteady flow around ROBIN fuselage with a rotor (µ = 0.15, CT = 0.0064). Results show that coupled CFD solver can predict periodical surface pressure also in good agreement with experimental data and existing CFD results. Furthermore, the vortex structure predicted has a good agreement between the coupled and existing structured grid CFD solvers. Finally, the coupled CFD solver is applied to a flow around the Eurocopter 135 model to demonstrate its capability for a realistic complicated helicopter geometry.
The purpose of this paper is to introduce a velocity and distance control system for leader-following UAVs. In our previous paper, we already proposed a velocity and distance control system, but the system has a problem of ``offsets'' due to aerodynamic errors and/or leader trajectories. So in this paper, in order to eliminate the offset, a new approach of the velocity and distance control design is introduced. Simulation results show that the proposed velocity and distance control system provides a good performance and there are no offsets.
Research of Long-Distance Human-Powered Flight has been performed through the following four items: Aircraft design, Risk management, Pilot performance, Weather prediction. Actual flight took place on August 12, 2009. The flight distance was 20.72km. In this study, results of weather prediction using 1-way downscaling technique are validated by surface observation data and feasibility of weather prediction for Long-Distance Human-Powered Flight is discussed. The weather prediction with 1-km mesh decreases RMSE of wind speed by 0.1--0.2m/s compared with that with 5-km mesh. The weather prediction with 1-km mesh also has a potential to reproduce nonstationary wind. The RMSE gradually increase with time, which is mainly caused by initial and boundary data given from coarse mesh model. To reduce the RMSE, it is desirable to use newest analysis data as possible for initial and boundary data.
This paper includes evaluations of composite tanks or pressure vessels based on fracture mechanics and an improved method for tank design. Problems of exfoliation between the mouthpiece and composite in current composite pressure vessels are shown, and the simple solution by inducing a slit into the mouthpiece near the bonding interface is proposed. The effect of the slit is evaluated using a geometrically simple model as well as a pressure vessel model designed for a rocket.