青山 剛史

We simulate unsteady flows over a 30P30N slat by taking account of velocity fluctuations inside the turbulent boundary layer (TBL) on the slat. Embedded Large Eddy Simulation method is employed to generate pseudo turbulences inside the TBL. Also, we conduct additional simulation by Delayed Detached Eddy Simulation (DDES), which has been made without the pseudo turbulence, for making comparisons with the ELES case. Comparisons between the ELES and DDES results suggests that the pseudo turbulence makes the vortex structures of a shear layer extending from the cusp more three-dimensionally. The difference of vortex structure leads to the shear layer in the ELES case curves with a smaller radius of curvature. The time-averaged flow field of the ELES case is closer to the experimental result than those in the DDES case. While the shear layer on the cusp side is affected by the pseudo turbulence, there is no significant difference between the ELES and DDES cases in the shear layer extending from the TE of the slat.

The Japan Aerospace Exploration Agency (JAXA) and The Korea Aerospace Research Institute (KARI) jointly started activities related to the research and development of "Active Tab," a helicopter noise reduction technique. KARI constructed the analytical methodology consisting of the aerodynamic, structural dynamic and acoustic codes for defining the requirements to be used in evaluating the performance of Active Tab when installed in a Mach scaled assumed blade. Based on the requirements defined, JAXA carried out a conceptual design study, developed the Active Tab drive mechanism and evaluated its performance. The analytical results show Active Tab satisfying the requirements has sufficient noise reduction capability. Evaluation for the Active Tab drive mechanism demonstrated the dynamic performance and durability required practical use installed in helicopter blades.

The influence of walls on the performance of multiple rotor type drones is numerically simulated. With the current wide-spread applications of autonomously flyable UAVs, there are potential needs to use the drones for inspections and observation near various structures, such as buildings and bridges. The flow fields around multiple rotors are influenced significantly by the existence of an upper or a side wall, so that the thrust, required torque, and other forces and moments are changed. It is found that when a rotor approaches an upper wall, as the distance between the rotor and the upper wall is less than a diameter of the rotor, the thrust suddenly increases, which causes the rotors to collide with the upper wall. When an isolated rotor is operated near a side wall, the thrust decreases and a rolling moment appears to tilt the rotor toward the wall as the distance becomes shorter. For a multiple rotor drone near a side wall, the rotors have different distances from the wall, which causes the whole aircraft tilts toward the wall. From the perspective of safety operations, the multi-rotor drone should be kept away from both the upper wall and the side wall at a distance of at least 1.5 times of the rotor diameter to prevent unexpected motions of the aircraft caused by the wall during hovering flight.