In Super Sonic Transport (SST), thin wing structure is necessary to satisfy the high speed, economic viability and environmental compatibility requirements. Among many structures in thin wing, the lug structure which is between the body and the main wing plays important role. However, it is difficult to design of the lug structure because it is subjected many loads that have uncertainties such as magnitude or direction of loading caused by aeroelastic forces. Robust topology optimization is, therefore, necessary to determine the optimal structural lay out solutions insensitive to loading uncertainties for design of the lug structure. The present paper proposes robust topology optimization using NSGA-IIa algorithm which is one of the most popular in Multi-Objective Evolutionary Algorithms (MOEA) with multiload formulation. In proposed method, Monte Carlo simulations were used to estimate the robustness of topology from Pareto optima obtained with NSGA-IIa. The obtained robust topology solutions are explored by Self-Organizing Map that is an appropriate tool to visualize and explore properties of the high dimension data. Finally, proposed method approach is applied for the lug structure robust topology optimization.
Experimental studies are conducted to investigate influence of crosswind on the aerodynamic performance of helicopter rotor hovering in close proximity to the ground with a structure. Experimental parameters are rotor height and relative wind velocity to the rotor and structure. Wind directions considered in this study are the following: 1) wind blows from the structure side to the rotor side, 2) wind blows from the rotor side to the structure side and 3) wind blows parallel to the rotor and structure. In experiments, the rotor torque is measured for various combinations of these parameters while adjusting the collective pitch angle to make the rotor thrust constant. In this paper, the torque coefficient of rotor and collective pitch angle of rotor blade are shown. Experimental results show that behavior of torque coefficient varies in various ways according to combinations of these parameters and the torque coefficient on low speed crosswind condition increases without depending on wind direction compared to that of Out of Ground Effect case.
In STOL, it is a critical factor to maintain lifting force stably at low speed. For this purpose, a jet from the engine flows along the wing surface to create a large uptrend centrifugal force which yields an additional uplift force on the wing. In this research, numerical calculation using the Large Eddy Simulation method is performed to find out about this special characteristic of a jet under the influence of inertial forces. It is observed that the secondary flow appears within the jet and its vicinity. The pressure gradient normal to the wing surface, which creates the lift force, is increased by the addition of the jet. It is also observed that the jet center moves relatively to the reference frame adopted in the simulation, and the direction of the movement slightly deviates from the centrifugal force if the jet is swirling. At the initial time, the mean flow is distributed axisymmetrically, and it is shown that the inhomogeneous distribution of Coriolis force, which is due to the swirl, causes most part of the jet center's spanwise movement. In the course of time, however, the influence of advection in the plane perpendicular to the jet magnifies the spanwise movement.
Aerodynamic performances of four kinds of airfoils are examined in flows with low-Reynolds number. The aim of the present study is to find the airfoil shape, which provides a large value of a maximum lift-drag ratio in order to develop a high efficiency propeller for the Mars exploration airplane. A triangle airfoil is a base contour of the test airfoils and effects of blunt trailing edges on airfoil characteristics are examined using numerical simulations. Furthermore, a variation of aerodynamic characteristics of one airfoil with a blunt trailing edge due to decreased thickness and increased camber is also examined. The numerical results are verified by experiments. As the trailing edge thickness is increased, the lift-drag ratio becomes larger and values of the lift and the drag forces become smaller at the angle of attack where the lift-drag ratio becomes maximum. By increasing the trailing edge thickness, the boundary layer separation is suppressed and the aerodynamic forces are reduced. The increased camber and decreased thickness yield a significant lift increase of the airfoil with the blunt trailing edge and a small amount of drag increase. As a result, the airfoil with the blunt trailing edge yields large value of the lift-drag ratio in the flows with low-Reynolds numbers.
Transient three-dimensional numerical computations were carried out to clarify the heat transfer rate characteristics of magnetothermal convection of paramagnetic air created by the magnetic force alone in a shallow cylindrical enclosure with the thermal and magnetic gradients in a non-gravitational field. The enclosure filled with a paramagnetic air was fixed at the location which is subjected to a more uniform axial magnetic force and a minimal radial magnetic force. This configuration was devised to compare the heat transfer rate for the Rayleigh-Benard convection generated in a uniform gravitational force and the heat transfer rate for the magnetothermal convection by the application of the magnetic Rayleigh number proposed by Braithwaite et al. The computed heat transfer rates, i.e., the average Nusselt numbers on the heat transfer wall, for various numerical conditions were plotted versus the magnetic Rayleigh number with the classical experimental data for the Rayleigh-Benard convection under a nonmagnetic field reported by Silveston. When the average Nusselt numbers were evaluated using the magnetic Rayleigh number Ram, our data computed in the range 1,000 < Ram < 11,430 were found to distribute along the averaged curve obtained experimentally by Silveston.