Hiromitsu Kawazoe

GROUND EFFECT ON THE DYNAMIC CHARACTERISTICS OF A WING-ROCK DELTA WING

Aerodynamic forces and moments of a delta wing in unsteady motion were experimentally studied in a low-speed wind tunnel. Its flight attitude was altered smoothly and periodically in the wind flow by means of a manipulator equipped with six stepping motors, which were controlled by a microcomputer. Since it had six degrees of freedom, the delta wing could move arbitrarily in pitching, yawing, rolling, translation motions, and their combinations. The objective of the research is to analyze dynamic characteristics of the wing-rock delta wing with regard to the altitude under the ground effect. The lateral translation motion as well as the roll and yaw angles of the delta wing were changed with the frequency of 0.5Hz in the research. A developed compact force balance with the weight of 5.6 grams was used to measure lift, drag, rolling and pitching moments. Lift and drag were largely and monotonously increased with the delta wing approaching the ground, and the rolling moment was also effected, especially in the case of a high angle of attack. These forces and moments had a large hysteresis with the wing-rock motion, especially in the case of a high attack angle accompanied by the leading edge vortex breakdown. From the previous study on a rolling delta wing at a high angle of attack under the ground effects, the rolling moment coefficient, Crm, drew a hysteresis loop with a roll angle in the anticlockwise direction and had a tendency to be lateral static unstable. On the opposite to the results, Crm of the wing-rock delta wing in the study made a clockwise and lateral static stable hysteresis loop with a roll/yaw angle. Flow visualization for the leading edge vortices and pressure measurements at the ground just below the wing-rock delta wing were also carried out to analyze the dynamic characteristics. It was found for the reason that the leading edge vortex on the moving-down side of the delta wing was changed from the broken to the reconstructed one, which was opposite to the result of the rolling delta wing.

Natural convection flow simulated by workstation cluster

Publisher Summary Natural convection flow is very important in practical applications. For example, the flow inside an electric transformer has not been investigated completely. The heat generated by electrical coils inside a transformer has to be cooled by natural or forced convection. As a practical application, the flow inside an electric transformer is simulated by using two workstations. There are many electrical coils inside it, which generate Joules heat. To cool this heat, oil is usually forced to flow through coils. However, oil is flammable and, furthermore, forced convection needs a driving force. As an alternative, it is possible to use a nonflammable gas by using natural convection. When the flow reaches the top of the coil section, it goes into the cold section, where the heat is given to the cold wall and then the flow goes down in the cold section. The temperature rises in the upper region in both the coil and flow sections. From simulation, useful information is obtained such as the optimum arrangement of flow passages inside an electric transformer, which can be used to design it.

A new domain decomposition method using virtual sub-domains

Publisher Summary This chapter describes a new Domain Decomposition Method for unstructured grids by using Virtual Sub-domains and a genetic algorithm. The domain decomposition technique is one of key issues in parallel computation, especially, when unstructured grid systems are employed, it influences the efficiency of parallel processing. Furthermore, this new method has a capability to perform partitioning grid in parallel processing. The new method was applied to the flow around a cylinder to examine its performance under a workstation cluster. The unstructured grid system has been widely used in computational fluid dynamics (CFD), because of its advantages over the structured grid to treat complicated geometries and to automatically generate grids. In parallel CFD, domain decomposition is mostly employed to distribute the work load of computation to each processor. The chapter discusses several standard domain decomposition methods, such as the graph bisection method, the coordinate bisection method, and the spectral bisection method. It concludes that the new method did not show so good a performance as expected for sample problems described in the chapter. However, it is expected that it would show a better result for a larger gird system.