Incompressible viscous flows around a circular cylinder placed at various heights above a moving plate have been investigated numerically using finite difference method for the high Reynolds number (Re=5×104). A Navier-Stokes equation solver employing an overset grid system was applied to treat the complex geometry. The calculated results of lift coefficients and the Strouhal number were compared with experimental ones. It is found that the calculated results are in a good agreement with the experimental ones. Furthermore the structure of the wake behind the cylinder is made clear with the flow patterns and the pressure distributions. These results also show that due to the effects of the plate the regular vortex shedding is suppressed for all gaps less than about 0.3 times of the cylinder diameter.
Incompressible viscous flows around a circular cylinder are investigated numerically using finite difference method for the high Reynolds number (Re=103-105). The effects of the boundary conditions of the pressure on the cylinder surface, the outer boundaries of the grid systems, the time steps and the mesh resolution are studied in detail. The calculated results of drag coefficients and pressure distributions on the cylinder surface are compared with experimental ones. The mesh must have nearly equal resolution in both the directions normal and tangential to the cylinder surface. The number of mesh that is necessary to resolve the flow is above ten in a boundary layer. Also, the calculated results that satisfied these conditions are in a good agreement with the experimental ones.
The fluid-structure interaction, especially the interaction between the elastic body and the ambient flow, is one of very complicated problems to be analyzed in engineering. The body is oscillated freely, consequently the information from the wake is fed back into the body motion. The interaction is a strong nonlinear one and it is so difficult to analyze it experimentally. In this article the problem on the oscillation of an elastic body is analyzed numerically, in which the features of the lock-in regime and the wake structure are made clear. The lock-in regime is captured clearly, in which the vortex shedding frequency, the body oscillation one, and the body eigen one are coincided each other and also the vortex street is redistributed to be switched over from one row to two. The self-limiting process is controlled by the phase difference between the body oscillation and the body forces (lift and force due to the virtual mass effect). Also the "pseudo-lock-in" regime is captured, in which, while the vortex shedding frequency and the body oscillation one are coincided each other, they are different from the body eigen one.
The phenomenon of three-dimensional separation of the flow over a slender body at high angles of attack is difficult to model and still challenging problem. The singularity of the flow is caused by mutual intervention of threedimensional separation and separated vortices. In this study, the flow in the cross-flow separation region of an axisymmetric paraboloid at 30, 40, and 50deg angle of attack has been investigated experimentally by hot wire anemometer. Reynolds numbers are 9.0×103 and 1.8×104 referred to the base diameter. X-type probe was used to measure three dimensional velocity fluctuations over the axisymmetric paraboloid at sampling time of 4kHz. It has been shown that the lift-off and mergence of vortices can be explained by r.m.s. distribution of velocity fluctuations. Reynolds stress and the difference between probability density function and normal distribution oscillates where the kink of vortex is observed.
In this paper, a guidance law for a flight vehicle during boost phase is presented. This guidance law is constructed by combining proportional navigation and pure pursuit navigation and the performance of the law depends on the combining ratio. Since the rado is the function of a parameter, which originally represents the deceleration due to the drag of the vehicle but actually can be chosen properly by the guidance system designer, it can be determined by adjusting the parameter. In fact, adjusting the parameter is more convenient than determining the ratio directly. The simulation results show that the guidance law presented is superior in performance to proportional navigation for wide off-boresight angles.