This is a continuation of the study of boundary layer transition along a concave wall with 1m radius of curvature. The flow pattern was visualized by smoke-wire technique, and the pattern was compared with the velocity distribution, the turbulence intensity and the frequency spectrum. It is noticeable that the horseshoe-type vortices grow by entrainment of the main airflow. Further down-stream as the vortices merge with each other, they break down in the outer layer, while fluctuating flows with high turbulence intensity are produced in the high velocity gradient regions below. According to the spectrum distribution, the fluctuating flows are generated by the behaviour of the vortices, and the turbulence intensity of the flows is remarkably amplified in the inner layer.
This paper describes an experimental study of the mutual interference between two spheres placed on plane boundary. The surface-pressure distributions of two spheres were measured for the oblique arrangement of two spheres and the drag, sideforce, and lift coefficients were determined from surface-pressure distributions. The formation of vortices was observed by the method of visualization. The distributions of velocities and turbulent intensities of the flow past two spheres were measured. The experimental results were compared with those of a single sphere and two spheres in tandem and side-by-side arrangements.
The mechanism of rearrangement of the vortex street in the wake behind a circular cylinder at low Reynolds numbers was investigated in a low speed wind tunnel. The pairing of two vortices in the streamwise vortex rows of the so-called Kármán vortex street took place downstream of the primary vortex street of regular arrangement at Reynolds numbers lower than about 160. As the result of the vortex pairing, the secondary vortex street was generated further downstream. The streamwise variation of the wave forms in the wake was shown to correspond to that in the arrangement of the vortices in the visualized flow patterns in the transition region from the primary to the secondary vortex street. The width of the wake increased in the downstream direction, and the wake became increasingly wider with merging of vortices. The spacing ratio of vortices both in the primary and the secondary street had a value of 0.45 when they have fully developed.
A vibration analysis method is proposed for sandwich beams with a viscoelastic core. This method is applicable to the beams with arbitrary boundary conditions, intermediate supports and concentrated masses. The partial differential equation for bending of sandwich beams is transformed to an ordinary differential equation by means of Laplace transformation with respect to time. The effect of intermediate supports and concentrated masses is introduced into the equation by adding undetermined concentrated forces. Linear equations for the boundary values and the concentrated forces are derived from the differential equation by means of one-dimensional boundary element method. The harmonic response is calculated by solving the linear equations directly and eigenvalues are obtained by finding the points where the determinant of coefficient matrix vanishes using an iteration method.
This paper presents a new control scheme for digital adaptive flight control systems, that satisfies C* criterion for aircraft which have continuously varying stability derivatives. A number of design methods for digital adaptive flight control systems have been reported based on the assumption that aircraft are linear time-invariant systems. But the equations of real aircraft motions have wide time-varying parameters in their flight envelopes. Only recently, new adaptive control system theories for the linear time-varying systems have been developed. By modifying the new theories, this paper presents a new parameter adjustment algorithm that can estimate the coefficents of powers of dynamic pressure, which are used to synthesize the input to aircraft instead of estimating the time-varying parameters. Computer simulations were performed on a jet fighter as a time-varying system by continuously changing flight conditions in the flight envelope. The results showed remarkable adaptability.