Experimental investigations have been made on the wake characteristics of groups of normal flat plates, consisting of two, three, or four plates placed side by side in a uniform flow with slits in between. When the ratio of the slit width to the plate width (slit ratio) was small, the gap flows were observed to be biassed either upward or downward in a stable way, leading to multiple, stable flow patterns for a single slit ratio value. Some regularities were found in the gap flow directions and the appearance of the flow patterns. The plate on the biassed side showed high drag and regular vortex shedding, while the plate on the unbiassed side showed the opposite. The variations with slit ratio of base pressure and STROUHAL number of individual plates showed similar tendencies when the neighboring gap flows were alike. In four-plate rows, the wake characteristics were compared with those of two dimensional perforated plates studied earlier by CASTRO.
Two disputable points in the spanwise integral are discussed in a MULTHOPP-type method for solution of the integral equation of subsonic lifting-surface theory. The first point is the coincidence of each collocation section with one of the spanwise integration points. This makes necessary the evaluation of regularized influence function at the coincident points which is very time consuming except in the case of steady wing. The second point is the relatively small but undesirable sharp variation of the regularized influence functions near the collocation sections which is the cause of the necessity of taking a large number of spanwise integration points. Devices for improvement to cope with these dificulties are proposed. Numerical examinations of the proposed method will be given in Part 2.
Probabilistic properties of nonlinear response of panels buckled by shear deformation to random excitation are studied in the use of a simulation method to disclose the effects of shear buckling and antisymmetric mode on the sonic fatigue. Simultaneous nonlinear vibrational equations where the effect of shear buckling is considered are derived in the use of a variational principle derived from the principle of virtual work with the aid of the LAGRANGE multiplyer method. These equations are solved numerically by NEWMARK's β method. The fatigue life is calculated with a cumulative damage rule. These results show that the effects of shear buckling are remarkable. When the sound pressure is small, the panel vibrates in the vicinity of the statically equilibrium point after buckling. When the pressure becomes large, the panel sometimes jumps to another equilibrium point on the opposite side. When the pressure is very large, the panel vibrates almost always through zero deflection with large amplitude like a flat panel. Namely, the larger the pressure becomes, the smaller the effect of shear buckling on the response of the deflection becomes. However the effect on the response of the strain does not become small. The fatigue life is greatly shortened by shear buckling for each pressure level.
Thermal stresses of adhesively bonded multilayer plates were analyzed including the bending effects. In the present analysis, the bending displacements in each layer were assumed to be the same. This assumption simplified the thermal stress analysis in general multilayer plates. Solutions obtained in the analysis were compared with other analytical and finite element solutions for 2-layer and 3-layer plates as examples. These results are shown as follows; 1. The present analysis is very simple to predict the shear stresses in adhesives and the normal stresses in members irrespectively of bending constraints. 2. When the bending is constrained, the shear stresses in adhesives and the normal stresses in members calculated by the present analysis agree with those by FEM. When the bending is free, the maximum shear stresses in adhesives arehigher than those by FEM and the maximum normal stresses in members agree with those by FEM. The present analysis is useful in the design of adhesively bonded mult layer plates.
A method is proposed to estimate the location, velocity and strength of the tipvortices of the helicopter rotor. The method uses three hotwire anemometers near the rotor plane, and the measured velocities are fed into a computer program, which modifies the above unknown parameters to adapt the measured results. The validity is confirmed by applying it to a model rotor experiment in hover. Smoke visualization study is also conducted and the vortices' fluctuations are shown to increase as they leave from the rotor plane, from which the sensor locations are determined.
To develop the design method of shock-inrotor type rotor in which radial equilibrium is considered, the flow condition which satisfies radial equilibrium both before and behind the normal shock is investigated assuming that (1) the flow is quasi-axisymmetric and (2) the meridional streamline is parallel to the axis. In this report only the uniform inlet flow with no swirl components is considered as the most typical and ideal example. The results suggests the following difficulties or questions when we apply the flow assumed in this report to a practical rotor. (1) The rotor should have a large hub-tip radius ratio. (2) A large turning is required in the supersonic portion between the rotor inlet and the normal shock. (3) The calculated absolute total pressure ratio is too high in connection with (2). (4) The blade section should be thicker at the tip than at the hub.