This paper describes an experimental study on the near wake behind bluff body in relation to the base drag reduction. The experiments were carried out using the models with two-dimensional blunt trailing edge and with periodically three-dimensional one. REYNOLDS number based on uniform velocity and base thickness is lessthan 8×103. Behind the two-dimensional bluff body, the periodic vortex shedding occurs and the static pressure reduces in the vortex formation region. In the case of the three-dimensional model, it is observed as a general tendency that the static pressure reduction and the concentration of periodic vortices are not notable. This seems to be the essential feature associated with the drag reduction of three-dimensional bluff body.
In the present paper, we investigated underexpanded sonic jets through axisymmetric conical nozzles both theoretically and experimentally and the effect of the convergence angle on those jets were investigated in all the range of the angles which can be used for practical purpose under various nozzle exit conditions as in our previous paper which had dealt with two-dimensional case. The flowfield inside the nozzle was solved by expanding the velocity components into power series in y up to the fourth order after OSWATI-TSCH and ROTHSTEIN and we derived a new differential equation which may be applied to the case of considerably large inclination angle of the wall, Furthermore, we dealt with the boundary conditions with special attention. Then, we obtained the shape of the sonic line and the jet boundary along with the location of the shock wave analytically and experimentally and both the results are in a reasonable agreement. Calculated sonic lines were also compared with other authors' ones and some comments were added.
The effect of the aerofoil suction side curvatures on the 2-D transonic turbine cascade performances is investigated by the numerical and the experimental methods. The Modified FLIC method is used to predict the cascade flows. The experiments are conducted in the wide range of the exit Mach number M2th=0.5 to 2.0 by the optical and the wake traverse methods using the suction-type shock tunnel and the blow-down type wind tunnel. The characteristics of the flow patterns around these four kinds of aerofoil sections are clarified and it is shown that the relation between energy loss and its exit Mach number clearly depends on their suction side curvatures.
The author has proposed a simple calculation formula capable of determining the wind load which acts on steel pipe towers from any angle of attack. The feature of this calculation formula is that is can be applied not only for the square section of steel pipe towers, but also for other sections, such as rectangles, equilateral triangles, hexagonal triangles, etc. When main pillers and diagonal bracings are exposed to high wind speeds, the drag-coefficients are actually reduced affected by the REYNOLDS number. This is due to the roundness of their structure. On thecontrary, the calculation formula proposed by the author is workable in the subcritical REYNOLDS regions. Under such circumstances, it was not possible to define the adequate value of the drag-coeffi cients to be used in the case of steel pipe towers in either the critical REYNOLDS region or in the super-critical REYNOLDS region. This paper com-pares the results of conventional studies on dragcoefficients in the critical REYNOLDS region with the author's wind tunnel test results. As a result, the author could identify that dragcoefficients in the square sections would be decreased to about 1.1 in the critical REYNOLDS regions, but increased to about 1.5 in the supercritical REYNOLDS regions. Using these results, the author attempted to come up with a calculation formula capable of determining the dragcoefficients for steel pipe towers in the regions above the critical REYNOLDS regions.
An analytical study has been carried out to clarify the mechanism of pogo. As a numerical example, the pogo instability of N-Launch Vehicle has been studied. The calculated result is in good agreement with the flight record for the occurrence time of pogo vibration. The following properties have been disclosed. (1) Main factors which govern the pogo occurrence are the mass ratio and the structural damping coefficient. (2) In the case of N-Vehicle, the pogo instability is mainly created at the oxidizer-structure loop with a short feed pipe. (3) The bubble frequency due to cavitation in the oxidizer pump plays an important role. The effectiveness of an accumulator at the pump inlet as a suppression device is also presented analytically.
The experimental results on the buckling of thin cylindrical shells with a reinforced circular hole under axial compressive load are presented and discussed. The shell around a hole is reinforced by thickening the annular area. The variation of buckling load with the thickness or the radius of the reinforcing area is measured experimentally for both cases of central loading and eccentric loading. It is found that the reinforcement by thickening the wall thickness is more effective compared with by broading the reinforcing radius in order to recover the buckling value of monocoque cylindrical shell with a circular hole. The specimens of cylindrical shells and reinforcement materials used for these tests were made of Lumirror Polyester Sheet.