抄録
Low speed experiments are carried out on the aerodynamic properties of three oblate spheroids and a sphere with their axis of symmetry parallel to the oncoming stream for the REYNOLDS number 1.7-8.5×105.The length ratios of the minor axis to the major one are 5/6, 4/6 and 3/6. The curves of drag coefficient versus REYNOLDS number for spheroids are shown to be similar to that of a sphere with translation to the higher regions of REYNOLDS number and drag coefficient with increasing flatness of spheroid. The flattest one, however, behaves like a circular disk, no critical region being found in the REYNOLDS number tested in the present experiment.
The drastic change in the pressure distribution from subcritical to supercritical regions and the appearance of the second separation line occur simultaneously for the sphere and the fullest model but this is not the case of the model with moderate flatness. This model seems to have a transient region in which the pressure distribution is of the supercritical type but separation is not axisymmetric, varing its position periodically, and when the line turns to near axisymmetric type and at the same time the pressure on the backside of the model rises, drag reduction occurs. The flattest model reveales no remarkable changes both in the pressure distribution and in the separation line.
Applying the CEBECI-SMITH method, calculations are also made of the laminar boundary layers in the subcritical range, giving distributions of boundary layer thickness, shape factor, surface shearing stress and the position of the separation line. The agreement between the measured and the calculated separation angles are fairly good except for the flattest spheroid.
