二次元流中における円柱の揚力係数について

抄録

In general, it is well known that the wind force acting on a circular cylinder undergoes a sudden fall of drag under the influence of REYNOLD's number. And it is also assumed that the mean lift does not act on a circular cylinder placed rectangularly in smooth flows. BEARMAN pointed out, however, that the base pressure was discontinuous in the case of a sudden decline of drag in critical REYNOLD'S region. He also indicates a large lift-coefficient (C_L=1.3), which is calculated from the pressure distribution of the surface of a circular cylinder. Taking the above into consideration, we attempted to explicate the evolution mechanism of lift-coefficient in critical REYNOLD'S region. Four kinds of cylinders with various diameters were used for the measurement. The measuring range extends from 3.0×10⁴ to 1.0×10⁶ in REYNOLD, S number. In experiments, not only the drag and lift were synchronously measured for four kinds of the circular cylinders each by means of a three-component-balance, but also vortexes were measured at the rear of the circular cylinders by a hot-wire-anemometer.
And also the pressure distribution of the surface of the circular cylinder with a diameter of 21.8cm was measured at three points: subcritical region (3.0×10⁴<Re<3.5×10⁵), critical region (3.5×10⁵<Re<5.0×10⁵), supercritical region (5.0×10⁵<Re<1.0×10⁶).
As a result of these, we confirmed the evolution of a extremely large lift-coefficient in critical region: (3.5×10⁵<Re<5.0×10⁵) in REYNOLD'S number. This phenomenon was also confirmed from the pressure distribution of the cylinder surface. In the measurement by the hot-wire, furthermore, the spectra of slip streams of cylinders and the discontinuity of the base pressure are very much in agreement with BEARMAN's results.