Oscillation of a Spring-Supported Sphere in Uniform Flow

Abstract

The dynamic instability of an elastic supported sphere in the uniform flow is studied experimentally by using the low speed open wind tunnel. If the oscillation was made by an initial deformation due to the outer disturbance, the oscillation was damped when the wind speed was below the some critical wind speed. However, if the wind speed increased over that critical wind speed, the limitcycle oscillation appeared. This oscillation disappeared and the small amplitude randam oscillation appeared, when the wind speed increased over the another higher critical wind speed, and the oscillation of the sphere damped rapidly even if the oscillation was made by the initial deformation due to outer disturbance. In the present study, eight series of the wind tunnel tests were done i. e. the two spheres and the four pairs of the spring were used. The limitcycle dynamic instability were observed in the Reynolds number range 3×10³<Re<4×10⁴. The ratio of the limitcycle dynamic instability disappearing critical wind speed to the one appearing wind speed was between 4.8 to 2.2 in the each wind tunnel test. The maximum vibration amplitude of the sphere oscillation was about 0.5d in the each test.