Fluid force acting on circular cylinder of finite length in lock-in condition

This paper describes the fluid force acting on circular cylinder of finite length in the locking-in region. The experiment was carried out in an N. P. L. blow-down type wind-tunnel with a working section of 500 mm × 500 mm × 2 000 mm at Reynolds number of 1.32 × 10⁴. The cylinder was forced to oscillate sinusoidally in the lift direction. The power spectrum of the fluctuating velocity in the wake behind a circular cylinder was measured to show the locking-in region in the present experiment. The time-mean pressure distribution and fluctuation pressure distribution on the circular cylinder were measured for the displacement in the vibration. Consequently it was found that the mean drag and fluctuating lift increase and become maximum in the locking-in region, while the base pressure in the rear surface (θ = 180°) of the cylinder becomes low and attains minimum.