自立型煙突に用いる渦励振抑制用螺旋板の効果に関する実験的研究

Abstract

Helical strakes are well-known as the devices to suppress the vortex excited oscillation of stacks. Hitherto the effectiveness of the strakes has been investigated by many wind tunnel experiments. However little data on the vibrations of actual stacks with the strakes have been reported. In order to find out the best configuration of the strakes to suppress the vibration of stacks, wind tunnel experiments of spring-sustained two-dimensional models were performed and an examination was made of the effects of the number, pitch angle and height of the helical strakes in reducing the vibrations. The necessary length of the strakes along height was investigated through the three-dimensional experiments in the wind tunnel. Based on the results of the wind-tunnel tests, the helical strakes were fitted to an actual steel stack. The measurements of the vibrations of the stack were carried out before and after the installation of the strakes. The observed maximum value of the double amplitude of the stack had been 80 cm before the installation and it became less than 5 cm after that. The designed helical strakes were proved to be successful. The sectionl areas of steel stacks are often determined by the conditions under the vortex excited oscillation rather than the maximum wind speed. In the design of the stack with helical strakes as mentioned above, the vortex excited oscillation need not be taken into account. As a result, the structure of the stack can be expected to be more economical than the plain stack without strakes.