双圆柱缝隙中的不稳定流

关于双圆柱相互干扰的实验研究已经进行多年,并得到了许多结果。本研究用频谱分析的方法对某些特定的斜置排列方式进行了详细的研究。用磁带记录仪记录了由热线探头在双圆柱尾迹中测得的速度信号,经过回放、微机采样与处理,研究了频谱与时间的关系。其结果表明,当双圆柱处于L/d=2,T/d=1的位置时,作为主体,绕流双圆柱可以看作为绕流一个单一的钝头物体,它的Strouhal数约为0.15左右,而在双圆柱缝隙中时有时无地出现一股不稳定流动,在频谱图上出现了双峰值,第二峰对应的Strouhal数约为0.33,这个第二峰值时高时低,有时还会高过第一峰而占了主导地位,但多数时间第二峰处于从属地位,甚至于消失。这种现象将是干扰引起振动的重要机理之一。

The Unstable Flow In The Gap Between Two Cylinders

In this paper,the behaviour of the gap flow between two cylinders in staggered arrangement was studied by experimental methods. The velocity signal in the wake behind the two cylinders was measured by TSI hot-wire anemometer and recorded by a TEAC tape recorder. After the experiments, the signal was sampled and processed by A/D interface and IBM PC/XT personal computer.There are 11 050 discrete points to be acquired. The spectrum analysis was made by FFT for 1024 points, the data number was delayed 50 points (also 50 milisecond) each time for processing, that is first for 1 to 1024, second for 51 to 1074, the last one is 10 000 to 11 024. Two hundred spectrum graphics have been got all together, and then the relationship between the spectrum and the time can be built.The results show that when two cylinders are arranged as T/D= 1 and L/D = 2, the flow in the gap is unstable. Mainly, it can be looked as a single blunt body, the Strouhal Number is 0.15. Sometimes the gap flow appears and there are two peaks in the spectrum graphics, the Strouhal Number corresponding to the second peak is about 0.33. The amplitude of the second peak waves with the time, sometime it may be higher than the first one and sometime it is lower, even disappeared. This is the evidence that the gap flow is unstable.