Experimental study on dynamic stability of vertical cantilevered pipe aspirating fluid immersed in various water depths

Abstract

This paper conducts an experimental study to investigate the effects of immersion water depth on the dynamic stability performance of vertical cantilevered pipe aspirating fluid. Two cantilevered pipes about 4 m long with different diameters are partially immersed in water at eight different depths. The pipe experiences clear dynamic instability when the internal flow exceeds critical velocity. The dynamic instability is in the manner of mixed regular large amplitude flutter and small amplitude shudder. Experimental data show that the deeper the pipe immersion depth, the bigger the difference between the critical and natural frequency of the pipe. It is found that increasing immersion depth can reduce the flutter amplitude in the post-critical range but has little effect in the pre-critical region. The critical velocity of the pipe increases significantly as the immersion depth increases. The trace of the pipe gradually shifts from expanding motion to periodical motion as immersion depth increases. A preliminary analytical study shows these phenomena can be accounted for by the fact that the external fluid supply damping to the fluid-pipe system and larger immersion water depth decreases pipe tension.