Page 153 - Fluid-Structure Interactions Slender Structure and Axial Flow (Volume 1)

PIPES CONVEYING FLUID: LINEAR DYNAMICS I 135

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Figure 3.45 Cin6-film sequences showing the limit-cycle motion of cantilevered rubber pipes
conveying fluid (a) air, L = 457 mm, frequency (f) = 1.56 Hz, /3 = 0.001; (b) water, L = 551 mm,
f = 3.25 Hz, p= 0.479; (c) water, L = 724 mm, f = 1.82 Hz, /3 = 0.556. The camera was located
upstream and above the horizontal pipe; the straight black line (drawn on a board just below the
flexible pipe) shows the equilibrium position of the pipe.

The limit-cycle amplitude of the free end at the onset of the flutter could be as large as
$L for the rubber pipes, but less than &L for the metal pipes.
The dimensionless critical flow velocities, uCf, and frequencies, wCf, are shown in
Figure 3.46 for rubber pipes. Two sets of experimental points are presented: those of
spontaneous instability and those of ‘induced instability’ - induced by the light taps on