A theoretical model is developed for the vibration and stability of a vertical pipe subjected concurrently to two dependent axial flows.The external fluid,after exiting the outer annular region between the pipe and a rigid cylindrical channel,is conveyed upwards inside the pipe.This configuration thus resembles of a pipe that aspirating fluid.The equation of planar motion is solved by means of the differential quadrature method (DQM).Calculations are conducted for a slender drill-string-like and a bench-top-size system,for different confinement conditions of the outer annular channel.It is shown that the vibrations of these two systems are closely related to the degree of confinement of the outer annular channel.For a drill-string-like system with narrow annuli,buckling instability may occur in the second and third modes.For a bench-top-size system,however,both buckling and flutter may occur in the lowest three modes.The form of instability depends on the annuli size.