Creation and observation of tensile waves in oil column

The idea of tensile stress in a liquid is not necessarily familiar in fluid engineering, and much less accepted is the belief that a tensile stress can be propagated through a liquid. The present paper offers evidence of those 'tensile waves' in a hydraulic oil. This experiment showed that a pipe with one end blocked, branching from the main line where column separation is started, creates transient waves exhibiting alternate tension and compression. Ordinary viscous wave theory proves to properly predict the measured pressure waves, which reveals that the propagation velocity of a tensile wave is no different from that of a compressive one. Visual observation with the use of a transparent acrylic tube as a branch has confirmed that an oil column ruptures under excessive tension at the blocked end and after rupture a minute bubble probably born through diffusive gas release from the oil remains.