Two-Phase-Flow-Induced Vibrations in a Horizontal Pulping System

Abstract

This paper deals with experimental and theoretical analyses of the excitation mechanism of vibrations induced by an air-and-water two-phase flow in a straight horizontal pipe. The experiment reveals a strong relationship between the first natural frequency of a piping system and the dominant frequency of void-signals -- that is, the frequency ratio being 1/2, 1/1, 3/2, -- when extraordinarily strong vibrations are observed. The equation of motion in a straight horizontal pipe conveying a two-phase fluid is derived by accounting for 1) inertia force, 2) the pipe's elastic restoring force, 3) Coriolis' force, 4) centrifugal force, 5) pressure fluctuations, 6) momentum change due to time-varying density of the two-phase flow and 7) gravity as an external force. The equation is transformed into a Mathieu's with a periodic external term ; instability analysis concludes that parametric excitation and resonance are the main causes of such strong vibrations. Good agreement can be seen between experimental and theoretical results.