Fluid-Structure Interaction of Multiphase Flow within a Pipe Bend

Multiphase flows are any fluid flow consisting of more than one phase or
component, such as gas-liquid flow, liquid-liquid flow, liquid-solid flow or gas-liquidsolid-
flow. It is commonly found in fluid transportation systems, particularly the
hydrocarbons transportation systems in the oil and gas industry, accounted by
simultaneous production of natural gases and crude oil. A significant response arising
from flow-induced vibration could lead to potential fatigue damage or uncontrolled
vibration when the excitation frequency matches the natural frequencies of the piping
system, particularly in cases where oil brings dense sand particles or when slug flow
develops in the flow-lines. This is therefore why the investigation of the effects of the
oil-gas-water mixture on the structure of pipelines is important. Multiphase flow
problems remain a challenge to the industry due to its complexity and unpredictability.
This paper presents an analysis of fluid-structure interaction between a two-phase flow
and a pipe bend to determine the resulting vibrations induced by the two-phase flow.
Two pipe bend models with different upstream and downstream lengths of the bend
are used for the analysis. Natural frequencies of the pipe bend structures are extracted
and numerical simulations are performed using a CFD solver (ANSYS CFX module)
and a FEA solver (ANSYS Mechanical module) coupled within ANSYS Workbench.
Through Fast Fourier transforming the time domain results into frequency domain, the
frequencies of vibrations are collected and compared with the natural frequencies to
determine the corresponding level of risks.