Numerical rebuilding of dynamic instabilities and forces in multiphase pipe bend flow

Abstract

The present paper focusses on the numerical rebuilding of different multiphase flow regimes in a medium scale pipe system (6 inch). Principal investigations are performed by CFD to initiate hydrodynamic instabilities and develop them into the correct flow pattern (slug, stratified, etc.) at a given downwind position without applying artificial models or boundary conditions. The numerical predictions of the flow obtained by a volume of fluid CFD method (OpenFoam) are compared with available experimental data. Numerical investigations are performed with respect to grid resolution, initial conditions and turbulence modelling but also for obtaining a representative, comparable set of numerical and experimental data. For different flow regimes from slug flow to stratified flow good agreement with the experimental data was achieved with respect to the predicted flow regime and topology but also the forces predicted on the bend. Especially the large variation of the root mean squared values but also peak-to-peak values of the forces are predicted well by the numerical solutions for the different flow regimes.

A study of the vibration of a horizontal U-bend subjected to an internal upwards flowing air–water mixture

“…Similar to what was discussed by Nakamura et al (1995), the impact by liquid slugs cannot be neglected. It should be noted that Mack et al (2018) validated the experimental work described by Belfroid et al (2016) and confirmed the conclusions.…”

Nature and magnitude of operating forces in a horizontal bend conveying gas-liquid slug flows

“…A study with OpenFoam by [7] predicted instantaneous component of forces on a bend that were well within the range of the experimental data. The shape of the power spectral density P SD of the forces was also in agreement with measurements.…”

“…The resultantes forces obtained here are one to two orders higher in magnitude than the maximum forces obtained with P F M model presented in [5]. The actual resultants are however well in the same range as the forces measured and predicted in [7]. Nevertheless, a criterion based solely on the liquid hold-up threshold has proved to be insufficient to distinguish forces due to slug impacts from those due to liquid films and waves.…”

Stochastic mechanistic modelling of two-phase slug flow forces on bends in horizontal piping

“…The conservatism in the bend-force estimation can be reduced by Computational Fluid Dynamics (CFD) simulations. Pontaza (2014), Pontaza et al (2017) and Mack et al (2018) presented accurate results of CFD calculations, but they also mentioned the extensive computational time required which limits the use of CFD in design and optimization. Hossain et al (2019) used CFD to calculate flow quantities as liquid holdup, pressure, and average velocity, to solve a force balance over a pipe bend.…”