Direct numerical simulation of two-phase pipe flow: influence of the domain length on the flow regime

TL;DR

This study uses direct numerical simulations to explore how domain length affects flow regimes in two-phase pipe flow, revealing the transition to turbulence and slug flow in kerosene-water mixtures, emphasizing the importance of domain size and nonlinear dynamics.

Contribution

It demonstrates the impact of domain length on flow regime transitions in two-phase pipe flow using phase field methods under realistic conditions.

Findings

Flow transitions to turbulence with sufficient pipe length.

Large-scale recirculation patterns are observed inside slugs.

Phase field methods reliably simulate experimental two-phase flows.

Abstract

We perform direct numerical simulations of a kerosene-water mixture in pipe flow under realistic experimental conditions by solving the Cahn-Hilliard-Navier-Stokes equations. We compute the linear stability of core-annular flow of kerosene and water in a vertical pipe and find that it is highly unstable. By performing DNS initialized with a slightly perturbed core-annular flow, we show that the system transitions to turbulence and finally relaxes into a turbulent slug flow regime provided that the pipe is sufficiently long. This configuration presents mild turbulence and large scale three-dimensional recirculation patterns inside the slugs. Our work highlights the need for applying nonlinear-dynamics approaches and carefully selecting the domain length to investigate the patterns observed in two-phase pipe flows and demonstrates the capabilities of phase field methods to reliably simulate experimental conditions.