## THERMAL SCIENCE

International Scientific Journal

### COMPARISON OF WELL-POSEDNESS CRITERIA OF TWO-FLUID MODELS FOR NUMERICAL SIMULATION OF GAS-LIQUID TWO-PHASE FLOWS IN VERTICAL PIPES

**ABSTRACT**

The purpose of the present study is to compare the well-posedness criteria of the free-pressure two-fluid model, single-pressure two-fluid model, and two-pressure two-fluid model in a vertical pipe. Two-fluid models were solved using the conservative shock capturing method. A water faucet case is used to compare two-fluid models. The free pressure two-fluid model can accurately predict discontinuities in the solution field if the problem's initial condition satisfies the Kelvin Helmholtz instability conditions. The single-pressure two-fluid model can accurately predict the behavior of flows in which the two phases are poorly coupled. The two-pressure two-fluid model is an unconditionally well-posed one. If in the free-pressure two-fluid model and single-pressure two-fluid model, the range of velocity difference of two phases exceeds certain limits, the models will be ill-posed. The two-pressure two-fluid model produces more numerical diffusion than the free-pressure two-fluid and single-pressure two-fluid models in the solution field. High numerical diffusion of two-pressure two-fluid models leads to failure to better comply with the problem's analytical solution. Results show that a single-pressure model is a powerful model for numerical modeling of gas-liquid two-fluid-flows in the vertical pipe due to a broader range of well-posed than free-pressure models and less numerical diffusion than the two-pressure mode.

**KEYWORDS**

PAPER SUBMITTED: 2020-04-20

PAPER REVISED: 1970-01-01

PAPER ACCEPTED: 2021-03-28

PUBLISHED ONLINE: 2021-05-16

**THERMAL SCIENCE** YEAR

**2022**, VOLUME

**26**, ISSUE

**Issue 2**, PAGES [1245 - 1265]

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