2019. Vol. 14. Issue 2, Pp. 82–88

URL: http://mfs.uimech.org/mfs2019.2.012,en

DOI: 10.21662/mfs2019.2.012

URL: http://mfs.uimech.org/mfs2019.2.012,en

DOI: 10.21662/mfs2019.2.012

Non-stationary process characteristics of the gas outflow into a liquid

Alekseev M.V.^{∗}, Vozhakov I.S.^{∗,∗∗}, Lezhnin S.I.^{∗,∗∗}

A numerical simulation of the process of the outflow of gas under pressure into a closed container partially filled
with liquid was carried out. For comparative theoretical analysis, an asymptotic model was used with assumptions about the adiabaticity of the gas outflow
process and the ideality of the liquid during the oscillatory one-dimensional motion of the liquid column. In this case, the motion of the liquid column
and the evolution of pressure in the gas are determined by the equation of dynamics and the balance of enthalpy. Numerical simulation was performed in
the OpenFOAM package using the fluid volume method (VOF method) and the standard

gas outflow,

high pressure chamber,

OpenFOAM,

gas injection into water,

gas injection into liquid lead

**Problem:** Analytical and numerical study of the process of outflow of gas under pressure into a closed container with liquid. Obtaining characteristic process parameters and comparing the calculation results by the asymptotic model and the results of numerical simulation.

**Methods:** For the theoretical analysis, an asymptotic model was used, in which assumptions were made about the adiabatic process of gas outflow and fluid ideality during oscillatory motion of the liquid column, and the movement of the liquid column and the evolution of pressure in the gas are determined by the dynamics equation and the enthalpy balance. As a numerical method for solving a system of model differential equations in partial derivatives, a finite-difference scheme was chosen, based on the use of the Euler method in the OpenFOAM package. The resolution of the interphase surface was carried out by the volume of fluid method (VOF method).

**In a study was determined:**

- The dynamics of pulsations in the gas cavity arising during the flow of gas into the closed region substantially depends on the physical properties of the liquid in the volume. In the case of water, the growth of a slug occurs vertically displacing the liquid and compressing the gas volume in the upper region. At a time of 5 ms, the compression of the gas volume ceases and then the expansion phase follows. The movement of the liquid forms a compression of the gas shell in its central part in the radial direction (8 ms). In the case of lead, the growth of a slug occurs both in the radial and vertical directions. At the same time, the shape of the gas shell takes on a “bell-shaped” appearance. Liquid displacement by compression of the upper gas volume ends in 12 ms. Then there is a return motion of the liquid and compression of the slug. A cumulative jet is formed at the upper boundary, which, when moving downward, breaks down from the oncoming gas stream inside the slug, and the interphase boundary of the slug becomes unstable, leading to the separation of small bubbles from the slug and the formation of jets and drops inside the slug.
- The difference in the numerical calculation of pressure from the asymptotic model during the injection of gas into water is characterized by uneven pulsations. This non-uniformity is because, when injected into water, a gas stream is formed that passes through the liquid column. In this case, an unsteady gas-dynamic structure of pressure surges is formed inside the gas shell. When the gas flows into the water “at the first pulsation”, the pressure near the nozzle is always lower than the critical pressure, which characterizes the possible blocking of the flow. In the numerical calculation of gas injection into the lead, the jet gas flow is not observed. Calculation of the pressure at the first pulsation of the slug is in good agreement with the pressure obtained from the asymptotic model.

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