Turbulent 3D simulation code application to the pressure “hysteresis” analysis in the gas ejector vacuum chamber

Аuthors

Larina E. V.^1*, Tsipenko A. V.^1**, Afanas’ev A. A.^***, Kryukov I. A.^2****

1. Moscow Aviation Institute (National Research University), 4, Volokolamskoe shosse, Moscow, А-80, GSP-3, 125993, Russia
2. Ishlinsky Institute for Problems in Mechanics of the Russian Academy of Sciences, 101-1, prospekt Vernadskogo, Moscow, 119526, Russia

*e-mail: larinaelenav@gmail.com
**e-mail: tsipenko_av@mail.ru
***e-mail: tempero@tempero.com
****e-mail: kryukov@ipmnet.ru

Abstract

While studying operation of the supersonic gas ejector as a vacuum pump, special attention was paid to the so-called “hysteresis” observed in the dependence of the pressure in the vacuum chamber on the working gas pressure. The “hysteresis curve” occurs during the ejector start-stop, and oscillatory flow mode, undesirable at the unit operation, is observed herewith. In this regard, a series of numerical experiments on the oscillatory flow mode modelling was performed, and experimental data on the gas ejector operation was analyzed.

The simulation presented in the article was being performed employing the scheme of the increased order of accuracy and a three-parameter k-ε-μt turbulence model. Simulation of the flow with the uniform shear was performed in the simplified and 3D formulation. Collating with the other models was made.

Simulation of a plane submerged jet in the boundary layer approximation was made. A good agreement with experimental data on the averaged flow velocity was obtained.

A simulation of the supersonic overexpanded jet in a three-dimensional formulation was performed. The Pitot pressure at the jet axis was collated with the experiment and other models. The qualitative conformity with the experiment was obtained.

The numerical simulation using the k-ε-μt turbulence model dempnstrated that the “hysteresis” at the ejector start-stop is associated with a non-stationary parameter changes during the ejector start-stop. Thus, the ejector channel and the vacuum chamber parameters will be determined unambiguously under the steady-state boundary conditions. However, when real-life installations operation, the time required to reach the optimum mode at the smooth pressure increase is noticeably longer, than with a first sharp coming to overestimated parameters and then a small smooth throttling of the working gas pressure. The hysteresis loop reflects just this process.

The transient mode with low-frequency pulsations is necessary for the turbulence model verification. These mode predictions are important for the ejector optimal operation. Thus, a 1D self-excited oscillation model should be developed in future.

The work was financially supported by the RFBR grant No. 16-38-60185.

Keywords:

gas ejector, vacuum pump, experimental data, supersonic gas jet, boundary layer separation point, numerical simulation, turbulence, function recovery procedure, homogeneous shear flow, boundary layer flow

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