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APPLICABILITY OF VARIOUS DIFFERENTIAL TURBULENCE MODELS IN THE CALCULATION OF SUPERSONIC GAS JETS

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Subject of study. The paper presents research results of the applicability of the most common turbulence models to the calculation of turbulent supersonic jets containing shock waves. The aim of the study is to develop an efficient method for calculating non-isobaric turbulent supersonic gas jets containing shock waves. In the axisymmetric case such jets are characterized by irregular reflection of shock waves from the axis of symmetry, that is followed by the formation of normal shock waves (Mach disks), which are compatible with the peaks of pressure and temperature on the jet axis. The flow behind the Mach disk is subsonic. The appearance of subsonic flow region and the abrupt change of flow parameters on the direct shock wave leads to some methodological difficulties in the application of the standard two-parameter differential models of turbulence. It is known that various turbulence models lead to significantly different parameters distribution along the axis of the jet. In particular, the degree of blurring for shock wave structure of the jet for some turbulence models is significantly different from the observed one by experiment. Main results. Comparison of widely represented in modern commercial computing packages turbulence models was completed: k-ωturbulence model, Realizable k-ε model, RNG k-ε model, SAS-model, Standard SST k-ω model, transition  SST- model. Testing has shown that Realizable k-ε and transition SST turbulence models provide the best results in the calculation of supersonic flows, typical for advanced jet engines. The first model provides reliable data about the distribution of pressure along the jet axis, bottom pressure, the pressure distribution on the walls of the nozzle and ejector at low differential pressure at the nozzle exit and the environment, which are typical for the normal operation of air-jet engines. Good accuracy can be obtained at a fairly coarse grid without the use of any special techniques and tricks. Transition SST turbulence model provides a better match with the experimental results in the case of a large pressure difference between the nozzle exit and the environment. It is more particular about the difference grid quality, boundary and initial conditions, characterized by essentially increasing calculation time.  At the same time, it guarantees qualitative accurate picture of shock-wave structure with acceptable accuracy of the pressure distribution determination along the jet axis. Practical significance.  Practical application of recommendations listed in the paper will give the possibility for researchers to avoid gross inaccuracies in the calculation of supersonic gas jets.

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