Computational fluid-dynamics modelling of supersonic ejectors: Screening of modelling approaches, comprehensive validation and assessment of ejector component efficiencies

The efficiency of ejector-based systems (the system-scale) relies on the behaviour of the ejector (the componentscale), related to the flow phenomena within the component itself (the local-scale). As a consequence of this multi-scale connection, the precise prediction of the local-scale is of fundamental importance to sustain the design of commercially viable ejector-based systems. Although it is widely accepted that computational fluiddynamics can achieve the prediction of the local-scale (CFD) modelling approaches, a broad agreement regarding the performances of numerical methods is not reached: different authors applied different methods, and a complete validation is missing so far. This paper contributes to the current discussion and closes the knowledge gap by assessing the performances of a CFD approach for single-phase supersonic ejectors. To this end, a comprehensive validation has been conducted, encompassing a wide range of ejector designs, boundary conditions and working fluids; besides, a screening of modelling approaches is conducted, encompassing a wide range of mesh criteria, geometrical modelling (2-Dimensional and 3-Dimensional approaches), solvers (densitybased and pressure-based) and turbulence models (k-epsilon RNG and k-omega SST). The extensive comparison with experimental data allowed assessing and determining the influence of mesh criteria, geometrical modelling, solvers and turbulence models. In particular, k-omega SST has shown the best agreement with the experimental measurements concerning both global and local flow quantities, with an average entrainment ratio error of 14% and a maximum of 20%, under on-design operating mode. Finally, the simulation outcomes have been further post-processed to derive ejector component efficiencies, to contribute to the present discussion regarding closures in lumped parameter ejector modelling approaches. In conclusion, this paper thoroughly assesses the performance of a CFD model for single-phase ejector simulations and poses precise guidelines to be applied in future research activities and to support the design of ejector-based systems.

Automated summary

This paper evaluates the performance of a CFD model for single-phase supersonic ejectors through comprehensive validation, considering a wide range of ejector designs, boundary conditions, and working fluids. Different modeling approaches, including mesh criteria, geometrical modeling, solvers, and turbulence models, are screened. The study shows that k-omega SST has the best agreement with experimental measurements, with an average entrainment ratio error of 14% and a maximum of 20% under on-design operating mode.