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

• Published in: Applied thermal engineering 2021-03, Vol.186, p.116431, Article 116431
• Main Authors: Besagni, Giorgio, Cristiani, Nicolò, Croci, Lorenzo, Guédon, Gaël Raymond, Inzoli, Fabio
• Format: Article
• Language: English
• Subjects: Boundary conditions; Computational fluid dynamics; Ejector; Ejector refrigeration; Ejectors; Entrainment; Finite element method; Fluid dynamics; Fluid flow; Heat transfer; Local flow; Numerical methods; Refrigeration; Screening; Simulation; Solvers; Three dimensional models; Turbulence; Turbulence models; Two dimensional models; Validation; Working fluids
• ISSN: 1359-4311; 1873-5606
• DOI: 10.1016/j.applthermaleng.2020.116431

•We present a comprehensive validation of a CFD approach.•We present a broad screening of modelling approaches.•We present ejector component efficiency maps.•k-ω SST exhibits the best performances for both global and local flow quantities. The efficiency of ejector-based systems (the “system-scale”) relies on the behaviour of the ejector (the “component-scale”), 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 fluid-dynamics 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 (density-based and pressure-based) and turbulence models (k-ε RNG and k-ω 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-ω 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.