Numerical Simulation of Two-phase CO2 Ejector Flows Using the Implicit Density-based SU2 Solver and Comparative Analysis of HEM and HRM Models

Two-phase CO2 ejector flows have become a main topic of discussion in the last few years. Indeed, the ejector device has proven to be a compelling mean of reducing the exergy losses associated to the expansion process in heat pump and cooling systems, even more so in high pressure cycles that are typically required when using carbon dioxide. Numerical methods, and especially CFD constitute one of the main predicting and analysis tools to study the complex flow physics that takes place within two-phase ejectors. This work focuses on the development of a fast Favre-Averaged Navier-Stokes (FANS) simulation tool to be used for the flow analysis and design of transcritical CO2 ejectors. The rapidity of the solver is achieved by first using an implicit Euler integration scheme within the Non-Ideal CFD SU2 solver, and secondly by using a tabulated equation of state. The wall-resolved simulations are performed using a common Homogeneous Equilibrium Model (HEM) and compared to an Homogeneous Relaxation Model (HRM). An exergy tubes analysis is then used to assess the exergy transfers between the primary and secondary streams. Lastly, the choking mechanism of the ejector is discussed in light of the so-called compound-choking theory