Supersonic ejector simulation and optimisation
The aims of this project were the implementation of Computational Fluid Dynamics (CFD) to the study of supersonic ejectors, and the investigation of the flow processes that occur. The conventional ejector has been in existence for more than a century yet the design has remained largely unchanged and is difficult to optimise. This has been attributed to a lack of understanding of the complex flow processes and phenomena that occur. CFD provides the ability to study these processes, and to rapidly assess geometrical influence upon operational performance. The CFD model was assessed through systematic appraisal of the numerical parameters that influence solution stability and simulation accuracy. Two proprietary CFD codes were utilised; a structured segregated code and an adaptive mesh coupled code. Assessed parameters included; mesh dependency, discretisation schemes, turbulence models, and boundary layer models that are shown highly influential. Simulation was validated through comparison of predicted and experimental entrainment values. Simulations of an ejector that is part of a steam-jet refrigeration cycle were used to assess the influence of geometry and operating conditions. The structured code was found suitable for geometrical studies however the coupled code was required for detailed flow analysis. Geometrical studies showed current ejector design guidelines to be well set. Operational studies highlighted the dominant influence of motive fluid flow rate upon entrainment levels. Shock systems and flow processes could be clearly identified. Simulations of ejectors utilised in vacuum and thrust augmenting applications were also conducted in assessment of the general applicability of CFD. CFD has the potential to be an effective and powerful tool III simulating and understanding ejectors. Qualitative and quantitative results can be obtained dependent upon the optimisation and validation of the mathematical model. This however can only be performed properly if the user fully understands the t10w physics and applied numerics.