An Integrated Lumped Parameter-CFD approach for off-design ejector performance evaluation

Abstract

This paper presents an Integrated Lumped Parameter Model-Computational Fluid-Dynamics approach for off-design ejector performance evaluation. The purpose of this approach is to evaluate the entrainment ratio, for a fixed geometry, in both on-design and off-design operating conditions. The proposed model is based on a Lumped Parameter Model (LPM) with variable ejector component efficiencies provided by CFD simulations. The CFD results are used for developing maps for ejector component efficiencies in a broad range of operating conditions. The ejector component efficiency maps couple the CFD and the LPM techniques for building an Integrated LPM-CFD approach. The proposed approach is demonstrated for a convergent nozzle ejector and the paper is structured in four parts. At first, the CFD approach is validated by global and local data and seven Reynolds Averaged Navier Stokes (RANS) turbulence models are compared: the k–ω SST showed good performance and was selected for the rest of the analysis. At second, a Lumped Parameter Model (LPM) for subsonic ejector is developed and the ejector component efficiencies have been defined. At third, the CFD approach is used to investigate the flow field, to analyze its influence on ejector component efficiencies and to propose efficiency correlations and maps linking ejector component efficiencies and local flow quantities. In the last part, the efficiency maps are embedded into the lumped parameter model, thus creating the Integrated LPM-CFD (ILPM-CFD) model. The ILPM-CFD model is validated over experimental and CFD data and is compared with LPM Constant Efficiency models showing better performance and a wider range of applicability. The average deviation between the ILPM-CFD results and the experimental and CFD data is less than 0.75%, whereas constant efficiency models showed a deviation up to 30%. The ILPM-CFD model is able to vary the value of the ejector component efficiencies depending on the operating condition, being able to evaluate both the on-design and off-design performance of the ejector.