Simulation of Single-Choked Supersonic Ejectors. Part 1: Turbulence Modelling

Supersonic Ejectors are devices widely used for different applications which exploit their multifaceted characteristics. The use of computational fluid-dynamics provides an important analysis tool for the ejectors design, complementary to 1D models. As in other fields, the effectiveness of numerical solutions depends on the reliability of the adopted models. Within Reynolds/Favre averaged simulations, the turbulence model plays an essential role. Existing validation studies mainly provide comparisons among results obtained with different models, without discussing the modelling differences that are reflected in their behaviour. The emerging picture does not allow clear unified statements on the subject.The present work is aimed to provide a clarifying contribution to this aspect, focussing on ejectors operating in single choked condition, at moderate Mach number. In the first part a detailed analysis is done on the main ejector flow features, on their interaction with turbulence and on the related characteristics of eddy viscosity models. A critical study is developed on existing two equations turbulence models in common use, highlighting their intrinsic limits. A new model is described, aimed to properly reproduce the turbulence response to different shear intensities, that characterise an ejector flow field. In the second part the analysed models are used to simulate two test cases, with available detailed measurements.