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Abstract
Ejectors are widely used in many applications such as aerospace, propulsion and refrigeration. Therefore, the present work describes and evaluates a new theoretical method for designing supersonic ejectors. The method predicts numerically the optimum geometry of an ejector which gives maximum efficiency. The numerical investigation is based on flow equations governing turbulent, compressible, two-dimensional, steady, time averaged and boundary layer equations. These equations are continuity, momentum and energy. In addition, turbulent shear stress and heat transfer are calculated using eddy viscosity model. These equations are solved iteratively using finite difference method under the conditions of different flow regimes which can be divided into several distinctive regions. The methods for estimating the mixing length are different for each How region. The first region depicts the wall boundary layer, jet shear layer and secondary and primary potential flows. The second one contains a single region of developing flow. The theoretical results are concerned with investigating the effect of both operational parameters (stagnation pressure coefficient, mass ratio and temperature ratio) and geometric parameters (area ratio, constant-pressure section length of the mixing duct, constant-area section length of the mixing duct and the diffuser section length) on the performance of supersonic ejectors. The results obtained help to understand the flow behavior and physical phenomena occurring in the flow through ejectors. For verification of the proposed model, the present theoretical results are compared with previously published experimental and theoretical data. This comparison showed a good agreement. The obtained theoretical results are used to develop optimum design charts and correlate the optimum ejector dimensionless geometry, pressure ratio and ejector optimum (maximum) efficiency as functions of the operational parameters and ejector area ratio. The resultant correlations help in selecting the optimum ejector geometry and its corresponding maximum efficiency for particular operating conditions.