This seminar addresses the modelling and physical mechanisms governing choking in ejectors. Ejectors are passive devices used for mixing, compression, or vacuum generation, with applications in aeronautics, refrigeration, and the process industry. They operate by expanding a high-pressure primary flow to entrain a lower-pressure secondary flow, both streams mixing before reaching an intermediate pressure. Their performance is largely governed by the maximal secondary mass flow rate attainable under choked conditions, yet the physical mechanism responsible for choking remains only partly understood. Two main theories exist: compound choking, which assumes both streams choke simultaneously under a uniform static pressure, and Fabri choking, where each stream reaches its own sonic condition.

These mechanisms are investigated through the development of reduced-order models. Conventional zero-dimensional models are too coarse to capture the relevant physics, while RANS simulations reproduce choking behaviour without clearly identifying its underlying cause. To bridge this gap, one-dimensional models retaining axial flow information are developed at a computational cost comparable to 0D approaches. Single- and double-stream formulations are constructed, calibrated, and analysed, with particular attention to the comparison between compound and Fabri choking in the double-stream configuration. Preliminary quasi-two-dimensional developments are also introduced to address the limitations of purely one-dimensional approaches.

 A general calibration framework is proposed, combining adjoint-based sensitivity analysis with machine-learning regression to identify appropriate closure relations. Finally, the models are assessed against an extensive numerical and experimental database. The resulting framework provides a consistent low-dimensional representation of ejector flows and offers new insight into the mechanisms governing choking and overall ejector performance.

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