Phenomenological Aerodynamic Analysis of an Ejector Exposed to Large Inlet Pulsations

Abstract

To enable the coupling of the unsteady, high-enthalpy flow exiting a Rotating Detonation Combustor (RDC) with a subsonic turbine, an ejector may be installed between the combustor and turbine. In the present work, a conventional ejector is investigated numerically using a Large-Eddy Simulation. Firstly, a stationary operating point is analyzed where sufficient agreement could be obtained with experimental data. Secondly, a new operating point is proposed where a sinusoidal acoustic pulsation is imposed at the primary ejector inlet. The pulsation generates a periodic fluctuation between sub- and supersonic velocity regimes at the primary nozzle exit, which is representative of local RDC exhaust velocities. In this first step, the exhaust gas temperature, flow angle, and gas composition are not considered. At this operating condition, a secondary normal shock appears periodically at the end of the constant-area mixing chamber and retracts upstream as a pressure wave. The shear layer, the boundary layer, the secondary shock, and the diffuser-induced separation are identified as kinetic energy loss sources within the ejector. The amplitude of total pressure fluctuations is reduced by 85% throughout the device, whereas the frequency is retained. The dampening characteristics are considered favorable for gas turbine integration.