Numerical modeling and geometric optimization of single-phase supersonic ejector

In the present study, the performance of the 2D single-phase supersonic ejector with working fluid of air is simulated in ANSYS CFX. The aim is to investigate the velocity field, pressure distribution, primary nozzle flow regime, and entertainment ratio in different operational conditions. The primary pressure inlet with bar and the secondary inlet as an opening with bar at different outlet pressures are simulated. The turbulence model is used. The sidewalls are considered symmetry boundary conditions and the no-slip condition is applied to the ejector walls. Then, the ejector geometry is optimized using Multi-Objective Genetic Algorithm (MOGA) in order to reach greater efficiency. Optimization is performed considering geometric parameters including primary nozzle exit diameter, nozzle exit position, diameter, and length of the constant area section.
Sensitivity analysis results show that the diameter of constant area section has major effect on the entertainment and pressure ratios as two objective functions. The nozzle exit position and external diameter of primary nozzle are the second and third dominant parameters that respectively influence the performance of the ejector, while the effect of constant area section length is negligible. Results indicate that by increasing the pressure ratio, the shock train moves upstream and at the design point, the last oblique shock is located in the exit of the constant area section, letting the remaining pressure recovery be done in the subsonic diffuser which reduces the pressure losses and increases the efficiency. Above the critical pressure ratio, due to the movement of the shock train to upstream weakening the shock strength, the suction pressure increases. Then, the pressure difference is reduced, leading to the lower secondary mass flow suction. The optimized ejector in the double choking condition has a % higher entertainment ratio and its operational range is enhanced by percent in comparison to the original geometry.