Ejectors have many uses, such as creating a vacuum or suction, and in some cases they are suitable alternatives to pumps. The efficiency of the ejector is defined as the entrainment ratio, which is equal to the ratio of the mass flow rate of the suctioned secondary fluid to the primary driving fluid. The efficiency of the ejectors is important both at the design point and at the off-design points with higher back pressures. Depending on the ratio of the outlet area to the throat area of the converging-diverging nozzle, the supersonic fluid coming out of the nozzle can have one of three states: under-expanded, isentropic and over-expanded. Considering the structural differences of the fluid flow coming out of the primary nozzle in the three mentioned states, the geometry of the ejector walls plays an important role in the efficiency of the ejector. In the first part of this research, the geometry optimization of the ejector was done separately in all three modes of underexpansion, isentropic and overexpansion. In the optimization, the fixed primary nozzle geometry and secondary duct walls, mixing chamber and diffuser were modified using a combination of parametric and adjoint optimization. In parametric optimization, the optimal height of the mixing chamber was obtained for different states of the initial supersonic flow. Then, the optimal profile of the walls of the secondary duct, the suction chamber and the mixing chamber was calculated by solving the adjoint equations in the adjoint module of AnsysFluent software. Additional optimization was able to increase the suction ratio by 20.5%, 15.3% and 16.5%for underexpanded, isentropic and overexpanded states, respectively. To eva‎luate the objective function, the compressible viscous flow solver of base pressure with the k_ω sst turbulence model has been used. Ejector efficiency loss at back pressures higher than the design back pressure is one of the challenges of ejector design. Therefore, in the second part of the research, the idea of adding an aerodynamic cavity to the mixing chamber of the ejector in order to increase the efficiency of the ejector at back pressures higher than the design point was numerically investigated and combined parametric and adjoint optimization on the added cavities. done. The results of this section showed that adding the optimal cavity after high pressures significantly increases the efficiency of the ejector, which significantly increases the functional range of the ejector. An ejector with a cavity has increased the suction ratio by 50% for a 10% increase in back pressure compared to an ejector without a cavity.

مهدي نيلي احمدآبادي

احمد سوهانكار اصفهاني، ايمان چيت ساز