Effect of a Bend on the Performance of an Oblong Ejector

Abstract

This paper presents the results of an experimental study on the performance of oblong ejectors with a bend in the mixing tube. In the aerospace industry, space limitations can lead to the design of exhaust ducts of oblong cross section. These ducts can also include ejectors for engine space ventilation or exhaust cooling or infrared signature suppression. In some cases these systems require bends after the primary driving nozzle. Each ejector consisted of a nozzle and a constant area mixing tube. A series of bent mixing tubes with the same radius of curvature was tested and the results were compared with the baseline straight ejector. A hot flow wind tunnel was used to provide the primary air flow at temperatures up to 450°C and mass flow rates up to 2 kg/s. Ambient air from the surroundings was allowed to enter the mixing tubes and mix with the primary air issuing from the primary nozzle. Velocity, pressure and temperature measurements were taken upstream of the nozzle, at the mixing tube inlet and at the exit of the mixing tube. Seven-hole probes were used to resolve the velocity vector at the exit of the mixing tube to identify large-scale flow structures. Mass flow ratio, temperature distribution and the losses in the different ejectors were compared to estimate the degradation of ejector performance with the degree of bend. Significant reduction in the performance was observed with the degree of bend in the ejector.