A Study of Subsonic Air-Air Ejectors with Short Bent Mixing Tubes

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Maqsood, Asim
Ejector , Mixing tube , Bent , Entraining
An experimental and numerical study of air-air bent exhaust ejectors was carried out. The objective of the study was to determine the effect of a bend on the performance of exhaust ejectors. The ejectors consisted of nozzles, mixing tubes and in some cases entraining diffusers. As part of this study the effect of swirl in the primary flow and the temperature ratio of the primary to the secondary flow were also investigated. The study included testing of round and oblong sectioned ejectors with and without entraining diffusers. The experimental testing was performed on two different wind tunnels capable of blowing air at a maximum mass flow rate of 2.2 kg/s at ambient and elevated temperatures. Flow measurements were made upstream of the nozzle, at the nozzle exit and at the exit of the ejector. Pumping, pressure rise and total efficiency of the ejector were studied with respect to the bend angle, swirl angle and the primary to secondary flow temperature ratio. A commercial CFD code was used to evaluate the effectiveness of commercial CFD using limited resources for designing of such devices. The pumping ratio and pressure rise decrease with the increase in the degree of bend. Swirl up to a certain angle has a useful effect on the performance of a bent ejector. The entraining diffuser enhances the performance of a bent ejector. The CFD models based on commercial solver were able to predict the flow structures and the variation of the performance parameters with the bend and swirl angle. However, generally the CFD models were not able to predict the exact values of the performance parameters.
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