Experimental Study of an Exhaust Ejector With Entraining Diffuser

Abstract

Air-air ejectors are used in a wide range of industrial applications. In gas turbine installations, ejectors are typically used for entraining ventilation air or cooling of exhaust ducting. In some gas turbine applications, the exhaust system must be cooled to limit temperatures inside the structure or to manage heat signatures. The ducts are usually cooled by ejectors with film or effusion cooled diffusers. Entraining diffusers typically have poor pressure recovery and as a result, the ejector performance is affected. This paper presents experimental results on the performance of an air-air ejector with an entraining diffuser. The effects of inlet swirl, and primary nozzle area ratio on the diffuser pressure recovery and ejector pumping were studied. The ejector experiments were carried out on a cold flow wind tunnel that can provide primary air flow rates up to 2.2 kg/s at ambient temperature. Velocity, pressure and temperature measurements were taken in the annulus upstream of the primary nozzle, at the nozzle exit, at the diffuser inlet, on the diffuser walls, and at the diffuser exit. The results show that swirl strongly improves flow non-uniformity at the diffuser exit. The peak pumping performance and the strongest diffuser gap flows was observed with 20° of swirl in the primary nozzle flow. At the no swirl condition, the nozzle area ratio slightly affected the overall entrainment ratio. However, the large nozzle area ratio resulted in the best pumping when swirl was applied.