CFD Study of a Variable Flow Geometry Radial Ejector

Abstract

-To achieve higher performance from ejectors at some working conditions, implementations of variable geometry might be possible. While axisymmetric ejectors with axial flow paths have limitations that make practical implementation of variable geometry difficult, radial ejector configurations have a flow path that is conducive to changes in nozzle and ejector throat area during operation. The geometric adjustment of the radial ejector could be made by simply changing the separation of the radial ejector duct walls and/or the separation of the nozzle walls in order to optimize performance over a range of different conditions. The effects of such changes on the performance of a radial ejector have been investigated using a Computational Fluid Dynamic (CFD) analysis with ANSYS FLUENT software. Axisymmetric CFD models were generated to assess performance for a primary nozzle throat area of 8.792 mm 2 and for ejector throat separations of 2.2 mm, 2.4 mm and 3.0 mm, corresponding to ejector throat areas of 497, 543 and 678 mm 2 , respectively. The CFD analysis reveals that changes ejector performance can be achieved by changing the ejector duct's separation. An increase of 34% in entrainment ratio can be achieved by increasing the ejector throat separation from 2.2 mm to 3.0 mm at fixed primary and secondary pressures of 160 kPa and 1.8 kPa, respectively. If an increase in the ejector malfunction pressure is needed, it could be achieved by decreasing the ejector duct separation. An overall malfunction pressure increase of 18% can be achieved by decreasing the ejector throat separation from 3.0 mm to 2.2 mm at primary and secondary pressures of 250 and 1.8 kPa, respectively.