Experimental Study: Effects of the Annulus’ Center Body End Shape on the Performance of Low Mach Number Air-Air Ejector With Entraining Diffuser
In the present paper, an experimental investigation of the performance of a low mach number round straight air-air ejector with a 4-ring entraining diffuser is reported. The ejector system was mounted on an annular flow wind tunnel. Based on the hydraulic diameter and average velocity and temperature at the nozzle exit, the tunnel provides cold flow at Mach 0.2 with a Reynolds number of 5.2×105 and hot flow at Mach 0.27 with a Reynolds number of 2.6×105. The end shape of the annulus’ center body has major effects on the core separation size and shape that strongly affects the ejector performance. The effects of the annulus’ center body with elliptical and square ends on the ejector pumping, wall static pressure distribution and back pressure were investigated under different flow temperatures and swirl angles: 0°, 10°, 20°, and 30°. These measurements were conducted at 129 mm standoff distance using two different nozzle exit diameters. It was found that for both nozzle exit diameters, using the annulus’ center body with a square end improved the total pumping ratio over its ratio with an elliptical end due to the flatness of the core separation at the nozzle exits. For all configurations tested, the maximum entrainment ratio was observed with 20° swirl angle and the back pressure coefficient decreased as swirl angle increased. Removing the elliptical end, creating the square shape, the flow has more space to spread after the annulus’ center body to give the higher centerline velocity which enhances the flow uniformity at the nozzle and diffuser exits.