The optimum nozzle exit position and the behaviour of a turbulent flow in an ejector designed for natural draft burner

Abstract

This study investigated the near and far stream behaviour of a turbulent flow through an ejector at different axial positions of the nozzle. The study was conducted numerically for a throat-to-nozzle exit axial distance of 5 mm-20 mm. The secondary to the primary stream velocity ratio and the magnitude of the boundary layer fluctuation at the nozzle exit increased with the reducing axial distance. The potential core decayed as the flow approached a critical Reynolds number, and the increase in boundary layer fluctuation suppressed the near stream turbulence and momentum transfer by turbulent eddies. The model of the core length as a function of the throat-to-nozzle exit distance revealed a linear profile. Two models described the species concentration along the jet axis as a function of the root mean squared value of the fluctuating velocity because the flow behaved differently near and far streams due to the different controlling mechanisms.