Studies on Flow Characteristics of Variable Ejector Systems

Abstract

Experimental and numerical studies have been carried out to understand the flow characteristics of variable geometry ejector systems. We observed that for a given pressure ratio the cone cylinder of the variable sonic ejector can control the re-circulation ratio of the secondary suction mass flow. The secondary mass flow rate of the variable sonic ejector is strongly influenced by the ejector throat area ratio essentially at the high operating pressure ratios. We have also been observed that the secondary flow entrainment ratio for the variable sonic ejector increases as the ejector throat area ratio increases for the constant operating pressure ratio, whereas the secondary flow entrainment ratio for variable supersonic ejector decreases for the constant operating pressure ratio. We concluded that the variable sonic/supersonic ejector systems can be operated to obtain the required entrainment ratio by altering the ejector throat area ratio and the operating pressure ratio. The numerical analysis revealed that accurate modeling of fluid flow in ejectors is strongly dependent upon grid resolution and the turbulence model employed. I. Introduction N ejector system is a device in which a primary fluid at high pressure is accelerated by a primary nozzle and the high speed stream entrains and compresses a secondary stream at low pressure. The principle of the ejector system is to entrain the secondary flow through the shear action generated in the primary jet. The performance of such an ejector system is absolutely determined by the pure shear action between the primary and the secondary streams. Ejectors are widely used in a range of propulsion applications. 1-12 The ejector is not as efficient as a turbofan or a turbo-pump; but an advantage of the ejector system is in its geometrical simplicity, and having no moving parts. Of late, several configurations of the ejector systems have been studied to improve the efficiency of the ejector systems for industrial applications. Nevertheless, the geometrical and physical parameters that affect the performance of the ejector systems are not yet well understood. The turbulent mixing, the interaction between shock waves, boundary layers, and shear layers, and flow unsteadiness make the flow features prediction of the ejector system extremely difficult. Literature review reveals that the existing data are not sufficed to provide an effective design of the ejector system. Although many experimental and theoretical studies have been carried out by the earlier investigators on ejectors, the understanding of the flow physics locally along an ejector system is still not fully understood. Note that the tangential shear action and turbulence mixing between the two streams, leading to even more complicated by the proximity of the walls of the mixing tube, are one of the most difficult problems of gas dynamics. No correct solution has been given for this problem even with the aid of the most powerful CFD techniques. This paper presents the experimental and the computational flow characteristics of sonic/supersonic