Multiple ducted streams with a periodic or a steady supersonic driver flow

Abstract

AN experimental investigation of the operating characteristics of a two-dimensional planar, constant area, supersonic-subsonic ejector with a steady or a periodically pulsed continuous driver flow is presented. Improvements in ejector pressure recovery and entrainment capabilities resulted from the periodic driver for a limited range of operating conditions. Contents The purpose of this study was to determine if periodic pulsation of the driver flow in an ejector would lead to improvements in ejector performance as a result of enhancing or exciting modes of flow interaction beyond those normally occurring in the ejector mixing duct. In particular, this investigation was concerned with pressure recovery applications in which the primary flow must pump the low pressure secondary to an appreciably higher pressure level. The approach taken to induce flow interaction was to periodically pulse the ejector driver flow with an efficient large scale fluidic oscillator developed for this purpose. This is similar to wave energy exchanger type ejectors13 in which slugs of primary flow are discharged periodically into the mixing duct. In the current case, however, the driver flow is continuous. A simple, one-dimensional inviscid control volume analysis, following that of Fabri and Siestrunk,4'5 was used to predict ejector operating characteristics; the descriptive features of the analysis are useful for the present discussion. Three regimes of ejector operation are considered. The supersonic regime, SR, occurs when the primary flow expands against the secondary after entering the ejector mixing duct and the secondary flow chokes at an aerodynamic throat in the mixing duct; this is the situation depicted in Fig. 1. The saturated supersonic regime, SSR, occurs when the secondary static pressure equals or exceeds that of the primary flow at the ejector inlet and the secondary flow chokes at the inlet. The mixed regime, MR, occurs when the back pressure at the ejector exit plane is too high to allow choking of the secondary flow either in the mixing duct or at the inlet.