Application of the One-Dimensional Theory to the Calculation of Supersonic Ejectors
This chapter is about the application of the theory of one-dimensional steady flows to the design of what is called an ejector, and more precisely, a supersonic ejector. We will see that by simple relations, it is possible to predict the aerodynamic performance of such a device, without the need for detailed modeling of flows that requires resolution of the Navier-Stokes equations. The principle is to replace the actual flows in the device by equivalent average uniform flows in each section to which we apply the relations of mass conservation, momentum, and energy. This model, which enables a remarkably precise prediction of the characteristics of the ejector, is still used to optimize ejectors.
An ejector is a device with one or more driver jets at a high velocity driving an adjacent fluid by transferring some of their energy to it. The aim is to increase the momentum (or stagnation pressure) of the driven fluid. Entrainment is provided, either by turbulent mixing along the boundary of the different flows, and which can extend to all involved flows, or by a suction effect resulting from a significant expansion of the primary flow which imposes a very low pressure at the confluence of the two streams. These two effects are usually combined.
There are many practical applications of ejectors, particularly in the aerospace area: extractors of various types, devices to ...