10.1 Introduction to Inlets and Nozzles

The inlet and exhaust nozzle are the two engine components that directly interface with the internal airflow and the flow about the aircraft. In fact, integration of the engine and the airframe is one of the most complex problems and has a major impact on the performance of the aircraft system. Many technical books, reports, articles, etc., are available in open literature (public domain) that concentrate on only small parts of this major technical challenge. This chapter identifies the major design considerations of inlets and exhaust nozzles and presents basic analysis tools for their preliminary sizing and design.

The results of the engine performance analysis provide a wealth of information about the required performance of both the inlet and the exhaust nozzle. For example, the required full-throttle, corrected engine airflow vs both Mach number and altitude can be obtained from the engine performance analysis program PERF (see Figs. 8.21, 8.31, 8.50, and 8.74b). Likewise, the engine airflow at specific partial-throttle conditions (corresponding to cruise, loiter, etc.) and the assumed inlet total pressure ratio vs Mach number can be obtained. The design information defines the requirements of the inlet in terms of total pressure ratio and mass flow rate, and preliminary design of the inlet starts with this information.

The simplest and most powerful design tool available for preliminary design of these components is one-dimensional compressible flow. Both the inlet and the exhaust nozzle can be modeled as simple one-dimensional adiabatic flows or a series...