Mechanical Design

Abstract

In preliminary design we run trade studies to make design choices. The figure of merit for optimization should consider the aircraft mission. In this chapter we show how it is possible at an early stage of the design to generate the flow path and make a reasonable estimate of the system weight. We look at each of the major components or sub-assemblies in a gas turbine and identify the main parameters which influence the flow path and weight. Seeing a diagram of the layout is a good way to check the compatibility and alignment of components. Special attention is placed on disk design as disks are such large contributors to engine weight. While it is recognized that absolute numbers generated by these simple methods, exemplified by GasTurb, may not be very accurate, the trends that they identify are useful in making design decisions. Moreover, if more details are available the results may easily be calibrated against real engines. A by-product of the mechanical design is valuable information such as rotor polar moment of inertia and heat capacity of casings, which heavily influence the transient performance.