Variable Cycle Engine Concepts and Component Technologies - An Overview

Abstract

The variable cycle engine (VCE) is of interest for military and supersonic civil platforms for its improved operational flexibility. However, the increase in degrees of freedom results in a more complex and non-intuitive engine behavior. Targeting this challenge, this review compiles published literature on VCEs and their variable compressor and turbine components. VCE concepts and the corresponding technology programs are presented in a chronological overview. Main optimization goals are discussed at engine level. This is followed by a discussion on the turbo-machinery components. The challenges of designing a compressor for a VCE are addressed, focusing on the main design aspects as well as operational topics, such as mode transition and control schedule design. The role of a variable geometry turbine is discussed along with associated losses. Two additional low technology readiness level variable turbine concepts are briefly presented as stimulation for future research.