Duct Aerodynamics for Intercooled Aero Gas Turbines: Constraints, Concepts and Design Methodology

Economic and environmental concerns are a major driving force behind the development of aero gas turbine technology, with ever more stringent legislation dictating significant reductions in specific fuel consumption and pollutant emissions. Intercooling has long been of interest as it has the potential for lower compressor delivery and turbine cooling air temperatures, together with reduced NOx and higher overall pressure ratios, which enable reduced fuel consumption. However, thus far the technical complexities, both aerodynamic and mechanical, have been prohibitive. For example, improvements in core cycle thermal efficiency could easily be offset by reduced component efficiencies and pressure losses in the intercooler and its associated ducting. This paper describes an intercooled concept typical of those that may be used for a large, high by-pass ratio, high OPR aero-engine. The paper goes on to describe the aerodynamic challenges of designing a duct system to transfer the core air, issuing from the low pressure compressors, into the intercooler modules. A design methodology is developed which includes consideration of: system loss, the inclusion of local constraints such as a radial drive shaft, the need to provide core access for ancillary services, and minimization of aerodynamic interaction with surrounding components. Finally a preliminary duct design is presented for a specific intercooled aero-engine design.Copyright © 2009 by Rolls-Royce plc