On Aero Engine Intercooling

Sammanfattning: Establishing an optimal intercooled aero engine constitutes a coupled problem where the conceptual design of the intercooler and the engine has to be considered simultaneously. The heat transfer and pressure loss characteristics will depend on the choice of the intercooler architecture. Hence, to be able to optimize the performance of an intercooled aero engine, the performance characteristics of a given intercooler architecture has to be known in the parameter range anticipated for the aero engine optimization. In this thesis, several design concepts of a two-pass cross flow tubular intercooler for aero engine application have been analyzed by the use of computational fluid dynamics simulations and system level assessments. The work comprises 3D coupled CFD analysis of the internal flow (in-flow, cross-over and out-flow duct) using porous media modelling for the tube stacks. Several design iterations on the internal flow configuration has been performed applying two splitter vanes and a flow guide vane. A parametric study of the external heat transfer and pressure loss is included. Correlations for two configurations (straight tube and involute spiral tube) are provided for system level assessments of this intercooler concept. In addition to providing heat transfer and pressure loss characteristics, the correlations are set up to allow intercooler installation space constraints to be taken into account. The fuel burn benefits of the presented intercooled engine are attributed to the use of a variable geometry separate exhaust nozzle and to providing an adequate amount of intercooling. The amount of intercooling should be sufficient to enable the high OPR at take-off, and allow a compact engine design. In cruise, on the other hand, it is beneficial to reduce the intercooling to establish an optimum between intercooling and incurred pressure losses.