Flow Management in Heat Exchanger Installations for Intercooled Turbofan Engines

Intercooled high bypass jet engines offer a means to raise the engine pressure ratio, reduce cooling flow temperatures, reduce engine core size and thus to reduce the specific fuel consumption and increase specific power of the jet engine. One of the major challenges of designing such an engine is the installation of the large heat exchanger between the intermediate and high pressure compressors. This thesis shows how the aerodynamic losses associated with a zigzag arrangement of compact heat exchanger matrices installed around the annulus of the engine may be minimised by the use of simple flow conditioning schemes. These were investigated using a series of experimental tests using engine scale analogues of the heat exchanger matrices. Pressure drop, flow magnitude and distribution with the approach and exit passages were characterised. The experimental results were used to validate a CFD model, which allowed more extensive investigation of geometric variants, including the development of novel integrated flow turning features. From sensibly chosen metrics of flow uniformity and inferred heat exchanger performance, it was possible to assess the value of the schemes employed. An installation geometry was recommended, of matrix volume and matrix frontal area 8.7% and 8.5% lower than a conventionally installed system. A large scale transient liquid crystal heat transfer test facility was constructed to characterise the heat exchanger performance of the integrated turning features when employed in cross-corrugated heat exchangers. Detailed measurements of local heat transfer coefficient distributions and pressure drop on models of the primary surfaces of the heat exchanger in the presence of external cross flow are reported. Importantly the full spanwise entrance region and connecting side walls were characterised, where thermal stresses are likely to most severe. The results show that the entrance features are capable of recovering much of the flow dynamic head at high cross flow to through flow ratios, and provide comparative heat transfer levels between the entrance and fully developed flow regions of cross-corrugated heat exchanger matrices for the first time. The data have been sensibly averaged and correlated to allow entry effects to be reliably predicted in future work. The existing methods of image processing liquid crystal experiments proved insufficiently robust for the inherently poorly lit environment and a novel robust processing technique has been developed which is able to reliably obtain data over a very wide range of convective heat transfer coefficients in a single transient test. Finally, the implications of the installation losses and heat transfer metric on overall design layout of the intercooler turbofan engine was investigated. This design study has shown that is it possible to accommodate the heat exchanger matrices (for a given matrix size requirement) with a minimal (2%) additional pressure loss penalty in the bypass duct