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Resumen:
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The path to future aero-engines with more efficient engine architectures requires advanced
thermal management technologies to handle the demand of refrigeration and lubrication. Oil
systems, holding a double function ...[+]
The path to future aero-engines with more efficient engine architectures requires advanced
thermal management technologies to handle the demand of refrigeration and lubrication. Oil
systems, holding a double function as lubricant and coolant circuits, require supplemental
cooling sources to the conventional fuel based cooling systems as the current oil thermal
capacity becomes saturated with future engine developments. The present research focuses on
air/oil coolers, which geometrical characteristics and location are designed to minimize
aerodynamic effects while maximizing the thermal exchange. The heat exchangers composed
of parallel fins are integrated at the inner wall of the secondary duct of a turbofan. The
analysis of the interaction between the three-dimensional high velocity bypass flow and the
heat exchangers is essential to evaluate and optimize the aero-thermodynamic performances,
and to provide data for engine modeling. The objectives of this research are the development
of engine testing methods alternative to flight testing, and the characterization of the
aerothermal behavior of different finned heat exchanger configurations.
A new blow-down wind tunnel test facility was specifically designed to replicate the engine
bypass flow in the region of the splitter. The annular sector type test section consists on a
complex 3D geometry, as a result of three dimensional numerical flow simulations. The flow
evolves over the splitter duplicated at real scale, guided by helicoidally shaped lateral walls.
The development of measurement techniques for the present application involved the design
of instrumentation, testing procedures and data reduction methods. Detailed studies were
focused on multi-hole and fine wire thermocouple probes.
Two types of test campaigns were performed dedicated to: flow measurements along the test
section for different test configurations, i.e. in the absence of heat exchangers and in the
presence of different heat exchanger geometries, and heat transfer measurements on the heat
exchanger. As a result contours of flow velocity, angular distributions, total and static
pressures, temperatures and turbulence intensities, at different bypass duct axial positions, as
well as wall pressures along the test section, were obtained. The analysis of the flow
development along the test section allowed the understanding of the different flow behaviors
for each test configuration. Comparison of flow variables at each measurement plane
permitted quantifying and contrasting the different flow disturbances. Detailed analyses of the
flow downstream of the heat exchangers were assessed to characterize the flow in the fins¿
wake region. The aerodynamic performance of each heat exchanger configuration was
evaluated in terms of non dimensional pressure losses. Fins convective heat transfer
characteristics were derived from the infrared fin surface temperature measurements through a
new methodology based on inverse heat transfer methods coupled with conductive heat flux
models. The experimental characterization permitted to evaluate the cooling capacity of the
investigated type of heat exchangers for the design operational conditions. Finally, the
thermal efficiency of the heat exchanger at different points of the flight envelope during a
typical commercial mission was estimated by extrapolating the convective properties of the
flow to flight conditions.
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