Thermally induced flows and ventilation within an aircraft wing leading edge compartment

Modern day airliners are subjected to a wide range of environmental conditions when operational across the globe. In order to ensure reliable aircraft performance and avoid thermal failure of heat sensitive components, consideration must be given to the wide range of temperatures that the aircraft will encounter when designing aircraft internal enclosures. This thesis presents an investigation into the fluid flow and heat transfer within an aircraft wing leading edge compartment due to solar loading and the presence of an internal bleed duct. A detailed experimental investigation into the thermal distribution, bleed duct heat transfer and flow structure was performed for 1 105 < Grasho f No: < 4 105 in a representative wing leading edge enclosure constructed for this purpose. Temperature measurements were recorded along the interior surfaces along with the internal air temperature in the cavity. Particle Image Velocimetery (PIV) was used to quantify the flowfield present in the leading edge. There were three main aspects to this thesis: The first was to characterise the enclosure conditions and bleed duct heat transfer within the sealed leading edge. This was performed firstly to gain an understanding of the heat transfer characteristics within the leading edge and secondly to use as a comparison for when ventilation was introduced. It was observed that the confining effect of the enclosure was only evident at the higher Gr range investigated, with the initial heat transfer similar to that of an unconfined cylinder. The interior temperature distribution was also dependent upon Gr, with the plume mixing effect creating a more homogeneous air temperature as Gr increased. The effect of enclosure ventilation was also considered with a view to helping reduce a thermally aggressive environment which can be present in a hot ambient environment. The placement of the ventilation openings was limited due to the geometric constraints of the leading edge, yet a 77% increase in the bleed duct heat transfer was observed for a dual vent opening configuration. Geometrical effects within the leading edge were investigated in order to appreciate their influence on heat transfer and ventilation. Partitioning of the leading edge (due to a front sub-spar) produced a blockage between the inlet and outlet vent which reduced the bleed duct heat transfer. Interior temperature and flowfield were also observed to be dependent upon the bleed duct position, as its buoyant plume was the main driver of the flow structure within. The effect of a larger, constant temperature cylinder was also considered with its position relative to the bleed duct important for heat transfer as it was effectively eliminated when located below the bleed duct with a higher surface temperature. The findings of this thesis allow for a detailed understanding of the thermal environment and flow structure in a non-standard enclosure shape subjected to exterior heating and internal heat source. This is of practical relevance for the design of aircraft enclosures to help eliminate the possibility of thermal failure of components and affect aircraft operations.