An experimental rig to investigate crosswind effects on intake flow behaviour
Aerospace design engineers are being pushed to invent greener and more efficient technology. The next generation of turbofan engines aims to drastically reduce their carbon emissions by improving propulsive efficiency. To accomplish this low fan pressure ratio, large engine technology has been developed. These new fans require slimmer and sharper, lower drag and weight intakes, which are at risk of experiencing boundary layer separation under aerodynamically difficult conditions. One particularly problematic condition is the crosswind experienced during runway operations, which can lead to downstream distortion of the flow at the fan plane. Due to the complex nature of the ingested crosswind flow field, it has been found to be difficult to study in detail experimentally without incurring extreme costs. The work in this thesis presents a method of studying nearside intake physics under strong crosswind and high-engine power conditions in quasi-two dimensions. This allows for unprecedented optical access at Reynolds numbers previously only obtained at high-cost facilities or full-scale engine testing. The rig functions via the use of three unique and controllable flow paths, allowing for some emulation of variations in crosswind speeds and engine power settings. A design process was conducted to match the pressure gradient that the intake would experience under a 25-knot crosswind and high engine power setting. The rig was de-risked using RANS computations before it was commissioned, establishing a baseline flow field with an attached shock wave-boundary-layer interaction present at the highlight. From this baseline, rig parameters were varied to test the experimental range of the rig, achieving all canonical crosswind flow fields and finding that shock-induced separation did not occur until a peak isentropic Mach number of 1.44 was present on the intake, beyond the usual limit for an attached interaction. Separation unsteadiness was also discovered on the boundary between critical supersonic separation, with a separation bubble forming and reattaching at high frequency. From these achieved flow fields, some effort was made to translate rig results to real engine physics. Although direct mapping was not completed, as the rig was able to achieve all canonical flow fields without changing any of the internal flow liners and only varying rig parameters, small variations from the achieved and well-matched attached supersonic case were deemed feasible with adequate calibration.
Aerodynamics, Crosswind, Engineering, SBLI
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