Inlet Vortex Formation Under Crosswind Conditions Public
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A jet engine operating near the ground at low aircraft speeds, high thrust, and subject to a crosswind, can experience a flow separation region on the windward inlet lip and the formation of a vortex that extends from the ground to the engine fan face, known as the inlet vortex. This structure forms from a single point on the ground and is ingested by the engine. Inlet vortices are often observed during engine power-up at the start of the take-off run. They create considerable stagnation pressure losses and flow distortions at the engine fan face, compromising fan efficiency, thrust, and increasing the potential for compressor surge. Inlet vortices have enough suction power to kick up sand and rocks that are then sucked into the engine when an aircraft is operating near the ground and especially over poorly-maintained tarmac. Thus foreign object damage (FOD) becomes a serious threat for an engine under these conditions, and may lead to compressor blade erosion, deteriorating engine performance and reducing service life. The work presented here used ANSYS FLUENT to model a jet engine under crosswind. The 3-D Navier-Stokes equations were solved for compressible, unsteady flow. The mesh generated contained 5.6 million tetrahedral and wedge elements. The goal of this research was to better understand the inlet vortex formation mechanisms by studying its transient formation process, and to provide new information for future development of vortex prevention techniques. This work has shown multiple smaller inlet vortices coexisting on the ground plane during the first 0.9s of the formation process. After about 1s, these vortices are shown to coalesce and form one single inlet vortex, containing the circulation of all the smaller vortices combined. The smaller vortices were weak enough to not present danger of FOD, but once coalesced could lift up a 16cm diameter chunk of tarmac asphalt. The conclusion of this work is a recommendation for the development of a solution to the inlet vortex problem focused on preventing the coalescing of the vortex during its formation, thus eliminating the threat of FOD.
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