This paper presents a computational investigation into the effects of inlet swirl on the fluid flows computed for a spiral bevel gear and shroud pairing. This is with a specific focus on aeroengine internal gearboxes where the power offtake gear is located in a chamber where a highly swirled environment exists.

Previous work for a single rotating gear and stationary shroud [1] has been performed in isolation and with idealised boundary conditions at both the inlet and outlet of the system. This effectively decouples the shrouded gear subsystem from the rest of the gearbox. In the present study a parametric investigation has been conducted varying the amount of inlet swirl and the effect this has on the mass flowrate of air “pumped” through the gear. The paper presents data showing that compared to no inlet swirl, a higher mass flowrate is induced when there is swirl, with up to 20% higher mass flowrate occurring when the tangential velocity at shroud inlet is 50% of the axial velocity component. For swirl above 50% the mass flowrate drops back somewhat remaining higher than for the no-swirl case for values investigated. Gear windage power loss is a function of mass flowrate and consequently higher windage losses occur for higher mass flowrates.

In an aeroengine flow through the gear exits through slots in the shroud and this paper shows that the swirl velocity component at the shroud exit holes is relatively insensitive to the velocity components entering the gear/shroud system for a given geometry.

Further to this, the effect of the shroud outlet geometry on the flow leaving the back of the gear has been investigated and quantified. It is shown that accurate geometric representation is required as the outlet geometry has a significant effect on the computed mass flow through the gear-shroud system and consequently on the computed windage power loss.

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