The flow in the heated rotating cavity of an aero-engine compressor is driven by buoyancy forces, which result in pairs of cyclonic and anticyclonic vortices.&nbsp;The resultant cavity flow field is three-dimensional, unsteady and unstable, which makes it challenging to model the flow and heat transfer.&nbsp;In this paper, properties of the vortex structures are determined from novel unsteady pressure measurements collected on the disc surface in the central rotating cavity of the Bath Compressor-Cavity Rig. The data were collected over a range of engine-representative parameters. No more than one vortex pair was detected over the conditions tested, despite the measurement of harmonic modes in the frequency spectra at low Rossby numbers. It is shown that for these cases, harmonic modes were present because the vortices were unequal in size, with the cyclonic vortex the larger of the pair. The structures slipped relative to the discs at a speed typically around 10% to 15% of that of the rotor, but the speed of precession was often unsteady.&nbsp;&nbsp;The coherency, strength and slip of the vortex pair increased with&nbsp;the buoyancy parameter due to the stronger buoyancy forces, but they were largely independent of the&nbsp;rotational Reynolds number. The slip of the vortices appeared to be influenced by vortex breakdown, which is dependent upon the Rossby number and was identified by a peak in the measured static pressure drop across the cavity. Under this condition, the slip can increase to 15% of the disc speed. The increase in slip is explained by an increase in radial mixing from vortex breakdown, encouraging an exchange of low momentum throughflow with the higher momentum in the cavity.

Unsteady Pressure Measurements in a Heated Rotating Cavity

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2021/volume/84898

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