Session: 14-02 Compressor Cavities 2

Paper Number: 129288

129288 - Windage Characteristics of a Compressor Stator Well Cavity 

Modern multistage core compressors are pushed to the limits of overall pressure ratio, considering wide range stable operation, with high efficiency values reaching levels above 92% polytropic efficiency. To do that, radial clearances on top of rotor blades and at the bottom of the stator segments need to be minimised by applying successful clearance management schemes accounting for centrifugal and thermal displacements on both rotating and stationary parts. Usually labyrinth seals are placed under the stator segments comprised of abradable linings or honeycomb structures and rotating teeth. The cavity formed by two successive rotor disks and a labyrinth seal underneath the stator segment below the main flowpath is called a stator well and it controls the leakage flow travelling from the downstream of the stator and to the upstream. Tight clearances are usually preferred to minimise spoiling of stator hub flow; as the leakage flow has lower angular momentum when it merges with the main flowpath stream and causes negative incidences on the stator leading edge, possibly a horseshoe vortex emanating on the pressure side. However, as nearly in all rotor stator cavities the leakage flow has to optimised both in terms of performance penalty and in terms of windage heating together with axial thrust [Bijay Sultanian]. Having a too small leakage would certainly increase windage temperature rise and axial thrust contribution to the rear of the compressor.

As the leakage flow travels radially inward from the downstream of the stator vane with a low swirl value, it adheres to the stator side and disk-pumping flow takes place on the rotor side. Leakage flow gains angular momentum by the torque exerted by the rotor disk. Only a portion of the circulating flow inside this rear section of the stator well, leaks through the labyrinth seal and once it does so it gains additional angular momentum. After leaving the labyrinth seal, leakage flow travels radially outward on the rotor side and merges at the upstream of the stator vane. There is entrainment from the main flowpath on the stator side as well, forming a circulating flow pattern. The swirl value is reduced on the left part of the cavity as leakage flow joins main flowpath at a higher radius. Throughout the path, leakage flow experiences windage transfer from upstream (right), downstream (left) cavities and the labyrinth seal.

Current investigation focusses on a compressor stator well cavity flowfield, which is a part of a multistage high pressure compressor, and swirl ratio, static pressure distributions are thoroughly investigated together with windage power for three different engine thrust levels and three different clearance levels at high thrust cases. An experimental test case from Kong et. al [2-3] has been selected to validate the numerical method at three rotational speeds and three pressure ratios considering measured/predicted labyrinth seal clearances. One-dimensional cavity solver with three cavity approach having upstream, downstream and seal cavities is also employed to compare the results.

Presenting Author: Erinc Erdem TEI

Presenting Author Biography: Erinc Erdem

Authors:

Erinc Erdem TEI
Ahmet Cuneyt Kahraman TEI
Onur Garip TEI
Sinan Sal TEI