Compressor Water Extraction

The effect of putting a bleed slot behind the rotor or stator of a modern representative intermediate pressure compressor stage has been investigated using a purpose-built test rig. The first part of the paper goes over the construction and operation of a rig, which for the first time allows for accurate measurement of water extraction and rapid testing of a variety of bleed slot geometries. Using this test rig, it was found that the use of a bleed slot behind the rotor increases water extraction by up to 40 percentage points compared to placing it behind the stator. The overall extraction efficiency for the rotor exit was above 70% for all bleed rates considered from 0% to 30% and is relatively constant. Whilst rotor exit bleed might be advantageous for water extraction, further improvements in extraction efficiency are required for future engines with low fan speed and low blade solidity. The final part of the paper looks at the effect of a bleed lip protrusion to improve water extraction, as this can be retrofitted in engines. An extra 5 percentage points can be achieved by doing this without a penalty operability. This has been explained using 3D computational fluid dynamics by examining the flow separation topology.