Casing treatment for a fluid compressor

A fluid compressor for a turbine engine, comprising:

• a hub rotatable about a rotational axis;
• a blade array extending outwardly from the hub, each blade of the array having a root, a tip, a leading edge a trailing edge and a projected tip chord, each blade spanning a fluid flowpath that channels a stream of fluid through the compressor;
• a casing having a flowpath surface circumscribing and spanwisely spaced from the blade tips, the casing having a compartment comprising a circumferentially extending pressure compensation chamber and a single passage circumferentially coextensive with the chamber, the chamber and passage each having a volume, the passage also having a slot connecting the passage to the chamber and a mouth connecting the passage to the flowpath, wherein the passage extracts fluid from and injects fluid into the flowpath, the passage being defined at least in part by an upstream wall and a downstream wall, both walls extending to and adjoining the flowpath surface at respective upstream and downstream lips bordering the passage mouth, the mouth having a streamwise length between about 2% and 25% of the projected tip chord and being positioned so that at least a portion of the mouth is streamwisely coextensive with the projected tip chord, the upstream wall being oriented at an acute angle relative to the adjoining flowpath surface, and the downstream wall being oriented at an obtuse angle relative to the adjoining flowpath surface, the chamber volume being sufficiently large to attenuate circumferential pressure differences across the blade tip and to keep fluid pressure within the compartment approximately circumferentially uniform during normal operation of the compressor thereby attenuating circumferential variation in flowpath pressure and resisting vorticity induced fluid dynamic instabilities.