Casing treatment for compressors

An assembly for a gas turbine engine compressor, the compressor includes a case and a rotor having a plurality of axial flow blades within the case, each of the blades having a tip section, a leading edge and a longitudinal axis, said assembly comprising:

• a vane having an outer platform, said platform defining an outer boundary for a main flow path;
• a passage formed in said platform, said passage having an inlet and an outlet, said inlet being disposed downstream and proximate to said leading edge of the blades, said outlet being disposed upstream of the leading edge of the blades, said passage circumferentially converges inward from said inlet to said outlet;
• and
• a circumferential groove in flow communication with said inlet, said circumferential groove disposed in a normal direction with respect to the main flow path and said circumferential groove selectively removes from the main flow path solely the low momentum, low axial velocity flow and prevents removal of high axial velocity flow;
• wherein said groove overlaps at a location on the tip section of the blade upstream of the longitudinal axis of the blade.