1. A gas turbine engine endwall treatment (32) comprising:
a plurality of main recirculation passages (34) distributed circumferentially around and extending generally axially in an endwall (19) or shroud (22),
each of the main recirculation passages (34) including a Venturi effect producing main throat (44) disposed between a main inlet passage (40) and a main outlet passage (42),
main inlet and outlet ports (36, 38) of the main inlet and outlet passages (40, 42) respectively extending through the endwall (19) or shroud (22), and
the main inlet port (36) located axially aft and downstream of the main outlet port (38) in each of the main recirculation passages (34).
2. The endwall treatment (32) as claimed in claim 1 comprising second inlet passages (50) connecting second inlet ports (52) in the endwall (19) or the shroud (22) to the main recirculation passages (34) at or near to the main throats (44) and the second inlet ports (52) distributed in a circular row (190) around the endwall (19) or the shroud (22).
3. The endwall treatment (32) as claimed in claim 2 comprising second throats (53) disposed in the second inlet passages (50) at or near intersections (149) of the second inlet passages (50) and the main recirculation passages (134).
4. The endwall treatment (32) as claimed in claim 2 comprising an annular groove (200) in the shroud (22) or endwall (19) and passing through and interconnecting the second inlet ports (52) distributed circumferentially around the endwall (19) or the shroud (22).
5. The endwall treatment (32) as claimed in claim 1 comprising two or

more clustered inlet passages (140) extending from two or more clustered secondary inlet ports (152) to two or more intersections (149) of the two or more clustered inlet passages (140) respectively and the main recirculation passage (134) in the shroud (22) or endwall (19).
6. The endwall treatment (32) as claimed in claim 5, comprising the two or more clustered inlet passages (140) extending from the two or more clustered secondary inlet ports (152) to two or more clustered secondary throats (144) at or near the two or more intersections (149) of the two or more clustered inlet passages (140) respectively and the main recirculation passage (134) in the shroud (22) or endwall (19).
7. The endwall treatment (32) as claimed in claim 6, comprising two or more annular grooves (200) in the shroud (22) or endwall (19) and the two or more annular grooves (200) passing through and interconnecting the second inlet ports (52) distributed circumferentially around the endwall (19) or the shroud (22) in circular rows (190) of the second inlet ports (52) respectively.
8. A gas turbine engine compressor stage (26) comprising:
a circular row of compressor blades (10) including axially spaced apart leading and trailing edges (12, 14) and airfoils (16) extending radially outwardly to blade tips (24),
an endwall (19) including a shroud (22) circumscribing the blade tips (24) and the tips (24) generally radially located in close proximity to the endwall (19) and the shroud (22),
an endwall treatment (32) located in the endwall (19) and including a plurality of main recirculation passages (34) or passages distributed circumferentially around and extending generally axially in an endwall (19) or shroud (22),
Venturi effect producing main throats (44) disposed between main inlet and outlet passages (40, 42) including main inlet and outlet ports (36, 38)

respectively extending through the endwall (19) or shroud (22),
the main inlet ports (36) located axially aft and downstream of the blade
tips (24) and the main outlet ports (38) located axially forward and upstream of
the blade tips (24), and
the main inlet ports (36) located axially aft and downstream of the main
outlet ports (38) in the main recirculation passages (34).
9. A gas turbine engine compressor assembly comprising:
upstream and downstream stages (226, 228) including upstream and downstream stage blades (320, 324),
the upstream and downstream stage blades (320, 324) including axially spaced apart leading and trailing edges (12, 14) and airfoils (16) extending radially outwardly to blade tips (24),
an endwall (19) including shrouds (22) circumscribing the blade tips (24) and the tips (24) generally radially located in close proximity to the endwall (19) and the shrouds (22),
an endwall treatment (32) located in the endwall (19) and including a plurality of main recirculation passages (34) distributed circumferentially around and extending generally axially in an endwall (19) or shroud (22),
Venturi effect producing main throats (44) disposed between main inlet and outlet passages (40, 42) including main inlet and outlet ports (36, 38) respectively extending through the endwall (19) or shroud (22),
the main inlet ports (36) located axially aft and downstream of the blade tips (24) of the downstream stage blades (324) and the main outlet ports (38) located axially forward and upstream of the blade tips (24) of the upstream stage blades (320), and
the main inlet ports (36) located axially aft and downstream of the main outlet ports (38) in the main recirculation passages (34).

10. The gas turbine engine compressor assembly (225) as claimed in claim 17, comprising the downstream stage (228) being two or more stages downstream from the upstream stage (226).