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A turbine airfoil includes sidewalls extending between leading and trailing edges, with an internal cooling circuit therein. A row of venturi slots commences inside the airfoil at the cooling circuit and terminates near the trailing edge. Each of the venturi slots includes an inlet, converging porti

A turbine airfoil includes sidewalls extending between leading and trailing edges, with an internal cooling circuit therein. A row of venturi slots commences inside the airfoil at the cooling circuit and terminates near the trailing edge. Each of the venturi slots includes an inlet, converging portion, throat, diverging portion, and outlet in serial flow communication from the cooling circuit. The converging portion is comparable in chordal length with the throat.

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1. A gas turbine engine airfoil comprising:pressure and suction sidewalls extending longitudinally in airfoil span between a root and a tip, and chordally between opposite leading and trailing edges, and spaced laterally apart therebetween to define an internal cooling circuit; a plurality of ventur

1. A gas turbine engine airfoil comprising:pressure and suction sidewalls extending longitudinally in airfoil span between a root and a tip, and chordally between opposite leading and trailing edges, and spaced laterally apart therebetween to define an internal cooling circuit; a plurality of venturi slots terminating adjacent said trailing edge and commencing inside said airfoil in flow communication with said cooling circuit; each of said venturi slots including in serial flow communication a flared inlet, a converging portion adjoining said inlet, a throat of minimum flow area adjoining said converging portion, a diverging portion adjoining said throat, and an outlet adjoining said diverging portion and exposed adjacent said trailing edge for discharging said coolant; and said slot converging portion being comparable in chordal length to said throat and tapering in radial span substantially linearly from said flared inlet to said throat. 2. An airfoil according to claim 1 wherein each of said venturi slots blends smoothly from said flared inlet to said outlet.3. An airfoil according to claim 2 wherein:said cooling circuit comprises a three-pass serpentine channel commencing at a first leg adjacent said leading edge and terminating at a last leg adjoining said venturi slots; and said venturi slots extend chordally from said last leg. 4. An airfoil according to claim 3 wherein said cooling circuit further comprises a plurality of crossover holes aligned in a row along said airfoil span, and disposed chordally between said venturi slots and said last serpentine leg to define a discharge manifold adjoining said slot inlets for discharging said coolant through said venturi slots.5. An airfoil according to claim 4 wherein:said venturi slots and crossover holes have oval cross sections greater in height along said airfoil span than in width between said sidewalls; and said crossover holes have a collective flow area greater than a collective flow area of said throats of said venturi slots. 6. An airfoil according to claim 5 wherein:said sidewalls comprise a casting, with said cooling circuit and venturi slots being casting voids therein; said slot outlets terminate forward of said trailing edge, and are exposed at said pressure sidewall; and said pressure sidewall is generally concave to effect a pressure drop in combustion gases flowable thereover. 7. An airfoil according to claim 6 wherein said crossover holes and slot throats have a corresponding area ratio of about 4/3.8. An airfoil according to claim 7 wherein said crossover holes and slot throats have height-to-width ratios greater than about two.9. An airfoil according to claim 6 wherein said crossover hole and said slot throats are sized in flow area to effect corresponding pressure drops of about 15 percent and about 75 percent, respectively, of the total pressure drop of said coolant through said airfoil.10. An airfoil according to claim 6 further comprising an inner band integrally joined to said airfoil root, and an outer band integrally joined to said airfoil tip; andsaid crossover holes and said slot throats are sized in flow area to effect a collective pressure drop thereacross substantially matching pressure drop in said combustion gases flowable outside said pressure sidewall along said crossover holes and venturi slots. 11. A gas turbine engine airfoil comprising:first and second sidewalls extending longitudinally in airfoil span between a root and a tip, and chordally between opposite leading and trailing edges, and spaced laterally apart therebetween to define an internal cooling circuit; a plurality of venturi slots terminating adjacent said trailing edge and commencing inside said airfoil in flow communication with said cooling circuit; each of said venturi slots including in serial flow communication an inlet, a converging portion adjoining said inlet, a throat of minimum flow area adjoining said converging portion, a diverging portion adjoining said throat, and an outlet adjoining said diverging portion and exposed adjacent said trailing edge for discharging said coolant; and said slot converging portion being comparable in chordal length to said throat and tapering in radial span substantially linearly from said flared inlet to said throat. 12. An airfoil according to claim 11 wherein said slot inlet is flared and blends smoothly with said slot converging portion.13. An airfoil according to claim 12 wherein said cooling circuit further comprises a plurality of crossover holes aligned in a row along said airfoil span, and disposed chordally between said venturi slots and said leading edge to define a discharge manifold adjoining said slot inlets for discharging said coolant through said venturi slots.14. An airfoil according to claim 13 wherein:said cooling circuit further comprises a multi-pass serpentine channel commencing at a first leg adjacent said leading edge and terminating at a last leg adjoining said crossover holes; said sidewalls comprise a casting, with said cooling circuit and venturi slots being casting voids therein; and said venturi slots extend chordally from said last leg. 15. An airfoil according to claim 14 wherein:said venturi slots and crossover holes have oval cross sections greater in height along said airfoil span than in width between said sidewalls; and said crossover holes have a collective flow area greater than a collective flow area of said throats of said venturi slots. 16. An airfoil according to claim 15 wherein said crossover holes and slot throats have a corresponding area ratio of about 4/3.17. An airfoil according to claim 15 wherein said crossover holes and slot throats have height-to-width ratios greater than about two.18. An airfoil according to claim 15 wherein said crossover holes and said slot throats are sized in flow area to effect corresponding pressure drops of about 15 percent and about 75 percent, respectively, of the total pressure drop of said coolant through said airfoil.19. An airfoil according to claim 15 wherein:said slot outlets terminate forward of said trailing edge, and are exposed at said first sidewall; said first sidewall is generally concave to define a pressure sidewall to effect a pressure drop in combustion gases flowable thereover; and said crossover holes and said slot throats are sized in flow area to effect a collective pressure drop thereacross substantially matching pressure drop in said combustion gases flowable outside said first sidewall along said crossover holes and venturi slots. 20. A method of making said airfoil according to claim 15 comprising:manufacturing a ceramic core corresponding with said cooling circuit and venturi slots, with core fingers for said slots being cantilevered from a common core leg for said discharge manifold; and casting said airfoil using said core to form said cooling circuit and venturi slots between said first and second sidewalls.