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A turbine blade includes a hollow airfoil joined to a dovetail and platform. The airfoil includes leading and trailing edge cooling circuits disposed between the opposite pressure and suction sidewalls of the airfoil along the leading and trailing edges thereof. The leading edge cooling circuit incl

A turbine blade includes a hollow airfoil joined to a dovetail and platform. The airfoil includes leading and trailing edge cooling circuits disposed between the opposite pressure and suction sidewalls of the airfoil along the leading and trailing edges thereof. The leading edge cooling circuit includes a radial inlet commencing in the base of the dovetail, and the trailing edge cooling circuit includes an axial inlet commencing in the aft face of the dovetail for receiving coolant having different pressure and temperature.

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1. A turbine blade comprising:a hollow airfoil joined to a supporting dovetail at a platform; said airfoil including pressure and suction sidewalls joined together at chordally opposite leading and trailing edges, and extending in span between a root at said platform and an outer tip; and said airfo

1. A turbine blade comprising:a hollow airfoil joined to a supporting dovetail at a platform; said airfoil including pressure and suction sidewalls joined together at chordally opposite leading and trailing edges, and extending in span between a root at said platform and an outer tip; and said airfoil further including a leading edge cooling circuit behind said leading edge having a radial first coolant inlet commencing in the base of said dovetail, a trailing edge cooling circuit in front of said trailing edge having an axial second coolant inlet commencing in the aft face of said dovetail, and a middle cooling circuit disposed between said leading edge circuit and trailing edge circuit, and having a radial third coolant inlet commencing in said dovetail base between said first and second inlets. 2. A blade according to claim 1 further comprising a sealing wing extending aft from said platform above said second inlet for directing coolant flow into said second inlet.3. A blade according to claim 2 wherein said dovetail is sealed closed at said base below said second inlet and aft of said first inlet in said base.4. A blade according to claim 3 wherein said second cooling circuit extends through said dovetail to said base and is sealed closed at said base by a plate fixedly joined to said base.5. A blade according to claim 3 in combination with a rotor disk having a dovetail slot in a perimeter rim thereof in which said blade dovetail is mounted for defining a turbine;said turbine further including a forward blade retainer mounted on a forward side of said disk rim, and an aft blade retainer mounted on an aft side of said disk rim to trap axially therebetween said blade dovetail; and said aft retainer terminates below said second inlet. 6. A turbine according to claim 5 wherein:said disk further includes a thinner web extending radially inwardly from said rim to a thicker hub having a center bore; said forward retainer is spaced from said web to channel a first-pressure coolant to said dovetail slot for flow into said dovetail first inlet; and said aft retainer seals closed said dovetail slot along said disk rim to contain said first-pressure coolant inside said dovetail slot. 7. A turbine according to claim 6 defining a first turbine in combination with a second turbine spaced aft from said first turbine to form an aft cavity therebetween for channeling a second-pressure coolant along an aft face of said first turbine disk to said second inlet.8. A turbine combination according to claim 7 wherein:said second turbine includes a row of second rotor blades extending outwardly from a rim of a second rotor disk; and said second rotor blades include a sealing wing extending forward to effect a rotary seal with said sealing wing on said first turbine rotor blade. 9. A turbine combination according to claim 8 further comprising:first means for channeling compressor discharge air through said forward blade retainer for flow through said first coolant inlet; and second means for channeling compressor interstage bleed air to said aft cavity between said first and second turbines for flow through said second coolant inlet. 10. A turbine combination according to claim 9 wherein:said leading edge cooling circuit includes a row of film cooling outlet holes adjacent said airfoil leading edge for discharging said compressor discharge air with a first backflow margin; said trailing edge cooling circuit includes a row of trailing edge outlet holes adjacent said trailing edge for discharging said bleed air with a second backflow margin; and said two backflow margins are within about 1.5. 11. A turbine blade comprising:a hollow airfoil joined to a supporting dovetail at a platform; said airfoil including pressure and suction sidewalls joined together at chordally opposite leading and trailing edges, and extending in span between a root at said platform and an outer tip; and said airfoil further including a leading edge cooling circuit behind said leading edge having a radial first coolant inlet commencing in the base of said dovetail, and a trailing edge cooling circuit in front of said trailing edge having an axial second coolant inlet commencing in the aft face of said dovetail. 12. A blade according to claim 11 wherein said dovetail is sealed closed at said base below said second inlet and aft of said first inlet in said base.13. A blade according to claim 12 further comprising a sealing wing extending aft from said platform above said second inlet for directing coolant flow into said second inlet.14. A blade according to claim 13 wherein said airfoil further comprises a middle cooling circuit disposed between said leading and trailing edge circuits having a radial third coolant inlet commencing in said dovetail base between said first and second inlets.15. A blade according to claim 13 in combination with a rotor disk having a dovetail slot in a perimeter rim thereof in which said blade dovetail is mounted for defining a turbine;said turbine further including a forward blade retainer mounted on a forward side of said disk rim, and an aft blade retainer mounted on an aft side of said disk rim to trap axially therebetween said blade dovetail; and said aft retainer terminates below said second inlet. 16. A blade according to claim 15 wherein:said disk further includes a thinner web extending radially inwardly from said rim to a thicker hub having a center bore; said forward retainer is spaced from said web to channel a first-pressure coolant to said dovetail slot for flow into said dovetail first inlet; and said aft retainer seals closed said dovetail slot along said disk rim to contain said first-pressure coolant inside said dovetail slot. 17. A blade according to claim 16 defining a first turbine in combination with a second turbine spaced aft from said first turbine to form an aft cavity therebetween for channeling a second-pressure coolant along an aft face of said first turbine disk to said second inlet.18. A turbine combination according to claim 17 wherein:said second turbine includes a row of second rotor blades extending outwardly from a rim of a second rotor disk; and said second rotor blades include a sealing wing 84 extending forward to effect a rotary seal with said sealing wing on said first turbine rotor blade. 19. A turbine combination according to claim 17 further comprising:first means for channeling compressor discharge air through said forward blade retainer for flow through said first coolant inlet; and second means for channeling compressor interstage bleed air to said aft cavity between said first and second turbines for flow through said second coolant inlet. 20. A turbine combination according to claim 19 wherein:said leading edge cooling circuit includes a row of film cooling outlet holes adjacent said airfoil leading edge for discharging said compressor discharge air with a first backflow margin; said trailing edge cooling circuit includes a row of trailing edge outlet holes adjacent said trailing edge for discharging said bleed air with a second backflow margin; and said two backflow margins are within about 1.5.