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A gas turbine engine includes a compressor powered by a turbine. The turbine includes a nozzle having vanes extending between outer and inner bands. Each vane includes an internal cooling plenum and a bypass tube extending through the bands. First and second manifolds surround the outer band and ar

A gas turbine engine includes a compressor powered by a turbine. The turbine includes a nozzle having vanes extending between outer and inner bands. Each vane includes an internal cooling plenum and a bypass tube extending through the bands. First and second manifolds surround the outer band and are disposed in flow communication with the plenums and bypass tubes, respectively. A bleed circuit joins the compressor to the manifolds for providing pressurized air thereto. A control valve modulates airflow to the first manifold and in turn through the cooling plenums of the vanes.

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Accordingly, what is desired to be secured by Letters Patent of the United States is the invention as defined and differentiated in the following claims in which we claim: 1. A gas turbine engine comprising: a compressor joined to a turbine for being powered thereby; said turbine including a nozzl

Accordingly, what is desired to be secured by Letters Patent of the United States is the invention as defined and differentiated in the following claims in which we claim: 1. A gas turbine engine comprising: a compressor joined to a turbine for being powered thereby; said turbine including a nozzle having a row of hollow vanes extending radially between outer and inner bands, and said outer band is supported in an annular outer casing; each of said vanes having an internal cooling plenum, and a bypass tube extending through said outer and inner bands; a two-ply septum disposed radially between said outer casing and said outer band, and defining independent first and second manifolds; said first manifold surrounding said outer band and disposed in flow communication with said plenums of said vanes; said second manifold surrounding said first manifold and disposed in flow communication with said bypass tubes of said vanes; a bleed circuit disposed in flow communication between said compressor and said first and second manifolds for channeling pressurized air therebetween; and a control valve disposed between said bleed circuit and said first manifold for modulating flow of said pressurized cooling air into said vane plenums. 2. An engine according to claim 1 wherein said first and second manifolds are disposed in parallel flow from said bleed circuit, and said second manifold is directly joined to said bleed circuit without a flow modulation valve. 3. An engine according to claim 2 wherein said septum comprises outer and inner plies spaced apart radially to define said first manifold therebetween, with said second manifold being defined radially between said outer ply and said outer casing. 4. An engine according to claim 3 wherein each of said bypass tubes has an outer end disposed in flow communication with said second manifold through said septum, and an inner end extending through said inner band. 5. An engine according to claim 4 wherein said septum outer ply includes a plurality of apertures disposed in flow communication with said second supply tubes. 6. An engine according to claim 5 further comprising: an inner spoolie joining each of said bypass tubes to said septum in flow communication with said second manifold; and an outer spoolie joining each of said second supply tubes to said septum in flow communication with said first manifold. 7. An engine according to claim 6 wherein said septum is single ply over forward ends of said vanes, and supports said inner spoolies therein, and is two-ply circumferentially between said forward ends of said vanes and supports said outer spoolies in said outer ply thereof. 8. An engine according to claim 7 wherein said septum is two-ply circumferentially between and over aft ends of said vanes for providing a circumferentially continuous first manifold over a plurality of adjacent vanes. 9. An engine according to claim 8 wherein: said septum inner ply includes a multitude of impingement holes along said first manifold for discharging said pressurized air therefrom to impingement cool said outer band; and each of said vanes includes an impingement baffle inside said plenum 48 thereof having an inlet through said outer band surrounding a corresponding bypass tube for receiving spent impingement air discharged through said impingement holes. 10. An engine according to claim 8 wherein: each of said vanes includes a partition dividing said plenum into forward and aft channels; said bypass tube comprises a forward impingement baffle disposed inside said forward channel; said aft channel includes an aft impingement baffle having an inlet through said outer band; and an aft spoolie joins said first manifold in flow communication with said inlet of said aft impingement baffle. 11. A gas turbine engine comprising: a compressor joined to a turbine for being powered thereby; said turbine including a nozzle having a row of hollow vanes extending radially between outer and inner bands; each of said vanes having an internal cooling plenum, and a bypass tube extending through said outer and inner bands; a first manifold surrounding said outer band and disposed in flow communication with said plenums of said vanes; a second manifold surrounding said first manifold and disposed in flow communication with said bypass tubes of said vanes; a bleed circuit disposed in flow communication between said compressor and first and second manifolds for channeling pressurized air therebetween; and a control valve disposed between said bleed circuit and first manifold for modulating flow of said pressurized air into said vane plenums. 12. An engine according to claim 11 wherein said first and second manifolds are disposed in parallel flow from said bleed circuit, and said second manifold is directly joined to said bleed circuit without a flow modulation valve. 13. An engine according to claim 12 further comprising an annular outer casing supporting said nozzle, and a septum disposed radially therebetween to separate radially said first and second manifolds. 14. An engine according to claim 13 wherein said bleed circuit comprises: a plurality of first supply tubes extending through said casing to said first manifold for channeling said pressurized air thereto; and a plurality of second supply tubes extending through said casing to said second manifold for channeling said pressurized air thereto. 15. An engine according to claim 14 wherein said each of said first tubes includes a corresponding one of said control valves for modulating airflow therethrough. 16. An engine according to claim 15 wherein said bleed circuit further comprises a common supply manifold joined in flow communication with said compressor, and said first and second tubes extend therefrom to said first and second manifolds, respectively. 17. An engine according to claim 15 wherein said septum comprises outer and inner plies spaced apart radially to define said first manifold therebetween, with said second manifold being defined radially between said outer ply and said outer casing. 18. An engine according to claim 17 wherein each of said bypass tubes has an outer end disposed in flow communication with said second manifold through said septum, and an inner end extending through said inner band. 19. An engine according to claim 18 wherein said septum outer ply includes a plurality of apertures disposed in flow communication with said second supply tubes. 20. An engine according to claim 19 further comprising: an inner spoolie joining each of said bypass tubes to said septum in flow communication with said second manifold; and an outer spoolie joining each of said second supply tubes to said septum in flow communication with said first manifold. 21. An engine according to claim 20 wherein said septum is single ply over forward ends of said vanes, and supports said inner spoolies therein, and is two-ply circumferentially between said forward ends of said vanes and supports said outer spoolies in said outer ply thereof. 22. An engine according to claim 21 wherein said septum is two-ply circumferentially between and over aft ends of said vanes for providing a circumferentially continuous first manifold over a plurality of adjacent vanes. 23. An engine according to claim 22 wherein said septum inner ply includes a multitude of impingement holes along said first manifold for discharging said pressurized air therefrom to impingement cool said outer band. 24. An engine according to claim 23 wherein each of said vane plenums includes an inlet through said outer band surrounding a corresponding bypass tube for receiving spent impingement air discharged through said impingement holes. 25. An engine according to claim 23 wherein each of said vanes includes an impingement baffle inside said plenum thereof having an inlet through said outer band surrounding a corresponding bypass tube for receiving spent impingement air discharged through said impingement holes. 26. An engine according to claim 22 wherein: each of said vanes includes a partition dividing said plenum into forward and aft channels; said bypass tube comprises a forward impingement baffle disposed inside said forward channel; and said aft channel includes an aft impingement baffle having an inlet through said outer band. 27. An engine according to claim 26 further comprising an aft spoolie joining said first manifold in flow communication with said inlet of said aft impingement baffle. 28. An engine according to claim 15 further comprising: a first stage nozzle and first stage rotor disk disposed forward of said turbine nozzle to define a forward cavity therebetween; a second stage rotor disk disposed aft of said turbine nozzle to define an aft cavity therebetween; and said bypass tubes extend through said inner band in flow communication with said forward cavity for discharging said pressurized air channeled therethrough. 29. An engine according to claim 28 wherein said inner band includes an inner manifold disposed in flow communication with said bypass tubes, and said inner manifold includes a row of discharge holes facing said forward cavity. 30. A method of cooling a turbine nozzle in a gas turbine engine having a row of hollow nozzle vanes extending radially between outer and inner bands and disposed axially between first and second turbine rotor disks comprising: channeling pressurized purge air from a compressor in said engine radially through said vanes to purge forward and aft cavities located between said nozzle inner band and said first and second disks, respectively; channeling pressurized cooling air from said compressor and inside said vanes to cool said vanes independently from said purge air; and modulating flowrate of said cooling air inside said vanes without modulating flowrate of said purge air through said vanes. 31. A method according to claim 30 further comprising channeling said purge air and cooling air from said compressor in parallel flowpaths through said vanes isolated from each other through said outer band. 32. A method according to claim 31 wherein: said purge air is channeled directly through said outer band to purge said forward and aft cavities; and said cooling air is first channeled in impingement against said outer band for impingement cooling thereof followed in turn by routing into said vanes for internal impingement cooling thereof.