Intercooled cooling air with auxiliary compressor control

1. A gas turbine engine comprising;

a fan for delivering air into a bypass duct and into main compressor section with a downstream most location;

a turbine section having a high pressure turbine;

a tap line configured to tap air from a location upstream of said downstream most location in said main compressor section, said tap line connected to a heat exchanger and then to a cooling compressor, said cooling compressor configured to compress air downstream of said heat exchanger, and connected to deliver air into said high pressure turbine;

a bypass valve positioned downstream of said main compressor section, and upstream of said heat exchanger, wherein said bypass valve is configured to selectively deliver air directly to said cooling compressor without passing through said heat exchanger under certain conditions; and

wherein said heat exchanger is cooled by air; and

wherein said turbine section drives a bull gear, said bull gear further driving an impeller of said cooling compressor.

2. The gas turbine engine as set forth in claim 1 , wherein said bypass valve is positioned on said tap line, and a separate bypass line connecting said tap line to said cooling compressor without passing through said heat exchanger.

3. The gas turbine engine as set forth in claim 1 , wherein said bypass valve completely bypasses said heat exchanger.

4. The gas turbine engine as set forth in claim 1 , wherein said bypass valve can be modulated to control the volume of air delivered through the heat exchanger.

5. The gas turbine engine as set forth in claim 1 , wherein said bypass valve is positioned by a control to bypass the heat exchanger at relatively low power conditions, including idle.

6. The gas turbine engine as set forth in claim 5 , wherein said bypass valve is positioned by said control to flow all air through the heat exchanger under higher power conditions, including take-off.

7. The gas turbine engine as set forth in claim 6 , wherein said cooling compressor includes a centrifugal compressor impeller.

8. The gas turbine engine as set forth in claim 1 , wherein said cooling compressor includes a centrifugal compressor impeller.

9. The gas turbine engine as set forth in claim 8 , wherein air temperatures at the downstream most location of said high pressure compressor are greater than or equal to 1350° F. (732° C.).

10. The gas turbine engine as set forth in claim 1 , wherein air temperatures at the downstream most location of said high pressure compressor are greater than or equal to 1350° F. (732° C.).

11. The gas turbine engine as set forth in claim 1 , wherein said bull gear also drives an accessory gearbox.

12. The gas turbine engine as set forth in claim 1 , wherein said heat exchanger is positioned within said bypass duct, and air delivered by said fan into said bypass duct cools aft from said tap line.

13. The gas turbine engine as set forth in claim 1 , wherein said turbine section has a fan drive turbine driving said fan through a gear reduction.

14. A gas turbine engine comprising:

a fan for delivering air into a bypass duct and into main compressor section with a downstream most location;

a turbine section having a high pressure turbine;

a tap line configured to tap air from a location upstream of said downstream most location in said main compressor section, said tap line connected to a heat exchanger and then to a cooling compressor, said cooling compressor configured to compress air downstream of said heat exchanger, and connected to deliver air into said high pressure turbine;

a bypass valve positioned downstream of said main compressor section, and upstream of said heat exchanger, wherein said bypass valve is configured to selectively deliver air directly to said cooling compressor without passing through said heat exchanger under certain conditions;

wherein said heat exchanger is cooled by air;

wherein said bypass valve is positioned by a control to bypass the heat exchanger at relatively low power conditions, including idle

wherein said bypass valve is positioned by said control to flow all air through the heat exchanger under higher power conditions, including take-off;

wherein said cooling compressor includes a centrifugal compressor impeller;

wherein air temperatures at the downstream most location of said high pressure compressor are greater than or equal to 1350° F. (732° C.); and

wherein said turbine section drives a bull gear, said bull gear further driving of said cooling compressor impeller.

15. The gas turbine engine as set forth in claim 14 , wherein said bull gear also drives an accessory gearbox.

16. A gas turbine engine comprising;

a fan for delivering air into a bypass duct and into a main compressor section with a downstream most location;

a turbine section having a high pressure turbine;

a tap line configured to tap air from a location upstream of said downstream most location in said main compressor section, said tap line connected to a heat exchanger and then to a cooling compressor, said cooling compressor configured to compress air downstream of said heat exchanger, and connected to deliver air into said high pressure turbine; and

a bypass valve positioned downstream of said main compressor section, and upstream of said heat exchanger, wherein said bypass valve is configured to selectively deliver air directly to said cooling compressor without passing through said heat exchanger under certain conditions; and

said cooling compressor being driven by a tower shaft driven by said turbine section.

17. The gas turbine engine as set forth in claim 16 , wherein said tower shaft drives a bull gear, said bull gear further driving said cooling compressor.

18. The gas turbine engine as set forth in claim 17 , wherein said bull gear also drives an accessory gearbox.