Crossover cooling flow for multi-engine systems

1. A multi-engine system comprising:

a first gas turbine engine comprising a first compressor, a first turbine, and a first power turbine, the first compressor and the first turbine of the first gas turbine engine each configured to rotate about a first engine central longitudinal axis of the first gas turbine engine;

a second gas turbine engine comprising a second compressor, a second turbine, and a second power turbine, the second compressor and the second turbine of the second gas turbine engine each configured to rotate about a second engine central longitudinal axis of the second gas turbine engine;

a main rotor gearbox mechanically coupled to both the first power turbine and the second power turbine; and

a first crossover cooling network for routing a first crossover airflow from the first compressor of the first gas turbine engine to the second turbine of the second gas turbine engine,

wherein the first gas turbine engine and the second gas turbine engine are identical engines.

2. A multi-engine system comprising:

a first gas turbine engine comprising a first compressor and a first turbine, the first compressor and the first turbine of the first gas turbine engine each configured to rotate about a first engine central longitudinal axis of the first gas turbine engine;

a second gas turbine engine comprising a second compressor and a second turbine, the second compressor and the second turbine of the second gas turbine engine each configured to rotate about a second engine central longitudinal axis of the second gas turbine engine;

a first crossover cooling network configured to route a first crossover airflow from the first compressor of the first gas turbine engine to the second turbine of the second gas turbine engine; and

a second crossover cooling network configured to route a second crossover airflow from the second compressor of the second gas turbine engine to the first turbine of the first gas turbine engine.

3. The multi-engine system of claim 2 , wherein the multi-engine system is configured to operate in a bi-directional crossover mode with both the first crossover cooling network and the second crossover cooling network having respective crossover flows flowing therethrough.

4. The multi-engine system of claim 2 , wherein:

the first crossover cooling network extends from the first compressor to a second vane row of the second turbine; and

the second crossover cooling network extends from the second compressor to a first vane row of the first turbine.

5. The multi-engine system of claim 4 , wherein:

the second vane row is a forward-most vane row of the second turbine; and

the first vane row is a forward-most vane row of the first turbine.

6. The multi-engine system of claim 5 , wherein:

the forward-most vane row of the second turbine comprises a plurality of second vanes, wherein each second vane of the plurality of second vanes defines a second leading edge chamber and a second body chamber aft of the second leading edge chamber, wherein the first crossover cooling network is configured to route the first crossover airflow to the second body chamber; and

the forward-most vane row of the first turbine comprises a plurality of first vanes, wherein each first vane of the plurality of first vanes defines a first leading edge chamber and a first body chamber aft of the first leading edge chamber, wherein the second crossover cooling network is configured to route the second crossover airflow to the first body chamber.

7. The multi-engine system of claim 6 , wherein:

the first gas turbine engine comprises a first intra-engine cooling network configured to route a first resident airflow from forward of the first turbine to the first leading edge chamber of the plurality of first vanes of the forward-most vane row of the first turbine; and

the second gas turbine engine comprises a second intra-engine cooling network configured to route a second resident airflow from forward of the second turbine to the second leading edge chamber of the plurality of second vanes of the forward-most vane row of the second turbine.

8. The multi-engine system of claim 2 , wherein in response to the multi-engine system operating in an intermediate rated power mode:

the first crossover airflow is between 5% and 20% of a first total compressor flow through the first compressor; and

the second crossover airflow is between 5% and 20% of a second total compressor flow through the second compressor.

9. The multi-engine system of claim 8 , wherein:

the first crossover airflow is 10% of the first total compressor flow through the first compressor; and

the second crossover airflow is 10% of the second total compressor flow through the second compressor.

10. The multi-engine system of claim 8 , wherein:

the first total compressor flow is 100% of a first compressor inlet corrected flow capacity of the first compressor;

the second total compressor flow is 100% of a second compressor inlet corrected flow capacity of the second compressor.

11. The multi-engine system of claim 2 , wherein in response to the multi-engine system operating in an asymmetric cruise mode:

the first crossover airflow is between 5% and 20% of a first total compressor flow through the first compressor; and

the second crossover airflow is 0% of a second total compressor flow through the second compressor.

12. The multi-engine system of claim 11 , wherein:

the first crossover airflow is 10% of the first total compressor flow through the first compressor; and

the second crossover airflow is 0% of the second total compressor flow through the second compressor.

13. The multi-engine system of claim 11 , wherein:

the first total compressor flow is between 90% and 100% of a first compressor inlet corrected flow capacity of the first compressor; and

the second total compressor flow is less than or equal to 40% of a second compressor inlet corrected flow capacity of the second compressor.

14. The multi-engine system of claim 2 , wherein the first gas turbine engine and the second gas turbine engine are identical engines.

15. The multi-engine system of claim 14 , wherein an electric load, via a generator, is applied to the second gas turbine engine.

16. The multi-engine system of claim 2 , wherein in response to the multi-engine system operating in a one-engine-inoperable mode:

the first crossover airflow is 10% of a first total compressor flow through the first compressor; and

the second crossover airflow is 0% of a second total compressor flow through the second compressor.

17. The multi-engine system of claim 16 , wherein:

the first total compressor flow is 105% of a first compressor inlet corrected flow capacity of the first compressor; and

the second total compressor flow is 0% of a second compressor inlet corrected flow capacity of the second compressor.

18. The multi-engine system of claim 2 , wherein:

the first crossover cooling network comprises at least one of a first check valve configured to prevent backflow of the first crossover airflow and a first controlled valve configured to control the first crossover airflow; and

the second crossover cooling network comprises at least one of a second check valve configured to prevent backflow of the second crossover airflow and a second controlled valve configured to control the second crossover airflow.

19. A multi-engine rotorcraft comprising:

a first gas turbine engine comprising a first compressor, a first turbine, and a first power turbine;

a second gas turbine engine comprising a second compressor, a second turbine, and a second power turbine;

a main rotor gearbox mechanically coupled to both the first power turbine and the second power turbine;

a first crossover cooling network configured to route a first crossover airflow from the first compressor of the first gas turbine engine to a second vane row of the second turbine of the second gas turbine engine; and

a second crossover cooling network configured to route a second crossover airflow from the second compressor of the second gas turbine engine to a first vane row of the first turbine of the first gas turbine engine.