Method and system for a combined air-oil cooler and fuel-oil cooler heat exchanger

1. A heat exchanger assembly for a gas turbine engine comprising:

an annular unitary body having:

a first internal flow path configured to channel a flow of oil to be cooled from a first inlet to a first outlet, the first internal flow path being enclosed within and formed integrally with the unitary body;

a second internal flow path in thermal communication with the first internal flow path and configured to channel a flow of a first coolant from a second inlet to a second outlet, wherein the first coolant comprises fuel, and wherein the second internal flow path is not in fluid communication with the first internal flow path, and the second internal flow path is enclosed within and formed integrally with the unitary body; and

an external flow path configured to receive a flow of a second coolant proximate a circumferentially extending surface of the unitary body, the external flow path including a plurality of metallic fins wherein the first internal flow path is positioned radially between the second internal flow path and the external flow path.

2. The system of claim 1 , wherein the first internal flow path and the second internal flow path are countercurrent flow.

3. The system of claim 1 , wherein the first internal flow path provides a buffer between the second internal flow path and the external flow path.

4. The system of claim 1 , wherein the second coolant comprises air.

5. A method of cooling a fluid using a three path heat exchanger assembly for a gas turbine engine, the heat exchanger assembly comprising an annular unitary body with a first internal flow path enclosed within and formed integrally with the unitary body, a second internal flow path enclosed within and formed integrally with the unitary body, and an exterior flow path, wherein the first internal flow path is not in fluid communication with the second internal flow path and the first internal flow path is positioned radially between the second internal flow path and the external flow path, the method comprising:

channeling one or more flows of a fluid to be cooled through the first internal flow path of the heat exchanger assembly, wherein channeling one or more flows of fluid to be cooled through the first internal flow path of the heat exchanger assembly comprises channeling one or more flow of oil to the first internal flow path of the heat exchanger assembly;

channeling one or more flows of cooling fluid through the second internal flow path of the heat exchanger assembly, wherein channeling one or more flows of cooling fluid through the second internal flow path of the heat exchanger assembly comprises channeling one or more flows of fuel to the second internal flow path of the heat exchanger assembly; and

channeling a flow of air proximate the exterior flow path of the heat exchanger assembly, the heat exchanger assembly including a plurality of fin members extending proximate the exterior flow path, wherein the first internal flow path is thermally coupled to the second internal flow path and the plurality of fin members.

6. The method of claim 5 , wherein channeling the flow of air proximate the exterior flow path of the heat exchanger assembly comprises channeling a flow of fan exhaust air proximate the plurality of fin members.

7. A gas turbine engine comprising:

a fan assembly comprising a bypass duct; and

a core engine comprising a heat exchanger assembly that includes:

an annular unitary body having:

a first internal flow path configured to channel a flow of oil to be cooled from a first inlet to a first outlet, the first internal flow path being enclosed within and formed integrally with the unitary body;

a second internal flow path coupled in thermal communication with the first internal flow path and configured to channel a flow of a first coolant from a second inlet to a second outlet, wherein the first coolant comprises fuel, and wherein the second internal flow path is not in fluid communication with the first internal flow path, and the second internal flow path is enclosed within and formed integrally with the unitary body; and

an external flow path configured to receive a flow of air proximate a circumferentially extending surface of the unitary body, the external flow path including a plurality of metallic fins in thermal communication with the first internal flow path wherein the first internal flow path is positioned between the second internal flow path and the external flow path.

8. The gas turbine engine of claim 7 , wherein the first internal flow path and the second internal flow path are countercurrent flow.

9. The gas turbine engine of claim 7 , wherein the first internal flow path provides a buffer between the second internal flow path and the external flow path.

10. The gas turbine engine of claim 7 , wherein the heat exchanger assembly is disposed on a radially outer surface of the core engine.

11. The gas turbine engine of claim 7 , further comprising a stationary annular casing at least partially surrounding the core engine, wherein the heat exchanger assembly is disposed on a radially inner surface of the annular casing.