Flow measurement for a gas turbine engine

1. A method of thermodynamic assessment of flow through a turbomachine having a compressor, the method comprising the steps of:

detecting sensor readings using a plurality of acoustic sensors and a plurality of further acoustic sensors located about an intake of the turbomachine located upstream of the compressor, the plurality of acoustic sensors arranged in an outer circumferential flow surface in a single plane about a central axis of the intake, the plurality of further acoustic sensors arranged entirely recessed in an inner component, the turbomachine further including an acoustic liner configured to absorb vibrations generated by rotation of a rotor, the acoustic liner being disposed entirely external to the outer circumferential flow surface and outside of an airflow into the intake, and the plurality of acoustic sensors being located upstream of the acoustic liner;

receiving stagnation temperature readings for the airflow into the intake;

determining a static temperature for the airflow into the intake and an average velocity of the airflow over an airflow area of the intake located upstream of the compressor using the detected acoustic sensor readings; and

outputting an airflow rate of the airflow through the intake, using the determined average velocity of the airflow to control one or more control processors for operating the turbomachine, wherein:

the acoustic liner is located upstream of a fan that is positioned at the intake of the turbomachine,

the plurality of further acoustic sensors is located upstream of the fan, and

the inner component is a nose cone.

2. The method of claim 1 , wherein the average velocity of the airflow is defined as a time-of-flight averaged airflow velocity, which is thermodynamically corrected.

3. The method of claim 2 , wherein:

the time-of-flight-averaged airflow velocity is thermodynamically corrected based on a predetermined airflow profile, and

the predetermined airflow profile is determined using tomographic data from the plurality of acoustic sensors and the plurality of further acoustic sensors.

4. The method of claim 1 , further comprising receiving pressure readings for the airflow into the intake, wherein the outputting of an airflow rate of the airflow through the intake includes using the received pressure readings to output a mass airflow rate of the airflow through the intake.

5. The method of claim 1 , wherein:

the turbomachine includes an engine core and a bypass airflow passage, and

a mass airflow rate of the engine core is deducted from a mass airflow rate of the intake to determine a mass airflow of the bypass airflow passage.

6. The method of claim 5 , wherein the mass airflow rate of the engine core is estimated based on a predetermined relationship between engine core airflow and one or more engine operation parameters.

7. The method of claim 5 , wherein the mass airflow rate of the bypass airflow passage is used to determine a thrust value of the bypass airflow.

8. The method of claim 5 , wherein the mass airflow rate of the airflow through the bypass airflow passage is used to determine a nozzle discharge coefficient for a bypass passage nozzle.

9. The method of claim 5 , wherein a mass airflow is determined for a downstream location of the bypass airflow passage by determining a mass airflow of an upstream location of the bypass airflow passage and applying an assumption of conservation of mass airflow or enthalpy for the downstream location.

10. The method of claim 5 , wherein a stagnation temperature downstream of the compressor is measured or derived based on a one or more characteristic of the compressor or an engine core turbine.

11. The method of claim 5 , wherein static pressure in the bypass airflow passage is measured using a pressure sensor.

12. The method of claim 4 , wherein the mass airflow rate of a bypass airflow passage is used with values of a stagnation temperature and a static pressure to derive a stagnation pressure for airflow entering a bypass passage nozzle, and

a value of bypass thrust is based on the derived stagnation pressure.

13. The method of claim 1 , wherein the average velocity is determined using:

the time of flight of the acoustic signal between the plurality of acoustic sensors and the plurality of further acoustic sensors through the intake airflow area, and

a determined value for a velocity of sound through air at the determined static temperature.

14. The method of claim 1 , wherein the plurality of acoustic sensors are mounted at angular spacing about the central axis of the intake.

15. A monitoring and control system for a turbomachine including a turbomachine intake upstream of a compressor, an engine core downstream of the compressor, and a turbine driven by exhaust gas from the engine core, the monitoring and control system comprising:

a plurality of acoustic sensors arranged in an outer circumferential flow surface in a single plane about a central axis of an intake of the turbomachine located upstream of the compressor, and the turbomachine further including an acoustic liner configured to absorb vibrations generated by rotation of a rotor, the acoustic liner being disposed entirely external to the outer circumferential flow surface and outside of an airflow into the intake, and the plurality of acoustic sensors being located upstream of the acoustic liner;

a plurality of further acoustic sensors located at the intake of the turbomachine, the plurality of further acoustic sensors being arranged entirely recessed in an inner component, and the plurality of further acoustic sensors being configured to receive sensor readings from the plurality of acoustic sensors; and

one or more processors arranged to receive sensor readings detected by the plurality of acoustic sensors and the plurality of further acoustic sensors and stagnation temperature readings for the airflow into the intake, wherein:

the one or more processors include machine readable instructions for determining a static temperature for the airflow into the intake and an average velocity of the airflow over an airflow area of the intake using the plurality of acoustic sensor and the plurality of further acoustic sensor readings, and

the one or more processors determine an airflow rate of the airflow through the intake, using the determined average velocity of the airflow to control one or more control processors for operating the turbomachine, wherein:

the acoustic liner is located upstream of a fan that is positioned at the intake of the turbomachine,

the plurality of further acoustic sensors is located upstream of the fan, and

the inner component is a nose cone.

16. The monitoring and control system of claim 15 , wherein the airflow rate is used to determine thrust produced by the turbomachine during operation or to determine a power setting parameter for the turbomachine during operation.