Flow measurement for a gas turbine engine

A system configured to determine air flow through a turbomachine, the system comprising:

• a plurality of acoustic sensors provided upstream of a compressor of the turbomachine, the plurality of acoustic sensors being configured to transmit acoustic waveforms through an intake airflow to a plurality of further acoustic sensors;
• a duct of the turbomachine defined by an inner circumferential flow surface and an outer circumferential flow surface, the intake airflow flowing between the inner circumferential flow surface and the outer circumferential flow surface;
• 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 the intake airflow, and the plurality of acoustic sensors being located upstream of the acoustic liner, and
• a processing system configured to receive signals from the plurality of acoustic sensors and the plurality of further acoustic sensors and determine a flow rate of the intake airflow, wherein:
• the plurality of further acoustic sensors are arranged entirely recessed in the inner circumferential flow surface, the plurality of further acoustic sensors being disposed outside of the intake airflow,
• the plurality of acoustic sensors are located in the outer circumferential flow surface in a single plane,
• the plurality of further acoustic sensors are configured to communicate with the plurality of acoustic sensors at a point intercepting the single plane, and
• the acoustic liner is located upstream of a fan that is positioned at an airflow intake of the turbomachine.

A method of determining air flow properties of an intake airflow of a turbomachine, the method comprising steps of:

• providing signal communication between a plurality of acoustic sensors and a plurality of further acoustic sensors located in a single plane defined by the plurality of acoustic sensors and the plurality of further acoustic sensors provided upstream of a compressor of the turbomachine;
• determining a time of flight of acoustic waveforms between the plurality of acoustic sensors and the plurality of further acoustic sensors;
• and
• using a time of flight between the plurality of acoustic sensors and the plurality of further acoustic sensors to determine an average flow velocity of the intake airflow, wherein
• the turbomachine includes:
• a duct defined by an inner circumferential flow surface and an outer circumferential flow surface, the intake airflow flowing between the inner circumferential flow surface and the outer circumferential flow surface, and
• 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 the intake airflow, and the plurality of acoustic sensors being located upstream of the acoustic liner,
• the plurality of further acoustic sensors are arranged entirely recessed in the inner circumferential flow surface, the plurality of further acoustic sensors being disposed outside of the intake airflow, and
• the acoustic liner is located upstream of a fan that is positioned at an airflow intake of the turbomachine.