Gas turbine engine

A turboshaft engine having a principal rotational axis, the turboshaft engine comprising:

• a power turbine, a tail bearing housing, and an exhaust collector arranged in axial flow series along the axis, the tail bearing housing having a radially central region defining a flow chamber for cooling air;
• an annular duct defined around the central region and which forms at least part of an exhaust flow passage for the flow of exhaust gases from the power turbine to the exhaust collector, the tail bearing housing having a plurality of vanes extending radially outwardly from the central region and across the annular duct, at least some of the plurality of vanes having respective airflow passages therethrough which are arranged in fluid communication with the flow chamber for the passage of cooling air;
• and
• a fan fluidly connected to at least one of the vane airflow passages, the fan being operable to draw cooling air radially outwardly from the flow chamber through the or each airflow passage to which it is connected, wherein
• the flow chamber is provided in fluid communication with the exhaust collector via at least one exhaust port formed in the tail bearing housing and the flow of exhaust gases through the exhaust collector during operation of the engine educes a flow of cooling air through the flow chamber.

A method of operating a turboshaft engine having a principal rotational axis, the method comprising:

• providing the turboshaft engine comprising:
• a power turbine, a tail bearing housing, and an exhaust collector arranged in axial flow series along the axis, the tail bearing housing including a labyrinth seal and having a radially central region defining a flow chamber for cooling air,
• an annular duct defined around the central region and which forms at least part of an exhaust flow passage for the flow of exhaust gases from the power turbine to the exhaust collector, and
• a compressor, wherein
• the flow chamber is provided in fluid communication with the exhaust collector via at least one exhaust port formed in the tail bearing housing, and
• the labyrinth seal is provided in fluid communication with the or each exhaust port,
• directing sufficient flow of exhaust gas through the exhaust collector to educe a flow of cooling air through the flow chamber and into the exhaust collector via the or each exhaust port;
• and
• drawing a flow of compressed air from the compressor and directing it through the labyrinth seal to pressurise the seal, and directing sufficient flow of exhaust gas from the power turbine along the exhaust collector to educe a flow of the compressed air from the labyrinth seal and into the exhaust flow via the or each exhaust port.

A method of operating a turboshaft engine having a principal rotational axis, the method comprising:

• providing the turboshaft engine comprising:
• a power turbine, a tail bearing housing, and an exhaust collector arranged in axial flow series along the axis, the tail bearing housing having a radially central region defining a flow chamber for cooling air, the flow chamber being provided in fluid communication with the exhaust collector via at least one exhaust port formed in the tail bearing housing;
• an annular duct defined around the central region and which forms at least part of an exhaust flow passage for the flow of exhaust gases from the power turbine to the exhaust collector, the tail bearing housing having a plurality of vanes extending radially outwardly from the central region and across the annular duct, at least some of the vanes being provided with respective airflow passages therethrough which are arranged in fluid communication with the flow chamber for the passage of cooling air, and
• a fan fluidly connected to at least one of the vane airflow passages,
• directing sufficient flow of exhaust gas through the exhaust collector to educe a flow of cooling air through at least some of the airflow passages, through the flow chamber, and into the exhaust collector via the or each exhaust port;
• and
• operating the fan to draw cooling air radially outwardly from the flow chamber through the or each vane airflow passage to which it is connected.