Method and apparatus for determining clearance between moving and static members in a machine

A gas turbomachine comprising:

• a static member fixedly mounted along a gas path of the gas turbomachine;
• a moving member rotatably mounted along the gas path of the gas turbomachine relative to the static member, the moving member including a central hub and at least one moving component, the at least one moving component including a first end portion fixedly connected to the central hub, a second end portion and an intermediate portion, the second end portion being spaced from the static member so as to form a gap;
• at least one passive transmitting element including an orifice provided at the second end portion of the at least one moving component, the at least one passive transmitting element emitting an acoustic wave having a predetermined frequency across the gap, wherein upon rotating the at least one moving component relative to the static member, an airflow passes through the orifice to create the acoustic wave;
• at least one receiving element mounted to the static member the at least one receiving element receiving the acoustic wave from the passive transmitting element;
• and
• a controller operatively connected to at least one of the at least one passive transmitting element and the at least one receiving element, wherein the controller determines a clearance distance extending between the moving member and the static member based on the acoustic wave passing across the gap.