Blades are twisted under load due to the aerodynamic pressure. The effect is more pronounced on long blades such as fan blades. Sudden untwist of a blade during operation of turbomachinery can be the sign of an upcoming stall or surge event. Real-time measurement of blade twist and untwist is therefore an important parameter to monitor.
Measuring Blade Twist With FOCIS™
Blade twist measurement is performed by placing several optical sensors along the blade and timing the difference of time of arrival between the sensors.
Blade Twist Measurement with FOCIS™ system
The FOCIS™ system includes a twist measurement program that calculates twist of each blade based on measurements made in two planes, typically one plane close to the leading edge and one plane close to the trailing edge.
Prime Photonics also makes specialized blade twist measurement probes with the ability to measure blade twist from a single penetration in the casing.