Optical Detection of Blade Flutter

Abstract

A joint Air Force-NASA flutter research program using full-scale turbine engines is being conducted at the NASA Lewis Research Center. The initial phase is a fan flutter program using a YF-100 turbofan engine. In these tests, dynamic strain gages mounted on rotor blades are being used as the primary instrumentation for detecting the onset of flutter and defining the vibratory mode and frequency. Optical devices however are being evaluated for performing the same measurements as well as providing supplementary information on the vibratory characteristics. Two separate methods are being studied: stroboscopic imagery of the blade tip and photoelectric scanning of blade tip motion. Both methods give visual data in real time as well as video tape records. The optical systems will be described and representative results will be presented. The potential of this instrumentation in flutter research will be discussed.