The Removal of Tunnel Vibration Induced Corruption in Aero-Optical Measurements

Wavefront measurements of a turbulent boundary layer were performed at the University of Notre Dame. Optical access windows to the tunnel were instrumented with 16 accelerometers to measure the tunnel-induced vibrations in the optical windows. A combination of spectral Proper Orthogonal Decomposition (POD) and Linear Stochastic Estimation (LSE) were used to remove vibration induced effects in the wavefronts. Through a combination of Tip/Tilt removal and LSE-POD filtering, a reduction of greater than 85% in OPDRMS was observed. A brief optimization study on accelerometer number requirements showed that even instrumenting each optical access window with a single accelerometer provided substantial improvement in vibration-induced error reduction. Wavefront statistics, including spectra, correlation lengths, and OPDRMS for LSE-POD filtered measurements of a M = 0.35 turbulent boundary layer were calculated. The resulting statistics were shown to be in good agreement with previous studies of subsonic turbulent boundary layers.