Comparison of window, smoothed-ensemble, and cycle-by-cycle data reduction techniques for laser Doppler anemometer measurements of in-cylinder velocity

The present study compares methods of data analysis for LDA measurements of in-cylinder velocity by using various methods to extract mean velocity and turbulence from the same data. Both the smoothed-ensemble and window methods use ensembled data to determine the mean velocity; hence these two methods are unable to distinguish cyclic variations in mean velocity from turbulence. The cycle-by-cycle method accounts for variations in mean velocity from one cycle to the next; the magnitude of the cyclic variations is largest when there is no strong well-directed mean flow, and can be several times as large as the turbulence in such cases. The window method also suffers from an error introduced by the finite window size; this is manifested as increased turbulence when large window sizes are used.