Comparison of frequency domain and time domain laser velocimeter signal processors

An experimental investigation was conducted in the 14- by 22-foot subsonic tunnel at NASA-Langley Research Center to measure the inflow into a scale model helicopter rotor in forward flight. These inflow measurements were acquired utilizing a two-component laser velocimeter, and the data were processed by a frequency-domain processor (FDP). As a subset of the experiment, a time-domain counter processor was utilized simultaneously with an FDP to make a comparison of the two processors possible. The results indicate that the FDP had a marked improvement in processing capability in conditions of low signal-to-noise ratios and had a reduction in the number of erroneous data points acquired. However, the FDP yielded a lower data rate in comparison to the counter when signal-to-noise ratios were high. Comparison of the data sets shows that the FDP consistently measures velocities which are 0.7% higher than those measured by the counter processor