Assessment of a fourier-transform Doppler signal analyzer and comparisons with a time-domain counter processor

Comparisons are performed between a frequency-domain processor, the Doppler signal analyzer (DSA), and a counter processor (PDPA) for phase Doppler particle size and two-component velocity measurements in a wall-characterized simplex spray with and without the presence of swirl. The minimize issues associated with repeatability, symmetry, and uncertainty in measurement location, an experiment that allowed simultaneous measurements by two independent instruments with overlapping sample volumes was conducted. It was observed that the sue of the frequency domain for both burst detection as well as signal processing resulted in a reduced sensitivity to detector gain for the DSA compared to the PDPA. In the particular sprays considered, consistent agreement between droplet size and droplet velocity measured by each instrument was observed. Indirect measurements (e.g., volume flux, number density) were also compared and, although good agreement was observed for the simplex spray, several issues associated with the swirling case prevented satisfactory comparison. The results demonstrate the utility of such comparative studies and also illustrate the difficulty in establishing performance in general in actual polydispersed sprays.