Time-Resolved Measurements of Spray Drop Size and Velocity

Abstract

The phase Doppler method was applied to the measurement of a swirl-stabilized spray flame. A discussion on the nature of the sampling statistics is provided to assist in the interpretation of the results. Comparisons of the mean drop size obtained in the burning and nonburning spray were made to assess the reliability of the data and to provide information on the drop evaporation rate. At the station considered, the mean sizes were similar at the center indicating a low evaporation rate. The mean drop size increased with radial distance in the burning case due to the loss of the small drops by evaporation. Time of arrival of the drops was measured and revealed pulsations or clustering of the spray. These clusters were most pronounced when injecting into a turbulent flow field with large scale eddies. In the spray flame, the drop clusters appeared to be correlated with the periodic instabilities in the flame. The local drop number density within the clusters was estimated to be an order of magnitude greater than the long time average number density. A fast Fourier transform analysis of the cluster arrival frequency showed that, over short time intervals, there was a periodicity to the cluster formation.