Phase Doppler measurements of spray impact onto rigid walls

In this work, an experimental study of spray impact onto a horizontal flat and rigid surface is presented. The phase Doppler technique has been used to characterize both the impacting and the secondary spray in terms of mass and number flux, size distribution and velocities of the droplets above the target. A high-resolution CCD camera has been used to measure the average liquid film thickness formed due to spray impact, whereas a high-speed CMOS camera has been used to characterize the splashing droplets from the wall. This visualization of the splashing phenomenon and the knowledge about the liquid film thickness are used to formulate a new physical model of the crown evolution. Furthermore, information about the incident-to-ejected mass fraction and number fraction are novel contributions of this study. Considerable data are provided comparing the impact of single drops onto a liquid film to impact of drops in a spray, and the significance of the observed differences for modelling efforts is discussed. The measurements of this study are also shown to be rather sensitive to the placement of the phase Doppler measurement volume above the surface and to the operating parameters of the instrument. These effects have been documented and discussed for this particular measurement situation.