Planar Rainbow Refractometry For Size, Refractive Index And Position Measurement Of Droplets In A Plane
C. Li (1), Q. Lv (2), X. Wu (2), C. Tropea (3)
(1) National Key Laboratory of Transient Physics, Nanjing University of Science and Technology, Nanjing 210094, China
(2) State Key Laboratory of Clean Energy Utilization, Zhejiang University, Hangzhou 310027, China
(3) Institute of Fluid Mechanics and Aerodynamics, Technische Universität Darmstadt, 64287, Darmstadt, Germany
Rainbow refractometry can simultaneously measure the temperature and geometric parameters of droplets by analyzing the recorded primary rainbow scattering signal of the droplet. The technique therefore has high potential in measurement applications involving reacting/non-reacting sprays. This study develops the planar rainbow refractometer technique, expanding the measurement dimension from a single "line" measurement to a "planar" measurement. The position of the droplet in the plane is determined by the contour of the rainbow signal, whereas the size and refractive index of the droplet are derived from the extracted rainbow image using the calibrated scattering angle. A simple and compact rainbow optical measurement system is constructed based on horizontal slit modulation, enabling the recording of spatially discrete rainbow signals of droplets in a plane. A novel scattering angle calibration method using a precisely traversed monodisperse droplet stream with a priori parameters is proposed and the algorithm for obtaining the calibration coefficients is evaluated by simulation. Spray verification experiments were carried out. The signal processing consists of image recognition, particle localization, and the rejection of non-spherical droplets. The possibility of estimating droplet number density is also discussed.