Abstract
Changes in diffusion of spray particles in time sequence are investigated experimentally in a turbulent field using the wind tunnel, which simply simulates the flow field inside the cylinder. To focus on the effects of turbulence intensity on the spray, RMS (Root Mean Square) velocity of turbulence varies from 1.2 m/s to 5.6 m/s, while other experimental conditions such as the velocity of the mean flow in the tunnel and the injection pressure are unchanged. The spray is visualized with the light sheet of pulse laser and the time series of images is captured by means of high-speed camera. The pixel resolution of camera in the system is not enough to capture the diameter of the individual particle. In order to measure the diffusion of particles in a turbulent field, a new image processing procedure is developed. Because the distribution of the particle diameters statistically averaged in one slice of image is not affected by the ambient turbulence, light intensity of each pixel in an image represents a distribution of density of particles. Therefore, by the distribution of light intensity expressed as PDF (Probability Density Function), which is calculated from an image, the distribution of the density of particles is expressed. By analysing the time series of PDF data, the diffusion of particles is evaluated. As a result of present procedure, PDF tends to be flat under a large turbulence, which shows that the diffusion of particles is enhanced as an increase of the turbulent intensity.
Keywords:Spray 2-D Visualization, Light intensity distribution, Image Processing, PDF of light intensity, Turbulent Diffusion