3D measurement of the local extinction coefficient

 

For the validation of numerical models describing the spray region, a statistical description of the spray over a large field-of-view is required. In this case, averaged imaging can be employed together with a 3D image reconstruction scheme. The most adequate laser imaging techniques for this task are based on the use of Structured Illumination.

 

In the recent years, large progresses in laser imaging techniques have allowed to extract spatially resolved 2D and 3D quantitative spray information even in optically dense situations. The main breakthrough of these techniques is the possibility of suppressing unwanted effects from multiple light scattering using Structured Illumination. Thanks to this new feature, effects due to light extinction can also be corrected allowing the measurement of the local extinction coefficient. These quantitative information which is available even in challenging conditions, where Phase Doppler does not work anymore, can be used for data comparison between experiment and simulation. The local extinction coefficient is particularly

valuable for the description of the droplet field, defined as the ‘‘spray region’’, as it contains information related to both droplets size and concentration.

 

In addition to the extinction coefficient, the droplet SMD can also be reconstructed in 3D. By combining those two quantities, the liquid mass in the spray region can be deduced. Note that for a cloud of monodispersed droplets, the extinction coefficient is directly related to the concentration (number density) of droplet. 3D spray representations of spray systems presents a step towards future validations of spray simulations - in the spray region - especially those based on Lagrangian Particle Tracking.