The Study On Particle Field Measurement Based On Laser Interferometric

Two-phase flows occur in many domains such as fuel spray in engine, medicine spray, pesticide spray and so on. Particle diameter and velocity measurement are very important to study the flow structure and to optimize process. For example in combustion processes precise information on velocity fields (for both gas phase and liquid phase), evaporation rate and droplets size are needed for pollution reduction and performance optimization. Therefore, techniques allowing to measure particle diameter and velocity at mean time are very useful tools in many research domains. The thesis reports on the development of two, conceptually different, interferometric measurement systems for two-phase flows characterization. The two methods are interferometric laser imaging droplet sizing (ILIDS) and digital in-line holography (DIH). The study contents include following parts.(1) The optical principle of the ILIDS technology has been studied. The relationship between the oscillating frequency of particle interferometric fringe and particle diameter is given by geometrical optics or by LMT in different scattering regions.(2) The image processing method for sizing and locating particles from interferometric pattern is developed.By applying this method, particle diameter and velocity can be obtained from the interferometric pattern automatically.(3) A series of experiments have been performed in order to validate ability of the method for particle field measurement. The droplet size distribution obtained by the method is estimated by comparing with a diffraction sizer. The velocity field measurement from interferometric pattern is presented and validated by comparison with the velocity fields obtained by PIV technique.(4)The principle of the numerical three-dimensional reconstruction algorithm for digital in-line holography is studied. Then we demonstrate how the recording-reconstruction process of in-line holography can be seen as a linear shift invariant system. The point-spread function of the system is described. The influence of wavelet aperture on reconstructed holographic image is analyzed. The depth of focus and the axial intensity oscillation and signal to noise ratio (SNR) of reconstructed image are analyzed. (5)The image processing methods for DIH has been developed. The image processing method includes particle three-dimensional locating and particle sizing and particle velocimetry and image noise filter.(6) A seris of the experimental have been performed to validate the ability of DIH method for particle field measurement. A comparison with the diameter distribution provided by a common diffraction particle sizer are presented.The two developped methods (ILIDS and DIH) can give statistically reliable results on particle size and particle spatial distribution and partice velocity distribution.