Measurement Of The Rainbow And Instability Of Circular Initial Jets

Liquid jets have been widely involved in massive industrial processes.Some scholars have established jet models with circular and elliptical cross sections to study jets instability and breakup mechanism.For experimental measruement of the instability of low-speed circular jets,high-speed photography is the main observation method at present.However,the measurement accuracy of this method is far from satisfying the measurement accuracy requirement of initial jet surface micro vibration near the nozzle.The geometric shape of the circular initial jet has three-dimensional curvature,so the theoretical study of its light scattering characteristics is a challenging task,and the theoretical calculation results have yet to be verified by experiments.Rainbow refractometry can measure the size and refractive index of spherical droplets and cylindrical particles on the order of tens of microns to millimeters with high speed and high precision,which the diameter measurement accuracy can reach several microns,the diameter variation measurement accuracy is on the order of tens of nanometers,and the acquisition speed can reach tens of thousands of frames per second.In this paper,a laser rainbow measurement system is designed and built to measure the rainbow characteristics and instability of the initial jet with three-dimensional curvature,even to study complex geometric shape of jets.The main research contents and conclusions are as follows:(1)A laser rainbow measurement system is designed and built in this paper with the following characteristics.The shape of incident light is adjusted and controlled in a collimated sheet shape to meet the measurement of localized light scattering properties of each order by the three-dimensional complex target.The rainbow ripple structure of threedimensional liquid jet can be produced by adjusting the shape of incident light in one dimension,which can meet the requirement of initial jet instability measurement.The independent control of the coaxial double rotation system can ensure the measurement of light scattering characteristics of non-circular jets at different azimuth angles.Using the above measurement system,the first-order and second-order rainbow positions of circular initial jets with spatial curvature are measured experimentally.The experimental results are in good agreement with the theoretical calculation results of Vectorial Complex Ray Model(VCRM),indicating that the developed laser rainbow measurement system can realize highprecision measurement of light scattering characteristics of three-dimensional liquid jets.(2)Using the first-order rainbow ripple structure of the circular initial jet,the jet diameter,vibration amplitude and frequency of jet instability at different heights are measured.The jitter frequency and surface wave amplitude of the initial jet with a certain excitation frequency are measured.The feasibility of rainbow refractometry to measure the jitter frequency of liquid jet is verified.The measurement results show that the measurement accuracy can reach 20 nm.The diameter and amplitude of the circular initial jet were measured experimentally.The results show that the amplitude of the surface wave of the initial jet increases exponentially with the drop height,and the measurement accuracy of the diameter can reach 5 microns.The application of rainbow refractometry in the measurement of initial liquid jet instability can effectively make up for the lack of precision in the measurement of initial jet micro-jitter by high-speed photography.