| The liquid rocket engine sprays the liquid propellant(fuel and oxidant)into the combustion chamber through the injector by means of collision atomization,which makes the jet impact break and atomize.The atomization of liquid propellant is the primary stage of the combustion process.The quality of atomization directly impacts on the combustion efficiency,thrust,thrust to weight ratio,working stability,pollution emissions and other important performance indicators of liquid rocket engine s.The last channel through which the propellant flows before being injected into the combustion chamber is the nozzle of the injector,which is located between the combustion chamber and the supply system.Its geometric structure parameters affect the atomization quality significantly.However,at present,it is still unclear how the geometric structure deviation of the impinging nozzle affects atom ization characteristics,which leads to the lack of corresponding theoretical basis and reference in the manufacturing tolerance design and processing error control of the impinging nozzle.Therefore,it is urgent to study the relationship between the scale deviation of the impinging nozzle and the atomization characteristics,so as to provide more sufficient theoretical basis and reference values for the manufacturing and processing of the impinging nozzle.Focusing on the demand of improving the atomizati on quality of the impinging nozzle,this topic aims at the problem that the prediction accuracy of the existing prediction models for the characteristic parameters of impinging atomized droplets is low because they do not include the scale deviation of the nozzle hole.Through theoretical analysis and numerical simulation of the influence relationship between the scale deviation of the nozzle hole and the cavitation effect of the internal flow field and the characteristic parameters of the atomized droplets,a prediction model for the characteristic parameters of impinging atomized droplets based on the scale deviation of the nozzle hole is established.An atomization droplet information extraction method based on laser interferometric particle imaging(IPI)technology is proposed,and the accuracy of the prediction model of the characteristic parameters of the impinging atomization droplet based on the scale deviation of the nozzle is experimentally verified by using this information extraction method.The main research contents of this paper are as follows:(1)Aiming at the problem that the prediction accuracy of the existing prediction models for the characteristic parameters of impinging atomized droplets is low because they do not include the scale deviation of the nozzle,the scale deviation of the orifice is introduced into the original prediction model.Through theoretical and simulation analysis of its influence on the flow field status and atomization field characteristics,a prediction model for the atomized droplet characteristic parameters based on the scale deviation of the orifice is established.Based on the influence of orifice diameter deviation on cavitation effect of internal flow field,a mathematical model of orifice diameter deviation and critical pressure of typical cavitation state is established,which can predict cavitation state of internal flow field.According to the relationship between the collision angle and the position of the collision point,the original prediction model is modified by introducing the collision angle deviation.The relationship between nozzle diameter and droplet size distribution was studied by numerical simulation,and the droplet statistical distribution model was modified on this basis.The prediction model of characteristic parameters of colliding atomized droplets based on scale deviation of nozzle takes into account the scale deviation of the nozzle and the cavitation effect of the internal flow field,which can improve the prediction accuracy of the characteristic parameters of the atomized droplets of the impinging nozzle,improve the theoretical research of the impinging atomization characteristics,and provide a new theoretical basis for the manufacturing and processing of impinging nozzle s.(2)Aiming at the problem of low measurement accuracy of high concentration particle field in atomized droplet particle size measurement method based on IPI technology,and fully considering the influence of particle field concentration on interference image process ing accuracy,an extracting droplet information algorithm based on Morphology-Hough-Fourier transform is proposed.Based on the geometrical optics approximation model,the particle size measurement model of laser interference particle imaging is establishe d by phase difference method.The structural elements are decomposed and recombined by the synthetic weighting method,and the improved multi-scale morphological anti noise edge detection operator is used to extract the edge of the droplet interference image.According to the corresponding relationship between image space and parameter space,the interference image is recognized by Hough transform;Fourier transform is used to transform the interference fringes from the spatial domain to the frequency domai n and extract the fringe frequency.This algorithm can improve the recognition rate and frequency extraction accuracy of interference images,and can completely recognize 10,30,and 50 particle field interference images.On this basis,the laser interference particle imaging measurement system is organized to measure the standard particle with a diameter of 24 μm,and the maximum and minimum particle diameters of the measurement points are 24.3 μm and 23.5 μm.The calculated SMD is 23.8 μm.The relative error is 2.1%,which verifies the feasibility and effectiveness of the particle size measurement method.(3)A visualization experiment of the flow field in the impinging nozzle is set up to jointly analyze the internal flow field state and the characteristics of the atomization field.According to the influence relationship between orifice diameter deviation and cavitation state of internal flow field,the accuracy of cavitation state prediction model is verified,and the prediction error is less than2.7%.The characteristic parameters of the droplets in the atomization field are measured by IPI measurement system.The experimental results show that the prediction errors of the SMD and particle size distribution correction models are less than 6.7% and 0.01,respectively,which achieve more accurate prediction of the droplet size and distribution.On this basis,t he SMD modified prediction model is used to study the influence of the fixed scale deviation band of the orifice on the droplet SMD.Considering the scale deviation of the orifice comprehensively,it is recommended that the machining errors of the diameter and angle of the impinging orifice be controlled within-5%～0 and 0°～+5°,respectively. |
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