As we all know, the overall performance of the combustion chamber is inseparable from the atomization performance of the nozzle, the nozzle with good atomization performance can make the liquid fuel or oxidizer form a large number of small and uniform droplets, thereby increasing the contact area between the droplets and the surrounding ambient air, promoting the heat transfer and evaporation process, which is conducive to promoting the formation of the mixture and improving the stability of combustion. This project took the spray formed by jet impact and atomization of water medium as the main research object, innovatively designed the positive and misaligned impact atomization nozzles of multiple circularly arranged impingment jets, defined the off-center impact factor B that characterized the misaligned impact degree of jets, and focused on the basic morphological characteristics and external macroscopic characteristics of the spray, as well as the morphology and size characteristics of the liquid sheet formed by jet impact. The statistical rule of spray droplets and droplet movement characteristics under multi-parameter were investigated experimentally.

In this study, high-speed backlight imaging technology was used to visually measure jet impact atomization spray. The results showed that different from the flat atomization structure of the bladed liquid sheet formed after the impact of two jets, the three ring-arranged jets impact at one point and then form a spatial structure composed of three half bladed liquid sheets downstream. Under the joint action of the surface waves of the liquid sheet and the surrounding air, The liquid sheet breaks to form liquid ligaments and large droplets, which then continue to break into a large number of small droplets. With the increase of the Weber number, the downstream tip of the structure changes from a closed rim to an open rim. Surface waves on the liquid film were analyzed, and the wavelength of surface waves was measured. By comparing with theoretical values, it was concluded that the surface waves on the liquid sheet were the nonlinear superposition of aerodynamic waves and impact waves. When the We was small, the wavelength was longer, while when the We was large, the wavelength was shorter, which was related to viscous dissipation and tensile stress. By processing the spray images obtained through visual measurement, parameters such as the length, width, and thickness of the atomized liquid sheet were calculated to characterize the size characteristics of the atomized liquid sheet. By comparing with theoretical values, it was found that the thickness of the liquid sheet was related to the impact We. The greater the impact We, the smaller the thickness of the liquid sheet. Both the length and width of the liquid sheet were related to the Wes. When the liquid sheet was in a closed-rim state, both the length and the maximum width of the liquid sheet increased as the We increased. When the liquid sheet was in an open-rim state, the length of the liquid sheet decreased as the We increased, while the maximum width of the liquid sheet increased as the We increased. This was consistent with theoretical predictions.

The particle number, particle size and velocity of atomized droplets were measured synchronously by using phase Doppler particle analysis and measurement technology, and the size distribution, spatial distribution and velocity distribution of droplets in atomization spray field were obtained. The results show that the structure of the Probability Density Function (PDF) curve of the droplet diameter in the atomization field is approximately symmetric, and the peak value appears in the range of 150to 250. In this distribution, the droplet size is mainly distributed in the range of 100to 300, indicating that the atomization effect is good. The probability density distribution of the normalized particle size in atomization field is also analyzed, and it is found that it has a good fitting effect with the Gamma distribution function. The Radical Nonuniformity Index (RNI) was used to characterize the spatial distribution of droplets in the atomization field. The results showed that RNI decreased with the increase of radial distance, that is, the closer to the spray edge, the more uniform the distribution of droplets.

The influence of the misaligned impingement of the jet on the atomization structure is reflected in two aspects: one is to deflect the atomization liquid sheet, the other is to accelerate the downstream tip of the liquid sheet from the closed rim to the open rim. The influence on the spray droplet characteristics is reflected in the increase of off-center impact factor, B, which will reduce the average size of atomization droplet but reduce the spatial distribution uniformity of atomization spray field. For the droplet size distribution, the analysis results shows that twith the increase of Wes and B, the droplet diameter decreases, which will be conducive to atomization.

Finally, the influence of the number of jets on atomization was analyzed. The results showed that under the same impact Weber number (We) , the atomization quality will deteriorate with the increase of the number of jets. Taking the impact of five jets as an example, a narrow liquid sheet is formed after jet impact, and droplets are distributed axially along the nozzle, while the number of radial droplets decreases. With the increase of impact Weber number (), the breaking length of liquid sheet becomes longer and the thickness of liquid sheet becomes smaller. The Sauter Mean Diameter (SMD) ,  of droplets in atomization spray decreased with the increase of liquid ligaments and droplets, but the atomization quality in the spray was still not satisfactory compared with the three and two jets impinging atomization spray under the same impact We. With the increase of off-center impact factor B, the atomized liquid sheet expansion Angle and axial extension distance increase, and the downstream liquid sheet changes from closed tip to open tip. The relative positions of two adjacent liquid sheets changed. Within a certain range, the increase of B is conducive to the formation and fragmentation of liquid sheet. Beyond a certain critical value, with the increase of B, the number of droplets in atomization field decreases and the liquid ligaments become coarser and shorter. The SMD of droplets in atomization spray field becomes larger, which is not conducive to the liquid sheet breaking into liquid ligaments and droplets.

In general, this paper designed and constructed a set of visual measuring experiment equipment based on PDPA and high-speed camera, and developed the structure of the nozzle of multiple circular arranged jets, quantified the extent of the atomization mechanism of multiple jet.