# Impacts of Micro-Deviations of Aperture on the Characteristics of Collision Atomization Field
## 1 Introduction  
The impinging nozzle, which applies kinetic energy to break the propellant jet, has the characteristics of brisk response, expeditious mixing and combustion, is universally employed in liquid rocket engines. Manufacturing practice establishes that the particle diameter and distribution of atomized droplets influence combustion and efficiency of liquid rocket engines significantly [1]. With the speedy advancement of high-precision machining and measurement technology, the diameter of the nozzle in a liquid rocket engine can be manufactured to hundreds or even tens of millimeters to the atomization performance. Many scholars have researched high-precision measurement approaches for micropores with large aspect ratio, which can earn high-precision measurement data of the internal geometry structure of an orifice, to upgrade the enhancement of micropore processing technology [2, 3, 4, 5, 6]. These consequences are also constructive to fathom and inspect the atomization excellence of the fuel atomization field involved by the relative position and geometry of nozzles comprehensively. The accuracy of the freshest measurement technology can attain nanometer level at a high aspect ratio [4, 5, 6]. Therefore, it is expedient to calibrate the orifice to glean more comprehensive data, which can confirm the consistency of the internal diameter of the orifice and ensure the disclosure of the individual microscopic deviation induced by machining deviation. The existing methods of manufacturing are challenging to produce ideal smooth ori-fices, which thoroughly conform to the expected ones, especially in volume production, due to the limitations of the manufacturing mechanisms and technical level, such as insufficient strength and rigidity of carving apparatuses. For bounteous pairs of orifices of the liquidrocket engine, the internal diameter of the nozzle directly affects the exit velocity of two jets [7]. According to extensive nozzle appraisal data, the machining deviation generally fluctuates within the range of 15% of the ideal value, which is diversified, such as the diameter of the impinging orifices, inclination angle and relative position, etc. However, in factual construction, more than one type of deviation will exist in the impinging nozzles, making it imperative to inspect heterogeneous deviation to explore the influence of specific deviation on the internal flow field and atomization characteristics. In addition, the influence of nozzle structure deviation on atomization characteristics must be considered when designing nozzle manufacturing tolerance and controlling machining error. The most influential structural deviation should be strictly controlled to ensure the atomization characteristics and appropriately tolerate microstructural deviation to enhance the construction efficiency and decrease the manufacturing costs. In double jet impingement atomization, two impinging jets are ejected from two nozzles, respectively, and then collide at a certain collision angle, forming an oval liquid membrane perpendicular to the plane of the two jets, whose boundary is closed at low velocity [8]. Under the condition of high-speed impact, the liquid membrane is disturbed by the surrounding air flow, and vibration waves will be generated on the surface [9]. When the amplitude of the vibration wave reaches a certain value, the liquid membrane will break, resulting in fracture zone and liquid filament, which belongs to the primary stage of atomization. When moving with the surrounding air relatively, the fracture zone and the liquid filament extend to break up, developing atomization droplets, which belongs to secondary atomization. When the fracture zone appears in the liquid membrane rupture, the fracture occurs at the two adjacent peaks of the liquid membrane vibration wave. Therefore, the width of the fracture zone is approximately half the wavelength of the liquid membrane rupture [10].