Advanced Laser Diagnostics Investigating the Fluid Mechanics of Primary Breakup

喷雾系统广泛应用于从燃油喷射到制药的各个行业，要提高喷雾系统的效率，需要对主要的破碎过程有更深入的了解。当液核离开喷嘴时，它会分解成较大的初级液滴，然后在称为初级破裂的过程中进一步分解为较小的液滴。然而，这一机制是喷雾系统中最不为人所知的领域，目前的数值模型必须依赖于显著的简化。缺乏对初级破碎的了解很大程度上是由于在较高的雷诺数(Re)和韦伯数(We)下喷雾的实验数据不足，这是因为在发生这种机制的喷雾的近场区域有高的光密度。因此，很难对初次破裂时的气液界面(LGI)进行成像。为了应对这一挑战，该博士项目旨在使用最先进的激光诊断工具，特别是双光子光诱导荧光(2P-LIF)和弹道成像。弹道成像和2P-LIF都被成功地用于显示高光密度区域。通过分解作用在初级液滴上的力可以确定破裂的有效性，这可以使用基于小波的光流(WOF)技术来实现。该项目的目标是开发一种精确的WOF平台，与先进的激光诊断工具一起使用，以确定初级液滴在LGI处的速度和加速度分量。这些喷雾将由各种孤立的破碎机制产生，包括剪切、湍流和空化，使用专门设计的喷雾设备。该设施将在不同的注射压力下通过定制设计的喷嘴流动液体，并将能够提供各种Re、We和空化(Ca)数。博士项目包括三个部分，前两部分为第三部分奠定了基础。首先，将利用RWTH亚琛大学合作伙伴提供的雾化喷雾数据库直接数值模拟的合成数据，开发WOF平台，以准确估计雾化喷雾的速度和加速度。其次，将设计一个喷雾设施，以隔离前面强调的各种破碎机制，以及各种液体和喷嘴几何形状。最后，喷雾设备将被用来为每种解体结构产生轻度雾化到高度雾化的喷雾，使用2P-LIF或弹道成像来可视化主要的解体过程，并与开发的用于解析速度和加速度分量的WOF平台相结合，以确定每种解体机制的有效性。该项目旨在解决雷诺数和韦伯数较高时喷雾初次分解的实验数据不足的挑战，为更广泛的喷雾界提供新的见解和数据，以进一步帮助建立喷雾系统的模型。来自基本喷雾设施的数据将作为理解布莱恩·彼得森博士提出的Prime项目的进一步研究的基础。

Spray systems are widely used in various industries, from fuel injection to pharmaceuticals, and improving their efficiency requires a deeper understanding of the primary breakup process. When a liquid core exits a nozzle, it breaks up into larger, primary drops, which then further divide into smaller droplets in a process called primary breakup. However, this mechanism is the least well-understood area of spray systems, and current numerical models have to rely on significant simplifications. The lack of knowledge about primary breakup is largely attributed to insufficient experimental data of sprays at higher Reynolds (Re) and Weber (We) numbers, this is due to the high optical density in the near-field region of a spray where this mechanism occurs. Thus, making imaging the liquid-gas interfaces (LGIs) at primary breakup difficult. To address this challenge, this PhD project aims to use state-of-the-art laser diagnostic tools, specifically two-photon light-induced fluorescence (2p-LIF) and ballistic imaging. Both ballistic imaging and 2p-LIF have been successfully employed to visualise high optical density regions The efficacy of breakup can be determined by resolving the forces acting on primary drops, which can be achieved using wavelet-based optical flow (wOF) techniques. The objective of this project is to develop an accurate wOF platform to be used with advanced laser diagnostic tools to determine the velocity and acceleration components at LGIs of the primary drops. These sprays will be generated from various isolated breakup mechanisms, including shear, turbulence, and cavitation, using a specially designed spray facility. The facility will flow liquid through custom-designed nozzles at different injection pressures and will be capable of providing a wide variety of Re, We, and cavitation (Ca) numbers. The PhD project comprises three sections, with the first two laying the groundwork for the third. Firstly, the development of a wOF platform to accurately estimate the velocity and acceleration of atomising sprays will be undertaken, using synthetic data from direct numerical simulation of atomising spray databases supplied by partners at RWTH Aachen University. Secondly, a spray facility will be designed to isolate the various breakup mechanisms highlighted earlier, with various liquids and nozzle geometries. Finally, the spray facility will be used to produce mildly atomising to highly atomising sprays for each breakup configuration, visualising the primary breakup process using 2p-LIF or ballistic imaging and coupled with the wOF platform developed to resolve the velocity and acceleration components to determine the efficacy of each breakup mechanism. The project aims to address the challenge of insufficient experimental data of the primary breakup of sprays at higher Reynolds and Weber numbers, providing new insights and data for the wider spray community to further aid in the modelling of spray systems. The data from the fundamental spray facility will serve as a basis of understanding for further research in the PRIME project proposed by Dr Brian Peterson.