Three-dimensional temperature and velocity measurements in fluids using thermographic phosphor tracer particles

湍流本质上是三维的。在过去的十年中，层析粒子图像测速技术（PIV）的发展使三维速度测量成为可能，从而促进了对湍流结构的理解的巨大进步。在许多湍流热传递过程中，无论是自然发生的（例如，海洋、大气或地幔中的自然对流）或被诱导以提高装置的效率或可靠性（例如，燃气涡轮机和电子电路），单独的速度场知识不足以明确地描述流动，并且同时的温度测量是非常期望的。该项目提出了一种新的概念，同时三维温度和速度测量的基础上结合热成像荧光粒子与三维粒子为基础的测速技术。与基于来自多个视图的体积信号的层析重建的三维标量测量概念不同，这里探测单个微米尺寸的热成像磷光体颗粒的温度。通过三角测量或Tomographic-PIV重建可以精确地确定颗粒位置，从而获得三维温度场。该概念允许高空间分辨率，并且仅需要添加两个成像传感器和一个UV激光器来激发颗粒并形成其发光的光谱过滤图像，用于基于比率的温度测量。此外，该附加视图具有短景深，其可用于通过减少鬼粒子的量来增强速度测量的质量。在本项目中，我们将使用申请人实验室已有的激光和摄像设备，设置一个6摄像机系统，并结合厚光片（约7-10 mm）。初始测量将在湍流加热射流中进行。由于该标准测试用例具有明确定义的等温区域，因此可用于评估温度精度方面的测量性能并检测潜在的定位误差。首先，将使用用于颗粒定位的三角测量和用于发光信号分配的简单针孔投影来开发用于低颗粒图像密度（每像素0.005个颗粒）的成像工具。然后将开发基于层析重建算法的更高粒子图像密度的测量方法和更精确的成像模型。作为一个示范，这个三维温度和速度诊断，然后将被应用到测量后面的加热圆柱体的唤醒，提供等温和等涡度表面的同时可视化，并展示了这种测量的重要性，为复杂的三维传热现象的理解。这些研究对于自然对流的基本理解或工业冷却装置的改进至关重要。

Turbulent flows are inherently 3-dimensional. Over the past decade, the development of Tomographic Particle Image Velocimetry (PIV) has enabled three-dimensional velocity measurements, thereby facilitating tremendous progress in the understanding of turbulent flow structures. In many turbulent heat transfer processes, whether naturally occurring (e.g., natural convection in the ocean, atmosphere or mantle) or induced to improve the efficiency or reliability of devices (e.g., gas turbines and electronic circuits), knowledge of the velocity field alone is insufficient to unambiguously describe the flow, and simultaneous temperature measurements are highly desirable. This project proposes a novel concept for simultaneous three-dimensional temperature and velocity measurements based on combining thermographic phosphor particles with 3-dimensional particle-based velocimetry techniques. Unlike the three-dimensional scalar measurement concept based on tomographic reconstruction of volumetric signals from multiple views, here the temperature of individual micron-size thermographic phosphor particles is probed. Particle locations can be accurately determined from eithertriangulation or Tomographic-PIV reconstruction so that a 3-dimensional temperature field will be obtained. This concept allows high spatial resolution and only requires the addition of two imaging sensors and a UV laser to excite the particles and form spectrally filtered images of their luminescence for ratio-based thermometry. Furthermore, this additional view has a short depth of field that can be used to enhance the quality of the velocity measurements by decreasing the amount of ghost particles. In this project we will set-up a 6-camera system in combination with thick light sheets (~7-10 mm) using laser and camera equipment already available at the applicants lab. Initial measurements will be performed in a turbulent heated jet. Since this standard test case has well-defined isothermal regions, it can be used to assess the measurement performance in terms of temperature precision and detect potential positioning errors. First, imaging tools for low particle image densities (0.005 particles per pixels) will be developed using triangulation for particle positioning, and simple pinhole projections for luminescence signal assignment. Methods for measurements at higher particle image densities based on tomographic reconstruction algorithm, and more accurate imaging models will then be developed. As a demonstration, this 3D temperature and velocity diagnostic will then be applied to measure the wake behind a heated cylinder, providing the simultaneous visualisation of isothermal and iso-vorticity surfaces, and demonstrating the importance of such measurements for the understanding of complex 3-dimensional heat transfer phenomena. Such investigations are crucial, e.g. for the fundamental understanding of natural convection, or to the improvement of industrial cooling devices.