非均匀气体折射环境下的示踪粒子高精度重构方法

基于示踪粒子成像的多相机三维测速方法是实验流体力学的核心研究方向，其关键在于利用多个不同视角的二维粒子图像来重构流动空间中的示踪粒子。非均匀气体折射环境会产生带有湍流多尺度特征的光学畸变效应，使粒子的二维成像位置发生偏移、甚至模糊，降低流动空间中的示踪粒子重构精度。基于高阶多项式的映射函数，即便使用体自标定技术也难以刻画流动自身的光学畸变效应。而基于针孔相机模型的映射函数则难以处理光程中的复杂折射率分布。本项目通过发展高空间分辨率的层析背景纹影技术，测量精细的气体三维折射率分布，以此建立光线追踪模型直接描述复杂流动的光学畸变效应；将该描述光学畸变效应的模型和针孔相机模型整合，构建能应用于非均匀折射气体环境下的映射函数；最后通过搭建湍流氦气射流平台来对新映射函数重构三维粒子的有效性进行实验验证。

3D Velocimetry techniques based on imaging tracing particles from multiple views are essential in the field of experimental fluid mechanics. These techniques rely on the accurate reconstruction of tracing particles in the flow space via the images from multiple 2D views. Gas flows of non-uniform refractive index inevitably result in image distortions with the multi-scale feature of turbulent flows. Such optical distortion will cause erroneous displacement, even blurriness of the particle images, significantly degrading the quality of particle reconstructions in the flow space. The mapping function based on high-order polynomials cannot fully characterize the optical distortions even with the volumetric self-calibration technique, while the one based on the pinhole camera model is inadequate to handle the non-uniform refractive index in the light path. In this project, the tomographic background-oriented schlieren technique of high spatial resolution will be developed to obtain the 3D refractive index of gaseous flows. Combined the measured refractive index with the ray-tracing model, the optical distortion effects could be modeled with sufficient accuracy. Furthermore, by integrating the ray-tracing model with the pinhole camera model, a new mapping function can be developed, which is capable to reconstruct tracing particles in gas environments of non-uniform refractive index. Finally, a turbulent helium jet experiment will be established to verify the effectiveness of the new mapping function in reconstructing the tracing particles.