3D Modeling of Flow Behind a Heated Backward-Facing Step using 3D Digital Particle Image Velocimetry & Thermometry

今天的湍流实验研究使用成像方法，如数字粒子图像测速（DPIV）和数字粒子图像测温测速（DPITV），比以前的单点测量技术（如热线测速、激光多普勒测速（LDV）、热电偶、热敏电阻、皮托管）有了巨大的改进。这些新方法允许同时对随时间变化的温度和速度进行二维测量，但本质上无法解决湍流问题，因为三维信息是绝对必要的。虽然新开发的三维速度技术允许三维随时间变化的速度测量，但我们没有技术可以同时提供三维的温度和速度。短期研究目标是开发一种新技术，3D散焦粒子图像测温测速（3DDPITV），同时测量体积内随时间变化的温度和速度场。长期的研究目标是应用这项新技术来研究相干结构，它们的相互作用，以及它们的传热/混合特性，以便了解与它们的相互作用相关的物理学。此外，有了这方面的了解和三维数据场的可用性，可以对LES模拟中使用的亚网格尺度模型进行测试，并在适当时提出新的模型。选择的实验是逆向的步骤。这种流动的优点是在其流动物理上具有明显不同和独特的区域：(1)分离的剪切层与混合层非常相似，从而提供了研究在加热剪切层上混合和传热的相干结构的作用和影响的机会。(2)剪切层再附着的非定常性将为研究再附着问题中相干结构对传热的影响提供机会。(3)由于初级涡旋的存在，再循环区以对流为主，这将为研究以相干结构为主的再循环区内的传热提供机会。(4)再附着区以外的再发展边界层以湍流热通量为主导，与再附着过程中剪切层内撞击壁面的涡的相互作用直接相关，将为研究发展中的边界层提供机会。这项研究将在三个主要领域探讨更广泛的影响：整合教育和研究、加强基础设施和促进社会效益。该奖项由化学和传输系统分部的热传输和热处理项目资助，是桑迪亚国家实验室和美国国家科学基金会在“建模、仿真、决策和新兴技术工程科学”领域联合项目的一部分。

Today's experimental studies of turbulence that use imaging methods, such as Digital Particle Image Velocimetry (DPIV) and Digital Particle Image Thermometry and Velocimetry (DPITV), are huge improvements over previous single-point measurement techniques (e.g. hot-wire anemometry, Laser Doppler Velocimetry (LDV), thermocouples, thermistors, pitot tubes). These new methods allow for simultaneous 2-D measurements of time-evolving temperature and velocity, but inherently cannot address turbulent flows, where 3-D information is absolutely essential. While newly developed 3-D velocity techniques allow for 3-D time-evolving velocity measurements, we have no technique to provide both temperature and velocity in 3-D. The short-term research goal is to develop a novel technique, 3D Defocusing Particle Image Thermometry and Velocimetry (3DDPITV), to simultaneously measure time-evolving temperature and velocity fields within a volume. The long-term research goal is to apply this new technique to study coherent structures, their interactions, and their heat transfer/mixing characteristics in order to develop an understanding of the physics associated with their interactions. In addition, with this gained understanding and with the availability of three-dimensional data fields, subgrid-scale models to be used in LES simulations can be tested and, when appropriate, new models will be proposed. The experiment of choice is the backward-facing step. This flow has the advantage of having areas distinctly different and unique in their flow physics: (1) The separated shear layer is very similar to a mixing layer, thereby providing the opportunity to study the role and effects of coherent structures on mixing and heat transfer across a heated shear layer. (2) The unsteadiness of the shear layer's reattachment will provide an opportunity to study the effects of coherent structures on heat transfer in reattachments problems. (3) The recirculation zone, dominated by convection due to the primary vortex, will provide the opportunity to study heat transfer within recirculating regions, also dominated by coherent structures. (4) The redeveloping boundary layer beyond the reattachment region, dominated by the turbulent heat flux and directly related to the interaction of vortices within the shear layer that impinge upon the wall during reattachment, will provide an opportunity to study developing boundary layers. This research will address broader impacts in three primary areas: integrating education and research, enhancing infrastructure, and promoting benefits to society. The award has been funded by the Thermal Transport and Thermal Processing Program of the Chemical and Transport Systems Division, and it is part of a joint program involving Sandia National Laboratory and the NSF in the area of "Engineering Sciences for Modeling, Simulation, Decision-Making and Emerging Technologies.