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首页> 外文期刊>Experiments in Fluids: Experimental Methods and Their Applications to Fluid Flow >Dense velocity reconstruction from tomographic PTV with material derivatives
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Dense velocity reconstruction from tomographic PTV with material derivatives

机译：具有材料导数的层析X射线摄影机的密集速度重构

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摘要

A method is proposed to reconstruct the instantaneous velocity field from time-resolved volumetric particle tracking velocimetry (PTV, e.g., 3D-PTV, tomographic PTV and Shake-the-Box), employing both the instantaneous velocity and the velocity material derivative of the sparse tracer particles. The constraint to the measured temporal derivative of the PTV particle tracks improves the consistency of the reconstructed velocity field. The method is christened as pouring time into space, as it leverages temporal information to increase the spatial resolution of volumetric PTV measurements. This approach becomes relevant in cases where the spatial resolution is limited by the seeding concentration. The method solves an optimization problem to find the vorticity and velocity fields that minimize a cost function, which includes next to instantaneous velocity, also the velocity material derivative. The velocity and its material derivative are related through the vorticity transport equation, and the cost function is minimized using the limited-memory Broyden-Fletcher-Goldfarb-Shanno (L-BFGS) algorithm. The procedure is assessed numerically with a simulated PTV experiment in a turbulent boundary layer from a direct numerical simulation (DNS). The experimental validation considers a tomographic particle image velocimetry (PIV) experiment in a similar turbulent boundary layer and the additional case of a jet flow. The proposed technique ('vortex-in-cell plus', VIC+) is compared to tomographic PIV analysis (3D iterative cross-correlation), PTV interpolation methods (linear and adaptive Gaussian windowing) and to vortex-in-cell (VIC) interpolation without the material derivative. A visible increase in resolved details in the turbulent structures is obtained with the VIC+ approach, both in numerical simulations and experiments. This results in a more accurate determination of the turbulent stresses distribution in turbulent boundary layer investigations. Data from a jet experiment, where the vortex topology is retrieved with a small number of tracers indicate the potential utilization of VIC+ in low-concentration experiments as for instance occurring in large-scale volumetric PTV measurements.
机译：提出了一种利用瞬时速度和稀疏速度物质导数从时间分辨体积粒子跟踪测速法（PTV，例如3D-PTV，层析X射线摄影和Shake-the-Box）重建瞬时速度场的方法示踪剂颗粒。对PTV粒子轨迹的时间导数的测量约束提高了重建速度场的一致性。该方法被称为将时间倒入太空，因为它利用时间信息来提高体积PTV测量的空间分辨率。在空间分辨率受播种浓度限制的情况下，此方法变得有用。该方法解决了优化问题，以找到使成本函数最小的涡流场和速度场，其除了瞬时速度外还包括速度材料导数。速度和它的材料导数通过涡度传输方程关联，并且使用有限内存的Broyden-Fletcher-Goldfarb-Shanno（L-BFGS）算法将成本函数最小化。该过程是通过直接数值模拟（DNS）在湍流边界层中通过模拟PTV实验进行数值评估的。实验验证考虑了在相似的湍流边界层中进行层析层析粒子图像测速（PIV）实验以及喷射流的其他情况。将拟议的技术（“单元内涡旋加法”，VIC +）与断层成像PIV分析（3D迭代互相关），PTV插值方法（线性和自适应高斯开窗）以及单元涡旋（VIC）插值进行比较没有物质衍生。在数值模拟和实验中，都可以通过VIC +方法获得湍流结构中分辨细节的明显增加。这样可以更精确地确定湍流边界层研究中的湍流应力分布。来自喷气机实验的数据（其中使用少量示踪剂检索到了涡旋拓扑）表明在低浓度实验中VIC +的潜在利用，例如在大规模体积PTV测量中会发生这种情况。

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