Abstract

This work presents a novel numerical procedure for reconstructing volumetric density and velocity fields from planar laser-induced fluorescence (PLIF) and stereoscopic particle image velocimetry (SPIV) data. This new method is theoretically and practically demonstrated to provide more accurate 3D vortical structures and density fields in high shear flows than reconstruction methods based on the mean convective velocity. While Taylor’s hypothesis of frozen turbulence is commonly applied by using the local mean streamwise velocity, the proposed algorithm uses the measured local instantaneous velocity for data convection. It consists of a step-by-step reconstruction based on a mixed Lagrangian–Eulerian solver that includes the 3D interpolation of scattered flow data and that relaxes the Taylor’s hypothesis by iterative enforcement of the incompressibility constraint on the velocity field. This methodology provides 3D fields with temporal resolution, spatial resolution, and accuracy comparable to that of real 3D snapshots, thus providing a practical alternative to tomographic measurements. The procedure is validated using numerical data of the constant-density channel flow available on the Johns Hopkins University Turbulence Database (JHTDB), showing the accurate reconstruction of the 3D velocity field. The algorithm is applied to an experimental dataset of PLIF and SPIV measurements of a variable-density jet flow, demonstrating its capability to provide 3D velocity and density fields that are more consistent with the Navier–Stokes equations compared to the mean flow convective method.

Graphic abstract

中文翻译：

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超越泰勒的假设：针对密度和剪切流的速度和密度场的新型体积重建

摘要

这项工作提出了一种新的数值程序，用于从平面激光诱导荧光（PLIF）和立体粒子图像测速（SPIV）数据重建体积密度和速度场。与基于平均对流速度的重建方法相比，该新方法在理论上和实践上都得到了证明，可以在高剪切流中提供更准确的3D涡旋结构和密度场。尽管通常通过使用局部平均流向速度来应用泰勒关于冻结湍流的假设，但所提出的算法使用测得的局部瞬时速度进行数据对流。它由基于拉格朗日-欧拉混合求解器的逐步重构组成，包括离散流数据的3D插值，并且通过对速度场进行不可压缩约束的迭代实施来放松泰勒的假设。这种方法为3D场提供了与真实3D快照相当的时间分辨率，空间分辨率和准确性，从而为层析成像测量提供了一种实用的替代方法。使用可在约翰霍普金斯大学湍流数据库（JHTDB）上获得的恒定密度通道流量的数值数据验证了该过程，该数据显示了3D速度场的准确重建。将该算法应用于可变密度射流的PLIF和SPIV测量的实验数据集，

图形摘要