An Optical Method for Reconstructing Coherent Structures in Fluid Flows With a Single Camera Perspective

Jet noise in turbulent round jets has been linked to coherent structures with low-rank azimuthal wavenumbers. This work proposes a novel, non-intrusive method for optically measuring and reconstructing the density fields of axisymmetric and helical coherent structures within fluid flows using a single-camera perspective. By performing the proper orthogonal decomposition (POD) on 2D vector-displacement fields generated from background-oriented schlieren (BOS) we can extract structures associated with azimuthal-Fourier wavenumbers m = 0 and m = 1. Tomographic reconstruction can then be performed using various Abel-inversion techniques. We present a modified-Abel-inversion algorithm that allows for reconstruction of m = 1 structures from a single camera perspective. This work shows that the POD accurately extracts the modes of interest, and several reconstruction algorithms including three-point Abel, modified Fourier-Hankel and a bi-directional method produce accurate results.