Tomographic background oriented schlieren using plenoptic cameras

Abstract

The development of a tomographic BOS implementation system utilizing up to four plenoptic cameras is presented. A systematic set of experiments was performed using a pair of solid dimethylpolysiloxan (PDMS) cylinders immersed in a nearly refractive index matched gylcerol/water solution to represent discrete flow features with known sizes, shapes, separation distances, and orientation. A study was conducted to assess the influence of these features on the accuracy of 3D reconstructions of the refractive index field. It was determined that the limited angular information collected by a single plenoptic camera is insufficient for single-camera 3D reconstructions. In multi-camera configurations, the additional views collected by a plenoptic camera were shown to improve the overall reconstruction accuracy compared to an equivalent single view per camera reconstruction, potentially reducing the number of overall cameras needed to achieve a desired accuracy. For the imaging of two cylinders, three or more cameras are generally needed to avoid significant ghosting artifacts in the reconstruction. Quantitative results are presented that show that: (1) two separate cylinders will be individually resolved as long as measurements from one camera are able to observe separation between the cylinders; (2) the error in the reconstructed 3D refractive index field increases as the size of the feature decreases; and (3) the use of volumetric masking within the reconstruction algorithm is critical in order to improve the accuracy of the solution.

A Mini-Review of Recent Developments in Plenoptic Background-Oriented Schlieren Technology for Flow Dynamics Measurement

“…Historical studies have shown that a single plenoptic camera in conventional plenoptic BOS systems is not sufficient for accurate BOS reconstruction [38]. Therefore, recent studies have explored plenoptic BOS systems based on multi-camera tomography technology and single-camera mirror-enhanced dual-view to achieve higher-accuracy 3D density field reconstruction, respectively.…”

“…Davis [38] has developed a tomographic BOS system using 1-4 plenoptic cameras and an iterative simultaneous algebraic reconstruction technique (SART) [39] algorithm to achieve the quantitative volume reconstruction of known 'static flow' fields. The workflow starts with the calibration of the microlens [40] and volume [27].…”

Simultaneous tomographic multi-component reconstructions using multispectral plenoptic cameras

“…5 The Advanced Flow Diagnostic Laboratory (AFDL) at Auburn University has demonstrated the ability to perform 3D reconstructions with a reduced number of cameras for particle image velocimetry (PIV), 2 particle tracking velocimetry (PTV), 6,7 and tomographic background oriented schlieren (Tomo-BOS). 8 Combustion processes are very complex with multiple reactions, oscillations, and potentially turbulent flow fields with multiscale features throughout the flow. All of these can effect the behavior of the combustion.…”