High Magnification Telecentric Background Oriented Schlieren (BOS) and its Application to a Supersonic Turbulent Boundary Layer

Zhou, Terry; Gaskins, Jonathan; Swaine, Suzanne; Bane, Sally P.; Poggie, Jonathan; Blaisdell, Gregory A.

doi:10.2514/6.2023-2437

Cited by 6 publications

(1 citation statement)

References 17 publications

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“…Application of this exact telecentric BOS system to a Mach 2 turbulent boundary layer demonstrated improved spatial resolution (172 µm) of wallnormal density gradient profile measurements. The acquired density gradient profile also showed excellent agreement with high-fidelity computational results Zhou et al (2023Zhou et al ( , 2024.…”

Section: Bos Measurementssupporting

confidence: 81%

Comparison of Displacement Estimation Techniques for Background Oriented Schlieren of High-speed Compressible Turbulent Flows

Zhou,

Gaskins,

Poggie

et al. 2024

Preprint

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Background oriented schlieren (BOS) is a non-intrusive optical method for measuring density gradients in a fluid flow based on changes of local refractive index.The density gradients can be obtained by observing the displacement betweentwo images of a background pattern, with and without the presence of the flow.Existing methods to estimate displacements include block matching and optical flow. Image registration in computer vision seeks reasonable transformationsbetween two images such that one matches the other and has been under-utilizedin determining the displacement for BOS image processing. Deformable imageregistration (DIR) methods allow non-global transformations and are proposedas displacement estimation methods for processing BOS images. Numerical raytracing simulations are performed to generate synthetic BOS images of variousflows. The estimated density gradient results of block matching, optical flow,and DIR methods are compared to the ground truth (the path-averaged densitygradient of the schlieren object used in ray tracing) to assess and compare theirperformances. The performances of these methods are also validated on experimental BOS images to determine the displacement estimation method that ismost suitable for high-speed, turbulent flows.

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Section: Bos Measurementssupporting

confidence: 81%

Comparison of Displacement Estimation Techniques for Background Oriented Schlieren of High-speed Compressible Turbulent Flows

Zhou,

Gaskins,

Poggie

et al. 2024

Preprint

Self Cite

View full text Add to dashboard Cite

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Optimization of optical systems for background oriented schlieren

Zhou,

Gaskins,

Poggie

et al. 2024

Meas. Sci. Technol.

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Background oriented schlieren (BOS) is a non-intrusive optical method for measuring density gradients in a fluid flow based on variations of the local refractive index. The type of BOS optical system used, i.e., entocentric vs. telecentric, and the system design determine the accuracy and quality of the measurement. This work aims to optimize both types of optical systems to minimize the error for measurements of high-speed compressible turbulent boundary layers. Claims of the advantages offered by telecentric optical systems over entocentric systems are investigated, as well as the out-of-focus effects for types of systems. Numerical ray tracing simulations are performed using density fields from large eddy simulations (LES) of a Mach 2 turbulent boundary layer to generate synthetic but realistic BOS images. The results show that telecentric systems have lower overall error and less sensitivity. Contrary to recommendations by early BOS work, the best accuracy is achieved when density gradient object is placed outside of the depth of field of the optical system, for both entocentric and telecentric systems.

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Simultaneous Analysis of Liquid Film Instabilities and Properties of Swirl Sprays by Telecentric Shadowgraphy

Machado

Costa

Dias

et al. 2023

Preprint

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High Magnification Telecentric Background Oriented Schlieren (BOS) and its Application to a Supersonic Turbulent Boundary Layer

Cited by 6 publications

References 17 publications

Comparison of Displacement Estimation Techniques for Background Oriented Schlieren of High-speed Compressible Turbulent Flows

Comparison of Displacement Estimation Techniques for Background Oriented Schlieren of High-speed Compressible Turbulent Flows

Optimization of optical systems for background oriented schlieren

Simultaneous Analysis of Liquid Film Instabilities and Properties of Swirl Sprays by Telecentric Shadowgraphy

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