Air Force Research Laboratory, Aero-Effects Laboratory optical metrology system and performance

Wilcox, Christopher C.; Healey, Keith P.; Agena, Brian D.; Tuffli, Andrea L.

doi:10.1117/12.2568789

Cited by 5 publications

References 11 publications

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Dynamic mode decomposition based predictive model performance on supersonic and transonic aero-optical wavefront measurements

et al. 2021

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Air density variations around an airborne directed energy system distort a beam’s wavefront, resulting in degraded performance after propagation into the far field. Adaptive optics (AO) can be used to correct for these rapidly evolving aero-optical aberrations; however, in some conditions, the inherent latency between measurement and correction in state-of-the-art AO systems results in significantly reduced performance. Predictive AO control methods utilize future state predictions to compensate for rapidly evolving distortions and are promising techniques for mitigating this limitation. This paper demonstrates an application of the dynamic mode decomposition (DMD) method on turbulent boundary layer wavefront data from supersonic and transonic wind tunnel flow from the Air Force Research Laboratory’s Aero-Effects Laboratory. DMD is a lightweight algorithm used to isolate spatiotemporal patterns in a dataset into physically meaningful modes with associated dynamics, which were used to predict future states from a given wavefront. This method showed notable improvements in simulated wavefront correction, providing a reduction of residual wavefront distortion, measured as root mean square over the aperture, by up to 25.4% over a simulated latency model, which could accordingly result in higher laser system performance.

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Dynamic mode decomposition based predictive model performance on supersonic and transonic aero-optical wavefront measurements

et al. 2021

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Methodology of designing compact schlieren systems using off-axis parabolic mirrors

2022

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Schlieren imaging is widely adopted in applications where fluid dynamics features are of interest. However, traditional Z-type schlieren systems utilizing on-axis mirrors generally require large system footprints due to the need to use high f-number mirrors. In this context, off-axis parabolic (OAP) mirrors provide an attractive alternative for permitting the use of smaller f-number optics, but well-documented methodologies for designing schlieren systems with OAP mirrors are lacking. The present work outlines a ray-tracing-based workflow applied to the design of a modified Z-type schlieren system utilizing OAP mirrors. The ray-tracing analysis evaluates the defocus and distortion introduced by schlieren optics. The results are used along with system size and illumination efficiency considerations to inform the selection of optimal optical components capable of producing high-quality schlieren images while minimizing the system footprint. As a step-by-step demonstration of the design methodology, an example schlieren system design is presented. The example schlieren design achieved an image resolution of 1.1 lp/mm at 50% contrast, with a 60% reduction in system length compared to traditional Z-type systems with f/8 mirrors; distortion characterizations of the designed schlieren system showed good agreement with ray-tracing predictions, and the distortion can be corrected through image post-processing. The current work provides a systematic approach for the design of compact schlieren systems with OAP mirrors and demonstrates the utility of this underutilized option.

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Investigation of the wake region behind a hemispherical turret via laser Rayleigh scattering

Feng,

Jenkins,

George

2023

Appl. Opt.

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Planar and volumetric density measurements in the wake region behind a mounted hemispherical turret are obtained using laser Rayleigh scattering. The measurements are conducted in a Mach 2 wind tunnel facility at the Kirtland Air Force Base. Quantitative measurements of density and contour plots with lines of constant density are computed, thus enabling visualization of the turret wake’s fluid dynamics. A new, to the best of our knowledge, laser diagnostic methodology and configuration for capturing laser images is also presented. This methodology enables further suppression of background light scattering. Multi-dimensional single-shot and time-average measurements are recorded at multiple axial locations behind the turret. The images acquired reveal turbulent regions of the wake flow, and a discussion of the observed phenomena is presented.

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Air Force Research Laboratory, Aero-Effects Laboratory optical metrology system and performance

Cited by 5 publications

References 11 publications

Dynamic mode decomposition based predictive model performance on supersonic and transonic aero-optical wavefront measurements

Dynamic mode decomposition based predictive model performance on supersonic and transonic aero-optical wavefront measurements

Methodology of designing compact schlieren systems using off-axis parabolic mirrors

Investigation of the wake region behind a hemispherical turret via laser Rayleigh scattering

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