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Remote sensing tool reliably measures statistical properties of supersonic turbulence. Tool neither affects nor is adversely affected by flow field. Device determines characteristics of supersonic flow with optical system and provides method and apparatus for separating translational and rotational motions of turbulent structures in supersonic flow.
Optical flow cells are critical measurement interfaces, yet sampling under harsh conditions — high pressure, high temperature, particles, moisture, or corrosive gases — makes it difficult to maintain optical quality without perturbing the measurement. To address this challenge, a new flow cell was developed using a laminar coaxial flow field that separates the purge and sample flows. A dedicated test system was built to evaluate particle size distribution (PSD) measurements using a Malvern Panalytical Insitec analyzer. Results demonstrated that the sample flow alone defines the measurement zone, while the purge flow effectively shields the optical windows from deposition, eliminating sampling bias. The flow cell enables reliable PSD measurement under high pressure and temperature in moist, corrosive environments. As a key demonstration, the instrument was successfully deployed for on-line PSD measurement of flue gas from a 100 kWth pressurized oxy-coal combustor at 15 bara.
Resolution level and reconstruction quality in nano-computed tomography (nano-CT) are in part limited by the stability of microscopes, because the magnitude of mechanical vibrations during scanning becomes comparable to the imaging resolution, and the ability of the samples to resist radiation induced deformations during data acquisition. In such cases, there is no incentive in recovering the sample state at different time steps like in time-resolved reconstruction methods, but instead the goal is to retrieve a single reconstruction at the highest possible spatial resolution and without any imaging artifacts. Here we propose a distributed optimization solver for tomographic imaging of samples at the nanoscale. Our approach solves the tomography problem jointly with projection data alignment, nonrigid sample deformation correction, and regularization. Projection data consistency is regulated by dense optical flow estimated by Farneback's algorithm, leading to sharp sample reconstructions with less artifacts. Synthetic data tests show robustness of the method to Poisson and low-frequency background noise. We accelerated the solver on multi-GPU systems and validated the method on three nano-imaging experimental data sets.
X-ray imaging offers unique possibilities for Digital Image Correlation (DIC), opening the door for full-field deformation measurements of a test article in complex environments where optical DIC suffers severe biases or is impossible. While X-ray DIC has been performed in the past with standard DIC codes designed for optical images, the path-integrated nature of X-ray images places constraints on the experimental setup, predominantly that only a single surface of interest moves/deforms. These requirements are difficult to realize for many practical situations and limit the amount of information that can be garnered in a single test. Other X-ray based diagnostics such as Digital Volume Correlation (DVC) and Projection DVC (P-DVC) overcome these obstacles, but DVC is limited to quasi-static tests, and both DVC and P-DVC necessitate high-resolution computed tomography (CT) scan(s) and often require a potentially invasive pattern throughout the volume of the specimen. Here this work presents a novel approach to measure time-resolved displacements and strains on multiple surfaces from a single series of 2D, path-integrated (PI) X-ray images, called PI-DIC. The principle of optical flow or conservation of intensity—the foundation of DIC—was reframed for path-integrated images, for an exemplar setup comprised of two plates moving and deforming independently. Synthetic images were generated for rigid translations, rigid rotations, and uniform stretches, where each plate underwent a unique motion/deformation. Experimental specimens were fabricated (either an aluminum plate with tantalum features or a plastic plate with steel features) and the two specimens were independently translated. PI-DIC was successfully demonstrated with the synthetic images and validated with the experimental images. Prescribed displacements were recovered for each plate from the single set of path-integrated, deformed images. Errors were approximately 0.02 px for the synthetic images with 1.5% image noise, and 0.05 px for the experimental images. These results provide the foundation for PI-DIC to measure motion and deformation of multiple, independent surfaces with subpixel accuracy from a single series of path-integrated X-ray images.
Real-time tracking of wildfires and smoke is crucial for effective response, minimizing damage, protecting lives, and efficiently managing resources during fire emergencies. We develop a web-based AI-powered pipeline that detects wildfires in aerial video and estimates deployment-relevant behavior metrics, including cumulative burned area, burned-area growth rate, fire spread direction, and smoke dispersion. The system combines a YOLO-based detector with YCbCr-based fire segmentation, HSV-based smoke segmentation, Farneback optical flow, and centroid-based spatiotemporal tracking. Using ground sampling distance (GSD), pixel-level fire masks are converted to physical burned-area measurements by correlating fire pixel counts with camera altitude and tilt angle. We benchmark YOLO variants and non-YOLO baselines (GoogLeNet, CNN, DBN, Autoencoder, U-Net, and AlexNet) on the IEEE FLAME dataset and a newly created aerial frame dataset, Wildfire-DB. Cross-dataset evaluation uses a strict threshold-transfer protocol: decision thresholds are selected on FLAME validation and transferred unchanged to Wildfire-DB to quantify generalization under domain shift. YOLOv6 achieves the strongest cross-dataset frame-level fire detection on Wildfire-DB (ROC-AUC 0.8200, PR-AUC 0.8044, and transferred-threshold F1 0.7596). For tracking-oriented deployment requiring oriented localization, YOLO11-OBB provides the most reliable cross-dataset behavior among OBB-capable models while remaining computationally feasible. To analyze the feasibility of UAV deployment, we further measure inference efficiency using synchronized GPU and CPU power logs on a fixed workload of 1569 frames. YOLO-family models process the video in 5.73–12.47 seconds with net energy of 1247.28–1775.39 J, substantially lower latency and energy than heavier classification and reconstruction baselines. Overall, model optimality depends on operational objectives: YOLOv6 is best for cross-dataset detection robustness, whereas YOL...
A specific set of problems must be overcome before an optical flow field can be derived from an image sequence. These problems are discussed and an outline of a scheme for overcoming these obstacles is presented. A two-dimensional motion sensor is presented which is capable of measuring edge velocity in twelve separate directions at any point in the image. However, because of the aperture problem, the sensors can only determine the velocity component in the direction orthogonal to the edge. A second stage which uses a cosine-weighted voting scheme is used to derive the true flow field from the edge velocities. The whole system is based on a parallel network of connections and weights and is potentially a very fast method of obtaining the two-dimensional flow field.
A general review is given of several decades of research on the scaling laws and flowfield structures of swept shock wave/turbulent boundary layer interactions. Attention is further restricted to the experimental study and physical understanding of the steady-state aspects of these flows. The interaction produced by a sharp, upright fin mounted on a flat plate is taken as an archetype. An overall framework of quasiconical symmetry describing such interactions is first developed. Boundary-layer separation, the interaction footprint, Mach number scaling, and Reynolds number scaling are then considered, followed by a discussion of the quasiconical similarity of interactions produced by geometrically-dissimilar shock generators. The detailed structure of these interaction flowfields is next reviewed, and is illustrated by both qualitative visualizations and quantitative flow images in the quasiconical framework. Finally, the experimental techniques used to investigate such flows are reviewed, with emphasis on modern non-intrusive optical flow diagnostics.
Density variations in the aircraft boundary layer, turret wakes and shock waves create distortion of an optical wavefront through associated refractive index variations. Such effects can be observed directly through optical flow visualization. The application of holographic interferometry, wave shearing interferometry, and laser shadowgraph to observe and quantify such effects is described. Examples of the results from five different wind tunnel tests are presented. The examples show that diagnostics have provided valuable qualitiative and quantitiative data. These include (1) wake dimensions, (2) optical strength of the flow field, (3) turbulence characterization, (4) shock location, and (5) direct observation of areo-optical effects.
A wind tunnel experiment was conducted in the NASA Langley Research Center (LaRC) Unitary Plan Wind Tunnel (UPWT) to determine the effects of passive surface porosity on vortex flow interaction about a general research fighter configuration at supersonic speeds. Optical flow measurement and flow visualization techniques were used and included pressure-sensitive paint (PSP), schlieren, and laser vapor screen (LVS) These techniques were combined with force and moment and conventional electronically-scanned pressure (ESP) measurements to quantify and to visualize the effects of flow-through porosity applied to a wing leading-edge extension (LEX) mounted to a 65 deg cropped delta wing model.
A wind tunnel experiment was conducted in the NASA Langley Research Center (LaRC) Unitary Plan Wind Tunnel (UPW7) to determine the effects of passive surface porosity on vortex flow interactions about a general research fighter configuration at supersonic speeds. Optical flow measurement and flow visualization techniques were used and included pressure-sensitive paint (PSP), schlieren, and laser vapor screen (LVS). These techniques were combined with force and moment and conventional electronically-scanned pressure (ESP) measurements to quantify and to visualize the effects flow-through porosity applied to a wing leading-edge extension (LEX) mounted to a 65 deg cropped delta wing model.
Flow characteristics of NASA's 16-Inch Shock Tunnel are determined for purposes of providing hypersonic propulsion simulation capability. The key tunnel operating parameters are the incident shock speed and reservoir pressure and enthalpy. Flow characteristics of concern are the nozzle exit pressure, temperature, Mach number, Reynolds number, chemical composition, and flow uniformity. Surface mounted gages (for pressure and heat transfer) and nonintrusive optical flow diagnostics (emission and absorption spectroscopy and holographic interferometry) are used to verify tunnel conditions. Experimental measurements are used to validate computational analysis for predicting facility performance, and CFD is used to interpret the free stream optical diagnostic measurements.
A flow cell is a necessary measurement interface for some important optical analyzers. In our application of the flow cell, we utilize a state-of-the-art optical analyzer (Malvern Insitec) to measure particle size distribution and concentration in-situ in a sampled flow from a novel pressurized oxygen-fuel combustion process. However, since this sampling flow is a flow of moist flue gas under high temperature and pressure, and the flow contains particles and corrosive acid gases, it is an extreme challenge to obtain a flow cell with a high optical quality that does not perturb the measurement. To address this challenge, we propose a new design for an optical flow cell. By using a unique flow field in the proposed flow cell, the measurement zone can be well defined by the sampling flow, minimizing the influence of purge flow. To demonstrate this flow cell, we have built a test system, and conduct measurements utilizing polydisperse-particle standards (10-100 µm and 1-10 µm). The results reveal that the optical windows are well protected by the purge flow field, without risk of deposition from the sampling flow, and the Malvern Insitec can measure the particle size distribution by using this flow cell, without generating sample bias.
A wind tunnel experiment was conducted in the NASA Langley Research Center (LaRC) Unitary Plan Wind Tunnel (UPWT) to determine the effects of passive surface porosity and vertical tail placement on vortex flow development and interactions about a general research fighter configuration at supersonic speeds. Optical flow measurement and flow visualization techniques were used that featured pressure sensitive paint (PSP), laser vapor screen (LVS), and schlieren, These techniques were combined with conventional electronically-scanned pressure (ESP) and six-component force and moment measurements to quantify and to visualize the effects of flow-through porosity applied to a wing leading edge extension (LEX) and the placement of centerline and twin vertical tails on the vortex-dominated flow field of a 65 cropped delta wing model. Test results were obtained at free-stream Mach numbers of 1.6, 1.8, and 2.1 and a Reynolds number per foot of 2.0 million. LEX porosity promoted a wing vortex-dominated flow field as a result of a diffusion and weakening of the LEX vortex. The redistribution of the vortex-induced suction pressures contributed to large nose-down pitching moment increments but did not significantly affect the vortex-induced lift. The trends associated with LEX porosity were unaffected by vertical tail placement. The centerline tail configuration generally provided more stable rolling moments and yawing moments compared to the twin wing-mounted vertical tails. The strength of a complex system of shock waves between the twin tails was reduced by LEX porosity.
We report on measurements of temperature and enthalpy in the 60-MW Interaction Heating Facility (IHF) Arcjet at the NASA Ames Research Center. These quantities were measured at sub-second temporal resolution using tunable diode laser absorption spectroscopy, employing four Distributed Feedback (DFB) lasers to simultaneously probe the arcjet flow. Optical access was achieved through a specially-designed optical disk mounted in series with the modules of the arc heater in the add-air plenum of the column, which is positioned between the downstream electrodes and the nozzle. Gas at this measurement location serves as the reservoir condition for the ensuing supersonic expansion. Conditions in the reservoir are extreme, with temperatures between 5000-8000 K and pressures between 1-9 atm. Absorption from the 5S state of atomic oxygen at 777.2 nm and the 4P state of atomic nitrogen at 868.0 nm, two electronically-excited quantum states, formed the basis of the flow characterization measurements. Fiber-coupled laser light was pitched through the IHF via 1/8" ports in the optical disks, permitting optical access with minimal intrusion to the flow. Data was collected at 3 nominal conditions, a Low condition (1600 A, 2000 V, 0.13 kg/s), a Medium condition (3500 A, 5700 V, 0.61 kg/s), and a High condition (5900 A, 6800 V, 0.84 kg/s). Measurements suggest agreement within 1-2% between excited oxygen and excited nitrogen thermometry, indicating approximate thermal and chemical equilibration of the arcjet reservoir state, a result in keeping with long-standing assumptions of CFD modelling. Spatial gradients are found in the flow due to enthalpy loss to the facility walls, but the measured spatial non-uniformities are consistent with axi-symmetry. Measurements of specific enthalpy in the reservoir are also made utilizing excited oxygen and excited nitrogen absorption under the assumption of chemical equilibration.
The aero-optical effects associated with propagating a laser beam through aircraft turbulent boundary layers and shear layers were examined. Observed laser optical performance levels were compared with those inferred from aerodynamic measurements of unsteady densities and correlation lengths within these random flows. Optical instrumentation included a fast shearing interferometer (FSI). A 9 cm diameter collimated helium neon laser beam made a double pass through the aircraft random flow via an airfoil mirror located one meter from the fuselage. Typical aircraft turbulent boundary layer thickness measured 0.3 meters. Averaging many FSI generated modulation transfer functions (MTFs) and Fourier transforming, this average yields the expected far field intensity degradation associated with an aircraft mounted laser system. Aerodynamic instrumentation included fine wire probes to measure unsteady temperature and mass flux. A laser doppler velocimeter measured unsteady velocity within the flows. An analysis of these data yielded point measurements of unsteady density and correlation length.
An analytical method is formulated to account for distortions of optical interferograms used for studies of flow over airfoils experiencing dynamic stall. It is shown that such distortions are generated primarily due to optical path deflections in the test flow, caused by large density gradients. Such in-flow optical path deflections are neglected in conventional optical techniques for flow studies. The present method employs a ray analysis to determine these in-flow optical path deflections, and accurately predicts the interferogram distortions.
A preliminary conceptual design of a space-based solar pumped iodide laser emitting 1 megawatt of laser power for space-to-space power transmission is described. A near parabolic solar collector focuses sunlight onto the t-C4F9I (perfluoro-t butyl iodide) lasant within a transverse flow optical cavity. Using waste heat, a thermal system was designed to supply compressor and auxiliary power. System components were designed with weight and cost estimates assigned. Although cost is very approximate, the cost comparison of individual system components leads to valuable insights for future research. In particular, it was found that laser efficiency was not a dominant cost or weight factor, the dominant factor being the laser cavity and laser transmission optics. The manufacturing cost was approx. two thirds of the total cost with transportation to orbit the remainder. The flowing nonrenewable lasant comprised 20% of the total life cycle cost of the system and thus was not a major cost factor. The station mass was 92,000 kg without lasant, requiring approx. four shuttle flights to low Earth orbit where an orbital transfer vehicle will transport it to the final altitude of 6378 km.
Time-resolved optical imaging technique has been used to image the spatial distribution of small droplets and jet sprays in a highly scattering environment. The snake and ballistic components of the transmitted pulse are less scattered, and contain direct information about the sample to facilitate image formation as opposed to the diffusive components which are due to multiple collisions as a light pulse propagates through a scattering medium. In a time-gated imaging scheme, these early-arriving, image-bearing components of the incident pulse are selected by opening a gate for an ultrashort period of time and a shadowgram image is detected. Using a single shot cooled CCD camera system, the formation of water droplets is monitored as a function of time. Picosecond time-gated image of drop in scattering cells, spray droplets as a function of let speed and gas pressure, and model calcification samples consisted of calcium carbonate particles of irregular shapes ranging in size from 0. 1 to 1.5 mm affixed to a microscope slide have been measured. Formation produced by an impinging jet will be further monitored using a CCD with 1 kHz framing illuminated with pulsed light. The desired image resolution of the fuel droplets is on the 20 pm scale using early light through a highly scattering medium. A 10(exp -6)m displacement from a jet spray with a flow speed of 100 m/sec introduced by the ns grating pulse used in the imaging is negligible. Early ballistic/snake light imaging offers nondestructive and noninvasive method to observe the spatial distribution of hidden objects inside a highly scattering environment for space, biomedical, and materials applications. In this paper, the techniques we will present are time-resolved K-F transillumination imaging and time-gated scattered light imaging. With a large dynamic range and high resolution, time-gated early light imaging has the potential for improving rocket/aircraft design by determining jets shape and particle sizes. Refinements to these techniques may enable drop size measurements in the highly scattering, optically dense region of multi-element rocket injectors. These types of measurements should greatly enhance the design of stable, and higher performing rocket engines.