Toward Simultaneous Velocity and Density Measurements Using FLEET and Laser Rayleigh Scattering

Femtosecond laser electronic excitation tagging (FLEET) velocimetry and laser Rayleigh scattering are conducted concurrently and are evaluated for their suitability to measure velocity and density simultaneously in NASA Langleys 0.3-m Transonic Cryogenic Tunnel. FLEET velocimetry measurements are shown to be accurate to within 1.5 percent of the measured velocity throughout the facility testing envelope and exhibit a zero-velocity precision of 0.4 m/s. Rayleigh scattering density measurements indicate a characteristically linear dependence on flow density while having an accuracy within 5.4 percent of the measured density and a precision less than or equal to 6 percent. The preliminary assessment indicates that the joint technique would be advantageous for deployment in high-pressure, cryogenic test facilities

Investigating Potential Quantitative Trait Loci for Susceptibility to Experimental Autoimmune Encephalomyelitis in the BXD Family of Mice

Multiple Sclerosis is an autoimmune inflammatory condition that causes disability, axonal damage in the central nervous system, and eventual paralysis. One of the main risk factors for developing MS is genetics, with recent studies identifying multiple risk alleles associated the major histocompatibility complex. By utilizing the BXD family of mice, we investigated genetic factors that affect a BXD strain’s susceptibility to EAE, an inducible disease model for MS. We induced EAE in several BXD mice strains via an emulsion of complete Freund’s adjuvant and MOG35-55, and then measured disease severity in each strain. From there, we measured incidence rate of EAE, average peak clinical score, average day of disease onset, average length of acute onset, and average end clinical score. Afterwards, we tested EAE severity in the BXD43 mouse by identifying changes in immune cell populations in the spinal cord, changes in cytokines and chemokines, and distribution of the Fc multimer drug M019. Out of 16 strains tested, we identified 6 BXD strains susceptible to developing EAE, and found suggestive evidence of QTLs on chromosomes 5 and 11. We also found that the BXD43 strain expressed an extreme phenotype, categorized by increased immune cell populations in the spinal cord comparable to the B6 EAE model with pertussis toxin. These results suggest the potential for QTLs to exist on chromosomes 5 and 11, though more BXD strains need to be tested. Additionally, the BXD43 strain shows promise as an extreme phenotype model for EAE, which may serve as an effective model for primary progressive multiple sclerosis

Nitric Oxide PLIF Measurements in the Hypersonic Materials Environmental Test System (HYMETS)

A nonintrusive laser-based measurement system has been applied for the first time in the HYMETS (Hypersonic Materials Environmental Test System) 400 kW arc-heated wind tunnel at NASA Langley Research Center. Planar laser-induced fluorescence of naturally occurring nitric oxide (NO) has been used to obtain instantaneous flow visualization images, and to make both radial and axial velocity measurements. Results are presented at selected facility run conditions, including some in simulated Earth atmosphere (75% nitrogen, 20% oxygen, 5% argon) and others in simulated Martian atmosphere (71% carbon dioxide, 24% nitrogen, 5% argon), for bulk enthalpies ranging from 6.5 MJ/kg to 18.4 MJ/kg. Flow visualization images reveal the presence of large scale unsteady flow structures, and indicate nitric oxide fluorescence signal over more than 70% of the core flow for bulk enthalpies below about 11 MJ/kg, but over less than 10% of the core flow for bulk enthalpies above about 16 MJ/kg. Axial velocimetry was performed using molecular tagging velocimetry (MTV). Axial velocities of about 3 km/s were measured along the centerline. Radial velocimetry was performed by scanning the wavelength of the narrowband laser and analyzing the resulting Doppler shift. Radial velocities of ±0.5 km/s were measured

Rapid Optical Shutter, Chopper, Modulator and Deflector

An optical device with a light source and a detector is provided. A digital micromirror device positioned between the detector and the light source may deflect light beams projected from the light source. An aperture in front of the detector may block an incoming light beam from the detector when the incoming light beam is incident on the detector outside of a passable incident range and including an aperture opening configured to pass the incoming light beam to the detector when the incoming light beam is incident on the detector within a passable incident range. The digital micromirror device may rotate between a first position causing the light beam to pass through the aperture opening and a second position causing the light beam to be blocked by the aperture. The optical device may be configured to operate as a shutter, chopper, modulator and/or deflector

Design of a Multi-Color Plenoptic Camera for Snapshot Hyperspectral Imaging

The design of a custom camera lens including: a two-lens optical system, filter array, and iris has been developed enabling a greyscale plenoptic camera to acquire full field-of-view, 2D, instantaneous hyperspectral measurements. This work focuses on the use of 7 discrete color filters and their effect on the image quality. It was determined that the placement of the filters inside the aperture plane of the camera was paramount to mitigating image artifacts. In addition, design rules were developed such that the optimal optical parameters (image distance, working distance, and focal length) can be easily determined from a few charts

Numerical Investigation of PLIF Gas Seeding for Hypersonic Boundary Layer Flows

Numerical simulations of gas-seeding strategies required for planar laser-induced fluorescence (PLIF) in a Mach 10 air flow were performed. The work was performed to understand and quantify adverse effects associated with gas seeding and to compare different flow rates and different types of seed gas. The gas was injected through a slot near the leading edge of a flat plate wedge model used in NASA Langley Research Center's 31- Inch Mach 10 Air Tunnel facility. Nitric oxide, krypton, and iodine gases were simulated at various injection rates. Simulation results showing the deflection of the velocity field for each of the cases are presented. Streamwise distributions of velocity and concentration boundary layer thicknesses as well as vertical distributions of velocity, temperature, and mass distributions are presented for each of the cases. Relative merits of the different seeding strategies are discussed

Application of STARFLEET Velocimetry in the NASA Langley 0.3-Meter Transonic Cryogenic Tunnel

Selective two-photon absorptive resonance femtosecond laser electronic excitation tagging (STARFLEET) velocimetry is demonstrated for the first time in a NASA Langley wind tunnel with high repetition-rate and single-shot imaging. Experiments performed in the 0.3-meter Transonic Cryogenic Tunnel (TCT) allowed for testing at 300 K over a range of pressures (124 to 517 kPa) and Mach numbers (0.2-0.8) for freestream conditions and flow behind a cylindrical model. Measurement precision and accuracy are determined for the current set of experiments, as are signal intensity and lifetime. Precisions of 3-5 m/s (based on one standard deviation) were typical in the experiment; precisions better than 2% of the mean velocity were obtained for some of the highest velocity conditions. Agreement within a mean error of 3 m/s between STARFLEET freestream velocity measurements and facility DAS readings is demonstrated. STARFLEET is also shown to return spatially-resolved velocity profiles, though some binning of the signal is required

Micro-LiDAR velocity, temperature, density, concentration sensor

A light scatter sensor includes a sensor body in which are positioned a plurality of optical fibers. The sensor body includes a surface, in one end of each of the optical fibers terminates at the surface of the sensor body. One of the optical fibers is an illumination fiber for emitting light. A plurality of second optical fibers are collection fibers for collecting scattered light signals. A light sensor processor is connected to the collection fibers to detect the scattered light signals

100-kHz Rate Rayleigh Imaging for Combustion and Flow Diagnostics

Two-dimensional (2D) Rayleigh scattering (RS) imaging at an ultrahigh repetition rate of 100 kHz is demonstrated in non-reacting and reacting flows employing a high-energy burst-mode laser system. Image sequences of flow mixture fraction were directly derived from high-speed RS images. Additionally, a 2D instantaneous flow velocity field at 100 kHz was obtained through optical-flow-based analysis of the RS images. The technique was also applied to study turbulent flames having a near-constant Rayleigh cross section. The demonstrated high-speed RS technique in conjunction with optical-flow-based analysis provides non-intrusive, simultaneous measurements of the flow mixing and velocity field, extending the measurement capability of the RS technique to high-speed non-reacting and reacting flows