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Evaporation of streams of liquid droplets in environments at vacuum pressures below the vapor pressure has not been widely studied. Here, experiments and simulations are reported that quantify the change in droplet diameter when a steady stream of \ensuremath{\approx}100 \ensuremath{\mu}m diameter drops is injected into a chamber initially evacuated to $l{10}^{--8}\phantom{\rule{0.16em}{0ex}}\mathrm{bar}$. In experiments, droplets fall through the center of a 0.8 m long liquid nitrogen cooled shroud, simulating infinity radiation and vapor mass flux boundary conditions. Experimentally measured changes in drop diameters vary from \ensuremath{\approx}0 to 6 \ensuremath{\mu}m when the initial vapor pressure is increased from ${10}^{--6}$ to ${10}^{--3}$ bar by heating the liquid. Measured diameter changes are predicted by a model based on the Hertz-Knudsen equation. One uncertainty in the calculation is the ``sticking coefficient'' \ensuremath{\beta}. Assuming a constant \ensuremath{\beta} for all conditions studied here, predicted diameter changes best match measurements with $\ensuremath{\beta}\ensuremath{\approx}0.3$. This value falls within the range of \ensuremath{\beta} reported in the literature for organic liquids. Finally, at the higher vapor pressure conditions considered here, the drop stream disperses transverse to the main flow direction. This spread is attributed to forces imparted by an absolute pressure gradient produced by the evaporating stream.

We present spatial profiles of temperature and soot-volume-fraction statistics from a sooting, 2-m base diameter turbulent pool fire, burning a 10%-toluene/90%-methanol fuel mixture. Dual-pump coherent anti-Stokes Raman scattering and laser-induced incandescence are utilized for simultaneous point measurements of temperature and soot. The research fuel-blend used here results in a lower soot loading than real transportation fuels, but allows us to apply high-fidelity laser diagnostics for spatially resolved measurements in a fully turbulent, buoyant fire of meter-scale base size. Profiles of mean and rms fluctuations are radially resolved across the fire plume, both within the hydrocarbon-rich vapor-dome region near fuel pool, and higher within the actively burning region of the fire. The spatial evolution of the soot and temperature probability density functions is discussed. Soot fluctuations display significant intermittency across the full extent of the fire plume for the research fuel blend used. Simultaneous, spatially overlapped temperature/soot measurements permit us to obtain estimates of joint statistics that are presented as spatially resolved conditional averages across the fire plume, and in terms of a joint pdf obtained by including measurements from multiple spatial locations. Within the actively burning region of the fire, soot is observed to occupy a limited temperature range between ∼1000 and 2000 K, with peak soot concentration occurring at 1600–1700 K across the full radial extent of the fire plume, despite marked changes in the local temperature pdf across the same spatial extent. A wider range of soot temperatures is observed in the fuel vapor-dome region low in the pool fire, with detectable cold soot persisting into conditionally averaged statistics. The results yield insight into soot temperature across a wide spatial extent of a fully turbulent pool fire of meaningful size, which are valuable for development of soot radiative-emission models and for validation of fire fluid-dynamics codes.

The breakup of liquids due to aerodynamic forces has been widely studied. However, the literature contains limited quantified data on secondary droplet sizes, particularly as a function of time. Here, a column of liquid water is subjected to a step change in relative gas velocity using a shock tube. A unique digital in-line holography (DIH) configuration is proposed which quantifies the secondary droplets sizes, three-dimensional position, and three-component velocities at 100 kHz. Results quantify the detailed evolution of the characteristic mean diameters and droplet size-velocity correlations as a function of distance downstream from the initial location of the water column. Accuracy of the measurements is confirmed through mass balance. These data give unprecedented detail on the breakup process which will be useful for improved model development and validation.

We present broadband, dual-pump coherent anti-Stokes Raman scattering (CARS) measurements of N2 and O2 in 2 m diameter methanol pool fires. The design of the fiber-optically coupled CARS instrument for fire measurements is described. Single-shot temperatures and O2/N2 ratios were obtained simultaneously from a single measurement point at the center of the fire plume, and the measured temperature–oxygen statistics are compared to results of a time-domain-filtered Reynolds-averaged Navier-Stokes simulation. The measured and simulated mean fire temperatures agree to within 2–4%, with larger turbulent fluctuations observed in the measured temperatures. The behavior of the mean temperature conditioned on the O2/N2 ratio is similar for both simulation and experiment, but with simulated temperatures that are up to 10% lower than measured values for O2/N2 below 0.18. The uncertainty in the CARS measurements is described. A single-shot detection limit of O2/N2 = 0.06 was determined from the observed signal to nois...

We present a dual-pump coherent anti-Stokes Raman scattering (CARS) instrument, which has been constructed for the probing of temperature fluctuations in turbulent pool fires of meter-scale. The measurements were performed at the Fire Laboratory for Accreditation of Models and Experiments (FLAME) facility at Sandia National Laboratories, which provides a canonical fire plume in quiescent wind conditions, with well-characterized boundary conditions and access for modern laser-diagnostic probes. The details of the dual-pump CARS experimental facility for the fire-science application are presented, and single-laser-shot CARS spectra containing information from in-fire N2, O2, H2, and CO2 are provided. Single-shot temperatures are obtained from spectral fitting of the Raman Q-branch signature of N2, from which histograms that estimate the pdf of the enthalpy-averaged temperature fluctuations at the center of the fire plume are presented. Results from two different sooting fire experiments reveal excellent test-to-test repeatability of the fire plume provided by FLAME, as well as the CARS-measured temperatures. The accuracy and precision of the CARS temperatures is assessed from measurements in furnace-heated air, where the temperature can be accurately determined by a thermocouple. At temperatures in excess of 500 K, the furnace results show that the CARS measurements are accurate to within 2–3% and precise to within ±3–5% of the measured absolute temperature.

We present a detailed set of measurements from a piloted, sooting, turbulent C 2 H 4 - fueled diffusion flame. Hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering (CARS) is used to monitor temperature and oxygen, while laser-induced incandescence (LII) is applied for imaging of the soot volume fraction in the challenging jet-flame environment at Reynolds number, Re = 20,000. Single-laser shot results are used to map the mean and rms statistics, as well as probability densities. LII data from the soot-growth region of the flame are used to benchmark the soot source term for one-dimensional turbulence (ODT) modeling of this turbulent flame. The ODT code is then used to predict temperature and oxygen fluctuations higher in the soot oxidation region higher in the flame.

Burning aluminized propellants eject reacting molten aluminum drops with a broad size distribution. Prior to this work, in situ measurement of the drop size statistics and other quantitative flow properties was complicated by the narrow depth-of-focus of microscopic videography. Here, digital in-line holography (DIH) is demonstrated for quantitative volumetric imaging of the propellant plume. For the first time, to the best of our knowledge, in-focus features, including burning surfaces, drop morphologies, and reaction zones, are automatically measured through a depth spanning many millimeters. By quantifying all drops within the line of sight, DIH provides an order of magnitude increase in the effective data rate compared to traditional imaging. This enables rapid quantification of the drop size distribution with limited experimental repetition.

Digital in-line holography (DIH) is an optical technique which measures particle sizes and their three-dimensional (3D) positions and velocities. Here DIH and a recently proposed hybrid method of particle detection are applied to quantify the secondary droplets generated by the impact of a single drop on a thin film. By leveraging the expected symmetry between in-plane and out-of-plane velocities, experimental depth uncertainty is measured to be approximately 0.7 of the mean droplet diameter. Furthermore, comparison with previous measurements using alternative techniques shows good agreement with the measured temporal evolution of drop number, size, and velocity components. Finally, the power of DIH to extract the complex 3D morphology of the protruding jets is demonstrated.

A new method to quantify three-dimensional particle fields using digital in-line holography is presented. From sequentially recorded holograms, the maximum cross correlation of edge sharpness within local particle windows yields an accurate measurement of particle displacements. Experiments demonstrate out-of-plane displacement uncertainty of approximately 0.15 mean particle diameters, which is roughly an order-of-magnitude improvement compared with alternative methods. Application to shotgun pellets demonstrates robustness despite experimental noise.

Thermal interface materials (TIMs) serve a critical role in thermal management by enhancing heat transfer across contact interfaces. Specifically, they are most commonly used in electronics to enhance the flow of heat from source to sink by decreasing the overall thermal resistance of the system. In space, these materials are exposed to high doses of Gamma radiation due to the lack of an atmosphere to serve as an absorbing medium. With typical design lifetimes of 5 to 10 years, total radiation exposure can be significant and can adversely affect the thermal contact resistance (TCR) of the TIM. In this manuscript, we report the effect of radiation-aging on the TCC of several commercially available electrically insulating, thermally conductive interface materials that are commonly used in satellite systems. Although radiation dose levels can vary significantly during the course of a space mission, a dosing of 10 Mrad per year for TIMs is a reasonable estimate. The TIMs were aged in a Gamma cell at a rate of 250 rad/s to total doses of 50 and 100 Mrad to simulate mission lengths of 5 and 10 years, respectively. The TCR of each radiation-aged sample, as well as un-aged samples, were measured under vacuum (less than 3 × 10−4 Pa). Radiation-aging of the TIMs led to a significant increase in the TCR of the tested samples. For example, the pressure-dependent TCR was shown to increase 20–150% for Cho-Therm 1671 and 50–250% for ThermaCool R10404 samples subjected to 50 Mrad of gamma-ray irradiation. These results show that radiation-aging of TIMs cannot be ignored in the design and simulation of space systems.Copyright © 2013 by ASME

We present what we believe to be the first application of the laser-induced incandescence (LII) technique to large-scale fire testing. The construction of an LII instrument for fire measurements is presented in detail. Soot volume fraction imaging from 2 m diameter pool fires burning blended toluene/methanol liquid fuels is demonstrated along with a detailed report of measurement uncertainty in the challenging pool fire environment. Our LII instrument relies upon remotely located laser, optical, and detection systems and the insertion of water-cooled, fiber-bundle-coupled collection optics into the fire plume. Calibration of the instrument was performed using an ethylene/air laminar diffusion flame produced by a Santoro-type burner, which allowed for the extraction of absolute soot volume fractions from the LII images. Single-laser-shot two-dimensional images of the soot layer structure are presented with very high volumetric spatial resolution of the order of 10(-5) cm3. Probability density functions of the soot volume fraction fluctuations are constructed from the large LII image ensembles. The results illustrate a highly intermittent soot fluctuation field with potentially large macroscale soot structures and clipped soot probability densities.

Pump-probe transient thermoreflectance (TTR) techniques are powerful tools for measuring the thermophysical properties of thin films, such as thermal conductivity, Λ, or thermal boundary conductance, G. This paper examines the assumption of one-dimensional heating on, Λ and G, determination in nanostructures using a pump-probe transient thermoreflectance technique. The traditionally used one-dimensional and axially symmetric cylindrical conduction models for thermal transport are reviewed. To test the assumptions of the thermal models, experimental data from Al films on bulk substrates (Si and glass) are taken with the TTR technique. This analysis is extended to thin film multilayer structures. The results show that at 11 MHz modulation frequency, thermal transport is indeed one dimensional. Error among the various models arises due to pulse accumulation and not accounting for residual heating.

Laser-induced incandescence measurements have recently been obtained from 10% and 30% toluene in methanol blended fuel pool fires of 2-m diameter. Calibration of the instrument was performed using an ethylene/air laminar diffusion flame produced by a Santoro-type burner which allowed the extraction of absolute soot-volume-fractions from these images. Performance of the optical probe was characterized using the laminar diffusion flame and corrections were implemented for signal dependence upon detector gain, flat field, and location within the probe laser sheet when processing the images. Probability density functions of the soot-volume fraction were constructed for the blended fuels used in this study and the mean values were determined to be 0.0077 and 0.028 ppm for the 10% and 30% blended fuels, respectively. Signal trapping was estimated for the two types of blended fuel and it was determined to be negligible for the 10% toluene/methanol blend and require {approx}10% correction for the 30% toluene/methanol blend.

A joint temperature/soot laser-based optical diagnostic was developed for the determination of the joint temperature/soot probability density function (PDF) for hydrocarbon-fueled meter-scale turbulent pool fires. This Laboratory Directed Research and Development (LDRD) effort was in support of the Advanced Simulation and Computing (ASC) program which seeks to produce computational models for the simulation of fire environments for risk assessment and analysis. The development of this laser-based optical diagnostic is motivated by the need for highly-resolved spatio-temporal information for which traditional diagnostic probes, such as thermocouples, are ill-suited. The in-flame gas temperature is determined from the shape of the nitrogen Coherent Anti-Stokes Raman Scattering (CARS) signature and the soot volume fraction is extracted from the intensity of the Laser-Induced Incandescence (LII) image of the CARS probed region. The current state of the diagnostic will be discussed including the uncertainty and physical limits of the measurements as well as the future applications of this probe.

The development of a combined dual-pump coherent anti-Stokes Raman scattering (CARS) and laser-induced incandescence (LII) instrument for the spatially resolved measurement of subgrid-scale temperature/soot data in liquid-fueled pool fires is discussed. Temperature pdfs obtained from the N2 Qbranch CARS signal at the center of a 2-m-diameter toluene/methanol pool fire are summarized. A more detailed discussion of the recent development of a water-jacketed, fiber-optically coupled LII probe for in-fire soot-volume-fraction imaging is presented. Tomographically resolved laser-light-extinction characterization of the soot field in a fuel-rich premixed ethylene-air flame used for calibration of the LII technique is reported, and the performance of the LII-imaging system in the calibration flame is discussed. Twodimensional LII images, which are representative of the spatially resolved, instantaneous soot-volumefraction distributions in a 2-m-diameter toluene/methanol pool fire are provided, and a histogram of the LII signal that is representative of the pdf of the soot-volume-fraction fluctuations at the center of the fire are extracted from these in-fire imaging results. These data demonstrate the potential of the CARS and LII instruments to determine temperature and soot volume fraction in a sooting fire with high temporal and spatial resolution.

Pump-probe transient thermoreflectance (TTR) techniques are powerful tools for measuring thermophysical properties of thin films, such as thermal conductivity, Λ, or thermal boundary conductance, G. This paper examines the assumption of one-dimensional heating on Λ and G determination in nanostructures using a pump-probe transient thermoreflectance technique. The traditionally used one dimensional and radial (3D) models are reviewed. To test the assumptions of the thermal models, experimental data from Al films on bulk substrates (Si and glass) are taken with the TTR technique. This analysis is extended to thin film multilayer structures. Results show that at 11 MHz modulation frequency, thermal transport is indeed one dimensional. Error among the various models arises due to pulse accumulation and not accounting for residual heating.Copyright © 2009 by ASME

A subscale experiment has been constructed using fins mounted on one wall of a transonic wind tunnel to investigate the influence of fin trailing vortices upon downstream control surfaces. Data were collected using a fin balance instrumenting the downstream fin to measure the aerodynamic forces of the interaction, combined with stereoscopic particle image velocimetry to determine vortex properties. The fin balance data show that the response of the downstream fin essentially is shifted from the baseline single-fin data dependent upon the angle of attack of the upstream fin. FreestreamMach number and the spacing between fins have secondary effects. The velocimetry shows the increase in vortex strength with upstream fin angle of attack, but no variation with Mach number can be discerned in the normalized velocity data. Correlations between the force data and the velocimetry indicate that the interaction is fundamentally a result of an angle of attack superposed upon the downstream fin by the vortex shed from the upstream fin tip. The Mach number influence arises from differing vortex lift on the leading edge of the downstream fin even when the impinging vortex is Mach invariant.

Particle-Image Velocimetry is used to study the cyclic modulation of the wall shear stress and turbulence properties of an oscillating channel flow. The PIV instrument employed here utilizes a dynamically adjusted delay between the laser pulses to accommodate the wide variations in velocity encountered in the oscillating flow. Both high- and low-magnification digital PIV recordings are obtained to reveal the near-wall boundary layer structure and wall shear stress, as well as the full-field turbulence throughout the channel. We present wall-shear-stress and global turbulence data for Stokes-thickness Reynolds numbers of Reδ = 1220, 2033, and 2875. The results reveal a fully developed turbulent state, relaminarization, and an explosive transition back to turbulence. The flow is examined in detail for the case at Reδ = 1220, where instantaneous PIV realizations at low magnification reveal the structure of the flow during relaminarization and transition back to turbulence. High-magnification PIV results are used to reveal the phase modulation of the mean velocity profiles in the viscous sublayer and logarithmic layers through the half cycle and quantitative profiles of in-plane Reynolds stresses and turbulence production are presented. To our knowledge, this is the first PIV investigation of this canonical unsteady turbulent channel flow and these results represent a needed contribution to the limited turbulence data which exists for unsteady wall flows.

Force and moment measurements have been made on an instrumented subscale fin model at transonic speeds in Sandia’s Trisonic Wind Tunnel to ascertain the effects of Mach number and angle of attack on the interaction of a trailing vortex with a downstream control surface. Components of normal force, bending moment, and hinge moment were measured on an instrumented fin downstream of an identical fin at Mach numbers between 0.85 and 1.24, and combinations of angles of attack between -5o and 10o for both fins. The primary influence of upstream fin deflection is to shift the downstream fin’s forces in a direction consistent with the vortex-induced angle of attack on the downstream fin. Secondary nonlinear effects of vortex lift were found to increase the slopes of normal force and bending moment coefficients when plotted versus fin deflection angle. This phenomenon was dependent upon Mach number and the angles of attack of both fins. The hinge moment coefficient was also influenced by the vortex lift as the center of pressure was pushed aft with increased Mach number and total angle of attack.

Presented here are broadband, dual-pump CARS measurements which were performed in a 2-meter diameter methanol pool fire. Single-shot temperature and relative mole fractions were obtained simultaneously. The temperatures were compared to traditional thermocouple measurements in the pool fire. It was found that the CARS mean temperatures agree to within 4% of the thermocouple measurements, while the RMS temperatures were an order of magnitude less for the thermocouple. The accuracy and precision of the single-shot temperature measurements were characterized by comparison to a laboratory standard. It was determined that between 500-1400 K the CARS instrument was accurate to better than 4% and the measurements were reproducible to within 6%.

A three-component balance system has been developed and implemented to measure the forces and moments on a sub-scale missile fin model interacting with the wake and shed vortex from an upstream fin. Measurements were made from Mach 0.5 – 0.8 with both the upstream and downstream fins pitched between -5° and 10° angle of attack. The results show that the downstream fin’s forces and moments are shifted from the baseline single fin values dependent on the angle of attack of the upstream fin. Mach Number had only a secondary effect and its influence was found to grow stronger as the angles of attack of the upstream and downstream fins diverged.

A method to measure interfacial mechanical properties at high temperatures and in a controlled atmosphere has been developed to study anodized aluminum surface coatings at temperatures where the interior aluminum alloy is molten. This is the first time that the coating strength has been studied under these conditions. We have investigated the effects of ambient atmosphere, temperature, and surface finish on coating strength for samples of aluminum alloy 7075. Surprisingly, the effective Young's modulus or strength of the coating when tested in air was twice as high as when samples were tested in an inert nitrogen or argon atmosphere. Additionally, the effective Young's modulus of the anodized coating increased with temperature in an air atmosphere but was independent of temperature in an inert atmosphere. The effect of surface finish was also examined. Sandblasting the surface prior to anodization was found to increase the strength of the anodized coating with the greatest enhancement noted for a nitrogen atmosphere. Machining marks were not found to significantly affect the strength.

A sub-scale experiment has been constructed using fins mounted on one wall of a transonic wind tunnel to investigate the influence of fin tip vortices upon downstream control surfaces. Data are collected using a fin balance mounted on the downstream fin to measure the aerodynamic forces of the interaction, combined with stereoscopic Particle Image Velocimetry to measure vortex properties. The fin balance data show that the response of the downstream fin essentially is shifted from the baseline single-fin data dependent upon the angle of attack of the upstream fin. Freestream Mach number and the spacing between fins have secondary effects. The velocimetry shows that the vortex strength increases markedly with upstream fin angle of attack, though even an uncanted fin generates a noticeable wake. No Mach number effect can be discerned in the normalized data, but measurements taken progressively further from the fin trailing edge show the decay in vortex strength with downstream distance. Correlations between the force data and the velocimetry suggest that the interaction is fundamentally a result of an angle of attack induced upon the downstream fin by the vortex shed from the upstream fin tip.

We report an application of coherent anti-Stokes Raman scattering (CARS) to full-scale fire testing. A CARS instrument has been constructed at the newly commissioned FLAME (Fire Laboratory for Accreditation of Models and Experiments) facility at Sandia, where the CARS system has been used for thermometry in 2-m-diameter, turbulent pool fires. The details of a CARS instrument for probing the challenging pool-fire environment are presented, along with the construction of the unique new FLAME facility itself, which has been designed to accommodate optical and laser-based diagnostics to full-scale fire experimentation. Single-shot CARS spectra and best-fit temperatures from turbulent pool fires are presented, and an estimate of the pdf of the temperature fluctuations from the pool-fire environment is obtained.

A previously-developed experimental facility has been used to determine gas-surface thermal accommodation coefficients from the pressure dependence of the heat flux between parallel plates of similar material but different surface finish. Heat flux between the plates is inferred from measurements of temperature drop between the plate surface and an adjacent temperature-controlled water bath. Thermal accommodation measurements were determined from the pressure dependence of the heat flux for a fixed plate separation. Measurements of argon and nitrogen in contact with standard machined (lathed) or polished 304 stainless steel plates are indistinguishable within experimental uncertainty. Thus, the accommodation coefficient of 304 stainless steel with nitrogen and argon is estimated to be 0.80 {+-} 0.02 and 0.87 {+-} 0.02, respectively, independent of the surface roughness within the range likely to be encountered in engineering practice. Measurements of the accommodation of helium showed a slight variation with 304 stainless steel surface roughness: 0.36 {+-} 0.02 for a standard machine finish and 0.40 {+-} 0.02 for a polished finish. Planned tests with carbon-nanotube-coated plates will be performed when 304 stainless-steel blanks have been successfully coated.

Joint fuel Raman and filtered Rayleigh-scattering (FRS) imaging is demonstrated in a laminar methane-air diffusion flame. These experiments are, to our knowledge, the first reported extension of the FRS technique to nonpremixed combustion. This joint imaging approach allows for correction of the FRS images for the large variations in Rayleigh cross section that occur in diffusion flames and for a secondary measurement of fuel mole fraction. The temperature-dependent filtered Rayleigh cross sections are computed with a six-moment kinetic model for calculation of major-species Rayleigh-Brillouin line shapes and a flamelet-based model for physically judicious estimates of gas-phase chemical composition. Shot-averaged temperatures, fuel mole fractions, and fuel number densities from steady and vortex-strained diffusion flames stabilized on a Wolfhard-Parker slot burner are presented, and a detailed uncertainty analysis reveals that the FRS-measured temperatures are accurate to within +/- 4.5 to 6% of the local absolute temperature.

A combined experimental/modeling study was conducted to better understand the critical role of gas-surface interactions in rarefied gas flows. An experimental chamber and supporting diagnostics were designed and assembled to allow simultaneous measurements of gas heat flux and inter-plate gas density profiles in an axisymmetric, parallel-plate geometry. Measurements of gas density profiles and heat flux are made under identical conditions, eliminating an important limitation of earlier studies. The use of in situ, electron-beam fluorescence is demonstrated as a means to measure gas density profiles although additional work is required to improve the accuracy of this technique. Heat flux is inferred from temperature-drop measurements using precision thermistors. The system can be operated with a variety of gases (monatomic, diatomic, polyatomic, mixtures) and carefully controlled, well-characterized surfaces of different types (metals, ceramics) and conditions (smooth, rough). The measurements reported here are for 304 stainless steel plates with a standard machined surface coupled with argon, helium, and nitrogen. The resulting heat-flux and gas-density-profile data are analyzed using analytic and computational models to show that a simple Maxwell gas-surface interaction model is adequate to represent all of the observations. Based on this analysis, thermal accommodation coefficients for 304 stainless steel coupled with argon, nitrogen, and helium are determined to be 0.88, 0.80, and 0.38, respectively, with an estimated uncertainty of {+-}0.02.

Simulation-based life-cycle-engineering and the ASCI program have resulted in models of unprecedented size and fidelity. The validation of these models requires high-resolution, multi-parameter diagnostics. Within the thermal-fluids disciplines, the need for detailed, high-fidelity measurements exceeds the limits of current engineering sciences capabilities and severely tests the state of the art. The focus of this LDRD is the development and application of filtered Rayleigh scattering (FRS) for high-resolution, nonintrusive measurement of gas-phase velocity and temperature. With FRS, the flow is laser-illuminated and Rayleigh scattering from naturally occurring sources is detected through a molecular filter. The filtered transmission may be interpreted to yield point or planar measurements of three-component velocities and/or thermodynamic state. Different experimental configurations may be employed to obtain compromises between spatial resolution, time resolution, and the quantity of simultaneously measured flow variables. In this report, we present the results of a three-year LDRD-funded effort to develop FRS combustion thermometry and Aerosciences velocity measurement systems. The working principles and details of our FRS opto-electronic system are presented in detail. For combustion thermometry we present 2-D, spatially correlated FRS results from nonsooting premixed and diffusion flames and from a sooting premixed flame. The FRS-measured temperatures are accurate to within {+-}50 Kmore » (3%) in a premixed CH4-air flame and within {+-}100 K for a vortex-strained diluted CH4-air diffusion flame where the FRS technique is severely tested by large variation in scattering cross section. In the diffusion flame work, FRS has been combined with Raman imaging of the CH4 fuel molecule to correct for the local light scattering properties of the combustion gases. To our knowledge, this is the first extension of FRS to nonpremixed combustion and the first use of joint FRS-Raman imaging. FRS has been applied to a sooting C2H4-air flame and combined with LII to assess the upper sooting limit where FRS may be utilized. The results from this sooting flame show FRS temperatures has potential for quantitative temperature imaging for soot volume fractions of order 0.1 ppm. FRS velocity measurements have been performed in a Mach 3.7 overexpanded nitrogen jet. The FRS results are in good agreement with expected velocities as predicted by inviscid analysis of the jet flowfield. We have constructed a second FRS opto-electronic system for measurements at Sandia's hypersonic wind tunnel. The details of this second FRS system are provided here. This facility is currently being used for velocity characterization of these production hypersonic facilities.« less

Filtered Rayleigh Scattering (FRS) is demonstrated in a premixed, sooting ethylene-air flame. In sooting flames, traditional laser-based temperature-imaging techniques such linear (unfiltered) Rayleigh scatting (LRS) and planar laser-induced fluorescence (PLIF) are rendered intractable due to intense elastic scattering interferences from in-flame soot. FRS partially overcomes this limitation by utilizing a molecular iodine filter in conjunction with an injection-seeded Nd:YAG laser, where the seeded laser output is tuned to line center of a strong iodine absorption transition. A significant portion of the Doppler-broadened molecular Rayleigh signal is then passed while intense soot scattering at the laser line is strongly absorbed. In this paper, we demonstrate the feasibility of FRS for sooting flame thermometry using a premixed, ethylene-air flat flame. We present filtered and unfiltered laser light-scattering images, FRS temperature data, and laser-induced incandescence (LII) measurements of soot volume fraction for fuel-air equivalence ratios of φ = 2.19 and 2.24. FRS-measured product temperatures for these flames are nominally 1500 K. The FRS temperature and image data are discussed in the context of the soot LII results and a preliminary estimate of the upper sooting limit for our FRS system of order 0.1 ppm volume fraction is obtained.

A Doppler global velocimetry (DGV) system has been designed, assembled, and tested for use in a Mach 3.7 overexpanded jet prior to future implementation in a hypersonic wind tunnel. Measurements were made using an iodine cell pressure-broadened with nitrogen buffer gas to selectively absorb light from a frequency-doubled Nd:YAG laser scattering from condensed ethanol particles in the jet flow. Details of the present implementation of the measurement technique and data reduction are presented herein. Calibrations of a pressure-broadened iodine cell have shown that the induced absorption line shift can create velocity biases unless a second iodine cell is scanned simultaneously to provide an independent frequency reference. Exploratory velocity data in the jet have been acquired that are experimentally repeatable and consistent with physical expectations, which lends confidence towards the performance of the assembled system.

This paper describes the application of a filtered-Rayleigh-scattering (FRS) instrument for nonintrusive temperature imaging in a vortex-driven diffusion flame. The FRS technique provides quantitative, spatially correlated temperature data without the flow intrusion or time lag associated with physical probes. Use of a molecular iodine filter relaxes the requirement for clean, particulate-free flowfields and offers the potential for imaging near walls, test section windows and in sooty flames, all of which are preculded in conventional Rayleigh imaging, where background interference from these sources typically overwhelms the weak molecular scattering signal. For combustion applications, FRS allows for full-field temperature imaging without chemical seeding of the flowfield, which makes FRS an attractive alternative to other laser-based imaging methods such as planar laser-induced fluorescencs (PLIF). In this work, the details of our FRS imaging system are presented and temperature measurements from an acoustically forced diffusion flame are provided. The local Rayleigh crosssection is corrected using Raman imaging measurements of the methane fuel molecule, which are then correlated to other major species using a laminar flamelet approach. To our knowledge, this is the first report of joint Raman/FRS imaging for nonpremixed combustion. Measurements are presented from flames driven at 7.5 Hz, where a single vortex stretches the flame, and at 90 Hz, where two consecutive vortices interact to cause a repeatable strain-induced flame-quenching event.

This paper reports non-intrusive temperature and velocity imaging measurements in gas-phase flows using acetone planar laser-induced fluorescence (PLIF) thermometry and particle image velocimetry (PIV). The details of the combined PLIF/PIV instrument and the demonstration flow facilities are provided and results are presented from a turbulent Rayleigh-Benard convection flow (PLIF only) and from an unsteady laminar impinging jet flow (combined PLIF/PIV). The data show that PLIF temperature imaging at laboratory scales is most effective for characteristic temperature differences on the order of 100 K of more. Simultaneous gas-phase temperature-velocity images are presented which show that PLIF-PIV holds promise for detailed laboratory scale measurements for gas-phase convective heat-transfer applications at high temperature differences.Copyright © 2002 by ASME