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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 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.

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.

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 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.

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.

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