A joint experimental and computational study was performed to evaluate the capability of the Sandia Fire Code VULCAN to predict thermocouple response temperature. Thermocouple temperatures recorded by an Inconel-sheathed thermocouple inserted into a near-adiabatic flat flame were predicted by companion VULCAN simulations. The predicted thermocouple temperatures were within 6% of the measured values, with the error primarily attributable to uncertainty in Inconel 600 emissivity and axial conduction losses along the length of the thermocouple assembly. Hence, it is recommended that future thermocouple models (for Inconel-sheathed designs) include a correction for axial conduction. Given the remarkable agreement between experiment and simulation, it is recommended that the analysis be repeated for thermocouples in flames with pollutants such as soot.4

The initiation and detonation properties of explosives are often empirically correlated to density, surface area, and particle size. Although these correlations are sometimes used successfully to predict the performance of bulk samples, the data are spatially averaged, which unfortunately muddles information critical to understanding fundamental processes. Density and surface area are essentially an indirect measure of porosity, which is arguably a more appropriate metric in many applications. We report the direct characterization of porosity in polycrystalline molecular crystal explosives by focused ion beam nanotomography, a technique that is typically reserved for robust materials such as ceramics and metals. The resulting three-dimensional microstructural data are incredibly rich, promising a substantial advance in our ability to unravel the processes governing initiation and detonation of molecular crystal explosives. In a larger context, this work demonstrates that focused ion beam nanotomography may be successfully extended to the investigation of nanoscale porosity in other molecular crystal or polymer materials.

This PIRT exercise identifies a number of factors which can influence thermocouple readings made in fires. Identified factors are: (a) the fuel/oxidizer equivalence ratio and its effect on readings, (b) the influence of the state of oxidation and variation with time for the thermocouple sheath, (c) the convection coefficient models and how experimental readings are influenced by thermocouple diameter and yaw angle, (d) response time of a MIMS thermocouple, and (e) thermocouple end effects.

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A virtual thermocouple model for high fidelity multiphysics computer simulation is introduced in this article. Detailed thermocouple and gas temperature (Coherent Anti-Stokes Raman Scattering) measurements were performed using a well-controlled, adiabatic, flat-flame Hencken burner, which provided data for validating the thermocouple model in a Sandia National Laboratories fire code. Comparison of simulation results to test data indicated a mean error of 6% between the thermocouple reading and predicted temperature.KEY WORDS: virtual thermocouple model, thermocouple heat balance, fire code development, fire temperature measurements.

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Measurements were taken of the exit velocity and turbulence intensity distributions for film cooling holes fed from a narrow plenum above the middle jet in a row of five jets using hot-wire anemometry. Parameters varied in the experiments included the length-to-diameter ratio of the holes, the coolant-to-mainstream blowing ratio, the angle of inclination of the holes, and the plenum flow direction, which was either in the same direction as, or opposite to, the mainstream. Flow visualization within the film cooling holes and in the plenum revealed large secondary flow structures that affected the jet exit velocity distributions. The exit velocity profiles for short holes had “peaky” signatures associated with jetting in the upstream portion of the 35° holes and in the downstream portion of the 90° holes. For the longer holes, the exit velocity profiles were more uniform. Crossflow boundary layer fluid was found to enter into the film cooling holes in some short hole configurations. The coolant feed direction affects the details of the flow separation at the hole entrance and within the hole, and consequently influences the jet exit velocity profile. These effects are most pronounced for higher blowing ratios.