Time filter

Source Type

Dayton, OH, United States

Katta V.,ISSI | Roquemore W.M.,U.S. Air force
Proceedings of the Combustion Institute | Year: 2013

Recent measurements of Barlow et al. in a bluff-body burner revealed that local atom balances were not conserved. They attributed the observed higher C/H atom ratios to the preferential diffusion of certain species and longer residence times in the recirculation zones (RZs). For verifying this hypothesis, detailed calculations for the reacting flows in the bluff-body burner were made using UNICORN code incorporated with GRI version 3.0 chemical kinetics. A lean mixture (U = 0.77) of methane and air was used as fuel jet. Time-dependent laminar simulations resulted in steady RZs for fuel jet velocities up to 7.0 m/s. Similar to experiments, calculations also revealed nonuniform distributions for C/H atom ratio in the flame at all heights. Results were compared to the data obtained for an unstrained 1D flame. Simulations for the bluffbody flame were repeated after setting diffusion coefficients of every species equal to that of O2. In the absence of preferential diffusion, C/H atom ratio was found to be equal to 0.25 everywhere in the flame. For understanding the effects of flame stretch on C/H atom ratio, calculations were made for the double flames formed between the opposing jets of premixed methane-air mixtures at different velocities. Distributions of C/H atom ratio in the RZ-supported nonpremixed flame were investigated through performing calculations for the Air Force centerbody burner fueled with ethylene. Both the attached and lifted-flame conditions were studied for understanding the role of RZs in enhancing C/H atom ratio. It was found that the hypothesis proposed by Barlow et al. in general, explains the higher C/H atom ratios found in bluffbody flames. However, RZs are not found to enhancing the preferential diffusion effects. Instead, the sharp velocity gradients near the fuel jet in the vicinity of the bluff-body surface increased the removal of H2O. © 2012 The Combustion Institute.

Gedalin M.,Ben - Gurion University of the Negev | Medvedev M.,University of Kansas | Medvedev M.,Copenhagen University | Medvedev M.,RAS Research Center Kurchatov Institute | And 5 more authors.
Physics of Plasmas | Year: 2010

The filamentation instability of counterstreaming beams is a nonresonant hydrodynamic-type instability whose growth rate is a smooth function of the wavelength (scale). As a result, perturbations with all unstable wavelengths develop, and the growth saturates due to the saturation of available current. For a given scale, the magnetic field at saturation is proportional to the scale. As a result, the instability develops in a nearly linear regime, where the unstable modes stop growing as soon as the saturation of the corresponding wavelength is reached. At each moment there exists a dominant scale of the magnetic field which is the scale that reached saturation at this particular time. The smaller scales do not disappear and can be easily distinguished in the current structure. The overall growth of the instability stops when the loss of the streaming ion energy because of deceleration is comparable to the initial ion energy. © 2010 American Institute of Physics.

Parthasarathy T.A.,Air Force Research Lab | Parthasarathy T.A.,UES, Inc. | Petry M.D.,Air Force Research Lab | Petry M.D.,UES, Inc. | And 3 more authors.
Journal of the American Ceramic Society | Year: 2013

Sharp leading edge (LE) samples of UHTC (20 vol%SiC-HfB2) and SiC were exposed to simulated hypersonic flight conditions using a direct-connect scramjet rig and their thermal and oxidation responses measured. The measured back-wall temperatures and scale thicknesses were significantly smaller than might be expected from stagnation temperatures at the LE. Furthermore, the scale that formed around the LE was more uniform than expected from the steep drop in cold wall heat flux with distance from the tip. These results were interpreted and rationalized using physics-based models. An aerothermal model in combination with an oxidation model accounted for the observed scale thicknesses at the tip and their slight variation with distance. The scale thicknesses were similar to values reported for exposures in furnaces at temperatures calculated for the tip, but less than those reported in arc jet tests. The formation of hafnon (HfSiO4) and the absence of external glassy layer and of silica in the outer portions of the oxide region are unique to scramjet tested samples, presumably due to the high fluid flow (high shear and evaporation) rates. © Published 2013. This article is a U.S. Government work and is in the public domain in the USA.

Parthasarathy T.A.,Air Force Research Lab | Parthasarathy T.A.,UES, Inc. | Petry M.D.,Air Force Research Lab | Petry M.D.,UES, Inc. | And 4 more authors.
International Journal of Applied Ceramic Technology | Year: 2011

A methodology to evaluate the aerothermal response of sharp leading edge materials by exposing them directly to hypersonic flow up to Mach 7 was developed and evaluated. The exposure was conducted using a prototype scramjet engine as a wind tunnel. A sample holder was designed using combustion fluid dynamics results as inputs into structural models. The rig conditions were evaluated and found to be close to those during free flight, with respect to aerothermal parameters of importance for material survivability. Samples of ultra high-temperature ceramics and SiC were found to withstand the short-term exposure that simulated Mach 6.5 at 25 km altitude. © 2010 The American Ceramic Society.

Estevadeordal J.,ISSI | Estevadeordal J.,General Electric | Marks C.,U.S. Air force | Sondergaard R.,U.S. Air force | Wolff M.,U.S. Air force
Experiments in Fluids | Year: 2011

Three-dimensional surface illumination using curved laser-sheet techniques is introduced for optical flow measurements in conformal curved surfaces. The illumination method is applicable to many different optical-based flow measurement techniques, with this paper focusing on application to flow visualization and particle image velocimetry. A brief discussion and example of curved laser-sheet generation is given followed by an example of the technique applied to PIV of low Reynolds number transitional flow around a low-pressure turbine blade. © 2010 US Government.

Discover hidden collaborations