The Experts below are selected from a list of 276 Experts worldwide ranked by ideXlab platform
R. Srinivasan - One of the best experts on this subject based on the ideXlab platform.
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Tensile behavior of SiC/C and Rene'41 following isothermal exposure and thermal fatigue
Journal of Materials Science, 2000Co-Authors: J. L. Pierce, L. P. Zawada, R. SrinivasanAbstract:The performance of a coated silicon carbide/carbon composite under isothermal and thermal fatigue conditions was investigated. The material studied is known as Ceracarb™ which consists of eight-harness satin weave Nicalon® silicon carbide cloth reinforcement, a carbonaceous matrix, and a silicon carbide composite coating. This advanced composite is being considered for replacing the nickel based superalloy Rene'41, as the exhaust nozzle components on military Afterburning turbine engines. Thermal fatigue experiments, performed in the laboratory using a thermal cycling test system, were intended to roughly simulate the thermal excursions of an Afterburning exhaust nozzle. Several thermal profiles were used to characterize the role of temperature, number of cycles, temperature range, and time at temperature, on the room temperature residual tensile strength of the material. The same thermal profiles were also conducted on test specimens of Rene'41 in order to compare its durability in the laboratory simulation test set-up to the composite. Both materials showed no loss in strength from the as-received condition following thermal testing. However, the Rene'41 showed evidence of microstructural instability at the maximum test temperature of 1093°C (2000°F) which did affect the toughness of the material. While the results from this study showed that both materials retained strength when thermally exposed in the laboratory under no loads, thermal testing under load may provide a more realistic view of how the materials perform in the Afterburning exhaust nozzle application.
K C Schadow - One of the best experts on this subject based on the ideXlab platform.
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Role of large coherent structures in turbulent compressible mixing
Experimental Thermal and Fluid Science, 1997Co-Authors: K C SchadowAbstract:Abstract Turbulent compressible shear layers of round supersonic jets were excited by placing an open cavity near the nozzle exit, which produced pressure oscillations due to flow-induced cavity resonance. As a result of the excitation, large coherent structures were created in the highly compressible shear layers, making it possible to study the effect of such structures on turbulent compressible mixing. For this study, pressure-matched Mach 2 jets were used under both nonreacting and Afterburning conditions. By varying the cavity dimensions, we could apply excitation over a wide range of frequencies and manipulate the coherent structure dynamics in the near field of the jets. Mie-scattering flow visualization images revealed that large coherent structures were generated when high-amplitude excitation occurred at frequencies close to the jet preferred mode, which was near the Strouhal number of about one-half. Growth rate of nonreacting shear layers was quantified as a function of excitation frequency; and, for Afterburning jets, the change in global flame luminosity due to excitation was measured. It was observed that the growth rate was drastically increased in the near field when the coherent structures were organized. The Afterburning characteristics were also modified by coherent structures and their dynamics. Under these conditions, Afterburning intensity increased when the excitation frequency was higher than the preferred mode frequency and decreased at lower frequencies. The results suggest that the initial size of the coherent structures not only determined the rate of large-scale entrainment, but also modified molecular-level mixing by affecting the timing of large-structure breakdown.
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cavity actuated supersonic mixing and combustion control
Combustion and Flame, 1994Co-Authors: K C SchadowAbstract:Abstract Compressible shear layers in supersonic jets are quite stable and spread very slowly compared with incompressible shear layers. In this paper, a novel use of a cavity-actuated forcing technique is demonstrated for increasing the spreading rate of compressible shear layers. Periodic modulations were applied to Mach 2.0 reacting and nonreacting jets using the cavities that were attached at the exit of a circular supersonic nozzle. The effect of cavity-actuated forcing was studied as a function of the cavity geometry, in particular, the length and the depth of the cavity. When the cavities were tuned to certain frequencies, large-scale highly coherent structures were produced in the shear layers substantially increasing the growth rate. The cavity excitation was successfully applied to both cold and hot supersonic jets. When applied to cold Mach 2.0 air jets, the cavity-actuated forcing increased the spreading rate of the initial shear layers with the convective Mach number (M c ) of 0.85 by a factor of three. For high-temperature Mach 2.0 jets with M c of 1.4, a 50% increase in the spreading rate was observed with the forcing. Finally, the cavity-actuated forcing was applied to reacting supersonic jets with ethylene-oxygen Afterburning. For this case, the forcing caused a 20%–30% reduction in the Afterburning flame length and modified the Afterburning intensity significantly. The direction of the modification depended on the characteristics of the Afterburning flames. The intensity was reduced with forcing for unstable flames with weak Afterburning while it was increased for stable flames with strong Afterburning.
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thermal imaging of Afterburning plumes
Journal of Propulsion and Power, 1991Co-Authors: E Gutmark, T P Parr, K J Wilson, K C Schadow, E AjdariAbstract:Afterburning and nonAfterburning exhaust plumes were studied experimentally for underexpanded sonic and supersonic conical circular nozzles. The plume structure was visualized using thermal imaging and regular photography. Thermal emission by the plume is mainly dependent on the presence of Afterburning. Temperature and reducing power (or unoxidized fuel content) of the exhaust gases, in addition to the nozzle configuration, determine the structure of the plume core, the location where the Afterburning is initiated, its size, and intensity. The temperature, through chemical kinetics, determines the presence of Afterburning and its initiation location. Its effect is especially critical in marginally Afterburning plumes. The fuel content determines the size and intensity of the plume when Afterburning occurs. Comparison between single shot and average thermal images of the plume show that Afterburning is a highly turbulent combustion process.
J. L. Pierce - One of the best experts on this subject based on the ideXlab platform.
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Tensile behavior of SiC/C and Rene'41 following isothermal exposure and thermal fatigue
Journal of Materials Science, 2000Co-Authors: J. L. Pierce, L. P. Zawada, R. SrinivasanAbstract:The performance of a coated silicon carbide/carbon composite under isothermal and thermal fatigue conditions was investigated. The material studied is known as Ceracarb™ which consists of eight-harness satin weave Nicalon® silicon carbide cloth reinforcement, a carbonaceous matrix, and a silicon carbide composite coating. This advanced composite is being considered for replacing the nickel based superalloy Rene'41, as the exhaust nozzle components on military Afterburning turbine engines. Thermal fatigue experiments, performed in the laboratory using a thermal cycling test system, were intended to roughly simulate the thermal excursions of an Afterburning exhaust nozzle. Several thermal profiles were used to characterize the role of temperature, number of cycles, temperature range, and time at temperature, on the room temperature residual tensile strength of the material. The same thermal profiles were also conducted on test specimens of Rene'41 in order to compare its durability in the laboratory simulation test set-up to the composite. Both materials showed no loss in strength from the as-received condition following thermal testing. However, the Rene'41 showed evidence of microstructural instability at the maximum test temperature of 1093°C (2000°F) which did affect the toughness of the material. While the results from this study showed that both materials retained strength when thermally exposed in the laboratory under no loads, thermal testing under load may provide a more realistic view of how the materials perform in the Afterburning exhaust nozzle application.
Zhitan Zhou - One of the best experts on this subject based on the ideXlab platform.
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Numerical analysis on thermal environment of liquid rocket with Afterburning under different altitudes
Applied Thermal Engineering, 2020Co-Authors: Zhitan Zhou, Xin WangAbstract:Abstract To achieve a detailed understanding of the characteristics of the liquid hydrogen-oxygen (LH2/LOX) rocket exhaust plume with Afterburning, the three-dimensional compressible Reynolds-averaged Navier-Strokes (RANS) equation with the realizable k-Ɛ turbulence model is applied to calculate the flow field of the supersonic exhaust gas. An optimized 9-species and 14-steps chemical mechanism is used for the Afterburning effects. Multi-grid method is adopted to establish structural grid of 8.87 million cells for the finite volume computation. The Afterburning model is established under six inflow conditions and then validated by experimental data. The validated model is applied to compare the under-expanded supersonic plume with and without Afterburning reaction at different flight altitudes. The simulation results indicate that Afterburning mainly occurs in the mixed layer. Compared to the frozen flow, the peak temperature of the reaction flow has increased from 123 K to 318 K, the mole concentrations of hydrogen and water vapor change in the reacting plume. The Afterburning has significant influence on the thermal environment of the exhaust plume at low altitude, but its effect becomes weak with the altitude increase. The results have provided a relevant evaluation of the flow field characteristics of supersonic plume and offer some usefulness to further numerical simulations of the liquid rocket exhaust jet with Afterburning.
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Numerical Studies of Afterburning on Impingement Flowfield of the Four-Engine Rockets
Journal of Spacecraft and Rockets, 2020Co-Authors: Zhitan Zhou, Liangjun ZhangAbstract:A four-engine liquid launch vehicle is studied to analyze the influence of Afterburning reactions on the plume flowfield of a rocket exhausted jet. To accurately simulate the Afterburning flow of t...
L. P. Zawada - One of the best experts on this subject based on the ideXlab platform.
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Tensile behavior of SiC/C and Rene'41 following isothermal exposure and thermal fatigue
Journal of Materials Science, 2000Co-Authors: J. L. Pierce, L. P. Zawada, R. SrinivasanAbstract:The performance of a coated silicon carbide/carbon composite under isothermal and thermal fatigue conditions was investigated. The material studied is known as Ceracarb™ which consists of eight-harness satin weave Nicalon® silicon carbide cloth reinforcement, a carbonaceous matrix, and a silicon carbide composite coating. This advanced composite is being considered for replacing the nickel based superalloy Rene'41, as the exhaust nozzle components on military Afterburning turbine engines. Thermal fatigue experiments, performed in the laboratory using a thermal cycling test system, were intended to roughly simulate the thermal excursions of an Afterburning exhaust nozzle. Several thermal profiles were used to characterize the role of temperature, number of cycles, temperature range, and time at temperature, on the room temperature residual tensile strength of the material. The same thermal profiles were also conducted on test specimens of Rene'41 in order to compare its durability in the laboratory simulation test set-up to the composite. Both materials showed no loss in strength from the as-received condition following thermal testing. However, the Rene'41 showed evidence of microstructural instability at the maximum test temperature of 1093°C (2000°F) which did affect the toughness of the material. While the results from this study showed that both materials retained strength when thermally exposed in the laboratory under no loads, thermal testing under load may provide a more realistic view of how the materials perform in the Afterburning exhaust nozzle application.