The Experts below are selected from a list of 846 Experts worldwide ranked by ideXlab platform
Chung S. Park - One of the best experts on this subject based on the ideXlab platform.
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Computational simulation of emission spectra from shock-layer flows in an arcjet facility
1998Co-Authors: Tahir Gokcen, Chung S. Park, Mark E. Newfield, Douglas G. FletcherAbstract:We report computational comparisons with experimental studies of a nonequilibrium blunt-body shock-layer flow in a high-enthalpy arcjet wind tunnel at NASA Ames Research Center. The experimental data include spatially resolved emission spectra of radiation emanating from a shock layer formed in front of a flat-faced cylinder model. Multitemperature nonequilibrium codes are used to compute the conical nozzle flow, supersonic jet, and shock-layer flow. A line-of-sight (LOS) radiation code is employed to predict the spectra from the computed flowfield. Computed LOS emission intensities are directly compared with the experimental data at several axial locations along the Stagnation Streamline. Various LOS-averaged flow properties, such as vibrational and rotational temperatures, and species number densities, deduced from the experimental spectra, are compared with computed results. Comparisons provide an assessment of thermochemical equilibration processes in an arcjet shock layer
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Computational Simulation of Emission Spectra from Shock-Layer Flows in an Arcjet Facility
Journal of Thermophysics and Heat Transfer, 1998Co-Authors: Tahir Gokcen, Chung S. Park, Mark E. Newfield, Douglas G. FletcherAbstract:This paper reports computational comparisons with experimental studies of a nonequilibrium bluntbody shock-layer e ow in a high-enthalpy arcjet wind tunnel at NASA Ames Research Center. The experimental data include spatially resolved emission spectra of radiation emanating from a shock layer formed in front of a e at-faced cylinder model. Multitemperature nonequilibrium codes are used to compute the conical nozzle e ow, supersonic jet, and shock-layer e ow. A line-of-sight (LOS) radiation code is employed to predict the spectra from the computed e owe eld. Computed LOS emission intensities are directly compared with the experimental data at several axial locations along the Stagnation Streamline. Various LOS-averaged e ow properties, such as vibrational and rotational temperatures, and species number densities, deduced from the experimental spectra, are compared with computed results. Comparisons provide an assessment of thermochemical equilibration processes in an arcjet shock layer.
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Theory of radiation from low velocity shock heated air
Journal of Thermophysics and Heat Transfer, 1993Co-Authors: Deborah A. Levin, R. T. Loda, Graham V. Candler, Chung S. ParkAbstract:Application of hypersonic computational fluid dynamics models to low velocity vehicles is examined. Important modeling aspects such as chemical kinetics, electronic excitation/de-excitation mechanisms, and existence of equilibrium vs nonequilibrium conditions in the flow were examined. Flowfield properties and in-band radiances in the wavelength region of 0.25 /i in the vicinity of the Stagnation Streamline are given for a hemisphere with a radius of 0.0762 m. Comparison with recent shock tube data is also shown.
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Theory of radiation from low velocity heated air
28th Aerospace Sciences Meeting, 1990Co-Authors: Deborah A. Levin, R. T. Loda, Graham V. Candler, Chung S. ParkAbstract:The application of hypersonic computational fluid dynamics models to low velocity vehicles is examined. Modeling aspects such as chemical kinetics, electronic excitation/deexcitation mechanisms, and existence of equilibrium versus nonequilibrium conditions in the flow were examined. Flowfield properties and in-band radiances in the wavelength region of .25 micron in the vicinity of the Stagnation Streamline are given for a three-inch hemisphere.
Douglas G. Fletcher - One of the best experts on this subject based on the ideXlab platform.
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Computational simulation of emission spectra from shock-layer flows in an arcjet facility
1998Co-Authors: Tahir Gokcen, Chung S. Park, Mark E. Newfield, Douglas G. FletcherAbstract:We report computational comparisons with experimental studies of a nonequilibrium blunt-body shock-layer flow in a high-enthalpy arcjet wind tunnel at NASA Ames Research Center. The experimental data include spatially resolved emission spectra of radiation emanating from a shock layer formed in front of a flat-faced cylinder model. Multitemperature nonequilibrium codes are used to compute the conical nozzle flow, supersonic jet, and shock-layer flow. A line-of-sight (LOS) radiation code is employed to predict the spectra from the computed flowfield. Computed LOS emission intensities are directly compared with the experimental data at several axial locations along the Stagnation Streamline. Various LOS-averaged flow properties, such as vibrational and rotational temperatures, and species number densities, deduced from the experimental spectra, are compared with computed results. Comparisons provide an assessment of thermochemical equilibration processes in an arcjet shock layer
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Computational Simulation of Emission Spectra from Shock-Layer Flows in an Arcjet Facility
Journal of Thermophysics and Heat Transfer, 1998Co-Authors: Tahir Gokcen, Chung S. Park, Mark E. Newfield, Douglas G. FletcherAbstract:This paper reports computational comparisons with experimental studies of a nonequilibrium bluntbody shock-layer e ow in a high-enthalpy arcjet wind tunnel at NASA Ames Research Center. The experimental data include spatially resolved emission spectra of radiation emanating from a shock layer formed in front of a e at-faced cylinder model. Multitemperature nonequilibrium codes are used to compute the conical nozzle e ow, supersonic jet, and shock-layer e ow. A line-of-sight (LOS) radiation code is employed to predict the spectra from the computed e owe eld. Computed LOS emission intensities are directly compared with the experimental data at several axial locations along the Stagnation Streamline. Various LOS-averaged e ow properties, such as vibrational and rotational temperatures, and species number densities, deduced from the experimental spectra, are compared with computed results. Comparisons provide an assessment of thermochemical equilibration processes in an arcjet shock layer.
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Investigations of Arcjet Flow Thermochemistry
1997Co-Authors: Douglas G. Fletcher, Paul WercinskiAbstract:An experimental and numerical investigation of the thermochemical state of arcjet flows is currently being conducted at NASA Ames Research Center. The experimental approach relies on the use of laser- and emission-spectroscopic diagnostic techniques in three regions of the flow. A fiber optic sensor is used to record spectrally resolved emission signals from the electrode package region, where the flow is most likely to be in thermochemical equilibrium. A second emission diagnostic measurement is made in the shock layer formed over a blunt-body test article placed in the stream, and a CCD camera is used to simultaneously record spectral emission from several measurement locations along the Stagnation Streamline. Downstream of the nozzle exit, but upstream of the test article, Laser-Induced Fluorescence (LIF) of atomic nitrogen is used to assess the nonequilibrium distribution of flow enthalpy in the free stream. Results from the measurements are compared with predictions from a two-temperature, axisymmetric flow model that solves the nozzle and shock-layer flows.
A. A. Markov - One of the best experts on this subject based on the ideXlab platform.
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Unsteady viscous shock layer in the case of supersonic motion through an inhomogeneity
Fluid Dynamics, 1992Co-Authors: A. A. MarkovAbstract:The model of a perfect gas is used in a numerical simulation of unsteady effects in a viscous shock layer near the Stagnation Streamline near the front part of a rotating blunt body in an inhomogeneous external flow with pressure difference Δ P _t8, temperature difference Δ T _t8, and vorticity difference ΔΩ. The evolution of nonlinear disturbances due to the passage of a heated region and a change of the injection regime is followed. A divergence finite-difference scheme of second order of approximation across the shock layer, realized by vector sweeps with allowance for the boundary conditions on the surface of the body and behind the separated bow shock wave, is used.
Richard G. Morgan - One of the best experts on this subject based on the ideXlab platform.
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Studying post-shock relaxation using a Mach Disk
2019Co-Authors: S.f.t. Apirana, Richard G. Morgan, Christopher M. James, Steven Lewis, Fabian ZanderAbstract:The X2 expansion tube facility, a hypervelocity wind tunnel at The University of Queensland, was used to simulate two planetary entry conditions over two model types. It was hypothesised that a Mach Disk could reproduce the same environment as that downstream of standing shocks on a reentry vehicle. The degree of similarity has been tested by comparing the post-shock regions of a Mach Disk and a blunt cylinder model (along the Stagnation Streamline). 2D filtered imaging techniques as well as emission spectroscopy were used to investigate nitrogen radiative emissions around the 740nm wavelength and oxygen emissions around the 777nm wavelength. A new test-condition, designed to produce a longer, highly non-equilibrium, post-shock region was tested and compared with an existing condition. A longer non-equilibrium region was observed for Condition-2 through 2D filtered imaging and emission spectroscopy for both model types.
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Quantitative emission spectroscopy for superorbital reentry in expansion tube X2
Journal of Thermophysics and Heat Transfer, 2017Co-Authors: Tobias Hermann, Richard G. Morgan, Stefan Löhle, Uwe Bauder, H. Wei, Stefanos FasoulasAbstract:A superorbital reentry flow was realized in the X2 expansion tunnel of the Centre for Hypersonics of the University of Queensland, resulting in measurements of electronic excitation temperature, electron density, and particle densities of neutral and ionized atomic nitrogen and oxygen. A rectangular cold wall model was exposed to a flow corresponding to a 12.2 km/s flight equivalent velocity. Vacuum ultraviolet optical emission spectroscopy in the wavelength range between 116 and 185 nm was conducted through a window at the Stagnation point. Spatially resolved optical emission spectroscopy of the Stagnation Streamline in the near-infrared wavelength range from 695 to 880 nm was conducted, analyzing the flow from the side. Population densities of excited atomic states, electronic excitation temperatures, and electron and ion densities were determined by analyzing the radiative transport in the flowfield. Additionally, the flowfield was numerically simulated using the code URANUS. Agreement in electron den...
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Optical Thickness Measurements of Vacuum Ultraviolet Radiation in the X2 Expansion Tube
AIAA Journal, 2016Co-Authors: Umar A. Sheikh, Richard G. Morgan, Timothy J. McintyreAbstract:Experiments were conducted in the X2 expansion tube to measure vacuum ultraviolet radiation from shock layers representative of reentry conditions at flight equivalent velocities of 10.0 and 12.2 km/s. Cylindrical models of varying lengths were used to make measurements of different depths of radiating gases. Spectral emission measurements were made, imaging parallel to the surface of the models along the Stagnation Streamline. Ratios of integrated spectral bands were compared to quantify increases in radiance with increasing depth of radiating gas. Significant increases in observed radiance were measured with increasing model length. Comparisons were made with simulations that assumed an optically thin shock layer, and it was found that over 98.9% of the total vacuum ultraviolet radiation emitted was self-absorbed. Good agreement was found between the simulations and measurements of total radiance for the different depths of radiating gas. These results highlight the need to accurately quantify the opac...
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Radiation measurements in a simulated non-terrestrial atmosphere
2007Co-Authors: Troy N. Eichmann, D. F. Potter, Timothy J. Mcintyre, Aaron M. Brandis, Michael M. Mallon, Richard G. Morgan, Halina Rubinsztein-dunlopAbstract:A high-speed wind tunnel has been used to experimentally simulate the flow experienced by a capsule entering a planetary atmosphere. High speed photography showed that a steady test time of approximately 50 μs existed in the facility. Holographic interferometry has been performed to measure the twodimensional density distribution around a cylinder in the flow. A peak density ratio (density normalised by the free-stream density) of about 14 was observed. Emission spectroscopy allowed the characterisation of the conditions along the Stagnation Streamline in front of the capsule model. The results showed a temperature that varied between 8,500 K and 11,000 K in this region.
C. Marmignon - One of the best experts on this subject based on the ideXlab platform.
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Vibrational relaxation of CO2(m, nl, p) in a CO2N2 mixture. Part 2: Application to a one-dimensional problem
Aerospace Science and Technology, 1999Co-Authors: V. Joly, C. Marmignon, P JacquetAbstract:Abstract In order to quantify the relaxation mechanism of CO2(m, nl, p), the vibrational level populations are calculated for a particular test-case: the vibrational relaxation of a CO2N2 mixture along the Stagnation Streamline in a reentry problem. The N2 species is chosen as a collision partner because it is a component existing in numerous gaseous mixtures (cf. Part. 1). Excitation and deexcitation processes are taken following Nickerson and Herzfeld. The Navier-Stokes code CELHYO for the simulation of hypersonic laminar viscous flows in chemical and thermal nonequilibrium is used with a new one-dimensional approach, reduction of the Navier-Stokes equations along the Stagnation Streamline. Mass fraction and ‘vibrational temperature’ distributions of every vibrational level, considered as an independent chemical species, are presented for the two different CO2N2 mixture compositions. The validity of the usual assumptions for the vibrational mechanism is examined on the basis of the obtained results.
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Vibrational relaxation of CO2(m,n(l),p) in a CO2-N2 mixture along a Stagnation Streamline
32nd Thermophysics Conference, 1997Co-Authors: J. William, J. Verant, A. Roblin, V. Joly, C. MarmignonAbstract:The knowledge of the vibrational relaxation reaction rates of diatomic and triatomic molecules is required for the modeling of numerous gazeous mixtures such as the earth atmosphere (involving the radiation tranfer phenomena), exhaust plumes, afterbody wakes, Mars atmosphere, shock waves and chemical lasers. It enables a better understanding of the rates and products of the chemical reactions that involve this species and provides the populations of the levels that radiate. In this study, we consider the few lowest vibrational levels of a CO-2 — N-z mixture and the V-T and V-V energy transfer processes between these levels. The reaction rates are given by experimental and theoretical studies and by different surveys of data supplied by a bibliographic search. Then, the population distributions along a Stagnation Streamline are determined for the various vibrational levels and according to the different models with the CELHYO code developed at ONERA, using a new one-dimensional approach. Usual assumptions concerning the vibrational relaxation of CO-2(m,nl,p) are discussed.