Arcjet Flow Properties Determined from Laser-Induced Fluorescence of Atomic Nitrogen (original) (raw)
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49th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, 2011
The spectroscopic diagnostic technique of two photon absorption laser-induced fluorescence (TALIF) of atomic species has been applied to single-point measurements of velocity and static temperature in the NASA Ames Interaction Heating Facility (IHF) arc jet. Excitation spectra of atomic oxygen and nitrogen were recorded while scanning a tunable dye laser over the absorption feature. Thirty excitation spectra were acquired during 8 arc jet runs at two facility operating conditions; the number of scans per run varied between 2 and 6. Curve fits to the spectra were analyzed to recover their Doppler shifts and widths, from which the flow velocities and static temperatures, respectively, were determined. An increase in the number of independent flow property pairs from each as-measured scan was obtained by extracting multiple lower-resolution scans. The larger population sample size enabled the mean property values and their uncertainties for each run to be characterized with greater confidence. The average € ±2σ uncertainties in the mean velocities and temperatures for all 8 runs were ±1.4% and ±11 %, respectively.
Two-photon laser induced fluorescence spectroscopy performed on free nitrogen plasma jets
Plasma Sources Science and Technology, 2002
The properties of free nitrogen plasma jets are examined by studying the ground-state nitrogen atom flow characteristics. The plasma is created by a cascaded arc and subsequently it expands freely into a low pressure vessel. In such a way supersonic flows with high Mach number are achieved. N(4 S) atoms are locally probed by means of two-photon absorption laser induced fluorescence spectroscopy. Axial and radial N(4 S) atom temperature and velocity profiles present the shape predicted by the neutral gas supersonic expansion theory. The adiabatic exponent γ is equal to 1.45 in the supersonic domain. A Mach number M of 4.4 is measured ahead of the normal shock wave. In contrast, density profiles reveal a departure from the classical expansion picture. Too small density jumps over the shock region indicate a non-conservation of the N(4 S) atom forward flux. Moreover the partial N(4 S) atom static pressure decreases in the subsonic domain. Loss of nitrogen atoms during the plasma expansion is a direct consequence of plasma-wall interactions. However, losses are limited because of the relatively high N atom mass and because of a low surface recombination probability of N atoms. The dissociation degree at the arc exit is around 40%. Under such circumstances N 2 (A) molecules cannot survive in the jet. The local electron density is estimated from a measure of the radiative lifetime of the nitrogen atom excited state.
42nd AIAA Thermophysics Conference, 2011
The centerline total enthalpy of arc jet flow is determined using laser induced fluorescence of oxygen and nitrogen atoms. Each component of the energy, kinetic, thermal, and chemical can be determined from LIF measurements. Additionally, enthalpy distributions are inferred from heat flux and pressure probe distribution measurements using an engineering formula. Average enthalpies are determined by integration over the radius of the jet flow, assuming constant mass flux and a mass flux distribution estimated from computational fluid dynamics calculations at similar arc jet conditions. The trends show favorable agreement, but there is an uncertainty that relates to the multiple individual measurements and assumptions inherent in LIF measurements.
TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, 2014
Two-photon absorption laser induced fluorescence (TALIF) is applied to atomic oxygen and nitrogen generated in the JAXA 750 kW arc-heated wind tunnel in order to obtain velocity, translational temperature and atomic number density distributions. Free stream velocity is estimated by Doppler shift and the translational temperature distributions are deduced from spectral broadening. The absolute center excitation wavelength and laser line width are estimated with the TALIF profiles from a static reference cell which is called as a flow reactor. In this flow reactor, atomic species are generated by microwave discharge. The spatial distributions of atomic number density are deduced from the integrated TALIF profiles. The absolute atomic number densities inside the flow reactor are estimated with a titration method. From the mass fraction estimation, it is found that the number densities of atomic oxygen are overestimated owing to the saturation effect. When oxygen is assumed to be totally dissociated, the fractional enthalpies are estimated.
Next-Generation Laser-Induced Fluorescence Diagnostic Systems for NASA Arc Jet Facilities
47th AIAA Aerospace Sciences Meeting including The New Horizons Forum and Aerospace Exposition, 2009
The spectroscopic diagnostic technique of two-photon laser-induced fluorescence (2P-LIF) of atomic species has been applied to measurements of flow properties in the NASA Ames Aerodynamic Heating Facility (AHF) arc jet since the mid-1990s. Current NASA program goals have placed renewed emphasis on flow stream thermochemistry characterization as part of efforts to develop and validate human-rated thermal protection materials and systems for the Orion crew exploration vehicle. New laser diagnostic laboratories at two other NASA arc jet facilities at Ames and the Johnson Space Center have been developed to support expanded testing and analysis of human-rated thermal protection materials. The new laboratories have benefited from previous experience with the Ames AHF arc jet laser laboratory, leading to new approaches to optical and mechanical systems design, software development, and systems integration. The new laboratories are highly automated and capable of quality measurements with minimal impact on facility operations. This paper documents the new system design for the Ames Interaction Heating Facility arc jet.
Nitrogen atom detection in low-pressure flames by two-photon laser-excited fluorescence
Applied Physics B Photophysics and Laser Chemistry, 1991
Nitrogen atoms have been detected in stoichiometric flat premixed H2/O2/N2 flames at 33 and 96 mbar doped with small amounts of NH3, HCN, and (CN)2 using two-photon laser excitation at 211 nm and fluorescence detection around 870nm. The shape of the fluorescence intensity profiles versus height above the burner surface is markedly different for the different additives. Using measured quenching rate coefficients and calibrating with the aid of known N-atom concentrations in a discharge flow reactor, peak N-atom concentrations in these flames are estimated to be on the order of 1012-5 × 1013 cm -3 ; the detection limit is about 1 × 1011 cm -3.
Diagnostics of an Argon Arcjet Plume with a Diode Laser
Applied Optics, 1999
The diode-laser absorption technique was applied for simultaneous velocity and temperature measurements of an argon plume exhausted by an arcjet. The Ar I absorption line at 811.531 nm was taken as the center absorption line. The velocity and the temperature were derived from the Doppler shift in the absorption profiles and the full width at half-maximum of the plume absorption profile, respectively. From the measured plume velocity and temperature, the total enthalpy of the exhausted plume, the thrust efficiency, and the thermal efficiency of the arcjet were derived, and the performance of the arcjet was examined. The results are demonstrated to agree with results derived by other methods, and the technique can be applied to the measurement of other arcjet systems without much modification.
Journal of Applied Physics, 2009
In this paper, two-photon absorption laser induced fluorescence spectroscopy is used to follow the nitrogen atom density in flowing dielectric barrier discharges fed with pure nitrogen and operating at atmospheric pressure. Two different dielectric barrier discharge regimes are investigated: the Townsend regime, which is homogeneous although operating at atmospheric pressure, and the more common filamentary regime. In both regimes, densities as high as 3 ϫ 10 14 / cm 3 are detected. However, the N atoms kinetic formation depends on the discharge regime. The saturation level is reached more rapidly with a filamentary discharge. For a given discharge regime, the N atom density depends strongly on the energy dissipated in the plasma between the gas inlet and the measurement position, whether the energy is varied by varying the position of the measurements, the gas flow, or the dissipated power. Experiments performed in the postdischarge show that the N atom decay cannot be simply attributed to three-body recombination of atomic nitrogen with nitrogen molecules, meaning that other mechanisms such as surface recombination or gas impurities play a role.
On Calibration of Laser-Induced Fluorescence Measurements in Plasma Flows Using Rare Gases
In plasma flows intended for the qualification of atmospheric re-entry maneuvers of spacecrafts, the plasma wall interaction strongly affects the heat load to the thermal protection system. Therefore, ground state densities have to be known for plasma flow characterization, where laser-induced fluorescence measurements are applied. Calibration can be performed using rare gases, while one interest is to calibrate atomic nitrogen using xenon. Three excitation schemes for two-photon laser-induced fluorescence (TALIF) on neutral xenon are presented. These excitation schemes include 5f and 6f states, lying energetically close to the 2x211nm resonance in atomic nitrogen. Characterization of these transitions will qualify them as reference transitions for same-order calibration procedures. Results of lifetime and collisional deactivation rate measurements for 5f levels are given in pressure regimes between 4 and 60 Pa. Lifetimes are found to be consistent with literature values. Collisional deactivation plays an extensive role in the studied pressure regime. Two-photon excitation of 6f states has been verified at pressures between 69 and 224 Pa, weak signal intensities require further investigations.
Plasma Chemistry and Plasma Processing, 2004
An investigation of the plasma jet generated by a dc argon-nitrogen plasma torch, operated in association with a controlled-pressure chamber, is presented. The purpose of this article is to describe a study of the properties of a subsonic plasma jet under such operating conditions, when its transition to supersonic flow regime is nearly complete. The goal is that of performing plasma diagnostics not only in the initial region of the jet but also in the downstream region where the plasma emission is weak. For this purpose two different diagnostic methods are used. The first approach is based on non-intrusive optical emission spectroscopy, which yields both excitation and rotational temperatures as well as electron number density fields. The zone investigated by this method extends from the torch exit to about 10 nozzle diameters downstream. The second approach consisted of the use of the intrusive enthalpy probe technique for the measurement of the plasma gas temperature, mainly in the tail region of the plasma jet. In the present work, the effects of axial and radial distances across the jet, on the temperature and electron density profiles are discussed for subsonic flow conditions. Interesting features revealed are the data shown for the various diagnostic methods, which either disagree or overlap with each other. Finally, our results show the need for involving nonequilibrium models for the argon-nitrogen plasma due to the presence of significant differences between the temperatures of light and heavy particles.