Free-jet Nozzle Research Articles

Numerical investigation of mixing characterstics of chevron nozzle by passive controls method

This paper deals with the Reduction of noise in the aircraft exhaust is done by installing Chevrons with particular parameters in the Nozzle section. Numerical investigations have been carried out on chevron Nozzles to evaluate the importance of Chevron parameters by adding number of Chevrons and the mixing characteristics of jet. After assessing the Chevron parameters we vary the Chevron shapes at the exit by installing the triangular wedge in order to regulate maximum noise reduction along with a negligible thrust loss. Finally the results is compared with free jet Nozzle with Chevron and Chevron with wedge has been analysed using CFX CFD software and the results of potential core decay of these Nozzles has been measured from the analysis.

Modeling and HIL Simulation of Flight Conditions Simulating Control System for the Altitude Test Facility

AbstractSimulated altitude test is an essential exploring, debugging, verification and validation means during the development of aero-engine. Free-jet engine test can simulate actual working conditions of aero-engine more realistically than direct-connect engine test but with relatively lower cost compared to propulsion wind tunnel test, thus becoming an important developing area of simulated altitude test technology. The Flight Conditions Simulating Control System (FCSCS) is of great importance to the Altitude Test Facility (ATF) but the development of that is a huge challenge. Aiming at improving the design efficiency and reducing risks during the development of FCSCS for ATFs, a Hardware- in-the-Loop (HIL) simulation system was designed and the mathematical models of key components such as the pressure stabilizing chamber, free-jet nozzle, control valve and aero-engine were built in this paper. Moreover, some HIL simulation experiments were carried out. The results show that the HIL simulation system designed and established in this paper is reasonable and effective, which can be used to adjust control parameters conveniently and assess the software and hardware in the control system immediately.

The in-gas-jet laser ion source: Resonance ionization spectroscopy of radioactive atoms in supersonic gas jets

New approaches to perform efficient and selective step-wise resonance ionization spectroscopy (RIS) of radioactive atoms in different types of supersonic gas jets are proposed. This novel application results in a major expansion of the in-gas laser ionization and spectroscopy (IGLIS) method developed at KU Leuven. Implementation of resonance ionization in the supersonic gas jet allows to increase the spectral resolution by one order of magnitude in comparison with the currently performed in-gas-cell ionization spectroscopy. Properties of supersonic beams, obtained from the de Laval-, the spike-, and the free jet nozzles that are important for the reduction of the spectral line broadening mechanisms in cold and low density environments are discussed. Requirements for the laser radiation and for the vacuum pumping system are also examined. Finally, first results of high-resolution spectroscopy in the supersonic free jet are presented for the 327.4nm 3d104s 2S1/2→ 3d104p 2P1/2 transition in the stable 63Cu isotope using an amplified single mode laser radiation.

Surface ionization detector with a supersonic free jet for gas chromatography some applications

A new design for a gas chromatographic surface ionization detector based upon hyperthermal positive surface ionization has been developed: There were two requirements: supersonic free jet nozzle and the high work function surface of Re-oxide. This detector, which is highly sensitive in response to all organic compounds, can be operated as an universal detector with an additional selectivity towards some species that have low ionization energy, but with selectivity to a much lesser degree than a conventional surface ionization detector. The minimum detectable amount of toluene is ca. 10 −12 g/s with a linearity greater than 10 4. Some applications are demonstrated using three examples for the analysis of different formulations: (1), terpene mixture, (2), polycyclic aromatic hydrocarbon mixture and (3), alkyl alcohol mixture.

A Surface Ionization Detector for Gas Chromatography: Use of a Supersonic Free Jet

A new design of a gas chromatographic surface ionization detector (SID) based on hyperthermal positive surface ionization is described. There are two requirements: use of a supersonic free jet nozzle and the high-work-function surface of rhenium oxide. This detector, which is sensitive in response to all the organics, can be operated as an universal detector with much higher sensitivity toward some species having low ionization energy but with selectivity to a lesser degree than that of a conventional SID. The minimum detectable amount (at S/N = 3) of pyrene is around 4.4 × 10(-)(13) g/s, with linearity greater than 10(6), while that of toluene is around 10(-)(12) g/s. Other unique properties are (1) the ability to control the degree of selectivity through molecular kinetic energy, the surface, and its temperature and (2) a very short response time.

Characterization of a gas chromatographic surface ionization detector based upon hyperthermal positive surface ionization

Characterization of a gas chromatographic surface ionization detector based upon hyperthermal positive surface ionization is described. The newly developed detector consists of a supersonic free-jet nozzle and the high-work-function surface of ReO 2. This detector, which is highly sensitive in response to all organic compounds, can be operated as a universal detector. There will be some additional selectivity toward some species having low ionization energy, but this will be much less than with conventional surface ionization detection. The minimum detectable amount of toluene is around 10 −12 g/s with linearity greater than 10 4.

An Apparatus for Isotopic Ratio Measurement in UF5 Formed by Infrared Multiphoton Dissociation of UF6 in Molecular Beam.

A Separation factor was measured in isotopically selective infrared multiphoton dissociation (IRMPD) of supercooled UF6 in a supersonic expansion by multiphoton ionization (MPI) and time-of-flight mass spectrometry (TOFMS). A pulsed free-jet nozzle was used to generate a UF6-molecular beam seeded in Ar (–10−7 Torr in UF6 partial pressure). Two-frequency ρ-H2 Raman laser beams around 16μm were used for the dissociation of UF6 under collisionless conditions in the molecular beam where the flow velocity for UF6 is about 500m/s. The 235U/238U isotopic ratios in nascent UF5 photoproducts were determined by selective MPI of UF5 at 532 nm followed by TOFMS with a mass resolution as high as 1200. A separation factor of about 2 was observed under the experimental conditions chosen for the demonstration of this method.

The dynamics of CO oxidation on Pd, Rh, and Pt studied by high-resolution infrared chemiluminescence spectroscopy

The dynamics of carbon monoxide oxidation on Pd, Rh, and Pt foils were probed under nearly collision-free conditions using high resolution infrared chemiluminescence. Auger electron spectroscopy was used to verify the absence of impurities on the surfaces. The reactants were supplied to the surface through a free jet nozzle source, while a Fourier transform infrared spectrometer operating at 0.012 cm−1 resolution was used to fully resolve the rotational structure of several vibrational transitions in the product CO2 (22 in the case of Pd). In all cases, the product CO2 is vibrationally excited and the apparent vibrational temperatures are in the same order as the peak reaction rates, i.e., Pd>Pt>Rh. The surface coverage of oxygen on Pd was varied by changing the CO:O2 ratio and the surface temperature and, in both cases, increasing oxygen coverage causes an increase in vibrational excitation of product CO2. On Pt and Rh, the apparent temperatures of different vibrational modes are similar, while on Pd, those levels involved in Fermi resonances that are traditionally called the symmetric stretch levels are selectively populated. From these results, evidence that the activated complex is bent on Pd relative to Pt and Rh and, in all cases, is aligned more or less along the surface normal is presented.

Infrared Emission Measurements of Vibrationally Excited CO2 Molecules Formed by Catalytic Oxidation of CO on Pt and Pd Surfaces.

Vibrational energy distributions in CO2 molecules formed by the catalytic oxidation of CO on Pt and Pd surfaces have been measured by using infrared emission spectroscopy. The reactants (the total flux of CO and O2: 1.3×1019 molecules/cm2·s) were supplied to the surface through two free jet nozzle sources, while an FT-IR spectrometer was used to obtain the infrared emission spectra (4 cm-1 resolution) of the product CO2. For all the experimental conditions (surface temperature in the range of 650∼1150K and O2/CO ratio from 5/1 to 1/5), the emission spectra observed in the 2400∼2100 cm-1 region were significantly red shifted from the fundamental of the asymmetric streth at 2349 cm-1, indicating that the CO2 molecules were vibrationally excited substantially beyond thermal equilibrium with the surface. The surface coverage of oxygen on both Pt and Pd was varied by changing the O2/CO ratio and, in both cases, increasing oxygen coverage caused an increase in the average vibrational temperature. This is in stark contrast with that by Brown and Bernasek who reported that the average apparent CO2 vibrational temperature decreased with increasing surface oxygen coverage. The average vibrational temperature was much higher on Pd than on Pt. This is in good agreement with that by Coulston and Haller who suggested that the activated complex is bent more on Pd than on Pt.

Direct measurement of vibrational level populations in CO2 produced during CO oxidation on Pd

The dynamics of carbon monoxide oxidation by O2 on a Pd foil were probed under nearly collision free conditions using high resolution infrared chemiluminescence. Auger electron spectroscopy was used to verify the absence of impurities on the Pd surface. The reactants were supplied to the surface through a free jet nozzle source while a Fourier transform infrared spectrometer (Bomem DA3002) operating at 0.012 cm−1 resolution was used to fully resolve the rotational structure of 14 vibrational transitions in the product CO2. It was found for reaction on a 600 K surface that the (1001, 2001, 3001) symmetric stretch levels were populated consistent with an apparent vibrational temperature of Tsymmetric=3150 K. However, the populations of the levels with no symmetric component (0001, 0111, 0201, 0221, 0311, 0331, 0002, 0401, 0421, 0441, 0003) were better characterized by a temperature Tnonsymmetric=1900 K, with individual mode temperatures for bending and antisymmetric stretch being equal to 1820 and 2130 K, respectively. Increasing the surface temperature by 75 K resulted in a disproportionate increase in each of the temperatures, i.e., Tsymmetric=3700 K, Tanitsymmetric=2530 K and Tbend=2050 K. It is likely that the observed changes in the vibrational populations are due to changes in the reactant coverages as the surface temperature is increased.

Time-resolved spectroscopic studies of the ultraviolet-laser photolysis of Al alkyls for film growth

Time-resolved optical emission spectroscopy, with a resolution of ∼10 ns, was used to investigate the formation of excited photofragments during KrF laser-irradiation of trimethylaluminum (TMA) and triethylaluminum (TEA). The gases were introduced into a vacuum chamber as pulsed molecular beams expanding from a free-jet nozzle. The time-dependence of the fluorescence intensity was measured at various positions, corresponding to different gas pressures P, along the molecular beam. In the case of TMA, the primary peaks observed were the Al 4s 2S→3p 2P atomic transition and the CH A 2Δ→X 2Π (0,0) band. The CH intensity ICH following a laser pulse decreased exponentially with a 1/e decay time τCH ranging from ∼530 ns, in agreement with the radiative lifetime of CH 2Δ(v=0), in the low pressure region of the molecular beam, to ∼150 ns at high pressures. The decrease in τCH with increasing PTMA was due to collisional quenching. The decay of the Al emission intensity IAl was nonexponential since the radiative lifetime of the Al 2S state, 6.8 ns, was less than the laser pulse width, ∼15 ns. The rise times of IAl and ICH, on the other hand, were both <10 ns indicating that CH, like Al, is formed photolytically rather than through subsequent collisions involving photofragments. Substituting TEA for TMA suppressed the CH signal while a new molecular band due to AlH [the (0,0) band of the A 1Π→X 1Σ+ transition] was observed in addition to the atomic Al 2S→2P transition. The rise time of IAlH was also <10 ns indicating that it too was formed photolytically. τAlH was ∼80 ns in agreement with the published AlH radiative lifetime. The significance of these results on the mechanisms of TMA and TEA photodecomposition and C incorporation in Al films grown by KrF-laser photolysis is discussed.