共查询到20条相似文献,搜索用时 636 毫秒
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B. Bork B. B?hm C. Heeger S. R. Chakravarthy A. Dreizler 《Applied physics. B, Lasers and optics》2010,99(3):487-491
Time-correlated sampling of quantities in transient combustion processes requires high-speed imaging at repetition rates in
the order of typical flame-inherent frequencies. The present study demonstrates the feasibility of temperature measurements
in turbulent flames along a line at 10 kHz using Rayleigh scattering. High signal intensities were gained using an 80 W Nd:YAG
laser for excitation in combination with an optimized combination of an achromatic lens, an objective lens and a CMOS camera.
This allowed achieving signal-to-noise ratios up to 140 at 10 kHz repetition rates. The experimental setup and data processing
aspects are described as well as details on the system characteristics are given. Temperature measurements of the DLR-A jet
flame with a Reynolds number of 15.200 were compared with high-quality conventional 10 Hz simultaneous Raman/Rayleigh data.
The data showed excellent agreement highlighting the reliability of the here demonstrated technique. 相似文献
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Richard G. Seasholtz Alvin E. Buggele Mark F. Reeder 《Optics and Lasers in Engineering》1997,27(6):543-570
Flow diagnostics based on molecular Rayleigh scattering are discussed along with the results of a feasibility study to non-intrusively measure flow properties in a small supersonic wind tunnel. The technique uses an injection seeded, frequency doubled Nd:YAG laser tuned to an absorption band of iodine. The molecular Rayleigh scattered light is filtered with an iodine cell to block light at the laser frequency. The Doppler-shifted Rayleigh scattered light that passes through the iodine cell is analyzed with a planar mirror Fabry-Perot interferometer used in a static imaging mode. An intensified CCD camera is used to record the images. The images are analyzed at several subregions, where the flow properties are determined. Each image is obtained with a single laser pulse, giving instantaneous measurements. 相似文献
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We describe a newly developed combustion diagnostic for the simultaneous planar imaging of soot structure and velocity fields
in a highly sooting, lifted turbulent jet flame at 3000 frames per second, or two orders of magnitude faster than “conventional”
laser imaging systems. This diagnostic uses short pulse duration (8 ns), frequency-doubled, diode-pumped solid state (DPSS)
lasers to excite laser-induced incandescence (LII) at 3 kHz, which is then imaged onto a high framerate CMOS camera. A second
(dual-cavity) DPSS laser and CMOS camera form the basis of a particle image velocity (PIV) system used to acquire 2-component
velocity field in the flame. The LII response curve (measured in a laminar propane diffusion flame) is presented and the combined
diagnostics then applied in a heavily sooting lifted turbulent jet flame. The potential challenges and rewards of application
of this combined imaging technique at high speeds are discussed. 相似文献
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Advances in high-speed laser and camera technology have made scientific kHz repetition rate combustion and flow laser diagnostics
feasible. While quantitative flow-field results have been shown to be possible via PIV, measuring scalars relevant to combustion
such as mixture fraction, temperature and species concentrations is still a significant challenge. Tracer-LIF has proven to
be a useful tool for imaging of mixture fraction. This paper highlights recent success at extending this technique for use
at 9.5 kHz acquisition rate. The measurements are taken near the exit of an isothermal round jet seeded with acetone. Results
taken at both maximum possible signal and a practical configuration for reacting flows are contrasted. Data are fully quantified
and corrected for not only absorption, optical uniformity and laser pulse variation, but also for individual CMOS pixel offset
and sensitivity. 相似文献
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为了对比激光对CCD、CMOS两种图像传感器的干扰效果,利用1.06 μm高重频激光开展了对CCD、CMOS两种相机的饱和干扰实验研究,分析了两种相机在干扰有效面积、饱和干扰面积、干扰前后图像相关度等与激光入射功率之间的关系。实验结果表明:CMOS相机达到单元像素饱和的激光功率阈值是CCD相机的20倍;要达到相同的干扰有效面积,所需的激光功率CMOS相机要大于CCD相机10倍~100倍;要达到相同的饱和像元数,所需的激光功率CMOS相机比CCD相机约大10倍~60倍。因此,CMOS相机要比CCD相机具有更好的抗1.06 μm激光干扰能力。 相似文献
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Doppler wind lidar (DWL) measurements by the fringe-imaging technique in front of aircrafts at flight speed require rapid
processing of backscattered signals. We discuss the measurement principle to derive the 3D wind vector from three line-of-sight
(LOS) measurements. Then we simulate realistic fringe patterns of a Fabry–Pérot-interferometer (FPI) on a 2D charge-coupled
device (CCD) localized at the focal plane behind it, taking atmospheric and instrument properties like scattering and noise
into account. A laser at 355 nm with pulse energies of 70 mJ at 100 Hz repetition rate and a range bin of only 10 m were assumed.
This yields count rates of 24 (13) million photons per pulse at 56 (76) m distance and 8.5 km altitude that are distributed
on a CCD with up to 960×780 pixels without intensification and therefore generate noisy pixel signals. We present two methods
for the precise determination of the radii, i.e., wavelengths of these simulated FPI rings and show that both are suitable
for eliminating pixel noise from the output and coping with fringe broadening by Rayleigh scattering. One of them proves to
reach the accuracy necessary for LOS velocity measurements. A standard deviation of 2.5 m/s including center determination
can be achieved with only 20 images to average. The bias is 7 m/s. For exactly known ring centers, each can be even better
than 2 m/s. The methods could also be useful for high-resolution laser spectroscopy. 相似文献
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An imaging system for the measurement of three-dimensional (3D) scalar gradients in turbulent hydrocarbon flames is described. Combined line imaging of Raman scattering, Rayleigh scattering, and CO laser-induced fluorescence (LIF) allows for simultaneous single-shot line measurements of major species, temperature, mixture fraction, and a one-dimensional surrogate of scalar dissipation rate in hydrocarbon flames, while simultaneous use of two crossed, planar LIF measurements of OH allows for determination of instantaneous flame orientation. In this manner the full 3D scalar dissipation can be estimated in some regions of a turbulent flame on a single-shot basis. 相似文献
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Mohy S. Mansour Ayman M. Elbaz William L. Roberts Mohamed F. Zayed Mrinal Juddoo Bassem M. Akoush Alaa M. Khedr Hazem M. Al-Bulqini Assaad R. Masri 《Proceedings of the Combustion Institute》2021,38(2):2597-2606
Turbulent flames with compositionally inhomogeneous mixtures are common in many combustion systems. Turbulent jet flames with a circular nozzle burner were used earlier to study the impact of inhomogeneous mixtures, and these studies showed that the nozzle radius affects the flame stability. Accordingly, planar turbulent flames with inhomogeneous turbulent jet are created in a concentric flow slot burner (CFSB) to avoid this effect in the present study. The stability characteristics, the mixing field structure, and the flame front structure were measured, and the correlations between stability and the mixing field structure were investigated. The mixture fraction field was measured in non-reacting jets at the nozzle exit using highly resolved Rayleigh scattering technique, and the flame front was measured in some selected turbulent flames using high-speed Planar Laser-Induced Fluorescence (PLIF) of OH technique. The data show strong correlations between flame stability and the range of mixture fraction fluctuations. The flames are highly stabilized within a mixing field environment with the range of fluctuation in mixture fraction close to the range of the flammability limits. The mixing field structure is also illustrated and discussed using a mixing regime diagram and showed that the scatter of the data of the different cases is consistent with the classified mixing regimes. Lean flames are stabilized in the current slot burner. The flame front structure topology varies consistently from thin, small curvature at the low level of turbulence and higher equivalence ratio to more wrinkled, larger curvature, but a thicker structure at a higher level of turbulence and lower equivalence ratio. 相似文献
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Condensation of gaseous monosilane-argon and monosilane-helium mixtures was investigated in free jets by a Rayleigh scattering laser diagnostic technique. The condensation of a SiH4-Ar mixture begins to develop at a lower stagnation pressure and at a shorter distance from the nozzle, and proceeds at a higher rate, as compared to condensation in monosilane-helium and pure argon jets. The results of Rayleigh scattering measurements in condensing monosilane-argon jets scale with the parameter P 0 d 0.8. An analysis of the results obtained in this study and found in literature suggests that simultaneous monosilane-argon condensation lead-ing to the formation of mixed clusters takes place in the monosilane-argon mixture. 相似文献
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Single-shot measurement of soot aggregate sizes by wide-angle light scattering (WALS) 总被引:1,自引:0,他引:1
The wide-angle light scattering (WALS) approach has been utilized for the measurement of soot aggregate sizes (radii of gyration)
in flames on a single-shot basis. Key elements are a pulsed laser and an ellipsoidal mirror, which images the light scattered
within a plane onto an intensified CCD camera, thus allowing for an instantaneous acquisition of a full scattering diagram
with high resolution. Results for a laminar premixed flame exhibit good agreement with averaged data and demonstrate the feasibility
of the method. The applicability of the technique to unsteady combustion processes is demonstrated by measuring aggregate
sizes in a weakly turbulent jet-diffusion flame. In both cases light scattering results are verified by data obtained from
electron microscopy analysis of sampled soot. 相似文献
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D. Mathew P. J. M. Peters H. M. J. Bastiaens K.-J. Boller 《Applied physics. B, Lasers and optics》2009,95(1):155-159
The effect of addition of xenon on the long term homogeneity of discharges in F2and ArF excimer laser gas mixtures was investigated in a small-volume discharge chamber. The gas mixture in the discharge
chamber was preionized by X-rays. A special electrical excitation circuit containing a pulse forming line provided a long,
square-shaped current pumping pulse of a predetermined duration to the discharge electrodes. The initiation and the development
of the discharge was monitored via its fluorescence signal with an intensified CCD camera. We found that adding Xe up to partial
pressures of 0.53 mbar extended the homogeneous phase of the discharge from 80 ns to approximately 200 ns in He/F2as well as in He/Ar/F2and Ne/Ar/F2excimer laser gas mixtures. Monitoring of the ArF and XeF spontaneous emission signals showed that the formation of ArF excimers
remained unaffected by the addition of xenon (up to 1.3 mbar) to the laser gas mixture. 相似文献
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Scalar length scales and spatial averaging effects in turbulent piloted methane/air jet flames 总被引:2,自引:0,他引:2
The effects of spatial averaging in measurements of scalar variance and scalar dissipation in three piloted methane/air jet flames (Sandia flames C, D, and E) are investigated. Line imaging of Raman scattering, Rayleigh scattering, and laser-induced CO fluorescence is applied to obtain simultaneous single-shot measurements of temperature, the mass fractions of all major species, and mixture fraction, ξ, along 7-mm segments. Spatial filters are applied to ensembles of instantaneous profiles to quantify effects of spatial averaging on the Favre mean and variance of mixture fraction and scalar dissipation at several locations in the three flames. The radial contribution to scalar dissipation, χr = 2Dξ (∂ξ/∂r)2, is calculated from the filtered instantaneous profiles. The variance of mixture fraction tends to decrease linearly with increasing filter width, while the mean and variance of scalar dissipation are observed to follow an exponential dependence. In each case, the observed functional dependence is used to extrapolate to zero filter width, yielding estimates of the “fully resolved” profiles of measured quantities. Length scales for resolution of scalar variance and scalar dissipation are also extracted from the spatial filtering analysis and compared with length scales obtained from spatial autocorrelations. These results provide new insights on the small scale structure of turbulent jet flames and on the spatial resolution requirements for measurements of scalar variance and scalar dissipation. 相似文献
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A high-speed technique that combines planar laser induced fluorescence (PLIF) detection of biacetyl and particle image velocimetry (PIV) for simultaneous imaging of scalar and velocity fields is demonstrated at a frame rate of 12 kHz for up to 32500 consecutive frames. A single diode-pumped, frequency-tripled Nd-YAG laser was used for excitation. Wavelength-separated recording was achieved for Mie scattering from silicone oil droplets with a CMOS camera and for the red-shifted fluorescence from biacetyl with an image-intensified CMOS camera. Interference between PIV and PLIF tracers was found to be negligible. Cross-talk between PIV and PLIF signals was low and a strategy to completely eliminate it was devised and is discussed. The signal-to-noise ratio is about 9 for single-shot scalar images. Example image sequences were recorded in an atmospheric pressure air jet at Re=2000. PACS 42.62.Fi; 33.50.Dq; 06.30.Gv; 06.60.Jn 相似文献
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Joseph D. Miller James B. Michael Mikhail N. Slipchenko Sukesh Roy Terrence R. Meyer James R. Gord 《Applied physics. B, Lasers and optics》2013,113(1):93-97
Simultaneous high-speed quantitative imaging of mixture fraction and velocity is demonstrated using the fourth- and second-harmonic outputs, respectively, of a burst-mode Nd:YAG laser. A tenfold increase in the record length and 16-fold increase in per-pulse energy are achieved compared with previous measurements of mixture fraction using burst-mode and continuously pulsed diode-pumped solid-state lasers, respectively. The high output energy is used for quantitative, high-speed mixture-fraction imaging with acetone planar laser-induced fluorescence, which also enables simultaneous particle-based velocimetry without interference from particle scattering. A semiquantitative model is used to determine the limitations on fourth-harmonic output energy due to the effects of transient absorption and thermal phase mismatch over a range of repetition rates. Data are presented for mixing within a turbulent jet (Reynolds number of 15,000) and are validated by comparisons with known turbulent mixing laws and previously published data. 相似文献