共查询到20条相似文献,搜索用时 31 毫秒
1.
Takayuki Fuyuto Helmut Kronemayer Burkhard Lewerich Jan Brübach Taketoshi Fujikawa Kazuhiro Akihama Thomas Dreier Christof Schulz 《Experiments in fluids》2010,49(4):783-795
A detailed understanding of transport phenomena and reactions in near-wall boundary layers of combustion chambers is essential
for further reducing pollutant emissions and improving thermal efficiencies of internal combustion engines. In a model experiment,
the potential of laser-induced fluorescence (LIF) was investigated for measurements inside the boundary layer connected to
flame-wall interaction at atmospheric pressure. Temperature and species distributions were measured in the quenching boundary
layer formed close to a cooled metal surface located parallel to the flow of a premixed methane/air flat flame. Multi-line
NO-LIF thermometry provided gas-phase temperature distributions. In addition, flame species OH, CH2O and CO were monitored by single-photon (OH, CH2O) and two-photon (CO) excitation LIF, respectively. The temperature dependence of the OH-LIF signal intensities was corrected
for using the measured gas-phase temperature distributions. The spatial line-pair resolution of the imaging system was 22 μm
determined by imaging microscopic line pairs printed on a resolution target. The experimental results show the expected flame
quenching behavior in the boundary layer and they reveal the potential and limitations of the applied diagnostics techniques.
Limitations in spatial resolution are attributed to refraction of fluorescence radiation propagating through steep temperature
gradients in the boundary layer. For the present experimental arrangements, the applied diagnostics techniques are applicable
as close to the wall as 200 μm with measurement precision then exceeding the 15–25% limit for species detection, with estimates
of double this value for the case of H2CO due to the unknown effect of the Boltzmann fraction corrections not included in the data evaluation process. Temperature
measurements are believed to be accurate within 50 K in the near-wall zone, which amounts to roughly 10% at the lower temperatures
encountered in this region of the flames. 相似文献
2.
M. C. J. Coolen R. N. Kieft C. C. M. Rindt A. A. van Steenhoven 《Experiments in fluids》1999,27(5):420-426
The application of Laser Induced Fluorescence (LIF) for temperature measurements in water using a Nd : YAG laser is investigated.
A natural convection problem is used to test the applicability of LIF in the temperature range of 20–60°C. The measured temperature
field is compared with numerical results and the influences of shadowgraph effects on the measured temperature field are investigated.
An accuracy of 1.7°C is attained if shadowgraph effects can be neglected. This only holds if correction for photobleaching
and variation of laser power output is applied.
Received: 8 July 1998/Accepted: 3 February 1999 相似文献
3.
Acetone laser induced fluorescence for low pressure/low temperature flow visualization 总被引:1,自引:0,他引:1
Acetone fluorescence provides a useful way to visualize the fluid mixing process within supersonic wind tunnels, some of
which operate in the low temperature (240–300 K) and low pressure range (0.1–1 atm). Measurements are presented to quantify
the dependence of the acetone laser induced fluorescence (LIF) signal on temperature and pressure in this range. The temperature
and pressure sensitivity of the acetone LIF signal resulted in less than an 8% variation over the experimental conditions
for a laser excitation wavelength of 266 nm. Condensation of the acetone vapor was identified as a potential problem for this
diagnostic technique. Methods to prevent and check for condensation are discussed.
Received: 5 October 1998/Accepted: 10 April 1999 相似文献
4.
M. Löffler S. Pfadler F. Beyrau A. Leipertz F. Dinkelacker Y. Huai A. Sadiki 《Flow, Turbulence and Combustion》2008,81(1-2):205-219
This work presents an experimental approach to the direct determination of the sub-grid scale scalar flux used in Large Eddy Simulation (LES). Two non-reacting jet-flow configurations were examined, one with the jet temperature similar to the ambient air temperature and one preheated jet. Hence data were obtained for varying viscosities. Each case was investigated for two different, high Reynolds numbers of 17,471 and 31,714. For the measurements of mixture fraction and flow velocity field a finest resolution of almost 100 μm was achieved. Thus both the sub-grid scale scalar flux as well as the spatially filtered quantities can be obtained from the same data set. The data were acquired by the simultaneous application of planar laser-induced fluorescence (LIF) and particle image velocimetry (PIV). 相似文献
5.
This paper aims to demonstrate the possibility to achieve droplet temperature measurements per droplet size class by combining
two-color laser-induced fluorescence (LIF) and phase Doppler analyzer (PDA). For that purpose, PDA and LIF signal acquisitions
are synchronized on the same time base. LIF signal is processed on each of the defined size classes in order to derive the
droplet temperature. Since PDA is roughly sensitive to D
2 and LIF roughly to D
3, the detection range of the combination of the two techniques in term of droplet size is carefully analyzed. Finally, the
technique is demonstrated on a spray of n-decane injected in a turbulent over-heated air flow. The influence of the droplet
size and Stokes number on the heating process of the droplets is clearly highlighted. 相似文献
6.
The interaction between oxygen absorption into liquids and bottom shear-induced turbulence was investigated in a grid-stirred tank using a laser-induced fluorescence (LIF) technique. The LIF technique enabled visualization as well as quantification of planar concentration fields of the dissolved oxygen (DO) near the air-water interface. Qualitative observation of the images provided more insight into the physical mechanism controlling the gas transfer process. The high data resolution is an advantage for revealing the concentration distribution within the boundary layer, which is a few hundreds of a micrometer thick. Mean and turbulent fluctuation characteristics were obtained and compared with previous results. 相似文献
7.
Optical distortions have previously prevented non-intrusive measurements of dissolved oxygen concentration profiles by Laser
induced fluorescence (LIF) to within 200 μm of the air–water interface. It is shown that by careful experimental design, reliable
measurements can be obtained within 28 μm of moving air–water interfaces. Consideration of previously unidentified optical
distortions in LIF imagery due to non-linear effects is presented that is critical for robust LIF data processing and experimental
design. Phase resolved gas flux measurements have now been accomplished along wind forced microscale waves and indicate that
the highest mean gas fluxes are located in the wave troughs. The local mean oxygen fluxes as determined by LIF techniques
can be reconciled to within 40% of those obtained by bulk measurement in the water. These data provide a new perspective on
wind-wave enhancement of low solubility gas transfer across the air–water interface. 相似文献
8.
Javad Aminian Chiara Galletti Shahrokh Shahhosseini Leonardo Tognotti 《Flow, Turbulence and Combustion》2012,88(4):597-623
A numerical study of a jet-in-hot coflow (JHC) burner emulating Moderate or Intense Low-oxygen Dilution (MILD) combustion conditions was carried out by solving the Reynolds Averaged Navier-Stokes equations in a two-dimensional axisymmetric domain and using the Eddy Dissipation Concept (EDC) for the turbulence-chemistry interaction treatment. A systematic methodology was used to analyze all possible sources of discrepancies observed between experimental and numerical data, trying to shedding light on the suitability of specific models for MILD combustion. In this regard, the deficiencies that may come from turbulence model or kinetic scheme have been shown by comparative study on four variants of the k-ε model (i.e. the standard, modified, realizable and RNG) together with the Reynolds stress model and three kinetic schemes namely KEE-58, DRM-19 and DRM-22. A variation of an EDC parameter (i.e. increasing the constant of the fine structure residence time) was proposed for better consideration of MILD combustion features and to overcome the over-prediction of peak temperature observed at downstream. In such a manner encouraging results were also obtained for the prediction of major combustion products as well as for CO and OH. 相似文献
9.
J. Scholz T. Wiersbinski P. Ruhnau D. Kondermann C. S. Garbe R. Hain V. Beushausen 《Experiments in fluids》2008,45(4):583-593
A concept for dynamic mixture formation investigations of fuel/air mixtures is presented which can equally be applied to several
other laser induced fluorescence (LIF) applications. Double-pulse LIF imaging was used to gain insight into dynamic mixture
formation processes. The setup consists of a modified standard PIV setup. The "fuel/air ratio measurement by laser induced
fluorescence (FARLIF)" approach is used for a quantification of the LIF images in order to obtain pairs of 2D fuel/air ratio
maps. Two different evaluation concepts for LIF double pulse images are discussed. The first is based on the calculation of
the temporal derivative field of the fuel/air ratio distribution. The result gives insight into the dynamic mixing process,
showing where and how the mixture is changing locally. The second concept uses optical flow methods in order to estimate the
motion of fluorescence (i.e., mixture) structures to gain insight into the dynamics, showing the distortion and the motion
of the inhomogeneous mixture field. For this "fluorescence motion analysis" (FMA) two different evaluation approaches—the
"variational gradient based approach" and the "variational cross correlation based approach"—are presented. For the validation
of both, synthetic LIF image pairs with predefined motion fields were generated. Both methods were applied and the results
compared with the known original motion field. This validation shows that FMA yields reliable results even for image pairs
with low signal/noise ratio. Here, the "variational gradient based approach" turned out to be the better choice so far. Finally,
the experimental combination of double-pulse FARLIF imaging with FMA and simultaneous PIV measurement is demonstrated. The
comparison of the FMA motion field and the flow velocity field captured by PIV shows that both results basically reflect complementary
information of the flow field. It is shown that the motion field of the fluorescence structures does not (necessarily) need
to represent the actual flow velocity and that the flow velocity field alone can not illustrate the structure motion in any
case. Therefore, the simultaneous measurement of both gives the deepest insight into the dynamic mixture formation process.
The examined concepts and evaluation approaches of this paper can easily be adapted to various other planar LIF methods (with
the LIF signal representing, e.g., species concentration, temperature, density etc.) broadening the insight for a wide range
of different dynamic processes.
相似文献
J. Scholz (Corresponding author)Email: Email: |
V. BeushausenEmail: |
10.
Atomic Resonance Absorption Spectroscopy (ARAS) was applied to measure the time dependent concentration of electronically
excited O(D)-atoms during the thermal decomposition of CO behind reflected shock waves. The experiments were performed in the temperature range 4102 K T 6375 K at pressures 0.2 to 1.9 bar with initial gas mixtures of 100 to 1000 ppm CO diluted in Ar. The measured O(D)-formation rate at early reaction times divided by the initial reactant concentrations was found to obey the Arrhenius
law: The assumption of a fast thermalisation between the O(P) and O(D) states is in agreement with previous measurements of the O(P) formation during the thermal decomposition of CO, see Burmeister and Roth (1990).
Received 24 January 1995 / Accepted 13 March 1996 相似文献
11.
A laser-induced fluorescence (LIF) method has been developed that provides simultaneous measurements of temperature, density, and their fluctuations owing to turbulence in unheated compressible flows. Pressure and its fluctuations are also deduced using the equation of state. Fluorescence is induced in nitric oxide that has been seeded into a nitrogen flow in concentrations of 100 ppm. Measurements are obtained from each laser pulse, with a spatial resolution of 1 mm and a temporal resolution of 125 ns. The method was applied to a supersonic, turbulent, boundary-layer flow with a free-stream Mach number of 2. For stream conditions in the range from 150–300 K and 0.3–1 atm, temperature is measured with an uncertainty of approximately 1% rms, while density and pressure uncertainties are approximately 2% rms. 相似文献
12.
13.
J. P. Crimaldi 《Experiments in fluids》1997,23(4):325-330
This study investigates the effect of photobleaching on laser-induced fluorescence (LIF) measurements. Photobleaching causes
the fluorescence to be velocity-dependent, which is undesirable if quantitative measurements are being made. To quantify this
effect, simultaneous and coincident measurements of fluorescence and velocity were made within the measuring volume of a three-beam
laser-Doppler anemometer (LDA), using both fluorescein and rhodamine 6G dyes in water. In addition, analytical expressions
were developed for photobleaching in the LDA measuring volume, and a parameter was identified which predicts the degree of
velocity sensitivity. Fluorescein was found to be far more susceptible to photobleaching than rhodamine 6G. Finally, the impact
of photobleaching on statistical quantities (such as scalar fluxes) obtained from simultaneous LDA/LIF measurements is discussed.
Received: 28 October 1996/Accepted: 17 March 1997 相似文献
14.
Henning Haessler Henning Bockhorn Christian Pfeifer Dietmar Kuhn 《Flow, Turbulence and Combustion》2012,89(2):249-259
The present work describes the imaging of laser induced fluorescence (LIF) of formaldehyde in a high pressure/high temperature atmosphere. Gaseous dimethyl ether (DME) is injected at 70 bar into the combustion chamber. Formaldehyde is detected by its fluorescence from excitation using the third harmonic of a Nd:YAG-laser with a wavelength of 355?nm at chamber pressures of 20, 30 and 40 bar. The experimental results are compared to 1D flamelet simulation of the auto-ignition processes applying a detailed reaction mechanism for DME. The results reveal a very good accordance to the experimental findings. 相似文献
15.
Abstract. Shock tubes often experience temperature and pressure nonuniformities behind the reflected shock wave that cannot be neglected
in chemical kinetics experiments. Because of increased viscous effects, smaller tube diameters, and nonideal shock formation,
the reflected-shock nonidealities tend to be greater in higher-pressure shock tubes. Since the increase in test temperature
() is the most significant parameter for chemical kinetics, experiments were performed to characterize in the Stanford High Pressure Shock Tube using infrared emission from a known amount of CO in argon. From the measured change
in vibrationally equilibrated CO emission with time, the corresponding ddt (or for a known time interval) of the mixture was inferred assuming an isentropic relationship between post-shock temperature
and pressure changes. For a range of representative conditions in argon (24–530 atm, 1275–1900 K), the test temperature 2
cm from the endwall increased 3–8 K after 100 s and 15–40 K after 500 s, depending on the initial conditions. Separate pressure measurements using a shielded piezoelectric transducer confirmed
the isentropic assumption. An analytical model of the reflected-shock gas dynamics was also developed, and the calculated
's agree well with those obtained from experiment. The analytical model was used to estimate the effects of temperature and
pressure nonuniformities on typical chemical kinetics measurements. When the kinetics are fast (s), the temperature increase is typically negligible, although some correction is suggested for kinetics experiments lasting
longer than 500 s. The temperature increase, however, has a negligible impact on the measured laser absorption profiles of OH (306 nm) and
CH (216 nm), validating the use of a constant absorption coefficient. Infrared emission experiments are more sensitive to temperature
and density changes, so nonuniformities should be taken into account when interpreting ir-emission data.
Received 25 April 2000 / Accepted 8 September 2000 相似文献
16.
17.
K. Peter Judd Supathorn Phongikaroon Geoffrey B. Smith Robert A. Handler 《Experiments in fluids》2005,38(1):99-111
The thermal structure of clean and contaminated free-surfaces subject to the transient flow of a gas jet were investigated experimentally. The interface and near-surface flow were examined using optical high-speed (HS) motion analysis, infrared (IR) imagery, and laser-induced fluorescence (LIF). IR imagery revealed an instability in the form of thermal scars on the expanding circular surfactant front. The nature of this instability was explored by performing experiments with both clean and contaminated surfaces. LIF visualization techniques were used to gain insight into the nature of the near-surface flow field. This revealed the presence of a vortex ring that underwent an instability in which ringlets surrounded the primary core. Using simultaneous IR/LIF imaging of a fixed spatial region, it is shown that the thermal scars are spatially and temporally correlated with the near-surface ringlet structures, suggesting that the scars are a surface manifestation of the near-surface structures.
相似文献
K. Peter JuddEmail: |
18.
The flow at the outer boundary of a submerged self-similar turbulent jet at Re=2᎒3 is investigated experimentally by means of combined particle image velocimetry (PIV) laser-induced fluorescence (LIF) measurements. The jet fluid contains a fluorescent dye so that the LIF data can be used to discriminate between the jet fluid and the ambient fluid. The axial velocity, Reynolds stress, and vorticity are determined relative to the jet boundary. The results are compared against the conventional profiles, and the results of a direct numerical simulation of the turbulent far-wake behind a flat plate. The results show a sharp transition between rotational and irrotational fluid at the fluid interface, and the existence of a layer of irrotational velocity fluctuations outside the turbulent region. 相似文献
19.
A quantitative thermometry technique, based on planar laser-induced fluorescence (PLIF), was applied to image temperature
fields immediately next to walls in shock tube flows. Two types of near-wall flows were considered: the side wall thermal
boundary layer behind an incident shock wave, and the end wall thermal layer behind a reflected shock wave. These thin layers
are imaged with high spatial resolution (15μm/pixel) in conjunction with fused silica walls and near-UV bandpass filters to
accurately measure fluorescence signal levels with minimal interferences from scatter and reflection at the wall surface.
Nitrogen, hydrogen or argon gas were premixed with 1–12% toluene, the LIF tracer, and tested under various shock flow conditions.
The measured pressures and temperatures ranged between 0.01 and 0.8 bar and 293 and 600 K, respectively. Temperature field
measurements were found to be in good agreement with theoretical values calculated using 2-D laminar boundary layer and 1-D
heat diffusion equations, respectively. In addition, PLIF images were taken at various time delays behind incident and reflected
shock waves to observe the development of the side wall and end wall layers, respectively. The demonstrated diagnostic strategy
can be used to accurately measure temperature to about 60 μm from the wall. 相似文献
20.
The purpose of this study is to clarify the existence of an ordered and large scale coherent motion in a turbulent plane thermal plume in a thermally-stable stratified fluid inside a comparatively large enclosure. First, the upper part of the thermal plume was carefully observed by a flow visualization. Secondly, a wave form of plume temperature variation was measured. Thirdly, a spectrum analysis was carried out on time series data of the thermal plume. Finally, physical characteristics were investigated on vortices in the thermal plume based on results of the wave form and the spectrum analysis of the plume temperature. As a result, the main conclusions are obtained as follows. (1) An existence of vortices near the upper part of the thermal plume was firstly found by careful flow visualization. (2) From the wave form of temperature variation and the spectrum analysis of the thermal plume, it was clarified that the vortices are generated in the transition state and are transported to the turbulent state. (3) The vortices are ordered and they behave as a large scale coherent motion in the turbulent thermal plume. 相似文献