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1.
Two-component laser anemometry measurements of non-reacting and reacting complex flows in a swirl-stabilized model combustor 总被引:5,自引:0,他引:5
Simultaneous two-component velocity measurements are acquired in a model, complex flow swirl-stabilized combustor using a two-color laser anemometer. A time base computer interface enables the direct measurement of Reynolds stress
as well as mean and rms axial (u,u) and azimuthal (w,w) velocities. The peak value of the normalized Reynolds stress
approaches 0.25 which is less than values (0.40) obtained by others using indirect, non-simultaneous measurement methods in complex flows, but similar to a direct measurement in a dump combustor without swirl. Isotropy is satisfied except in regions of high unidimensional shear, and both turbulence intensity and normalized Reynolds stress are reduced in the absence of reaction. Relatively small-scale form intermittencies, associated with a fluctuation of the stagnation point and a precessing vortex core, serve to reduce the measured values of the normalized Reynolds stress at the centerline by increasing the apparent turbulence intensity. At an elevated fuel loading, a global-scale form intermittency is invoked and, while likely realistic relative to practical devices, may not be a viable condition for time-averaged calculations.A version of this paper was presented at the ASME Winter Annual Meeting of 1984 and printed in AMD, Vol. 66 相似文献
3.
Pushover分析方法近年来引起了地震工程界的广泛兴趣,我国新的抗震设计规范已将其作为大震下结构弹塑性变形分析的一种方法。结构不规则性是影响Pushover分析应用的一个主要因素,而加载模式的选取则是Pushover分析的一个关键问题。本文采用FEMA273建议的3种加载模式对两个典型的三维偏心结构(刚度偏心和质量偏心)进行了Pushover分析,并与非线性动力时程分析的结果进行了比较,给出了三维偏心结构Pushover分析加载模式选取的建议。 相似文献
4.
The bimodulus material is a classical model to describe the elastic behavior of materials with tension-compression asymmetry.Due to the inherently nonlinear properties of bimodular materials,traditional iteration methods suffer from low convergence efficiency and poor adaptability for large-scale structures in engineering.In this paper,a novel 3D algorithm is established by complementing the three shear moduli of the constitutive equation in principal stress coordinates.In contrast to the existing 3D shear modulus constructed based on experience,in this paper the shear modulus is derived theoretically through a limit process.Then,a theoretically self-consistent complemented algorithm is established and implemented in ABAQUS via UMAT;its good stability and convergence efficiency are verified by using benchmark examples.Numerical analysis shows that the calculation error for bimodulus structures using the traditional linear elastic theory is large,which is not in line with reality. 相似文献
5.
W. Hubschmid R. Bombach A. Inauen F. Güthe S. Schenker N. Tylli W. Kreutner 《Experiments in fluids》2008,45(1):167-182
Laser-induced fluorescence and chemiluminescence, both phase-locked to the dominant acoustic oscillation, are used to investigate
phenomena related to thermoacoustic instability in a swirl-stabilized industrial scale gas turbine burner. The observed sinusoidal
phase-averaged flame motion in axial (main flow) direction is analyzed using different schemes for defining the flame position.
Qualitative agreement between experimental data and theoretical analysis of the observed flame motion is obtained, interpreted
as originating primarily from variation of the burning velocity. The heat release variation during an acoustic cycle is determined
from the sinusoidally varying total OH* chemiluminescence intensity.
相似文献
W. HubschmidEmail: |
6.
Stereoscopic imaging and reconstruction of turbulent impinging diffusion flames have been demonstrated. The 3D geometry of the flame surface is reconstructed from any pair of stereo images through digital image processing and computer vision. Only one camera is required to capture the pair of stereo images due to the use of a stereo adapter. As a result the pair of flame images is captured on a single CCD chip. They are then post-processed to produce a 3D geometry of the flame. The 3D results and surface area calculations demonstrate the potential of stereo visualisation, data extraction and the validity of the proposed methodology. 相似文献
7.
Topology optimization of continuum structures with design-dependent loads has long been a challenge. In this paper, the topology optimization of 3D structures subjected to design-dependent loads is investigated. A boundary search scheme is proposed for 3D problems, by means of which the load surface can be identified effectively and efficiently, and the difficulties arising in other approaches can be overcome. The load surfaces are made up of the boundaries of finite elements and the loads can be directly applied to corresponding element nodes, which leads to great convenience in the application of this method. Finally, the effectiveness and efficiency of the proposed method is validated by several numerical examples. 相似文献
8.
Jong-Ryul KimGyung-Min Choi Duck-Jool Kim 《Experimental Thermal and Fluid Science》2011,35(1):165-171
The influence of varying combustor pressure on flame oscillation and emission characteristics in the partially premixed turbulent flame were investigated. In order to investigate combustion characteristics in the partially premixed turbulent flame, the combustor pressure was controlled in the range of −30 to 30 kPa for each equivalence ratio (Φ = 0.8-1.2). The r.m.s. of the pressure fluctuations increased with decreasing combustor pressure for the lean condition. The combustor pressure had a sizeable influence on combustion oscillation, whose dominant frequency varied with the combustor pressure. Combustion instabilities could be controlled by increasing the turbulent intensity of the unburned mixture under the lean condition. An unstable flame was caused by incomplete combustion; hence, EICO greatly increased. Furthermore, EINOx simply reduced with decreasing combustor pressure at a rate of 0.035 g/10 kPa. The possibility of combustion control on the combusting mode and exhaust gas emission was demonstrated. 相似文献
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High-speed laser diagnostics for the study of flame dynamics in a lean premixed gas turbine model combustor 总被引:1,自引:0,他引:1
Isaac Boxx Christoph M. Arndt Campbell D. Carter Wolfgang Meier 《Experiments in fluids》2012,52(3):555-567
A series of measurements was taken on two technically premixed, swirl-stabilized methane-air flames (at overall equivalence
ratios of ϕ = 0.73 and 0.83) in an optically accessible gas turbine model combustor. The primary diagnostics used were combined
planar laser-induced fluorescence of the OH radical and stereoscopic particle image velocimetry (PIV) with simultaneous repetition
rates of 10 kHz and a measurement duration of 0.8 s. Also measured were acoustic pulsations and OH chemiluminescence. Analysis
revealed strong local periodicity in the thermoacoustically self-excited (or ‘noisy’) flame (ϕ = 0.73) in the regions of the flow corresponding to the inner shear layer and the jet-inflow. This periodicity
appears to be the result of a helical precessing vortex core (PVC) present in that region of the combustor. The PVC has a
precession frequency double (at 570 Hz) that of the thermo-acoustic pulsation (at 288 Hz). A comparison of the various data
sets and analysis techniques applied to each flame suggests a strong coupling between the PVC and the thermo-acoustic pulsation
in the noisy flame. Measurements of the stable (‘quiet’) flame (ϕ = 0.83) revealed a global fluctuation in both velocity and heat-release around 364 Hz, but no clear evidence of
a PVC. 相似文献
11.
We have proved that any 3-dimensional dynamical system of ordinary differential equations (in short, 3D ODE) with time-independent
invariants can be rewritten as Hamiltonian systems with respect to generalized Poisson brackets and the Hamiltonians are these
invariants. As an example, we discuss the Kermack-Mckendrick model for epidemics in detail. The results we obtained are generalization
of those obtained by Y. Nutku.
First Received Nov. 22, 1993 相似文献
12.
This paper presents a 3D topology optimization approach for designing shell structures with a porous or void interior. It is shown that the resulting structures are significantly more robust towards load perturbations than completely solid structures optimized under the same condi-tions. The study indicates that the potential benefit of using porous structures is higher for lower total volume fractions. Compared to earlier work dealing with 2D topology opti-mization, we found several new effects in 3D problems. Most notably, the opportunity for designing closed shells signifi-cantly improves the performance of porous structures due to the sandwich effect. Furthermore, the paper introduces improved filter boundary conditions to ensure a completely uniform coating thickness at the design domain boundary. 相似文献
13.
An advanced incremental crack growth algorithm for the three-dimensional (3D) simulation of fatigue crack growth in complex 3D structures with linear elastic material behavior is presented. To perform the crack growth simulation as effectively as possible an accurate stress analysis is done by the boundary-element method (BEM) in terms of the 3D dual BEM. The question concerning a reliable 3D crack growth criterion is answered based on experimental observations. All criteria under consideration are numerically realized by a predictor–corrector procedure. The agreement between numerically determined and experimentally observed crack fronts will be shown on both fracture specimens and an industrial application. 相似文献
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结合简化阻抗法建立了三维相互作用结构的动力有限元分析模型,导出了考虑群桩刚体、惯性效应作用时的结构相互作用时程积分方程式,以近乎纯结构有限元的建模途径合理地反映出桩-土-上部结构在水平地震作用下的动力相互作用特性。模型中引入具有桩(筏)-土阻抗特性的弹阻单元来描述不同群桩布置、土层状况因素对体系反应的参与作用,而在动力方程中竖向SV剪切波经桩土刚体相互作用产生的水平、摇摆分量对体系的影响亦得以体现。20层桩承刚框架结构的动力分析表明:较柔的桩、土基础使得体系的SSI效应增强,但其参与程度与群桩效应相关,而结构构件内力较不考虑相互作用时有较大折减;应用该法可精确、快速地进行复杂上、下部结构时程反应分析。 相似文献
17.
3D composite materials are characterized by complex internal yarn architectures, leading to complex deformation and failure development mechanisms. Net-shaped preforms, which are originally periodic in nature, lose their periodicity when the fabric is draped, deformed on a tool, and consolidated to create geometrically complex composite components. As a result, the internal yarn architecture, which dominates the mechanical behaviour, becomes dependent on the structural geometry. Hence, predicting the mechanical behaviour of 3D composites requires an accurate representation of the yarn architecture within structural scale models. When applied to 3D composites, conventional finite element modelling techniques are limited to either homogenised properties at the structural scale, or the unit cell scale for a more detailed material property definition. Consequently, these models fail to capture the complex phenomena occurring across multiple length scales and their effects on a 3D composite’s mechanical response. Here a multi-scale modelling approach based on a 3D spatial Voronoi tessellation is proposed. The model creates an intermediate length scale suitable for homogenisation to deal with the non-periodic nature of the final material. Information is passed between the different length scales to allow for the effect of the structural geometry to be taken into account on the smaller scales. The stiffness and surface strain predictions from the proposed model have been found to be in good agreement with experimental results.The proposed modelling framework has been used to gain important insight into the behaviour of this category of materials. It has been observed that the strain and stress distributions are strongly dependent on the internal yarn architecture and consequently on the final component geometry. Even for simple coupon tests, the internal architecture and geometric effects dominate the mechanical response. Consequently, the behaviour of 3D woven composites should be considered to be a structure specific response rather than generic homogenised material properties. 相似文献
18.
Marco Gherlone Priscilla Cerracchio Massimiliano Mattone Marco Di Sciuva Alexander Tessler 《International Journal of Solids and Structures》2012,49(22):3100-3112
A robust and efficient computational method for reconstructing the elastodynamic structural response of truss, beam, and frame structures, using measured surface-strain data, is presented. Known as “shape sensing”, this inverse problem has important implications for real-time actuation and control of smart structures, and for monitoring of structural integrity. The present formulation, based on the inverse Finite Element Method (iFEM), uses a least-squares variational principle involving section strains (also known as strain measures) of Timoshenko theory for stretching, torsion, bending, and transverse shear. The present iFEM methodology is based on strain–displacement relations only, without invoking force equilibrium. Consequently, both static and time-varying displacement fields can be reconstructed without the knowledge of material properties, applied loading, or damping characteristics. Two finite elements capable of modeling frame structures are derived using interdependent interpolations, in which interior degrees of freedom are condensed out at the element level. In addition, relationships between the order of kinematic-element interpolations and the number of required strain gauges are established. Several example problems involving cantilevered beams and three-dimensional frame structures undergoing static and dynamic response are discussed. To simulate experimentally measured strains and to establish reference displacements, high-fidelity MSC/NASTRAN finite element analyses are performed. Furthermore, numerically simulated measurement errors, based on Gaussian distribution, are also considered in order to verify the stability and robustness of the methodology. The iFEM solution accuracy is examined with respect to various levels of discretization and the number of strain gauges. 相似文献
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High-resolution 2-D imaging of laser Rayleigh scattering is used to measure the detailed structure of the thermal dissipation
field in a turbulent non-premixed CH4/H2/N2 jet flame. Measurements are performed in the near field (x/d = 5–20) of the flame where the primary combustion reactions interact with the turbulent flow. The contributions of both the
axial and radial gradients to the mean thermal dissipation are determined from the 2-D dissipation measurements. The relative
contributions of the two components vary significantly with radial position. The dissipation field exhibits thin layers of
high dissipation. Noise suppression by adaptive smoothing enables accurate determination of the dissipation-layer widths from
single-shot measurements. Probability density functions (PDF) of the dissipation-layer widths conditioned on temperature are
approximately log-normal distributions. The conditional layer width PDFs are self-similar functions with the layer widths
scaling with temperature to the 0.75 power. The high signal-to-noise ratio of the Rayleigh scattering images coupled with
an interlacing technique for noise suppression enable fully resolved measurements of the mean power spectral density (PSD)
of the temperature gradients. These spectra are used to determine the turbulence microscales by measuring a cutoff wavelength,
λ
C
, at 2% of the peak PSD. The Batchelor scale is estimated from λ
C
, and the results are compared with estimates from scaling laws in non-reacting flows. At x/d = 20, the different approaches to determining the Batchelor scale are comparable on the jet centerline. However, the estimates
from non-reacting flow scaling laws are significantly less accurate in off-centerline regions and at locations closer to the
nozzle exit. Throughout the near field of the jet flame, the measured ratio of a characteristic dissipation-layer width to
the local Batchelor scale is larger than values previously reported for the far field of non-reacting flows. 相似文献