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991.
P. Habisreuther C. Bender O. Petsch H. Büchner H. Bockhorn 《Flow, Turbulence and Combustion》2006,77(1-4):147-160
The most common and reliable technique used for flame stabilization of industrial combustors with high thermal loads is the application of strongly swirling flows. In addition to stabilization, swirl flames offer the possibility to influence emission characteristics by simply changing the swirl intensity or the type of swirl generation. Despite of these major advantages, swirling flows tend to evolve flow instabilities, that considerably constitute a significant source of noise. In general, noise generation is substantially enhanced, when such a swirling flow is employed for flames. Thus, the minimization of the resulting noise emissions under conservation of the benefit of high ignition stability is one major design challenge for the development of modern swirl stabilized combustion devices. The present investigation makes an attempt to determine mechanisms and processes to influence the noise generation of flames with underlying swirling flows. Therefore, a new burner has been designed, that offers the possibility to vary geometrical parameters as well as the type of swirl generation, typically applied in industrial devices. Experimental data has been acquired for the isothermal flow as well as swirl flames by means of 3-D-LDV-diagnostics comprising the components of long-time averaged mean and rms-velocities as well as spectrally resolved velocity fluctuations for all components. The noise emission data was acquired with microphone probes resulting in sound pressure levels outside the zone of the perceptible fluid flow. Along to the experiments, numerical simulations using RANS and LES have been carried out for isothermal cases with different burner outlet geometries. The results of the measurements show a distinct rise of the sound pressure level, obtained by changing both the test setup from the isothermal into the flame configuration as well as the geometrical parameters. This is also resembled by the LES simulation results. Furthermore, a physical model has been developed from experiments and verified by the LES simulation, that explains the formation of coherent flow structures and allows to separate their contribution to the overall noise emission from ordinary turbulent noise sources. 相似文献
992.
根据HAN基液滴LP-1846点火的挂滴实验[1],提出了点火模型。应用分歧理论找出了相应的点火判据。按二维定态投影法给出了分歧分析解。通过对点火判据的分析,发现理论与实验符合得较好。 相似文献
993.
Nomenclatureci Massfraction ;cix,ciy,ciz Derivativesofgradientofcicp ConstantpressurespecificheatcD Dragcoefficientd DropletdiameterD TotaldiffusioncoefficientE TotalenergyperunitvolumeF Dragforceofdropletsfx,fy,fz ComponentsofF^Hg,^Hl Sourcetermsofga… 相似文献
994.
倪明康 《应用数学和力学(英文版)》1991,12(5):461-468
This paper deals with the problem on the periodic solution for the singularly perturbeddifferential equations of parabolic type originating from chemical kinetics in stratifiedmedia,A uniformly valid asymptotic solution is constructed and the related asymptoticestimate is given. 相似文献
995.
为了探索液体碳氢燃料参与旋转爆轰所产生的不完全燃烧现象,采用守恒元与求解元方法,开展柱坐标系下的汽油/空气两相旋转爆轰燃烧室三维数值模拟研究,针对燃料喷注压力和反应物当量比对旋转爆轰流场结构及燃烧室性能的影响进行分析。分析结果表明:保持总当量比为1.00,随着燃料喷注压力的上升,燃烧室内燃料不均匀分布增强,产生局部富燃区,燃料在燃烧室未能完全反应,导致燃烧室燃料比冲下降;保持喷注压力不变,减小当量比,在贫燃工况下依然存在局部富燃区,导致燃烧室内出现不完全燃烧现象,降低燃烧室比冲性能。由此可知,反应物喷注方案对气液两相旋转爆轰的不完全燃烧有显著影响。 相似文献
996.
分层流体中内孤立波在台阶上的反射和透射 总被引:2,自引:0,他引:2
基于匹配渐近展开和格林函数的方法,研究了两层流体系统中内孤立波在台阶地形上透射、
反射及其分裂的演化特征. 通过保角变换和求解奇异Fredholm积分方程,获得了反映地形
效应对Boussinesq方程影响的约化边界条件,藉此建立了KdV演化方程的``初值'问题,
根据散射反演理论获得了反射波和透射波的解析表达式. 分析结果表明:上下流体层的厚度
比、密度比以及台阶高度对于反射和透射波振幅及其分裂具有显著的影响. 尤其当上层流体
厚度小于下层厚度时,由于存在临界点,在其附近反射波的幅值随台阶高度的演化由单调增
变为单调减,透射波的幅值由单调减变为单调增;上台阶的反射波与入射波反相,其最大幅
值可达到入射波的数倍;此外,下台阶反射波也可发展为单支孤立波,它区别于单层流体中
反射波仅为衰减的振荡波列. 相似文献
997.
In this article, the non-isothermal Poiseuille flow and its stability in a vertical annulus filled with porous medium are investigated. The flow is induced by external pressure gradient and buoyancy force due to linearly varying inner wall temperature. The non-Darcy model along with Boussinesq approximation has been used. The Chebyshev spectral-collocation method has been adopted to solve the governing equations related to basic flow as well as its stability. Special attention is given to understand the effect of curvature parameter of the annular geometry on the flow, heat transfer rate and stability of the stably stratified flow. A comprehensive numerical experiment indicates that reducing gap between two concentric cylinders decreases the heat transfer rate as well as the maximum magnitude of the flow velocity. It stabilizes the flow which has been shown through stability analysis. Furthermore, appropriateness of the Forchheimer term in the momentum equation has been examined by investigating the flow regime as well as its stability in the presence and absence of Forchheimer term. Finally, it has been found from the energy analysis at critical point that the thermal-buoyant instability is the only mode of instability for the considered range of different parameters. 相似文献
998.
A presumed probability density function (PDF) model for temperature fluctuation is proposed and formulated in this paper. It incorporates the four-step reaction mechanism of methane combustion. A set of analytical expressions is derived for the time-averaged four-step reaction rates. The model is employed to numerically simulate methane turbulent swirling flame in the TECFLAM combustor. The calculated gas axial, radial and tangential velocities, species mass fractions, temperature, and temperature fluctuation are compared with the measured test data. Agreement is achieved between the calculation and the measurement. 相似文献
999.
1000.
应用FTIR和脉冲反应技术研究了CO_2和O_2在Ag-Ba-Ca-K/α-Al2O3上的吸附及CO2对C2H4环氧化、完全氧化及环氧乙烷(EO)深度氧化反应的影响.研究结果表明,CO2和表面吸附氧在负载银催化剂表面存在竞争吸附,CO2对表面吸附氧有置换作用,该作用降低了银催化剂表面吸附氧的浓度,并且所形成的碳酸根物种改善了乙烯环氧化反应活住氧种的表面分布,对C_2H_4的环氧化反应有一定的抑制作用,但是对C2H4和EO的深度氧化反应的抑制作用更强,使得乙烯环氧化反应的选择性得到改善. 相似文献