共查询到17条相似文献,搜索用时 140 毫秒
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四气门汽油机缸内滚流运动对燃烧过程影响的研究 总被引:1,自引:0,他引:1
1引言近年来,四气门汽油机由于性能优越,已成为车用发动机的发展方向,而我国在这方面的研究和开发还没有开展。对其缸内空气运动的研究发现[1-4]:当两个进气门都打开时,缸内空气运动主要是绕与气缸轴线垂直方向旋转的滚流运动(Tumblemotion),与传统二气门发动机缸内形成的绕气缸轴线旋转的涡流运动(Swirlmotion)不同;它在压缩末期很容易破碎,大大增加了湍流强度,促进燃烧过程明显改善。但在低速时,由于进气速度下降,燃油在进气道蒸发和雾化变差,使燃烧过程恶化,发动机扭矩下降。为此,一些汽车公司采用在低速时将一个进气… 相似文献
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四气门汽油机分层EGR的试验研究 总被引:1,自引:0,他引:1
针对可以产生较强滚流运动的1.6 L四气门产品汽油机,设计了一套独特的分层废气再循环(EGR)装置。通过废气导入管将废气引到进气阀处,利用缸内气体滚流运动,实现废气与新鲜可燃混合气分层。在发动机台架上通过试验详细地研究该分层EGR装置对汽油机性能和燃烧的影响。试验结果表明,采用该装置后,相比于传统的EGR方式,EGR 率有所增加,在大量降低NOx排放同时,经济性有所改善, CO和HC排放有所降低,燃烧效率提高,但点火时刻应适当提前。 相似文献
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对单摆运动周期计算的讨论陆荷琴,葛宇宏(盐城商业学校224001)(盐城建筑工程学校224001)物理教学过程中,常常要涉及计算处于超重、失重状态和处于迭加场中单摆的周期,在特定条件下,这些单摆周期计算的结果,可能式.于是平时勤学好问的学生提出了:根... 相似文献
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液固两相流中流体旋涡对固体粒子运动影响的数值研究 总被引:9,自引:0,他引:9
基于离散涡方法求得的非定常、不稳定流场和颗粒的Lagrangian运动方程,数值计算了四种St数下的泥沙粒子在圆柱绕流场中的运动。计算结果证明了颗粒运动与流体旋涡存在着明确的相关结构:在钝体(圆柱)表面附着泥沙,当流体流过钝体时产生具有剧烈分离的不稳定流动,带动钝体表面泥沙起浮。对于小St数(0.15~0.59)与中等St数(1.33~2.36)的泥沙颗粒被流体旋涡所带起,井被卷入流体旋涡结构内,被卷入流体旋涡结构内的泥沙颗粒在运动过程中始终分布于旋涡区,即在旋涡区聚集。 相似文献
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内燃机气道及缸内气体流动特性研究 总被引:2,自引:0,他引:2
本文对某型号内燃机气道稳态流动和缸内气流运动特性进行了研究.气道流动特性稳态计算结果与气道稳流试验结果相吻合,流动特征参数偏差在3%左右.瞬态计算结果表明,在进气行程初期,缸内涡流和湍流迅速增强,随后涡流变化缓慢,而湍流强度迅速下降.在气门叠开时,存在进气和排气回流现象.进气时,进气阀边缘处是缸内气体最大速度出现位置,气门最大升程时该处速度达到134.4m/s;切向气道缩口处最大速度高达134.7m/s,此处存在一定的进气节流损失. 相似文献
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再入尾迹湍流对雷达散射截面影响分析 总被引:4,自引:0,他引:4
通过探讨高超声速再入湍流尾迹等离子体场中电磁波的散射机制,推导出在工程上描述湍流亚密等离子体雷达散射的一阶畸变波Born近似模型,分析了该模型在充分发展湍流尾迹等离子体场中的适用性,完成了适用于三维尾迹等离子体场的程序设计.以已有的湍流尾迹等离子体流场数据为基础,分析了再入尾迹湍流等离子体流动对雷达散射截面的影响.选取考察的几个有代表性的因素为:湍流模型、转捩过程、湍流尺度、电子组分脉动初始条件等.由结果可以看到,湍流转捩过程和湍流尺度对雷达散射截面值影响不大;电子组份脉动强度初始值影响较明显;湍流模型在特定条件下影响亦不大. 相似文献
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《Physics letters. A》1988,126(4):243-248
The build up of coherent large amplitude helicity fluctuations is detected in numerical experiments on 3-D homogeneous turbulence. 相似文献
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Gleizes A. Rahal A.M. Papadopoulos S. Vacquie S. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1988,16(6):615-622
For pt.I see ibid., vol.16, no.6, p.606-14 (1988). The experimental results presented concern the variations of the mean electric field and gas mass flow during this phase. The most important part consists of a modeling of the evolution of the interruption arc during the decrease of the current from 1000 A to 0. In this modeling, based on the conservation equations of mass and energy, the boundary conditions are determined by an approximate separate modeling of the arc whereas turbulence is treated through Prandtl's approximation. This theoretical study has been developed in the case of SF6 and nitrogen. The computed values of the electric field and temperature show that the arc has a quasi-stationary behaviour as long as the current intensity is greater than a few tens of amperes, for a decay rate of 1.35 A/μs. The energy losses are governed by radiation at high current and by turbulence conduction at low current. The most important results concern the conductance, whose evolution time constant, immediately prior to current zero, is 3.5 μs in SF6 and 15 μs in nitrogen. The difference is essentially due to variations with temperature of thermal conductivity and specific heat in two gases 相似文献
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提出在湍流边界层近壁区采用三维波的理论模型描述湍流相干结构,根据理论模型计算了Reynolds应力输运方程中的脉动速度与脉动压力梯度的相关项,理论计算结果与直接数值模拟(DNS)符合很好。表明该理论方法不仅有益于对湍流机制的了解,而且可能为湍流的近壁模型化开辟一条新的途径。 相似文献
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A numerical wave optics approach for simulating multiplex super Gaussian beam combination in high-power laser facility is presented. The approach involves the application of a sequence of random phase screens and von Karman turbulence phase to an initial beam field and the summation of the intensity results. The analytical and numerical calculation results have been given to illustrate the properties of the resulting far-field pattern after coherent, incoherent and spatially coherent combination, and some of that are compared with experimental results. The approach can be used for modeling and evaluating applications such as high-power laser shooting that might utilize different beams combining approach. 相似文献
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A numerical study of three-dimensional liquid sloshing in tanks 总被引:1,自引:0,他引:1
A numerical model NEWTANK (Numerical Wave TANK) has been developed to study three-dimensional (3-D) non-linear liquid sloshing with broken free surfaces. The numerical model solves the spatially averaged Navier–Stokes equations, which are constructed on a non-inertial reference frame having arbitrary six degree-of-freedom (DOF) of motions, for two-phase flows. The large-eddy-simulation (LES) approach is adopted to model the turbulence effect by using the Smagorinsky sub-grid scale (SGS) closure model. The two-step projection method is employed in the numerical solutions, aided by the Bi-CGSTAB technique to solve the pressure Poisson equation for the filtered pressure field. The second-order accurate volume-of-fluid (VOF) method is used to track the distorted and broken free surface. Laboratory experiments are conducted for both 2-D and 3-D non-linear liquid sloshing in a rectangular tank. A linear analytical solution of 3-D liquid sloshing under the coupled surge and sway excitation is also developed in this study. The numerical model is first validated against the available analytical solution and experimental data for 2-D liquid sloshing of both inviscid and viscous fluids. The validation is further extended to 3-D liquid sloshing. The numerical results match with the analytical solution when the excitation amplitude is small. When the excitation amplitude is large where sloshing becomes highly non-linear, large discrepancies are developed between the numerical results and the analytical solutions, the former of which, however, agree well with the experimental data. Finally, as a demonstration, a violent liquid sloshing with broken free surfaces under six DOF excitations is simulated and discussed. 相似文献