Based on FLUENT software, the flow field of cooling oil between a friction pair in an engaged wet dual clutch is simulated and the influence of groove structural parameters on the flow filed characteristics of cooling oil is studied. The results show that the structural parameters of radial groove have a great influence on the cooling oil flow field between a friction pair. When the inclination direction of groove is opposite to the rotation direction of friction pair, the groove inclination angle has a great influence on oil flow field between fiction pair, and the influence is relatively small when the groove inclination angle is consistent with the rotation direction of friction pair. In addition, the velocity distribution trend in the inclined radial groove is the same as that of the inclination angle = 0, but the velocity magnitude is larger and the highest velocity appears near the opposite side of the groove to the inclined direction of the grooves either for clockwise or counter-clockwise rotation of the friction pair. On the other hand, when the cross sectional area of the groove is kept constant, the average velocity in the central circumferential section of the groove is decreased rapidly with the increase of the groove aspect ratio (width to depth ratio) until the aspect ratio is equal to 5, and then slowly.

In this paper, a set of direct numerical simulations on the thermocapillary flow of 2cSt silicone oil with Prandtl number of 28.01 in annular pools heated from inner cylinder were carried out. The critical Marangoni number of flow destabilization was determined, and the flow pattern evolution with Marangoni number was revealed when the aspect ratios of the annular pools were 0.375 and 0.75. It was found that the axisymmetric steady flow will transit into different types of oscillatory flows. The critical Marangoni number of flow destabilization depends on types of flow instability. At a small aspect ratio, the flow transits to the oscillatory concentric ring pattern firstly, then into the combination of the oscillatory concentric ring pattern and azimuthal non-uniform temperature fluctuation, and eventually into rotating wave, while it transits directly into the rotating wave at a large aspect ratio. With the increase of Marangoni number, the oscillation frequency of the oscillatory flow increases, and the wave number is almost unchanged. However, when the oscillatory flow pattern transition happens, there is always an abrupt drop of the oscillation frequency.

This paper presented a set of direct numerical simulations on the thermocapillary flow instability of moderate-Prandtl number fluids in annular pools heated from inner cylinder. The emphasis is on the aspect ratio dependence of the critical Marangoni number of flow destabilization and the formation mechanism of the different flow patterns. It was found that the two-dimensional axisymmetric steady flow will bifurcate into three types of oscillatory flows, including the oscillatory concentric rings, the alternating straight spoke and the rotating wave patterns. The bifurcation process depends mainly on the aspect ratio of the annular pool when the radius ratio is fixed. With the increase of the aspect ratio, the first instability flow pattern is oscillatory concentric rings and the corresponding critical Marangoni number and the oscillatory frequency decrease first, and then increase slightly. When the flow pattern transits to the alternating straight spoke pattern at the aspect ratio of 0.415, there are an abrupt increase of the critical Marangoni number and a sudden decrease of the oscillatory frequency. Furthermore, when the rotating wave pattern appears, the critical Marangoni number decreases gradually, but the corresponding oscillatory frequency has only a slight decrease.

为了预测双离合自动变速器在工作过程中各热源的产热量及元件的温度状况,基于热网络理论建立了变速器轴承受力计算、内部热源产热量计算及传热计算耦合仿真模型,并对变速器在稳态与瞬态工况下的产热与传热进行了仿真计算与试验验证.结果表明,在稳态工况下,变速器的总产热量仿真值与试验测试结果吻合较好,瞬态工况下的变化趋势与试验测试结果一致;各测试点温度在稳态与瞬态工况下的仿真值与试验测试结果均吻合较好,模型具有较高的计算精度.

从"内燃机原理"课程教学现状出发,根据该课程的特点提出了课程的教学改革原则.并依据该原则,通过期末考试与大作业并举的方式,并引入动态教学目标,对教学方法进行了改革.针对目前该课程缺少实验基础的问题,该方法在课程大作业中尝试了将内燃机总体模拟设计与单个构件的仿真结合.实践证明,此方法提高了学生的听课积极性和教学满意度,获得了良好的教学效果.

This paper presents a series of numerical simulations on the effect of heat dissipation on the thermocapillary convection of a low Prandtl number (Pr = 0.011) fluid in an annular pool heated from its inner cylinder. The radius ratio and the aspect ratio of the annular pool set as η = 0.5 and ε = 0.1, respectively. The results show that with the increase of Biot number, the isotherms of the two-dimensional basic flow are seriously compressed near the hot inner cylinder and the thermocapillary flow pattern will be impaired. With the increase of Marangoni number, the thermocapillary convection first evolves from the basic flow to a three-dimensional stationary flow with longitudinal stationary stripes on the free surface, and then to a three-dimensional oscillatory flow featured with the combination of stationary stripes and azimuthal waves, which is caused by the mutual effect of the radial convection, azimuthal local flow and heat dissipation. After the flow destabilization, the amplitude of temperature fluctuation increases and the wave number decreases with the increase of Marangoni number when the free surface is adiabatic. Furthermore, the temperature fluctuation pattern is changed due to the surface heat dissipation. In addition, with the increase of Biot number, the wave number almost keeps constant when Marangoni number is small, but it increases significantly at a large Marangoni number.

In order to reduce the influence of fuel sloshing on the interior noise of a passenger car, the fuel tank sloshing noise was first evaluated with a subjective evaluation method to determine the driving cycle of the car and the fuel filling percentage of the fuel tank in which the fuel tank sloshing noise is serious, and then two anti-wave boards with different structural characteristics were designed to reduce the fuel sloshing. On this basis, fuel sloshing in the fuel tank equipped with the newly designed and original anti-wave boards was simulated numerically; then, the anti-wave board with the best effect of inhibiting fuel from sloshing was selected based on the numerical results; finally, the anti-sloshing effect of the selected board was evaluated through the car road test. The test results show that the vibration acceleration magnitude at each monitoring point of the tank with the selected anti-wave board is significantly reduced compared with the original fuel tank, which indicates that the selected anti-wave board inhibits fuel from sloshing greatly.

为了消除发动机连杆轴承在做功行程中两端出现的偏磨损,减少轴承的摩擦功耗,建立了某发动机曲轴系柔性多体动力学分析模型并进行了动力学仿真计算.根据连杆轴瓦内孔变形量仿真结果对轴瓦表面轮廓进行了修形设计.计算结果表明:对轴瓦轮廓修形后,轴承的润滑性能变化较小,最大油膜压力及最小油膜厚度随曲轴转角的变化趋势及数值大小均与原圆柱轮廓基本接近,消除了做功行程中的轴瓦偏磨问题,轴承的粗糙接触摩擦功耗无论是最大值还是平均值均降低,轴瓦表面粗糙接触压力沿轴瓦宽度方向分布均匀.

This paper presented a linear-stability analysis on thermocapillary-buoyancy convection in radially heated annular pool filled in 5cSt silicone oil / HT-70 two-layer fluids. The influences of the aspect ratio, radius ratio and thickness ratio on the flow stability were discussed. Results indicate that the system is most unstable when the thickness ratio is close to 0.375. Flow bifurcation appears when the thickness ratio varies from 0.625 to 0.875. Three corresponding destabilization mechanisms were revealed. Effect of buoyancy convection and the upper boundary condition on the flow stability were also analyzed. The upper rigid wall can enhance the flow stability in the annular two-layer system, especially when the thickness ratio is near 0.75. Furthermore, the buoyancy can greatly reduce the flow stability comparing with that under the microgravity condition.

齿轮搅油功率损失与其影响因素形成复杂的关系,难以直接用理论方法确定.一对齿轮的搅油由于存在齿轮啮合过程中的泵吸效应,与单齿搅油存在一定的差别,而现有的搅油损失计算公式大多是针对单齿搅油,在试验数据基础上通过量纲分析得到,受试验条件的限制,其应用范围非常有限.采用计算流体动力学(CFD)软件FLUENT对一对啮合齿轮空载时的搅油损失进行仿真并将计算结果与试验结果进行了比对;分析了齿轮旋转方向和传动比对搅油损失的影响,比较了直齿轮与斜齿轮搅油损失的差异.结果表明,仿真结果与试验测试结果接近,所采用仿真方法能较准确地预测啮合齿轮的搅油功率损失;齿轮旋转方向、传动比和螺旋角对齿轮对的搅油功率损失均有较大影响.

A series of three-dimensional numerical simulations on thermal-solutal capillary-buoyancy flow in an annular pool were carried out. The pool was filled with silicon-germanium melt with an initial silicon mass fraction of 1.99%. The Prandtl number and the Lewis number of the working fluid are 6.37 × 10−3 and 2197.8, respectively. Both the radial temperature gradient and the solute concentration gradient were applied to the annular pool. The capillary ratio was assumed to be −1, which means that the solutal and thermal capillary effects were equal and opposite. Results show that the thermal-solutal capillary-buoyancy flow always occurs at this special case with the capillary ratio of −1, and even in a shallow annular pool with an aspect ratio of 0.05. With the increase of the thermal Marangoni number, four kinds of flow patterns appear orderly, including concentric rolls, petal-like, spoke, and rosebud-like patterns. These flow patterns are strongly influenced by the local interaction between the solutal and thermal capillary effects and the vertical solute concentration gradient near the outer cylinder. A small vortex driven by the dominant solutal capillary effect emerges near the inner cylinder, which is different from the flow pattern in a pure fluid. In addition, the critical thermal Marangoni number of the initial three-dimensional flow decreases with the increase of the aspect ratio of the annular pool.

本文从《内燃机设计》课程教学现状出发,根据课程特点提出了课程教学改革的原则.并依据该原则,通过翻转课堂、期末考与大作业并举的方式,对教学方法进行了改革.实践证明,此方法提高了学生的听课积极性和教学满意度,获得了良好的教学效果.

A 3D simulation method was used to simulate the flow and combustion of micro-lobed burner and splitter burner, and the influence law of equivalence ratio between methane and oxygen on combustion characteristics was studied.The results showed that the streamwise vortices and augmentation in the mixing area between methane and oxygen could improve the mixing between fuel and oxidant, which can thus strengthen combustion to increase the combustion efficiency and temperature.Besides, although the combustion efficiency and temperature of micro-lobed burner are higher than that of the splitter burner, the combustion temperature and efficiency differences between these two burners at the same position go down as equivalence ratio decreases.

In this paper, the tapered roller bearing supported on the output shaft of the dual clutch transmission was studied. During the operating process of the DCT (Dual Clutch Transmission) gearbox, the heat generation of the bearing is very large due to the large operating load and high operating speed, which will easily result in bearing failure, such as pitting and abrasion, so it is necessary to investigate the lubrication performances and thermal characteristics of the tapered roller bearing. The simulation models considering or not considering the roller’s spinning (the rollers rotating on their own axles) were established based on Ansys Fluent software. The influences of the roller’s spinning on the lubrication performances of the bearing were analyzed. Furthermore, the transit heat transfer properties of the bearing were simulated and analyzed. The roller’s spinning and transit heat boundary specification were realized by using UDF (user-defined functions). At the same time, the lubrication performances and heat transfer properties of the bearing with different operating conditions are presented and analyzed.

To investigate the effect of the engine block elastic deformation on the lubrication characteristics of main bearings, a multi-flexible body dynamic model was developed with considering the elastic deformation of the whole engine block and crankshaft.Coupled with the generalized Reynolds equation and Greenwood/Tripp contact model based on the mass conserving boundary condition, the lubrication performances of main bearings were obtained.The results show that when the block elastic deformation is taken into account,the variation trend of the lubrication characteristics are coincident with that without considering the deformation of the engine block;the average of outflow and the total friction power loss show little difference,at the same time,the minimum oil film thickness,the peak oil film pressure and the peak asperity contact pressure have significant variation at certain times of an operating cycle.

Numerical simulation based on Navier-Stokes equations was applied to the lobed forced mixing exhaust system of turbofan engine. The effects of ratio of lobe height to lobe width,when area at lobe exit equals to the one at the exhaust entrance, on the performance and structure of lobed mixer were obtained. Based on this, approximation models about change of lobe performance with ratio of lobe height to width were created by polynomial response surface methodology (RSM) with different order of polynomial. In the respect of fitting pre?cision of polynomial response surface methodology, compared with second-order and third-order RSM meth?ods,the forth-order RSM method can well reflect the change of thermal mixing efficiency,total pressure recov?ery coefficient,relative thrust and lobe relative weight with the ratio of lobe height to width. Moreover,the er? rors of calculation results between the forth-order RSM method and numerical simulation are very small. In the re?spect of effects of ratio of lobe height to weight on performance of mixing exhaust system,at the exit of mixing ex?haust system,as increasing the ratio of lobe height to width,in general,the thermal mixing efficiency increas?es at first and then declines in the wavy changing tendency. The total pressure recovery coefficient appears to change like this“slowly increases-sharply declines-augments-quickly reduces”;as for the relative thrust of ex?haust system,when ratio of lobe height to width is larger than 3,although it changes like wave,the variation is very small. For the lobe relative weight,it increases with increasing the ratio of lobe height to width.

应用AMESim软件并结合AMESet二次开发平台,建立了某重型汽车变速器润滑系统流动与传热耦合仿真模型,并在变速器专用试验台上进行了模型的实验验证.应用所建模型完成了不同工况条件下润滑系统的流动与传热仿真,对典型润滑节点的润滑状况进行了分析评价及改进.结果表明:变速器在低速大负荷及高速小负荷工况下工作时,除中间轴左轴承润滑不足外,其余轴承均润滑良好;采取加大轴承润滑油道直径使节点流量率增大来改善中间轴左轴承润滑状况的措施是可行的.

为了明确混合排气系统内涵进气预旋角对环形混合器混合排气系统气动热力性能的影响,采用基于Navier-Stokes方程组的三维流场数值仿真方法对某环形混合器混合排气系统在不同进气预旋角工况下的流场进行了分析,并将结果同轴向进气的情况进行了对比.结果表明:内、外涵之间剪切层的厚度以及剪切层的扭曲程度随进气预旋角的增加而增大.在环形混合器混合排气系统出口处,随着进气预旋角的增加,热混合效率小幅升高,其中30°进气预旋角模型热混合效率为轴向进气模型的1.36倍;总压恢复系数和环形混合器混合排气系统推力逐渐降低,较轴向进气模型,30°进气预旋角模型总压恢复系数降低了0.003 4,而相对推力下降了0.081.

Piston skirt-liner is one of the primary friction pairs influencing the friction power loss of an internal combustion engine, so it is feasible to improve the fuel economy of engines by studying the lubrication characteristics of the piston skirt-liner to reduce the friction power loss. The piston skirt lubrication is related to the piston secondary motion and the elastic deformation of the piston and liner, and there exists a strong coupled relationship between them. Therefore, it may be more reasonable to couple the elastic deformation equation of piston and liner than ignore the deformation of piston and liner, when the piston skirt lubrication and the piston secondary motion equations are solved. In order to reveal the effects of the piston elastic deformation on the piston secondary motion and skirt lubrication characteristics, the structural dynamics equations of the piston and liner were established based on the finite element modal reduction method, the piston secondary motion equation, the average Reynolds equation and the possible solid-to-solid contact equation in mixed lubrication were solved iteratively based on the parameters of a single-cylinder diesel engine, and the difference between the skirt lubrication performances with or without considering the elastic deformations of piston was analyzed. The results showed that the elastic deformation configurations of the piston skirt thrust and anti-thrust sides experienced different variations with crank angles and the deformation was significant at work stroke. Besides, the maximum deformation region of the piston skirt side was variable at different crank angles, sometimes in the middle of the piston skirt side, and sometimes at the bottom edges of the piston skirt side. It could be found that the piston secondary motion quantities including the piston deformation became bigger, when compared with those excluding the deformation of piston, especially at compress and work strokes. The eccentricity of piston at the bottom of the skirt including the piston deformation was about 1.3 times as big as those excluding the piston deformation in the region from 370 to 500°CAat work stroke. The minimum film thickness was increased at intake, compress and work strokes, with fluctuating at exhaust stroke and significant changes at work stroke. Furthermore, the minimum film thickness considering the deformation of piston were about 2 times as big as those excluding the deformation of piston at work stroke. While the total friction power loss was reduced significantly and was about 0.4 times as big as those excluding the deformation of piston at work stroke,and varied slightly at other strokes. Also, the configurations of the oil film pressure field experienced different variations with crank angles, from parabolic to saddle-shaped ones, when the deformation of piston was not considered and considered. The peak values of oil film pressure field became smaller and were about 0.5 times as big as those excluding the deformation of piston at intake, compress and work strokes. It is necessary to consider the effect of the piston deformation in order to obtain reliable solutions when the piston skirt lubrication is investigated.