Bingham流体在旋转圆盘上流动的数值解

导出了描述Ｂｉｎｇｈａｍ流体在旋转圆盘上流动的基本方程，用差分方法数值解薄膜厚度分布方程，得到二种类型的厚度分布。数值解分别和计算机磁盘的厚度分布，Ｊｅｎｅｋｈｅ等的实验结果定性一致。     

低Pr数流体自然对流边界层流动的直接数值模拟

在太阳能采暖通风系统中,空气在太阳辐射作用下于吸热壁上所形成的非稳态自然对流边界层流动是决定系统热性能的关键所在. 对于线性分层的低普郎特数($Pr<1$)流体而言,标度分析表明在起始阶段边界层的发展是与高度无关而只依赖于时间的,而处于稳态时,各项标度关系与处于起始阶段终结时刻的大不相同,且都与高度和时间无关,而只与$Pr$数和线性分层度相关. 直接数值模拟计算结果表明由标度分析所得的各项标度关系揭示了流动的特性参数与控制参数之间的决定性内在联系. 但同时也表明标度关系并没有充分体现出对$Pr$数的所有依赖关系,这一不足可利用直接数值模拟计算结果得到弥补.     

水基MWCNTs/MoS2复合纳米流体的摩擦学性能研究

使用离子液体[EMIm]BF₄分散多壁碳纳米管(MWCNTs),再以[EMIm]BF₄-阿拉伯树胶(GA)为添加剂分散二硫化钼(MoS₂),二者的水溶液复配得到复合纳米流体. 采用拉曼光谱分析了MWCNTs的改性度,通过吸光度和粒度对复合纳米流体的分散与悬浮稳定性进行了表征. 对不同纳米颗粒配比的复合纳米流体润湿性能和摩擦学性能进行测试,结果表明:MWCNTs和MoS₂质量分数为0.6%、1.2%时复合纳米流体的铺展成膜能力最好,其接触角约为63.04°,相比于去离子水降低了23.55%. 摩擦磨损测试结果也表明此配比下的减摩抗磨性能最佳,平均摩擦系数为0.073,比去离子水降低了61.98%,同时体积磨损率降低了67.87%. 磨痕形貌观测表明,最优配比下磨痕浅,且表面光滑、无犁沟. X射线光电子能谱(XPS)表明MWCNTs和MoS₂共同参与摩擦并在基底成膜,由此协同实现了高效润滑.      

黏弹性纳米流体在垂直板上的自然对流与传热分析

基于分数阶Maxwell模型和分数阶Fourier定律构建黏弹性纳米流体在垂直板上的非定常二维边界层自然对流与传热控制方程,利用有限差分和L1算法获得数值稳定解,对不同物理参数下的速度、温度、平均表面摩擦系数和平均Nusselt数的变化趋势进行图形化分析。结果显示,速度和温度边界层均表现出短暂记忆和延迟特性;速度分数导数参数削弱了自然对流,而速度松弛时间的影响却相反;温度分数导数参数削弱了自然对流和热传导,而温度松弛时间的影响却相反。     

管道凸起激波/湍流边界层干扰的数值模拟

采用基于部分平均的湍流方程组,模拟了管道凸起流动中两种不同强度的激波-湍流边界层干扰现象,对流场的时均参数与实验值进行了比较,计算得到的壁面压力分布、摩阻系数分布、边界层厚度和速度型与实验值比较吻合很好.结果表明基于部分平均的湍流方程组既能够准确模拟小分离的激波/湍流边界层干扰流动又能够准确模拟大分离的激波/湍流边界层干扰流动,较好地预测了典型的λ激波结构.     

磁控溅射氮化钛/氮化铝纳米多层膜的抗磨性能及其在金属加工刀具中的应用研究

采用新型高速反应真空磁控溅射系统制备了氮化钛/氮化铝纳米多层膜,探讨了周期(λ)对多层膜力学性能及抗磨性能的影响;在微钻针及车刀表面分别制备了上述多层膜,并分别对电路板以及中碳钢棒进行实机加工测试,以验证其实用性.结果表明:通过控制溅射参数可以制备出周期范围为2.4～67.6nm的氮化钛/氮化铝多层膜;当周期λ≤3.6nm时,相应的多层膜具有较高的硬度、良好的粘附性能及优异的抗磨性能.实机测试结果显示,所制备的多层膜可以改善金属车削和微钻削加工条件,改善程度优于单层氮化钛镀膜.     

Flow and heat transfer of nanofluid past stretching/shrinking sheet with partial slip boundary conditions

The boundary layer flow of a nanofluid past a stretching/shrinking sheet with hydrodynamic and thermal slip boundary conditions is studied. Numerical solutions to the governing equations are obtained using a shooting method. The results are found for the skin friction coefficient, the local Nusselt number, and the local Sherwood number as well as the velocity, temperature, and concentration profiles for some values of the velocity slip parameter, thermal slip parameter, stretching/shrinking parameter, thermophoresis parameter, and Brownian motion parameter. The results show that the local Nusselt number, which represents the heat transfer rate, is lower for higher values of thermal slip parameter, thermophoresis parameter, and Brownian motion parameter.     

Unsteady three-dimensional boundary layer flow due to a permeable shrinking sheet

The unsteady viscous flow over a continuously permeable shrinking surface is studied. Similarity equations are obtained through the application of similar transformation techniques. Numerical techniques are used to solve the similarity equations for different values of the unsteadiness parameter, the mass suction parameter, the shrinking parameter and the Prandtl number on the velocity and temperature profiles as well as the skin friction coefficient and the Nusselt number. It is found that, different from an unsteady stretching sheet, dual solutions exist in a certain range of mass suction and unsteadiness parameters.     

A THEORY OF CLASSICAL SPACETIME (I)—FOUNDATIONS

Despite its beauty and grandeur the theory of GR still appears to be incomplete in thefollowing ways:(1)It cannot accommodate the asymmetric total energy momentum tensor whoseasymmetry has been shown to exist in the presence of electromagnetism.(2)The law of angular momentum balance as an exact equation is not an automaticconsequence of the field equations as is the case with the law of linear momentum balance.(3)The four degrees of arbitrariness left by the contracted second Bianchi identitymakes a unique solution of the field equations unattainable without extra (unphysical)postulates.To answer the challenge posed by the above assertions we propose in this paper tocomplete Einstein’s theory by postulating the principle fibre bundle P[M,SU(2)]for theunderlying geometry of the 4-dimensional spacetime,where the structre group SU (2) isthe real representation of the special complex unitary group of dimension 2. SU (2) leavesconcurrently invariant the metric form dS~2=g_(αβ)dx~αdx~β and the fundamenta     

一种新的工程流体力学课程教学方法探讨1)

针对工程流体力学课程的教学特点,提出了\"理论推演-实验研究-数值模拟-互动式案例\"的教学模式。该模式将相关的知识点联系起来,以点带面,由浅入深,采用多种方式讲解。以边界层分离现象为例,使用理论推演分析其机理,采用实验方法展示分离现象,引入数值模拟方法,提升教学效果,扩展知识面,使用网络互动方法,提高学习兴趣,加深理解。该模式将传统技术与新兴的技术相结合,可以为该课程的教学提供有益的帮助。