基于格子Boltzmann方法的动压气体轴承黏性热耗散研究

箔片气体轴承微间隙内的流场常处于滑移区,甚至过渡区,会出现一些微观效应,其热特性的研究采用宏观方法已不再合适。为研究不同工况下动压气体轴承间隙热特性变化规律,基于格子Boltzmann方法建立包含黏性热耗散项的径向轴承间隙传热数值模型;采用总能形式的双分布函数热模型,通过有限差分离散将其应用到贴体网格中,同时引入速度滑移和温度阶跃边界条件,通过数值计算得到不同参数下的轴承间隙气膜温度分布,并分析了不同埃克特数(Ec)、偏心率和转速条件以及温度阶跃对黏性热耗散的影响。结果表明,当Ec数、偏心率和转速增大时,气膜最高温度增加,两侧的温度阶跃增加;温度阶跃效应的忽略均会导致黏性热耗散量不同程度的低估。

微裂缝板吸声性能研究

宽频微穿孔板结构因面板较薄、孔径较小且穿孔率较高难以大规模推广应用,因此提出将微穿孔板分离为支撑部件和吸声部件,形成大孔基板复合微缝薄膜的微裂缝吸声板。理论计算了该结构的声阻抗率,仿真分析了孔缝内外声场以及各部段的声阻抗率,并基于仿真数据提出了考虑热黏性效应的狭长缝声阻抗末端修正模型。实验验证了微裂缝板的吸声性能,理论、仿真和实验结果一致性良好。研究表明,大孔基板的厚度占比较大,声学贡献较小,为整体结构提供了良好的支撑、通透和保护作用;微缝薄膜的厚度占比较小,为整体结构提供了优异的吸声功能。

回油槽结构对高速插齿机静压主轴性能影响研究

为提高数控高速插齿机静压主轴工作性能,以摩擦学和流体力学理论为基础,通过理论分析、数值模拟,探究了不同工况条件下有、无回油槽对静压主轴性能的影响规律。首先,建立了有、无回油槽油膜流体仿真模型和流固耦合模型,基于实际工况参数进行了仿真计算,探究了有、无回油槽对油膜承载力、刚度、剪切力和轴套最大变形量的影响规律;然后,利用瞬态计算,分析了在10次冲程运动内有、无回油槽结构对静压主轴油膜黏性生热现象的影响,探究了相同工况下不同回油槽形状对油膜承载力与刚度的影响;最后,搭建了静压导轨实验平台,通过实验数据证明了有限元仿真模型的有效性。研究结果表明:添加回油槽结构可以使油膜承载力和刚度提升约1.5倍,可小幅降低油膜黏性阻力,并使油膜平均温度保持稳定;在低偏心率时,无回油槽轴套相对有回油槽轴套变形量最大相差40%,高偏心率时则相反;偏心率较低时,回油槽形状对油膜刚度影响相对较大。该研究可为高速插齿机静压主轴结构参数优化和工程应用提供参考。

基于总能形式的耦合的双分布函数热晶格玻尔兹曼数值方法

双分布函数热晶格玻尔兹曼数值方法在微尺度热流动系统中得到广泛的应用.本文基于晶格玻尔兹曼平衡分布函数低阶Hermite展开式,创新性地提出了包含黏性热耗散和压缩功的耦合的双分布函数热晶格玻尔兹曼数值方法,将能量场内温度的变化以动量源的形式引入晶格波尔兹曼动量演化方程,实现了能量场与动量场之间的耦合.研究了考虑黏性热耗散和压缩功的和不考虑的两种热自然对流模型,重点分析了不同瑞利数和普朗特数下流场内的流动情况以及温度、速度和平均努赛尔数的变化趋势.本文实验结果与文献结果一致,验证了本文数值方法的可行性和准确性.研究结果表明:随着瑞利数和普朗特数的增大,方腔内对流传热作用逐渐增强,边界处形成明显的边界层;考虑黏性热耗散和压缩功的模型对流作用相对增强,黏性热耗散和压缩功对自然对流的影响在微尺度流动过程中不能忽略.

流体微振动隔振器的热振耦合特性研究

隔振是一种航天器振动控制的重要方法,隔振器动力学特性的理论研究是隔振设计的重要基础。针对一种航天新型黏性流体微振动隔振器,基于非牛顿流体物理属性、隔振器宏观传热特性、运载火箭-卫星轴向振动特性,提出了发射段的隔振器及运载火箭-卫星-隔振器系统的非线性热-振耦合模型;通过自行设计基础激励试验测试平台,对不同环境温度下的流体阻尼系数和体积刚度系数进行测试,并将试验得到的阻尼、刚度数据输入隔振模型中进行仿真分析。研究结果表明,隔振系统具有时变性和非线性,流体黏性热导致共振频率漂移、共振幅值变化,隔振器性能与激励幅值、激励频率相关,需要采用新的“共振带”和“隔振带”的概念进行设计;理论模型和研究方法可为隔振器热振耦合特性评估、优化设计及工程应用提供理论依据和参考。

油封温度场的数值模拟与实验研究

利用有限元模拟得到油封唇口的柯西接触应力和接触宽度,并计算得到油膜厚度;建立二维轴对称CFD数值模型,考虑油封橡胶的导热和散热作用,模拟油封唇口温度场分布;通过红外测温实验对模拟结果进行验证。CFD数值模拟结果表明:生热率、唇口最高温度和油封唇口与轴表面最大温差都随轴转速增加而增加;生热率和油封唇口与轴表面最大温差随油温增加而减小,唇口最高温度随油温增加而增加;油温对油膜厚度的影响大于轴转速对油膜厚度的影响,而转速是影响唇口最高温度的最主要因素;考虑油封橡胶的导热和散热作用,能够更加真实地反应出油封的摩擦生热和散热机制。红外测温实验结果与CFD数值模拟结果的偏差小于2%,说明CFD数值模拟得到的油封温度场与实际相符。

大陆岩石圈塑性流动网络的延性弱面效应

岩石圈下层的网状塑性流动 ,作为包含塑性流动网络的黏塑性流动 ,控制着大陆板块内部的构造变形和动力学过程。塑性流动网络由两组网带共轭相交而成 ,而塑性流动网带是黏塑性流动过程中因剪切局部化、黏性摩擦生热和网带介质的弱化而形成的延性弱面 (弱带 )。研究表明 ,类似于断裂和节理等脆性弱面 ,延性弱面对介质强度的影响也具有条件性 ,即当应力方向改变时 ,只有在滑移角θ不超出一定限值的条件 (θ1≤θ≤θ2 )下才可能沿原有弱面滑移 ,显示其弱化效应 ;延性弱面可以用弱化度R表示其屈服限的相对降低程度 ,弱化度与滑移角下限值之间的关系为R =sin2θ1;根据亚洲中东部地区“塑性流动 -地震”网络的最大共轭角推算 ,网带的弱化度R近似于 0 81。基于延性弱面效应的认识 ,文中就网带由剪切滑移向压性褶皱的转化。

Viscous warm pressure bulging process of AZ31B magnesium alloy with different ellipticity dies

Based on the bulging principle of different ellipticity dies, the methyl vinyl silicone rubber with excellent thermal stability and heat transfer performance was chosen as the viscous medium. The finite element analysis and experiments of viscous warm pressure bulging （VWPB） of AZ31B magnesium alloy were conducted to analyze the influence of different ellipticity dies on the formability of AZ31B magnesium alloy. At the same time, based on the grid strain rule, the forming limit diagram （FLD） of VWPB of AZ31B magnesium alloy was obtained through measuring the strain of bulging specimens. The results showed that at the temperature range of viscous medium thermal stability, the viscous medium can fit the geometry variation of sheet and generate non-uniform pressure field, and as the die ellipticity increases, the difference value of non-uniform pressure reduces. Meanwhile, according to the FLD, the relationship between part complexity and ultimate deformation was investigated.

Three-dimensional unsteady squeezing flow with irreversibility

This exploration examines unsteady magnetohydrodynamic(MHD) three-dimensional flow of viscous material between rotating plates subject to radiation,Joule heating and chemical reaction.The non-linear partial differential system is re-structured into the ordinary differential expressions by the implication of appropriate transformations.The developed differential equations are computed by homotopy analysis technique.Numerical consequences have been accomplished by various values of emerging parameters.Coefficients of skin friction and heat and mass transfer rates have been scrutinized.Irreversibility analysis is carried out.Influence of various prominent variables on entropy generation is presented.Moreover,the temperature increases for higher Dufour number and concentration distribution reduces against Soret number.Higher squeezing parameter enhances velocity while concentration reduces with an increment in squeezing parameter.Both entropy rate and Bejan number increase against higher diffusion parameter.

Heat transfer and nanofluid flow over a porous plate with radiation and slip boundary conditions

Presence of different terms with various values can alter the thermal behavior of the nanofluids flow over porous surfaces.The aim of this research is to study the influence of nanoparticles volume fraction,nanoparticles type,suction or injection,the heat generation or absorption,the Eckert number,thermal and velocity slip parameters,and radiation on the velocity and temperature fields on the flow and heat transfer over a porous flat plate.Four different types of nanoparticles including metal nanoparticles (Cu),metal oxide nanoparticles (Al2O3) and carbon-based nanomaterials (MWCNTs and SWCNTs) which were dispersed in the water (as based fluid) are studied.The governing equations are converted into the ordinary differential equations using similarity solution and solved numerically by the RKF45 algorithm.The results of the simulations showed a contradiction with the results of other researchers who expressed that using nanoparticles with higher thermal conductivity and volume fraction led to increasing heat transfer rate in nanofluids;this study proves that,in some cases,boosting the volume fraction of nanoparticles has a potential to decrease the heat transfer rate due to significant changes in values of some parameters including radiation,heat generation,and viscous dissipation.

Magnetohydrodynamic flow and heat transfer impact on ZnO-SAE50 nanolubricant flow over an inclined rotating disk

The present article has been fine-tuned with the investigation of mixed convection Darcy-Forchheimer flow of ZnO-SAE50 oil nanolubricant over an inclined rotating disk under the influence of uniform applied magnetic field applied to various industries.The current study has been enriched with additional consideration of slip flow,thermal radiation,viscous dissipation,Joulian dissipation and internal heating.In view of augmentation of thermal conductivity of nanolubricant,a new micro-nano-convection model namely Patel model has been invoked.The specialty of this model involves the effects of specific surface area and nano-convection due to Brownian motion of nanoparticles,kinetic theory based micro-convection,liquid layering and particle concentration.Suitably transformed governing equations have been solved numerically by using Runge-Kutta-Fehlberg scheme.An analysis of the present study has shown that applied magnetic field,porosity of the medium,velocity slip and inertia coefficient account for the slowing down of radial as well as tangential flow of ZnO-SAE50 oil nanolubricant,thereby leading to an improvement in velocity and thermal boundary layers.

Exponential Stability of Weak Solutions to Linear Thernioviscoelastic Systems

This paper is concerned with the exponential stability of weak solutions to a linear one-dimensional thermoviscoelastic system with clamped boundary conditions. This system defines a C0-semigroup {S（t）}t≥0 on the space L^2（0, 1） × C^1 （0,1） × H^1（0, 1）, which processes the property of the exponential stability.

Effect of aluminum particle on properties of viscous medium during warm viscous pressure bulging

Incorporating aluminum particles into viscous medium was proposed to improve the thermal conductivity of the viscous medium and the efficiency of warm viscous pressure forming(WVPF)process.The influence of aluminum particles on a viscous medium was investigated through settling,thermal conductivity,and compression experiments.Warm viscous pressure bulging(WVPB)experiments were conducted on polyetherimide(PEI)and AZ31B magnesium alloy sheets to determine the influence of the aluminum particles size and fraction on the forming efficiency and formed specimens based on the heating preparation times and profile curves,wall thicknesses and surface roughness values of the bulging specimens.The results show that the thermal conductivity of the viscous medium and the WVPF efficiency can be greatly improved via the addition aluminum particles with appropriate size and fraction under certain temperature condition,but have less influence on other properties of viscous medium.

热采耦合数学模型定量化研究及数值模拟

针对稠油油藏开发过程的薄弱环节,提出了油藏热质传递过程的黑箱分析法和白箱分析法,建立了包含蒸汽相的稠油热采耦合黑箱模型和白箱模型,使得储层温度场模型得以完整化和系统化。应用CMG软件进行数值模拟,验证了所建数学模型的合理性,并得到了孔隙度对油藏温度的影响关系。最后,对油藏热流体的指进现象进行了机理分析,并总结了热流体指进现象的产生范围。