激光加工微凹坑轴表面对唇形密封泵吸及摩擦特性的影响

为了研究轴表面形貌对径向唇形密封泵吸作用及摩擦特性的影响,利用Nd:YAG固体脉冲激光对旋转轴表面进行微凹坑织构化处理,在油封密封试验机上,针对不同转速、不同表面形貌等工况,完成了一系列对比试验,获取了试验过程中的泵吸量、摩擦力以及密封圈温升等参数.并通过扫描电镜对试验后各密封唇表面进行了分析.结果表明:三角形微凹坑顶点朝向油液侧的表面能够增强泵吸作用,且转速对泵吸率影响很大,而其他形状和参数的微凹坑表面不利于泵吸作用的产生;与未织构面相比,圆形凹坑面积占有率为7%和21%的表面具有良好的减摩效果,三角形凹坑顶点沿周向的两表面间减摩效果较好.     

Compact model and identification process for friction induced damping in a rotational joint with flawed surfaces

It is well known that bolted joints have significant influence on the dynamical behavior of assembled structures due to formation of damping. This paper focuses on damping caused by dry friction in a rotational joint. Friction can be either induced by micro-slipping or macro-slipping. This paper describes the design of a new experimental device intended to measure damping caused by friction and partial slip in rotational joints. An original method for measuring dissipated energy in rotational joints with plan-plan contact is proposed. This method is based on Lagrange formalism and allows to measure accurately forces and torques only with accelerometers. These techniques are available for very small displacements that occur in micro-slip and partial slip of surfaces in contact and are still available for large displacements (macro-slip). An analytical compact model based on the Greenwood model is studied. The experimental results and simulations used to quantify the dissipated energy in order to compute the damping ratio are presented and discussed.     

Boundary conditions for flows of multiatomic gases

We consider the problem of obtaining macroscopic boundary conditions for the equations of a strongly nonuniform, multitemperature boundary later in a gas with translational, rotational, and vibrational degrees of freedom and for arbitrary catalyticity of the solid surface with respect to various vibrational modes. The boundary conditions are analyzed on surfaces with properties favorable to flow modes with population inversion in the quantum equations.     

表面织构对内燃机缸套-活塞环系统摩擦性能的影响

设计了一种微凹坑表面织构,通过数控精密机械加工的方法制备于缸套切片表面,利用往复式摩擦磨损试验机研究了微凹坑织构在不同工况下的摩擦性能和对内燃机缸套-活塞环摩擦副摩擦性能的影响.试验数据表明:与无织构化表面相比,微凹坑织构的平均摩擦系数均有不同程度的变化,最大降幅达41.83%,最大增幅达33.68%.当微凹坑织构工作在合适的工况条件时,其摩擦性能比无织构化表面有明显的改善.对于某种具有固定几何参数的表面织构,存在一个合适工况条件使其能够最有效地改善摩擦学性能,该工况可为进一步研究提供依据并便于实际应用.此外,转速是影响表面织构改善表面润滑性能的主要因素,试样在不同转速下具有不同的接触电阻阻值变化规律和不同的摩擦系数变化趋势.而在不同转速下,载荷的变化对表面摩擦性能的影响规律也具有明显的差异性.     

Surface shapes of fluids in rotating vessels

The shape of the phase boundary of two fluids in systems with a rotational symmetry, and particularly the level of the liquid in a rotating vessel, is studied. The knowledge of the shape of the surface of such a liquid is necessary for centrifugal moulding of optical surfaces. The dimensionless surface equations are formulated, and the solutions of these equations, taking into account the boundary conditions, are discussed.     

Dispersion properties of vortex-type monatomic lattices

The paper presents a systematic study of dispersive waves in an elastic chiral lattice. Chirality is introduced through gyroscopes embedded into the junctions of a doubly periodic lattice. Bloch–Floquet waves are assumed to satisfy the quasi-periodicity conditions on the elementary cell. New features of the system include degeneracy due to the rotational action of the built-in gyroscopes and polarisation leading to the dominance of shear waves within a certain range of values of the constant characterising the rotational action of the gyroscopes. Special attention is given to the analysis of Bloch–Floquet waves in the neighbourhoods of critical points of the dispersion surfaces, where standing waves of different types occur. The theoretical model is accompanied by numerical simulations demonstrating directional localisation and dynamic anisotropy of the system.     

Floquet–Bloch Waves in Periodic Networks of Rayleigh Beams: Cellular System,Dispersion Degenerations,and Structured Connection Regions

The paper is dedicated to Professor N. F. Morozov on the occasion of his 85th birthday. In the paper, we consider new dispersive properties of elastic flexural waves in periodic structures with rotational inertia. The structure is represented as a lattice with elementary bonds of Rayleightype beams. Although such beams in the semiclassical regime react as the classical Euler–Bernoulli beams, they exhibit new interesting characteristics as the dispersion frequency of flexural waves increases. Special attention is paid to degenerate cases related to the so-called Dirac cones on dispersion surfaces and to the directed anisotropy for the doubly periodic lattice. A comparative analysis accompanied by numerical simulation is carried out for the Floquet–Bloch waves propagating in periodic flexible lattices of different geometry.     

模型昆虫翼作非定常i运动时的气动力特性

基于Navier-Stokes方程的数值解,研究了一模型昆虫翼在小雷诺数(Re=100)下作非定常运动时的气动力特性.这些运动包括翼启动后的常速转动,快速加、减速转动,常速转动中快速上仰(模拟昆虫翼的上挥或下拍、翻转等运动).有如下结果在小雷诺数下,模型昆虫翼以大攻角(α=35°)作常速转动运动时,由于失速涡不脱落,可产生较大的升力系数.其机理是翼转动时,翼尖附近(该处线速度大)上翼面压强比翼根附近(该处线速度小)的小得多,因而存在展向压强梯度,同时存在着沿展向的离心力,此展向压强梯度和离心力导致的展向流动在失速涡的轴向方向,其可避免失速涡脱落.模型昆虫翼在快速加、减速转动和快速上仰运动中,虽然雷诺数小,但由于在短时间内产生了大涡量,也可产生十分大的气动力,例如在快速上仰运动中,升力系数可大于10.     

Steady rotational motions of fluid masses at low reynolds numbers

The problem of steady rotational motions of an incompressible viscous fluid at small Reynolds numbers (R<1) between surfaces of rotationspecified in parametric form (1.3) is considered. Solutions of the Navier-Stokes equation are sought using the method of expansion in terms of the small parameter R. It is shown that in the case of twice continuously differentiable surfaces the solution of the problem in the first approximation enables the friction force torque on a fixed solid surface (1.3) to be determined with accuracy to R². Some solutions of Eq. (1.2) and the corresponding families of surfaces of revolution (1.3) are studied.     

Impingement cooling in a rotating curved square annular duct with crossflow effect from Rib-roughened surfaces

An experimental investigation was carried out to determine the effects of jets in crossflow on impingement heat transfer from rib-roughened curved duct with rotational speeds of 120 and 240 rpm. The jet impinged on curved surface in crossflow having repeated square ribs (3 2 3mm). The curvature of the duct was fixed and has a value of 300 mm. The rib height (e) was fixed at 1.5 mm and pitch-to-height ratio (p/e) kept at 2. The study covered jet Reynolds number in the range 6500 to 26000, and duct stream crossflow Reynolds number from 3250 to 13000 based on jet nozzle diameter, respectively, which gave M = 0.12 to 2. Results were presented for rotational, crossflow, roughened surfaces and curvature effects on local Nusselt numbers. Significant heat transfer enhancement was found for the present physical geometry and within the ranges of operating parameters considered in the study.     

Investigation of horizontal-axis wind turbine (HAWT) blade threedimensional rotational effect based on field experiments

Field experiments are performed on a two-bladed 33 kW horizontal-axis wind turbine (HAWT). The pressures are measured with 191 pressure sensors positioned around the surfaces of seven spanwise section airfoils on one of the two blades. Three-dimensional (3D) and two-dimensional (2D) numerical simulations are performed, respectively, on the rotor and the seven airfoils of the blade. The results are compared with the experimental results of the pressure distribution on the seven airfoils and the lift coefficients. The 3D rotational effect on the blade aerodynamic characteristics is then studied with a numerical approach. Finally, some conclusions are drawn as follows. From the tip to the root of the blade, the experimental differential pressure of the blade section airfoil increases at first and then decreases gradually. The calculated 3D result of the pressure distribution on the blade surface is closer to that of the experiment than the 2D result. The 3D rotational effect has a significant impact on the blade surface flow and the aerodynamic load, leading to an increase of the differential pressure on the airfoils and their lift coefficient than that with the 2D one because of the stall delay. The influence of the 3D rotational effect on the wind turbine blade especially takes place on the sections with flow separation.     

Flow of a viscous fluid in a cylindrical vessel with a rotating cover

The problem considered arises in solving various technical problems associated with flows of a viscous fluid in a closed space near rotating plane surfaces, turbomachine disks, thrust bearings, rotational viscosimeters, etc. The approximate solution of the problem on the basis of a simplified flow scheme was first obtained by Schultz-Grunow [1], The most complete investigation has been made recently by Grohne [2], who outlined a program for solving the problem by joining several partial solutions on the basis of definite hypotheses concerning the flow core.With the development of electronic digital computers and the necessary numerical methods, the most effective means of solving the considered problem is the use of the grid methods for solving partial differential equations. The present paper is devoted to presenting the results of the solution of the problem using the grid method on a digital computer.     

Lift force on rotating sphere at low Reynolds numbers and high rotational speeds

The lift force on an isolated rotating sphere in a uniform flow was investigated by means of a three-dimensional numerical simulation for low Reynolds numbers (based on the sphere diameter) (Re&lt;68.4) and high dimensionless rotational speeds (Г5). The Navier-Stokes equations in Cartesian coordinate system were solved using a finite volume formulation based on SIMPLE procedure. The accuracy of the numerical simulation was tested through a comparison with available theoretical, numerical and experimental results at low Reynolds numbers, and it was found that they were in close agreement under the above mentioned ranges of the Reynolds number and rotational speed. From a detailed computation of the flow field around a rotational sphere in extended ranges of the Reynolds number and rotational speed, the results show that, with increasing the rotational speed or decreasing the Reynolds number, the lift coefficient increases. An empirical equation more accurate than those obtained by previous studies was obtained to describe both effects of the rotational speed and Reynolds number on the lift force on a sphere. It was found in calcttlations that the drag coefficient is not significantly affected by the rotation of the sphere. The ratio of the lift force to the drag force, both of which act on a sphere in a uniform flow at the same time, was investigated. For a small spherical particle such as one of about 100μm in diameter, even if the rotational speed reaches about 10^6 revolutions per minute, the lift force can be neglected as compared with the drag force.     

基于高阶变形理论的夹层板的弯曲与振动

考虑面板和夹芯的面内刚度和横向剪切刚度以及抗弯刚度,考虑了高阶剪切变形,根据横向剪应变分布情况给出横向剪切转角的位移函数,基于哈密尔顿原理,推导了基于高阶变形理论、适用于软、硬夹芯情况夹层板的基本方程。作为算例,以四边简支条件下的夹层板的弯曲与振动,在不同的面板与芯层的弹性模量比和厚度比下进行了计算,并与Reissner理论、Hoff理论以及邓宗白基于Reissner理论的修正模型的计算结果进行了对比。与前述理论与方法相比,本文方法考虑因素更为全面,对夹层板的适用范围更为广泛,计算结果更为精确。针对Nastran软件计算夹层板的振动问题,对其适用范围作了简要分析。     

Squeeze-flow and vane rheometry of a gas–liquid foam

The rheology and slip of a dry shaving foam are investigated using squeeze-flow and rotating-vane methods. Constant-force squeeze flow between planar surfaces is used to study the effect of surface roughness on slip and to obtain the yield stress. Non-slip vane measurements are used to obtain the linear shear viscosity and elasticity at small strains, and the yield stress and strain at large strains. Data are compared with the small-strain Maxwell and Kelvin–Voigt linear-viscoelastic models. An apparent dependence of the yield stress and elasticity on the rotational speed of the vane is shown to result from time-dependent rheological parameters as the foam ages. The effect of viscosity in the pre-yield region may give an erroneous identification of yield.     

Experimental and numerical studies of rotational relaxation behind a strong shock wave in air

This paper describes the experimental and numerical investigations of unknown characteristics of the rotational nonequilibrium phenomena behind a strong shock wave in air. Experiments were carried out using a piston-driven shock tube with helium as driving gas and air as driven (test) gas, operated as a two-stage shock tube. In the experiments, emission spectra of NO were measured to evaluate the rotational temperature behind a strong shock wave. The numerical calculations use the computational code for the thermal and chemical nonequilibrium flow behind a strong shock wave developed by the present author's group, where 11 chemical species (N, O, NO, N, O, N, O, NO, N, O, e) and 48 chemical reactions of high-temperature air are considered. The thermal nonequilibrium is expressed by introducing an 8 temperature model composed of translational temperature, rotational and vibrational temperatures for N, O, NO, and electron temperature. The coupling of a rotation, vibration and dissociation (CRVD) model was incorporated to take sufficiently into account the rotational nonequilibrium. The calculations were conducted for the same conditions as the experimental ones. From the calculated flow properties, emission spectra were re-constructed using the code for computing spectra of high temperature air “SPRADIAN”. Furthermore, rotational and vibrational temperatures of NO (0,1) were determined from a curve fitting method and compared with the computed results. Received 12 September 2001 / Accepted 18 February 2002     

Dynamical responses of non-isothermal flow between two independently rotating disks with time-dependent wall conditions

The present work develops a theoretical model of rotational convection and uses it to investigate the dynamical responses of the flow and heat transfer between two disks rotating at different rates under the influences of time-dependent disturbances. The unsteady non-isothermal flow model is formulated by extending a recently developed steady-state similarity model of axi-symmetric rotational convection. In the new model all the rotation-induced buoyancy forces are considered. Using one disk as reference, effects of the time-dependent changes in wall temperature or rotating rate of the other disk on the flow and heat transfer are explored. Various rotational modes with asymptotic or fluctuating change in boundary condition of temperature or disk rotation are studied. The present time-dependent model for this non-isothermal rotating flow is numerically solved by a finite-difference method. By using the present results, the complicated flow and heat transfer mechanisms with thermal-flow coupling in the class of time-dependent rotational convection are manifested.     

A self-aligning parallel plate (SAPP) fixture for tribology and high shear rheometry

This paper introduces a novel self-aligning parallel plate fixture for rotational rheometers. The ring-shaped shearing surface of this fixture is held on a low friction single contact point bearing and uses hydrodynamic lubrication forces in order to maintain the parallelism of the freely tilting surfaces over a full rotation. The optimized parallelism of the plates enables to conduct tribological measurements of low frictional stress between the shearing surface materials and a fluid at normal loads down to 1.3 kPa. Limited only by the degree of non-flatness of the surfaces, the new fixture can determine boundary lubrication sliding frictions within 10 % and down to angular velocities of 400 μrad/s. In a controlled gap mode, this setup reaches a gap error of 3.4 μm which enables to reliably conduct rheological measurements down to absolute gaps of the parallel plates of 10 μm and to reach high shear rates up to $10^{5}\;{\rm s}^{-1}$ .     

A geometrically nonlinear analysis of rotational shells using B-spline function

In this paper, based on the nonlinear thin shell theory, a geometrically nonlinear formulation using the total Lagrangian approach for rotational shells, as well as rotational shells on the Winkler-type elastic foundation, is presented. The displacements of the middle surface are approached by a B-spline function. All nonlinear terms of membrane strains are reserved. Two cases in which the arc length as well as ordinate is used as the coordinate parameter along meridional direction are discussed at the same time.The project supported by National natural Science Foundation of China.