Vortex-Induced Vibrations of a Circular Cylinder at Low Reynolds Numbers

The vortex-induced vibrations of a circular cylinder at low Reynolds (Re) numbers are simulated by applying a method of the two-dimensional computational fluid dynamics coupled with the structural dynamics based on the multi-physics. The fluid solver is first tested on the case of a fixed cylinder at Re≤ l60, and shows a good agreement with the previous high-resolution numerical results. The present study then reports on the detailed findings concerning the vibrations of an elastic cylinder with two degrees of translational freedom for a number of cases in which Re is fixed at 200, a reduced damping parameter Sg=0.01, 0.1, 1.0, 10.0 and the mass ratio M^002A;= 1, 10.     

Unsteady viscous flow over elliptic cylinders at various thickness with different reynolds numbers

Two-dimensional incompressible Navier-Stokes equations are solved using SIMPLER method in the intrinsic curvilinear coordinates system to study the unsteady viscous flow physics over two-dimensional ellipses Unsteady viscous flows over various thickness-to-chord ratios of 06, 08, 10, and 1 2 elliptic cylinders are simulated at different Reynolds numbers of 200, 400, and 1,000 This study is focused on the understanding the effects of Reynolds number and elliptic cylinder thickness on the drag and lift forces The present numerical solutions are compared with available experimental and numerical results and show a good agicement Through this study, it is observed that the Reynolds number and the cylinder thickness affect significantly the frequencies of the force oscillations as well as the mean values and the amplitudes of the drag and lift forces     

Comparison of flow characteristics around an equilateral triangular cylinder via PIV and Large Eddy Simulation methods

The flow structures around an equilateral triangular cylinder, which is commonly used as a vortex shedder in the vortex flowmeter, were investigated experimentally and numerically. Flow characteristics such as vorticity contours, patterns of sectional streamlines, velocity vectors, velocity fields, Reynolds stress correlations, Strouhal numbers and drag coefficients were examined using the Particle Image Velocimetry (PIV) technique and the Large Eddy Simulation (LES) turbulence model. Experimental studies were performed in an open water channel for Re=2.9×10³, Re=5.8×10³ and Re=1.16×10⁴ based on the equilateral triangle edge. A sharp-tip corner of the cylinder with a triangle cross-section was exposed to the upstream side while the other two sharp-tip corners were placed on the downstream side. Numerical studies were also completed at Reynolds numbers in the range of 2.9×10³≤Re≤1.16×10⁵ to obtain the changes in the Strouhal numbers and drag coefficients. When the results of PIV and LES are considered in the same interval of Reynolds numbers, the maximum and minimum values of each flow pattern were nearly the same. The time-averaged patterns had considerable symmetry with respect to the axis line passing through the sharp-tip corner of the cross-section of the triangular cylinder. The Strouhal number was independent of the Reynolds number and was found to be approximately 0.22. The drag coefficient decreased with increasing Reynolds numbers while increasing the Power Spectral Density (PSD) and the vortex shedding frequency. For the same Reynolds numbers, the experimental and numerical results were in good agreement. Therefore, the LES turbulence model is recommended for applications of flow around this type of bluff body that is generally used in the design of vortex flowmeters to generate vortex shedding.     

An experimented study on the flow characteristics in a three-dimensional cylindrical branching channel

In this paper, we report on an experimented study on incompressible Newtonian flow in a three-dimensional cylindrical branching channel. The flow configuration studied in the present investigation is such that a fully developed laminar flow enters an abruptly expanded cylinder and the flow leaves this cylinder by two identical cylindrical outlet branch pipes. Representative velocities in the flow field were recorded by LDV (Laser Doppler Velocimetry) measurements, and volume flow rate from each outlet branch pipe was measured. Flow visualization in representative symmetric planes was also carried out. Based on results of the present investigation, the flow field in the three-dimensional cylindrical branching channel was clarified within the range of laminar flow. The characteristics of the branch flow rate were obtained and showed that there exist two distinct domains of strong asymmetric flow distribution from the outlet branch pipes, depending upon Reynolds numbers. It was further observed that the flow became time periodic as the Reynolds number was increased.     

Particle image velocimetry study of parameter influence for synthetic-jet application

Flow separation control of a circular cylinder using a synthetic jet positioned at the front stagnation point is experimentally investigated by the particle image velocimetry (PIV) technique. The control results for different excitation parameters, including the stroke length, the excitation frequency, and the momentum coefficient, are compared to distill the essential control parameters, and the influence of the cylinder Reynolds number on the control effect is discussed. The separation control mechanism for the present control configuration is also revealed. It is suggested that the effective control ability of the synthetic jet is attributed to the increment of the turbulent kinetic energy (TKE) and the dissipation rate surrounding the circular cylinder. High level of TKE enhances the dynamics of the fluids and thus flow around the leeward surface is endured a considerable vertical acceleration pointing to the centerline from both sides, which is more resistant to flow separation.     

Unsteady Lift and Drag Forces Acting on the Elliptic Cylinder

A parametric study has been accomplished to figure out the effects of elliptic cylinder thickness, angle of attack, and Reynolds number on the unsteady lift and drag forces exerted on the elliptic cylinder. A two-dimensional incompressible Navier-Stokes flow solver is developed based on the SIMPLER method in the body-intrinsic coordinates system to analyze the unsteady viscous flow over elliptic cylinder. Thickness-to-chord ratios of 0.2, 0.4, and 0.6 elliptic cylinders are simulated at different Reynolds numbers of 400 and 600, and angles of attack of 10°, 20°, and 30°. Through this study, it is observed that the elliptic cylinder thickness, angle of attack, and Reynolds number are very important parameters to decide the lift and drag forces. All these parameters also affect significantly the frequencies of the unsteady force oscillations.     

内燃机活塞裙部配缸间隙对裙部润滑影响的研究

本文建立的数学模型主要是结合动力学方程及缸套 -活塞裙部间的流体动力润滑方程 ,采用数值分析方法来研究活塞的二阶运动 ,并从减小活塞裙部摩擦功耗和减小活塞横向运动的角度 ,对活塞与缸套的最佳油膜间隙进行了确定 ,使得活塞裙部与缸套的间隙更为合理     

Numerical simulation of flow past rectangular cylinders with different aspect ratios using the incompressible lattice Boltzmann method

This paper presents a numerical study of a uniform flow past a rectangular cylinder using the incompressible lattice Boltzmann method (ILBM). Firstly, we use the ILBM to simulate the flow past a square cylinder symmetrically placed in a two-dimensional channel and results are validated against the well-resolved results obtained using finite-difference method and finite-volume method. Secondly, the effects of the aspect ratio defined as R = width/height on the fluid forces, vortex shedding frequency and the flow structures in the wake are investigated. Aspect ratios ranging from 0.15 to 4.00 and four Reynolds numbers Re = 100, 150, 200 and 250 are selected for the investigation. The results show that the effects of aspect ratio on physical quantities such as drag and lift coefficients, Strouhal number and the vortex shedding mechanism are very notable in the range between 0 and 2. In general, the drag coefficient decreases with the aspect ratio and the decreasing rate is more distinct in the range of 0.15 ≤ R ≤ 2.0. There is no local maximum found at around R = 0.6 in the drag coefficient as reported for higher Reynolds numbers in the literature. However the root-mean-square value of the lift coefficient shows a maximum value at R ≈ 0.5 for all Reynolds numbers selected. The variation of Strouhal number with R appears to be different for four selected Reynolds numbers. Especially for Re = 250, a discontinuity in St, as has been observed for higher Reynolds numbers, is observed at around R = 1.45 where multiple peaks are found in the result of Fourier spectrum analysis of the lift force and irregular vortex shedding behavior with no fixed shedding frequency is observed from the instantaneous vorticity contours. Such discontinuity is not observed for Re = 100, 150 and 200. The present results using the LBM are compared with some existing experimental data and numerical studies. The comparison shows that the LBM can capture the characteristics of the bluff body flow well and is a useful tool for bluff body flow studies.     

圆柱绕流气动流场在临界区的动力试脸研究

本研究以试验方式探讨了圆柱表面流场在雷诺数改变情况下的空气动力特性。试验首先测量临界区中基部压力随雷诺数的变化情形,再利用圆柱左右两侧±90°位置的扰动压力系数来判断圆柱流场进入单分离区的最低雷诺数,即可定义出圆柱流场在临界区及单分离区中雷诺数分布的范围,然后通过对瞬时频率的分析,由小波变换进行数据处理,进一步证实雷诺数分布的范围。     

Measurements of the flow fields around two square cylinders in a tandem arrangement

The velocities, turbulence intensities, Reynolds shear stresses, and turbulent kinetic energies of the flow fields around two square cylinders in a tandem arrangement were investigated using particle image velocimetry (PIV). The experiments were made for the spacing between the two cylinders ranging from s/D = 0.5 to 10.0 and two Reynolds numbers of 5,300 and 16,000. The results showed that the flow patterns at s/D≤2.0 were drastically different from those at s/D≥2.5 for both Reynolds numbers. The sudden change in the flow patterns depended on the reattachment of the shear layer separated from the upstream cylinder.     

Passive control of circular cylinder wake in shallow flow

The control of vortex shedding of a circular cylinder in shallow water using a splitter plate located in the downstream of the circular cylinder was studied by employing particle image velocimetry (PIV) technique. Experiments were carried out in a water channel having a test section of 8000 mm × 1000 mm × 750 mm dimensions at a Reynolds number of 6250. The length of the splitter plate (L) was varied within the range of 0.5 ? L/D ? 2 with an increment of 0.5. The plate was submerged into water at different height ratios (h_p/h_w) such as 0.25, 0.5, 0.75 and 1.0. Mean velocity vector field, corresponding vorticity contours, streamline topologies and turbulent quantities were calculated using 300 instantaneous velocity vector field measured by PIV. As the ratio of h_p/h_w increases, the effect of the splitter plate on the suppression of the vortex shedding increases. Flow characteristics and examination of spectra indicate that Karman vortex shedding is attenuated pronouncedly for the cases of L/D ? 1 and h_p/h_w ? 0.75. The transverse Reynolds normal stress is more effective on the attenuation of turbulent kinetic energy than the streamwise Reynolds normal stress. The value of peak transverse Reynolds normal stress is reduced to 90% of that of the bare cylinder at most.     

浅谈发动机拉缸产生的原因及防止措施

简述发动机拉缸的机理，分析造成发动机拉缸的原因，并提出了防止拉缸的措施。     

Spatial resolution effects on unsteady turbulent flow computations for the rectangular cylinders byκ-ε turbulence models

In predicting unsteady turbulent flows around a square cylinder usingκ-ε turbulence models, choice of right turbulence models was found to be critical. If a proper care is taken to choose a convection scheme and near-wall resolution, the conventional turbulence models may predict an unsteady turbulent flow at low Reynolds numbers with reasonable accuracy. A systematic computation is carried out to identify the effects of the aspect ratio of a rectangular cylinder and of the flow Reynold number on the spatial resolution requirement. It is found in general that the grid resolution requirement is more stringent for a cylinder with a smaller aspect ratio. By investigating high Reynolds number computations, the grid refinement in terms of viscous wall units is found unimportant in accurately predicting the unsteady aerodynamic forces on the cylinder. Instead, resolution of shear layers formed at the forward separation corners is found to be more critical.     

Quantification of the cold worked material inside the deep honing grooves on cylinder liner surfaces and its effect on wear

The increased presence of cold work material on cylinder liners due to the introduction of the diamond honing is undesirable as it seals the oil-bearing honing grooves. The most of it is a smeared metal inside the deep honing grooves (blechmantel) that may break and act as abrasive wear particles increasing the bore wear. An attempt has been made to estimate the extent of removal of blechmantel for different wear regimes present at the middle and top region (near the top dead centre) of the liner surface using the least worn bottom region as a reference for comparison. A number of truck grey iron cylinder liners were axially sectioned after varying periods of engine running under similar conditions of load, engine speed and lubrication. 3D surface measurements were taken at the three regions and a range of standard parameters was extracted. Combining the profile and image analysis, an algorithm was developed to identify and quantify the blechmantel. The algorithm has successfully identified/quantified the blechmantel and can be used for automatic surface quality and process control. It was found that the amount of the blechmantel in the middle section was approximately the same (though slightly lower) as that in the bottom section, while there was a considerable dislocation and removal of blechmantel in the top section and thereby it represents one of the possible causes for wear. Axial wear scratches of different size and distribution were observed not only through the whole stroke area, but also in the bottom region. All engines and liners performed well throughout the tests, and the observed quantities of blechmantel and axial scratches are acceptable for the time being.     

A Model for Wear and Friction in Cylinder Liners and Piston Rings

Abstract

A one-dimensional elstohydrodynamic mixed lubrication wear and friction model is developed. The model can predict the effects of surface roughness, asperity contact, temperature-pressure-viscosity on wear, lubrication, and friction of the piston rings and cylinder liner. Wear is predicted based on the surface asperity contact pressure. The cylinder bore wear and the ring pack friction during an engine break-in are simulated and compared with the experimental results. The influence of cylinder wall temperature and surface roughness on friction and wear is investigated. The ring pack friction due to oil viscous shearing and asperity contact is found to reach its minimum at a certain oil temperature.     

Comparison of DNS and Reynolds stress modelling of flow around a rotating cylinder

The low Reynolds number stress-omega model is applied to flow associated with a rotating cylinder operating in a larger, stationary cylinder. The working fluid fills the gap between the cylinders. Direct numerical simulation data are used to test the predictions by this turbulence model. Previous work has shown that simpler models are unable to predict with reasonable accuracy the wall shear stress experienced by the rotating cylinder. The present study with a more complex turbulence model shows that the wall shear stress on the rotating cylinder is underestimated significantly. Examination of turbulence velocity fluctuation intensity distributions points to underprediction of the streamwise turbulence level and excessive values of the wall normal turbulence level. Results are given for no shear and a wall shear at the outer cylinder surface but no effect on the inner cylinder statistics was found. An examination of the Reynolds stress anisotropy tensor components highlights a significant deficiency in this parameter which is an essential component of the pressure-strain modelling of Reynolds stress models. The most significant aspect is a rapid decrease of the streamwise component of the Reynolds stress anisotropy tensor relative to the direct numerical simulation results and values which are too low for the other two components.     

Analysis of surface texture of plateau-honed cylinder liner – A review

The surface of cylinder liner is tribologically important. In most cases, it has a two-process cross-hatched structure created by the plateau honing process. Because the surface topography of cylinder liners is complicated, its analysis is challenging. Special methods have been used to analyse the textures. In this article, first, the parameters in the standard are reviewed. Next, the methods for selecting the reference elements are presented. Other comprehensive methods of cylinder surface analysis are described. Finally, methods of cylinder texture modelling are analysed.     

缸孔珩磨工艺及表面特征参数浅析

珩磨作为缸孔加工方法,因能修正前道工序产生的几何形状误差和表面波度误差,通过在缸孔表面形成细小的沟槽,这些沟槽有规律地排列形成网纹,并由专门的珩磨工艺削掉沟槽的尖峰,形成微小的平台,平台保证承载,原硬度保证耐磨,而被广泛应用。根据我公司所使用的美国NAGEL珩磨机,介绍了珩磨缸孔后表面质量的评定理论及工艺,并对影响其表面特征参数的因素进行了简要的分析。     

Frictional evaluation of thermally sprayed coatings applied on the cylinder liner of a heavy duty diesel engine: Pilot tribometer analysis and full scale engine test

The piston system accounts for roughly half of the mechanical friction of an internal combustion engine, thus it is important to optimize. Different thermally sprayed cylinder liners were investigated in order to optimize the frictional impact of the contact between cylinder liner and piston ring/piston. A novel tribometer test setup was used to scan through different materials at different running conditions. Two cylinder liner materials showed significantly lower friction than the other tested materials, CrC–NiCr and MMC. All the thermally sprayed cylinder liners were worn significantly less than the reference material. Based on these results a full-scale single cylinder test was performed to validate the results from the rig. Comparing the thermally sprayed cylinder liner MMC with reference cylinder liner the test showed higher friction torque for the MMC cylinder liner except in one case; at low speed and high pressure. An analysis of the results between the tribometer and the engine points at the importance of the ratio between viscous and mechanical friction losses. The most probable cause of higher friction torque for the thermally sprayed coating (MMC) is that the functional surface of the cylinder liner promotes an increase in viscous friction.     

柱面扁壳面畸变形成机理及控制

以矩形柱面扁壳为模型,从小变形、简单加载的前提条件出发,推导了矩形柱面扁壳切边后曲面方向回弹的理论解。试验研究了柱面扁壳面畸变现象,得到了面畸变分布。提出了面畸变理论评价指标,对比试验结果分析了面畸变形成机制,得到了屈服点、凸模曲率半径、板料厚度、弹性模量及张拉力对面畸变的影响规律,并提出了减小面畸变的工程控制方法。