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磁流变液的流变学特性检测方法与仪器研究 总被引:1,自引:0,他引:1
根据磁流变液装置设计和材料性能评价的需要,分析了磁流变液的流变学特性描述模型:在不同温度和磁场下,磁流变液的剪切应力与剪切应变率之间的关系.为实现磁流变液的高剪切率和高磁场强度,提出一种基于双边圆筒剪切模式的磁流变液流变特性检测方法,利用磁流变液剪切流动平衡微分方程和边界条件,研究了通道中磁流变液标称剪切应力与传递力矩之间的理论关系,标称剪切应变率与转子角速度之间的理论关系,并给出相应的算法,实验得到剪切通道中磁感应强度与励磁电流的关系.合理选择了扭矩传感器、转速测量仪、温度测试仪和电流计等,研制出磁流变液测试仪器,通道磁感应强度超过了6 000 Gs,剪切率超过了1 000 s-1.对某种牌号的磁流变液测试,并与重庆大学工程力学系测试结果能够良好吻合. 相似文献
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通过数值仿真试验研究,验证利用FLUENT仿真软件进行数值仿真的可行性,并且得出在单相流以及气为连续相的低含液率气液两相流这两种情况下,50 mm口径涡街流量计探头的相对最佳安装位置,其中单相流的涡街探头最佳安装位置在发生体后0.4D处,气为连续相的低含液率气液两相流涡街探头的最佳安装位置在发生体后1D处。利用FLUENT仿真软件的后处理功能对流场进行分析,得出低含液率下采集的信号在发生体后1D处最优的本质原因——在发生体后1D处,旋涡达到成熟,涡街信号最强,流场信息最为丰富稳定。以含液率0.04%的气液两相流流场与单相流流场进行对比,分析得出单相流和低含液率两种情况下,涡街探头最佳安装位置不同的原因。 相似文献
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为了评价实际应用中广泛使用的新式波形板气液分离性能,试验研究了在液滴粒径分布范围为10~200μm的情况下,气速和加液浓度对波形板分离效率和压降的影响,并采用计算流体力学方法对波形板内部流场进行了数值模拟分析。结果表明,与旧式波形板相比,新式波形板具有效率高、压降增长率低、临界气速大以及对小液滴分离效果好等优势;通过波形板的液滴浓度增大,波形板分离效率升高,新式波形板在液滴浓度低时性能较佳;袋式排液结构比钩式排液结构所带来的压降更小,并且能够减小二次夹带的影响;新式波形板更适用于实际应用的复杂工况。 相似文献
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溴化锂吸收式制冷机发生器水平圆管外滴状布液降膜流动的研究 总被引:1,自引:0,他引:1
建立了溴化锂吸收式制冷机降膜式发生器水平圆管外滴状布液降膜流动的数学物理模型,通过计算得到了滴状布液降膜流动的液膜厚度和流动速度沿圆周方向的分布情况,为传热传质研究提供了基础。模型中考虑了液膜流动的初速以及液滴与管顶部碰撞的影响,计算所得的液膜厚度分布比Nusselt膜型更加合乎实际情况。 相似文献
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喷液单螺杆压缩机内液滴运动规律及其对传热的影响 总被引:5,自引:1,他引:4
建立了喷液单螺杆压缩机基元容积内液滴的空间运动学模型,并依此研究了压缩机转速、液滴尺寸、喷液速度及角度等参数与液滴在压缩腔内自由飞行时间的关系,同时从理论上分析了喷液参数对汽液换热的影响,并用实验加以验证。 相似文献
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针对小液滴均匀分布在气相中的两相润滑状态下的密封工况,建立气液混合物理模型,推导气液两相混合流体的等效黏度,建立气液混合润滑动压密封端面间的气液混合润滑Reynolds方程。利用MATLAB软件编写有限元程序求解气液混合润滑Reynolds方程,得到动压密封端面间气液混合流体的压力分布及密封性能参数,并分析在操作工况一定时,液气比对密封性能的影响。分析结果表明:在相同的膜厚下,液滴增强了端面流体动压效应;动压密封在运转过程中,端面密封间隙、摩擦功耗和质量泄漏率随液气比的增加而增加,体积泄漏率随液气比的增加而减少,而刚度随液气比的增加先增加后降低,存在最大值。 相似文献
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针对高转速下液膜密封空化区界面发生强烈波动导致密封失稳的问题,为寻找波动抑制方法,考察了微流道槽底面剪切条件对液膜空化流场特性的影响。选用Schnerr-Sauer空化模型,运用Laminar和转捩SST模型,对比研究了不同转速槽底面无滑移和无剪切条件下的开启力Fo、泄漏率Q、空化占比和空化区速度分布规律。结果表明:流动模型的选择(Laminar和转捩SST模型)对Fo和Q的影响可以忽略,但对空化影响十分显著;液膜空化泡在膜厚方向呈不规则曲面状,在槽区膜厚中部位置的轴截面空化面积占比最大,无滑移时向非开槽端面单侧减小,无剪切时向密封端面双侧减小;可分开判定非槽区和槽区流态,非槽区始终为层流,槽区在11 300 r/min以下为层流,高于11 300 r/min为转捩流,若存在局部区域流动因子9/16<ζ<1或有空化发生,均应采用转捩SST模型;槽底面进行超滑水改性,可显著提高Fo(15 000 r/min时提高51.6%),降低Q(1 000 r/min时降低2.8%),有效降低空化率(15000r/min时... 相似文献
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Accurate measurement of flow in microchannels is imperative to better understand their flow behaviour, which aids in the design of microfluidic devices. In this work, we present an improved VOF model based on smoothing functions that can effectively minimise the issue of spurious velocities, which causes numerical simulations in microchannels to be less accurate. We use the smoothed VOF to simulate the velocity fields and droplet lengths in microchannels and compare the results with experimental data. The results show that the smoothed VOF is able to simulate flow in microchannels more accurately than the standard VOF model. Microchannel simulations using the standard VOF model are less accurate because the spurious velocities produces artificially higher velocity regions in the flow field results. The spurious velocities also induce a higher but non-physical shear stress during the droplet formation process, resulting in droplets forming prematurely with shorter lengths. Hence the smoothed VOF which resolves the issue of spurious velocities is shown to be a more viable tool in predicting the flow in microchannels by means of numerical simulations. 相似文献
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Dongshin Shin Seungbae Lee Yang Na 《Journal of Mechanical Science and Technology》2005,19(8):1682-1691
Direct numerical simulation database of an axial turbulent boundary layer is used to compute frequency and wave number spectra
of the wall shear-stress fluctuations in a low-Reynolds number axial turbulent boundary layer. One-dimensional and two-dimensional
power spectra of flow variables are calculated and compared. At low wave numbers and frequencies, the power of streamwise
shear stress is larger than that of spanwise shear stress, while the powers of both stresses are almost the same at high wave
numbers and frequencies. The frequency/streamwise wave number spectra of the wall flow variables show that large-scale fluctuations
to the rms value is largest for the streamwise shear stress, while that of small-scale fluctuations to the rms value is largest
for pressure. In the two-point auto-correlations, negative correlation occurs in streamwise separations for pressure, and
in spanwise correlation for both shear stresses. 相似文献
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航空发动机轴承腔精确的润滑与换热设计依赖于对其内油气两相润滑介质流动与换热本质的认识。针对轴承腔内复杂的油气两相润滑介质流动状态,建立轴承腔均匀流体/壁面油膜分层流动分析模型,开展腔内油气两相润滑介质流动特性研究,探讨转子转速和润滑油供油量对均匀流体和壁面油膜两相介质压力、速度以及温度分布的影响。分析模型中,气相介质(含油滴)的等效物理特征参数通过离散油滴和气相介质的组分比例关系确定,各固体壁面与流体介质的对流换热系数根据其各自的传热特性确定。研究结果表明,均匀流体与壁面油膜两相介质的压力随着润滑油供油量的增加而增大,受转子转速的影响较为复杂;均匀流体与壁面油膜两相介质的速度随着转子转速的增高而增大,受润滑油供油量影响较小;均匀流体的温度随着润滑油供油量的增加而减小,受转子转速的影响较小;与均匀流体温度不同,壁面油膜的温度随着转子转速的增加而增大,随着润滑油供油量的增加而减小。建立了轴承腔试验台系统,开展了轴承腔油气两相流动状态下的压力和温度测试,压力和温度试验结果与理论计算结果均具有较好的吻合性,验证了提出的理论分析方法的可靠性。 相似文献
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An enhanced model for predicting worn tool cutting forces in metal cutting without the need for any worn tool calibration tests is presented in this paper. The new model utilizes a previously developed slip-line field approach in conjunction with a mechanistic force model to predict the shear flow stress and shear angle for a range of cutting conditions with only a minimal number of sharp tool calibration tests. The shear flow stress and shear angle values are then used as inputs into a worn tool force model to predict the cutting forces due to tool flank wear. Predictions of worn tool cutting forces from the new model have been compared to experimental data from both a steel and a ductile iron workpiece. Ductile iron tests are significant because previous shear flow stress and shear angle models require chip measurements which cannot be made with the chips produced by iron workpieces. Model predictions are also compared to literature data obtained using an aluminum workpiece. An excellent comparison between the model predictions and the experimental data is found for all of the materials considered. 相似文献
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Man Yeong Ha 《Journal of Mechanical Science and Technology》1992,6(1):49-57
In order to study the oscillating flow induced by a high intensity acoustic field, a computer code which employs the two-dimensional, unsteady mass and momentum conservation equations for laminar flow in spherical coordinates has been developed. The displacement amplitude of the incident sound wave is large compared to the characteristic length of particles, and the acoustic Reynolds number based on the particle diameter and the velocity amplitude of the oscillating flow is less than about 100. Numerical solutions of these equations give the velocity field, axial pressure gradient, shear stress and flow separation angle around the particle for acoustically oscillating flow as a function of acoustic Reynolds number and Strouhal number. The axial pressure gradient, shear stress and separation angle are proportional to the magnitude of oscillating flow at low frequency (~50Hz) and can be approximated by the quasi-steady analysis. The effects of flow oscillation increase with increasing frequency (~2000Hz) due to combined effects of curvature and flow acceleration, giving different values of axial pressure gradient, shear stress and separation angle for different frequencies of 500, 1000 and 2000 Hz. 相似文献
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Steady flow of blood through catheterized arteries is studied by assuming the blood as a two-fluid model with the suspension
of all the erythrocytes in the core region as a non-Newtonian fluid and the plasma in the peripheral layer as a Newtonian
fluid. The non-Newtonian fluid in the core region of the artery is modeled as (i) Casson fluid and (ii) Herschel-Bulkley fluid.
The expressions for the shear stress, velocity, flow rate, wall shear stress and flow resistance, obtained by Sankar and Lee
(2008a, 2008b) for the two-fluid Casson model and two-fluid Herschel-Bulkley model are used to get the data for comparison.
It is noticed that the plug flow velocity, velocity distribution and flow rate for the two-fluid H-B model are considerably
higher than that of the two-fluid Casson model for a given set of values of the parameters. Further, it is found that the
resistance to flow is significantly lower for the two-fluid H-B model than that of the two-fluid Casson model. Thus, the two-fluid
H-B model is more useful than the two-fluid Casson model to analyze the blood flow through catheterized arteries. 相似文献
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喷射油滴沉积油膜的流动铺展特性研究* 总被引:4,自引:0,他引:4
航空齿轮和航空发动机主轴轴承都采用喷油润滑的方式进行润滑,喷射油滴与机械零件表面碰撞后形成的沉积油膜的流动特性影响着机械零件的润滑状态和功能。由于有关喷射油滴与固体表面碰撞形成沉积油膜及其流动铺展特性研究较为鲜见,已有的相关研究集中于液滴/固体壁面正碰撞条件下的非油类液膜流动分析,故而对机械零件相关润滑分析计算支持极为有限。采用VOF方法建立了喷射油滴/固体壁面斜碰撞及其沉积油膜流动铺展数值分析模型,通过试验研究对数值分析模型进行了修正,进而基于此数值分析模型分析了航空传动零件润滑等效条件下喷射油滴/固体壁面斜碰撞沉积油膜流动铺展特性,通过与国外相关试验结果的对比验证了所提出的数值分析模型的正确性和实用性。所开展的喷射油滴沉积油膜的流动铺展特性研究,为航空机械零部件润滑计算提供了技术方法和基础数据,对于实现航空机械零部件精确润滑设计有明显的工程意义。 相似文献
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L. S. Kim H. K. Jeong M. Y. Ha K. C. Kim 《Journal of Mechanical Science and Technology》2008,22(4):770-779
This study investigates droplet formation in a micro-channel using the lattice Boltzmann (LB) method. A cross-junction micro-channel
and two immiscible, water and oil phase fluids, were used to form the micro-droplets. Droplets are formed by the hydrodynamic
instability on the interface between two immiscible fluids when two immiscible fluids are imported simultaneously in a cross-junction
micro-channel. The Shan & Chen model, which is a lattice Boltzmann model of two-phase flows, is used to treat the interaction
between immiscible fluids. The detailed process of the droplet formation in the cross-junction micro-channel was illustrated.
The results of the droplet formation by the LBM predicted well the experimental data by PIV (particle image velocimetry).
The effect of the surface tension and the flow rate of water phase fluid on the droplet length and the interval between droplets
was also investigated. As the surface tension increased, the droplet length and the interval between droplets were increased.
On the other hand, when we increased the flow rate of the water phase fluid under the condition of the fixed oil-phase fluid
flow rate, the droplet size was increased while the interval between droplets was decreased. 相似文献
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Kyungjae Yun Jongwoon Choi Sung-Kyun Kim Ohseop Song 《Journal of Mechanical Science and Technology》2012,26(12):3911-3920
The free vibration and flow-induced flutter instability of cantilever multi-wall carbon nanotubes conveying fluid are investigated and the nanotubes are modeled as thin-walled beams. The non-classical effects of the transverse shear, rotary inertia, warping inhibition, and van der Waals forces between two walls are incorporated into the structural model. The governing equations and associated boundary conditions are derived using Hamilton’s principle. A numerical analysis is carried out by using the extended Galerkin method, which enables us to obtain more accurate solutions compared to the conventional Galerkin method. Cantilevered carbon nanotubes are damped with decaying amplitude for a flow velocity below a certain critical value. However, beyond this critical flow velocity, flutter instability may occur. The variations in the critical flow velocity with respect to both the radius ratio and length of the carbon nanotubes are investigated and pertinent conclusions are outlined. The differences in the vibration and instability characteristics between the Timoshenko beam theory and Euler beam theory are revealed. A comparative analysis of the natural frequencies and flutter characteristics of MWCNTs and SWCNTs is also performed. 相似文献