NUMERICAL STUDY OF WALL WETTABILITIES AND TOPOGRAPHY ON DRAG REDUCTION EFFECT IN MICRO-CHANNEL FLOW BY LATTICE BOLTZMANN METHOD

The dynamics of two-phase flows with a constant driving force inside a micro-channel is studied by using the Lattice Boltzmann Method (LBM) and the Shan-Chen multiphase model in this article. Flow regimes under different wall wettabilities and over smooth and grooved geometric surfaces are investigated. It is found that flow behaviors are strongly affected by the wall wettability and topography. Our results show that the LBM is efficient and accurate, and has very good application prospect in the study of drag reduction of microscopic seepage of reservoir.     

Forced convection and entropy generation inside a channel with a heat‐generating porous block

The flow pattern and heat transfer in a composite system containing a porous region has received considerable attention due to its importance in many engineering applications. In this study a thermal lattice Boltzmann model with nine velocities, D2Q9, is employed to investigate the fluid flow, heat transfer, and entropy generation inside a channel with a heat‐generating porous block. The effects of the porous block's length, porosity, and the Reynolds number, overflow pattern, heat transfer, and entropy generation were studied. The mentioned parameters have different effects on heat transfer and conjugate phenomena. By increasing the block length, Reynolds number, and porosity the dimensionless entropy generation will reduce. © 2012 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21017     

NUMERICAL STUDIES ON LOCOMOTION PERFROMANCE OF FISHLIKE TAIL FINS

Flapping plates of typical fishlike tail shapes are simulated to investigate their locomotion performance using the multi-block Lattice Boltzmann Method (LBM) and Immersed Boundary (IB) method. Numerical results show that fishlike forked configurations have better locomotion performance compared with unforked plates. Based on our results, the caudal fin in carangiform mode has greater thrust, and the lunate tail fin in thunniform mode has higher efficiency. These findings are qualitatively consistent with biological observations of fish swimming. Analysis of wake topology shows that the wake of the forked plate consists of a chain of alternating reverse horseshoe-like vortical structures. These structures induce a backward jet and generate a positive thrust. Moreover, this backward jet has a more favorable direction compared with that behind an unforked plate.     

西藏罗布莎科学钻孔冲洗液技术

通过西藏罗布莎科学钻孔施工过程冲洗液应用实践,结合现场试验室试验情况及实际生产过程中使用的泥浆类型、配方、性能特点、使用情况,总结出适合罗布莎铬铁矿区易坍塌、破碎、漏失、缩径等复杂地层钻探施工的冲洗液配方,并对不同类型冲洗液使用情况及存在的不足进行了阐述,对同一配方冲洗液在不同钻探工艺条件下使用所取得的不同效果做出了说明,为今后坍塌、破碎、漏失、缩径等复杂地层深部钻探的冲洗液配方选择提供了一些参考。     

含裂隙煤体瓦斯渗流规律的LBM数值模拟

通过模拟外力驱动渗流以及部分填充多孔介质的剪切渗流,验证了广义LBM模型可以对含有裂隙的煤体内瓦斯渗流规律进行模拟研究;裂隙内的流速明显高于在煤基质内的流速,定量研究了渗流速度和流量随着裂隙宽度增加的变化规律;而在裂隙宽度相等的条件下,煤体渗透率越低则流速和流量的提高越显著;与顺流向的裂隙相比,垂直流向裂隙的存在对提高渗流速度及流量的影响相对较为有限。模拟结果表明：裂隙的存在,尤其是在渗透性较差的煤层中,对提高瓦斯抽放的效果更为明显;而对于不同方向的裂隙,则应该重点关注与瓦斯流动方向相同或大体相同的裂隙分布。     

High surface quality micro machining of monocrystalline diamond by picosecond pulsed laser

In micro machining of monocrystalline diamond by pulsed laser, unique processing characteristics appeared only under a few ten picosecond pulse duration and a certain overlap rate of laser shot. Cracks mostly propagate in parallel direction to top surface of workpiece, although the laser beam axis is perpendicular to the surface. This processed area can keep diamond structure, and its surface roughness is smaller than R_a = 0.2 μm. New laser micro machining method to keep diamond structure and small surface roughness is proposed. This method can contribute to reduce the polishing process in micro machining of diamond.     

沥青路面裂缝细观渗流特性及试验研究

采用格子Boltzmann方法(LBM)研究分析沥青路面裂缝的细观渗流特性,建立了压力梯度作用下复杂单裂隙面细观渗流的数值模型,然后使用光滑平板裂隙渗流的经典立方定律对模型进行了验证,并且讨论了沥青混合料裂隙面的粗糙度与弯曲度对其渗流特性的影响.结果表明:随着裂隙面相对粗糙度的增大,裂隙渗流明显偏离了立方定律;随着裂隙面弯曲度的增大,裂隙渗流与弯曲度的-3.8327次方成正比.最后,采用自行研制的可加围压的侧壁橡胶膜止水渗透仪测量沥青混合料裂隙面的渗透系数,并与立方定律实用修正公式的计算结果进行对比,结果发现两者误差较小,修正公式的计算结果更加准确合理,可以为路面水渗入率计算提供准确的基本参数,从而为路面排水设计提供有价值的参考.     

Lattice Boltzmann Method Based Simulation of Natural Convection in Partially Open Enclosure

A thermal lattice Boltzmann method‐based analysis was performed to numerically investigate the heat transfer by natural convection from an enclosure with a large vertical side opening. The height of the opening was less than the enclosure height and the vertical wall opposite to the opening was maintained at constant temperature. A parametric study was carried out for different values of Rayleigh number (Ra) ranging from 10³ to 10⁵ with air as the working fluid for three opening sizes and three opening locations. The Prandtl number was fixed at 0.71 and the enclosure aspect ratio was also fixed at 2 in all calculations. With Boussinesq approximation, the temperature distribution and stream functions in the enclosure were predicted. The profile of the normal velocity component at the opening location was determined. The opening size affects the stratification and recirculation pattern within the enclosure. The average Nusselt number at the heated wall was determined for all cases. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21110     

镍基高温合金喷射液束电解-激光复合加工特性的试验研究

针对镍基高温合金材料激光打孔时存在的再铸层,采用喷射液束电解—激光复合加工对镍基高温合金GH3030进行打孔试验,研究复合加工去除再铸层的特性,以及复合加工参数对再铸层残余率和材料去除率的影响规律。试验结果表明:在复合加工过程中,喷射液束的电解作用能有效在线去除激光加工产生的再铸层,提高激光加工的质量;得到了各加工参数对再铸层残余率和材料去除率的影响规律,建立了再铸层残余率和材料去除率二次回归方程,并采用验证试验说明了二次回归方程能很好地预测复合加工特性。基于二次回归方程,优化工艺参数,进行群孔和刻字的样品加工试验,试验结果证明了该方法可以满足工程应用的需要。
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煤微观结构三维表征及其孔–渗时空演化模式数值分析

 探讨煤岩微观孔隙结构统计意义上的等效构建方法,并于孔隙尺度下模拟流体运移行为的时空演化过程。首先,结合煤岩孔隙结构的各向异性及非线性特征,采用修正的四参数随机生长(QSGS)算法构建煤岩多孔介质模型。随后,采用格子Boltzmann方法(LBM)模拟孔隙中气体单相流的运移过程,并基于数值试验结果,分析煤岩介质中影响渗透率的主要因素及流体运移达到平衡态前的演化模式。分析结果表明：(1) 多孔介质的渗透性能受控于少量、连通性好的大孔所形成的通道,而小孔及微孔中气体的行为基本属于浓度扩散过程;(2) 孔隙属性空间变异条件相同情况下,孔隙度同渗透率之间满足乘幂关系,但幂率系数随孔隙属性变异因子的降低而增加;(3) 渗透率随时间呈减少趋势,自运移开始达到动态平衡的耗时量同孔隙度之间是一种负相关的幂率关系。