WALL EFFECTS ON FLOWS PAST TWO TANDEM CYLINDERS OF DIFFERENT DIAMETERS

Flows past two tandem cylinders of different diameters placed centrally in a channel with fixed centre-to-centre spacing 6D and diameter ratio are simulated based on the Lattice Boltzmann Method(LBM).In all the simulations,the diameter of the smaller cylinder is chosen as the characteristic length.The Reynolds number based on the average inflow velocity is 20-120 and studies are over the range of blockage ratio 2-8.In both Small-Big Arrangement(SBA)and Big-Small Arrangement(BSA),the effects of the channel width and Reynolds number on the flow structures and force coefficients are studied.Results show that the flows in BSA are more regular than those in SBA for the same flow fields.In BSA with and,the force coefficients all fluctuate with constant amplitudes and a coupled frequency,the coupled frequency becomes small as the blockage ratio decreases and by an exact test we give out the relation of the blockage ratio and Strouhal number.As the blockage ratio decreases to 2,there exist pitchfork bifurcations in both SBA and BSA,and results show that the critical Reynolds numbers of pitchfork bifurcations for SBA and BSA are both between 60 and 80.In SBA with,the flow structure has a static asymmetric mode.It is found that the channel width has also an effect on the critical spacing where the flow changes from single body mode into co-shedding mode.By an accurate survey on flows past two cylinders with equal diameters placed inside a channel with the width,the relation between channel width and the critical spacing is given and results show that the critical spacing increases as the channel width increases.     

泥石流堵江影响因素试验研究

对影响泥石流堵江的各因素进行了试验研究。结果表明，泥石流入汇角、泥石流与主河的流量比、泥石流入汇总量等的增大有利于堵江现象的发生，而主河宽度和主河比降的增大则不利于泥石流堵江，泥石流密度与主河临界堵江流量呈现一种抛物线性关系。     

利用河流平衡理论检验推移质输沙函数的应用性

推移质输沙函数多根据试验资料建立,在实际应用中往往会给出相去甚远的预测,对河流平衡形态影响显著。本研究利用河流平衡理论检验推移质输移通式Φ=cb(τ0*-τ*c)β中各参数对河道平衡形态的影响,式中Φ为无量纲推移质输沙强度,τ0*为无量纲水流平均剪切应力,cb、τ*c和β为输沙参数,分别代表输沙系数、无量纲水流临界剪切力和输沙指数。引入河道过水断面的宽度与平均水深的比值作为表征断面形态的无量纲参数,基于变分原理的图形分析结果表明,输沙通式中指数β的选取是影响平衡河道形态的重要因素。结合长江中游监利河段河道形态实际观测数据,对比分析已有推移质输沙函数对河道平衡形态的定量影响,结果表明β=5/3时河流平衡理论具有很好的实际应用性。     

SIMULATION OF THE TWO PHASE FLOW OF DROPLET IMPINGEMENT ON LIQUID FILM BY THE LATTICE BOLTZMANN METHOD

A Lattice Boltzmann Method (LBM) with two-distribution functions is employed for simulating the two-phase flow induced by a liquid droplet impinging onto the film of the same liquid on solid surface.The model is suitable for solution of twophase flow problem at high density and viscosity ratios of liquid to vapor and phase transition between liquid and its vapor.The roles of the vapor flow,the density ratio of liquid to vapor and the surface tension of the droplet in the splashing formation are discussed.It is concluded that the vapour flow induced by the droplet fall and splash in the whole impinging process may affect remarkably the splash behaviour.For the case of large density ratio of liquid to vapor a crown may engender after the droplet collides with the film.However,for the case of small density ratio of liquid to vapor a "bell" like splash may be observed.     

表面活性剂减阻流体传热与阻力关系试验研究

针对在水中添加表面活性剂可以出现阻力系数减少而同时传热性能发生变化的现象,采用测压差装置和热电偶测温系统分别对二维流道内不同的减阻流体的减阻性能、传热性能进行了试验,研究了浓度、配比、雷诺数和热流密度对减阻流体传热与阻力系数之比值的影响。结果表明,表面活性剂减阻流体的传热系数考尔朋（Colburn）因子与阻力系数之比和水的情况有较大的差异;当减阻流体的减阻率稳定时,随着雷诺数的增大,考尔朋恩因子与阻力系数比值缓慢下降;达到临界雷诺数后,考尔朋因子与阻力系数之比值波动较大,并且比值迅速增大到接近没有添加减阻剂的水平。     

水闸规模对河道水动力水环境的影响研究

水闸规模与所处河道宽度的差异一定程度上会阻碍水流流通,造成水体置换周期延长,极易诱发水体富营养化,故确定水闸建设规模对河道水动力水环境的影响对维护水安全具有重要意义。以上海市青浦区跃进圩区内的闸坝为研究对象,采用一维水动力水质模型模拟预测了不同闸宽条件下跃进片各断面最大流量、总进水量等水动力变化特征以及COD、NH3-N、TP等营养物质的浓度变化,探讨了圩区水闸闸孔宽度与河道断面匹配关系,分析了闸孔宽度变化对水量水质的影响。模拟结果表明：闸门宽度的增加将直接引起过闸的最大流量线性增大,而总进水量与水质改善情况更大程度地受限于闸门河宽比。在现有引排水量及闸泵调度规则下,跃进片区的临界闸门河宽比约为2/5。     

冲积河流稳定平衡条件与断面几何形态的数理分析

冲积河流稳定平衡条件长期以来被认为无闭合解,致使众多经验假说得以应用。本文通过将两个无量纲断面形态参数宽深比和边坡角度引入到冲积河流三大基本运动方程中,详细分析了推移质输沙率与这两个变量之间的复杂关系,从数学上推导得出冲积河流达到稳定平衡的水动力学条件是推移质输沙率最大。河流达到稳定平衡时的过水断面形态数学表达式表明,天然冲积河流在平滩水位时所展现的水力几何关系是河流通过调整过水断面形态达到的稳定平衡的结果。     

A MATHEMATICAL MODEL OF MIGRATION AND EXPANSION OF MEANDER LOOPS

This article presents a mathematical model of the plane evolution of alluvial meandering streams,through downstream migration and lateral expansion of meander loops.Under the conditions prevailing in natural streams,the channel centerlines follow sine-generated curves,with an assumed steady-state turbulent and subcritical flow,of large width-to-depth ratio(≥ 15,for example) and small Froude number(Fr ).The plane deformation of the channel is caused by the action on the banks of the convective vertically-averaged meandering flow.The growth(migration and expansion) of meander loops is attributed to the regime-trend.The computational results of the model show that the obtained migration and expansion patterns of the meander loops are in good agreement with those of observations and measurements in similar meandering streams.     

Energy losses and hydraulic friction of open and ice-covered river flow

Laws governing flow in open and ice-covered river flows are investigated. The dimensionless Darcy – Weisnbach coefficient is used to evaluate the hydraulic resistance of channel flow. A shape factor is introduced for the cross section of a channel flow, which makes it possible to account for the complex shape of the channel in analyzing hydraulic resistance. A relationship derived to show the dependence of resistance on Reynolds number is used to evaluate the ratio of energy losses during viscous dissipation to the total energy of the flow. Results of calculations based on mock-up formulas are compared with results obtained for flows in rivers and flumes.     

均质土坝漫顶溃坝过程数学模型研究及应用

国内外大量模型试验表明,"陡坎"式冲蚀是均质土坝漫顶溃决的重要机理。近年来,各国学者开发了一系列的考虑"陡坎"式冲蚀的溃坝过程数学模型,但模型均采用了"陡坎"出现在下游坡脚的假设。通过大比尺均质土坝漫顶溃决模型试验发现,对于坝高较大的均质土坝,"陡坎"出现的位置与漫顶水头和下游坝坡坡比存在内在联系,且"陡坎"的移动速率与坝料的物理力学指标相关,因此初始冲坑的位置和"陡坎"移动参数的选取对于溃坝过程模拟结果的合理性具有重要意义。本文借鉴国内外的漫顶溃坝过程数学模型,提出一个可考虑均质土坝漫顶溃决过程中"陡坎"移动的数学模型。该模型通过漫顶水流特征和坝体形状参数确定下游坡初始冲坑的位置,采用能量分析方法模拟"陡坎"移动,并通过室内与现场模型试验提出可考虑坝料黏粒含量、含水率、干密度等指标的"陡坎"移动参数;利用基于水流剪应力原理的冲蚀速率公式模拟溃口纵向下切与横向扩展;采用宽顶堰流量公式计算溃口流量,通过极限平衡法分析溃坝过程中溃口边坡的稳定性,采用迭代的数值计算方法模拟整个溃坝过程。选择国内外典型的大比尺均质土坝漫顶溃坝试验和有实测资料的溃坝案例对模型进行验证,并研究了是否考虑"陡坎"冲蚀对溃坝模拟结果的影响;通过模型计算分析可以得出,本文提出的数学模型可合理模拟均质土坝的漫顶溃坝过程。     

Stability of fluid flow in a Brinkman porous medium–A numerical study

The stability of fluid flow in a horizontal layer of Brinkman porous medium with fluid viscosity different from effective viscosity is investigated. A modified Orr-Sommerfeld equation is derived and solved numerically using the Chebyshev collocation method. The critical Reynolds number cRe, the critical wave number αc and the critical wave speed cc are computed for various values of porous parameter and ratio of viscosities. Based on these parameters, the stability characteristics of the system are discussed in detail. Streamlines are presented for selected values of parameters at their critical state.     

黄河下游游荡性河道水位涨率偏大的主要影响因素分析

认为影响黄河下游游荡性河道水位涨率的因素是多方面的 ,河宽只是其中的原因之一。利用黄河下游花园口、夹河滩等水文站历次实测大洪水测流断面资料 ,计算了各水文断面不同槽宽的水位流量关系。在洪水涨水阶段 ,同样的流量涨幅 ,等河宽的平均河底高程变化 ,河南河道和山东河道没有明显差别 ,但河南河道的比降是山东河道的 2倍 ,同河宽的水位涨率必然小于山东河道。对游荡性河道已发生的几场水位涨率偏大的原因作了分析 ,认为游荡性河道十分宽浅 ,河势摆动频繁 ,大洪水时形成顶冲、局部壅水 ,它对水位涨率的影响远大于河宽缩窄的影响 ;复式河槽在洪水漫滩后 ,由于滩槽水流的动量交换 ,引起主槽的阻力增大 ,也是导致水位涨率增大的重要原因。     

Flow choking characteristics of slit-type energy dissipaters

In this paper, the behavior of the flow choking, including the critical and developing states, was experimentally investigated by means of five slit-type outlets, characterized by the outlet width, the contraction angle and the opening of the working gate. The results showed that the approach flow Froude number of the critical choking decreases if the outlet width increases, or the contraction angle decreases, or the opening increases. There is the hysteresis when the flow choking develops, i.e., the Froude numbers of the appearance and disappearance of the flow choking at the increasing discharge regime are all larger than those at the decreasing discharge regime. For various widths of the outlets, the differences between the critical Froude numbers at small opening are much larger than thoset at large opening. The change range from appearance to disappearance of the flow choking at small opening is smaller than that at large opening.     

河岸与河底相对粗糙度对河道平衡形态的影响研究

边界条件对河流地貌形态具有重要影响,基于河道边界阻力水力半径分割方法,利用变分方法研究河岸与河底相对粗糙度对冲积河流平衡河道形态的影响.结果表明,河岸与河底相对粗糙度对河流达到平衡时的最大输沙率有一定的影响,但对河道平衡形态的影响非常显著.在临界和平均水力几何形态关系式中,随着河岸与河底相对粗糙度的增大,河宽关系式的系...     

不同来源区洪水对黄河下游游荡河段河床横断面形态调整过程的影响

以黄河下游实测流量过程等水文资料为基础 ,从流域系统的角度出发 ,以洪水作为联系流域系统各子系统耦合关系的指标 ,揭示了不同来源区洪水对黄河下游游荡河段洪水前后河床横断面形态变化的不同影响及其原因。上少沙来源区洪水使河床形态变宽浅为主 ,变宽浅主要由于主槽淤积所造成 ;下少沙来源区洪水使河床宽深比以变窄深为主 ,主要由于主槽冲刷所造成 ;多沙粗沙来源区洪水造成河床宽深比减小 ,主要由于高含沙洪水淤滩刷槽所造成 ;多沙细沙来源区的洪水后宽深比变化不大 ,仅略减小 ,也存在淤滩刷槽的过程     

90°等宽明渠交汇水流污染物混合规律数值模拟

为研究明渠交汇水流污染物混合规律,针对90°等宽顺直明渠水流交汇口,建立三维水动力-污染物耦合输运数学模型,对6 种不同汇流比情况进行数值模拟研究。计算结果表明:交汇水流污染物分布存在明显的三维特征,且与二次流密切相关;水体表层污染带最大宽度与汇流比的关系和水体内部不同,表层水体污染带最大宽度在小汇流比工况下为主渠宽度,不随汇流比的变化而改变,在大汇流比工况下与汇流比呈良好的一次函数关系;中下层水体污染带最大宽度与汇流比呈二次曲线关系;汇流比越接近0. 5,污染物混合越不均匀,且汇流比越大,污染物混合速率越快。     

非对称尾部形状水翼水力阻尼识别方法研究

水力阻尼是影响流激振动幅值预测精度的关键参数,是水力机械流激振动领域研究的热点问题。非对称尾部形状水翼在涡激振动和升力的联合作用下,振动响应的平衡位置具有时变特性,采用传统自由振动衰减法获得的水力阻尼比误差大幅度增加,甚至失效。为了克服传统自由振动衰减法应用局限,本文借助双向流固耦合数值模拟方法获得流激振动响应位移,通过带通滤波结合平衡位置校准,研究了动水环境中对称和非对称尾部形状水翼水力阻尼的识别方法。结果表明,数值模拟可较准确获取低阶结构模态和尾部旋涡脱落频率,相比实验结果,低阶弯曲模态频率、低阶扭曲模态频率和15 m/s流速下脱落涡频率最大偏差分别为7.58%、2.90%和1.42%;带通滤波可消除周期性涡激振动对响应信号的影响,水力阻尼比识别偏差度从7.51%下降到1.92%;平衡位置校准方法可采用多项式拟合法、线性插值法和光滑样条曲线法,所对应的水力阻尼比识别偏差度分别为34.93%、3.53%和0.16%。工程上,可优先推荐滤波结合线性插值法,在需要高精度水力阻尼比的场合,则必须采用滤波结合光滑样条曲线法。     

小颗粒堆积多孔体传热特性实验研究

对平行平板间填充小颗粒后的换热实验结果进行了归纳和分析，发现板间距不变，平均Nu数不随颗粒直径单调变化，说明存在最佳填充层数，并对此进行了初步分析。实验表明，小颗粒填充可以得到较好的换热强化效果，而流动阻力却远小于微颗粒填充情况，因此有可能利用小颗粒填充方法在常规条件下强化平板间的换热。     

THE ORIENTATION DISTRIBUTION OF FIBER SUSPENSIONS AND ITS EFFECT ON THE CONSTITUTIVE RELATIONSHIP

BRIEF INTRODUCTION OF THE PAPER:Under- standing the physical properties of fiber suspen- sions is currently of great interest in many areas . Different fromspherical particle suspensions ,the properties of fiber suspensions mostly rely on the orientation distribution of fibers due to their slen- der bodies .It is i mportant tostudythe particle ori- entation distribution of fibers suspensions during flows . In the dilute planar converging channel flow in laminar regi me , the Orienta…     

黄河下游丁坝缩窄河道泥沙冲淤特性试验研究

通过动床模型试验研究了黄河下游裴峪至官庄峪丁坝缩窄河段,在河道不同位置布设丁坝,不同情况下丁坝相对长度(丁坝长度与原河道宽度之比值)对河道泥沙冲淤变化的影响。结果表明：水沙运动要素变化受丁坝布设位置和长度等影响较大,随着丁坝相对长度的增加,汛期主河槽冲刷量和滩地淤积量逐渐增大,主槽范围相应扩大,其高程普遍呈下降趋势,特别是缩窄断面导流堤顶端部位出现明显的局部冲刷坑,束水冲沙、增大输沙能力的效果明显。当丁坝相对长度大于0.50时,主流线偏移、断面流速分布和河床冲淤的变化速率明显增大,不利于河道稳定。