THEORETICAL AND EXPERIMENTAL STUDY ON THE CONICAL SWIRLING WATER JET FLOW

This paper is concerned with theoretical and experimental study on theconical swirling water jet flow.Based upon the theoretical analysis,the experiment on thestructural characteristics of swirling water jet flow including the velocity and pressure dis-tribution laws,on which the parameters of the jet,nozzle and directional blades havemore or less influence,was carried out in CSSRC by using a 3-D LDV in order to optimizea new high-efficiency jet instead of swirling drilling bit for rock-breaking and continuouslydrilling,and to meet the demand of radial horizontal drilling technology.Meanwhile basedon the experimental results,the numerical simulation was conducted for the conicalswirling water jet in the immersed well-bottom flow by solving the RANS equations in the3-D body-fitted coordinate system with the k-ε turbulence model.The numerical resultsare consistent with the experimental data,and lead to some conclusions which are impor-tant for applying the conical swirling water jet to the petroleum drill     

THREE-DIMENSIONAL NUMERICAL SIMULATION OF THERMAL-HYDRAULIC PERFORMANCE OF A CIRCULAR TUBE WITH EDGEFOLD-TWISTED-TAPE INSERTS

Three-dimensional numerical simulations and experiments were carried out to study the heat transfer characteristics and the pressure drop of air flow in a circular tube with Edgefold-Twisted Tape (ETT) inserts and with classic Spiral-Twisted-Tape (STT) inserts of the same twist ratio. The RNG turbulence model for mildly swirling flows, the enhanced wall treatment for low Reynolds numbers, and the SIMPLE pressure-velocity method were adopted to simulate the flow and heat transfer characteristics. Within the range of Reynolds number from 2 500 to 9 500 and the twist ratio y from 5.4 to 11.4, the Nusselt number of the tube with ETT inserts is found to be 3.9% ? 9.2% higher than that with STT inserts, and the friction factor of the tube with ETT inserts is 8.7% ? 74% higher than that of STT inserts. The heat enhancement is due to higher tangential velocity and asymmetrical velocity profile with the increase and decrease of the periodic velocity within an edgefold length. It is found that main factors affecting the heat transfer of ETT inserts are the twist angle and the gap width between the tube and inserts. A larger twist angle leads to a higher tangential velocity, and larger Nusselt number and friction factor. The thermal-hydraulic performance slowly decreases as the twist angle increases. The gap width between tube and inserts has a significant influence on the heat transfer, while little influence on pressure drops. The thermal-hydraulic performance increases in average by 124% and 140% when the gap width reduces from 1.5 mm to 1.0 mm and 0.5 mm. The larger the gap width, the higher velocity through the gap will be, which would reduce the main flow velocity and tangential velocity. So a small gap is desirable. Comparing experimental and numerical results at variable air flow and tube wall temperature, the numerical results are found to be in a reasonable agreement with the experiment results, with difference of the Nusselt number in a range of 1.6% ? 3.6%, and that of the friction factor in a range of 8.2% ? 13.6%.     

静水环境中径向紊动射流数值模拟

为了对径向射流的流速场进行分析研究,进行了静水环境中径向射流的实验。基于PIV测速仪得到了多种工况射流中线流速分布资料。进而分别采用Realizable k-ε模型和RNG k-ε模型对径向射流进行了数值计算,计算结果与实验资料的对比表明,Realizable k-ε模型比较适合径向射流的数值模拟,然后利用Realizable k-ε模型对6种不同工况下静止环境中径向射流进行了数值模拟。数值模拟的结果分析表明,径向射流横截面上流速分布为高斯分布、射流速度半宽沿程增大且与距射流出口的距离成正比以及中线流速沿程衰减与距射流出口的距离成反比,通过引入特征长度的概念,使射流的无量纲中线流速衰减和无量纲速度半宽沿程变化呈现出较强的规律性。     

双浅水垫消力池水力特性的数值模拟与试验研究

结合大渡河泸定水电站右岸2#泄洪洞出口消力池体型优化试验,在一般浅水垫消力池体型的基础上,提出了一种双浅水垫消力池的新体型。为了深入探究该型消力池的消能机理及其水力特性,采用三维RNGk-ε紊流模型对双浅水垫消力池进行了数值模拟计算研究,并与传统的底流消力池及单浅水垫消力池(跌坎式)的数值计算结果进行了对比分析。结果表明,双浅水垫消力池更能充分发挥浅水垫的"垫层"作用,能有效地降低消力池临底流速,水跃流态更好且稳定,消能效果较佳;同时,消力池底板动水压力分布也更加均匀,对消力池稳定性和安全有利。     

排沙漏斗流场特性与排沙机理研究

排沙漏斗是一种截沙率高、耗水率小的二级泥沙处理设施。为了进一步探明排沙漏斗的流场特性和排沙机理,该文采用声学多普勒流速仪(ADV)对排沙漏斗立轴螺旋流进行了三维流场测试,采用雷诺应力模型(RSM)和VOF方法数值模拟了排沙漏斗内清水流场,计算的水流时均流速分布与实测结果吻合良好。通过数值模拟方法得到了全面详细的排沙漏斗流场结构信息,并据此分析了排沙漏斗的排沙机理,提出二次流是排沙漏斗能够顺畅高效排沙的关键。     

同侧竖缝式鱼道水力特性的数值模拟

分别采用标准的k-ε模型和雷诺应力方程模型(RSM)对同侧竖缝式鱼道池室内的水流进行了三维数值模拟。对鱼道池室内的流场、雷诺剪切应力等相关水力要素进行了分析,并应用水工模型试验成果对2种紊流模型的结果进行了验证比较。结果表明：2种紊流模型均可模拟同侧竖缝式鱼道水流基本特性,但 RSM 模型流速场的计算结果与水工模型试验结果更为吻合。     

开敞式宽大单泄槽溢洪道水力特性及优化布置研究

开敞式宽大单泄槽溢洪道与一般溢洪道相比易发生水流流态复杂、掺气效果差等工程安全问题。以马来西亚Baleh水电工程为例,采用VOF法与RNG k-ε双方程紊流模型对溢洪道流场进行三维数值模拟。计算分析了不同工况下溢洪道流态、流速、沿程压强等水力特性的分布规律。同时开展1∶50物理模型试验,对比分析数值模拟结果与模型试验结果发现,两者基本一致,验证了开敞式宽大单泄槽溢洪道水力特性数值模拟的准确性与可行性。进而利用紊流模型计算分析了溢洪道掺气坎的优化布置方案,结果表明:1#掺气坎抬高20 cm后,坎后掺气空腔长度由11.03 m增大至19.84 m,消能率提高了6.11%;3#掺气坎沿泄槽陡坡上移15 m后,挑流水舌冲击位置上移,减轻了对挑流鼻坎段水流流态的影响。研究结果对同类工程的优化设计有一定的借鉴作用。     

分汊河道分流比对河道水流流态影响分析

结合曹继文关于明渠岸边横向取水的水槽试验成果,应用RNG紊流模型,采用两种自由表面处理方法即刚盖假定和VOF法,对分汉河道不同分流比工况下的水流运动进行三维数值模拟。通过数值模拟计算,得出不同表面处理方法下分汉河道不同分流比工况下的流速分布、水流特性等结果,分流比对分流宽度影响较为明显。     

生态型鱼巢砖水力特性研究

生态型鱼巢砖是一种新型的河道护岸构件,本文以它的水力特性为研究对象,根据几种常见鱼类的水流习性提出了鱼巢砖的基本结构尺寸,然后通过模型试验和数值计算分析了鱼巢砖的三种连接形式在不同主槽流速下的流场分布以及它们各自不同的适用性。两种研究方法的成果基本一致,从水力特性方面说明这种鱼巢砖能够为鱼类提供一个安全的避难场所,有助于河道生物多样性的保护,也为鱼巢砖以后进一步的体型优化和推广应用提供了理论基础。     

水平管内螺旋流涡特性数值模拟

螺旋流是工程上常见的流动现象,具有增强湍流度、促进传热传质和提高对颗粒的携带能力等特性。该文采用雷诺应力湍流模型(RSM)对水平管内由短螺旋扭带起旋的螺旋流流动特性进行了数值模拟研究,通过激光多普勒测速仪(LDV)测速实验验证了数学模型的准确性和可靠性。结果表明,水平管内螺旋涡首先在扭带吸力面形成,且形成初期,涡量的大小受主涡影响较大,二次涡形成后,涡量大小主要受二次涡影响。在形成过程中二次涡增强了壁面附近的速度脉动,能够有效地增加介质的掺混。此外,由于二次螺旋涡的存在,使水平径向压力梯度增加,靠近壁面处的轴向速度减小,近壁处切向速度值增大1倍,且径向速度在螺旋流中不可忽略。     

THREE-DIMENSIONAL MEAN AND TURBULENCE CHARACTERISTICS OF AN IMPINGING DENSITY JET IN A CONFINED CROSSFLOW IN NEAR FIELD

The three-dimensional mean and turbulence characteristics of an impinging density jet in a confined crossflow were numerically investigated using the RNG turbulence model. The comparison of the subregion structures and gross features between the numerical results and the experimental data show good agreement. The velocity, Turbulent Kinetic Energy (TKE) and concentration distributions of the impinging jet in near field were obtained and analyzed. The results indicate that the flow and concentration fields of the impinging jet in the crossflow exhibit distinguished three-dimensionality in the near field. There exist upstream wall vortices and downstream wall jet zones in the impinging region, and the TKE and concentration decays are asymmetrical in relation to the stagnation point. The lateral concentration distributionrange in the impinging region spreads considerably. The enhanced entrainment and mixing of the impinging jet in the confined crossflow are mostly associated with the impinging action and lateral expansion in the impinging region. The presence of the bottom wall restrains the formation of the spanwise rollers in the transverse jet region and vertical entrainment and mixing in the impinging region and the transition region.     

MODELLING AND COMPUTATION OF UNSTEADY TURBULENT CAVITATION FLOWS

1. INTRODUCTION Cavitatating flows are important phenomena happened in industry setups and many under-water vehicles. It leads to performance losses and modifications of blade load when happened in machines, especially turbo-machinery. Nevertheless, cavit…     

复式河槽漫滩水流的三维数值计算

采用紊流模型中的雷诺应力模型(RSM)对非对称复式河槽水流的三维紊流进行了数值模拟。数值模拟计算结果与试验结果的比较表明RSM能够很好地模拟滩槽交互区内的二次流、主流速分布和床面剪切力,此模型模拟复式河槽是可靠的。最后用RSM模拟了对称复式河槽在不同水深下的流速场及床面剪切力分布,得出当水深增加时,滩槽交互区二次流动纵向涡增强,而浅滩主流速及床面剪切力迅速增大的结论。     

辐流式沉淀池液固两相流力学特性三维数值模拟

采用两相流混合模型,选取RNG k-ε湍流模型封闭两相流时均方程,对辐流式二次沉淀池液固两相流力学特性进行三维数值模拟。采用有限体积法求解微分方程;紊动能、紊流耗散均采用Quick离散格式;速度与压力耦合求解时使用了压力隐式算子分裂PISO(Pressure-Implicit with Splitting of Operators)算法。通过模拟获得了速度场、紊动能和污泥质量浓度等参量在空间的分布规律,对沉淀池的设计有一定的参考价值。     

NUMERICAL SIMULATION OF THE ENERGY DISSIPATION CHARACTERISTICS IN STILLING BASIN OF MULTI-HORIZONTAL SUBMERGED JETS

3-D numerical simulation was carried out for the water flow in a stilling basin with multi-horizontal submerged jets by using two different turbulence models, namely, the VOF RNG k - ? and Mixture RNG k - ? turbulence models. The calculated water depth, velocity profile and pressure distribution are in good agreement with the data obtained in experiments. It indicates that the numerical simulation can effectively be used to study the water flow movement and the energy dissipation mechanism. The numerical simulation results show that the turbulent kinetic energy distribution obtained by using the Mixture turbulence model covers a region about 18% larger than that calculated by using the VOF turbulence model, and is in better agreement with the actual situation. Furthermore, the Mixture turbulence model is better than the VOF turbulence model in calculating the air entrainment.     

复式断面明渠水流三维数值模拟

复式断面渠道水流流场结构比较复杂,本文用耦合式求解器对复式断面明渠水流的三维流场进行了模拟.采用交错网格,界面上的动量差值采用Roe格式,紊流数学模型选用雷诺应力模型.将计算结果与实验结果进行比较,两者的吻合度较好,从而验证了数学模型的可靠性,最后又对复式断面明渠横剖面上水流运动特性进行了分析.     

浑水水力分离清水装置的流场数值模拟

对新型净水装置-浑水水力分享清水装置内部清水流场进行三给数值模拟。应用雷诺应力模型建立数学模型，采用有限体积法离散方程，运用SIMPLEC算法进行求解，初步得到浑水水力分享清水装置清水流场的颁规律。经分析发现，该装置内的流动是典型的三维非轴对称流场，其中的切向流速分布呈现出明显的强迫涡特征，其垂直面上，形成一内侧向下、外侧向上的环形流动。同时，通过与试验结果进行对比，证明利用雷诺应力模型可以有效模拟装置内的清水流场。     

等宽明渠交汇口流速分布特性数值模拟

明渠水流的交汇现象在涉水工程中十分常见,其中交汇口流速的分布特性复杂,对渠道的设计与维护有着直接的影响。针对明渠交汇流的流速分布特性,基于雷诺方程模型（RSM）与体积函数法（VOF）建立等宽明渠交汇流三维数值模型,结合物理试验数据进行模型验证,对不同交汇角与流量比组合工况进行模拟研究,对交汇口水流流速的分布特性进行分析。计算结果表明,交汇口流速存在分区特征,交汇口内流线弯曲流速偏转,下游会出现回流结构与断面环流现象。当交汇角增大时,水流的偏转幅度更大,回流结构与环流现象增强,分区特征更明显,渠道边壁受到的水体冲击更大;当流量比增大时,主渠水体受到的挤压效应减弱,流速分区特征受到抑制,水流交汇更平顺,边壁受到的冲刷更少。     

复杂旋转回流 PIV 速度整场实验研究

复杂旋转回流流动的实验测量研究中,最受关注的是子午面上的速度分布,流动的复杂性对实验测量提出了较高要求,如测点数目多,对流场干扰限制严等。本文从PIV(粒子图象速度场测量)速度场测量技术的工作原理出发,分析了复杂旋转流动子午面上速度场测量中的双曝光时间间隔,示踪粒子的选取问题,得到了封闭圆柱空腔内旋转流动子午面上速度分布PIV实验测量速度场。实验测量结果可以清楚地观测到随着雷诺数的逐步增加,旋转流动流态的变化以及旋涡破裂现象的出现、发展以及消失的过程。     

水力自动滚筒闸门水动力特性数值模拟

水力自动滚筒闸门是一种新型水力自动闸门，它利用水压力产生的推动力矩、闸门自重以及闸门配重产生的回复力矩进行自动启闭，以实现水流的自动调节、运行和排沙。鉴于对该类闸门的水力特性还没有充分研究，本文利用RNG 湍流模型对圆筒闸体绕流流场进行了模拟，并对自由水面引入了水－气两相流分层理论中的流体体积分数法（VOF）迭代求解。通过数值模拟，得到不同时刻计算域内的相体积分布、圆筒闸体附近速度场、压力场以及各工况的受力，并与模型试验实测结果进行对比分析，两者吻合较好。说明VOF法可以在圆筒闸体绕流流场自由表面的计算中应用推广，同时，所得结果对水力自动滚筒闸门的设计具有指导意义。