Numerical simulation of rotating arm test for prediction of submarine rotary derivatives

The numerical method is used for predicting the rotary-based hydrodynamic coefficients of a submarine. Unsteady RANS simulations are carried out to numerically simulate the rotating arm test performed on the SUBOFF submarine model. The dynamic mesh method is adopted to simulate the rotary motions. From the hydrodynamic forces and moments acting on the submarine at different angular velocities, the rotary derivatives of the submarine can be derived. The computational results agree well with the experimental data. The interaction between the sail tip vortex and the cross flow in the hull boundary layer is discussed, and it is shown that the interaction leads to the "out-of-plane" loads acting on the submarine.     

NUMERICAL SIMULATION OF TURBULENT JETS WITH LATERAL INJECTION INTO A CROSSFLOW

1. INTRODUCTION The interaction of jets with crossflow generates complex flow fields which exist in a variety of industrial applications, e.g. internal film cooling of turbine blades, dilution air jets in combustion chambers, jet from V/STOL aircraft in transition flight. Systematic experimental, theoretical and numerical investigations of the flow fields began several decades ago, where the parameters studied include the jet injection angel, the jet-to-crossflow velocity ratio, the jet …     

NUMERICAL SIMULATION OF FLOW AND HEAT TRANSFER CHARA-CTERISTICS OUTSIDE A PERIODICALLY VIBRATING TUBE

Fluid flow and heat transfer characteristics outside a vibrating tube were numerically simulated by the dynamic mesh method. The mechanism of heat transfer enhancement via periodic vibration of the tube was explored by using the field synergy principle. It is found that the field synergy angle between fluid velocity vector and temperature gradient vector for a periodically vibrating tube is significantly smaller than that for a stationary tube, and it changes approximately according to the sinusoidal law in a vibration period. The effect of time phase of the vibration on the field synergy angle and convective heat transfer coefficient were also discussed. Results indicate that the vibration can enhance heat transfer and this effect is more remarkable when time phase angle ranges between 50° and 1400 in a half period. Especially when the time phase angle is 90°, the average field synergy angle outside the tube reaches the minimum, which leads to the best heat transfer performance.     

Tracking methods for free surface and simulation of a liquid droplet impacting on a solid surface based on SPH

With some popular tracking methods for free surface, simulations of several typical examples are carried out under various flow field conditions.The results show that the Smoothed Particle Hydrodynamics (SPH) method is very suitable in simulating the flow problems with a free surface.A viscous liquid droplet with an initial velocity impacting on a solid surface is simulated based on the SPH method, and the surface tension is considered by searching the free surface particles, the initial impact effect is co...     

基于SPH方法的二维宽顶堰溢流数值模拟

光滑粒子水动力学方法(SPH)是一种基于纯拉格朗日思想的无网格粒子方法,在众多科学和工程领域得到了初步应用。采用SPH方法对二维宽顶堰溢流进行了数值模拟,并利用机群进行并行计算来提高计算效率,将模拟数据与试验数据进行了对比。结果表明,SPH方法可以模拟出二维宽顶堰自由出流和淹没出流时水流流态、水跌、回流区、水跃现象,计算出溢流流量、流速等水力参数,并且采用数据拟合得出与理论相符的断面流速分布图。结果表明了SPH方法可以较好模拟二维宽顶堰溢流中的流速分布以及水面曲线。     

INFLUENCE OF INCLINATION ANGLE ON THE MOTION OF TAYLOR BUBBLES IN UPWARD SLUG FLOW

1 .　ＩＮＴＲＯＤＵＣＴＩＯＮＳｌｕｇｆｌｏｗｉｓｏｎｅｏｆｔｈｅｍｏｓｔｃｏｍｐｌｉｃａｔｅｄｆｌｏｗｐａｔｔｅｒｎｓａｎｄｏｃｃｕｒｓｏｖｅｒａｗｉｄｅｒａｎｇｅｏｆｇａｓａｎｄｌｉｑｕｉｄｆｌｏｗｒａｔｅｓｉｎｓｍａｌｌａｎｄｍｅｄｉｕｍｓｉｚｅｔｕｂｅｓ .Ｉｔｉｓｃｈａｒａｃｔｅｒｉｚｅｄｂｙｌａｒｇｅｂｕｌｌｅｔ ｓｈａｐｅｂｕｂｂｌｅｓ (ｒｅ ｆｅｒｒｅｄｔｏａｓｔｈｅＴａｙｌｏｒｂｕｂｂｌｅｓ) ,ａｌｍｏｓｔｆｉｌｌｉｎｇｔｈｅｔｕｂｅ ,ｗｈｉｃｈａｒｅｓｅｐａｒａｔｅｄｂｙｌｉｑｕｉ…     

三角形迷宫流道滴灌灌水器结构参数及水力特性研究

以滴灌灌水器三角形迷宫流道结构为研究单元,利用均匀设计方法,结合计算流体动力学软件Fluent6.2对流道内部流体的流动进行了数值模拟,通过多元回归计算,获得流道各结构参数与流量系数和流态指数的量化关系。分析这一量化关系表明,流道转角与流量成负相关,与流态指数成正相关;流道宽与流量成正相关,与流态指数成负相关;齿高与流量成负相关,与流态指数成正相关。同时分析了灌水器内部流道的水力性能和流场特性,为三角形迷宫流道滴灌灌水器的研发提供了相应的理论依据。     

岩屑组成对高位滑坡-碎屑流运动特性影响离散元模拟研究

采用三维颗粒离散元模拟方法,对4种由不同粒径碎屑颗粒组成的岩屑滑坡运动过程进行全程数值模拟,研究了碎屑粒径组成对于岩石碎屑滑坡的运动特性影响。结果表明:碎屑颗粒粒径组成对岩石碎屑滑坡的运动总时间和达到速度最大值的时刻没有影响;物源碎屑粒径的组成对滑坡运动速度、破坏力和滑动距离影响大。粒径组成越不均匀,滑坡运动速度和破坏力越大,滑动距离也越远;碎屑流物源前缘部分是滑坡-碎屑流灾害影响范围大小的控制性因素。成果可为岩石碎屑滑坡灾害的预测和评估提供参考。     

A NEW METHOD FOR NUMERICAL SIMULATION OF TWO TRAINS PASSING BY EACH OTHER AT THE SAME SPEED

A new method is proposed to numerically simulate problems of trains passing by each other at the same speed, and is implemented in UDF language of commercial software Fluent. Because only a half of the computational domain is required and the dynamic mesh technique is avoided, the computational efficiency is greatly improved. A two-dimensional test case is used for validation, which shows that the flow field and the pressure wave during the train-passing events can be correctly calculated by this new method. This method can be easily extended to three-dimensional simulations, to deal with practical problems.     

底部均匀加热的倾斜腔体中的对流特性

利用二维流体力学基本方程的数值模拟,探讨了普朗特数Pr=6.99时矩形腔体在一定倾斜角度下均匀加热后的对流特性,讨论了不同的控制参数对对流斑图及流速分布的影响。主要计算两种情况:控制相对瑞利数,改变腔体倾斜角度;控制腔体倾斜角度,改变相对瑞利数。结果表明:给定倾斜角度且角度较小时,随着相对瑞利数的增大,滚动圈个数逐渐增多,流速绝对值增大;给定相对瑞利数,随着倾斜角度的增大,滚动圈个数逐渐减少,流速绝对值减小。     

DLM/FD SIMULATION OF CHANNEL FLOW WITH FENE POLYMER CHAIN SUSPENSION

Distributed Lagrange Multiplier/Fictitious Domain （DLM/FD） method was employed to simulate the channel flow with polymer suspension. The polymer molecules were modeled as Finitely Extensible Nonlinear Elastic （FENE） chains and FENE chain cluster. The coiled stretched transition of FENE chains was examined and the change in configuration of FENE chains was presented. The average velocity profile of the fully developed channel flow with 64 FENE chains was given and fitted well with the power-law curve. The change of chain cluster configuration was also simulated. These simulations show that DLM/FD method is capable of simulating the motion of not only FENE chain, but also FENE chain cluster.     

RESEARCH ON THE BASE CAVITY OF A SUB-LAUNCHED PROJECTILE

The finite volume method based on a multiphase model is adopted to solve the Reynolds-Averaged Navier-Stokes (RANS) equations,which takes into account the effects of fluid compressibility,viscosity,gravity,medium mixture and energy transfer of water and combustion gas.The program Fluent User Define Function (UDF) module combined with the dynamic mesh method is employed to simulate the coupling flow field of combustion gas,water field and trajectory of projectile.The results show that the volume of gas cavity at the bottom of projectile and tail pressure will fluctuate after bottom of the projectile leaving the launch tube.The cause of the fluctuation is analyzed and its effects on the trajectory of projectile are presented.The numerical and experimental results agree well with each other.     

二维造流水槽整流装置数值模拟

水槽盲沟整流装置因其结构的复杂性难以在数学模型中建模。本文基于Owen等的金属筛网整流理论,建立了应用于SPH(WCSPH)方法的数值整流区域。基于弱可压SPH方法,建立了二维波流水槽的数值模型。通过将流速边界条件与周期性边界条件相结合,实现了稳定的流场。经过粒子间距有效性分析和与物理模型实验结果的对比,验证了数值模型的合理性。通过有无数值整流区域时水槽内部流场的稳定性对比分析,论证了数值整流区域可以降低水槽出水口处流态的不均匀性,达到与实际盲沟整流网相近的效果。因此,本文中的数值整流段可以模拟实际的整流装置。     

NUMERICAL SIMULATION OF IRREGULAR WAVE-SIMULATING IRREGULAR WAVE TRAIN

In real sea states, damage incidents on offshore floating structures are not due to the whole time series of wave elevation characterized as statistical one but due to few extreme waves or wave groups in irregular wave train. So, using CFD tools to precisely simulate predetermined irregular wave train will lay sound basis for understanding the local characteristic of the flow field and impact loads on offshore floating structures when damage incidents occur. In this article, the generation of single extreme wave is investigated in a numerical wave tank. First, experimental irregular wave train is decomposed into certain number of small-amplitude waves. The Fourier series expansion is performed to determine the amplitude and initial phase angle of each wave component. A hydrodynamic transfer function is used to calculate the amplitude of wave-maker motion associated with each wave component. Then superposition is carried out on all of the wave-maker motion components to get the final wave-maker motion. With the wave-maker motion as input, simulation of the single extreme irregular wave train is modeled successfully. Then the method is applied to simulating a much more complicated irregular wave train. Once again main features of the complicated irregular wave train are reproduced compared with experiment carried out in the new deepwater experimental basin at Shanghai Jiao Tong University. In the simulation, dynamic mesh method is enabled to model the piston-type wave-maker, the Volume Of Fluid (VOF) method is employed to capture the free surface and a dissipation zone is introduced to deal with wave reflection.     

基于对数螺旋破坏机制的三维边坡稳定性分析

为研究三维边坡在对数螺旋破坏机制下的稳定性,基于极限分析上限法提出了非相关联流动法则下的速度场及安全系数的求解方法,可有效的解决相关联法则中摩擦角过大可能导致速度场不收敛的问题。基于Michalowski构建了考虑体积应变的均质三维边坡的对数螺旋线破坏机制,并利用MATLAB编制计算程序计算不同内摩擦角φ、不同边坡倾角β工况下边坡的稳定系数,分析内摩擦角、边坡倾角对稳定系数和破坏模式的影响规律,引入强度折减技术计算边坡安全系数,通过与Michalowski方法对比发现计算结果接近。研究结果表明:在三维边坡对数螺旋破坏机制下相对于一定宽度的边坡适用,且经过计算稳定系数符合规律。研究成果为边坡的设计计算提供参考。     

三角形迷宫流道滴灌灌水器结构参数及水力特性研究

以滴灌灌水器三角形迷宫流道结构为研究单元,利用均匀设计方法,结合计算流体动力学软件Fluent6．2对流道内部流体的流动进行了数值模拟,通过多元回归计算．获得流道各结构参数与流量系数和流态指数的量化关系。分析这一量化关系表明．流道转角与流量成负相关,与流态指数成正相关;流道宽与流量成正相关,与流态指数成负相关;齿高与流量成负相关,与流态指数成正相关。同时分析了灌水器内部流道的水力性能和流场特性．为三角形迷宫流道滴灌灌水器的研发提供了相应的理论依据。     

颗粒反序现象及对滑坡碎屑流冲击作用的影响

滑坡碎屑流的堆积形态、运动速度及冲击力影响着滑坡碎屑流的致灾程度。颗粒反序现象是滑坡碎屑流动力行为的典型特征,探究反序现象的成因机制、反序堆积过程中冲击力变化的主控因素是滑坡碎屑流防灾减灾工作的重要切入点。运用三维离散元素法,结合模型试验的结果,以控制粒径d_(60)为参数,探索了滑体颗粒运动过程中的反序分离对滑体的堆积形态、运动速度及冲击力的影响,并对滑坡碎屑流颗粒反序现象的成因机制进行了讨论。研究表明,滑坡碎屑流运动过程中的颗粒分选能大大增强滑体的流动性、平均速度峰值及最大冲击力,滑体最终形成反序堆积结构。对于单一粒径滑体模型,粒径为14 mm时滑体流动性最差,滑体平均速度峰值和冲击力峰值随着粒径的增大而增大;对于混合粒径滑体模型,滑体流动性、平均速度峰值和冲击力峰值随控制粒径d_(60)尺寸的增大而增大;颗粒反序现象的形成是由消散压力、振动筛分、大颗粒碰撞分离、小颗粒率先停积等因素共同作用的结果。     

APPLICATION OF VOF TECHNIQUE TO CHANNEL IMPROVEMENT FOR PANJIATAI SHOAL IN THE YELLOW RIVER

In this paper, Volume Of Fluid (VOF) technique is used to simulate the free surface and the flow field affected by the groynes in the experimental flume and the natural river. A series of flume experiments are carried out. According to the orientation of groynes, angles from the flow direction to the axis of the groyne used in the experiments are assorted into obtuse angle, right angle, and acute angle as well. For each arrangement option, flow conditions are classified as the submerged and the non submerged one. Velocities and the water level affected by single groyne or double-groyne are measured. The calculated results are agreement well with the experimental data. Because of the high demands in the mesh quality and the computer capability, the VOF technique is seldom used to simulate the natural river. In this paper, the VOF technique is also used to simulate the Panjiatai Shoal of 2km long, one of the important improvement reaches in the Yellow River. Two improvement schemes are compared and analyzed, and the better one is recommended.