LATTICE BOLTZMANN SCHEME TO SIMULATE TWO-DIMENSIONAL FLUID TRANSIENTS

This paper proposes a lattice Boltzmann scheme to simulate two-dimensionalfluid transients. A set of multi-scale equations, which characterize the relations between thelattice Boltzmann equation and its corresponding macroscopic equations, were derived by using theChapman-Enskog expansion. Based on these multi-scale equations and the basic equations ofmultidimensional fluid transients, two special lattice Boltzmann models were established. Numericalsimulation of one-dimensional pressure wave transmission and reflection, two-dimensional wave cornerdiffraction and hydraulic transients in a concrete spiral case show that the Lattice BoltzmannMethod (LBM) is a feasible and promising approach to simulate multidimensional transient flows.

Transient fluid flow in the Binbei district of the Songliao Basin, China Evidence from apatite fission track thermochronology

The Songliao Basin is famous for the Daqing Oilfield, the biggest in China. However, no economic hydrocarbon reservoir has been found in the northeastern Binbei district. Its thermal history, which is of great importance for hydrocarbon generation and migration, is studied with apatite fission track （AFT） thermochronology. Samples with depositional ages of the late Cretaceous （-108-73 Ma） are analyzed. The AFT ages of the samples from reservoir rock （depositional age 〉 76.1 Ma） fall between the late Cretaceous （724-5 Ma） and the early Eocene （414-3 Ma） period, indicating their total annealing after deposition. In contrast, two samples from the main seals of the Qingshankou （depositional age 〉 89.3 Ma） and the Nenjiang Formation （depositional age 〉 73.0 Ma） are not annealed or partially annealed （AFT ages of 974-9 Ma and 704-4 Ma, respectively）. Because the maximum burial temperature （〈90 ℃） evidenced by low vitrinite reflectance （Ro〈0.7） is not high enough to account for the AFT total annealing （110-120 ℃）, the transient thermal effect arising from the syntectonic fluid flow between the late Cretaceous and the early Eocene is proposed. Transient thermal effects from fluid flow explains the indicated temperature discrepancies between the AFT thermometer and the Ro thermometer because the transient thermal effect from the fluid flow with a temperature high enough （110-120 ℃） to anneal the AFT thermometer does not last long enough （104-105 yrs.） for an enhancement of the Ro （minimum 106- 107 yrs. under the same temperature）. This indicates that dating thermal effect from fluid flow might be a new means to reconstruct the tectonic history. It also answers why the samples from the main seals are not annealed because the seals will prohibit fluid flow and supply good thermal insulation. The large-scale fluid flow in the Binbei district calls for a new idea to direct the hydrocarbon exploration.

CHAOTIC TRANSIENTS IN A CURVED FLUID CONVEYING TUBE

The chaotic transients of a curved fluid conveying tube subjected to a nonlinear foundation are investigated. The assumption of the inextensibility of the tube is applied to derive the nonlinear differential equation of motion via the Newtonian approach, with the differential quadrature method used to discretize the curved tube model in the spatial domain. And the nonlinear dynamic motion equation is obtained. The numerical analysis shows that, the final steady states are sensitive to the initial system conditions in a large parameter region of the fluid speed. This phenomenon of chaotic transients is infrequent for fluid conveying tubes.

Application of Computational Fluid Dynamics and Fluid Structure Interaction Techniques for Calculating the 3D Transient Flow of Journal Bearings Coupled with Rotor Systems

Journal bearings are important parts to keep the high dynamic performance of rotor machinery. Some methods have already been proposed to analysis the flow field of journal bearings, and in most of these methods simplified physical model and classic Reynolds equation are always applied. While the application of the general computational fluid dynamics （CFD）-fluid structure interaction （FSI） techniques is more beneficial for analysis of the fluid field in a journal bearing when more detailed solutions are needed. This paper deals with the quasi-coupling calculation of transient fluid dynamics of oil film in journal bearings and rotor dynamics with CFD-FSI techniques. The fluid dynamics of oil film is calculated by applying the so-called ＂dynamic mesh＂ technique. A new mesh movement approacb is presented while the dynamic mesh models provided by FLUENT are not suitable for the transient oil flow in journal bearings. The proposed mesh movement approach is based on the structured mesh. When the joumal moves, the movement distance of every grid in the flow field of bearing can be calculated, and then the update of the volume mesh can be handled automatically by user defined function （UDF）. The journal displacement at each time step is obtained by solving the moving equations of the rotor-bearing system under the known oil film force condition. A case study is carried out to calculate the locus of the journal center and pressure distribution of the journal in order to prove the feasibility of this method. The calculating results indicate that the proposed method can predict the transient flow field of a journal bearing in a rotor-bearing system where more realistic models are involved. The presented calculation method provides a basis for studying the nonlinear dynamic behavior of a general rotor-bearing system.

Transient growth in Poiseuille-Rayleigh-Bénard flows of binary fluids with Soret effect

The transient growth due to non-normMity is investigated for the Poiseuille- Rayleigh-Benard problem of binary fluids with the Soret effect. For negative separation factors such as ψ = -0.1, it is found that a large transient growth can be obtained by the non-normal interaction of the two least-stable-modes, i.e., the upstream and downstream modes, which determine the linear critical boundary curves for small Reynolds numbers. The transient growth is so strong that the optimal energy amplification factor G（t） is up to 10^2 - 10^3. While for positive separation factors such as ψ = 0.1, the transient growth is weak with the order O（I） of the amplification factor, which can even be computed by the least-stable-mode. However, for both cases, the least-stable-mode can govern the long-term behavior of the amplification factor for large time. The results also show that large Reynolds numbers have stabilization effects for the maximum amplification within moderate wave number regions. Meanwhile, much small negative or large positive separation factors and large Rayleigh numbers can enlarge the maximum transient growth of the pure streamwise disturbance with the wavenumber α= 3.14. Moreover, the initial and evolutionary two-dimensional spatial patterns of the large transient growth for the pure streamwise disturbance are exhibited with a plot of the velocity vector, spanwise vorticity, temperature, and concentration field. The initial three-layer cell vorticity struc- ture is revealed. When the amplification factor reaches the maximum Gmax, it develops into one cell structure with large amplification for the vorticity strength.

THE THEORY OF CURRENT TRANSIENTS AT TUBULAR ELECTRODES IN A FLOWING FLUID

A theoretical equation is developed which describes the response of the current transients to a constant potential at tubular electrodes for a reversible electrode reaction in the flowing fluid.

THE TRANSIENT ELLIPTIC FLOW OF POWER-LAW FLUID IN FRACTAL POROUS MEDIA

The steady oil production and pressure distribution formulae of vertically fractured well for power-law non-Newtonian fluid were derived on the basis of the elliptic flow model in fractal reservoirs. The corresponding transient flow in fractal reservoirs was studied by numerical differentiation method: the influence of fractal index to transient pressure of vertically fractured well was analyzed. Finally the approximate analytical solution of transient flow was given by average mass conservation law. The study shows that using elliptic flow method to analyze the flow of vertically fractured well is a simple method.

STEADY-SHEAR VISCOSITY AND TRANSIENT STRESS RESPONSE FOR ELASTO-THIXOTROPIC FLUIDS

A phenomenological model for dispersed systems which exhibit complex theological behaviour such as shear and time-dependent viscosity, yield stress, and elasticity is proposed. The model extends the Quemeda model to describe the viscosity function with a structural parameter λ which varies according to differ- ent kinetic orders of particle aggregation and segregation. The transient stress response is obtained by solving an instantaneous Maxwell model with an assumed shear modulus function G of the same form as the viscosity function η. Accuracy of the proposed model is verified experimentally with the results obtained for two oil (creosote)/water emulsions. The model that gives the best fit of experimental data appears to be the one with kinetic orders n = m = 2.

THE VERIFICATION OF THE CURRENT TRANSIENT EQUATION AT TUBULAR ELECTRODES IN A FLOWING FLUID UNDER POTENTIAL STEP

The equation derived for the response of the current transients in the flowing fluid is verified experimentally.

二次水断供核主泵屏蔽电机冷却水瞬态热分析

核主泵屏蔽电机在热态极端环境参数额定(简称热态额定)工况下,二次水突然断供(secondary water supply outage,SWSO)300 s时刻,一次下导轴承润滑水温不超过警报温度95℃是产品出厂的重要指标,研究该情况下热流场计算方法及各种参数随时间演变特性对于电机热安全非常重要。首先,以北方工厂冷态环境参数下额定(简称冷态额定)工况该电机SWSO前后稳/瞬态厂内测量入出口试验数据为边界条件,采用有限体积法,进行流场和温度场的流固耦合数值模拟,模拟值与试验值300 s时的误差为5.97%,验证了计算方法准确性。然后,数值反演热态额定工况SWSO一/二次冷却水的温度场随时间变化规律。结果表明:SWSO 300 s内,二次水流速及对流传热系数随时间变化存在特征明显不同的2个阶段,二次水与螺旋槽壁面间对流换热系数h由稳态时7808.06 W/(m^(2)⋅K),13 s内减少到480.07 W/(m^(2)⋅K),随后h变化很小;热态额定参数时,下导轴承润滑水温远低于报警值95℃。为核主泵屏蔽电机轴承润滑水热安全计算提供参考。

超临界碳氢燃料流动不稳定的频域分析与数值模拟

再生冷却通道中的流动失稳是高超声速飞行器发动机热防护技术中的核心问题之一。为研究超临界碳氢燃料在冷却通道中的流动不稳定特性,基于有限体积法及流体物性近似,发展了高效的一维瞬态模拟方法;同时,基于小扰动假设,进一步提出了用于预测稳定行为的频域分析方法。通过相关实验,验证了模型的可靠性。基于时域和频域方法的综合分析,沿内特征曲线讨论了主要失稳类型,重点分析了受密度波及Ledinegg不稳定共同影响的复合不稳定性。随后,进一步分析了工作压力和入口温度对稳定特性的耦合影响,并基于N_(tpc)-N_(spc)空间划分了稳定区域。研究发现,复合不稳定、Ledinegg不稳定以及密度波不稳定,随入口温度升高而相继消失。Ledinegg不稳定及密度波不稳定的稳定边界在N_(tpc)-N_(spc)空间具有高度相似性,而复合不稳定性的区域在较高的压力下略有缩小。

高速开关阀瞬态流场仿真特性研究

高速开关阀工作时,内部流体由于阀杆的运动形成了复杂的流动状态。而在实际情况中,很难观察到阀体内部流道中阀芯运动时的流体瞬态变化。基于此,采用计算流体力学动网格方法分析了高速开关阀3种工况下的状态,得到了流场的压力、速度、出口质量流率等数据。结果表明:出口的质量流率随着阀口的开闭呈线性变化;流体压力、速度在阀座到出口的通道中间变化最大;出口区域与开关阀角落区域在大流速差下易形成漩涡现象,并且流体的漩涡现象会随着流体的速度差变化,而顶部的动铁周围压力、流速变化不大。该结果可为设计高速开关阀时获取对应的最大通过流量及优化开关阀结构提供技术参考。

Attenuation analysis of hydraulic transients with laminar-turbulent flow alternations

An improved compound mathematical model is established to simulate the attenuation of hydraulic transients with laminar-turbulent alternations,which usually occur when the pipeline flow velocity fluctuates near the critical velocity.The laminar friction resistance and the turbulent friction resistance are considered respectively in this model by applying different resistance schemes to the characteristics method of fluid transient analysis.The hydraulic transients of the valve closing process are simulated using the model.A more reasonable attenuation of hydraulic transients is obtained.The accurate attenuation is more distinct than that obtained from the traditional mathematical model.The research shows that the hydraulic transient is a type of energy waves,and its attenuation is caused by the friction resistance.The laminar friction resistance is more important than the turbulent friction resistance if the flow velocity is smaller than the critical velocity.Otherwise the turbulent friction resistance is more important.The laminar friction resistance is important in the attenuation of hydraulic transients for the closing process.Thus,it is significant to consider the different resistances separately to obtain more accurate attenuation of hydraulic transients.

基于Fluent的加气混凝土搅拌机数值模拟分析

以加气混凝土搅拌机为原型,利用流体仿真软件Fluent,采用欧拉多相流模型、Realizable k-ε湍流模型和滑移网格法相结合的方法,对搅拌机内3种不同类型的搅拌器分别进行瞬态计算,模拟研究搅拌机内3种不同类型搅拌器的流体流动特性和物料浓度变化,分析转速对搅拌效果的影响。通过仿真结果比对可知,四斜叶开启涡轮-螺杆式搅拌器的搅拌效果最优,可为加气混凝土搅拌机的设计提供参考。

长输供热管线中AFT Impulse软件的水力瞬态分析与应用

结合同类煤电机组余热利用长距离大温差供热项目经验,从基本原理开始阐述,介绍了AFT Impulse软件在工程实例中的应用,逐步说明有压管道水力瞬态分析,并结合工程案例,分析出非恒定流体向恒定流体变化过程中产生的水击波对供热系统的危害,结合数学模型分析提出的心得及建议,以便将水力瞬态分析的成果在供热系统中更好地推广和应用,有效地指导设计与工程建设。

Analysis on reactivity initiated transient from control rod failure events of a molten salt reactor

In a molten salt reactor(MSR), the fuel is dissolved in fluoride salt. In this paper, the reactivity worth and reactivity initiated transient of Molten-Salt Reactor Experiment(MSRE) in the control rod failure events are analyzed. The point kinetic coupling heat-transfer model with decay character of six-group delayed neutron precursors due to the fuel motion is applied. The relative power and temperature transient under reactivity step and ramp initiated at different power levels are studied. The results show that the reactor power and temperature increase to a maximum, where they begin to decrease to stable values. Comparing with full power level, the transient result at low power level is more serious. The results are of help in our study on safety characteristics of an MSR system.

Transient Hydroelastic Response of VLFS by FEM with Impedance Boundary Conditions in Time Domain

A time-dependent finite element method (FEM) is developed to analyze the transient hydroelastic responses of very large floating structures (VLFS) subjected to dynamic loads. The hydrodynamic problem is formulated based on the linear theory of fluid and the structural response is analyzed based on the thin plate theory. The FEM truncates the unbounded fluid domain by introducing an artificial boundary surface, thus defining a finite computational domain. At this boundary surface an impedance boundary conditions are applied so that no wave reflections occur. In the proposed scheme, all of the procedures are processed directly in time domain, which is efficient for nonlinear analyses of structure floating on unbounded fluid. Numerical results indicate acceptable accuracy of the proposed method.

Flux vector splitting solutions for coupling hydraulic transient of gas-liquid-solid three-phase flow in pipelines

The gas-liquid-solid three-phase mixed flow is the most general in multiphase mixed transportation. It is significant to exactly solve the coupling hydraulic transient problems of this type of multiphase mixed flow in pipelines. Presently, the method of characteristics is widely used to solve classical hydraulic transient problems. However, when it is used to solve coupling hydraulic transient problems, excessive interpolation errors may be introduced into the results due to unavoidable multiwave interpolated calculations. To deal with the problem, a finite difference scheme based on the Steger- Warming flux vector splitting is proposed. A flux vector splitting scheme is established for the coupling hydraulic transient model of gas-liquid-solid three-phase mixed flow in the pipelines. The flux subvectors are then discretized by the Lax-Wendroff central difference scheme and the Warming-Beam upwind difference scheme with second-order precision in both time and space. Under the Rankine-Hugoniot conditions and the corresponding boundary conditions, an effective solution to those points located at the boundaries is developed, which can avoid the problem beyond the calculation region directly induced by the second-order discrete technique. Numerical and experimental verifications indicate that the proposed scheme has several desirable advantages including high calculation precision, excellent shock wave capture capability without false numerical oscillation, low sensitivity to the Courant number, and good stability.

Conduction-radiation effect on transient natural convection with thermophoresis

This paper discusses the effect of thermophoretic particle deposition on the transient natural convection laminar flow along a vertical fiat surface, which is immersed in an optically dense gray fluid in the presence of thermal radiation. In the analysis, the radiative heat flux term is expressed by adopting the Rosseland diffusion approximation. The governing equations are reduced to a set of parabolic partial differential equations. Then, these equations are solved numerically with a finite-difference scheme in the entire time regime. The asymptotic solutions are also obtained for sufficiently small and large time. The obtained asymptotic solutions are then compared with the numerical solutions, and they are found in excellent agreement. Moreover, the effects of different physical pa- rameters, i.e., the thermal radiation parameter, the surface temperature parameter, and the thermophoretic parameter, on the transient surface shear stress, the rate of surface heat transfer, and the rate of species concentration, as well as the transient velocity, temperature, and concentration profiles are shown graphically for a fluid （i.e., air） with the Prandtl number of 0.7 at 20℃ and 1.013 × 10^5 Pa.

基于CFD方法的轮毂电驱动行星齿轮搅油功率损失仿真与分析

轮毂电驱动技术的研究是未来新能源驱动体系研究的重要方向。随着轮毂电驱动对转速的要求越来越高,搅油功率损失成为不可忽略的部分,甚至高达功率总损失的50%~80%。现有的计算搅油损失的方法主要是采用简单的经验公式,无法适用于复杂的行星齿轮传动。为此,采用计算流体力学(Computational Fluid Dynamics,CFD)软件与C语言用户自定义函数(User Defined Function,UDF)对两级行星齿轮传动飞溅润滑进行联合仿真,实现了油-气两相瞬态流场可视化;通过提取表面的压力和黏性力,得到了太阳轮、行星轮及行星架的搅油损失;对25种工况进行仿真与分析,得到了搅油功率损失随转速和浸油深度的变化趋势。结果表明,搅油功率损失随转速和浸油深度的增加而增大,且无明显的拐点,实现最小搅油损失应当在保证充分润滑的前提下取最小的浸油深度。