NUMERICAL SIMULATION OF BROWNIAN COAGULATION AND MIXING OF NANOPARTICLES IN 2D RAYLEIGH-B?NARD CONVECTION

采用泰勒展开矩方法对二维瑞利-贝纳德热对流系统(1×10⁶ ≤Ra ≤1 ×10⁸) 中纳米颗粒群的混合和凝并特性进行了数值模拟. 结果显示颗粒群随时间演化经历了扩散阶段、混合阶段、充分混合阶段3 个阶段, 随着颗粒群混合和凝并的进行, 颗粒数目浓度减少, 颗粒群的平均体积增大; 得到了颗粒分布函数各特征量与温度相关系数以及各特征量的空间分布标准偏差在3 个阶段的不同特征; 得到了颗粒分布函数各阶矩以及平均体积长时间演化的渐近行为, 结果与零维渐近解析解一致. 最后, 本文进一步研究了无量纲数(包括瑞利数Ra, 斯密特数Sc_M, 达姆科勒数Da) 对颗粒群达到自保持分布时间的影响, 发现该时间随着Ra和Sc_M的增大呈对数率减小, 随着Da的增大呈线性增大     

EXTENDED SELF SIMILARITY OF PASSIVE SCALAR IN RAYLEIGH-BNARD CONVECTION FLOW BASED ON WAVELET TRANSFORM

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EXTENDED SELF SIMILARITY OF PASSIVE SCALAR IN RAYLEIGH-BNARD CONVECTION FLOW BASED ON WAVELET TRANSFORM

Wavetet transform was used to analyze the scaling law of temperature data (passive scalar) in Rayleigh-Bénard convection flow from two aspects. The first one was to utilize the method of extended self similarity, presented first by Benzi et al., to study the scaling exponent of temperature data. The obtained results show that the inertial range is much wider than that one determined directly from the conventional structure function, and find the obtained scaling exponent agrees well with the one obtained from the temperature data in an experiment of wind tunnel. The second one was that, by extending the formula which was proposed by A. Arneodo et al. for extracting the scaling exponent ζ(q) of velocity data to temperature data, a newly defined formula which is also based on wavelet transform, and can determine the scaling exponent ξ(q) of temperature data was proposed. The obtained results demonstrate that by using the method which is named as WTMM (wavelet transform maximum modulus) ξ(q) correctly can be extracted.     

THE BNARD CONVECTION IN A LAYER OF FLUID WITH A TIME-DEPENDENT MEAN TEMPERATURE

The onset of Benard convection. or the critical Rayleigh number in a layer of fluid witha time-dependent mean temperature has been investigated theoretically. The criticalRayleigh number is regarded as a function of time and is expanded in series of a smallparameter. Up to second approximation a simple expression of critical Rayleigh number isobtained for the time region for away from the point of zero.     

THE BNARD CONVECTION IN A LAYER OF FLUID WITH A TIME-DEPENDENT MEAN TEMPERATURE

The onset of Bénard convection, or the critical Rayleigh number in a layer of fluid with a time-dependent mean temperature has been investigated theoretically. The critical Rayleigh number is regarded as a function of time and is expanded in series of a small parameter. Up to second approximation a simple expression of critical Rayleigh number is obtained for the time region for away from the point of zero.     

THE NUMERICAL SOLUTION OF THE UNSTEADY NATURAL CONVECTION FLOW IN A SQUARE CAVITY AT HIGH RAYLEIGH NUMBER USING SADI METHOD

The unsteady natural convection flow in a square cavity at high Rayleigh numberRa=10~7 and 2×10~7 has been computed using cubic spline integration.The requiredsolutions to the two dimensional Navier-Stokes and energy equations have been obtainedusing two alternate numerical formulations on non-uniform grids.The main features of thetransient flow have been briefly discussed.The results obtained by using the present methodare in good agreement.with the theoretical predictions.The steady state results havebeen compared with accurate solutions presented recently for Ra=10~7.     

ON THE APPLICATION OF ADI METHOD TO NUMERICAL SIMULATION OF THE MARANGONI CONVECTION CONTROLLING IN LIQUID BRIDGE MODEL

An ADI scheme is suggested to simulate the Marangoni convection controlling with emphasis on investigating application of the technique numerically. Numerical experiments conducted in the present paper turn out both successful and efficient. Hence, ADI scheme is expected to be extended to the study of other convection processes related to material manufacturing.     

EFFECTS OF TENSOR CLOSURE MODELS AND 3-D ORIENTATION ON THE STABILITY OF FIBER SUSPENSIONS IN A CHANNEL FLOW

IntroductionFlowoffibresuspensionshasbeenveryfamiliarinmanyindustrialfields.Fibreadditivesplayanimportantroleindragreductioninmanytypesofflow[1- 3].Inthesuspensions,somebehavioroftheflowmaybealteredbythefibres.Oneoftheimportantexamplesisthehydrodynamicsta…     

EXACT SOLUTION TO THE PROBLEM OF FLOW OF SLIGHTLY COMPRESSIBLE FLUIDS IN A BOUNDED CONFINED“PRACTURE-PORE”MEDIUM AND ITS APPLICATION TO WELL TESTING

The problem of flow of slightly Compressible fluids through abounded confined“fracture-pore”medium is solved and studiedthoroughly in this paper.Some essential natures of flow ofelastic liquids through a medium with double porosity underthe condition of neglecting the flow in matrix system were re-vealed and clarified further.The method of estimating all para-meters commonly interested in a bounded confined“fracture-pore”medium reservoir through a series of flow tests in wells by useof the solution obtained is presented.     

EXACT SOLUTION TO THE PROBLEM OF FLOW OF SLIGHTLY COMPRESSIBLE FLUIDS IN A BOUNDED CONFINED “PRACTURE-PORE” MEDIUM AND ITS APPLICATION TO WELL TESTING

The problem of flow of slightly compressible fluids through a bounded confined fracture-pore medium is solved and studied thoroughly in this paper. Some essential natures of flow of elastic liquids through a medium with double porosity under the condition of neglecting the flow in matrix system were revealed and clarified further. The method of estimating all parameters commonly interested in a bounded confined fracture-pore medium reservoir through a series of flow tests in wells by use of the solution obtained is presented.     

AN APPLICATION OF TOPOLOGICAL METHOD TO ANALYSING THE THREE-DIMENSIONAL FLOW IN CASCADES(Ⅱ)-TOPOLOGICAL ANALYSIS ON THE VECTOR FIELD PATTERNS OF SKINFRICTIONS AND SECTION STREAMLINES

With an application of topological analysis,in this paper the skin-friction line patternson compressor and turbine cascade surfaces are depicted and the streamline patterns of thesecondary flow fields in the cross-section of a curved pipe and a turbine cascade are drawnunder given conditions.In addition the structures of vortices within three-dimensionalviscous flow fields in cascades are analysed.     

NONLINEAR SATURATION OF BAROCLINIC INSTABILITY IN THE GENERALIZED PHILLIPS MODEL(Ⅱ)- THE LOWER BOUND ON THE DISTURBANCE ENERGY AND POTENTIAL ENSTROPHY TO THE NONLINEARLY UNSTABLE BASIC FLOW

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NONLINEAR SATURATION OF BAROCLINIC INSTABILITY IN THE GENERALIZED PHILLIPS MODEL(Ⅱ)-THE LOWER BOUND ON THE DISTURBANCE ENERGY AND POTENTIAL ENSTROPHY TO THE NONLINEARLY UNSTABLE BASIC FLOW

On the basis of the nonlinear stability theorem in the context of Arnol’d’s second theorem for the generalized Phillips model,nonlinear saturation of baroclinic instability in the generalized Phillips model is investigatedThe lower bound on the disturbance energy and potential enstrophy to the nonlinearly unstable basic flow in the generalized Phillips model is presented,which indicates that there may exist an allocation between a nonlinearly unstable basic flow and a growing disturbance