空泡流非稳态现象的流动控制

处于跨临界阶段的空泡流必然导致强烈的周期性冲击和振动,空泡流的激振来源于空泡云的周期性大规模脱落,空泡云的形成和发展与流动的边界层效应有着强烈的相关性,且空泡末端的局部流动直接影响空泡流的整体稳定性,本试验在NACA16012水翼表面粘附一条展向1mm厚10mm宽的挡流条,尝试以干扰水翼上表面局部流动的方法来影响整个空泡流的形态及其流动稳定性,最终在一定的空泡数范围内抑制了空泡流激振现象,并从试验研究的角度探索了空泡云脱落的机理。     

Flow Regimes of Interaction of a Turbulent Plane Jet into a Rectangular Cavity: Experimental Approach and Numerical Modelling

The present work is devoted to the experimental and numerical study ofthe interaction of a turbulent plane jet with a rectangular cavity.Several flow regimes have been found to occur: the non-oscillationregime, the stable oscillation regime and an unstable oscillationregime. The first two regimes have been particularly considered. Theexperimental study has been carried out using hot wire anemometry andsome visualisations. The numerical predictions based on statisticalmodelling have been made using on the one hand the standard k– model and on the other hand a two-scales split spectrum model. The structuralproperties of the flow have been described for the different situations.For the oscillatory regime, a parametrical study allowed to determinethe influence of the jet exit location and the Reynolds number on thefrequency of the jet flapping. The one point closures have been able topredict the oscillatory regime, and in particular the two-scales modelled to improved results because better account is taken of lag effectsin unsteady non-equilibrium situations.     

Formation and stability of a charged jet in a strong electric field

The shape of a charged jet is determined in the approximation of a strong electric field. The stability of the jet with respect to both axisymmetric and nonaxisymmetric perturbations of the sinusoidal type is investigated in the linear approximation. The domains of predominance of the axisymmetric and bending modes and the longitudinal partition mode are determined. Experimental data on the longitudinal partition of a polymeric jet into several daughter jets are given.     

Transient behavior of an axisymmetric turbulent jet

The prediction of the response of unsteady flows submitted to external excitation is a real challenge for the optimization of industrial processes. As the jet flow is a very basic turbulent flow related to mixing and entrainment phenomena via turbulent structure dynamic, we investigate the transient behavior of an axisymmetric jet submitted to a large and sudden decrease of its ejection velocity. The non stationary flow evolution is studied experimentally. Measurements along the jet axis based on pure ensemble averaging show clearly the convective motion of the perturbation and the adaptation of the local interaction to the local jet time scale. A transverse investigation in the non stationary region show that the mean flow and its turbulence is deeply affected during the local velocity decrease.     

激励小尺度模式在湍流圆管射流中的应用

采用非涡黏性的激励小尺度（Stimulated Small Scale)模式对空间发展的轴对称湍流圆管射流进行了大涡模拟。以雷诺数为10000的流动为例,考证了激励小尺度模式在自由剪切流模拟中的可行性,描述了湍流强度、雷诺应力和湍流耗散量的变化,同时与标准的Smagorinsky涡黏性模式的计算结果进行了比较。数值结果显示,激励小尺度模式能够更为合理地描述湍流的耗散特性和能量传输特性,从而较为准确地展示出空间发展射流中由于流动不稳定而出现的旋涡产生、发展、破碎及合并等过程。     

Modeling of dynamics, heat transfer, and combustion in two-phase turbulent flows: 2. Flows with heat transfer and combustion

The objective of this part of the paper is to summarize the information concerning the authors' works in the field of simulation of two-phase gas-particle turbulent flows with heat transfer and combustion. A kinetic equation had been derived for the probability density function (PDF) of the particle velocity, temperature, and mass distributions in turbulent flows. This PDF equation is used for the construction of the governing conservation equations of mass, momentum, and heat transfer in the dispersed particle phase.The numerical scheme incorporates two-phase fluid dynamics, convective and radiative heat transfer, and combustion. The proposed models have been applied to the calculation of various particle-laden turbulent flows in jets, combustion and gasification chambers, and furnaces.     

Modelling of the pressure-velocity correlation in turbulence diffusion

Most current computations of trubulent flows with second-moment closure adopt the diffusion models which neglect the effect of pressure-velocity correlation. In the present paper the importance of this correlation effect is elucidated the neglect of this effect accounts for some major defects in the wide application of the second-moment closures. Through the relation between and , established by Lumley, we propose here a new turbulence diffusion model which takes into consideration the pressure effect. Applications of this new model in the computation of shearless turbulence mixing layer and plane and round-jet flows show that the spreading rate of these flows can be satisfactorily captured.     

Prediction of the performance of air-lift pumps

Equations are developed for predicting the performance of air-lift pumps. The form of the equations allows simple expressions to be obtained for conditions at the ‘maximum flow rate condition’