描述两相湍流的二阶动量模型

Zhou L X
Sci China Phys Mech Astron
June (2011) Vol. 54 No. 6
1099
this theory the only motive force of particle fluctuation is particle following the local gas fluctuation; particle fluctuation should be always weaker than gas fluctuation and it should decrease with the increase of particle size. In the framework of two-fluid models, this algebraic model of particle fluctuation was used by many investigators, Rizk et al. [6] for example, by combining the gas k- turbulence model with algebraic particle fluctuation models like Hinze-Tchen’s model (we call it a k--Ap model). In fact, similar approaches have been taken by Melville and Bray [7], Chen and Wood [8], Mostafa and Mongia [9]. However, our experiments and the experiments done by other investigators show that in many cases the particle fluctuation is stronger than the gas fluctuation and larger particles diffuse faster than smaller particles. Hence the concept of “particle turbulence” was proposed, by which the particle fluctuation has the nature of gas turbulence, and it obeys its own conservation law, i.e. it has its own convection, diffusion, shear production and dissipation to gas turbulence and is determined not only by local gas turbulence. Based on this consideration a transport equation of particle turbulent kinetic energy (kp equation) is derived and closed by the present author and afterwards a k--kp two-phase turbulence model was proposed. The superiority of the k--kp model over the k--Ap model (Ap denotes the Hinze-Tchen’s algebraic model) is just like that of the k-equation model over the mixing length model for single-phase flows. Subsequently, it is found that most of two-phase turbulence is anisotropic and the anisotropy of particle turbulence is much stronger than that of the gas. Hence a two-phase Reynolds stress equation model was proposed and then improved to become a unified second-order moment (USM) two-phase turbulence model with a more elaborated closure model of the two-phase velocity correlation. The k--kp model is found to be a reduced form of the USM model. Simultaneously, the k- and Reynolds stress equation models of gas turbulence were combined with a PDF transport equation model of particle turbulence to form k--PDF and DSM-PDF models. In order to simplify the USM model and retain its anisotropic features, a non-linear k--kp model was proposed. All of these models were applied to simulate gas-particle jets, sudden-expansion and swirling gas-particle flows. Subsequently, a second-order moment bubble-liquid two-phase turbulence model was proposed. In the following text a detailed description of derivation and closure of these models and their validation and application will be stated.
ZHOU LiXing
Department of Engineering Mechanics, Tsinghua University, Beijing 10008mber 23, 2010; accepted March 10, 2011; published online March 30, 2011
Turbulent dispersed multiphase flows, including gas-particle, gas-droplet and bubble-liquid flows, are widely encountered in various engineering facilities. Modeling of two-phase turbulence, in particular the dispersed phase turbulence, is the key problem in the Eulerian-Eulerian simulation of practical dispersed multiphase flows. Although different models were developed and used, the experimental validation shows that they cannot always give satisfactory prediction results. In this paper the present author give a detailed review of the unified second-order moment (USM), k--kp and nonlinear k--kp two-phase turbulence models, proposed by him. The derivation and closure of these models are described in detail and the experimental validation and application of these models are extensively discussed. dispersed multiphase flows, second-order moment model, two-phase turbulence PACS: 47.27.E-, 47.27.ep, 47.55.Ca, 47.55.Kf
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Introduction
Turbulent dispersed multiphase reacting flows, such as turbulent gas-solid (particle), gas-droplet and bubble-liquid flows, are widely encountered in various engineering facilities, such as boiler and industrial furnaces, internal combustion engines, gas turbine combustors, ram-jet and rocket engine combustors, and chemical and nuclear reactors. The turbulence of gas itself is already a complex phenomenon. Turbulent multiphase reacting flows with dispersed phase (particles, droplets, bubbles) and continuous phase (gas, liquid) and homogeneous or heterogeneous chemical reactions are much more complex. Although in recent years there are remarkable strides in the basic studies on physics of turbulence, such as the results using the direct numerical simulation, theory of coherent structures, theory of chaos and detailed PIV measurements, these results cannot directly solve practical engineering problems. It is well known that about 60 years ago Chou [1] first proposed the