共查询到20条相似文献,搜索用时 15 毫秒
1.
Transport in Porous Media - Given the analogy between the filtered equations of large eddy simulation and volume-averaged Navier–Stokes equations in porous media, a subgrid-scale model is... 相似文献
2.
气固两相流场的湍流颗粒浓度理论模型 总被引:8,自引:0,他引:8
本文进行了气固两相流动颗粒湍流扩散现象的理论分析,提出了颗粒湍流扩散系数和气流弥散效应二个颗粒湍流模化新概念,在此基础上建立了气固两相流场湍流颗粒浓度模型。理论模型包括离心力和其它外加力场作用下颗粒运动和浓度分布的计算方法。运用湍流颗粒浓度模型,对直管气固两相流动、受限射流气固两相流动和90°弯管气固两相流动等三种流动做了数值模拟,计算获得颗粒速度、颗粒浓度等主要流动参数。讨论了湍流颗粒浓度模型的适用性。 相似文献
3.
EMMANUELLE DECLERCQ ALAIN FORESTIER JEAN-MARC HÉRARD XAVIER LOUIS GÉRARD POISSANT 《International Journal of Computational Fluid Dynamics》2013,27(2):117-131
The main objective of this paper is to provide some adequate way to compute the non-conservative hyperbolic system which describes a multicomponent turbulent flow. The model is written for an isentropic gas. The exact solution of the Riemann Problem (RP) associated to the hyperbolic system is exhibited. It is composed of constant states separated by rarefaction waves, or shock waves and a contact discontinuity. The selection of the admissible part of the shock curve is obtained using an entropy criterion. This entropy is the total energy of the system. Thanks to the latter, one may compute the exact solution of the Riemann problem, assuming genuinely non linear fields contain sufficiently weak shocks. 相似文献
4.
5.
A Hybrid RANS/LES Simulation of Turbulent Channel Flow 总被引:1,自引:0,他引:1
Fujihiro Hamba 《Theoretical and Computational Fluid Dynamics》2003,16(5):387-403
Hybrid models combining large eddy simulation (LES) with Reynolds-averaged Navier–Stokes (RANS) simulation are expected to
be useful for wall modeling in the LES of high Reynolds number flows. Some hybrid simulations of turbulent channel flow have
a common defect; the mean velocity profile has a mismatch between the RANS and LES regions due to a steep velocity gradient
at the interface. This mismatch is reproduced and examined using a simple hybrid model; the Smagorinsky model is switched
to a RANS model increasing the filter width. It is suggested that a rapid spatial variation in the eddy viscosity is responsible
for an underestimate of the grid-scale shear stress and for the steep velocity gradient. To reduce the mean velocity mismatch
a new scheme is proposed; additional filtering is introduced to define two kinds of velocity components at the interface between
the two regions. The two components are used to remove inconsistency in the velocity equations due to a rapid variation in
the filter width. Using the new scheme, simulations of channel flow are carried out with the simple hybrid model. It is shown
that the grid-scale shear stress becomes large enough and most of the mean velocity mismatch is removed. Simulations for higher
Reynolds numbers are carried out with the k–ε model and the one-equation subgrid-scale model. Although it is necessary to improve the turbulence models and the treatment
of the buffer region, the new scheme is shown to be effective for reducing the mismatch and to be useful for developing better
hybrid simulations.
Received 5 April 2002 and accepted 8 January 2003 Published online 25 March 2003
Communicated by M.Y. Hussaini 相似文献
6.
The anisotropy analysis of Lumley provides a useful tool to quantify the degree of anisotropy in turbulent flows. Also included
in the analysis are relations which may be used to check if the flow is axisymmetric or two-dimensional. However, the method
does not provide any scale information about the structures. The analysis has therefore been extended here to Fourier space,
which allows scale information to be derived. The method was applied to fully developed pipe flow and it was shown that the
large-scale motion is everywhere close to axisymmetric. The intermediate scales are strongly influenced by the restrictions
posed by the pipe walls. At the centre line, the flow structure appears axisymmetric at all scales, but the measurement sindicate
that true axisymmetry is lost very quickly away from the centre line. The structure of the smallest scales could not be determined
reliably due to a singularity in the analysis which develops as the scales go to zero.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
Particle Collision Rate in Turbulent Flow 总被引:6,自引:0,他引:6
An analytical model for determining the particle collision rate in a turbulent flow with account for the effects of shear and the gravity force is presented. The model is tested by comparison with the results of direct numerical calculations performed for isotropic turbulence, the near-axis zone of a plane channel, a flow with uniform shear, and a binary mixture of particles with different densities. 相似文献
8.
A kinetic statistical model for describing the dispersion and clustering of heavy particles in homogeneous isotropic turbulence is presented. The model developed is used for calculating the relative velocities and the radial distribution function of a pair of particles in a steady suspension. The results obtained are compared with the known data obtained by direct numerical simulation. 相似文献
9.
Jacek Pozorski Sergei Sazhin Marta Wacławczyk Cyril Crua David Kennaird Morgan Heikal 《Flow, Turbulence and Combustion》2002,68(2):153-165
Analytical expressions for mass concentration of liquid fuel in a spray are derived taking into account the effects of gas
turbulence, and assuming that the influence of droplets on gas is small (intitial stage of spray development). Beyond a certain
distance the spray is expected to be fully dispersed. This distance is identified with the maximum spray penetration. Then
the influence of turbulence on the spray stopping distance is discussed and the rms spray penetration is computed from a trajectory
(Lagrangian) approach. Finally, the problem of spray penetration is investigated in a homogeneous two-phase flow regime taking
into account the dispersion of spray away from its axis. It is predicted that for realistic values of spray parameters the
spray penetration at large distances from the nozzle is expected to be proportional to t
2/3 (in the case when this dispersion is not taken into account this distance is proportional to t
1/2). The t
2/3 law is supported by experimental observations for a high pressure injector.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
Eric Lamballais Olivier Métais Marcel Lesieur 《Theoretical and Computational Fluid Dynamics》1998,12(3):149-177
A new subgrid-scale model called the spectral-dynamic model is proposed. It consists of a refinement of spectral eddy-viscosity models taking into account nondeveloped turbulence in
the subgrid-scales. The proposed correction, which is derived from eddy-damped quasi-normal Markovian statistical theory,
is based on an adjustment of the turbulent eddy-viscosity coefficient to the deviation of the spectral slope (at small scales)
with respect to the standard Kolmogorov law. The spectral-dynamic model is applied to large eddy simulation (LES) of rotating
and nonrotating turbulent plane channel flows. It is shown that the proposed refinement allows for clear improvement of the
statistical predictions due to a correct prediction of the near-wall behavior. Cases of rotating and nonrotating low (DNS)
and high Reynolds (LES) numbers are then compared. It is shown that the principal structural features of the rotating turbulent
channel flow are reproduced by the LES, such as the presence of the near-zero mean absolute vorticity region, the modification
of the anisotropic character of the flow (with respect to the nonrotating case), the enhancement of flow organization, and
the inhibition of the high- and low-speed streaks near the anticyclonic wall. Only a moderate Reynolds number dependence is
exhibited, resulting in a more unstable character of the longitudinal large-scale roll cells at high Reynolds number, and
a slight increase of the laminarization tendency on the cyclonic side of the channel.
Received 16 October 1997 and accepted 1 October 1998 相似文献
11.
离心风机子午通道内湍流场数值模拟 总被引:6,自引:0,他引:6
由进风口-叶轮-无叶扩压器-蜗壳等部件组成的离心风机通道内流分析是非常复杂的,目前还只能是分别计算各部件内的流场,但必须考虑部件间的相互影响。本文采用轴对称N-S方程,根据三维叶轮通道计算给出的叶片力分布,求解了考虑叶片力的进风口-叶轮-无叶扩压器组成的子午通道问题,所得结果可用来给出三维叶轮通道计算的进口条件,并可用于优化设计进风口及叶轮前、后盘形状。该方法已得到实践检验。 相似文献
12.
Flow structure of premixed propane–air swirling jet flames at various combustion regimes was studied experimentally by stereo
PIV, CH* chemiluminescence imaging, and pressure probe. For the non-swirling conditions, a nonlinear feedback mechanism of
the flame front interaction with ring-like vortices, developing in the jet shear layer, was found to play important role in
the stabilisation of the premixed lifted flame. For the studied swirl rates (S = 0.41, 0.7, and 1.0) the determined domain of stable combustion can be divided into three main groups of flame types: attached
flames, quasi-tubular flames, and lifted flames. These regimes were studied in details for the case of S = 1.0, and the difference in the flow structure of the vortex breakdown is described. For the quasi-tubular flames an increase
of flow precessing above the recirculation zone was observed when increased the stoichiometric coefficient from 0.7 to 1.4.
This precessing motion was supposed to be responsible for the observed increase of acoustic noise generation and could drive
the transition from the quasi-tubular to the lifted flame regime. 相似文献
13.
Simulation and Modelling of Turbulent Trailing-Edge Flow 总被引:1,自引:0,他引:1
Computations of turbulent trailing-edge flow have been carried out at a Reynolds number of 1000 (based on the free-stream
quantities and the trailing-edge thickness) using an unsteady 3D Reynolds-Averaged Navier–Stokes (URANS) code, in which two-equation
(k–ε) turbulence models with various low-Re near wall treatments were implemented. Results from a direct numerical simulation
(DNS) of the same flow are available for comparison and assessment of the turbulence models used in the URANS code. Two-dimensional
URANS calculations are carried out with turbulence mean properties from the DNS used at the inlet; the inflow boundary-layer
thickness is 6.42 times the trailing-edge thickness, close to typical turbine blade flow applications. Many of the key flow
features observed in DNS are also predicted by the modelling; the flow oscillates in a similar way to that found in bluff-body
flow with a von Kármán vortex street produced downstream. The recirculation bubble predicted by unsteady RANS has a similar
shape to DNS, but with a length only half that of the DNS. It is found that the unsteadiness plays an important role in the
near wake, comparable to the modelled turbulence, but that far downstream the modelled turbulence dominates. A spectral analysis
applied to the force coefficient in the wall normal direction shows that a Strouhal number based on the trailing-edge thickness
is 0.23, approximately twice that observed in DNS. To assess the modelling approximations, an a priori analysis has been applied using DNS data for the key individual terms in the turbulence model equations. A possible refinement
to account for pressure transport is discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
15.
Large-eddy simulation (LES) has been applied to calculate the turbulent flow over staggered wall-mounted cubes and staggered random arrays of obstacles with area density 25%, at Reynolds numbers between 5 × 103 and 5 106, based on the free stream velocity and the obstacle height. Re = 5 × 103 data were intensively validated against direct numerical simulation (DNS) results at the same Re and experimental data obtained in a boundary layer developing over an identical roughness and at a rather higher Re. The results collectively confirm that Reynolds number dependency is very weak, principally because the surface drag is predominantly form drag and the turbulence production process is at scales comparable to the roughness element sizes. LES is thus able to simulate turbulent flow over the urban-like obstacles at high Re with grids that would be far too coarse for adequate computation of corresponding smooth-wall flows. Comparison between LES and steady Reynolds-averaged Navier-Stokes (RANS) results are included, emphasising that the latter are inadequate, especially within the canopy region. 相似文献
16.
We detail a new method of generating kinematic simulation fields in a channel. We employ a new decomposition for kinematic
simulation which ensures that the boundary conditions are automatically satisfied while preserving incompressibility. We impose
statistics up to second order, including the Reynolds shear-stress and one-dimensional spectral densities. We observe streak-like
structures kinematically similar to those observed in the laboratory, with a similar scaling with the wall-normal distance.
We explain the appearance and scaling of the streak-like structures in terms of the two-dimensional spectra imposed on the
fields. 相似文献
17.
High-Velocity Laminar and Turbulent Flow in Porous Media 总被引:1,自引:0,他引:1
We model high-velocity flow in porous media with the multiple scale homogenization technique and basic fluid mechanics. Momentum and mechanical energy theorems are derived. In idealized porous media inviscid irrotational flow in the pores and wall boundary layers give a pressure loss with a power of 3/2 in average velocity. This model has support from flow in simple model media. In complex media the flow separates from the solid surface. Pressure loss effects of flow separation, wall and free shear layers, pressure drag, flow tube velocity and developing flow are discussed by using phenomenological arguments. We propose that the square pressure loss in the laminar Forchheimer equation is caused by development of strong localized dissipation zones around flow separation, that is, in the viscous boundary layer in triple decks. For turbulent flow, the resulting pressure loss due to average dissipation is a power 2 term in velocity. 相似文献
18.
用有限元法计算径流式叶轮机械蜗壳的紊流时均流场.有关紊流模型采用K-ε两方程模型,用关于压力p的罚函数方法求解.所得结果可供分析蜗壳流场用.文中方法也可用于计算其他形状的二维通道流动. 相似文献
19.
Brian F. Farrell Petros J. Ioannou 《Theoretical and Computational Fluid Dynamics》1998,11(3-4):237-250
The strong mean shear in the vicinity of the boundaries in turbulent boundary layer flows preferentially amplifies a particular
class of perturbations resulting in the appearance of coherent structures and in characteristic associated spatial and temporal
velocity spectra. This enhanced response to certain perturbations can be traced to the nonnormality of the linearized dynamical
operator through which transient growth arising in dynamical systems with asymptotically stable operators is expressed. This
dynamical amplification process can be comprehensively probed by forcing the linearized operator associated with the boundary
layer flow stochastically to obtain the statistically stationary response.
In this work the spatial wave-number/temporal frequency spectra obtained by stochastically forcing the linearized model boundary
layer operator associated with wall-bounded shear flow at large Reynolds number are compared with observations of boundary
layer turbulence. The verisimilitude of the stochastically excited synthetic turbulence supports the identification of the
underlying dynamics maintaining the turbulence with nonnormal perturbation growth.
Received 30 January 1997 and accepted 27 March 1998 相似文献
20.
L. Kh. Ingel 《Journal of Applied Mechanics and Technical Physics》2018,59(2):206-211
The nonlinear integral model of a turbulent thermal is extended to the case of the horizontal component of its motion relative to the medium (e.g., thermal floating-up in shear flow). In contrast to traditional models, the possibility of a heat source in the thermal is taken into account. For a piecewise constant vertical profile of the horizontal velocity of the medium and a constant vertical velocity shear, analytical solutions are obtained which describe different modes of dynamics of thermals. The nonlinear interaction between the horizontal and vertical components of thermal motion is studied because each of the components influences the rate of entrainment of the surrounding medium, i.e., the growth rate of the thermal size and, hence, its mobility. It is shown that the enhancement of the entrainment of the medium due to the interaction between the thermal and the cross flow can lead to a significant decrease in the mobility of the thermal. 相似文献