Large Eddy Simulations of turbulent particle-laden channel flow

This paper scrutinises the Large Eddy Simulation (LES) approach to simulate the behaviour of inter-acting particles in a turbulent channel flow. A series of simulations that are fully (four-way), two-way and one-way coupled are performed in order to investigate the importance of the individual physical phenomena occurring in particle-laden flows. Moreover, the soft sphere and hard sphere models, which describe the interaction between colliding particles, are compared with each other and the drawbacks and advantages of each algorithm are discussed. Different models to describe the sub-grid scale stresses with LES are compared. Finally, simulations accounting for the rough walls of the channel are compared to simulations with smooth walls. The results of the simulations are discussed with the aid of the experimental data of Kussin J. and Sommerfeld M., 2002, Experimental studies on particle behaviour and turbulence modification in horizontal channel flow with different wall roughness, Exp. in Fluids, 33, pp. 143–159 of Reynolds number 42,000 based on the full channel height. The simulations are carried out in a three-dimensional domain of 0.175 m × 0.035 m  × 0.035 m where the direction of gravity is perpendicular to the flow. The simulation results demonstrate that rough walls and inter-particle collisions have an important effect in redistributing the particles across the channel, even for very dilute flows. A new roughness model is proposed which takes into account the fact that a collision in the soft sphere model is fully resolved and it is shown that the new model is in very good agreement with the available experimental data.     

Large Eddy simulation for engineering applications

In the field of fluid engineering, controlling turbulent flows remains a crucial problem. This paper presents a basis of numerical methods and turbulence models for the large Eddy simulation. Simulation results include the unsteady analyses of complex flows, such as the vortex dynamics of turbulent jets subject to inlet perturbations and the reacting flow with flame propagation in a gas–turbine combustor flow. Applications employing large Eddy simulation are emerging as one of the most important aspects of the “Frontier Simulation Software for Industrial Science” project for the next generation of fluid dynamic design and development.     

Large eddy simulation of turbulent channel flow using an algebraic model

In this paper an algebraic model from the constitutive equations of the subgrid stresses has been developed. This model has an additional term in comparison with the mixed model, which represents the backscatter of energy explicitly. The proposed model thus provides independent modelling of the different energy transfer mechanisms, thereby capturing the effect of subgrid scales more accurately. The model is also found to depict the flow anisotropy better than the linear and mixed models. The energy transfer capability of the model is analysed for the isotropic decay and the forced isotropic turbulence. The turbulent plane channel flow simulation is performed over three Reynolds numbers, Re_τ=180, 395 and 590, and the results are compared with that of the dynamic model, Smagorinsky model, and the DNS data. Both the algebraic and dynamic models are in good agreement with the DNS data for the mean flow quantities. However, the algebraic model is found to be more accurate for the turbulence intensities and the higher‐order statistics. The capability of the algebraic model to represent backscatter is also demonstrated. Copyright © 2005 John Wiley & Sons, Ltd.     

Coupling tabulated chemistry with Large Eddy Simulation of turbulent reactive flows

A new modeling strategy is developed to introduce tabulated chemistry methods in the LES of turbulent premixed combustion. The objective is to recover the correct laminar flame propagation speed of the filtered flame front when the subgrid scale turbulence vanishes. The filtered flame structure is mapped by 1D filtered laminar premixed flames. Closure of the filtered progress variable and the energy balance equations are carefully addressed. The methodology is applied to 1D and 2D filtered laminar flames. These computations show the capability of the model to recover the laminar flame speed and the correct chemical structure when the flame wrinkling is completely resolved. The model is then extended to turbulent combustion regimes by introducing subgrid scale wrinkling effects on the flame front propagation. Finally, the LES of a 3D turbulent premixed flame is performed. To cite this article: R. Vicquelin et al., C. R. Mecanique 337 (2009).     

Large Eddy Simulation of the sound field of a round turbulent jet

In this paper we will use Large Eddy Simulation (LES) to obtain the flow field of a turbulent round jet at a Reynolds number based on the jet orifice velocity of 11000. In the simulations it is assumed that the flow field is incompressible. The acoustic field of the jet is calculated with help of the Lighthill acoustic analogy. The coupling between the flow solver and the acoustic solver is discussed in detail. The Mach number used in the acoustic calculation was equal to 0.6. It is shown that the decay of the jet centerline velocity and centerline rms are in good agreement with experimental data of [12]. Furthermore, it is shown that the influence of the LES modeling on the acoustic field is very small, if the dynamic subgrid model is used.     

Large eddy simulation of turbulent premixed and stratified combustion using flame surface density model coupled with tabulation method

Large eddy simulations (LESs) are performed to investigate the Cambridge premixed and stratified flames, SwB1 and SwB5, respectively. The flame surface density (FSD) model incorporated with two different wrinkling factor models, i.e., the Muppala and Charlette2 wrinkling factor models, is used to describe combustion/turbulence interaction, and the flamelet generated manifolds (FGM) method is employed to determine major scalars. This coupled sub-grid scale (SGS) combustion model is named as the FSD-FGM model. The FGM method can provide the detailed species in the flame which cannot be obtained from the origin FSD model. The LES results show that the FSD-FGM model has the ability of describing flame propagation, especially for stratified flames. The Charlette2 wrinkling factor model performs better than the Muppala wrinkling factor model in predicting the flame surface area change by the turbulence. The combustion characteristics are analyzed in detail by the flame index and probability distributions of the equivalence ratio and the orientation angle, which confirms that for the investigated stratified flame, the dominant combustion modes in the upstream and downstream regions are the premixed mode and the back-supported mode, respectively.     

Large eddy simulation of supersonic flow in ducts with complex cross-sections

Large Eddy Simulation(LES) has been employed for the investigation of supersonic flow characteristics in five ducts with varying cross-sectional geometries.The numerical results reveal that flow channel configurations exert a considerable influence on the mainstream flow and the near-wall flow behavior.In contrast to straight ducts,square-to-circular and rectangular-to-circular ducts exhibit thicker boundary layers and a greater presence of vortex structures.Given the same inlet area,rectangular...     

Propagation of an underexpanded turbulent jet in a parallel supersonic flow

The characteristics of supersonic off-design turbulent jets discharging into parallel supersonic flows are investigated numerically using approximate equations for the effective turbulent viscosity which are derived by analysis of the experimental data.     

高精度PPM格式在湍流燃烧中的应用

利用处理三维可压缩粘性流体流动问题中的沉浸边界法,并结合基于PPM方法的高精度TVD格式,对三维方形管道中部的圆柱火焰绕流及惰性气体绕流问题进行了数值模拟。计算湍流时采用大涡模拟(LES),化学反应速率采用EBU漩涡破碎模型。通过计算结果与实验结果的比较,发现高精度PPM格式能精确模拟两类圆柱绕流问题。计算中还发现,火焰圆柱绕流算例中,在火焰翻越圆柱前,由于燃烧的膨胀作用,使得火焰正面前的未燃气体流动并形成惰性气体绕流,这与无燃烧时的惰性气体绕流类似。但当火焰翻越圆柱过程中及完全翻越圆柱后,两种算例绕流流场出现明显变化。     

Development of a hybrid-fuzzy air temperature controller for a supersonic combustion test facility

 Hydrogen gas is burned in air to raise and maintain the stagnation temperature of a supersonic combustion test facility to a desired setpoint. In order to reach the desired operating conditions for stagnation temperature, there are three phases to the hydrogen control; H₂ ignition at facility start-up, H₂ ramp-up while the facility is ramped-up, and H₂ iteration to achieve the desired temperature setpoint. Each phase incorporates a different type of control. Fuzzy logic is used to design a computer based supervisory controller that recognizes the different phases of operation and chooses the appropriate control method. Received: 28 November 1999/Accepted: 2 November 2000     

Effect of an angular bias on LDA measurements in supersonic turbulent flow

The problem of a laser Doppler anemometer's statistical response to the velocity direction of particles scattering in space has been studied for many years. This phenomenon introduces a statistical bias distinct from the classical bias related to velocity fluctuations. Though the latter has corrected some controversial application, the only answer found to counter the angular bias remains, for most experimenters, the utilization of Bragg cells. It is not always possible to use such a device, however, and this is particularly true in supersonic flows. The angular bias, inevitable in this case, shows increased effects when the normal to the fringe plane is inclined with respect to the mean velocity direction. Analysis of the phenomenon in the more complex case of a two-component anemometer and a supersonic flow helps to show how measurements of velocity fluctuations in a boundary layer quite close to the wall may include significant errors because of this bias.     

Numerical simulation of an electric discharge in supersonic flow

The two-dimensional problem of supersonic air flow past a spherical electrode is considered on the basis of a joint solution of the Navier-Stokes equations for a neutral gas and the charged-particle transport equations in the diffusion-drift approximation. The self-sustained discharge is considered in the cathode regime of operation of the test electrode in a formulation analogous to that of the experimental study [1]. The thermal and non-thermal (action of the electrostatic force in the cathode layer of the space charge) mechanisms of action of the discharge on the flow field are investigated. Within the framework of the numerical model considered the effect of the electrostatic force turns out to be negligibly small and the main effect of the action on the flow is the heat release driven by the electric currents. The influence of the discharge on the flow field was manifested itself in a reduction of the aerodynamic drag by up to 25%.     

Large eddy simulation of vertical turbulent jets under JONSWAP waves

The effect of random waves on vertical plane turbulent jets is studied numerically and the mechanism behind the interaction of the jet and waves is analyzed. The large eddy simulation method is used and the σ-coordinate system is adopted. Turbulence is modeled by a dynamic coherent eddy model. The σ-coordinate transformation is introduced to map the irregular physical domain with a wavy free surface and an uneven bottom onto a regular computational domain. The fractional step method is used to solve the fil...     

Large eddy simulation of cross-flow through a staggered tube bundle at subcritical Reynolds number

The Large Eddy Simulation (LES) technique is used to study the vortex shedding characteristics inside a staggered tube array consisting of six rows with intermediate spacings (S_L/D×S_T/D=1.6×3.6) at the subcritical Reynolds number of 8600 (based on the gap velocity). The filtered equations are discretised using the finite volume method in an unstructured, collocated grid arrangement with second-order accurate methods in space and time. The predictions of mean velocities and Reynolds stresses are in very good agreement with detailed LDA measurements performed in 17 stations along the depth of the array. The sizes of the recirculation zones behind the cylinders in the first and third row also compare favourably with available correlations. Two distinct and independent shedding frequencies are detected behind the first two rows, but the high-frequency component vanishes in the downstream rows. The corresponding Strouhal numbers agree well with measurements available in the literature for similar tube spacings. The lift coefficient as well as instantaneous flow patterns of the whole array are also examined.     

Large Eddy Simulation of an Initially-Confined Triangular Oscillating Jet

This paper reports the first large eddy simulation (LES) of a self-excited oscillating triangular jet (OTJ) issuing from a fluidic nozzle that consists of a small triangular orifice inlet followed by a large circular chamber and an orifice outlet. The case simulated is identical to that measured experimentally by England et al. (Exp Fluids 48(1):69–80, 2010). The present prediction agrees well with the previous measurement. The simulation reveals that the central oscillating jet exhibits axis-switching in the cross-section and rotates by 60° approximately over a downstream distance of x = 0.5D (chamber diameter). Three strong longitudinal vortices occur associated with the three vertices of the inlet triangle. These vortices strongly interact with the central jet and also the surroundings, in the region at x/D ≤ 1, and appear to merge finally with the outer secondary swirling flow. These observations are consistent with the deduction from previous experiments.     

Numerical simulation of cross-flow around four cylinders in an in-line square configuration

Successful numerical simulations can reveal important flow characteristics and information which are extremely difficult to obtain experimentally. Two- and three-dimensional (3-D) numerical simulations of cross-flow around four cylinders in an in-line square configuration are performed using a finite-volume method. For 2-D studies, the Reynolds numbers (Re) are chosen to be Re=100 and 200 and the spacing ratio L/D is set at 1.6, 2.5, 3.5, 4.0 and 5.0. For the 3-D investigation, the simulation is only performed at a Re=200, a spacing ratio L/D=4.0 and an aspect ratio H/D=16. The 2-D studies reveal three distinct flow patterns: (I) a stable shielding flow; (II) a wiggling shielding flow and (III) a vortex shedding flow. A transformation of the flow pattern from (I) to (II) at Re=100 will increase the amplitude of the maximum fluctuating pressure on the downstream cylinder surface by 4–12 times, while a transformation of the flow pattern from (II) to (III) will enhance the maximum fluctuating pressure amplitude by 2–3 times. There is a large discrepancy between 2-D simulation and flow visualization results at L/D=4.0 and Re=200. A probable cause could be the strong 3-D effect at the ends of the cylinder at low H/D. It was found that, for an in-line square configuration at critical L/D and when H/D is lower than a certain value, 3-D effects are very significant at the ends of the cylinders. In such cases, a time-consuming 3-D numerical simulation will have to be performed if full replication of the flow phenomenon were to be achieved.