Numerical study of an annular gas turbine combustor with dump diffuser

INTRODUCTIONThemainfunctionofagasturbinediffusersystemistoreduceinletvelocityoftheflametubeandtoachieveminimaltotalpressurelossforimprovedcombustionprocesses.Inmoderngasturbinecombustors,thedumpdiffuserhasbeenwidelyused,becausethesuddenexpansionatpre...     

数值模拟环形燃烧室两相反应流场

在任意曲线坐标系下,采用一种整体分区结合法,对包扩压器和火焰筒在在内的环形燃烧室三维两相反应流进行了数值模拟。所相采用Ｅｕｌｅｒ方法处理,并采用标准ｋ－ε双方程紊流模型、ＥＢＵ－Ａｒｒｈｅｎｉｕｓ紊流燃烧模型,六通量热辐射模型;液相采用Ｌａｇｒａｎｇｅ法处理。在非交错网格体系下,气相用ＳＩＭＰＬＥ法求解,液相采用颗粒群轨道模型,并用ＰＳＩＣ算法对其进行数值求解,计算结果表明这种新方法是可行的。     

Numerical Study of Spray Dispersion in a Premixing Chamber for Low-NOx Engines

IntroductionThe present work is devoted to particle dispersionin confined two-phase turbulent jets, which has become amajor domain of research attracting increasingly interestand with challenging fundamental aspects. Describingthe motion of a dispersed phase is complex and is ofgreat interest in several practical systems. Theapplications that require the solution of this problem areas varied as the dispersion of passive pollutant particlesin the atmosphere to combustion systems with dispersing…     

Large Eddy Simulations of gaseous flames in gas turbine combustion chambers

Recent developments in numerical schemes, turbulent combustion models and the regular increase of computing power allow Large Eddy Simulation (LES) to be applied to real industrial burners. In this paper, two types of LES in complex geometry combustors and of specific interest for aeronautical gas turbine burners are reviewed: (1) laboratory-scale combustors, without compressor or turbine, in which advanced measurements are possible and (2) combustion chambers of existing engines operated in realistic operating conditions. Laboratory-scale burners are designed to assess modeling and fundamental flow aspects in controlled configurations. They are necessary to gauge LES strategies and identify potential limitations. In specific circumstances, they even offer near model-free or DNS-like LES computations. LES in real engines illustrate the potential of the approach in the context of industrial burners but are more difficult to validate due to the limited set of available measurements. Usual approaches for turbulence and combustion sub-grid models including chemistry modeling are first recalled. Limiting cases and range of validity of the models are specifically recalled before a discussion on the numerical breakthrough which have allowed LES to be applied to these complex cases. Specific issues linked to real gas turbine chambers are discussed: multi-perforation, complex acoustic impedances at inlet and outlet, annular chambers…. Examples are provided for mean flow predictions (velocity, temperature and species) as well as unsteady mechanisms (quenching, ignition, combustion instabilities). Finally, potential perspectives are proposed to further improve the use of LES for real gas turbine combustor designs.     

Current status of droplet and liquid combustion

The present understanding of spray combustion in rocket engine, gas turbine, Diesel engine and industrial furnace applications is reviewed. In some cases, spray combustion can be modeled by ignoring the details of spray evaporation and treating the system as a gaseous diffusion flame; however, in many circumstances, this simplification is not adequate and turbulent two-phase flow must be considered. The behavior of individual droplets is a necessary component of two-phase models and recent work on transient droplet evaporation, ignition and combustion is considered, along with a discussion of important simplifying assumptions involved with modeling these processes. Methods of modeling spray evaporation and combustion processes are also discussed including: one-dimensional models for rocket engine and prevaporized combustion systems, lumped zone models (utilizing well-stirred reactor and plug flow regions) for gas turbine and furnace systems, locally homogeneous turbulent models, and two-phase models. The review highlights the need for improved injector characterization methods, more information of droplet transport characteristics in turbulent flow and continued development of more complete two-phase turbulent models.     

Modelling of combustion performances and emission characteristics of coal gases in a model gas turbine combustor

In recent years, gas mixtures are being used as alternative fuels in combustors. These gas mixtures are obtained by different methods. For instance, coal gasification and carbonization as coal have the largest reserves among fossil fuels. Gas mixtures obtained via coal gasification and carbonization are called water gas, generator gas, town gas and coke oven gas. These fuels contain various gases. As a result of this, heating values of fuels are also different. Therefore, combustion performances and emission characteristics of these fuels need to be investigated. In this study, combustion performances and emissions including CO, CO₂ and NO_X of water gas, generator gas, town gases, coke oven gas and methane were numerically investigated in a model gas turbine combustor. The numerical modelling of turbulent nonpremixed diffusion flames has been performed in this combustor. Mathematical models used in this study involved the k–ε model of turbulent flow, the PDF/mixture fraction model of nonpremixed combustion and P‐1 radiation model. A CFD code ANSYS Fluent was used for all numerical investigations. Temperature distributions of axial and radial directions were determined. A NO_X post‐processor was used for the prediction of NO_X emissions from the gas turbine combustor. Modelling was performed for 60 kW thermal power and different equivalance ratios (i.e. Ф = 0.91, Ф = 0.77 and Ф = 0.67). The studied type 1 model gas turbine combustor was modelled for Ф = 0.91 equivalance ratio. Then, Other equivalance ratios were analysed for type 2 model gas turbine combustor. The effect of dilution air on combustion performances and emission characteristics was also investigated. It is concluded that the coke oven gas, the town gas I, town gas II and the water gas are appropriate for usage as alternative fuel, whereas the generator gas is not suitable for gas turbine combustors. Copyright © 2013 John Wiley & Sons, Ltd.     

Fundamentals of turbulent gas-solid flows applied to circulating fluidized bed combustion

A summary is made of the present state of knowledge of turbulent gas-solid flow modeling and in particular its application to circulating fluidized bed combustion chambers. Models are presented to close the set of equations describing isothermal non-reacting turbulent gas-particle flows applied to fluidization, and it is shown under which assumptions the models can be derived. With the kinetic theory of granular flow, transport equations for the velocity moments and closure laws for the stress tensor and the energy flux are derived for the particle phase. Closure equations for the drift velocity and for the fluid-particle velocity correlation tensor are presented, first based on algebraic models and, second, based on transport equations with the fluid-particle joint probability density function. An alternative derivation of the fluid-particle velocity covariance transport equation is compared to the formulation based on the fluid-particle joint probability density function. Two-way coupling is discussed, and a transport equation for the second-order velocity moments is used to derive a two-equation model accounting for the modulation of gas phase turbulence by particles. Boundary conditions for the set of equations describing a turbulent gas-solid flow are discussed. Provided that the domain of applicability of the models is known, a discussion on the usefulness of the models is given, as well as an application to fluidization and especially to circulating fluidized bed combustors. Prospects for improvement of the existing models are presented.     

Numerical simulation data for assessment of particle-laden turbulent flow models

This paper presents a collection of numerical simulation data which provides a reference for the assessment of various statistical/stochastic models in incompressible homogeneous particle-laden turbulent flows. Four different homogeneous flow configurations are studied, namely, homogeneous shear flow, homogeneous plane strain flow, homogeneous axisymmetric expansion and contraction. An Eulerian-Lagrangian formulation is used for the two-phase flow simulation. A Fourier pseudospectral method is used for the solution of the Eulerian carrier-phase equations without resorting to any turbulence model. The Lagrangian equations for the dispersed phase are integrated using a modified Stokes drag. For the shear flow, both monodispersed and polydispersed particles have been considered. In this paper, only the results that are relevant for assessment of various statistical models for both the fluid and dispersed phases are presented.     

A KIVA code with Reynolds-stress model for engine flow simulation

To properly simulate the highly anisotropic turbulent engine flows, higher order turbulence model should be used to correctly reproduce flow physics inside the engine. The popular KIVA computer code has been modified to include the Reynolds-stress turbulence model (RSTM) for this purpose. The objective of this paper is to present our recent research on the use of RSTM and the KIVA code for engine flow simulation, which include gas turbine combustors and IC engines.     

3D ALE Finite-Element Method for Two-Phase Flows With Phase Change

We seek to study numerically two-phase flow phenomena with phase change through the finite-element method (FEM) and the arbitrary Lagrangian–Eulerian (ALE) framework. This method is based on the so-called “one-fluid” formulation; thus, only one set of equations is used to describe the flow field at the vapor and liquid phases. The equations are discretized on an unstructured tetrahedron mesh and the interface between the phases is defined by a triangular surface, which is a subset of the three-dimensional mesh. The Navier–Stokes equation is used to model the fluid flow with the inclusion of a source term to compute the interfacial forces that arise from two-phase flows. The continuity and energy equations are slightly modified to take into account the heat and mass transport between the different phases. Such a methodology can be employed to study accurately many problems, such as oil extraction and refinement in the petroleum area, design of refrigeration systems, modeling of biological systems, and efficient cooling of electronics for computational purposes, which is the aim of this research. A comparison of the obtained numerical results to the classical literature is performed and presented in this paper, thus proving the capability of the proposed new methodology as a platform for the study of diabatic two-phase flows.     

Free radical imaging techniques applied to hydrocarbon flames diagnosis

introductionThe current industrial needs for hydIDcrton-fuelcombushon systems involve simul~s assessllled ofdecreasing pollutal emissions, increasing equipmentlifetime and reducing fuel consumphon. withoutcompromising final PIDduct quality and Promotingflexible and clean Operation modes. Ih thes context,exhaust endssions chendcal composition have been arelevant issue for researchers and engineers, namelyunbumed hydrocboons and nitric and carbon Oboes,Which can direCtly or indireCtly hann e…     

Modeling of lean premixed combustion in stationary gas turbines

Lean premixed combustion (LPC) of natural gas is of considerable interest in land-based gas turbines for power generation. However, modeling such combustors and adequately addressing the concerns of LPC, which include emissions of nitrogen oxides, carbon monoxide and unburned hydrocarbons, remains a significant challenge. In this paper, characteristics of published simulations of gas turbine combustion are summarized and methods of modeling turbulent combustion are reviewed. The velocity–composition PDF method is selected for implementation in a new comprehensive model that uses an unstructured-grid flow solver. Reduced mechanisms for methane combustion are evaluated in a partially stirred reactor model. Comprehensive model predictions of swirl-stabilized LPC of natural gas are compared with detailed measurements obtained in a laboratory-scale combustor. The model is also applied to industrial combustor geometries.     

Numerical analysis of discrete phase induced effects on a gas flow in a turbulent two-phase free jet

The paper addresses numerical simulation of turbulent two-phase flow in a long vertical tube and turbulent two-phase free jet formed at the tube outlet, analyzing agreement between the numerical results and the results of corresponding experimental investigation carried out earlier.In the numerical analyses conducted, gas phase was modeled as an air flow (having a mass flow-rate in the range of 1.25–4.00 g/s), while the sand particles of two different sizes (0.25–0.30 and 0.8–1.0 mm) represented a discrete phase (particle to gas mass flow ratio of 0.72–4.08) in the two-phase flow considered. Gas-particle interaction was analyzed based on the gas velocities in the particle-laden two-phase flow and the particle-free gas flow, calculated and measured at various locations along the longitudinal axis and radius of the jet.Mathematical model of continuous phase flow was developed based on the single phase flow models, with certain corrections introduced to account for the effects of particles in the flow. In the simulation model developed, the flow analyzed was modeled as a two-phase mixture, with Eulerian simulation used to account for the gas phase behavior and the Lagrangian simulation modeling the particle movement in the two-phase flow considered. In order to appropriately close the system of time-averaged equations, k–ε turbulent model, deemed the most reliable, was used. Phase coupling i.e. fluid-particle interaction was modeled using the PSI-CELL concept. The results obtained via numerical simulation have shown a good agreement with the experimental data acquired.     

A Simple Finite-Volume Formulation of the Lattice Boltzmann Method for Laminar and Turbulent Flows

A finite-volume formulation commonly employed in the well-known SIMPLE family algorithms is used to discretize the lattice Boltzmann equations on a cell-centered, non-uniform grid. The convection terms are treated by a higher-order bounded scheme to ensure accuracy and stability of solutions, especially in the simulation of turbulent flows. The source terms are linearized by a conventional method, and the resulting algebraic equations are solved by a strongly implicit procedure. A method is also presented to link the lattice Boltzmann equations and the macroscopic turbulence modeling equations in the frame of the finite-volume formulation. The method is applied to two different laminar flows and a turbulent flow. The predicted solutions are compared with the experimental data, benchmark solutions, and solutions by the conventional finite-volume method. The results of these numerical experiments for laminar flows show that the present formulation of the lattice Boltzmann method is slightly more diffusive than the finite-volume method when the same numerical grid and convection scheme are used. For a turbulent flow, the finite-volume lattice Boltzmann method slightly underpredicts the reattachment length in a separated flow. In general, the finite-volume lattice Boltzmann method is as accurate as the conventional finite-volume method in predicting the mean velocity and the pressure at the wall. These observations show that the present method is stable and accurate enough to be used in practical simulations of laminar and turbulent flows.     

Experimental study of humid air reverse diffusion combustion in a turbulent flow field

Experiments were performed to investigate the differences between the propane/air turbulent diffusion reactive flows past bluff-body and the propane/humid air turbulent diffusion reactive flows in the same conditions. The velocity distributions of the non-humid reactive flow fields and the humid reactive flow fields were measured by particle image velocimetry (PIV) techniques. The temperature fields were measured by high temperature thermocouples, and NO_x distributions were obtained by using gas detection instruments. The results show that although humid air reactive flow fields are similar to non-humid flow fields in general, there are some differences in the humid air combustion flow field comparing with the non-humid combustion flow field: the center of the reversed-flow region goes forward; the dimension of the reversed-flow region is smaller; the peak temperature and NO_x formation are reduced. It is suggested that humid air combustion is helpful to shorten the axial length of combustors, and reduce the formation of pollutants. __________ Translated from Journal of Shanghai Jiaotong University, 2006, 40(8): 1 287–1 292 [译自: 上海交通大学学报]     

MULTIGRID ACCELERATION OF COMPUTATIONS OF TURBULENT PARTICLE-LADEN FLOWS

A computational procedure is presented with a multigrid-acceleration scheme for an efficient modeling of turbulent recirculating and highly curved two-phase flows in general coordinates. The two-phase flows consist of a fluid phase governed by Eulerian equations and a particle phase governed by Lagrangian equations. The fluid turbulence-induced particle dispersion is simulated with an eddy-interaction model. Numerical results are presented and compared with available experimental measurements for a particle-laden liquid flow in a sudden-expansion pipe and a particle-laden gaseous flow in a 90° bend. The multigrid computational efficiency is assessed against the conventional single-grid iteration. Results show that the multigrid method substantially enhances the computational efficiency on the fine grids as compared to the single-grid method. In addition, numerical predictions agree favorably with experimental measurements.     

燃气轮机环形燃烧室内燃烧流动的数值模拟

对一个复杂的GE—F101型工业燃气轮机环形燃烧室，采用Reynolds应力湍流模型(RSM)、EBU—Arrhenius湍流燃烧模型和六通量热辐射模型描述其燃烧流动，应用FLUENT软件进行了三维化学反应流场的数值模拟研究。研究结果表明：旋流和燃料进口射流对燃烧室流内温度和流场分布有着重要的影响；利用数值手段得到燃烧室出口的温度分布以判断其能否满足透平叶片进口温度的要求是可行的；燃烧室工作压强对出口的NO分布有着重要影响。在燃用气体燃料时，燃气轮机的NO排放主要来自于热NO，瞬时NO只占很小一部分。图11参6     

Population balance modelling of polydispersed particles in reactive flows

Polydispersed particles in reactive flows is a wide subject area encompassing a range of dispersed flows with particles, droplets or bubbles that are created, transported and possibly interact within a reactive flow environment - typical examples include soot formation, aerosols, precipitation and spray combustion. One way to treat such problems is to employ as a starting point the Newtonian equations of motion written in a Lagrangian framework for each individual particle and either solve them directly or derive probabilistic equations for the particle positions (in the case of turbulent flow). Another way is inherently statistical and begins by postulating a distribution of particles over the distributed properties, as well as space and time, the transport equation for this distribution being the core of this approach. This transport equation, usually referred to as population balance equation (PBE) or general dynamic equation (GDE), was initially developed and investigated mainly in the context of spatially homogeneous systems. In the recent years, a growth of research activity has seen this approach being applied to a variety of flow problems such as sooting flames and turbulent precipitation, but significant issues regarding its appropriate coupling with CFD pertain, especially in the case of turbulent flow. The objective of this review is to examine this body of research from a unified perspective, the potential and limits of the PBE approach to flow problems, its links with Lagrangian and multi-fluid approaches and the numerical methods employed for its solution. Particular emphasis is given to turbulent flows, where the extension of the PBE approach is met with challenging issues. Finally, applications including reactive precipitation, soot formation, nanoparticle synthesis, sprays, bubbles and coal burning are being reviewed from the PBE perspective. It is shown that population balance methods have been applied to these fields in varying degrees of detail, and future prospects are discussed.     

Feasibility of pulse combustion in micro gas turbines

In gas turbines, a fast decrease of efficiency appears when the output decreases; the efficiency of a large gas turbine (20…30 MW) is in the order of 40 %, the efficiency of a 30 kW gas turbine with a recuperator is in the order of 25 %, but the efficiency of a very small gas turbine (2…6 kW) in the order of 4…6 % (or 8…12 % with an optimal recuperator). This is mainly a result of the efficiency decrease in kinetic compressors, due to the Reynolds number effect. Losses in decelerating flow in a flow passage are sensitive to the Reynolds number effects. In contrary to the compression, the efficiency of expansion in turbines is not so sensitive to the Reynolds number; very small turbines are made with rather good efficiency because the flow acceleration stabilizes the boundary layer. This study presents a system where the kinetic compressor of a gas turbine is replaced with a pulse combustor. The combustor is filled with a combustible gas mixture, ignited, and the generated high pressure gas is expanded in the turbine. The process is repeated frequently, thus producing a pulsating flow to the turbine; or almost a uniform flow, if several parallel combustors are used and triggered alternately in a proper way. Almost all the compression work is made by the temperature increase from the combustion. This gas turbine type is investigated theoretically and its combustor also experimentally with the conclusion that in a 2 kW power size, the pulse flow gas turbine is not as attractive as expected due to the big size and weight of parallel combustors and due to the efficiency being in the order of 8 % to 10 %. However, in special applications having a very low power demand, below 1000 W, this solution has better properties when compared to the conventional gas turbine and it could be worth of a more detailed investigation.