Yu Lv

Zhejiang University, Hangzhou, Zhejiang Sheng, China

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Publications (7)7.47 Total impact

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    ABSTRACT: To efficiently model the selective noncatalytic reduction (SNCR) process in a larger utility boiler, a decoupling numerical simulation approach, to separately treat coal combustion and SNCR NOx reduction in the furnace, was presented in this study. The simulated boiler has a full capacity of 100 MW, and the SNCR system is installed at the height of the furnace arch, mainly including groups of reagent nozzles. Urea solution was used as a reactive reagent, so that a relatively complex chemistry, along with the eddy dissipation concept (EDC) model, was introduced to accurately mimic the NOxOUT process in turbulent flow. Simulations are validated with experimental measurements. The reaction temperature, reagent amount, and reagent droplet momentum effects on the SNCR performance, primarily NOx removal and NH3 slip, were investigated in detail. The results show that, only at certain temperature regions, NOx removal gives a continuous rise with the increase of the reagent amount but commonly with a more serious NH3 slip; increasing reagent droplet momentum can be an available technique to enhance the poor global mixing between reagent droplets and flue gas in such a large furnace space. In addition, an empirical optimization of the simulated SNCR system was conducted, and potential methods to benefit SNCR system design and operation were demonstrated, such as multi-level nozzle arrangement and the application of flat atomizers.
    Energy & Fuels. 09/2010; 24(10):5432–5440.
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    ABSTRACT: Direct numerical simulation (DNS) is a kind of ultimate numerical simulation tool for studying fundamental turbulent flows, mixing, chemical reactions and interactions among them. In the present work, a fully explicit method of implementing DNS is presented for investigating transient multi-component methane/air jet flame in the near field. The detailed methodology, enclosing non-dimensional governing equations, inlet velocity disturbance, chemical scheme and fluid property, was discussed. An explicit eighth-order finite-difference scheme was used combined with an explicit tenth-order filter. Conservative variables are temporally advanced in two segmented stages that handle Euler terms and viscous terms respectively. A modified non-reflecting boundary condition was used, which has better performance about the characteristic waves on boundary planes. The developed code was firstly tested with an air jet and evaluated in terms of accuracy and parallel efficiency. Then a methane/air combusting jet was simulated to study the characteristics of the chemical heat-release in turbulence.
    Computers & Fluids 09/2010; · 1.47 Impact Factor
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    ABSTRACT: Direct numerical simulation(DNS) of spatially developing round turbulent jet flow with Reynolds number 4,700 was carried out. Direct numerical simulation(DNS) of spatially developing round turbulent jet flow with Reynolds number 4,700 was carried out. Over 20 million grid points were used in this simulation. Fully compressible three-dimensional Navier–Stokes equations were Over 20 million grid points were used in this simulation. Fully compressible three-dimensional Navier–Stokes equations were solved. High order explicit spatial difference schemes and Runge–Kutta time integration scheme were used to calculate derivatives solved. High order explicit spatial difference schemes and Runge–Kutta time integration scheme were used to calculate derivatives and time marching, respectively. Non-reflecting boundary conditions and exit zone techniques were adopted. Some refined computational and time marching, respectively. Non-reflecting boundary conditions and exit zone techniques were adopted. Some refined computational grids were used in order to capture the smallest turbulent structures near the centerline of the jet. Low level disturbance grids were used in order to capture the smallest turbulent structures near the centerline of the jet. Low level disturbance were imposed on the jet inflow velocity to trigger the developing of turbulence. Turbulent statistics such as mean velocity, were imposed on the jet inflow velocity to trigger the developing of turbulence. Turbulent statistics such as mean velocity, Reynolds stresses, third order velocity moments were obtained and compared with experimental data. One-dimensional velocity Reynolds stresses, third order velocity moments were obtained and compared with experimental data. One-dimensional velocity autospectra was also calculated. The inertial region where the spectra decays according to the k − 5/3 was observed. The quantitative profiles of mean velocity and all of the third order velocity moments which were difficult autospectra was also calculated. The inertial region where the spectra decays according to the k − 5/3 was observed. The quantitative profiles of mean velocity and all of the third order velocity moments which were difficult to measure via experimental techniques were presented here in detail. The jet flow was proven to be close to fully self-similar to measure via experimental techniques were presented here in detail. The jet flow was proven to be close to fully self-similar around 19 jet diameters downstream of jet exit. The statistic data and revealed flow feature obtained in this paper can provide around 19 jet diameters downstream of jet exit. The statistic data and revealed flow feature obtained in this paper can provide valuable reference for round turbulent jet research. valuable reference for round turbulent jet research. KeywordsDNS-Jet-Boundary condition-Turbulent statistics KeywordsDNS-Jet-Boundary condition-Turbulent statistics
    Flow Turbulence and Combustion 06/2010; 84(4):669-686. · 1.27 Impact Factor
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    ABSTRACT: Direct numerical simulation is employed to investigate the premixed jet flame of methane in lean, combined with a detailed chemical kinetics including 17 species and 58 elemental steps and distinct Lewis numbers. Cold methane-air mixture at 0.55 equivalence ratio is injected into the coflow area with 9500 Reynolds number. The coflow ambient gas is set to be the burnt gas of the methane-air mixture in main jet and temperature is assigned to be the corresponding adiabatic flame temperature 1515 K. The whole simulation process is run based on paralleled calculation method, and chemical sources are acquired by dynamically calling CHEMKIN library function. The flame structure at 6.98 ms is shown to demonstrate the obvious dependence of flame structure and reaction rate on vortices motion. Then by tracing the interaction between different flame elements and vortices, the mechanism behind this dependence is found. The concepts including surface density function, mean curvature and stretch rate are used to describe the geometrical structure of vortex-affected flame. Those are all calculated according to simulation result and statistically associated with heat release rate that indicates reaction intensity. The statistical results show that surface density function and reaction rate own direct positive correlation; largely wrinkled flames with greater curvatures magnitude tend to become thick and weaken surface density function and reaction rate, appearing local extinction phenomena; large tangential stretch rates exerted on flame usually produce a local thinning effect in normal making reaction rate intensified. The DNS presented will supply beneficial references to better understanding of flame-vortex interaction and development of more accurate general model for turbulent premixed combustion. Keywordsdirect numerical simulation-premixed flame-turbulence-geometrical structure
    Chinese Science Bulletin 05/2010; 55(13):1231-1239. · 1.37 Impact Factor
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    ABSTRACT: Abstract The figures show the 3D flow pattern of a circular jet with different swirling intensity. Reynolds number is approximately 4300 computed based on the nozzle diameter (d), jet velocity (U), and air fluid property at 1 atm and 300 K. The overall computational domain is set to be 4 × 4 × 12 d in spanwise, height, and streamwise direction. The governing equations are the fully compressible Navier–Stokes equations, firstly differenced by eighth-order explicit scheme and then advanced temporarily by using the fourth-order explicit Runge–Kutta method. 3D characteristics non-reflecting boundary condition including transverse source contribution is imposed on all other boundaries except the inflow boundary handled by assigning fixed profiles of temperature and velocity. To ensure the simulation resolution, here over 16 million grids are employed in sum, combined with a handful of grids located at buffer zones of outflow boundaries. To correctly represent the vortex in the flow field, velocity gradient tensor invariant Q is used here. And ψ refers to the swirling intensity defined as the ratio of tangential momentum to axis momentum. As shown in velocity profile, the flow pattern of the jet changes from a close mode to a totally open mode as ψ increases from 0.4 to 1.5. Accordingly, the recirculation zone gradually moves upstream and backflow velocity is enlarged as well. It is inteseting to found that the obvious drops of the momentums in two shown directions always occur at the same position downstream, no matter how large the ψ value is. Therefore, a momentum compensatory mechanism is expected to exist in the vortex-abundant zone. With the increase of ψ value, the increased strain rate in tangential direction can induce vortex more quickly, intensifying the entrainment and velocity-attenuation, which can be observed in Q value profile. Graphical Abstract
    Journal of Visualization 01/2010; 13:3-4. · 0.51 Impact Factor
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    ABSTRACT: To accurately predict hybrid NOx control process, a joint mechanism is initially developed based on the NOxOUT mechanism of Rota et al. and the ÅA scheme of Zebetta et al. Directed, related graphs and rate-of-product were employed to make the joint mechanism simplified, finally leading to a scheme including 44 species and 150 elementary reactions. Validation of the joint mechanism is strictly conducted at selective noncatalytic reduction, reburning, and hybrid NOx reducing conditions, by comparing the predicted results of the joint mechanism with reported experimental data. Then in order to handle CFD simulation of practical problems, a reduced mechanism, including 18 global steps and 22 species, was accordingly established. The testing of the reduced mechanism was carried out by comparing its predicted results with those of the joint one. Perfect coherency between them is observed at different operating conditions, and the deviation is negligible compared with the general measuring uncertainty. The joint mechanism can serve as the main chemical scheme in simple flow computations and the reduced one is expected to be directly integrated to CFD modeling of industrial equipments with complex flow and geometry configuration.
    09/2009;
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    ABSTRACT: This paper reports a reduced mechanism used in urea-based SNCR process for NOx control that is developed from the detailed mechanism originally proposed by Rota et al. (Chem. Eng. Sci. 2002, 57, 27-38) consisting of 173 elemental reactions and 31 chemical species. Sensitivity analysis and rate-of-production analysis are first conducted to exclude redundant elemental reactions and species, forming a skeletal mechanism. After that, quasi-steady-state species are identified and a 12-step 16-species reduced mechanism is established. The balance equations for quasi-steady-state species are innovatively solved by means of QSS graph method presented by Lu and Law (J. Phys. Chem. A2006, 110, 13202-13208) with the avoidance of efficiency compromise stemming from algebraic iterations. The predictions of the reduced mechanism show satisfactory agreement with those of the detailed one over a wide range of operating conditions, including various temperatures, molar ratio of CO(NH)/NO and O and CO concentrations. The performances of QSS graph method and traditional QSSA by iteration are compared in plug-flow computations. The deviation in accuracy is only in order of 0.01%, while QSS graph creates nearly 40% speed-up significantly superior to QSSA by iteration. 30 refs., 9 figs., 3 tabs.
    Energy & Fuels 01/2009; 23(7):3605-3611. · 2.85 Impact Factor