Author

# Haifeng Wang

Other affiliations: Cornell University, University of Science and Technology of China

Bio: Haifeng Wang is an academic researcher from Purdue University. The author has contributed to research in topics: Large eddy simulation & Jet (fluid). The author has an hindex of 17, co-authored 49 publications receiving 917 citations. Previous affiliations of Haifeng Wang include Cornell University & University of Science and Technology of China.

##### Papers published on a yearly basis

##### Papers

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TL;DR: In this article, a parametric study was performed to understand the effects of pressure, temperature, equivalence ratio along with geometric factors such as orifice diameter and spark position on the ignition mechanisms and probability.

156 citations

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01 Jan 2007TL;DR: In this article, Cao et al. compared the performance of three mixing models (EMST, IEM and MC) and their dependence on the specified value of Cϕ, and showed that only the EMST model is capable of calculating accurately both the observed burning indexes and the mixture fraction variance.

Abstract: For turbulent flames containing significant turbulence–chemistry interactions, the accuracy of PDF model calculations depends on the accurate representation of the chemistry and on the mixing model (including the value of the mixing-model constant, Cϕ). In recent work, Cao and Pope demonstrated that accurate calculations of the Barlow and Frank piloted jet flames D, E and F are achieved using the GRI3.0 mechanism and the EMST mixing model (with Cϕ = 1.5). In the present paper, further PDF model calculations (using GRI3.0) are performed in order to investigate the performance of three mixing models (EMST, IEM and MC) and their dependence on the specified value of Cϕ. It is shown that all three models are capable of yielding levels of local extinction (quantified by a burning index) comparable to the experimental observations, but this is achieved using Cϕ = 3.3 for IEM, and Cϕ = 3.8 for MC (compared to Cϕ = 1.5 for EMST). However, in these calculations with IEM and MC, the mixture fraction variance is significantly underpredicted: only the EMST model is capable of calculating accurately both the observed burning indexes and the mixture fraction variance. The findings of this study, the first comparative study of mixing models in the Barlow and Frank flames, are related to previous observations.

114 citations

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01 Jan 2011TL;DR: In this article, a large-eddy simulation (LES)/probability density function (PDF) simulation capability for turbulent combustion was developed and applied to a turbulent CH 4 / H 2 / N 2 jet flame (DLR Flame A).

Abstract: In this work, we develop the large-eddy simulation (LES)/probability density function (PDF) simulation capability for turbulent combustion and apply it to a turbulent CH 4 / H 2 / N 2 jet flame (DLR Flame A). The PDF code is verified to be second-order accurate with respect to the time-step size and the grid size in a manufactured one-dimensional test case. Three grids ( 64 × 64 × 16 , 192 × 192 × 48 , 320 × 320 × 80 ) are used in the simulations of DLR Flame A to examine the effect of the grid resolution. The numerical solutions of the resolved mixture fraction, the mixture fraction squared, and the density are duplicated in the LES code and the PDF code to explore the numerical consistency between them. A single laminar flamelet profile is used to reduce the computational cost of treating the chemical reactions of the particles. The sensitivity of the LES results to the time-step size is explored. Both first and second-order time splitting schemes are used for integrating the stochastic differential equations for the particles, and these are compared in the jet flame simulations. The numerical results are found to be sensitive to the grid resolution, and the 192 × 192 × 48 grid is adequate to capture the main flow fields of interest for this study. The numerical consistency between LES and PDF is confirmed by the small difference between their numerical predictions. Overall good agreement between the LES/PDF predictions and the experimental data is observed for the resolved flow fields and the composition fields, including for the mass fractions of the minor species and NO. The LES results are found to be insensitive to the time-step size for this particular flame. The first-order splitting scheme performs as well as the second-order splitting scheme in predicting the resolved mean and rms mixture fraction and the density for this flame.

95 citations

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01 Jan 2013TL;DR: In this paper, a large-eddy simulation (LES)/probability density function (PDF) study of a non-premixed CO/H2 temporally-evolving turbulent planar jet flame, which has previously been studied using direct numerical simulations (DNS) with a skeletal chemical mechanism, is reported.

Abstract: We report a large-eddy simulation (LES)/probability density function (PDF) study of a non-premixed CO/H2 temporally-evolving turbulent planar jet flame, which has previously been studied using direct numerical simulations (DNS) with a skeletal chemical mechanism. The flame exhibits strong turbulence–chemistry interactions resulting in local extinction followed by re-ignition. In this study, the filtered velocity field in LES and the PDF transport equations with the interaction-by-exchange with the mean (IEM) mixing model (with molecular transport) are solved by the highly-scalable NGA/HPDF codes with second-order accuracy in space and time. The performance of the hybrid LES/PDF methodology is assessed through detailed a posteriori comparisons with DNS of the same flame. The comparison shows overall good agreement of the temporal evolution of the temperature and mass fractions of major chemical species, as well as the prediction of local extinction and re-ignition. The modeling of multi-scalar mixing is analyzed using the DNS and LES/PDF results. The DNS results exhibit an attracting manifold of the streamlines of the diffusion velocity in composition space, and the LES/PDF results show qualitative agreement on the manifold and joint PDFs of compositions.

71 citations

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TL;DR: A new variance reduction technique by way of an implicit smoothing methodology that is shown to satisfy conservation, boundedness and regularity criteria, and for an appropriate choice of the smoothing length scale, significant improvements in accuracy can be achieved for an incremental increase in computational cost.

54 citations

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14 Jul 1996TL;DR: The striking signature of Bose condensation was the sudden appearance of a bimodal velocity distribution below the critical temperature of ~2µK.

Abstract: Bose-Einstein condensation (BEC) has been observed in a dilute gas of sodium atoms. A Bose-Einstein condensate consists of a macroscopic population of the ground state of the system, and is a coherent state of matter. In an ideal gas, this phase transition is purely quantum-statistical. The study of BEC in weakly interacting systems which can be controlled and observed with precision holds the promise of revealing new macroscopic quantum phenomena that can be understood from first principles.

3,530 citations

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TL;DR: Probability density function (PDF) methods have been widely used for modeling chemically reacting turbulent flows as discussed by the authors, where one models and solves an equation that governs the evolution of the one-point, one-time PDF for a set of variables that determines the local thermochemical and/or hydrodynamic state of a reacting system.

572 citations

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TL;DR: A strategy capable of simulating polydisperse flows in complex geometries is employed where the fluid transport equations are solved in an Eulerian framework and the dispersed phase is represented as Lagrangian particles.

414 citations

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01 Jan 2013TL;DR: A review of the state-of-the-art in modeling turbulent combustion can be found in this article, with a focus on gas-phase, non-premixed flames, and the significant remaining challenges facing models of turbulent combustion are examined.

Abstract: A major goal of combustion research is to develop accurate, tractable, predictive models for the phenomena occurring in combustion devices, which predominantly involve turbulent flows. With the focus on gas-phase, non-premixed flames, recent progress is reviewed, and the significant remaining challenges facing models of turbulent combustion are examined. The principal challenges are posed by the small scales, the many chemical species involved in hydrocarbon combustion, and the coupled processes of reaction and molecular diffusion in a turbulent flow field. These challenges, and how different modeling approaches face them, are examined from the viewpoint of low-dimensional manifolds in the high-dimensional space of chemical species. Most current approaches to modeling turbulent combustion can be categorized as flamelet-like or PDF-like. The former assume or imply that the compositions occurring in turbulent combustion lie on very-low-dimensional manifolds, and that the coupling between turbulent mixing and reaction can be parameterized by at most one or two variables. PDF-like models do not restrict compositions in this way, and they have proved successful in describing more challenging combustion regimes in which there is significant local extinction, or in which the turbulence significantly disrupts flamelet structures. Advances in diagnostics, the design of experiments, computational resources, and direct numerical simulations are all contributing to the continuing development of more accurate and general models of turbulent combustion.

286 citations

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TL;DR: The interaction between turbulence and radiation (TRI) in reactive flows has been demonstrated experimentally, theoretically and numerically, and results from the highly nonlinear coupling between fluctuations of radiation intensity and fluctuations of temperature and chemical composition of the medium.

210 citations