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Chen, J.-Y.

Publications and source records attributed to Chen, J.-Y..

9 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Effects of Gravity on Triple Flame Propagation and Stability

Numerical simulations of 2-D triple flames under gravity force have been implemented to identify the effects of gravity on triple flame structure and propagation properties and to understand the mechanisms of instabilities resulting from both heat release and buoyancy effects. A wide range of gravity conditions, heat release and mixing widths for a scalar mixing layer are computed for downward-propagating (in the same direction with the gravity vector) and upward-propagating (in the opposite direction of the gravity vector) triple flames.

Chen, J.-Y.↗
NASA NTRS1995

Modeling of turbulent chemical reaction

Viewgraphs are presented on modeling turbulent reacting flows, regimes of turbulent combustion, regimes of premixed and regimes of non-premixed turbulent combustion, chemical closure models, flamelet model, conditional moment closure (CMC), NO(x) emissions from turbulent H2 jet flames, probability density function (PDF), departures from chemical equilibrium, mixing models for PDF methods, comparison of predicted and measured H2O mass fractions in turbulent nonpremixed jet flames, experimental evidence of preferential diffusion in turbulent jet flames, and computation of turbulent reacting flows.

Chen, J.-Y.↗
NASA NTRS1992

Comments on PDF methods

Viewgraphs are presented on the following topics: the grand challenge of combustion engineering; research of probability density function (PDF) methods at Sandia; experiments of turbulent jet flames (Masri and Dibble, 1988); departures from chemical equilibrium; modeling turbulent reacting flows; superequilibrium OH radical; pdf modeling of turbulent jet flames; scatter plot for CH4 (methane) and O2 (oxygen); methanol turbulent jet flames; comparisons between predictions and experimental data; and turbulent C2H4 jet flames.

Chen, J.-Y.↗
NASA NTRS1992

A new unsteady mixing model to predict NO(x) production during rapid mixing in a dual-stage combustor

An advanced gas turbine engine to power supersonic transport aircraft is currently under study. In addition to high combustion efficiency requirements, environmental concerns have placed stringent restrictions on the pollutant emissions from these engines. A dual-stage combustor with the potential for minimizing pollutants such as NO(x) emissions is undergoing experimental evaluation. A major technical issue in the design of this combustor is how to rapidly mix the hot, fuel-rich primary stage product with the secondary diluent air to obtain a fuel-lean mixture for combustion in the secondary stage. Numerical design studies using steady-state methods cannot account for the unsteady phenomena in the mixing region. Therefore, to evaluate the effect of unsteady mixing and combustion processes, a novel unsteady mixing model is demonstrated here. This model has been used in a stand-alone mode to study mixing and combustion in hydrogen-air nonpremixed jet flames. NO(x) production in these jet flames was also predicted. Comparison of the computed results with experimental data show good agreement thereby providing validation of the mixing model.

Menon, Suresh↗
NASA NTRS1991

Second order modeling of boundary-free turbulent shear flows

A set of realizable second order models for boundary-free turbulent flows is presented. The constraints on second order models based on the realizability principle are re-examined. The rapid terms in the pressure correlations for both the Reynolds stress and the passive scalar flux equations are constructed to exactly satisfy the joint realizability. All other model terms (return-to-isotropy, third moments, and terms in the dissipation equations) already satisfy realizability. To correct the spreading rate of the axisymmetric jet, an extra term is added to the dissipation equation which accounts for the effect of mean vortex stretching on dissipation. The test flows used in this study are the mixing shear layer, plane jet, axisymmetric jet, and plane wake. The numerical solutions show that the unified model equations predict all these flows reasonably. It is expected that these models would be suitable for more complex and critical flows.

Shih, T.-H.↗
NASA NTRS1991

Segregation parameters and pair-exchange mixing models for turbulent nonpremixed flames

The progress of chemical reactions in nonpremixed turbulent flows depends on the coexistence of reactants, which are brought together by mixing. The degree of mixing can strongly influence the chemical reactions and it can be quantified by segregation parameters. In this paper, the relevance of segregation parameters to turbulent mixing and chemical reactions is explored. An analysis of the pair-exchange mixing models is performed and an explanation is given for the peculiar behavior of such models in homogeneous turbulence. The nature of segregation parameters in a H2/Ar-air nonpremixed jet flame is investigated. The results show that Monte Carlo simulation with the modified Curl's mixing model predicts segregation parameters in close agreement with the experimental values, providing an indirect validation for the theoretical model.

Chen, J.-Y.↗
NASA NTRS1991

A continuous mixing model for pdf simulations and its applications to combusting shear flows

The problem of time discontinuity (or jump condition) in the coalescence/dispersion (C/D) mixing model is addressed in this work. A C/D mixing model continuous in time is introduced. With the continuous mixing model, the process of chemical reaction can be fully coupled with mixing. In the case of homogeneous turbulence decay, the new model predicts a pdf very close to a Gaussian distribution, with finite higher moments also close to that of a Gaussian distribution. Results from the continuous mixing model are compared with both experimental data and numerical results from conventional C/D models.

Hsu, A. T.↗