The scalar filtered mass density function (FMDF) is further developed and employed for large-eddy simulations (LES) of high speed turbulent flows in complex geometries. LES/FMDF is implemented via an efficient, hybrid numerical method. In this method, the filtered compressible Navier-Stokes equations in curvilinear coordinate systems are solved with a generalized, high-order, multi-block, compact differencing scheme. Turbulent mixing and combustion are modeled with the FMDF. The LES/FMDF method is used for simulations of isotropic turbulent flow in a piston-cylinder assembly, the flow in a shock tube and a supersonic co-axial helium-air jet. The critical role of pressure in the FMDF equation when applied to compressible flows is studied. It is shown that LES/FMDF is reliable and is able to simulate compressible turbulent mixing and combustion in supersonic flows.

JF - 48th AIAA Aerospace Sciences Meeting PB - AIAA CY - Orlando, FL ER - TY - CONF T1 - Numerical Investigations of Shock-Turbulence Interactions in a Planar Mixing Layer T2 - 48th AIAA Aerospace Sciences Meeting Y1 - 2010 A1 - Li, Z. A1 - Jaberi, F.A. AB -Direct numerical simulation (DNS) and large-eddy simulation (LES) of spatially developing supersonic mixing layer, interacting with an oblique shock wave are conducted with a new high-order Monotonicity-Preserving scheme. Without the incident shock, the mixing layer grows linearly and exhibits self-similar behavior after the transition. With the shock, significant small-scale turbulence is generated just behind the shock. With an increase in shock angle, the intensity of the shock-generated turbulence is increased and its peak position shifts away from the mixing layer centerline. The effects of turbulence on the shock are also shown to be very significant, such that normal shocklets and large adverse pressure gradients are created in some conditions. Comparison with the DNS data indicates that the LES with the modified kinetic energy viscosity (MKEV) subgrid stress model is able to predict the main features of the flow and shock-turbulence interactions.

JF - 48th AIAA Aerospace Sciences Meeting PB - AIAA CY - Orlando, FL ER - TY - JOUR T1 - Constraints on the Density Dependence of the Symmetry Energy JF - Physical Review Letters Y1 - 2009 A1 - M. B. Tsang A1 - Yingxun Zhang A1 - P. Danielewicz A1 - M. Famiano A1 - Li, Z. A1 - W. G. Lynch A1 - A. W. Steiner AB -Collisions involving {112Sn} and {124Sn} nuclei have been simulated with the improved quantum molecular dynamics transport model. The results of the calculations reproduce isospin diffusion data from two different observables and the ratios of neutron and proton spectra. By comparing these data to calculations performed over a range of symmetry energies at saturation density and different representations of the density dependence of the symmetry energy, constraints on the density dependence of the symmetry energy at subnormal density are obtained. The results from the present work are compared to constraints put forward in other recent analyses.

VL - 102 N1 - Copyright {(C)} 2010 The American Physical Society; Please report any problems to prola@aps.org ER - TY - CONF T1 - Large-Scale Simulations of High Speed Turbulent Flows T2 - 47th AIAA Aerospace Sciences Meeting Y1 - 2009 A1 - Li, Z. A1 - Jaberi, F.A. AB -This paper briefly describes a new class of high-order Monotonicity-Preserving (MP) finite difference methods recently developed for direct numerical simulation (DNS) and large-eddy simulation (LES) of high-speed turbulent flows. The MP method has been implemented together with high-order compact (COMP) and weighted essentially non- oscillatory (WENO) methods in a generalized three-dimensional (3D) code and has been applied to various 1D, 2D and 3D problems. For the LES, compressible versions of the gradient-based subgrid-scale closures are employed. Detailed and extensive analysis of various flows indicates that MP schemes have less numerical dissipation and faster grid convergence than WENO schemes. Simulations conducted with high-order MP schemes preserve sharp changes in flow variables without spurious oscillations and capture the turbulence at the smallest simulated scales. The non-conservative form of the scalar equation solved with MP schemes are shown to generate the same results as COMP schemes for supersonic mixing problems involving shock waves.

JF - 47th AIAA Aerospace Sciences Meeting PB - American Institute of Aeronautics and Astronautics CY - Orlando, FL ER - TY - CONF T1 - A New Model for Numerical Simulations of Two-Phase Turbulent Combustion T2 - National Combustion Meeting Y1 - 2009 A1 - Li, Z. A1 - Jaberi, F.A. JF - National Combustion Meeting PB - National Combustion Meeting CY - Ann Arbor, MI ER - TY - JOUR T1 - Turbulence-Interface Interactions in a Two-Fluid Homogeneous Flow JF - Physics of Fluids Y1 - 2009 A1 - Li, Z. A1 - Jaberi, F.A. AB -The two-way interactions between the turbulent velocity field and the interface in an incompressible two-fluid homogeneous turbulent flow are studied with a recently developed Lagrangian–Eulerian interfacial particle level-set method. The numerical results confirm that the rate of change of the interface area is directly related to the work done by the surface tension force. While the surface tension damps the surrounding turbulence in the “interface stretching period” to oppose the increase in interface area, it is shown to actually increase the turbulent kinetic energy when the interface experiences compression. Additionally, the surface tension force is found to generate strong vortical motions close to the interface through the baroclinic torque effects. There is also an increase in strain rate and the viscous dissipation rate of turbulent kinetic energy in the interface region. The effect of interface on the surrounding turbulence appears primarily in the direction perpendicular to the interface. Analysis of the vorticity and kinetic energy equations indicates that the turbulence-interface interactions are strongly dependent on the fluids’ density ratio and the Weber number.

VL - 21 IS - 9 ER - TY - CONF T1 - Filtered Mass Density Function for Numerical Simulations of Spray Combustion T2 - 46th AIAA Aerospace Sciences Meeting and Exhibit Y1 - 2008 A1 - Li, Z. A1 - Jaberi, F.A. A1 - Yaldizli, M. AB -This paper briefly describes our recent efforts on the modeling and numerical simulations of two-phase turbulent reacting flows in realistic combustion systems with a new large-eddy simulation (LES) model. The model is constructed based on the two-phase extension of scalar filtered mass density function (FMDF) and a Lagrangian-Eulerian- Lagrangian mathematical/numerical methodology. In this methodology, the “resolved” fluid velocity field is obtained by solving the filtered form of the compressible Navier-Stokes equations with a high-order finite difference scheme. The liquid (droplet) phase and scalar (temperature and species mass fractions) fields are both obtained by stochastic Lagrangian models. There are two-way interactions between the phases and all the Eulerian and Lagrangian fields. The LES/FMDF is used for systematic analysis of turbulent combustion in the spray-controlled dump combustor and double-swirl spray burner for various flow and spray parameters. The effects of fuel type, spray angle, mass loading ratio, droplet size distribution, fuel/air composition, wall, and inflow/outflow conditions on the combustion are investigated. It has been found that the main features of the turbulence and combustion are modified by changing the inflow/outflow conditions. The LES/FMDF results also confirm the significance of the spray parameters.

JF - 46th AIAA Aerospace Sciences Meeting and Exhibit PB - AIAA CY - Reno, Nevada ER - TY - JOUR T1 - A Hybrid Langrangian-Eulerian Particle-Level Set Method for numerical Simulations of Two-Fluid Turbulent Flows JF - International Journal for Numerical Methods in Fluids Y1 - 2008 A1 - Li, Z. A1 - Jaberi, F.A. A1 - Shih, T. I-P. KW - two-fluid turbulent flows; particle-level set method; interface tracking AB -A coupled Lagrangian interface-tracking and Eulerian level set (LS) method is developed and implemented for numerical simulations of two-fluid flows. In this method, the interface is identified based on the locations of notional particles and the geometrical information concerning the interface and fluid properties, such as density and viscosity, are obtained from the LS function. The LS function maintains a signed distance function without an auxiliary equation via the particle-based Lagrangian re-initialization technique. To assess the new hybrid method, numerical simulations of several ‘standard interface-moving’ problems and two-fluid laminar and turbulent flows are conducted. The numerical results are evaluated by monitoring the mass conservation, the turbulence energy spectral density function and the consistency between Eulerian and Lagrangian components. The results of our analysis indicate that the hybrid particle-level set method can handle interfaces with complex shape change, and can accurately predict the interface values without any significant (unphysical) mass loss or gain, even in a turbulent flow. The results obtained for isotropic turbulence by the new particle-level set method are validated by comparison with those obtained by the ‘zero Mach number’, variable-density method. For the cases with small thermal/mass diffusivity, both methods are found to generate similar results. Analysis of the vorticity and energy equations indicates that the destabilization effect of turbulence and the stability effect of surface tension on the interface motion are strongly dependent on the density and viscosity ratios of the fluids. Copyright q 2007 John Wiley & Sons, Ltd.

VL - 56 IS - 12 ER - TY - JOUR T1 - The influence of cluster emission and the symmetry energy on neutron-proton spectral double ratios JF - Physics Letters B Y1 - 2008 A1 - Yingxun Zhang A1 - P. Danielewicz A1 - M. Famiano A1 - Li, Z. A1 - W. G. Lynch A1 - M. B. Tsang AB -The emissions of neutrons, protons and bound clusters from central {124Sn} + {124Sn} and {112Sn} + {112Sn} collisions are simulated using the Improved Quantum Molecular Dynamics model for two different density-dependent symmetry-energy functions. The calculated neutron-proton spectral double ratios for these two systems are sensitive to the density dependence of the symmetry energy, consistent with previous work. Cluster emission increases the double ratios in the low energy region relative to values calculated in a coalescence-invariant approach. To circumvent uncertainties in cluster production and secondary decays, it is important to have more accurate measurements of the neutron-proton ratios at higher energies in the center of mass system, where the influence of such effects is reduced.

VL - 664 ER - TY - CONF T1 - Large Eddy Simulations of Two-Phase Turbulent Reacting Flows T2 - 46TH AIAA Aerospace Sciences Meeting and Exhibit Y1 - 2008 A1 - Jaberi, F.A. A1 - Li, Z. JF - 46TH AIAA Aerospace Sciences Meeting and Exhibit PB - AMERICAN INSTITUTE OF AERONAUTICS AND ASTRONAUTICS CY - Reno, Nevada ER - TY - CONF T1 - Filtered Mass Density Function for Numerical Simulations of Spray Combustion T2 - 46th AIAA Aerospace Sciences Meeting and Exhibit Y1 - 2007 A1 - Yaldizli, M. A1 - Li, Z. A1 - Jaberi, F.A. AB -This paper briefly describes our recent efforts on the modeling and numerical simulations of two-phase turbulent reacting flows in realistic combustion systems with a new large-eddy simulation (LES) model. The model is constructed based on the two-phase extension of scalar filtered mass density function (FMDF) and a Lagrangian-Eulerian- Lagrangian mathematical/numerical methodology. In this methodology, the “resolved” fluid velocity field is obtained by solving the filtered form of the compressible Navier-Stokes equations with a high-order finite difference scheme. The liquid (droplet) phase and scalar (temperature and species mass fractions) fields are both obtained by stochastic Lagrangian models. There are two-way interactions between the phases and all the Eulerian and Lagrangian fields. The LES/FMDF is used for systematic analysis of turbulent combustion in the spray-controlled dump combustor and double-swirl spray burner for various flow and spray parameters. The effects of fuel type, spray angle, mass loading ratio, droplet size distribution, fuel/air composition, wall, and inflow/outflow conditions on the combustion are investigated. It has been found that the main features of the turbulence and combustion are modified by changing the inflow/outflow conditions. The LES/FMDF results also confirm the significance of the spray parameters.

JF - 46th AIAA Aerospace Sciences Meeting and Exhibit PB - AIAA CY - Reno, Nevada ER - TY - CONF T1 - A New Model for Large Eddy Simulations of Multi-Phase Turbulent Combustion T2 - Proceedings of the 43rd AIAA/ASME/SAI/ASEE Joint Propulsion Conference Y1 - 2007 A1 - Yaldizli, M. A1 - Li, Z. A1 - J.A. Jaberi AB -Numerical simulations of a spray-controlled lean premixed dump combustor are con- ducted via a two-phase large eddy simulation (LES) methodology. In this methodology, the velocity field is obtained by a high-order finite difference method. The subgrid gas- liquid combustion closure is based on the two-phase filtered mass density function (FMDF) method and the spray is modeled with a Lagrangian scheme. The effects of spray, fuel/air composition, and inflow/outflow conditions on the combustion are investigated. It has been found that the main features of the turbulence and combustion inside the dump combustor are very differently modified by the spray for different spray parameters. The LES/FMDF results also indicate the significance of the inflow and outflow conditions.

JF - Proceedings of the 43rd AIAA/ASME/SAI/ASEE Joint Propulsion Conference PB - AIAA/ASME/SAI/ASEE CY - Cincinnati, Ohio ER - TY - Generic T1 - Numerical Simulations of Two-Phase Turbulent Combustion in Spray Burners T2 - ASME Conference Proceedings, Computers and Information in Engineering Conference Y1 - 2007 A1 - Li, Z. A1 - Yaldizli, M. A1 - Jaberi, F.A. AB -The complex interactions among turbulence, combustion and spray in liquid-fuel burners are modeled and simulated via a new two-phase Lagrangian-Eulerian-Lagrangian large eddy simulation (LES) methodology. In this methodology, the spray is modeled with a Lagrangian mathematical/computational method which allows two-way mass, momentum and energy coupling between phases. The subgrid gas-liquid combustion is based on the two-phase filtered mass density function (FMDF) that has several advantages over “conventional” two-phase combustion models. The LES/FMDF is employed in conjunction with non-equilibrium reaction and droplet models. Simulations of turbulent combustion in a spray-controlled double-swirl burner are conducted via LES/FMDF. The generated results are used for better understanding of spray combustion in realistic turbulent flow configurations. The effects of spray angle, mass loading ratio, fuel type, droplet size distribution, wall and inflow/outflow conditions on the flow and combustion are investigated. The LES/FMDF predictions are shown to be consistent with the experimental results.

JF - ASME Conference Proceedings, Computers and Information in Engineering Conference PB - ASME CY - Las Vegas, Nevada SN - 0-7918-4803-5 ER -