Experimental study of velocity-scalar filtered joint density function for LES of turbulent combustion

Abstract The velocity-scalar filtered joint density function (FJDF) used in large eddy simulation (LES) of turbulent combustion is experimentally studied. Measurements are made in the fully developed region of an axisymmetric turbulent jet using an array consisting of three X-wires and resistance-wire temperature sensors. Filtering in the cross-stream and streamwise directions is realized by using the array and by invoking Taylor’s hypothesis, respectively. The means of the FJDF conditional on the subgrid-scale (SGS) turbulent kinetic energy and the SGS scalar variance at a given location range from close to joint normal to bimodal with the peaks separated in both velocity and scalar spaces, which correspond to qualitatively different mixing regimes. For close to joint normal FJDFs, the SGS fields are well mixed. For bimodal FJDFs, the conditionally filtered scalar diffusion and dissipation strongly depend on the SGS velocity and scalar, consistent with a combination of diffusion layers and plane strain in the SGS fields, which is similar to the counter-flow model for laminar flamelets. The results suggest that in LES, both mixing regimes could potentially be modeled accurately. The velocity field affects the SGS variance and the filtered scalar dissipation rate primarily by changing the degree of nonequilibrium of the SGS scalar and the SGS time scale, respectively. This study further demonstrates the importance of including velocity in mixing models.

[1]  S. Pope,et al.  Direct numerical simulations of the turbulent mixing of a passive scalar , 1988 .

[2]  J. Wyngaard,et al.  Resolvable- and Subgrid-Scale Measurement in the Atmospheric Surface Layer: Technique and Issues , 1998 .

[3]  C. Tong,et al.  On conditional velocity increment statistics , 2003 .

[4]  Galilean invariance of velocity probability density function transport equation , 2003 .

[5]  Stephen B. Pope,et al.  Experimental study of velocity filtered joint density function for large eddy simulation , 2004 .

[6]  J. Wyngaard,et al.  Experimental Study of the Subgrid-Scale Stresses in the Atmospheric Surface Layer , 1998 .

[7]  Chenning Tong,et al.  Experimental investigation of scalar-scalar-dissipation filtered joint density function and its transport equation , 2002 .

[8]  Chenning Tong,et al.  Measurements of conserved scalar filtered density function in a turbulent jet , 2001 .

[9]  S. Pope,et al.  Velocity filtered density function for large eddy simulation of turbulent flows , 2000 .

[10]  Chenning Tong,et al.  Conditionally filtered scalar dissipation, scalar diffusion, and velocity in a turbulent jet , 2002 .

[11]  L. Chua,et al.  Calibration ofX-probes for turbulent flow measurements , 1988 .

[12]  Stephen B. Pope,et al.  Direct numerical simulation of a passive scalar with imposed mean gradient in isotropic turbulence , 1996 .

[13]  Feng Gao,et al.  A large‐eddy simulation scheme for turbulent reacting flows , 1993 .

[14]  R. Schefer,et al.  Mixture fraction field in a turbulent nonreacting propane jet , 2001 .

[15]  N. Peters.  Laminar diffusion flamelet models in non-premixed turbulent combustion , 1984 .

[16]  G. G. Stokes.  "J." , 1890, The New Yale Book of Quotations.

[17]  S. Pope,et al.  Filtered density function for large eddy simulation of turbulent reacting flows , 1998 .

[18]  Stephen B. Pope,et al.  Computations of turbulent combustion: Progress and challenges , 1991 .

[19]  Steven H. Frankel,et al.  Johnson-Edgeworth Translation for Probability Modeling of Binary Scalar Mixing in Turbulent Flows , 1993 .

[20]  S. Pope.  The vanishing effect of molecular diffusivity on turbulent dispersion: implications for turbulent mixing and the scalar flux , 1998, Journal of Fluid Mechanics.

[21]  P. Moin,et al.  A dynamic model for subgrid-scale variance and dissipation rate of a conserved scalar , 1998 .

[22]  S. Pope.  PDF methods for turbulent reactive flows , 1985 .

[23]  R. Chevray,et al.  Probability distributions in a round heated jet , 1975 .