Cremer, M
1992
Effects of Turbulence Length Scale Distribution on Scalar Mixing in Homogeneous Turbulent Flow
McMurtry, P.A.; Cremer, M. and Kerstein, A.R.
APS Division of Fluid Dynamics, Tallahassee, FL, November 1992. Funded by US Department of Energy and ACERC.
The linear eddy-mixing model is used to study effects of the turbulence length scale distribution on the transient evolution of a passive scalar in a statistically steady, homogeneous turbulent flow. Model simulations are carried out using length-scale distributions that are respectively wide-banded and narrow-banded, representing mixing at high and low Reynolds number. The two cases found to exhibit qualitative differences in mixing behavior. The low Reynolds number linear eddy results exhibit behaviors not seen in DNS studies, such as trimodal transient scalar pdf's. It is found that asymptotically non-Gaussian scalar pdf's may be obtained both for high and low Reynolds number cases.
The sensitivity of mixing behavior to flow bandwidth is interpreted mechanistically. In particular, a geometrical representation of scalar fields in turbulence based on a lamellar picture is shown to exhibit analogous sensitivity to bandwidth. Under assumptions corresponding to narrow-band mixing, this "Clipped laminar profile" representation reproduces the pdf evolution previously obtained using mapping closure. Thus, the mapping closure solution as well as the DNS is found to be narrow-band in character. This interference is consistent with the absence of length-scale considerations in the mapping closure analysis, and with the good agreement of the mapping closure solution with DNS results.
Cremer, M
1992
Effects of Turbulence Length Scale Distribution on Scalar Mixing in Homogeneous Turbulent Flow
McMurtry, P.A.; Cremer, M. and Kerstein, A.R.
APS Division of Fluid Dynamics, Tallahassee, FL, November 1992. Funded by US Department of Energy and ACERC.
The linear eddy-mixing model is used to study effects of the turbulence length scale distribution on the transient evolution of a passive scalar in a statistically steady, homogeneous turbulent flow. Model simulations are carried out using length-scale distributions that are respectively wide-banded and narrow-banded, representing mixing at high and low Reynolds number. The two cases found to exhibit qualitative differences in mixing behavior. The low Reynolds number linear eddy results exhibit behaviors not seen in DNS studies, such as trimodal transient scalar pdf's. It is found that asymptotically non-Gaussian scalar pdf's may be obtained both for high and low Reynolds number cases.
The sensitivity of mixing behavior to flow bandwidth is interpreted mechanistically. In particular, a geometrical representation of scalar fields in turbulence based on a lamellar picture is shown to exhibit analogous sensitivity to bandwidth. Under assumptions corresponding to narrow-band mixing, this "Clipped laminar profile" representation reproduces the pdf evolution previously obtained using mapping closure. Thus, the mapping closure solution as well as the DNS is found to be narrow-band in character. This interference is consistent with the absence of length-scale considerations in the mapping closure analysis, and with the good agreement of the mapping closure solution with DNS results.