N. Swaminathan et Rw. Bilger, Scalar dissipation, diffusion and dilatation in turbulent H-2-air premixedflames with complex chemistry, COMB TH MOD, 5(3), 2001, pp. 429-446
Characteristics of the scalar dissipation rate, N, of a progress variable,
c, based on temperature in turbulent H-2-air premixed flames are studied vi
a direct numerical simulation with complex chemical kinetics for a range of
flow/flame conditions (Baum et al 1994 J. Fluid Mech. 2811). The flames ar
e in the usually designated wrinkled-flamelet and well-stirred reactor regi
mes. The normalized conditional average, N-zeta(+) is observed to be higher
than the corresponding planar laminar value because of strain thinning and
the augmentation of laminar transport by turbulence within the flame front
. Also, NI:varies strongly across the flame-brush when u ' /S-l is high. N
has a log-normal distribution when u ' /S-l is small and has a long negativ
e tail for cases where u'/S-l is large. In the flame with phi = 0.5, (N) ov
er tilde (+)(zeta)/(N) over tilde (+) shows some sensitivity to P-zeta and
the sensitivity seems to be weak in a phi = 0.35 flame. The effect of turbu
lence on (cb, I) is observed to be marginal. The conditional diffusion and
the conditional dilatation, < del .u \ zeta >, peak on the unburnt side of
the flame-front and are higher than the corresponding laminar flame values
in all cases. The inter-relationship among the conditional dissipation, dif
fusion, dilatation and velocity is discussed. A model for u(zeta) obtained
from the conditional dilatation is found not to perform as well as a linear
model. The above results are limited, however, because, the flow field is
two dimensional, hydrogen is used as the fuel, the range of dynamic length
scales is small and the sample size is small.