Reaction in a scalar mixing layer

Abstract

Reaction in a scalar mixing layer in grid-generated turbulence is studied experimentally by doping half of the flow with nitric oxide and the other half with ozone. The flow conditions and concentrations are such that the chemical reaction is passive and the flow and chemical timescales are of the same order. Conserved scalar theory for such flows is outlined and further developed; it is used as a basis for presentation of the experimental results. Continuous measurements of concentration are limited in their spatial and temporal resolution but capture sufficient of their spectra for adequate second-order correlations to be made. Two components of velocity have been measured simultaneously with hot-wire anemometry. Conserved scalar mixing results, deduced from reacting and non-reacting measurements of concentration, show the independence of concentration level and concentration ratio expected for passive reacting flow. The results are subject to several limitations due to the necessary experimental compromises, but they agree generally with measurements made in thermal mixing layers. Reactive scalar statistics are consistent with the realizability constraints obtainable from conserved scalar theory where such constraints apply, and otherwise are generally found to lie between the conserved scalar theory limits for frozen and very fast chemistry. It is suggested that Toor's (1969) closure for the mean chemical reaction rate could be improved by interpolating between the frozen and equilibrium values for the covariance. The turbulent fluxes of the reactive scalars are found to approximately obey the gradient model but the value of the diffusivity is found to depend on the Damköhler number.

Hybrid binomial Langevin-multiple mapping conditioning modeling of a reacting mixing layer

“…28,29 In the discussion below, the streamwise direction is denoted by x 1 , while the direction across the mixing layer is with negligible heat release due to the low concentrations.…”

“…However, the trend for the standard deviation to increase with Damköhler number is reproduced. Bilger et al 28 noted that all measurements were made in the initial region x / M Ͻ 100, hence the potential for variability in the statistics due to the Reynolds number and initial conditions. The skewness ͑Fig.…”

Conditional statistics for passive-scalar mixing in a confined rectangular turbulent jet

“…11 Tavoularis and Corrsin 12 confirmed this assumption in their experimental investigation of homogeneous turbulent shear flow with a uniform mean scalar gradient. However, Sreenivasan and Antonia 13 and Bilger et al 14 found that for inhomogeneous turbulent flows the joint PDF between the velocity and the conserved scalar is generally not Gaussian. Li and Bilger 11 compared their experimental data with the conditional mean transverse velocity predicted by the linear model, and found that the linear model produces large errors when ͉ − ͗ ͉͘ is large.…”

Evaluation of Closure Models of Turbulent Diffusion Flames

“…Specifically we have addressed the subgrid-scale modeling of the filtered mixture fraction, its second moment, and its dissipation rate (de Bruyn Kops et al, 1998), quantities which are called for in the subgrid-scale modeling procedure. To test the model further, we have recently performed very high resolution direct numerical simulations of the nitric oxide/ozone experiments of Bilger et al (1991) de Bruyn Kops and Riley, 2000b); the results are being used for further validation of the subgrid-scale model. The general result of our validation studies to date is that the model works very well for the range of problems that it was intended, i.e., continuous burning, non-premixed, somewhat high Damkohler number cases.…”