ON THE ALIGNMENT OF THE ALPHA-STRAIN AND VORTICITY IN TURBULENT NONPREMIXED FLAMES

Evolution of the strain and vorticity fields in a turbulent nonpremixe d flame is examined using direct numerical simulations. The results sh ow that the how is strain dominated for both the buoyant and nonbuoyan t cases. The evolution equation for the cosine of the angle between th e vorticity and the principal strain directions is derived. It is show n that the strain dominance causes vorticity to align with the alpha-s train, in contrast to the beta-strain/vorticity alignment in constant density flows. The divergence term in the evolution equation changes t he time-scale of the process. The rotation term (due to the strain coo rdinates rotation) and the baroclinic term reduce the vorticity/alpha- strain alignment. (C) 1996 American Institute of Physics.