Large-Eddy Simulation of Swirling Turbulent Jet Flows in Absence of Vortex Breakdown

Abstract

This paper reports the results of numerical investigations of swirling turbulent jet flows by large-eddy simulation. Reynolds-averaged Navier–Stokes simulations are used to generate mean inflow data. Fluctuations are added to the profiles of themeans to produce instantaneous inflowdata.The instantaneous inflowdata are correlated such that the characteristic length and time scales of inflowing turbulent eddies are consistent with the corresponding Reynolds-averaged Navier–Stokes profiles imposed at the inlet. The resulting large-eddy simulation method is validated against experimental data of both swirling and nonswirling turbulent jets. The application of the validated large-eddy simulation method to studies of the mechanism of swirl effects shows the following. Swirl breaks apart the typical ring structures of nonswirling turbulent jets into twomodes: a helical mode and streamwise braid structures. The interaction of these two modes generates unorganized turbulence that enhances the turbulent mixing. An analysis of the mixing enhancement by swirl shows a significant increase of the turbulent mixing efficiency of scalars with the swirl number (of up to 21.7 % for the cases considered). Nomenclature aij = matrix formed by eigenvectors of the Reynolds stress ij (i, j 1, 3) Ck = dynamic kinetic energy model stress model parameter Cs = Smagorinsky constant ck = forcing model parameters (k 1, 3), see Eq. (7) D = nozzle exit diameter D0 = nozzle inlet diameter I = intensity of segregation, I 2=1 k = turbulent kinetic energy kni = random numbers (i, n 1, 3), kni 2 N0; 12 ksgs = subgrid-scale kinetic energy k0 = normalization variable for k, U