CALCULATION OF ISOTHERMAL TURBULENT 3-DIMENSIONAL FREE MULTIJET FLOWS

Numerical predictions of the turbulent three-dimensional isothermal free flow in the near-exit region of an industrial burner model are presented and compared with detailed measurements of mean and turbulent flow fields. The geometrical flow configuration consists of a central axisymmetric jet surrounded by 16 circular jets, simulating the injection of oxygen in practical oxyfuel burners. A numerical procedure is outlined for the calculation of free flows comprising elliptic flow regions. The computational domain is divided into a number of subdomains, and elliptic calculations are performed sequentially in each of the domains, keeping constant the number of grid nodes and allowing radial grid expansion for each domain. By using a higher-order accurate quadratic upstream scheme for convection discretization it was possible to minimize the effect of numerical diffusion. This was confirmed by an error estimation analysis. The predictions of the mean flow characteristics exhibit satisfactory agreement with the experiments. However, the k - epsilon-eddy viscosity model proved to be inadequate for calculating the individual normal stresses around the recirculating region and at the outer jet boundaries where the values were underpredicted. Structure parameters suggest that far from the recirculating region the zones of directional preference decrease with increasing distance from the multijet exit and that the k - epsilon-model eddy viscosity model performs satisfactorily.