The three-dimensional numerical aerodynamics of a movable block burner

Abstract

Abstract. Computational fluid-dynamics techniques were employed to study the aerodynamics of a movable block swirl burner, developed by the International Flame Research Foundation, IFRF, which is characterized by the ability to adjust continuously and dynamically the intensity of the swirl by means of the simultaneous rotation of eight movable blocks, inserted between eight fixed blocks. Five three-dimensional grids were constructed for the burner, corresponding to five positions of the movable blocks. Both the k-ε and RNG k-ε isotropic turbulence models were applied. Only the latter described the existence of a central reverse flow along the annular duct. The employment of first-order and second-order interpolation schemes provided distinct results. The later provided results closer to the experimental tests. The swirl number decayed in the annular duct. The predicted swirl numbers for this movable block swirl burner were lower than the corresponding IFRF's experimental data, as was also observed by other researchers. This gave rise to the suspicion of some possible measurement error in the IFRF's experiments. On the other hand, the lack of agreement between the experimental data and the predictions regarding swirling flows could be attributed to the possible inadequate performance of the k-ε model, as a consequence of its isotropic approximation. Still another possible explanation could be a phenomenon called bifurcation, in which one given swirl number can be associated with two distinct conditions of steady state flow. In addition, this complex flows requires a scrupulous development of the grids for the boundary condition and the employment of adequate interpolation schemes.

A numerical investigation of the aerodynamics of a furnace with a movable block burner

“…The comparison of the velocity distribution in the burner and quarl of the furnace, obtained in the present study, with the results of Fudihara et al, 2003, for the array burner plus quarl, where the mass flow rate boundary condition was applied at the quarl exit, showed analogous results for ξ/ξ m = 0.75 and 1.0. Unlike the previous study, however, no numerical convergence was found for ξ/ξ m = 0.5, probably due to the very unstable flow verified in the combustion chamber, owing to the low swirl intensity.…”

“…The burner in this study was the same as that analyzed by Fudihara et al, 2003 with eight movable blocks located in between eight fixed blocks. The quarl used corresponded to Nozzle 2 of the experiments performed in the Delft furnace, with a quarl half expansion angle, γ, of 35°.…”

“…which are functions of the tangential velocity, w, of the axial velocity, u, and of the static pressure, P. A modified swirl number S' is defined by removing the term containing the static pressure from G u , as in Fudihara et al,2003 andin Widmann et al,2000, who observed that S' was very different from S.…”

“…The aerodynamics of a movable block-MBburner, developed by the International Flame Research Foundation -IFRF ( Wu and Fricker, 1971) was numerically investigated by Fudihara et al in 2003. Five numerical grids, corresponding to five positions of the movable blocks were developed.…”

“…In the present study, the aerodynamics of the Delft-IFRF vertical furnace was computationally investigated by applying the finite volume method by means of the CFX-4 simulator and adopting the RNG k-ε turbulence model, due to its greater reliability as discussed below, and its capacity to predict a reverse flow for an intermediary swirl, not only in the quarl, as with the k-ε model, but also in the burner annular section (Fudihara et al, 2003). The aerodynamics of the furnace was obtained avoiding the intermediary determination of the burner/quarl outlet velocity profiles to serve as the inlet velocity profiles in the combustion chamber.…”