Vortex generators in lean-premix combustion

A novel fuel-air mixing technique on the basis of vortex generators has bee n developed and successfully implemented in the worlds first lean-premix re heat combustor of ABB's GT24/GT26 series industrial gas turbines. This tech nique uses a special arrangement of delta-wing type vortex generators to ac hieve rapid mixing through longitudinal vortices, which produce low pressur e drop and no recirculation zones along the mixing section. In this paper, after a short introduction to the topic, the motivation for utilizing vorte x generators and the main considerations in their design are explained. A d etailed analysis of the flow field pressure drop and the strength of the vo rtices generated by a single vortex generator are presented as one of the t hree main geometrical parameters is varied. The results obtained through wa ter model tests indicate that an optimum vortex generator geometry exists, which produces the maximum circulation at a relatively low pressure drop pr ice. Moreover, the axial velocity distribution along the mixing section sta ys uniform enough to assure flash-back free operation despite the elevated inlet temperatures encountered in a reheat combustor. After selecting this optimized geometry, the process of the arrangement of multiple vortex gener ators in art annular combustor segment is described. The optimum arrangemen t presented here is suitable both for gaseous and liquid fuel injection, si nce it requires only one injection location per combustor segment.