A combustor assembly is disclosed. The combustor assembly may include an annular trapped vortex cavity located adjacent to a downstream end of a bundle of air/fuel premixing injection tubes. The annular trapped vortex cavity may include an opening at a radially inner portion of the annular trapped vortex cavity adjacent to the head end of the bundle of premixing tubes. The annular trapped vortex cavity may also include one or more air injection holes and one or more fuel sources disposed about the annular trapped vortex cavity such that the one or more air injection holes and the one or more fuel sources are configured to drive a vortex within the annular trapped vortex cavity.