A combustor for a gas turbine engine is disclosed which is able to operate with high combustion efficiency, and low nitrous oxide emissions during gas turbine operations. The combustor consists of a can-type configuration which combusts fuel premixed with air and delivers the hot gases to a turbine. Fuel is premixed with air and is delivered to the combustor with a high degree of swirl motion. This swirling mixture of reactants is conveyed through a flowpath that expands; the mixture reacts, and establishes a central recirculation zone. An imperforate trapped vortex cavity is disposed proximal to the swirler apparatus which provides for a second reaction zone. Fresh fuel/air reactants are exchanged with burned products in the trapped vortex and a pilot flame is established in the trapped cavity. The imperforate trapped cavity is not supplied with either fuel or air, but is cooled on a backside of the cavity with a flow of cooling air. The cooling air is then conveyed to the combustion chamber so as to not interfere with the critical flame holding flow features of the combustor.