Can-annular combustor comprising: a combustor liner; a flow sleeve at least partially circumferentially surrounding the combustor liner, such that an annulus is defined between the liner and the flow sleeve; a source of air being a first fluid, a source of air being a second fluid and a source of gaseous or liquid fuel being a third fluid; and a fluid mixing apparatus configured to radially inject a fuel/air mixture into the combustor liner as part of an axially staged fuel delivery system, the fluid mixing apparatus comprising: a first annular wall defining a first inlet, a first outlet, and a first passage extending between the first inlet and the first outlet, the first passage in fluid communication with the source of the first fluid at a first pressure; a second wall defining a first plenum in fluid communication with the source of the second fluid at a second pressure, wherein the combustor is configured such that the first pressure is less than the second pressure; a third wall defining a second plenum, wherein the third wall is at least partially surrounded by the second wall; a mixing conduit extending through the second plenum and fluidly connecting the first plenum and the first passage; a tube disposed upstream of the first inlet, the tube in fluid communication with the source of the third fluid and having an opening to distribute the third fluid from the tube; wherein the fluid mixing apparatus is configured such that a flow of the second fluid through the mixing conduit draws a flow of the first fluid and a flow of the third fluid into and through the first passage to produce a mixture of the first fluid, the second fluid, and the third fluid. a combustor liner; a flow sleeve at least partially circumferentially surrounding the combustor liner, such that an annulus is defined between the liner and the flow sleeve; a source of air being a first fluid, a source of air being a second fluid and a source of gaseous or liquid fuel being a third fluid; and a fluid mixing apparatus configured to radially inject a fuel/air mixture into the combustor liner as part of an axially staged fuel delivery system, the fluid mixing apparatus comprising: a first annular wall defining a first inlet, a first outlet, and a first passage extending between the first inlet and the first outlet, the first passage in fluid communication with the source of the first fluid at a first pressure; a second wall defining a first plenum in fluid communication with the source of the second fluid at a second pressure, wherein the combustor is configured such that the first pressure is less than the second pressure; a third wall defining a second plenum, wherein the third wall is at least partially surrounded by the second wall; a mixing conduit extending through the second plenum and fluidly connecting the first plenum and the first passage; a tube disposed upstream of the first inlet, the tube in fluid communication with the source of the third fluid and having an opening to distribute the third fluid from the tube; wherein the fluid mixing apparatus is configured such that a flow of the second fluid through the mixing conduit draws a flow of the first fluid and a flow of the third fluid into and through the first passage to produce a mixture of the first fluid, the second fluid, and the third fluid. a first annular wall defining a first inlet, a first outlet, and a first passage extending between the first inlet and the first outlet, the first passage in fluid communication with the source of the first fluid at a first pressure; a second wall defining a first plenum in fluid communication with the source of the second fluid at a second pressure, wherein the combustor is configured such that the first pressure is less than the second pressure; a third wall defining a second plenum, wherein the third wall is at least partially surrounded by the second wall; a mixing conduit extending through the second plenum and fluidly connecting the first plenum and the first passage; a tube disposed upstream of the first inlet, the tube in fluid communication with the source of the third fluid and having an opening to distribute the third fluid from the tube; wherein the fluid mixing apparatus is configured such that a flow of the second fluid through the mixing conduit draws a flow of the first fluid and a flow of the third fluid into and through the first passage to produce a mixture of the first fluid, the second fluid, and the third fluid.