A method for assembling a gas turbine engine includes coupling a transition piece between a combustor liner and a nozzle assembly. The method also includes extending a first portion of a flow sleeve from the transition piece about at least a portion of the combustor liner. The method further includes coupling a second portion of the flow sleeve to the first portion of the flow sleeve such that the flow sleeve second portion extends from the flow sleeve first portion and at least partially about at least a portion of the transition piece. The flow sleeve second portion includes a scoop that cooperates with the transition piece to at least partially define a unitary cooling air passage that includes a unitary scoop-shaped opening. The scoop is oriented to introduce a substantially uniform cooling air flow to the transition piece.