A simple-cycle gas turbine system comprising an exhaust processing system configured to process exhaust gas generated by a gas turbine engine , wherein the exhaust processing system comprises a selective catalytic reduction (SCR) system configured to reduce a level of nitrogen oxides (NO x ) within the exhaust gas , the simple-cycle gas turbine system comprising: an injection system comprising a plurality of injection tubes configured to inject a fluid comprising cooling air into a transition duct of the exhaust processing system , and characterized in that the simple-cycle gas turbine system further comprises: a mixing system positioned adjacent to the plurality of injection tubes and within the exhaust processing system , wherein the mixing system comprises a mixing module having a plurality of turbulators configured to swirl the fluidand the exhaust gas in a first swirl direction to encourage turbulent flow along a longitudinal axis of the exhaust processing system and thereby facilitate mixing and heat exchange between the fluid and the exhaust gas , wherein the mixing module has a centerline axis crosswise to the longitudinal axis and a dimension perpendicular to the centerline axis and the longitudinal axis ; wherein the mixing system is disposed within the transition duct and wherein the transition duct is fluidly coupled to a turbine of the gas turbine engine and is positioned upstream of an exhaust duct containing a catalyst of the SCR system , wherein each of the plurality of turbulators comprises a plurality of fins radially extending from a center of the turbulator, wherein a fin of the plurality of fins is configured to rotate about the longitudinal axis of the exhaust processing system in the first swirl direction , and wherein the plurality of turbulators are disposed along the dimension of the mixing module at various vertical and horizontal positions relative to the centerline axis of the mixing module . a mixing system positioned adjacent to the plurality of injection tubes and within the exhaust processing system , wherein the mixing system comprises a mixing module having a plurality of turbulators configured to swirl the fluidand the exhaust gas in a first swirl direction to encourage turbulent flow along a longitudinal axis of the exhaust processing system and thereby facilitate mixing and heat exchange between the fluid and the exhaust gas , wherein the mixing module has a centerline axis crosswise to the longitudinal axis and a dimension perpendicular to the centerline axis and the longitudinal axis ; wherein the mixing system is disposed within the transition duct and wherein the transition duct is fluidly coupled to a turbine of the gas turbine engine and is positioned upstream of an exhaust duct containing a catalyst of the SCR system , wherein each of the plurality of turbulators comprises a plurality of fins radially extending from a center of the turbulator, wherein a fin of the plurality of fins is configured to rotate about the longitudinal axis of the exhaust processing system in the first swirl direction , and wherein the plurality of turbulators are disposed along the dimension of the mixing module at various vertical and horizontal positions relative to the centerline axis of the mixing module . <EOS>