A system comprising: a gas turbine comprising a main flow path, a plurality of turbine blades and at least one shaft disposed along the main flow path, at least one flow control area disposed along the main flow path, and at least one fluid injection port (83, 100) fluidly coupled to the main flow path; and a fluid supply system fluidly coupled to the at least one fluid injection port (83, 100), wherein the fluid supply system is configured to supply a fluid to the at least one fluid injection port (83, 100) to adjust an effective area of the at least one flow control area; characterized in that: the fluid supply comprises a steam supply, an inert gas supply, a carbon dioxide supply, or a combination thereof, wherein waste heat from exhaust gas, or from other waste heat sources within the system is utilized to increase a temperature and/or pressure of the supply of fluid to generate a pressurized fluid; and the system comprises a controller having a memory storing instructions to control the supply of the fluid to the at least one fluid injection port (83, 100) to adjust the effective area of the at least one flow control area; wherein the controller has instructions to adjust the supply of the fluid to adjust the effective area to vary a flow of working fluid through the at least one flow control area of the main flow path. a gas turbine comprising a main flow path, a plurality of turbine blades and at least one shaft disposed along the main flow path, at least one flow control area disposed along the main flow path, and at least one fluid injection port (83, 100) fluidly coupled to the main flow path; and a fluid supply system fluidly coupled to the at least one fluid injection port (83, 100), wherein the fluid supply system is configured to supply a fluid to the at least one fluid injection port (83, 100) to adjust an effective area of the at least one flow control area; characterized in that: the fluid supply comprises a steam supply, an inert gas supply, a carbon dioxide supply, or a combination thereof, wherein waste heat from exhaust gas, or from other waste heat sources within the system is utilized to increase a temperature and/or pressure of the supply of fluid to generate a pressurized fluid; and the system comprises a controller having a memory storing instructions to control the supply of the fluid to the at least one fluid injection port (83, 100) to adjust the effective area of the at least one flow control area; wherein the controller has instructions to adjust the supply of the fluid to adjust the effective area to vary a flow of working fluid through the at least one flow control area of the main flow path. the fluid supply comprises a steam supply, an inert gas supply, a carbon dioxide supply, or a combination thereof, wherein waste heat from exhaust gas, or from other waste heat sources within the system is utilized to increase a temperature and/or pressure of the supply of fluid to generate a pressurized fluid; and the system comprises a controller having a memory storing instructions to control the supply of the fluid to the at least one fluid injection port (83, 100) to adjust the effective area of the at least one flow control area; wherein the controller has instructions to adjust the supply of the fluid to adjust the effective area to vary a flow of working fluid through the at least one flow control area of the main flow path.