An airflow control system for a combined cycle turbomachine system in accordance with an embodiment includes: an airflow generation system for attachment to a rotatable shaft of a gas turbine system, the airflow generation system drawing in an excess flow of air through an air intake section; a mixing area for receiving an exhaust gas stream produced by the gas turbine system; an air extraction system for extracting a first portion of the excess flow of air to provide bypass air, and for diverting the bypass air into the mixing area to reduce a temperature of the exhaust gas stream; and an airflow regulation system for diverting a second portion of the excess flow of air into the compressor component and, in response to an under-frequency grid event, for increasing the second portion of the excess flow of air diverted into the compressor component.