Steam may be generated using an apparatus that creates shockwaves in a supersonic gaseous vortex. The apparatus includes a chamber configured to receive, pressurize, and heat fuel gas and/or oxygen containing gas. One or more inlets positioned at a first end of the chamber and arranged to emit fuel gas, oxygen containing gas, or water as one or more jet streams tangentially to an internal surface of the chamber may create a gaseous vortex rotating about a longitudinal axis within the chamber. The inlet(s) may include one or more inlet nozzles structured to accelerate the one or more fuel gas, oxygen-containing gas, or water to a supersonic velocity and adjustably control frequency of shockwaves emitted into the gaseous vortex. Water can be injected into the chamber to stabilize internal chamber temperature where it may be converted into steam. An outlet may be configured to emit product gases and/or steam from the chamber.