A turbine airfoil for relative movement in an ambient fluid, comprising: a main spar having a cross-sectional shape of an airfoil with a top side wall and a bottom side wall, a leading edge, a trailing edge, and a camber line extending from the leading edge to the trailing edge, the movement of the airfoil relative to the ambient fluid such that the ambient fluid flows over the main spar in a downstream direction from the leading edge to the trailing edge, and whereby a side wall of the main spar comprises sequentially from the leading edge to the trailing edge a first hill formation and a second hill formation, each hill formation comprising a first region of progressively increasing distance from the camber line, a second region of progressively decreasing distance from the camber line, and a crest at an interface between the first and second regions, whereby, the first region of the first hill formation is operable to interact with the ambient fluid to accelerate it from a high subsonic relative speed to a sonic relative speed over the crest of the first hill formation and supersonic speed after the crest of the first hill formation; the first region of the second hill formation is operable to interact with the ambient fluid to decelerate and maintain the ambient fluid at supersonic relative speed over the crest of the second hill formation, and characterised in that the turbine airfoil comprises discharge means operable to discharge fluid outwardly into the ambient fluid flowing over the main spar, whereby the discharge means discharges an evaporative fluid to evaporate into the ambient fluid before condensation onset in the second region of the first hill formation, said second region of the first hill formation interacts with the ambient fluid to accelerate the ambient fluid from supersonic relative speed to higher supersonic relative speed; and the discharge means is further operable to discharge a condensing fluid to capture or nucleate condensation shock in the ambient fluid flowing over the second region of the second hill formation which decelerate the ambient fluid from supersonic relative speed to subsonic relative speed and generate a pressure on the side wall and thereby impart thrust on the air foil. a main spar having a cross-sectional shape of an airfoil with a top side wall and a bottom side wall, a leading edge, a trailing edge, and a camber line extending from the leading edge to the trailing edge, the movement of the airfoil relative to the ambient fluid such that the ambient fluid flows over the main spar in a downstream direction from the leading edge to the trailing edge, and whereby a side wall of the main spar comprises sequentially from the leading edge to the trailing edge a first hill formation and a second hill formation, each hill formation comprising a first region of progressively increasing distance from the camber line, a second region of progressively decreasing distance from the camber line, and a crest at an interface between the first and second regions, whereby, the first region of the first hill formation is operable to interact with the ambient fluid to accelerate it from a high subsonic relative speed to a sonic relative speed over the crest of the first hill formation and supersonic speed after the crest of the first hill formation; the first region of the second hill formation is operable to interact with the ambient fluid to decelerate and maintain the ambient fluid at supersonic relative speed over the crest of the second hill formation, and characterised in that the turbine airfoil comprises discharge means operable to discharge fluid outwardly into the ambient fluid flowing over the main spar, whereby the discharge means discharges an evaporative fluid to evaporate into the ambient fluid before condensation onset in the second region of the first hill formation, said second region of the first hill formation interacts with the ambient fluid to accelerate the ambient fluid from supersonic relative speed to higher supersonic relative speed; and the discharge means is further operable to discharge a condensing fluid to capture or nucleate condensation shock in the ambient fluid flowing over the second region of the second hill formation which decelerate the ambient fluid from supersonic relative speed to subsonic relative speed and generate a pressure on the side wall and thereby impart thrust on the air foil.