Aerofoil module for propeller and turbine blades with passive variable air passage cover

An aerofoil module for use in a blade of a propeller or turbine, the aerofoil module comprising:

• a body comprising a suction surface and a pressure surface;
• an air passage traversing the body, wherein the air passage has an entrance opening on the pressure surface and an exit opening on the suction surface;
• a cover configured to cover a variable portion of the cross-section of the air passage;
• and
• a mechanism configured to vary the portion of the cross-section of the air passage covered by the cover, wherein the mechanism is configured to react passively to the oncoming air speed of oncoming air in the axial direction of the propeller or turbine;
• wherein the mechanism is configured to vary the portion of the cross-section of the air passage covered by the cover such that the cover covers a smaller portion of the cross-section of the air passage in response to a higher oncoming air speed, and covers a larger portion of the cross-section of the air passage in response to a lower oncoming air speed;
• and
• wherein the mechanism is configured to react passively to a thrust from the oncoming air acting on the pressure surface, such that the cover covers a smaller portion of the cross-section of the air passage in response to a higher thrust, and covers a larger portion of the cross-section of the air passage in response to a lower thrust.

A propeller or turbine blade comprising:

• a body comprising a suction surface and a pressure surface;
• an air passage traversing the body, wherein the air passage comprises an elongate slot arranged substantially in a spanwise direction of the aerofoil module, and wherein the air passage has an entrance opening on the pressure surface and an exit opening on the suction surface;
• a cover configured to cover a variable portion of the cross-section of the air passage, wherein the cover has a variable spanwise extent and is configured to cover a variable spanwise length of the air passage;
• and
• a mechanism configured to vary the portion of the cross-section of the air passage covered by the cover, wherein the mechanism is configured to react passively to the oncoming air speed of oncoming air in the axial direction of the propeller or turbine;
• wherein the mechanism is configured to vary the portion of the cross-section of the air passage covered by the cover such that the cover covers a smaller portion of the cross-section of the air passage in response to a higher oncoming air speed, and covers a larger portion of the cross-section of the air passage in response to a lower oncoming air speed;
• wherein the mechanism is configured to react passively to the centrifugal force induced by the rotation of the propeller or turbine, such that the cover covers a smaller portion of the cross-section of the air passage in response to a higher rotational speed of the propeller or turbine, and to cover a larger portion of the cross-section of the air passage in response to a lower rotational speed of the propeller or turbine;
• and
• wherein the mechanism comprises a sliding mass configured to slide in the spanwise direction of the aerofoil module, wherein the cover has a tip-side end and a root-side end, the root-side end is connected to the sliding mass, and the spanwise extent of the cover is variable by the sliding mass moving the root-side end of the cover.