A blade for a rotor of a wind turbine, the blade comprising: an inboard portion; an outboard portion connected to the inboard portion, wherein the outboard portion is deflectable by a variable sweep angle in an edgewise direction of the blade; and a passive mechanism configured to adjust the sweep angle in response to an amount of flapwise moment acting on the blade, such that the magnitude of the sweep angle increases in response to an increased flapwise moment, and decreases in response to a decreased flapwise moment.

A blade is used in fluid and includes: a base member; and a coat layer that is formed on the base member, a plurality of first grooves and a plurality of second grooves are formed on a surface of the coat layer, a pitch of the plurality of first grooves is different from a pitch of the plurality of second grooves.

Described herein is a rotor blade assembly (100) and a method for generating a lift in a fluid installation. The rotor blade assembly includes an arcuate rotor blade (102) that is configured to be rotated about its axis Y. One or more motion transmitting members (106, 114, 116) are provided that connect the arcuate rotor blade with at least one power generating member (104) for transmitting torque from the arcuate rotor blade to the at least one power generating member (104). The fluid incident on the arcuate rotor blade is caused to flow over a first leading edge L1 of a rotor blade towards a central rib R of the rotor blade (102). This fluid flow is then caused to flow along the central rib R of the rotor blade towards a stem section of the rotor blade from where the fluid exits, thereby causing rotation of the rotor blade.