Abstract: A wind turbine includes at least one turbine blade coupled to a rotor and configured to rotate about a central axis, a gearbox having an input configured to receive rotational input from the rotor, and an output configured to direct rotational output to a generator, a flow passageway configured to receive a lubrication fluid and direct the lubrication fluid to at least one component within the gearbox and a primary variable orifice device positioned along the flow passageway and configured to selectively vary an area of an orifice within the passageway in dependence upon at least one of a temperature or a viscosity of the lubrication fluid.