A fluid machine includes: a shaft portion; a shroud having an inside surface with a diameter decreasing from an upstream side toward a downstream side, a flow path being formed between the shroud and the shaft portion and having a flow path cross-sectional area decreasing toward the downstream side; a propeller rotatably provided about an axis between the shaft portion and the shroud and configured to pump a fluid from the upstream side toward the downstream side; and a motor provided to correspond to the propeller and including a rotor having a ring-like shape fixed to an outer circumference portion of the propeller and accommodated in the shroud and a stator having a ring-like shape surrounding the rotor and fixed in the shroud, in which a plurality of the propellers are provided to be spaced apart in the axis direction, the motors are provided in an identical number to the propellers to correspond to each of the propellers, and of a plurality of motors, the rotor of the motor positioned more on the downstream side has a smaller average outside diameter.

A fluid machine includes: a shaft portion; a shroud having an inside surface with a diameter decreasing from an upstream side toward a downstream side, a flow path being formed between the shroud and the shaft portion and having a flow path cross-sectional area decreasing toward the downstream side; a propeller rotatably provided about an axis between the shaft portion and the shroud and configured to pump a fluid from the upstream side toward the downstream side; and a motor provided to correspond to the propeller and including a rotor having a ring-like shape fixed to an outer circumference portion of the propeller and accommodated in the shroud and a stator having a ring-like shape surrounding the rotor and fixed in the shroud, in which a plurality of the propellers are provided to be spaced apart in the axis direction, the motors are provided in an identical number to the propellers to correspond to each of the propellers, and of a plurality of motors, the rotor of the motor positioned more on the downstream side has a smaller average outside diameter.

In order to provide an arrangement with at least one rudder and with at least one accommodating space for a propeller, which accommodating space is formed in the direction of travel of the watercraft in front of the rudder and allows for a reduction of a propulsion power requirement of a watercraft with such an arrangement, it is proposed that, in the direction of travel in front of the accommodating space of the propeller, at least one pre-nozzle comprising at least one guide surface and at least one side fin is arranged on the rudder.

In order to provide an arrangement with at least one rudder and with at least one accommodating space for a propeller, which accommodating space is formed in the direction of travel of the watercraft in front of the rudder and allows for a reduction of a propulsion power requirement of a watercraft with such an arrangement, it is proposed that, in the direction of travel in front of the accommodating space of the propeller, at least one pre-nozzle comprising at least one guide surface and at least one side fin is arranged on the rudder.

The invention relates to an arrangement for multi screw vessels, in particular twin screw vessels, with external propeller shafts, as well as to a method for producing such an arrangement. The arrangement according to the invention is in particular suitable for a drive system of an above-mentioned multi screw vessel and to improve the energy efficiency thereof.

The invention relates to an arrangement for multi screw vessels, in particular twin screw vessels, with external propeller shafts, as well as to a method for producing such an arrangement. The arrangement according to the invention is in particular suitable for a drive system of an above-mentioned multi screw vessel and to improve the energy efficiency thereof.

A structure adapted to traverse a fluid environment includes an elongate body having a root, a wingtip, a leading edge and a trailing edge; and a plurality of rigid projections each extending from a respective position along the leading edge and/or the trailing edge generally along the same plane as a front surface of the body.

A fluid-redirecting structure includes a rigid body having an upstream end, a downstream end, and an axis of rotation, the rigid body incorporating a plurality of troughs each spiralled from a tip at the upstream end to the downstream end about the axis of rotation, the troughs being splayed with respect to the axis of rotation thereby to, proximate the downstream end, direct incident fluid along the troughs away from the axis of rotation.

A structure adapted to traverse a fluid environment includes an elongate body having a root, a wingtip, a leading edge and a trailing edge; and a rigid winglet associated with the wingtip and having a winglet body extending substantially normal to one of a suction side and a pressure side of the elongate body to a termination point that is rearward of the trailing edge. In an embodiment, the structure is a rotor blade that may be incorporated into a wind turbine.

This disclosure relates to a system for reducing cavitation at a surface that moves relatively with respect to a first fluid. The system comprises a degasser configured to at least partially degas a second fluid. The system also comprises a reservoir in communication with the degasser and configured to house the at least partially degassed second fluid, the reservoir having an outlet that is arranged for directing the second fluid towards the surface. The system is configured such that the directing of the at least partially degassed second fluid towards the surface forms a boundary layer at the surface. The boundary layer is adapted to at least partially increase the negative pressure required to initiate cavitation at the surface so as to reduce the occurrence of cavitation during such relative movement.