Propulsion apparatus

Abstract

Propulsion apparatus for an aquatic vessel comprises an aerodynamic body which extends along a longitudinal axis between first and second ends and in a transverse direction between a leading edge and trailing edge. The aerodynamic body has one or more external wind-receiving surfaces which extend between the leading edge and the trailing edge, thereby defining an aerodynamic profile of the aerodynamic body in cross-section substantially perpendicular to the longitudinal axis. The propulsion apparatus further comprises at least one air vent and at least one air flow generator configured to expel air through the at least one air vent. The at least one air vent and/or the at least one air flow generator are configured to direct expelled air across at least a portion of the one or more or more external wind-receiving surfaces.

Claims

1. Propulsion apparatus for an aquatic vessel, the propulsion apparatus comprising an aerodynamic body which extends along a longitudinal axis between first and second ends and in a transverse direction between a leading edge and trailing edge, the aerodynamic body having one or more external wind-receiving surfaces which extend between the leading edge and the trailing edge, thereby defining an aerodynamic profile of the aerodynamic body in cross-section substantially perpendicular to the longitudinal axis, wherein the propulsion apparatus further comprises at least one air vent and at least one air flow generator configured to expel air through the at least one air vent, the at least one air vent and the at least one air flow generator being configured to direct expelled air across at least a portion of the one or more or more external wind-receiving surfaces, and wherein the at least one air vent is located in a leading region of the aerodynamic body.

2. The propulsion apparatus according to claim 1, wherein the at least one air vent comprises at least one elongate vent aperture.

3. The propulsion apparatus according to claim 1, wherein the at least one air flow generator is configured to expel air from within the aerodynamic body, through the at least one vent, to outside the aerodynamic body.

4. The propulsion apparatus according to claim 1, wherein the at least one air flow generator comprises a fan or a pump.

5. The propulsion apparatus according to claim 4, wherein the at least one air flow generator is located inside the aerodynamic body.

6. The propulsion apparatus according to claim 4 further comprising one or more channels provided between the or one of the at least one air flow generators and the or one of the at least one air vents, the one or more channels being configured to guide air from the or one of the at least one air flow generators towards the or one of the at least one air vents, wherein the or each of the one or more channels narrows along a length of the said channel from the at least one air flow generator towards the at least one air vent.

7. The propulsion apparatus according to claim 1 further comprising at least one air vent flow regulator operable to regulate the speed and direction of flow of air through the at least one vent.

8. The propulsion apparatus according to claim 1 further comprising at least one air intake, located at or adjacent to the trailing edge of the aerodynamic body, the at least one air flow generator being configured to draw air through the at least one air intake.

9. The propulsion apparatus according to claim 1 further comprising at least one flap projecting from the aerodynamic body.

10. The propulsion apparatus according to claim 1, wherein: the propulsion apparatus further comprises at least one air intake; and the at least one air flow generator is further configured to draw air through the at least one air intake, the at least one air intake being, in an operating configuration, located at or extending across the trailing edge of the aerodynamic body.

11. The propulsion apparatus according to claim 10 wherein the at least one air flow generator is configured to expel air through the at least one air vent, the at least one air vent and the at least one air flow generator being configured to direct expelled air across at least a portion of the one or more or more external wind-receiving surfaces.

12. The propulsion apparatus according to claim 10, wherein the at least one air intake comprises a plurality of open apertures through which air may be drawn.

13. The propulsion apparatus according to claim 1, wherein: the propulsion apparatus further comprises at least one air intake, the at least one air flow generator is configured to draw air through the at least one air intake, the propulsion apparatus further comprises at least one flap, the at least one air intake is located at or extending across the trailing edge of the aerodynamic body in an operating configuration, and the at least one flap is movable between a first flap position, in which the at least one flap is provided to one side of the trailing edge, and a second flap position, in which the at least one flap is provided to an opposing side of the trailing edge.

14. The propulsion apparatus according to claim 13, wherein, when the at least one flap is in the first or the second flap positions, at least a portion of the at least one air intake is covered by at least a portion of the flap.

15. The propulsion apparatus according to claim 13, wherein, when the at least one flap is in the first or the second flap positions, the at least one air intake is not covered by the at least one flap and wherein the at least one flap is releasably retainable in the first flap position and the at least one flap is releasably retainable in the second flap position.

16. The propulsion apparatus according to claim 13, wherein the at least one flap is configured such that, when the flap is in the first or the second flap position, at least one external wind-receiving surface of the said flap extends substantially tangentially away from one or more of the external wind-receiving surfaces of the aerodynamic body.

17. The propulsion apparatus according to claim 13, wherein the at least one flap is substantially triangular or substantially trapezoidal in cross-section perpendicular to the longitudinal axis of the aerodynamic body.

18. The propulsion apparatus according to claim 17, wherein one or more sides of the substantially triangular or substantially trapezoidal cross-sections of the at least one flap are flat.

19. The propulsion apparatus according to claim 17, wherein one or more sides of the substantially triangular or substantially trapezoidal cross-sections of the at least one flap are concave.

Description

DESCRIPTION OF THE DRAWINGS

(1) An example embodiment of the present invention will now be illustrated with reference to the following Figures in which:

(2) FIG. 1 shows a ship fitted with three rigid, modular sails;

(3) FIG. 2 shows the ship of FIG. 1 from an alternative view point;

(4) FIG. 3 shows one of the rigid, modular sails of FIGS. 1 and 2;

(5) FIG. 4 shows an individual sail module from the rigid, modular sail of FIG. 3;

(6) FIG. 5 shows a simplified internal structure of the individual sail module of FIG. 4 with circular end plates removed;

(7) FIG. 6 shows a schematic cross-section through the individual sail module of FIG. 4, the cross-section taken perpendicular to a longitudinal axis of the sail module;

(8) FIG. 7 shows a more detailed internal structure of the individual sail module of FIG. 4 than shown in FIG. 5;

(9) FIG. 8 shows an alternative internal structure of an individual sail module using an internal frame structure and external shell;

(10) FIG. 9 shows schematically the flow path of wind across the suction surface of the individual sail module of FIG. 4; and

(11) FIG. 10 shows schematically the flow path of wind across the suction surface of the individual sail module of FIG. 4 when air is drawn into the sail module at the geometrical trailing edge and ejected through a vent at the geometrical leading edge;

(12) FIG. 11 shows the calculated flow path of wind around the entire cross-section of the individual sail module of FIG. 4 when air is drawn into the sail module at the geometrical trailing edge and ejected through the vent at the geometrical leading edge;

(13) FIG. 12 shows the flow path shown in FIG. 11 in more detail; and

(14) FIG. 13 shows iso-pressure contour lines between the vent and the air inlet of the individual sail module of FIG. 4 when air is drawn into the sail module through the air inlet at the geometrical trailing edge and ejected through the vent at the geometrical leading edge.

DETAILED DESCRIPTION OF AN EXAMPLE EMBODIMENT

(15) FIGS. 1 and 2 show a ship 1 provided with first, second and third rigid sails 2, 3 and 4. The rigid sails each extend generally vertically upwards away from a top deck 5 of the ship 1. Movement of air across external surfaces of the rigid sails 2, 3 and 4 generates a lift force on the said sails, driving movement of the ship through the water. The ship is also typically provided with a primary propulsion system (including, for example, a propeller). The rigid sails typically provide the ship with an auxiliary propulsive thrust which reduces the power requirements of the primary propulsion system.

(16) The rigid sail 4 is shown in more detail in FIG. 3. The sail 4 has a modular construction, comprising seven sail modules 6A, 6B, 6C, 6D, 6E, 6F and 6G stacked substantially vertically on top of one another. As shown in FIG. 4, each individual sail module 6 is formed from a sail module body 7 provided between first and second substantially circular end plates 8A and 8B. An elongate vent 9 is located at a first, geometrical leading edge end 10A of the sail module body 7, and a trailing edge flap 11 is located adjacent to a second, geometrical trailing edge end 10B of the sail module body 7.

(17) As can be seen in FIG. 5, the sail module body 7 is substantially hollow and is substantially tubular in shape. The elongate vent 9 extends substantially parallel to the longitudinal axis of the tubular sail module body 7. The trailing edge flap 11 is substantially prismatic in shape, having first and second wind-receiving flap surfaces 12A and 12B and a trailing edge surface 13 which, together with a portion of the external surface of the sail module body 7, form a substantially trapezoidal shape in cross-section perpendicular to the longitudinal axis of the sail module body.

(18) The trailing edge flap 11 is slidably mounted to the sail module by way of two sliding blocks 14A and 14B provided at a first end of flap surfaces 12A and 12B. The sliding blocks 14A and 14B are retained within slot 26 in the first circular end plate 8A when the trailing edge flap 11 is mounted to the sail module body 7. Similar sliding blocks (not shown) are provided at a second end of the flap 11 and are retained within a similar slot (not shown) of the second circular end plate 8B. The trailing edge flap is movable around a trailing edge portion of the sail module body by the support blocks sliding within the end plate slots.

(19) The trailing edge flap 11 is mounted to the sail module such that a longitudinal axis of the said flap extends substantially parallel to the longitudinal axis of the sail module body 7. In addition, a central axis (which bisects the trapezoidal flap in cross-section perpendicular to the longitudinal axis) extends away from the external surface of the sail module body at approximately 90°.

(20) A cross-section through the sail module perpendicular to the longitudinal axis of the sail module body 7 is illustrated in FIG. 6. The tubular sail module body 7 has a generally rounded cross-section which extends from the geometrical leading edge to the geometrical trailing edge along a chord (indicated by arrow C), and which also extends along a thickness (indicated by arrow T) perpendicular to the chord. The ratio of the thickness to the chord length is approximately 2:3, which the inventors have found to provide a good structural to aerodynamic interaction, although in practice ratios between 1:2 and 1:1 are suitable.

(21) The cross-sectional perimeter of the sail module body is substantially elliptical between the geometrical leading edge and a point approximately 75% of the way along the chord towards the geometrical trailing edge. The cross-sectional perimeter of the sail module body at the geometrical trailing edge is formed by a circular arc which extends for 90° (i.e. the arc extends symmetrically over 45° either side of the chord) and whose centre is located at the point approximately 75% of the way along the chord from the geometrical leading edge towards the geometrical trailing edge. The remainder of the cross-sectional perimeter which connects the elliptical portion to the circular portion is formed by an opportune curve which guarantees C.sup.2 continuity between the two portions (i.e. continuity up to and including the second derivative of the curve).

(22) The trailing edge flap extends away from the sail module body over a distance which is approximately one quarter of the chord length, although the inventors have found that distances between one quarter and one half of the chord length are suitable. Longer trailing edge flaps typically provide better aerodynamic performance.

(23) As can be seen from FIG. 6, the sail module body is substantially symmetrical in cross-section (e.g. a mirror plane extends along the chord, dividing the sail module body into two substantially identical halves). The symmetrical design means that the sail module has substantially similar aerodynamic properties no matter from which side the wind approaches.

(24) As can also be seen in FIG. 6, the sail module body 7 includes a perforated air intake 12 located at the geometrical trailing edge. The air intake is formed from a perforated area of the external surface of the sail module body. The trailing edge flap 11 is movable between two extremal positions 13A and 13B (indicated by dashed lines in FIG. 6) either side of the air intake 12.

(25) FIG. 7 shows the internal structure of the sail module body 7 in more detail. An intake duct 14 connects the air intake 12 to an intake side of a fan assembly 15. A vent duct 16 connects a vent side of the fan assembly 15 to the vent 9. The fan assembly 15 houses a fan (not shown). The intake duct houses a plurality of intake sub-ducts (not shown), each intake sub-duct shaped to guide air from the air intake towards a specific portion of the fan-swept area. Similarly, the vent duct houses a plurality of vent sub-ducts (not shown), each vent sub-duct shaped to guide air away from a respective portion of the fan-swept area towards the vent. In use, when the fan is switched on, air is drawn (i.e. sucked) into the intake duct 14 from outside the sail module body through the air intake 12. Air is also ejected from the sail module body through the vent duct 16 and then through the vent 9. Accordingly, in use, air is drawn into the body at the geometrical trailing edge and expelled from the body at the geometrical leading edge.

(26) A vent flow regulator 17 is provided at the vent end of the vent duct 16 within the sail module body 7. The vent flow regulator 17 is rotatable between first and second positions such that the direction of ejection of air through the vent may be controlled. When the vent duct regulator is held in the first position, air is ejected through the vent such that it flows around the sail module body in a first direction, and when the vent duct regulator is held in the second position, air is ejected through the vent such that it flows around the sail module body in a second direction opposite the first direction. As each vent sub-duct approaches the vent 9, it narrows in a direction parallel to the thickness of the air module body and expands in a direction parallel to the longitudinal axis of the sail module body. This ensures that a longitudinally elongate, pressurised jet of air is typically ejected through the vent 9 at a high speed.

(27) Also shown in FIG. 7, the external walls of the sail body module have a double-layer structure, being formed from an external shell 18 and an internal shell 19. Vertical stiffeners 20, each having an I-shaped cross-section, are provided between the external and internal shells. The internal structure of the flap is not shown in detail in FIG. 7. FIG. 8 shows an alternative construction in which a truss or frame structure is formed by struts 23 jointed at nodes 24, which supports an outer shell 25. The truss or frame structure provides the primary mechanical strength, and supports the fans, end plates and flap, and supports the outer shell which defines the shape of the wind-receiving surface.

(28) In use, when the ship is moving through the water and/or when the wind blows, air flows over the external surfaces of each of the sail modules. The ship and/or the rigid sail is oriented such that the angle between the horizontal component of the apparent wind direction and the chord of each sail module body is non-zero (unless the wind velocity is very high, in which case the angle may be reduced to zero in order to reduce loads exerted on the sail, or if the apparent wind angle is so small that the drag force would exceed any lift generated). The trailing edge flap of each sail module is moved towards the direction from which the air flow approaches. This configuration is illustrated in FIG. 9 which shows air flow over the suction surface of the sail module. The incoming air flow, indicated by arrow 21, flows over the suction surface but detaches prior to reaching the geometrical trailing edge. Air flowing over the surface of the sail module body results in a non-zero circulation and, therefore, a lift force exerted on the sail module body according to the Kutta-Joukowski theorem. The amount of lift generated is proportional to the lift coefficient c.sub.L for the particular shape and settings of the sail module.

(29) FIG. 9 shows the effect of switching on the internal fan such that air is drawn into the air module body through the trailing edge air intake and ejected as a jet through the leading edge vent.

(30) Suction of air through the air intake reduces air pressure at the geometrical trailing edge, increasing circulation of air around the sail module and causing the flow of air across the suction surface to remain attached over the geometrical trailing edge, beyond the point at which the air flow detaches in FIG. 9. In addition, ejection of air through the vent increases the speed of air flow across the suction surface, improving air circulation and further displacing the point of flow detachment towards the flap trailing edge. The inventors have found that by ejecting air through the vent at a speed between 1 to 8 times greater than the unaided windspeed, the air flow may remain attached across the trailing edge air inlet and up to the trailing edge of the flap. As shown in FIG. 10, the combined effect of drawing air into the sail module body through the air intake and ejecting pressurised air out through the leading edge vent is that the detachment point is shifted back to the trailing edge of the trailing edge flap. As attached air flows over a greater suction surface area (including both a portion of the external surface of the sail module body and an external surface of the trailing edge flap), the lift coefficient c.sub.L is increased and therefore so is the amount of lift which can be generated. The inventors have found that values of between 12.5 and 14.5 are achievable.

(31) The shape and orientation of the trailing edge flap also causes an increase in c.sub.L. By holding the central axis of the trailing edge flap at approximately 45° to the sail module body chord, air typically flows smoothly from the suction surface, past the geometrical trailing edge and onto the flap. In particular, the trapezoidal shape of the trailing edge flap causes the air flow to remain attached as it approaches the transition between the sail module body and the trailing edge flap, increasing the total area of suction surface and consequently increasing the circulation and so also the lift force generated.

(32) The effect of drawing air into the sail module body through the air intake and ejecting pressurised air out through the leading edge vent is illustrated in more detail in FIGS. 11, 12 and 13. FIGS. 11 and 12 show the air flow around the sail module body when air is drawn into and ejected from the sail module body. The arrow 22 indicates the predominant incoming air flow direction at large distances from the sail module body. FIG. 13 shows iso-pressure contour lines between the leading edge vent and the air intake.

(33) An aerodynamic suction region, in which the air pressure is reduced and the air velocity is increased (relative to the undisturbed air flow far from the sail), extending between the aerodynamic leading edge (i.e. the stagnation point) and the aerodynamic trailing edge, is visible in FIGS. 11, 12 and 13. A corresponding aerodynamic pressure region, in which the air pressure is increased and the air velocity is decreased (relative to the undisturbed air flow far from the sail), extending between the aerodynamic leading edge and the aerodynamic trailing edge on an opposite side of the sail module body from the aerodynamic suction region, is also visible.

(34) The aerodynamic suction and pressure regions do not correspond with the geometrical suction and pressure surfaces which extend between the geometrical leading and trailing edges around opposing sides of the sail module body (the geometrical pressure surface comprising the surface of the sail module body which would be impacted by air flow in a passive device and the geometrical suction surface being located on the side of the sail module body opposite the geometrical pressure surface). In fact, it can be seen that the deflection of the air flow is so significant that the aerodynamic leading edge (i.e. the stagnation point) is displaced away from the geometrical leading edge, along the geometrical pressure side, towards the geometrical trailing edge. Displacement of the aerodynamic leading edge leads to a reduction in the surface area of the aerodynamic pressure region and an increase in the surface area of the aerodynamic suction region. In particular, it can be seen that the stagnation point almost coincides with the trailing edge of the trailing edge flap. At the same time, the flow separation point is moved away from the geometrical leading edge, along the geometrical suction surface, towards the trailing edge of the trailing edge flap. This further reduces the surface area of the aerodynamic pressure region and increases the surface area of the aerodynamic suction region. In FIG. 12, the aerodynamic leading edge almost coincides with the aerodynamic trailing edge, approaching the ideal condition of a zero-length aerodynamic pressure region in which the circulation, and therefore the lift, is maximised.

(35) The trailing edge air inlet may be formed by circular or triangular perforations in the external surface of the sail module body. Alternatively, the trailing edge air inlet may be louvred, rather than perforated, meaning that the inlet may be formed by an array of elongate slats and apertures. The louvre slats may be rectangular in cross-section, or they may be shaped as aerofoils. A good air inlet permeability is of the order of 45%, meaning that 45% of the exposed inlet surface is open aperture. The permeable area of the air inlet typically extends back from the geometrical trailing edge towards the geometrical leading edge along between 2% and 7% of the length of the chord. In order to maintain flow attachment right up to the geometrical trailing edge or the trailing edge of the trailing edge flap, between 1% and 7% of air flow approaching the sail (calculated as the product of the wind velocity, the chord length, the longitudinal axis length and a factor of ⅔) should be sucked into the sail module bodies. A flow ratio of 6% typically ensures that flow remains attached for an angle of attack of 30° and a jet velocity ⅛ times greater than the undisturbed wind velocity.

(36) In use, the angle of attack may be adjusted by rotating each sail about its longitudinal axis. The position of each trailing edge tail may be adjusted such that it is always provided on the pressure surface of the respective sail module body.

(37) The ship and/or the sails may include one or more wind-characterising sensors operable (i.e. configured) to determine one or more properties (such as the wind velocity, i.e. wind speed and wind direction) of an approaching wind field. Wind-characterising sensors may comprise LIDAR sensors. Each sail may be rotated, and each trailing edge flap may be moved, in response to the outputs from the wind-characterising sensors, in order to achieve an optimum angle of attack for maximum lift generation.

(38) In use, the trailing edge flap may also sometimes be held at the trailing edge (i.e. at equal distances from the first and second extremal positions either side of the air intake), in order to reduce drag forces acting on the sail. Reduction in drag is important when the apparent wind angle is so small that the driving force is mainly composed of drag, or when the apparent wind velocity is so high that the air flow cannot stay attached to the device even with the assistance of the air inlet suction and the leading edge jet.

(39) It will be understood that different sail geometries are possible. It may be that the cross-section of the sail module body is substantially elliptical. It may be that the elliptical cross-sectional shape begins at the geometrical leading edge and extends up to between 50% and 100% of the chord length. The remaining portion of the cross-sectional shape may be circular.

(40) The trailing edge flap may be rectangular in shape, or shaped like an aerofoil. The trailing edge flap can be mounted to the end plates and/or directly to the sail module body. If the trailing edge flap is mounted only to the end plates and not directly to the sail module body, typically one sliding rail is provided on each end plate. If the trailing edge flap is mounted to the sail module body, typically two, three or more sliding rails are provided, spaced apart along the longitudinal axis. The sliding rails may extend across the air inlet.

(41) The end plates may be circular or they may take other shapes. For example, the end plates may be elliptical.

(42) Each sail body module is typically around 2.5 metres to 5 metres in height. The length of the chord of each sail module body is typically similar to (e.g. equal to) the height of the said sail module body. The thickness of each sail module body is typically ⅔ times the length of the respective chord.

(43) The modular sail structure means that individual sail module bodies can be removed, replaced and transported easily. It also means that the sail can be reconfigured for use on different ships. The periodic array of end plates tends to restrict flow of air in a direction parallel to the longitudinal axis of the sail, ensuring that air flows principally from the leading towards the trailing edge of each sail module body.

(44) Further variations and modifications may be made within the scope of the invention herein disclosed.