KR20080113019A - Apparatus and method for reducing fluid drag on a submerged surface - Google Patents

Abstract

An apparatus and method for reducing surface friction drag on the hull of a surface vessel by entraining air into water flowing in the boundary layer flow along the hull. The apparatus creates a reduced pressure region by diverting a first portion of the flow away from the surface of the hull. An air pocket is formed in the reduced pressure region and a second portion of the flow is directed through the air pocket by nozzles, which acts as a plunging jet and entrains air into the boundary layer. ® KIPO & WIPO 2009

Description

Apparatus and method for reducing fluid drag on submerged surfaces {APPARATUS AND METHOD FOR REDUCING FLUID DRAG ON A SUBMERGED SURFACE}

The present invention relates to an apparatus and method for reducing surface friction drag in the hull of a ship moving in water.

Surface friction drag or "skin friction" drag is a significant component of the total power required to propel a watership in water. As the surface friction drag is reduced, the ship can move at higher speeds and / or more efficiently. Thus, reducing surface friction drag is a significant area of research in the field of ship hull design for sea vessels and submarines.

The magnitude of the surface friction drag on a particular ship's hull depends on the viscosity of the liquid (pure water or saline) to which the hull is moved, the density of the liquid and the surface tension between the liquid and the submerged surface of the hull.

As shown schematically in FIG. 2, the effect of surface friction drag is centered in the "boundary layer 22", with momentum transferred from the surface 16 of the hull 14 to the liquid 12 in the layer of liquid. do. Momentum transfer is greatest at the portion of the liquid closest to the surface 16 of the hull 14 and is reduced at the edge 26 of the boundary layer 22. The transfer of momentum in the boundary layer 22 reduces the velocity of water 12 with respect to the surface 16 of the hull 14 as well as turbulence. Velocity gradient 24 is shown as the relative velocity of water 12 decreases from the edge of boundary layer 26 to the surface 16 of hull 14. Relative speed is indicated by the length of each arrow.

One means of reducing surface friction drag is to introduce gas into the boundary layer 22 such that the density and viscosity of the fluid in the boundary layer 22 is reduced. The relatively low density and viscosity of the gas results in less moment transfer and hence less surface friction drag. This technique is often referred to as "air lubrication" in the prior art.

Air lubrication has been used successfully in hovercrafts, where ships are positioned on top of large cushions of air. Air cushions are not practical for ships with significant drafts, but air cushions quickly rise to the surface of the water as water pressure increases with depth. A significant amount of power is required to push the air cushion down several inches into the water. This problem is partially solved by using small bubbles of air (ie microbubbles) instead of relatively large air cushions. Small bubbles rise more slowly in water than large air cushions.

Practically using micro-bubbles has proven very difficult. The inventions according to the prior art have faced three major technical problems in the successful use of micro-bubbles to reduce surface friction, which are (1) at a sufficient volume fraction to fill a substantial part of the boundary layer. Injecting the micro-bubbles, (2) preventing the micro-bubbles from moving out of the boundary layer, and (3) adjusting the volume flow rate of the micro-bubbles as the speed of the vessel is varied.

Most prior art air lubrication systems use pumps or pressurized air to supply the volume of micro-bubbles. This solution is not suitable in some cases. First, power must be consumed to pump air or pressurize it. In this case, the power consumed to blow up or pressurize the power offsets the reduced surface friction drag. Secondly, it is very difficult to infuse blown or pressurized air into the boundary layer. The typical boundary layer is only a few millimeters at a location adjacent to the bow of the ship where air is injected into the conventional system. The micro-bubbles provided have a diameter of at least 1 millimeter and are injected at an angle to the flow direction F of the boundary layer, and it is difficult to prevent the micro-bubbles from flowing through the boundary layer into the free-flowing number region. Very difficult. Third, the prior art does not provide injection flow rates for micro-bubbles that vary in proportion to the speed of the vessel. The rate of injection of the micro-bubbles is thus ideal only at one rate. At all other speeds, the infusion rate is faster or slower than the ideal rate.

Other prior art air lubrication systems, such as the system disclosed in U.S. Patent No. 6,125,781, have one or more ports at the submerged surface of the ship's hull and use tubes open to the air at opposite ends of the ship's hull. It consists of passing the flow of water to the boundary layer. In this conventional system, it is assumed that air is drawn into the boundary layer through the port.

This hypothesis is based on faulty assumptions. This type of system works only on ships with very shallow drafts moving at high speeds. For example, air is not drawn into the boundary layer along the hull of a ship with a draft of 3.973 inches until the ship reaches a speed of 90.6 miles per hour. This is not the speed that most aquatic vessels can perform.

Other prior art systems for reducing surface drag are referred to in the prior art as ventilated step chines, which are mainly used in high performance vessels. An example of a vented step chine is described in US Pat. No. 5,452,676. Although ventilated step chines provide some performance and efficiency improvements, prior art ventilated step chines do not incorporate significant amounts of air into the boundary layer. Accordingly, the prior art ventilated step chine does not form turbulent mixing of water and air at the portion of the step. Conventional ventilated step chines only reduce the effective surface area of the hull, so that the friction effect of the water acts on a relatively small area. This reduction is only a small percentage of the total surface area of the hull, whereby the ventilated step chine provides a small reduction in surface friction.

Therefore, there is a need for an efficient air lubrication system capable of incorporating air bubbles into various vessel boundary layers with drafts and systems functioning at more suitable speeds.

The present invention includes an apparatus for incorporating a secondary fluid into the primary fluid while the primary fluid flows in the boundary layer adjacent the surface of the object moving through the primary fluid. Such an apparatus includes a flow diverting member that redirects the first portion of the primary fluid to be spaced apart from the surface of the object, thereby providing a reduced pressure region between the surface of the object and the first portion of the primary fluid. The apparatus also includes an opening for allowing secondary fluid to flow into the reduced pressure region, and includes an array of nozzles located downstream from the inlet, through which the second portion of the primary fluid flows. The second portion of the primary fluid is accelerated as it passes through the nozzle. The nozzle is directed to guide the second portion of the primary fluid through the reduced pressure region, whereby at least a portion of the secondary fluid is incorporated into the portion of the primary fluid.

In other embodiments, the present invention includes a method for reducing friction drag on a hull of an object designed to be propelled through the primary fluid, the hull comprising a surface that is at least partially submerged in the primary fluid. The method includes redirecting the first portion of the primary fluid in a direction away from the surface of the object, thereby providing a reduced pressure region located between the surface of the object and the first portion of the primary fluid. An opening is provided to allow the secondary fluid to flow into the reduced pressure region, where the secondary fluid has a lower density than the primary fluid. At least a portion of the secondary fluid is incorporated into the portion of the primary fluid by guiding the second portion of the primary fluid through the reduced pressure region.

1 shows a ship moving underwater in a pushing direction D. FIG.

FIG. 2 is a diagram showing detail region 2-2 from FIG. 1; FIG.

3 shows a lower side of the first embodiment of the mixing apparatus;

4 is a cross-sectional view taken along the line 4-4 of FIG.

5 shows a second embodiment of the incorporation device, shown from the lower side and the rear side;

6 is a bottom view of the mixing device.

7 is a cross-sectional view taken along the line 7-7 of FIG.

8 shows a ship integrated with a third embodiment of the incorporation device, shown from the lower side and the rear side;

9 is a cross-sectional view taken along the line 9-9 of FIG. 8.

The principle and operation of the entrainment device according to the invention will be better understood according to the accompanying description and the drawings. BRIEF DESCRIPTION OF DRAWINGS To aid the understanding of the present invention, reference numerals referred to in the description of at least one of the drawings are shown in the additional drawings without specific reference to the additional drawings in the specification. The terminology used in this specification and in the claims to describe the relative position of elements of the invention, such as “above” and “below,” refers to the invention in the directions shown in FIGS. 4, 7 and 9. To do this.

3 and 4, reference numeral 30 denotes the mixing device 30 of the present invention. The incorporation device 30 may be formed as part of the hull 14 of the ship 10 or may be retrofitted to the formed hull. The mixing device 30 includes an inlet 34, a flow diverting member 36, a plurality of nozzles 37 and a base 38. The term "nozzle" as used in the specification and claims means an apparatus for guiding the flow of fluid and is not limited to nozzles that vary the speed of the fluid.

Since the mixing device 30 is part of a ship 10 that is submerged and moved in an open waterway, the mixing device 30 has the durability to adequately withstand impacts from small objects and is resistant to corrosion. It must be designed to be resistant. Thus, the incorporation device 30 is preferably made from rigid plastic or metal with corrosion-resistant properties.

As shown in FIG. 1, the incorporation device 30 is designed to be positioned along the hull 14 of the ship 10, preferably adjacent the bow 18 of the ship 10. As described herein, the surface friction reduction benefit is implemented from downstream of the incorporation device 30. Thus, placing the incorporation device 30 in a position adjacent the bow of the ship 10 maximizes the preferred effect of the incorporation device 30.

4 shows the incorporation device 30 protruding downward from the lower surface 16 of the hull 14 to the boundary layer 22 and attached to the hull 14. As shown in FIG. 4, water flows in the direction F. FIG. The water flowing towards the incorporation device 30 in the boundary layer 22 flows in the manner shown in FIG. 4 as two parts of the boundary layer flow, the inflow stream stream 50 and the redirected flow stream 52. .

As water reaches the inlet 34, the inlet flow portion 50 moves through the opening 35 to the inlet 34 and is guided through the nozzle 37. The shape of the inlet 34 can vary depending on the draft and normal operating speed of the vessel 10 and is preferably shaped to minimize drag. Low drag inlet shapes are suitable according to guidelines established by the National Advisory Committee on Aeronautics (NACA).

The redirected flow stream 52 is directed downward by a flow diverter and separated from the inlet flow stream 50. Separation of streams 50, 52 occurs between points F ₁ and F ₂ . Maximum flow separation occurs at point F _2, at which point the redirected flow stream 52 passes over the trailing edge 40 of the flow transducer 36. The speed of the redirected flow stream 52 increases with the flow above the flow transducer 36.

The trailing edge 40 of the flow transducer 36 has a surface 16 of the hull 14 located immediately downstream from the trailing edge 40 of the flow transducer 36 in order to generate a flow separation. Extend into water in addition to A portion of the surface 16 of the hull 14 is referred to in the claims and in the specification as the downstream leading edge 41 of the hull 14.

In an embodiment of the invention, the flow transducer 36 including the trailing edge 40 protrudes downward from the hull 14. Alternatively, the downstream leading edge 41 of the hull 14 may be formed in a recessed structure with respect to the trailing edge 40 of the flow transducer 36. Alternative shapes are shown and mentioned in accordance with FIGS. 8 and 9.

The reduced pressure zone is located between the hull 14 and the trailing edge 40 at the point F ₂ according to the flow separation and the increased speed of the flow. Vent 27 opens into the air at its upper end (not shown). Vent 27 includes an opening 28 located downstream from nozzle 37. The reduced pressure region provided by the diversion of the redirected flow 52 causes the pocket 42 of air to move downward into the reduced pressure region. As used herein, the terms “zone” and “reduced pressure zone” are to be understood as meaning a three-dimensional zone, ie a volume. Between points F ₂ and F ₃ , an area is provided where pockets of air 42 adjoin the surface 43 of the redirected flow stream 52. This region will be referred to in the claims and in the specification as "free surface 45".

The nozzle 37 preferably increases the velocity of the inlet stream stream 50 with respect to the outlet velocity V ₄ and directs the inlet stream stream 50 through the pockets 42 of air. Inlet stream stream 50 then contacts free surface 45. The inlet flow stream 50 thus functions as a flushing jet that entrains the air bubbles 56 from the pocket 42 into the redirected stream stream 52. Preferably, the nozzle 37 is located just below the surface 16 of the hull 14 such that the inflow stream stream 50 forms parallel to the flow F of the boundary layer 22 when formed in the nozzle 37. do.

As shown in Fig. 3, three nozzles 37 are provided in this embodiment. A relatively large or small number of nozzles 37 may be provided in various fields.

The size of the convergence of each nozzle 37 (i.e., the ratio of the diameter of the nozzle throttle to the diameter of the inlet) is chosen so that the inlet flow stream 50 has sufficient discharge rate to entrain the air. exit velocity) (V ₄ ).

Unnecessarily high convergence should be avoided because the back pressure at the nozzle is directly proportional to the magnitude of the convergence of each nozzle.

The velocity V ₄ (including direction and magnitude) of the inlet flow stream 50 to entrainment differs from the velocity V ₅ of the flow stream 52 redirected along the free surface 45 in the contact region. Should be. In this embodiment, the velocity V ₅ of the redirected flow stream 52 is guided at an angle of approximately 45 degrees with respect to the velocity V ₄ of the inlet flow stream 50 at point F ₃ .

Downstream from the incorporation device 30, the incoming flow stream 50 and the redirected flow stream 52 meet again. As air enters the inflow stream 50, the viscosity and density of the boundary layer flow 22 is reduced. As mentioned above, the skin friction drag is correspondingly reduced due to the reduced viscosity and density in the boundary layer. For example, a 50% water / air mixture will reduce skin friction in the hull of a submerged ship by approximately 50%.

The basic function of the mixing device 30 is to form a reduced pressure zone through which air is discharged and to incorporate air into the boundary layer flow 22 through turbulent mixing located downstream from the mixing device 30. It is to let. In this embodiment, this turbulence mixing is formed by directing the second flow stream through the air at increased speed. The position, size and arrangement of the incorporation device 30 depends on the size and shape of the vessel 10 and the hull 14. In most installations, it is preferred to have an array of incorporation devices 30 arranged in a row across the hull 14 at a location adjacent the bow 18. This arrangement of incorporation device 30 is preferably transverse to the propulsion direction D of the vessel 10. The number of mixing devices 30 depends on the width of the hull 14. In some installations it is preferred to include a plurality of rows of incorporation devices 30, especially for ships with fairly long hulls.

Various shapes may be used for the incorporation device 30 as in the alternative embodiment shown in FIGS. 5 to 7, the features corresponding to the features shown in the first embodiment of the incorporation device 30 are shown by reference numerals increased by a factor of 100. For example, a second embodiment of the incorporation device is shown at 130. In FIG. 4, the velocity reference points V ₁ to V ₄ and the flow reference points F ₁ to F ₄ correspond to V _1B to V _4B and F _1B to F _4B in FIG. 7, respectively. The mixing device 130 is similar to the first embodiment of the mixing device 30 and includes an inlet 134, a turning member 136 and a plurality of nozzles 137. The main difference between the first embodiment 30 and the second embodiment of the incorporation device 130 lies in the shape of the inlet 134 and the relatively shallow slope of the redirecting member 136. This difference is shown in detail in FIG. 7.

8 and 9, the features corresponding to the features shown in the first embodiment of the incorporation device 30 are shown by reference numerals increased by a factor of 200. For example, a second embodiment of the incorporation device is shown at 230. In FIG. 4, the velocity reference points V ₁ to V ₄ and the flow reference points F ₁ to F ₄ correspond to V _1C to V _4C and F _1C to F _4C in FIG. 7, respectively.

The mixing device 230 shown in FIGS. 8 and 9 functions the same as the two other embodiments described herein but is suitable for use in a high speed power boat. Incorporation device 230 includes vent 226 including a channel extending transversely across hull 214 of vessel 210. Vent 226 may extend to a point above water line 270 such that air may flow out of vent 226 and into the vent.

In this embodiment, the trailing edge 240 of the flow transducer 236 is coincident with the front edge of the vent 226 and the downstream leading edge 241 of the hull 214 is with the rear edge of the vent 226. Matches. The flow transducer 236 does not protrude downward from the surface 216 of the hull 214. In addition, the downstream leading edge 241 of the hull 214 is formed in a recessed structure with respect to the trailing edge 240 of the flow transducer 236, that is, the number is greater than the trailing edge 240 of the flow transducer 236. Is located somewhat higher.

In other embodiments of the present invention, this embodiment includes an inlet 234 that guides the inlet stream stream 250 through the nozzle 237. Including the inlet 234 and the nozzle 237 results in impingement mixing, which in turn introduces more air than conventional ventilated step chines. The incorporation device of the present invention may also be used in other applications than surface vessels. For example, a mixing device can be used to reduce friction in the pipe by placing the mixing device on the inner surface of the pipe.

Those skilled in the art will recognize that the above-mentioned embodiments of the present invention are variable without departing from the scope of the present invention. Therefore, it is intended that the present invention not be limited to the particular embodiments described, but include all modifications that fall within the spirit and scope of the invention.

Claims (20)

An apparatus for incorporating a secondary fluid into a primary fluid while the primary fluid flows along a surface of an object, the apparatus comprising: A inlet, wherein a first portion of the primary fluid flows through the inlet, the first portion of the primary fluid enters the inlet through the first opening and exits from the inlet through the one or more nozzles, A flow diverting member located downstream from the first opening of the inlet, the second portion of the primary fluid flows above the flow diverting member, A second opening for flowing the secondary fluid into the first region, the second opening being located between the second portion of the primary fluid and the surface of the object and downstream from the flow diverting member or in the flow diverting fluid, The second portion of the primary fluid comprises a free surface adjacent to the first region, At least one nozzle guides the first portion of the primary fluid through the free surface such that at least a portion of the secondary fluid is incorporated into the portion of the primary fluid. The flow diverting member of claim 1, wherein the flow diverting member includes a trailing edge at a downstream end of the flow diverting member, the surface of the object includes a downstream leading edge located downstream from the trailing edge of the flow diverting member, The trailing edge is located below the downstream leading edge. 3. The apparatus of claim 2 wherein the flow diverting member projects downward from the surface of the object. The device of claim 2, wherein the one or more nozzles are located above the trailing edge and below the downstream leading edge. 5. The apparatus of claim 4, wherein the first portion of the primary fluid is formed in one or more nozzles along a path parallel to the surface of the object. The apparatus of claim 1 wherein the second opening is located downstream from the one or more nozzles. The apparatus of claim 1 wherein the one or more nozzles comprise a plurality of nozzles. The apparatus of claim 1 wherein the density of the secondary fluid is lower than the density of the primary fluid. 9. The apparatus of claim 8, wherein the primary fluid is a liquid and the secondary fluid is a gas. In a vessel, the vessel is A hull designed to be propelled through the primary fluid, the hull having a surface that is at least partially submerged in the primary fluid, One or more incorporation devices attached to the surface, each one or more incorporation devices A inlet, wherein a first portion of the primary fluid flows through the inlet, the first portion of the primary fluid enters the inlet through the first opening and exits from the inlet through the one or more nozzles, A flow diverting member located downstream from the first opening of the inlet, the second portion of the primary fluid flows over the flow diverting member, A second opening for flowing the secondary fluid into the first region, the second opening being located between the second portion of the primary fluid and the surface of the object and downstream from or in the flow diverting member, The second portion of the primary fluid comprises a free surface positioned adjacent the first region, and the one or more nozzles guide the first portion of the primary fluid through the free surface such that at least a portion of the secondary fluid is part of the primary fluid. A ship characterized by being incorporated. 11. The ship of claim 10, wherein the one or more incorporation devices comprise a plurality of incorporation devices. 12. The ship according to claim 11, wherein the hull is designed to be driven in a direction D, and the plurality of incorporation devices are arranged in rows in the transverse direction with respect to the propulsion direction D. The vessel of claim 10, wherein the second opening is located downstream from the one or more nozzles. The ship of claim 10, wherein the one or more nozzles comprise a plurality of nozzles. 11. The vessel of claim 10, wherein the density of the secondary fluid is lower than the density of the primary fluid. 12. The flow diverting member of claim 10 wherein the flow diverting member includes a trailing edge at a downstream end of the flow diverting member, the surface of the object includes a downstream leading edge located downstream from the trailing edge of the flow diverting member, And the trailing edge is located below the downstream leading edge. The vessel of claim 16, wherein the first portion of the primary fluid is formed at one or more nozzles along a path parallel to the surface of the object. A method for reducing frictional drag on a hull of an object designed to be propelled through a primary fluid, the hull having a surface that is at least partially submerged in the primary fluid. Separating the first portion of the primary fluid from the second portion of the primary fluid, thereby forming a reduced pressure region between the surface of the object and the second portion of the primary fluid, Providing an opening to allow the secondary fluid to flow into the reduced pressure region, the secondary fluid having a lower density than the primary fluid, -Incorporating at least a portion of the secondary fluid into the portion of the primary fluid by contacting the second portion of the primary fluid with the first portion of the primary fluid. 19. The method of claim 18, wherein at least the incorporation of the portion of the secondary fluid into the portion of the primary fluid by contacting the second portion of the primary fluid with the first portion of the primary fluid comprises: removing the first portion of the primary fluid through the reduced pressure region. Guiding a step. 20. The method of claim 19, wherein at least incorporating the portion of the secondary fluid into the portion of the primary fluid by contacting the second portion of the primary fluid with the first portion of the primary fluid comprises: a nozzle for increasing the velocity of the first portion of the primary fluid. Moving the first portion of the primary fluid through the method.

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