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WO2015001315A2 - Génération de cavitation - Google Patents

Génération de cavitation Download PDF

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Publication number
WO2015001315A2
WO2015001315A2 PCT/GB2014/051950 GB2014051950W WO2015001315A2 WO 2015001315 A2 WO2015001315 A2 WO 2015001315A2 GB 2014051950 W GB2014051950 W GB 2014051950W WO 2015001315 A2 WO2015001315 A2 WO 2015001315A2
Authority
WO
WIPO (PCT)
Prior art keywords
liquid
region
cavitation
receptacle
vicinity
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/GB2014/051950
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English (en)
Other versions
WO2015001315A3 (fr
Inventor
Rade Vignjevic
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Cranfield University
Original Assignee
Cranfield University
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from GB201311813A external-priority patent/GB201311813D0/en
Priority claimed from GB201319908A external-priority patent/GB201319908D0/en
Application filed by Cranfield University filed Critical Cranfield University
Publication of WO2015001315A2 publication Critical patent/WO2015001315A2/fr
Publication of WO2015001315A3 publication Critical patent/WO2015001315A3/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
    • B63B1/00—Hydrodynamic or hydrostatic features of hulls or of hydrofoils
    • B63B1/16—Hydrodynamic or hydrostatic features of hulls or of hydrofoils deriving additional lift from hydrodynamic forces
    • B63B1/24—Hydrodynamic or hydrostatic features of hulls or of hydrofoils deriving additional lift from hydrodynamic forces of hydrofoil type
    • B63B1/248—Shape, hydrodynamic features, construction of the foil
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
    • B63B1/00—Hydrodynamic or hydrostatic features of hulls or of hydrofoils
    • B63B1/32—Other means for varying the inherent hydrodynamic characteristics of hulls
    • B63B1/34—Other means for varying the inherent hydrodynamic characteristics of hulls by reducing surface friction
    • B63B1/38—Other means for varying the inherent hydrodynamic characteristics of hulls by reducing surface friction using air bubbles or air layers gas filled volumes
    • B63B2001/382—Other means for varying the inherent hydrodynamic characteristics of hulls by reducing surface friction using air bubbles or air layers gas filled volumes by making use of supercavitation, e.g. for underwater vehicles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
    • B63B1/00—Hydrodynamic or hydrostatic features of hulls or of hydrofoils
    • B63B1/32—Other means for varying the inherent hydrodynamic characteristics of hulls
    • B63B1/34—Other means for varying the inherent hydrodynamic characteristics of hulls by reducing surface friction
    • B63B1/38—Other means for varying the inherent hydrodynamic characteristics of hulls by reducing surface friction using air bubbles or air layers gas filled volumes
    • B63B2001/387—Other means for varying the inherent hydrodynamic characteristics of hulls by reducing surface friction using air bubbles or air layers gas filled volumes using means for producing a film of air or air bubbles over at least a significant portion of the hull surface
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63H—MARINE PROPULSION OR STEERING
    • B63H1/00—Propulsive elements directly acting on water
    • B63H1/02—Propulsive elements directly acting on water of rotary type
    • B63H1/12—Propulsive elements directly acting on water of rotary type with rotation axis substantially in propulsive direction
    • B63H1/14—Propellers
    • B63H1/18—Propellers with means for diminishing cavitation, e.g. supercavitation
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T70/00—Maritime or waterways transport
    • Y02T70/10—Measures concerning design or construction of watercraft hulls

Definitions

  • the present invention relates to the generation of cavitation in liquids, inter alia for the purposes of drag reduction in liquid flow.
  • Drag reduction of marine vessels has conventionally been achieved in a number of ways. It has been well established that order 50-100 micron sized flow aligned (plus or minus 10 degree) V, U or L profile grooves defining so-called "riblets" therebetween can reduce turbulent skin friction drag, with 'standard' uniform height V-groove riblets offering 7% drag reduction per unit area covered over a wide range of Reynolds and Mach numbers.
  • Riblets have been shown to combine successfully with a variety of other passive drag reduction techniques such as polymer coating - see again E.Coustols & A.M.Savill above, also Choi, K.-S., Gadd, G.E., Pearcey, H.H., Savill, A.M. & Svenson, S. (1989) Test of drag reducing polymer coated on riblet surface. Applied Scientific Research 46, 209-216.
  • Hydrofoil technology has also been used to achieve improved performance in both military and commercial sectors. Hydrofoils, when operating within the optimal regime, are characterized by the highest lift to drag ratio among all types of water-borne craft.
  • Various operating regimes for a plano-convex hydrofoil have been depicted by Le Q., Franc J.P. & Michel J.M. 1993 "Partial cavities : global behaviour and mean pressure distribution" J. of Fluids Eng. 115 243-248. This document indicates the sub-cavitating operating regime, the boundary of the sub-cavitating domain for a particular hydrofoil profile being a function of the lift coefficient, profile thickness-chord ratio, and cavitation number.
  • Optimum sub- cavitating (fully wetted) foil sections have an upper speed limit of about 45 to 50 knots - see Conolly, A.C., Prospects for very-high-speed hydrofoils, Marine Technology, 12(4), 1975, 367-377.
  • the overall (“global") shape and orientation of a hydrofoil can result in sufficiently low pressure being generated in a region towards the rear of the convex surface of the foil that cavitation results in that region.
  • cavitation is initiated at surface excrescences, roughness and pitting within that region.
  • Such features are not predetermined but rather the by-product of manufacturing and/or wear. Increased foil curvature will also bring forward the onset and degree of cavitation.
  • partial cavitation is a highly unsteady and three- dimensional phenomenon, but under some conditions a "sheet-like" form of cavitation will originate from near the leading edge that has a stable smooth glassy surface.
  • US6684801 discloses an underwater vehicle body having a cavitator positioned at its forward end.
  • the cavitator causes a low-pressure wake to form aft of the cavitator.
  • the pressure in the wake falls as the speed of the vehicle is increased.
  • Eventually the pressure in the wake falls sufficiently such that a vapour pressure is reached and fluid changes state from liquid to gas, forming a gas filled cavity surrounding the body.
  • the cavitator is designed with a blunt forward section and sharp detachment points, the cavity forming at the detachment points.
  • This behaviour is also described in US6684801 as "supercavitation".
  • the cavity surrounding the vehicle body is on all sides rather than just on a suction surface as illustrated in the bottom right-hand of figure 4.
  • a hull 70 having a bow 72 and stern 74 is provided with cavitators in the form of discontinuities 76 on either side of the hull surface.
  • the length L2 of each discontinuity is typically of the order of a metre.
  • the database abstract for GB894627 discloses a method of treating liquids, e.g. emulsions including mineral oil distillate or methyl alcohol, by forcing the liquid through an annular working gap at a predetermined speed and subjecting the liquid in the working gap to periodically repetitive shearing, pulsation and cavitation.
  • the cavitation occurs as a result of the low pressures generated by the high shear stresses in the liquid in the working gap, in particular adjacent the surfaces defining the working gap.
  • the surface has a plurality of predetermined regions spaced in the predetermined direction, the surface in each region having at least one discontinuity configured to generate, in liquid in the vicinity of that region, a pressure sufficient to initiate cavitation in that liquid.
  • Such an arrangement results in the formation of a plurality of cavitation cavities spaced over the surface in the flow direction, thereby providing a reduction in drag similar to that provided by the aforementioned super cavity extending from the leading edge and covering (at least partially) the surface in the flow direction.
  • the pressure necessary to initiate each of these cavities in liquid in the vicinity of each region may be achieved at lower liquid flow velocities than would be required to achieve the pressure necessary to initiate the corresponding super cavity. This enables the benefits of lower drag to be realised at lower flow velocities than in the known arrangements discussed above.
  • each region may only need to be configured to generate cavitation in liquid in the vicinity of that region alone.
  • each region is a sub-global feature.
  • each region can be a microfeature, i.e. at least three orders of magnitude smaller than the surface to which it relates.
  • the features of each region are typically of millimetre size.
  • the predetermined regions of the surface may be configured so as to generate a respective plurality of cavities that coalesce to form a single cavity. Such a single coalesced cavity generated in this way may fit more closely to the surface than a super cavity generated by the known techniques discussed above.
  • the present invention comprises a plurality of regions that are predetermined, i.e. intentionally configured to generate a desired pattern of cavitation over the surface, inter alia to reduce drag.
  • the surface of the present invention has a plurality of predetermined regions, the surface in each region having at least one discontinuity. It is this discontinuity that is configured to generate, in liquid in the vicinity of that region, a pressure sufficient to initiate cavitation in the liquid.
  • the predetermined regions of the surface may be spaced across the surface in a non- random fashion. In particular, they may be regularly spaced across the surface in at least one direction. They may be regularly spaced across the surface in the predetermined direction of liquid flow relative to the surface.
  • the surface may meet the liquid flow at a leading edge and part from the liquid flow at a trailing edge, the predetermined regions of the surface being spaced in the predetermined direction from the leading and trailing edges.
  • At least one of the predetermined regions of the surface may have a discontinuity configured, in liquid in the vicinity of that region, to accelerate that liquid so as to generate a pressure drop sufficient to cause cavitation in that liquid (so-called "inertial" cavitation).
  • a discontinuity in a region of the surface may be configured to generate a vortex resulting in rapid rotational motion of liquid contiguous with that region away from the centre of the vortex leading to pressure drop sufficient to cause cavitation.
  • a predetermined region of the surface may comprise a discontinuity in the form of a protuberance or riblet.
  • the protuberance may be triangular in cross-section.
  • the protuberance may be defined between U-shaped grooves.
  • the protuberance may have an L- shaped profile.
  • the protuberance may be configured so as not to protrude beyond the viscous part of the boundary layer of the liquid flow.
  • the protuberance may be configured to protrude into the turbulent part of the boundary layer.
  • a predetermined region of the surface may have a discontinuity configured to cause the pressure in liquid contiguous with that region alone to oscillate to a level sufficient to initiate cavitation in that liquid.
  • the discontinuity may be configured to generate resonant pressure oscillation in that liquid.
  • the discontinuity may be formed by a recess configured to act as a Helmholtz resonator with liquid contiguous with that region.
  • a discontinuity in a predetermined region of the surface may be configured to generate pressure oscillation in liquid contiguous with that region alone by mechanical vibration.
  • the discontinuity may comprise a mechanical resonator.
  • the present invention also provides a liquid in contact with a surface as set out above and moving relative to the liquid in a predetermined direction.
  • the liquid may be water.
  • the invention also provides a water-borne vessel, such as a boat or ship, having a drag-reducing wetted surface (i.e. a surface exposed to water flow) as set out above.
  • a water-borne vessel such as a boat or ship
  • a drag-reducing wetted surface i.e. a surface exposed to water flow
  • the wetted surface may be a hull or a hydrofoil.
  • the invention also provides a liquid-bearing vessel, such as a pipe, having a drag- reducing wetted surface (i.e. a surface exposed to liquid flow) as set out above.
  • the invention provides a method of reducing the drag of liquid flow in a predetermined direction over a surface, the method comprising the steps of:
  • the invention also provides a method of manufacturing a surface to be exposed to liquid flow in a predetermined direction relative to the surface, the method comprising the steps of:
  • determining the location of a plurality of regions of the surface to be configured to generate, in liquid in the vicinity of each respective region, a pressure sufficient to initiate cavitation in that liquid
  • the invention provides apparatus for generating cavitation in a liquid, the apparatus comprising a receptacle for liquid and a cavitation- generating surface as set out above.
  • the apparatus may comprise a member within the receptacle.
  • the cavitation- generating surface may be a surface of the receptacle and/or of the member within the receptacle.
  • the receptacle and the member may be moveable relative to one another.
  • the receptacle may be stationary and the member moveable relative thereto.
  • the receptacle and the member may be rotatable relative to one another.
  • the receptacle may have a liquid-wetted surface of cylindrical form, and which may also be a cavitation-generating surface.
  • the member may have a surface of cylindrical form, and which may also be a cavitation-generating surface.
  • the receptacle and member may define between them a first space of annular cross- section.
  • the receptacle and member may further define between them a second space of circular cross-section in liquid communication with the first space.
  • the apparatus may comprise a first liquid port in direct communication with the first space and a second liquid port in direct communication with the second space.
  • the first port may lie adjacent one end of the cylindrical liquid- wetted surface of the receptacle and/or the member.
  • the second port may lie adjacent the longitudinal axis of the cylindrical liquid-wetted surface of the receptacle and/or the member.
  • the receptacle may have a further liquid-wetted surface lying substantially perpendicular to the longitudinal axis of the cylindrical liquid-wetted surface of the receptacle and/or the member.
  • the first and/or second ports may be formed in said further liquid- wetted surface.
  • the invention provides a method of generating cavitation in a liquid comprising the steps of:
  • the invention provides a method of manufacturing an emulsion, the method comprising the steps of:
  • each region being configured to generate, in mixture in the vicinity of that region, a pressure sufficient to initiate cavitation in that mixture;
  • each of the predetermined regions may be configured to act as a Helmholtz resonator with mixture contiguous with that region.
  • the first liquid may be a liquid fuel, in particular diesel oil.
  • the second liquid may be water.
  • the invention provides an emulsifier comprising:
  • a cavitation-generating surface having a plurality of predetermined regions spaced in a predetermined direction, each region being configured to generate, in mixture in the vicinity of that region, a pressure sufficient to initiate cavitation in, and emulsification of, that mixture.
  • Each of the predetermined regions may be configured to act as a Helmholtz resonator with mixture contiguous with that region.
  • the invention provides a liquid fuel-fired power plant comprising an emulsifier as set out above.
  • the power plant may comprise a liquid fuel-fired engine.
  • the engine may comprise a combustion chamber configured to receive liquid fuel.
  • the engine may be an internal combustion engine, in particular a reciprocating piston engine.
  • the invention provides a vehicle comprising a liquid fuel-fired power plant as set out above and having a liquid fuel-fired engine configured to provide motive power to the vehicle.
  • the vehicle may have wheels, the engine being configured to provide motive power to the wheels.
  • Figure 1 illustrates the formation of a conventional super cavity forming off sharp leading and trailing edges of a foil
  • Figure 2 is a plan view of the hull of a marine vessel incorporating conventional cavitation-generating features
  • Figure 3 A illustrates a marine vessel having surfaces according to the present invention
  • Figure 3B shows a liquid carrying pipe having an internal bore according to the present invention
  • Figure 4A shows a first embodiment of a surface according to the present invention
  • Figures 4B and C are detail and plan views of figure 4A respectively;
  • Figures 5A-C show a second embodiment of a surface according to the present invention.
  • Figures 6A-C show a third embodiment of a surface according to the present invention.
  • Figures 7A-C show a fourth embodiment of a surface according to the present invention.
  • Figure 8 is a sectional view through a cavitator in accordance with the present invention
  • Figure 9 illustrates an alternative embodiment of the cavitator of figure 8;
  • Figure 10 illustrates an alternative embodiment of the cavitator of figure 8.
  • Figure 11 is a schematic illustrating an implementation of the invention in a wheeled vehicle.
  • Figure 3A shows a marine vessel 90 travelling on the surface 98 of a body of water and having various surfaces exposed to liquid (water) flow including surfaces of hydrofoils 92, 94 and the surface of the aft portion 96 of the hull.
  • Figure 3B is a cross-sectional view of a liquid-bearing vessel in the form of a pipe 400 having an internal surface or bore 420 exposed to flow of liquid 410 in a predetermined direction F.
  • Figure 4A is a sectional view through one such surface 1 10 taken along the direction of liquid flow (indicated by arrow F) in a predetermined direction relative to the surface.
  • the liquid flow is in a direction F substantially parallel to the surface, the surface meeting the flow at a leading edge 1 12 and parting from the flow at a trailing edge 114.
  • Surface 110 has a plurality of predetermined regions 120 mutually spaced in the direction F by a pitch 130. As shown, the group of regions is spaced in the direction F from the leading and trailing edges by distances 126 and 124 respectively.
  • the surface in each region 120 has at least one discontinuity configured to accelerate the liquid local to the region so as to cause a pressure drop sufficient to cause cavitation in the liquid local to each region.
  • the resulting blanket of cavitation bubbles 122 reduces the wetted area of the surface 110, thereby reducing liquid drag.
  • the invention can achieve drag reduction and hence higher speed for nominally zero propulsive power increase.
  • the typical cavitation number lies in the range 0.1 to 0.2. Moreover, this cavitation initiates at a velocity of liquid flow that is lower than that velocity at which cavitation might conventionally be initiated at the leading or trailing edge of said surface. This enables the benefits of lower drag to be realised at lower flow velocities than in known arrangements in which cavitation is generated at the leading and/or trailing edges of a body.
  • the plurality of predetermined regions 120 on the surface 1 10 can be configured so as to coalesce to form a single cavitation cavity, also known as "sheet cavitation".
  • This single cavitation cavity can cover substantially the entire surface 1 10, from leading edge 112 to trailing edge 114.
  • a "global” or “super” cavity generated in this way may fit more closely to the surface than supercavities generated by the known techniques discussed above.
  • each region 120 has a discontinuity in the form of a protuberance or riblet 140 that extends above other, non-cavitating regions 150 of the surface and that generates vortices that result in rapid rotational motion of liquid away from the centre of the vortex leading to pressure drop sufficient to cause cavitation.
  • each riblet is elongate, extending at an angle a to a perpendicular P to the flow direction F.
  • angle a is chosen so as to generate, in liquid in the vicinity of each respective region, a pressure sufficient to initiate cavitation in that liquid.
  • angle a is about 30 degrees.
  • Each region may then be configured accordingly.
  • each riblet is triangular in cross-section, a group of riblets being of uniform height h (of around 0.25mm) and spaced at a pitch p substantially equal to their height h.
  • riblets defined between U-shaped grooves or having an "L" shaped profile may also be possible.
  • the height of the riblets 140 may lie in the range 0.1 to 1mm: at the upper end of this range they may be manufactured or cut directly into the surface 1 10 in question whilst at the lower end of the range the riblets may be formed in a plastic film applied to the surface (and available e.g. from 3M and from Hoescht).
  • a riblet 140 may operate within the viscous part of the boundary layer only or protrude into the turbulent part of boundary layer.
  • the riblets 140 can also regularise and maintain the generated cavitation bubbles over their surface area, their sharp peaks providing bubble nucleation sites and their valleys acting to contain bubbles formed within. This may promote coalescence of the cavitation bubbles into a more uniform cavitation sheet, the advantages of which are outlined in the Background Art section above. It is noted that, even in the absence of cavitation, such riblets operating within the viscous part of the boundary layer only can still be inherently drag reducing to drag neutral for the reasons outlined in the Background Art section above.
  • a riblet extends into the turbulent part of the boundary layer, drag may increase and a larger cavitation effectiveness would need to be achieved to offset this.
  • the riblet peak may act to align the bubbles, again promoting coalescence of the cavitation bubbles.
  • predetermined surface regions can also have discontinuities configured to initiate cavitation by pressure oscillation, a phenomenon known per se but only in the context of entire surfaces such as the flutter of hydrofoils discussed above.
  • predetermined regions 120 of the surface 1 10 are formed as Helmholtz resonators.
  • Resonant Helmholtz cavities or recesses 200 extend a distance L below non- cavitating regions 150 of the surface. Liquid fills the recesses 200 and is subsequently excited to resonance by the action of the liquid flow F over the open tops of the recesses. In oscillating, the liquid pressure in the recess periodically drops to a level sufficient to cause cavitation bubbles 122.
  • each region 120 is cylindrical having a diameter D, a depth L and a longitudinal axis X.
  • each region is spaced across the surface 110 in a non-random fashion, in particular they are spaced across the surface in the predetermined direction F by a uniform pitch 130 between respective axes X.
  • the regions are arranged in columns 160, 161, 162 spaced in a direction P perpendicular to the flow direction F by a uniform distance 170.
  • the regions of adjacent columns may be offset in the flow direction F by a distance 180.
  • FIGS 6A-C illustrate the implementation of inertial cavitation together with pressure oscillation induced cavitation, each region comprising a recess 200 formed between two protuberances or riblets 140.
  • each riblet 140 is elongate and extends at an angle a to a perpendicular P to the direction F of liquid flow.
  • adjacent columns 160, 161, 162 of recesses 200 are offset in the flow direction F.
  • Successive riblets and recesses in the direction F are uniformly spaced as indicated at 130.
  • Figure 7A is a view of a further embodiment of the invention viewed along the direction F of flow (into the page as viewed). Regions 120 of the surface 1 10 at predetermined locations thereof are formed with discontinuities in the form of protuberances 300 of rectangular cross-section perpendicular to the flow direction and attached to the surface on a shorter side 305 thereof. In the embodiment shown, the aspect ratio of each cross-section is about 2: 1. Referring to the plan view of figure 7B, each protuberance 300 is also rectangular in plan form and of aspect ratio of about 2: 1 in the particular embodiment shown.
  • Each protuberance 300 is a mechanical vibrator which, when exposed to liquid flow F, vibrates in bending in a direction perpendicular to the flow direction F as indicated by dashed lines in the detail view of figure 7C. Such vibration, typically known as “flutter", gives rise to pressure oscillations in the liquid - particularly between the vibrating protuberances - which in turn causes cavitation bubbles. Additional ventilation through the "valleys" 320 between the protuberances is also possible, e.g. by micro-bubble injection.
  • the mechanical vibrators 300 are spaced in the direction of liquid flow by a uniform pitch 130.
  • Multiple columns 160, 161, 162 of protuberances are provided at a uniform pitch 330.
  • adjacent columns are not offset; however, such offset is possible in the manner of earlier embodiments.
  • a global sub cavitating regime In the case of super-cavitating hydrofoils the following three regimes of operation have to be considered: a global sub cavitating regime, attached partial cavitation (unstable), and the supercavitating regime.
  • the global sub-cavitating regime local riblet induced cavitation forming a micro-bubble filled boundary layer or a sheet cavity would be limited to the vicinity of the foil. Expansion and collapse of the generated cavities is then controlled by global hydrofoil sub-cavitating flow properties.
  • the presence of cavitating riblets would be expected to have a stabilising effect on the cavity on the suction side of the foil and maintain a micro-bubble filled boundary layer or a sheet cavity on the high pressure side of the foil.
  • the riblets In the supercavitating regime, the riblets should be effective only on the wetted part of the foil.
  • Figure 8 illustrates a cavitator 400 in accordance with the present invention for generating cavitation in a controlled way in liquids, which may include liquid mixtures, liquids containing biological material and liquid/solid mixtures.
  • the apparatus comprises a liquid receptacle or housing 410 having an internal, liquid-wetted surface 420 of cylindrical form.
  • the cylindrical wall 41 1 of the housing is made of a transparent material so as to allow the liquid to be observed.
  • a member or rotor 430 Mounted within the housing is a member or rotor 430 having an external, liquid- wetted surface 440 of cylindrical form configured for cavitation generation as outlined above.
  • surface 440 has a plurality of regions each having a discontinuity in the form of a resonant Helmholtz cavity or recess 200.
  • rotor 430 is rotated about its longitudinal axis 450 while the housing remains stationary. This results in relative motion in a predetermined circumferential direction F (tangential to cylindrical surface 440) between liquid 470 in the housing and the surface 440 with its plurality of recesses 200 spaced around the circumference of the rotor. Recesses are also spaced perpendicular to the circumferential direction F in the manner of figure 5C. A typical speed at the rotor surface is 63 m/s. As previously explained, these recesses generate, in liquid in their vicinity, a pressure sufficient to initiate cavitation in that liquid.
  • Such cavitation can be used, inter alia, in drinking water to kill bacteria, in sewage to break up organic material, in algal biomass as a precursor to fuel extraction, in animal feed for treatment purposes, for mixing and emulsification purposes and in oil for the cracking of heavy fractions.
  • the recesses have been found to be self- cleaning.
  • the housing is closed either end by bottom and top plates 480, 490, the liquid- wetted surfaces 481,491 of which lie substantially perpendicular to longitudinal axis 450.
  • Surface 491 is formed with an inlet port 500 lying adjacent to or directly on the longitudinal axis 450.
  • the liquid to be processed is fed through this port from where it flows radially outwards through space 510 of circular cross-section to space 520 of annular cross section defined between the outer periphery 440 of the rotor and the inner periphery 420 of the housing. Cavitation takes place in this space, processed liquid then leaving the housing via port 530 located adjacent one end of the cylindrical liquid-wetted surface 420,440 of the housing or rotor.
  • the liquid flow does not need to be under high pressure in order to operate and can be connected into a flow loop without any special requirements.
  • a number of cavitators can be integrated into a flow loop either in parallel or series in order to achieve a desired effect.
  • the cavitator utilises a single rotor having a single type of Helmholtz oscillator.
  • Typical dimensions are as follows: rotor diameter 350mm, internal diameter of housing 400mm, height of rotor and internal height of housing 182mm.
  • Recesses may be circular of diameter 10mm, depth 5mm and spaced about the circumference at a pitch of 10 ° in three rows vertically spaced by 30mm.
  • a cavitator may comprise more than one rotor and a range of oscillators with different geometries and characteristics could be used.
  • oscillators may be mounted on the peripheral liquid wetted surface of the housing. Cavitation generation mechanisms other than Helmholtz cavities could also be used.
  • rotor 430 may have the form of a frustum of a cone, the exterior, cavitation-generating surface 440 being inclined to the axis of rotation 450.
  • liquid introduced at the narrower end 600 of the frustum e.g. via inlet port 500
  • rotor 430 may have first and second axially-spaced portions 650,660 of different diameter D2, Dl, the housing around the second portion being correspondingly reduced in diameter as indicated at 410'.
  • FIG 11 is a schematic illustrating the implementation of this concept in a wheeled vehicle, in particular the tractor unit 700 of a heavy goods vehicle.
  • the vehicle wheels 710 are driven - via a transmission 720 - by a power plant in the form of a reciprocating piston diesel engine 730.
  • a power plant in the form of a reciprocating piston diesel engine 730.
  • such an engine is configured to receive liquid fuel into its internal combustion chamber(s), specifically an emulsion of liquid diesel oil and liquid water.
  • the emulsion which may be stored in a buffer tank 750 prior to use, is made by a cavitator 400 of the kind described above with reference to figures 8-10 and supplied with a mixture of diesel oil and water from respective tanks 760,770.

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  • Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • Ocean & Marine Engineering (AREA)
  • Structures Of Non-Positive Displacement Pumps (AREA)
  • Physical Or Chemical Processes And Apparatus (AREA)

Abstract

Une surface (110) devant être exposée à un écoulement de liquide dans une direction prédéterminée (F) par rapport à la surface comprend une pluralité de régions prédéterminées (120) espacées dans la direction prédéterminée, la surface dans chaque région comprenant au moins une zone de discontinuité (200) conçue pour générer, dans un liquide à proximité de cette région, une pression suffisante pour déclencher une cavitation dans ledit liquide.
PCT/GB2014/051950 2013-07-02 2014-06-26 Génération de cavitation Ceased WO2015001315A2 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
GB201311813A GB201311813D0 (en) 2013-07-02 2013-07-02 Cavitation generation
GB1311813.8 2013-07-02
GB1319908.8 2013-11-12
GB201319908A GB201319908D0 (en) 2013-11-12 2013-11-12 Cavitation Generation

Publications (2)

Publication Number Publication Date
WO2015001315A2 true WO2015001315A2 (fr) 2015-01-08
WO2015001315A3 WO2015001315A3 (fr) 2015-09-11

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CN115017609A (zh) * 2022-05-23 2022-09-06 中国船舶科学研究中心 一种实尺度船舶附体空化部位有效攻角评估方法
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