EP2171291A1 - Procédé destiné à réduire le frottement visqueux entre un fluide et un objet - Google Patents

Procédé destiné à réduire le frottement visqueux entre un fluide et un objet

Info

Publication number
EP2171291A1
EP2171291A1 EP08774109A EP08774109A EP2171291A1 EP 2171291 A1 EP2171291 A1 EP 2171291A1 EP 08774109 A EP08774109 A EP 08774109A EP 08774109 A EP08774109 A EP 08774109A EP 2171291 A1 EP2171291 A1 EP 2171291A1
Authority
EP
European Patent Office
Prior art keywords
projections
external surface
periodic trajectory
viscous
fluid
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.)
Withdrawn
Application number
EP08774109A
Other languages
German (de)
English (en)
Inventor
Maurizio Quadrio
Paolo Luchini
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.)
Universita degli Studi di Salerno
Politecnico di Milano
Original Assignee
Universita degli Studi di Salerno
Politecnico di Milano
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
Application filed by Universita degli Studi di Salerno, Politecnico di Milano filed Critical Universita degli Studi di Salerno
Publication of EP2171291A1 publication Critical patent/EP2171291A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15D—FLUID DYNAMICS, i.e. METHODS OR MEANS FOR INFLUENCING THE FLOW OF GASES OR LIQUIDS
    • F15D1/00—Influencing flow of fluids
    • F15D1/10—Influencing flow of fluids around bodies of solid material
    • F15D1/12—Influencing flow of fluids around bodies of solid material by influencing the boundary layer
    • 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
    • B63B1/36—Other means for varying the inherent hydrodynamic characteristics of hulls by reducing surface friction using mechanical means
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B64—AIRCRAFT; AVIATION; COSMONAUTICS
    • B64C—AEROPLANES; HELICOPTERS
    • B64C21/00—Influencing air flow over aircraft surfaces by affecting boundary layer flow
    • B64C21/10—Influencing air flow over aircraft surfaces by affecting boundary layer flow using other surface properties, e.g. roughness
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15D—FLUID DYNAMICS, i.e. METHODS OR MEANS FOR INFLUENCING THE FLOW OF GASES OR LIQUIDS
    • F15D1/00—Influencing flow of fluids
    • F15D1/002—Influencing flow of fluids by influencing the boundary layer
    • F15D1/0025—Influencing flow of fluids by influencing the boundary layer using passive means, i.e. without external energy supply
    • F15D1/003—Influencing flow of fluids by influencing the boundary layer using passive means, i.e. without external energy supply comprising surface features, e.g. indentations or protrusions
    • F15D1/0035—Influencing flow of fluids by influencing the boundary layer using passive means, i.e. without external energy supply comprising surface features, e.g. indentations or protrusions in the form of riblets
    • F15D1/004—Influencing flow of fluids by influencing the boundary layer using passive means, i.e. without external energy supply comprising surface features, e.g. indentations or protrusions in the form of riblets oriented essentially parallel to the direction of flow
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15D—FLUID DYNAMICS, i.e. METHODS OR MEANS FOR INFLUENCING THE FLOW OF GASES OR LIQUIDS
    • F15D1/00—Influencing flow of fluids
    • F15D1/02—Influencing flow of fluids in pipes or conduits
    • F15D1/06—Influencing flow of fluids in pipes or conduits by influencing the boundary layer
    • F15D1/065—Whereby an element is dispersed in a pipe over the whole length or whereby several elements are regularly distributed in a pipe
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B64—AIRCRAFT; AVIATION; COSMONAUTICS
    • B64C—AEROPLANES; HELICOPTERS
    • B64C2230/00—Boundary layer controls
    • B64C2230/26—Boundary layer controls by using rib lets or hydrophobic surfaces
    • 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
    • Y02T50/00—Aeronautics or air transport
    • Y02T50/10—Drag reduction
    • 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 a method for reducing the viscous friction due to the relative movement of a fluid and an object, in particular in the case of turbulent viscous friction.
  • the present invention also relates to an object comprising an external surface configured so as to reduce the viscous friction due to the relative movement of a fluid and the object, in particular in the case of turbulent viscous friction.
  • a frictional force usually called "viscous friction”
  • This frictional force tends to reduce the velocity of the relative movement of object and fluid.
  • US 5,971 ,326 describes a surface for a wall which is subject to a turbulent flow having a main direction, where the surface has projecting ribs which have an elongated form in the main direction (called “riblets”) and are spaced relative to each other in the direction perpendicular to the main direction of the flow.
  • the projecting ribs have the function of reducing the turbulent exchange of moment between the flow and the wall along the surface. In this way it is possible to obtain a reduction in the friction of 7% compared to a smooth surface.
  • US 5,595,205 describes control of turbulence by means of a system with delta-shaped protrusions positioned in the transverse direction with respect to the direction of the flow.
  • US 6,345,791 describes a series of riblets extending longitudinally along a surface and having a triangular cross-section in the transverse direction.
  • the apex of the cross-section defines a continuous, undulated ridge with peaks and valleys. Measured from the surface, the peaks have a greater height than the valleys.
  • the interaction of the riblets with the structure of the turbulent boundary layer of the airstream reduces the skin friction drag coefficient of the surface by approximately 12% over an identical smooth surface without the riblets.
  • the present inventors have noted that the known solutions referred to above disadvantageously are not particularly efficient as regards reduction of the viscous friction.
  • the present inventors have faced the problem of providing a method for reducing the viscous friction due to the relative movement of a fluid and an object, in particular in the case of turbulent friction, which is able to overcome this drawback.
  • the present inventors have faced the problem of providing a method for reducing the viscous friction due to the relative movement of a fluid and an object, in particular in the case of turbulent friction, which is able to achieve a reduction in the viscous friction considerably greater than that of the known solutions, so that the actual reduction in friction in real conditions is high enough for use of the method to be advantageous.
  • the present invention provides a method for reducing the viscous friction due to the relative movement of a fluid and an object, wherein the object has an external surface in contact with a layer of the fluid, the external surface having a base plane.
  • the method comprises the following steps: forming on the external surface a plurality of projections projecting from the base plane; and imparting to the layer of fluid, by means of the plurality of projections, a profile with a periodic trajectory parallel to the base plane.
  • the periodic trajectory is a sinusoidal wave or a triangular wave or a square wave.
  • the periodic trajectory has a wavelength preferably of between 500 and 2000 viscous units, and more preferably of between 900 and 1250 viscous units.
  • the periodic trajectory has an overall amplitude of between 100 and 500 viscous units.
  • the step of forming comprises a step of forming on the external surface the plurality of projections which extend in a longitudinal direction of the flow, each of the plurality of projections having a peak which follows the periodic trajectory.
  • the step of forming comprises a step of forming on the external surface the plurality of - A -
  • the step of forming comprises a step of forming on the external surface the plurality of projections having a cross-section which is constant in the longitudinal direction.
  • the step of forming comprises a step of forming on the external surface the plurality of projections aligned in a transverse direction perpendicular to a longitudinal direction of the flow and arranged along the periodic trajectory in the longitudinal direction.
  • the step of forming comprises a step of forming on the external surface the plurality of projections, each of the plurality of projections having the form of a wedge with a triangular-shaped base, the triangle having a vertex directed in the direction opposite to that in which the flow travels.
  • the step of providing comprises a step of forming on the external surface the plurality of projections, each of the plurality of projections having a height which is substantially equal to zero at the vertex.
  • the present invention provides an object comprising an external surface configured so as to reduce the viscous friction due to the relative movement of a fluid and the object, wherein the external surface has a base plane, the fluid having a layer in contact with the external surface.
  • the object is characterized in that the external surface comprises a plurality of projections formed so as to impart to the layer of fluid a profile with a periodic trajectory parallel to the base plane.
  • FIG. 1 b is a cross-sectional view along the plane a-a indicated in Figure 1 a;
  • - Figure 2a is a schematic top plan view of a portion of a surface of object according to a second embodiment of the present invention;
  • Figure 2b is a cross-sectional view along the plane b-b indicated in Figure 2a;
  • FIG. 3 is a graph showing the percentage reduction in friction as a function of the oscillation wavelength.
  • Figures 1 a, 1 b, 2a and 2b show a set of three Cartesian axes the mutually perpendicular directions of which are indicated by x, y and z.
  • the direction x coincides with the main direction of flow (indicated by the arrow F in Figures 1 a and 2a) and will be referred to as "longitudinal direction”.
  • the direction y is the direction perpendicular to the plane of the surface and will therefore be referred to as "normal direction”.
  • the direction z perpendicular to the longitudinal direction x and parallel to the plane of the surface will be called “transverse direction”.
  • the various figures are not shown in scale.
  • the surface has a base plane B parallel to the directions x and z.
  • a plurality of projections project from the base plane B, extending in the longitudinal direction x preferably parallel to each other and preferably equally spaced in the transverse direction z .
  • Figures 1 a and 1 b only four projections r1 , r2, r3 and r4 are shown.
  • the projection r2 has preferably a cross-section which is constant in the longitudinal direction x.
  • the projection r2 is shown as having a cross-section with a substantially triangular shape, the base of which coincides with the base plane B.
  • the projection r2 could have the form of a blade (i.e. blade ribs or infinitely deep grooves) or of a parabola (scalloped grooves).
  • the height of the projection r2, indicated as h in Figure 1 b is preferably between 5 and 35 viscous units, more preferably between 10 and 25 viscous units, and even more preferably is equal to 15 viscous units.
  • a viscous unit is a length which depends on the kinematic viscosity of the fluid and the fhctional velocity. For example, in the case of a aircraft flying at a height of 10000 m at a speed of 300 m/s, a viscous unit is equal to about 2.7 ⁇ m.
  • the height h of the projection r2 is preferably equal to 15 ⁇ 2.7 ⁇ m, namely about 40 ⁇ m.
  • the projection r2 has a peak c and is delimited by two valleys av1 , av2 which are substantially parallel to the peak c.
  • the distance between the valleys av1 , av2, indicated in Figure 1 a as Lz, corresponds both to the width of the projection r2, and to the distance between the projection r2 and the projections r1 and r3 adjacent to it.
  • the distance Lz is between 5 and 35 viscous units, more preferably between 10 and 25 viscous units, and even more preferably is equal to 15 viscous units. Therefore, in the example referred to above in which a viscous unit is equal to about 2.7 ⁇ m, the distance Lz is preferably equal to 15 ⁇ 2.7 ⁇ m, namely about 40 ⁇ m.
  • the peak c (and therefore also the valleys av1 an av2 parallel to them) follows, in the longitudinal direction x, a periodic trajectory which has an amplitude A and a wavelength ⁇ x .
  • the peak c shown in Figure 1 a follows a sinusoidal trajectory which in mathematical terms is described by the following equation: This is only an example since the peak c could follow any periodic trajectory, for example square wave trajectory, triangular wave trajectory, etc.
  • the wavelength ⁇ x is between 500 and 2000 viscous units, more preferably between 900 and 1250 viscous units.
  • the wavelength ⁇ x is preferably equal to 1250 ⁇ 2.7 ⁇ m, namely about 3.4 mm.
  • the amplitude A of the periodic trajectory is between 100 and 500 viscous units, more preferably is between 250 and 350 viscous units, and even more preferably is equal to 300 viscous units. Therefore, in the example above in which one viscous unit is equal to about 2.7 ⁇ m, the amplitude
  • A is preferably equal to 300 ⁇ 2.7 ⁇ m, namely about 810 ⁇ m.
  • This mechanism advantageously weakens or even interrupts the viscous cycle of turbulence regeneration near the wall, since it creates a transversal alternate laminar boundary layer upon the wall. This advantageously reduces the viscous friction considerably, as will be described below with reference to Figure 3.
  • the surface has a base plane B' which is parallel to the directions x and z and from which a plurality of projections project.
  • B' which is parallel to the directions x and z and from which a plurality of projections project.
  • the projections d1 1 , ... , d16, d21 , ... , d26, d31 , ... , d36, and d41 , ... , d46 are shown.
  • the projection d35 has the form of a wedge with a substantially triangular shaped base. The vertex of the triangle is directed upstream, namely in the direction opposite to that in which the flow indicated by the arrow F travels.
  • the projection d35 may have the form described by US 5,595,205 (delta-shaped). The arrangement of the projections according to these embodiments is, however, different from that described by US 5,595,205, as will be described in greater detail herein below.
  • the projection d35 has a height which is substantially equal to zero at the vertex of the triangle and gradually increases up to a height h'.
  • the height h' of the projection d35 is preferably between 1 and 10 viscous units, more preferably between 4 and 7 viscous units, and even more preferably, is equal to 5.5 viscous units. Therefore, in the example above in which a viscous unit is equal to about 2.7 ⁇ m, the height h' is preferably equal to 5.5 ⁇ 2.7 ⁇ m, namely about 15 ⁇ m.
  • the projection d35 has a width L'.
  • the width L' is preferably between 100 and 300 viscous units, more preferably between 150 and 250 viscous units, and even more preferably is equal to 200 viscous units. Therefore, in the example above in which a viscous unit is equal to about 2.7 ⁇ m, the width L' is preferably equal to 200 ⁇ 2.7 ⁇ m, namely about 540 ⁇ m.
  • the projections are arranged on the surface in a manner aligned in the transverse direction z.
  • the projections d1 1 , d21 , d31 and d41 are aligned with each other in the transverse direction z and are equally spaced from each other by a distance indicated in
  • the distance Lz' is between 160 and 360 viscous units, more preferably between 210 and 310 viscous units, and even more preferably is equal to 260 viscous units. Therefore, in the example above in which a viscous unit is equal to about 2.7 ⁇ m, the distance Lz' is preferably equal to 260 ⁇ 2.7 ⁇ m, namely about 700 ⁇ m.
  • the projections are arranged on the surface in the longitudinal direction z following a periodic trajectory.
  • the projections d1 1 , ... , d16 are arranged so that the respective vertices follow a periodic trajectory.
  • the same comments are applicable to the projections d21 , ... , d26, the projections d31 , ... , d36 and the projections d41 , ... , d46.
  • the trajectories followed by the vertices of the projections d1 1 , ... , d16, by the vertices of the projections d21 , ... , d26, by the vertices of the projections d31 , ... , d36 and by the vertices of the projections d41 , ... , d46 preferably are parallel to each other.
  • Figure 2a shows only the trajectory along which the projections d31 , ... , d36 are arranged.
  • the periodic trajectory has a wavelength ⁇ x '.
  • Figure 2a shows a sinusoidal trajectory which in mathematical terms is described by the following equation: This is only an example since the projections could be arranged so as to follow any periodic trajectory, for example square wave trajectory, triangular wave trajectory, etc.
  • the projections d31 , ... , d36 are arranged so that four projections are included in a wavelength ⁇ x '.
  • a wavelength ⁇ x ' may comprise a different number of projections. This number is preferably greater than or equal to 2.
  • the wavelength ⁇ x ' is between 500 and 2000 viscous units, more preferably between 900 and 1250 viscous units. Therefore, in the example above in which a viscous unit is equal to about 2.7 ⁇ m, the wavelength ⁇ x ' is preferably equal to 1250 ⁇ 2.7 ⁇ m, namely about 3.4 mm.
  • This second embodiment is also advantageously able to achieve a reduction in friction considerably greater than that of the known solutions.
  • the projections have a transverse position variable in the longitudinal direction z and therefore displace in the transverse direction the turbulent structures included in the layer of fluid closest to the wall, such that the latter lose their phase relationship with the turbulent structures situated at a greater distance from the wall. Therefore, advantageously, in this second embodiment also, the viscous wall cycle is weakened or even interrupted and therefore the viscous friction is reduced considerably.
  • the rate of the flow F was kept constant during the simulation and therefore the reduction in viscous friction corresponds to the reduction in the longitudinal pressure gradient which must be applied to the flow in order to cause it flow with a constant flow rate.
  • the dimensions of the wall used for the simulations are as follows: 21 hi in the longitudinal direction x and 6 In 1 in the transverse direction z, where In 1 is the half- height of the channel which was set to 200 viscous units.
  • the dimension in the longitudinal direction z was in each case adjusted so as to contain an integer number of wavelengths ⁇ x .
  • Each simulation was performed for a time period 1000U p /hi , where U p is the central velocity of a laminar flow with the same flow rate.
  • the simulations were performed on a supercomputer comprising 10 Xeon PCs with a dual processor connected together in a ring.
  • the amplitude A of the periodic trajectory was set to 350 viscous units and it was simulated using Taylor's frozen turbulence hypothesis and the convective character of the flow in the vicinity of the wall.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Aviation & Aerospace Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Ocean & Marine Engineering (AREA)
  • Lubricants (AREA)

Abstract

La présente invention expose un procédé destiné à réduire le frottement visqueux dû au mouvement relatif entre un fluide et un objet, l'objet présentant une surface externe en contact avec une couche du fluide et ladite surface externe présentant un plan de base. Le procédé comprend les étapes suivantes consistant à : former une pluralité de saillies sur la surface externe dépassant du plan de base; et attribuer à la couche de fluide, à l'aide de la pluralité de saillies, un profil avec une trajectoire périodique parallèle au plan de base.
EP08774109A 2007-06-25 2008-06-17 Procédé destiné à réduire le frottement visqueux entre un fluide et un objet Withdrawn EP2171291A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
IT001271A ITMI20071271A1 (it) 2007-06-25 2007-06-25 Metodo per ridurre l'attrito viscoso tra un fluido ed un oggetto
PCT/EP2008/057622 WO2009000703A1 (fr) 2007-06-25 2008-06-17 Procédé destiné à réduire le frottement visqueux entre un fluide et un objet

Publications (1)

Publication Number Publication Date
EP2171291A1 true EP2171291A1 (fr) 2010-04-07

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
EP08774109A Withdrawn EP2171291A1 (fr) 2007-06-25 2008-06-17 Procédé destiné à réduire le frottement visqueux entre un fluide et un objet

Country Status (3)

Country Link
EP (1) EP2171291A1 (fr)
IT (1) ITMI20071271A1 (fr)
WO (1) WO2009000703A1 (fr)

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US8684310B2 (en) 2009-01-29 2014-04-01 The Boeing Company Rigid tipped riblets
US9352533B2 (en) * 2009-01-29 2016-05-31 The Boeing Company Elastomeric riblets
US8413928B2 (en) * 2009-09-25 2013-04-09 The Boeing Company Structurally designed aerodynamic riblets
GB2476801A (en) * 2010-01-08 2011-07-13 Stephen Martin Redcliffe Surface features for increasing the efficiency of wind turbine Flettner rotors.
DE102013013817A1 (de) * 2013-08-22 2015-02-26 Airbus Defence and Space GmbH Strukturbauteil mit einer Ribletoberfläche
US9932481B2 (en) * 2015-04-21 2018-04-03 The Boeing Company Actuatable microstructures and methods of making the same
JP6714925B2 (ja) 2016-03-03 2020-07-01 国立研究開発法人宇宙航空研究開発機構 リブレット構造及び物体
FR3076540B1 (fr) * 2018-01-08 2021-04-16 Airbus Operations Sas Element aerodynamique d'un aeronef, pourvu d'un ensemble d'elements protuberants.
WO2020203284A1 (fr) * 2019-03-29 2020-10-08 国立大学法人東北大学 Structure surélevée et aile
JP7369386B1 (ja) 2022-05-23 2023-10-26 三菱重工業株式会社 隆起構造、翼、隆起構造の設計方法及びその設計プログラム

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Also Published As

Publication number Publication date
WO2009000703A1 (fr) 2008-12-31
ITMI20071271A1 (it) 2008-12-26

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