WO2010096411A2 - Surfaces présentant un écoulement glissant de continuum - Google Patents

Surfaces présentant un écoulement glissant de continuum Download PDF

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Publication number
WO2010096411A2
WO2010096411A2 PCT/US2010/024364 US2010024364W WO2010096411A2 WO 2010096411 A2 WO2010096411 A2 WO 2010096411A2 US 2010024364 W US2010024364 W US 2010024364W WO 2010096411 A2 WO2010096411 A2 WO 2010096411A2
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WIPO (PCT)
Prior art keywords
coating
smooth
gas
extended
continuum
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Application number
PCT/US2010/024364
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English (en)
Other versions
WO2010096411A3 (fr
Inventor
George Emanuel
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Ksy Corporation
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Publication date
Application filed by Ksy Corporation filed Critical Ksy Corporation
Publication of WO2010096411A2 publication Critical patent/WO2010096411A2/fr
Publication of WO2010096411A3 publication Critical patent/WO2010096411A3/fr

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B61—RAILWAYS
    • B61D—BODY DETAILS OR KINDS OF RAILWAY VEHICLES
    • B61D17/00—Construction details of vehicle bodies
    • B61D17/02—Construction details of vehicle bodies reducing air resistance by modifying contour ; Constructional features for fast vehicles sustaining sudden variations of atmospheric pressure, e.g. when crossing in tunnels
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
    • B62D—MOTOR VEHICLES; TRAILERS
    • B62D35/00—Vehicle bodies characterised by streamlining
    • 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
    • Y02T30/00—Transportation of goods or passengers via railways, e.g. energy recovery or reducing air resistance

Definitions

  • the technology relates to the fields of fluid dynamics and heat transfer, and more particularly relates to ultra-smooth extended surfaces that exhibit viscous slip and/or temperature jump when a gas flows over these surfaces.
  • Diamond-like carbon is an amorphous carbon and, when it is hydrogen free, it is called “tetrahedral amorphous carbon" (ta-C).
  • ta-C tetrahedral amorphous carbon
  • Diamond, diamond-like carbon (DLC), and other related materials are some of the hardest materials known and offer several other outstanding properties, such as high mechanical strength, chemical inertness, and very attractive friction and wear properties, that make them good prospects for a wide range of tribological applications, including rolling and sliding bearings, machining, mechanical seals, biomedical implants, micro-electromechanical systems (MEMS), etc.
  • DLC is also used as a protective coating on magnetic and optical storage disks, and optical windows. This type of coating, however, should not be confused with a diamond film coating.
  • Atomic force microscopy has shown that ta-C (and amorphous metal oxide) coatings, when properly deposited, have a root mean square (“rms”) roughness, ⁇ , on the order of 1 A (10 '10 m). This type of surface is referred to as ultra-smooth or nano-smooth.
  • An ultra-smooth surface using DLC, amorphous metal oxide and similar coatings can be applied directly to a metal surface, such as platinum, using elastic emission machining, microstiching interferonometry and relative angle determinable stiching interferonometry.
  • the surface is used to focus hard x-rays by a total reflection mirror.
  • the ultra- smooth area was created by coating deposition, either by a high current arc (HCA) system, with a depth ranging from 1-20 nm, or by a filtered cathodic vacuum arc (FCVA), with a depth ranging from 4-70 nm.
  • HCA high current arc
  • FCVA filtered cathodic vacuum arc
  • cold plasma was utilized in which lateral relaxation of the deposited ions produces an ultra-smooth surface.
  • the plasma has a pressure of about 10 "4 Pa and is at room temperature.
  • the C + ion energy is in the 20-40 eV range. It is known that if the plasma temperature exceeds a critical value of about 150 - 250 0 C, or if the ion energy exceeds about 100 eV, then the film surface loses its ultra- smoothness.
  • the small surface area may accommodate experimental and computational simulation requirements.
  • the measurement edge distance is 5 x 10 "7 m, large compared to the mean free path of air at sea level, which is about 6.6 x 10 " m. There is no specific indication that the area is also free of micro-and macro-roughness or that roughness elements larger than 0.1 nm, and other flaws, are buried inside the coating.
  • Sub-One Technology (of pleasanton, CA) has developed deposition technology for forming a smooth multi-layer coating on metal surfaces, such as inner surfaces of pipes, valves and other mechanical equipment, used in the oil and gas industry.
  • the technology is sold under the trademark InnerArmor® and the multi-layer coating is said to have a DLC outer layer.
  • the InnerArmor® coating is said to reduce the (sliding) coefficient of friction to as low as 0.01.
  • An exemplary embodiment provides an apparatus that has a surface exposed to a continuum gas during use when there is relative motion between the apparatus and the continuum gas.
  • the exposed surface has an extended, nano-smooth, homogeneous coating directly on the exposed surface. This extended nano-smooth coating interfaces with the gas continuum. As a result, the extended nano-smooth surface of the apparatus exhibits slip flow when in motion relative to the gas continuum.
  • Another exemplary embodiment provides an apparatus immersed in a continuum of gas.
  • the apparatus has a surface in motion relative to the gas continuum, when the apparatus is in use.
  • the surface has an underlying surface of a material different from an extended nano- smooth, homogeneous coating applied to the surface in motion.
  • the coating exhibits slip flow when the surface is in motion relative to the gas continuum gas.
  • Another exemplary embodiment provides an apparatus having a surface in motion relative to the gas continuum when the apparatus is in use.
  • the surface in motion includes an underlying surface of a material different from material of an extended, homogeneous, nano- smooth coating applied to the underlying surface.
  • the extended nano-smooth coating exhibits slip flow when the surface is in motion relative to the gas continuum and the coating is at least twice as thick as an rms roughness of the underlying surface.
  • any roughness features of the underlying surface extending through the coating are spaced apart by a lateral distance greater than about three times the mean free path of the gas.
  • FIG. 1 is an illustration of an exemplary embodiment of a process flow block diagram for making extended ultra-smooth surfaces
  • FIG. 2 is a partial cross-sectional view through an object having a surface that is exposed to a continuum gas during ordinary use;
  • FIG. 3 is an exemplary embodiment of a partial cross-sectional view through an object having a surface that is coated with an ultra-smooth extended coating that will be exposed to a continuum gas during ordinary use;
  • FIG. 4 is an illustration depicting, in cross-sectional view, air flow and boundary layer effects on an aerofoil.
  • FIG. 5 is an illustration depicting, in cross-sectional view, a laminar flow boundary layer on an exemplary aerofoil coated with an ultra-smooth extended coating.
  • viscous slip is a phenomenon that significantly reduces skin friction, or "viscous drag," at the interface between a surface and a continuum gas flow.
  • viscous slip permits boundary-layer control at the interface between a surface and a continuum gas flow.
  • Viscous slip may, for example, delay or eliminate the transition of a laminar boundary layer to a turbulent one, hasten the reversion to laminar flow ("re- laminarization") of a turbulent boundary layer, and delay or eliminate boundary-layer separation (from the surface).
  • Temperature jump provides a significant reduction in the rate of heat transfer from a surface into a continuum of gas flow.
  • slip flow hereinafter encompasses viscous slip, drag reduction, temperature jump, and boundary- layer control.
  • slip flow over a surface is dependent upon the surface smoothness, or to put it another way, the measured surface roughness.
  • Surfaces may be classified according to extent of their roughness.
  • surface texture may be characterized as including (1) roughness (nano- roughness and micro-roughness) that extends vertically ("hills and valleys") and laterally (the spacing between successive hills or successive valleys), (2) waviness (macro-roughness), (3) lay, and (4) flaws.
  • Lay refers to the orientation of the waviness and is not significant for velocity slip, unlike characteristics (1), (2) and (4).
  • a surface may be locally nano-smooth but still subject to the other types of roughness, including micro-roughness.
  • the mean lateral distance between roughness features on the surface is at least about three times greater than the mean free path of the gas.
  • the goal is to cover substantially the entire surface subject to exposure to motion relative to the continuum gas.
  • coating thickness should be sufficient to bury within itself and cover substantially all surface roughness features such that the mean distance between any residual surface roughness is at least about 3 times greater than the mean free path of the gas.
  • a variety of surface coatings may be used to achieve extended ultra-smooth surfaces. These coatings are desirably able to cover surface imperfections (roughness), have low friction vis-a-vis the continuum gas, and have appropriate hardness and chemical inertness for its intended use.
  • surface coatings such as DLC, metal oxides, metals nitrides, carbides, and the like. These techniques include cold plasma-based processes, including but not limited to HCA and FCVA.
  • Exemplary embodiments of useful coatings may have one or more of the following characteristics, depending upon the conditions they will encounter in normal use: smoothness, relatively low friction coefficient, hardness, high mechanical strength, chemical inertness, and an appropriate thermal expansion coefficient that reduces separation or spalling of the coating from its underlying surface.
  • Some exemplary embodiments, such as DLC, are strongly hydrophobic. This property is useful in a variety of applications, for example, to minimize water on the surface of an aircraft wing that has an extended ultra-smooth homogeneous coating and thereby minimize or prevent ice build up in bad weather conditions. This may eliminate the need for de- icing of aircraft outer surfaces in icy conditions.
  • the extended ultra-smooth coatings are "homogenous," i.e.
  • the coatings may be referred to as "single- layered" due to the homogeneity of the coating material throughout the thickness of the coating.
  • the extended ultra-smooth homogeneous single layer coatings are applied directly to the underlying surface.
  • the underlying surface may be the surface of a substrate or it may be the surface of a substrate that has been pre-coated to reduce the roughness of the substrate's surface or to facilitate tight bonding of the coating over the substrate.
  • the mean free path of air at sea level (10 5 Pa, 293 K) is substantially larger than a nano-smooth roughness length.
  • the mean free path is comparable in magnitude to the micro-roughness of a conventionally very smooth surface.
  • a surface becomes an extended ultra- smooth surface (or “mirror-like" to the continuum medium) when it is made continuously nano- smooth over distances multiples greater than the lateral roughness of the underlying surface, and is without flaws.
  • the tangential momentum component of the gas molecules is largely unaltered on impact and both velocity slip and temperature jump occur.
  • the flow regime ("slip flow”) over such an ultra-smooth extended surface is independent of a conventional Knudsen number, as well as the Reynolds and Mach numbers.
  • an extended nano-smooth surface may be achieved by selecting a surface to be smoothed, in process 110.
  • An example of such a surface is depicted schematically and not to scale in FIG. 2, which illustrates a curved plate 200 having an upper surface 210 that has Nl roughness, as depicted for illustrative purposes in the magnified insert.
  • the selected surface 210 is then subjected to surface smoothing operations, as appropriate, to achieve at least an Nl smooth surface, in process 120.
  • the surface smoothing process 120 may include initial cleaning, which may include chemical cleaning. This may be followed by grinding, abrading, polishing, and the use of other surface smoothing techniques.
  • the clean Nl surface 220 is then provided with a nano-smooth coating 250, as depicted illustratively in FIG. 3, of sufficient thickness, for example about 30 to about 100 nm, to cover flaws and other roughness features of the Nl surface.
  • a homogeneous extended nano-smooth coating may be applied by a cold plasma process, as discussed above.
  • preparing an Nl smooth surface is not necessarily essential and that in some exemplary embodiments rougher surfaces may be coated.
  • Providing an ultra- smooth coating on a rougher surface means that the coating has to be thicker to substantially completely bury within itself the "Mils and valleys" of the surface because these surface features will be more pronounced on a rougher surface. Accordingly, preparing an Nl surface has the advantage of requiring less coating material and a thinner coating.
  • a base coating may be applied to pre-smooth a surface that is rougher than Nl to enable a less thick coating to be applied to achieve an extended ultra-smooth surface.
  • FIG. 4 is a schematic, not-to-scale depiction of air flow over a rough surface 210 of an object, such as an aerofoil 200.
  • the continuum of air or other medium flows smoothly over the frontal end of the aerofoil 200, as indicated by regions 330, but the boundary layer, laminar or turbulent, separates at some point from the aerofoil 200 upper surface due to the strength of the adverse pressure gradient creating a turbulent region of gas separation, depicted as region 340.
  • the aerofoil 200 of FIG. 5 which has a surface 250 supplied with a nano-smooth extended surface coating, shows little or no separation of continuum air flow over the surfaces.
  • Slip flow and temperature jump are generally associated with a rarefied gas flow, as occurs when a comet, meteorite, ballistic missile, or space vehicle enters into the upper atmosphere.
  • the flow is characterized by a Knudsen number
  • I is a characteristic body dimension.
  • I is the radius of the blunt nose of the body and ⁇ is the mean free path of the undisturbed air upstream of a bow shock wave.
  • ⁇ air 2.69X lO- 7 T 0740 (5b) where T is in Kelvin, ⁇ is in Pa-s, and the constants stem from a curve fit to tabulated values in Svehla, R. A., "Estimated Viscosities and Thermal Conductivities of Gases at High Temperatures," NASA Tech. Rept. R-132, 1962.
  • any type of ground vehicle for example bicycles, cars, trucks, busses, motorcycles, with all or part of its surface exposed to aerodynamic drag forces covered with an extended ultra- smooth coating, experiences drag reduction and improved boundary-layer control.
  • Components that may be coated include, for example, outer surfaces of roofs, hoods, trunks, doors, fairings, and other exposed exterior structural features. Improved fuel efficiency will be realized in motor driven vehicles. As is evident, this would have a favorable economic and environmental impact.
  • any type of airborne vehicle with part, or all, of its surface that would be exposed to aerodynamic drag forces covered with an extended ultra-smooth coating will experience drag reduction and improved boundary-layer control.
  • the coating could be applied to the fuselage as well as other aerodynamic surfaces, such as wings, flaps, tail assemblies, nacelles, rudders, etc.
  • the initial laminar boundary layer on a coated wing surface would not transition to turbulence and would remain attached for an appreciable angle of attack. This may result in improved wing design to take advantage of the slip flow effect. For instance, stall speed may be reduced, thereby allowing a slower and safer landing speed, a shorter runway and reduced tire wear. Vehicle fuel efficiency also increases.
  • a protective ultra- smooth coating would also be beneficial on the optical turret located at the fore end of the fuselage of the Airborne Laser aircraft of the U.S. Air Force.
  • the turret transmits a high power, large diameter infrared laser beam whose beam quality is adversely altered by the turbulent boundary layer that forms around the outer surface of the turret.
  • the turbulent boundary layer With an extended ultra-smooth turret outer surface, the turbulent boundary layer would be reduced to a relatively thin laminar boundary layer, thereby enhancing laser performance.
  • turbine blades used ir wind-turbines used to generate electricity.
  • These turbine blades range in shape from thost resembling aircraft impeller blades to those that are of a helical structure that are orientec longitudinally in service.
  • nozzle flow There are a variety of other specialized applications, such as nozzle flow.
  • nozzle flow For instance the nozzle for a quiet supersonic wind tunnel, especially for one with a high test section Macl number.
  • this type of wind tunnel suffers from rapid boundary-layer growth This growth would be diminished if the laminar boundary layer persists and has slip.
  • Diffusers both subsonic and supersonic are prone to boundary-layer separation, which adversely affect; the performance of the diffuser. Separation might be suppressed with an extended ultra-smooti coating.
  • the enclosing walls of the optical cavity of gas flow lasers would similarly benefit fr ⁇ n the coating.
  • the extended ultra-smooth coating should start upstream of the cavity foi maximum benefit to the optical beam.
  • the reflected shock wave in a shock tube flow causes tht boundary layer, established by the incident shock wave, to separate. This might be prevented bj an extended ultra-smooth wall coating. This also applies to shock tunnels, hi this case, the operating time would increase significantly.
  • Case 1 is based on a Moody Chart for gas flow in a circular pipe.
  • the selected Moody Chart curve represents a pipe of relative roughness, e/D, of 5 x 10 "5 that is close to that for a "perfectly smooth" wall.
  • D is the inner diameter and e approximately equals ⁇ . With an inner diameter of 2 cm, results for case 1 are obtained.
  • the wall is nominally considered smooth, the flow is without slip.
  • Cases 2-4 do not assume pipe flow. Cases 2 and 3 are from tribology. As mentioned, surfaces are graded from Nl to Nil. Case 2 is an Nl surface that is not a nano-smooth surface, and case 3 is an Nl 1 surface.
  • Case 4 presents an extended nano-smooth surface.
  • the large value for Kn 0 indicates that slip is expected.

Abstract

L'invention porte sur un appareil présentant une surface en mouvement par rapport au continuum de gaz, lorsque l'appareil est en utilisation. La surface en mouvement comprend une surface sous-jacente d'un matériau différent d'un matériau de revêtement nano-lisse, homogène, étendu, appliqué à la surface sous-jacente. Le revêtement nano-lisse étendu présente un écoulement glissant lorsque la surface est en mouvement par rapport au continuum de gaz et le revêtement est au moins deux fois plus épais qu'une rugosité rms de la surface sous-jacente. En conséquence, toutes les caractéristiques de rugosité de la surface sous-jacente s'étendant à travers le revêtement sont espacées d'une distance latérale supérieure à environ trois fois le trajet libre moyen du gaz.
PCT/US2010/024364 2009-02-20 2010-02-17 Surfaces présentant un écoulement glissant de continuum WO2010096411A2 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
US15425509P 2009-02-20 2009-02-20
US61/154,255 2009-02-20
US42042409A 2009-04-08 2009-04-08
US12/420,424 2009-04-08

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WO2010096411A2 true WO2010096411A2 (fr) 2010-08-26
WO2010096411A3 WO2010096411A3 (fr) 2010-12-02

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2012148794A3 (fr) * 2011-04-25 2013-12-12 Waters Technologies Corporation Valves dotées de revêtements protecteurs

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20040101629A1 (en) * 2000-11-09 2004-05-27 Hubert Baumgart Colour-and/or effect-producing multicoat lacquer, method for production and use thereof
JP2004532113A (ja) * 2001-05-16 2004-10-21 サン−ゴバン グラス フランス 光触媒コーティングを備えた基材
JP2005500427A (ja) * 2001-08-16 2005-01-06 ビーエーエスエフ　コーティングス　アクチェンゲゼルシャフト 熱および化学線により硬化する被覆材料およびその使用
JP2008513781A (ja) * 2004-09-17 2008-05-01 ナノシス・インク． ナノ構造薄膜およびその使用

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20040101629A1 (en) * 2000-11-09 2004-05-27 Hubert Baumgart Colour-and/or effect-producing multicoat lacquer, method for production and use thereof
JP2004532113A (ja) * 2001-05-16 2004-10-21 サン−ゴバン グラス フランス 光触媒コーティングを備えた基材
JP2005500427A (ja) * 2001-08-16 2005-01-06 ビーエーエスエフ　コーティングス　アクチェンゲゼルシャフト 熱および化学線により硬化する被覆材料およびその使用
JP2008513781A (ja) * 2004-09-17 2008-05-01 ナノシス・インク． ナノ構造薄膜およびその使用

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2012148794A3 (fr) * 2011-04-25 2013-12-12 Waters Technologies Corporation Valves dotées de revêtements protecteurs
EP2702303A2 (fr) * 2011-04-25 2014-03-05 Waters Technologies Corporation Valves dotées de revêtements protecteurs
EP2702303A4 (fr) * 2011-04-25 2014-10-29 Waters Technologies Corp Valves dotées de revêtements protecteurs
US10428967B2 (en) 2011-04-25 2019-10-01 Waters Technologies Corporation Valves having protective coatings

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