Ships – Building – Antifriction surfaces
Reexamination Certificate
2000-07-21
2002-03-19
Basinger, Sherman (Department: 3617)
Ships
Building
Antifriction surfaces
C244S130000
Reexamination Certificate
active
06357374
ABSTRACT:
TECHNICAL FIELD
This invention relates to a much more efficient method and apparatus to reduce the drag of plates or vessels moving relative to a fluid and of internal flows such as liquids moving through marine water-jet propulsors. The invention can be used to eject additives into specific regions of the boundary layer to modify the rheological properties of the fluid without the undesirable disruption of the boundary layer and without the rapid diffusion of the additive across the boundary layer inherent in traditional ejection techniques.
BACKGROUND ART
In the past, the effectiveness and efficiency of drag reduction obtained by ejecting non-Newtonian additives in “external” turbulent boundary layer flows has been limited relative to the effectiveness and efficiency observed in “internal” or pipe flows. In high Reynolds number turbulent pipe flows, reductions in friction drag of 70 to 80 percent are observed, while for ejection into high Reynolds number turbulent flows over a flat-plate, the maximum observed reduction in friction drag has been only about 40 to 60 percent. Further, the high additive expenditure rates experienced for external boundary layers have limited the economic benefit of implementing additive systems on maritime transport craft. Ejection techniques to introduce additives into external flows also have introduced unsteadiness and, in some cases, unfavorable viscosity gradients into the boundary layer, such that the penalties associated with the ejection process resulted in a greatly reduced net benefit. A more efficient method for introducing additives into the near-wall region of the boundary layer for drag reduction is needed.
In the prior art, advances were directed toward additive mixing or bubble generation and little attention was given to the ejector itself. U.S. Pat. No. 4,186,679 to Fabula et al (which issued Feb. 5, 1980), is representative of the modest attention paid to the ejector system itself. In this case, the ejector is identified as “a plurality of rearwardly raked ejection apertures.” Similarly, in U.S. Pat. No. 4,987,844 to Nadolink (which issued Jan. 29, 1991), the focus is on methods and apparatus to pump solvent passively, to mix multiple additives or suspensions, and to direct the mixture to the location of minimum pressure coefficient for ejection. The ejection apparatus is only identified as being one of many options, specifically “either screening, mesh, a porous media, perforated material, drilled holes of specific geometry, a circumferential slot, etc., ” and that “other forms of ejection apparatus . . . may be employed to achieve the result of the present invention.” In U.S. Pat. No. 5,445,095, by Reed et al (which issued Aug. 29, 1995), longitudinal riblets are combined with polymer ejection to predictably control the rate of diffusion of the polymer. However, the maximum downstream distance at which the material has completely diffused away from the riblets was identified as about 400 riblet widths, which scales to the order of centimeters for a marine vehicle, while the diffusion distance for the present invention has been shown to be on the order of tens of meters. As with the other inventions, no specific ejection technique is identified; only a series of “feasible” methods are listed. In Japanese Laid Open Patent Applications 09 151913 and 09 151914 by Mitsutake Hideo and Yoshida Yuki, respectively, both published 29-11-95, air bubbles are distributed along the submerged surface of a ship to reduce drag. In the first laid open patent application the ejectors are simply straight tubes, one for air bubbles and one upstream for a liquid. The purported purpose of the upstream “high kinetic energy” ejector is to entrain the air bubbles from the downstream ejector on the inside of the boundary layer near the submerged surface. The second laid open patent application is entitled “Microbubble Generator”, but a key component is a backwards (upstream) slanting flexible bubble generator with a sinusoidal fluid path. The ejection port is the outlet of the bubble generator, which faces upstream against the flow. The effects with regard to ejecting additives against the flow or disrupting the established boundary layer with a high-energy wall jet are not addressed.
A classical discussion of boundary layer theory, including formulation of Navier-Stokes and turbulent boundary layer equations, is provided in
Boundary-Layer Theory
, by Dr. Hermann Schlichting, published by McGraw Hill, New York, seventh edition, 1979. A discussion of structures and scales in turbulent flows can be found in
Turbulence
, 1975, McGraw Hill, written by J. O. Hinze, and in “Coherent Motions in the Turbulent Boundary Layer,” in
Annual Review of Fluid Mechanics
, 1991, Volume 23, pp. 601 to 639, written by Steven K. Robinson. The potential of dilute aqueous solutions of long-chain polymer molecules to reduce drag, now known as the Toms' Effect, was introduced by B. A. Toms at the First International Congress on Rheology in Amsterdam in 1948 and was published in the proceedings of that conference. P. S. Virk et al introduced the concept of drag reduction limits with polymer solutions in turbulent pipe flows in a paper entitled, “The Ultimate Asymptote and Mean Flow Structures in Toms' Phenomenon,” published in the
ASME Journal of Applied Mechanics
, 37, pages 488 to 493, in 1970. Virk et al related the level of drag reduction to an increase in the thickness of the buffer zone which, in turn, was limited by the pipe diameter. For external flows, no such physical constraint is imposed. However, D. T. Walker, his professor W. G. Tiederman, and colleague T. S. Luchik, in a paper entitled, “Optimization of the ejection process for drag-reducing additives,” which was published in
Experiments in Fluids
, 4, pages 114 to 120, in 1986, obtained drag reduction limits for slot ejection in a channel flow were 20 to 40 percent less than the maximum drag reduction observed in pipe flows. These observations were confirmed by others, such as Yu. F. Ivanyuta and A. A. Khomyakov in their article on the “Investigation of Drag Reduction Effectiveness with Ejection of Viscoelastic Polymer Solutions,” which was published in the
Proceedings of the International Shipbuilding Conference
, KRSI, October, 1994, St. Petersburg, pages 163 to 170, in Russian.
While dilute solutions of polymer behave as Newtonian fluids in laminar flows, A. Gyr and H. W. Bewersdorff, in their text,
Drag Reduction of Turbulent Flows by Additives
, Kluwer Academic Publishers, 1995, point out that in certain laminar flows, such as laminar contraction flows, polymer solutions exhibit non-Newtonian behavior. The hypothesis cited is that in such a flow, as in turbulent flow, the long molecules of the additive become stretched (uncoiled and elongated) and aligned in the flow which are necessary conditions for the solution to exhibit non-Newtonian behavior. V. G. Pogrebnyak, Y. F. lvanyuta, and S. Y. Frenbel, in their paper, “The Structure of the Hydrodynamic Field and Directions of the Molecular Slope of Flexible Polymers Under Free-Converging Flow Conditions” published in Russian in
Polymer Science USSR
. Vol. 34, No. 3, 1992, define the conditions under which the polymer molecules can be uncoiled, aligned, and sufficiently stretched to become effective in drag reduction.
Experiments by C. S. Wells and J. G. Spangler, described in their paper, “Injection of a Drag-reducing Fluid into Turbulent Pipe Flow of a Newtonian Fluid” published in
The Physics of Fluids
, Vol. 10, No. 9, pages 1890 to 1894, September, 1967, by M. M. Reischman and W. G. Tiederman described in an article, “Laser-Doppler Anemometer Measurements in Drag-reducing Channel Flows,” published in the
Journal of Fluid Mechanics
, Vol. 70, Part 2, pages 360 to 392, in 1975, and by W. D. McCombs and L. H. Rabie in “Local Drag Reduction Due to Injection of Polymer Solutions into Turbulent Flow in a Pipe,” Parts I and II, published in the
AlChE Journal
, Vol. 28, No. 4, pages 547 to 565, in July 1982, have clearly demonstrated that po
Babenko Victor V.
Gorban Vladimir A.
Moore Kenneth J.
Ryan Thomas D.
Arnold Bruce Y.
Arnold International
Basinger Sherman
Cortana Corporation
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