Fluid handling – Flow affected by fluid contact – energy field or coanda effect – Means to cause rotational flow of fluid
Reexamination Certificate
2000-04-03
2001-05-29
Chambers, A. Michael (Department: 3753)
Fluid handling
Flow affected by fluid contact, energy field or coanda effect
Means to cause rotational flow of fluid
C137S809000, C137S811000, C137S826000, C137S833000
Reexamination Certificate
active
06237636
ABSTRACT:
BACKGROUND OF INVENTION
Injection of high molecular weight materials such as polymers into the boundary layer of a fluid flow has been shown to reduce skin friction drag significantly for both vessels moving relative to water and for pipeline applications. The large polymer molecules interact with the turbulent activity in the near-wall region, absorbing energy and reducing the frequency of burst (high energy fluid moving away from the wall) and sweep (low energy fluid replacing the high energy fluid in the near-wall region) cycles. The reduced burst frequency results in less energy dissipation from the wall and can result in skin friction drag reductions up to 80%. Experiments have shown that the efficacy of polymer molecules for drag reduction is closely related to their molecular weight, their location in the boundary layer, and the degree to which they have been stretched, or “conditioned”.
In the past, polymer mixture ejectors have been simple slots that ejected a mixture/solution of polymer and a fluid at an angle to the wall. To attain high drag reduction for a reasonable distance downstream with this ejection approach, large quantities and high concentrations of polymers must be ejected in order to flood the entire boundary area, creating a “polymer ocean” effect. The high polymer consumption rates of these systems have made them impractical for many drag reduction applications.
To be useful for practical applications, a more efficient method for ejecting polymer mixtures for drag reduction needed to be devised.
BRIEF SUMMARY OF THE INVENTION
This invention enables the efficient ejection of fluid mixtures/solutions into the near-wall region of a boundary layer of a fluid flow. The ejector of the present invention has, as a first object of the invention, to condition the polymer prior to ejection so that drag reduction occurs almost immediately following ejection. A second object of the invention is to release polymer only into the boundary layer region, where it can provide the greatest drag reduction. A third object of the invention is to retain the polymer in the near-wall region of the boundary layer, the most effective region for drag reduction, as long as possible.
The ejector system of the present invention preconditions the polymer mixture/solution for improved drag reduction performance using a unique arrangement of flow area restrictions, as well as by employing dimples, grooves and elastomeric materials. The dimples, grooves and flow area restrictions are sized relative to one another and to the Reynolds number of the flow for optimal polymer molecule conditioning (lengthening, unwinding, or stretching) so as to provide optimal drag reduction after ejection into the fluid flow. In addition, the ejector of the present invention uses a new approach to structuring the flow in order to reduce migration/dissipation of the polymer away from the near-wall region. This is achieved by a unique system of slots, each having a carefully designed surface curvature and surface features which establish a duct-like system of longitudinal (i.e., in the direction of the flow) Görtler vortices. Görtler vortices are formed by the centrifugal effect of a fluid flow that is given angular velocity by a concave surface. The duct-like system of Görtler vortices formed by the present invention mimic the spacing of naturally occurring quasi-longitudinal vortex pairs in the boundary layer, but are paired in the opposite orientation. The pairing of naturally occurring quasi-longitudinal vortex pairs is such that they migrate from the wall and are believed to contribute to the development of bursts and sweeps that account for a large portion of hydrodynamic drag. The vortices created by the present invention pair, such that the pressure differentials they create cause the vortices to remain near the wall. This advantageously causes the polymer that has been ejected into the boundary layer to remain in the near-wall region.
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McInville R M et al: “Analysis of large vortical structures in shear layers” AIAA Journal, Aug. 1985, USA vol. 23, No. 8, Aug. 1995, pp. 1165-1171.
Arnold Bruce Y.
Arnold International
Chambers A. Michael
Cortana Corporation
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