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Research Papers: Fundamental Issues and Canonical Flows

Hysteresis of the Coanda Effect

[+] Author and Article Information
Aldona Skotnicka-Siepsiak

Institute of Building Engineering,
University of Warmia and Mazury in Olsztyn,
Olsztyn 10-719, Poland
e-mail: aldona.skotnicka-siepsiak@uwm.edu.pl

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received March 10, 2017; final manuscript received July 23, 2017; published online September 20, 2017. Assoc. Editor: Praveen Ramaprabhu.

J. Fluids Eng 140(1), 011202 (Sep 20, 2017) (9 pages) Paper No: FE-17-1149; doi: 10.1115/1.4037522 History: Received March 10, 2017; Revised July 23, 2017

For scientist, the Coanda effect has been an object of interest for a long time. All the time, some new applications of it are found although it has been more than a hundred years since Henri Coanda got a patent that was critical for that issue. Apart from aviation, it is more and more often used in ventilation systems to control the manner of air division and the design nozzles and ventilators. It is surprising, however, that a good command of that phenomenon and a need to apply it in different solutions did not entail a significant increase of the interest in the Coanda effect hysteresis, although it was mentioned for the first time by Newman in 1961. This article presents results of experimental measurements for a two-dimensional incompressible plane jet by an inclined plate. The hysteresis has been observed as a different jet behavior (a free jet or a jet attached to a flat plate) depending on the direction in which the plate deflection angle changes. The observed hysteresis area, defined by critical values for the αca attachment and αcd detachment angles, spanned from 8 deg to 14 deg. Its dependency on the Reynolds number has also been examined for Re ranging from 3500 to 26,500. Considering the Coanda effect hysteresis, a pressure distribution on the plate and the xR reattachment distance has been examined. The distribution of forces on a plate has been identified, which has facilitated a graphical mirroring of the Coanda effect hysteresis loop.

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Figures

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Fig. 1

Scheme of measuring post—side view: 1—air intake with the flow regulated by a rotating element, 2—sucking duct, 3—orifice plate for measuring static pressure, 4—ventilator, 5—elastic joints, 6—the Witoszyński nozzle, 7—measuring post case made of a rack and Plexiglas slates, and 8—plate; the Witoszynski nozzle element—three-dimensional detail

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Fig. 2

Witoszynski's nozzle section and reattachment of a two-dimensional jet to an inclined flat plate in local coordinate system

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Fig. 3

Dependency between values of critical angles related to plate length l=1.00 and nozzle slot b

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Fig. 4

Dependency between values of critical angles of detachment αcd and attachment αca and values of the Reynolds number

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Fig. 5

Reattachment distance xR examined in direction from α=0 deg to αcd

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Fig. 6

Reattachment distance xR examined in direction from αcd to plate deflection angle of α=0 deg

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Fig. 7

Pressure distribution on plate—research into α=0 deg to αcd; l/b=100.00; Re=13,428

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Fig. 8

Presse distribution on plate—research into αca to plate deflection angle α=0 deg; l/b=100.00; Re=13,428

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Fig. 9

Comparison of pressure distribution on plate for critical angles αcd and αca; Re=26,038 at l/b=500.00 and Re=26,038 at l/b=200.00

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Fig. 10

Maximum and minimum values of the Rp force noted inresearch into α=0 deg to αcd (detachment) and into αca toplate deflection angle α=0 deg (attachment); cases for l/b=50.00 at Re=26,038, 25,752, 21,8320, and 8971; l/b = 66.70 at Re=21,399, 18,488, and 10,071; l/b=100.00 at Re=13,428 and 8100; l/b=200.00 at Re=4364 and 3567

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Fig. 11

Rp/R0 force ratio distribution depending on α; (a) l/b=50.00; Re=26,038, (b) l/b=50.00; Re=8971, (c) l/b=66.70; Re=21,399, (d) l/b=66.70; Re=10,701, (e) l/b=100.00; Re=13,428, and (f) l/b=200.00; Re=4364

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