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Research Papers: Multiphase Flows

Shaping Air Flow Characteristics of a High-Speed Rotary-Bell Sprayer for Automotive Painting Processes

[+] Author and Article Information
Ch. Stevenin

LAMCOS,
UMR 5259 - INSA Lyon,
Villeurbanne 69621, France
e-mail: christophe.stevenin@centrale-marseille.fr

Y. Béreaux

LAMCOS,
UMR 5259 - INSA Lyon,
Villeurbanne 69621, France
e-mail: yves.bereaux@insa-lyon.fr

J.-Y. Charmeau

IMP,
UMR 5223 - INSA Lyon,
Villeurbanne 69621, France
e-mail: jean-yves.charmeau@insa-lyon.fr

J. Balcaen

IMP,
UMR 5223 - INSA Lyon,
Villeurbanne 69621, France
e-mail: jean.balcaen@insa-lyon.fr

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received January 14, 2015; final manuscript received May 26, 2015; published online July 10, 2015. Assoc. Editor: John Abraham.

J. Fluids Eng 137(11), 111304 (Jul 10, 2015) (8 pages) Paper No: FE-15-1025; doi: 10.1115/1.4030703 History: Received January 14, 2015

Electrostatic rotary bell sprayers (ERBS) are widely used in automotive painting applications. These processes involve complex airflows to shape paint sprays and transport droplets toward automotive parts to be coated. Despite the importance of shaping airflow on global spray characteristics, a detailed characterization of this aerodynamic flow is still missing. For this purpose, an experimental study was conducted on the influence of some ERBS operating parameters on the development and characteristics of shaping airflow. Results show that, for low swirl numbers, the flow behavior is close to that of annular swirling jets and a good agreement is found between ERBS flow characteristics and data available in literature. When rotational speed of the bell cup is sufficiently fast, a change of regime is observed with a shift in the longitudinal flow development and an increase of recirculation zone length. This change of regime is attributed to vortex breakdown instability, known to occur when high swirl strength is beyond a critical value. Experimental results obtained in this study put forward a clear link between the shaping air flow rate and the rotation frequency on the aerodynamics and also provide valuable leads to design shaping air flow in modern ERBS.

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Figures

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Fig. 1

High-speed rotary bell PPH 308 (Sames Technologies, France)

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Fig. 2

Isolines of velocity (m/s) obtained from Pitot tube measurements Q = 230 Nl/min, N = 30 krpm. Highest velocity is found close to the cup edge. Zero velocity isoline marks the outer limit of the recirculation zone.

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Fig. 3

Airflow pattern involved in conventional rotary bell atomizers

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Fig. 4

Maximum of the mean longitudinal velocity at x/dcup = 0 obtained from all the operating conditions tested in this work (see Table 1)

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Fig. 6

Evolution of the centerline velocity

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Fig. 7

Centerline velocity decrease rate as a function of diameter ratio

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Fig. 8

Evolution of the length of the recirculation region with blockage ratio DR2

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Fig. 9

Radial profile of the normalized axial velocity for x/dcup > 2

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Fig. 10

Evolution of maximum centerline mean velocity with swirl number

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Fig. 11

Radial (left) and centerline (right) profiles of mean longitudinal velocity for N = 30, 40, 50, and 60 krpm and three swirl numbers: S = 1.05 (top), S = 1.25 (middle), and S = 1.5 bottom)

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Fig. 12

Evolution of recirculation zone length with swirl number

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Fig. 13

Evolution of maximum mean centerline velocity with swirl number

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Fig. 14

Radial profiles of longitudinal mean velocity at x = 0

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