Experimental investigation of nozzle shape effect on wall shear stress beneath impinging round jetReport as inadecuate

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* Corresponding author 1 LaSIE - Laboratoire des Sciences de l-Ingénieur pour l-Environnement 2 BIA - Unité de recherche sur les Biopolymères, Interactions Assemblages

Abstract : This paper reports on measurements of velocities and wall shear rates for an impinging round jet. The test parameter that we consider is the nozzle shape. The Particle Image Velocimetry PIV was used to measure the axial and radial velocity components. The limitations of the PIV technique in the vicinity of the target wall are addressed by using the electrodiffusion technique to achieve wall shear rate distribution. A round orifice perforated either on a flat plate RO-P or on a hemispherical surface RO-H, is compared to a reference convergent nozzle CONV. All the nozzles have the same exit diameter D. The exit volumetric flow rate was also conserved and led to the same Reynolds number based on the exit bulk-velocity, Re0=5290. The nozzle-to-wall distance was constant and equal to 2 D. The whole velocity field and wall shear rates in the three impinging round jets having different features are compared. This has improved the understanding of the jet-wall interaction. The wall shear rate is in a close relationship with the near field flow features, themselves affected by nozzle geometry. The orifice nozzles generate narrower exit profiles compared to the convergent nozzle. The vena contracta effect in orifice jets, more intense with RO-P than with RO-H, generates an increase of the exit centerline velocity. The hemispherical surface of RO-H nozzle leads to a venna-stretching attenuating somewhat the venna contracta effect at the jet exit. The instantaneous PIV fields indicated the formation of secondary vortices in the region where a secondary peak in the mean and rms distributions of wall shear rate emerged.

Keywords : Electrodiffusion hemispherical nozzle impinging round jet PIV wall shear rate

Author: B. Montagné - K Sodjavi - P. Bragança - A. Meslem - Magdalena Kristiawan -

Source: https://hal.archives-ouvertes.fr/


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