Impinging jet passive control fo wall shear stress enhancementReport 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 3 Building Services Faculty

Abstract : Heat, mass and momentum transfer induced on a wall by an impinging jet are linked to vortices organization at the jet exit, themselves influenced by jet nozzle geometry. Particle Image Velocimetry PIV and electrodiffusion techniques were used to investigate the characteristics of three impinging jets. Two cruciform jets, one issuing from a plane orifice nozzle CO-P and the second from a hemispherical orifice nozzle CO-H, were compared to a reference round jet issuing from a convergent nozzle. The distance between the jet exit and the target wall is equal to 2 nozzle equivalent diameters De. The Reynolds number based on De and on the exit bulk-velocity was equal to 5290 in each flow. The analysis of mean and fluctuating flow fields from PIV enables the identification of flows characteristics. The jet spreading rate and the turbulence intensities before impingement were found to be higher in the jet issuing from CO-H nozzle. The switching-over phenomena observed in CO-P nozzle jet does not occur in CO-H nozzle jet. Electrodiffusion measurements reveal some differences in the shape and the level of radial distributions of wall shear rates. Of the most important observations is the large difference between the three jets in the wall shear stress levels. For the same exit bulk-velocity, the maximum wall shear rate in CO-P and CO-H nozzle jets are almost two and three times respectively higher than the one of the reference convergent jet.

Keywords : wall shear rate Impinging jet lobed jet PIV Electrodiffusion

Author: K. Sodjavi - B. Montagné - Magdalena Kristiawan - A. Meslem - I. Nastase -



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