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Analysis of flow structures and instabilities developed by and air curtain sheared laterally by an external stream : application to the case of refrigerated display cabinets.

Analyse des structures des écoulements et des instabilités développées par un rideau d'air cisaillé latéralement par un courant externe : application au cas des meubles frigorifiques de vente.

Author(s) : KAFFEL A.

Type of monograph: Doctoral thesis

Summary

In this study, the aerodynamic behavior of the plane wall jet (Re = 8000) sheared laterally by an external lateral stream (ELS) of a uniform velocity profile (Ulf) was studied and analyzed. The experiments were carried out by PIV and LDV on a reduced-scale isothermal aeraulic model of a refrigerated display cabinet. The study focuses on the near-field region of the jet (x / e <10) which corresponds to the zone of transition to turbulence and onset and development of instabilities.
The results obtained with and without perturbation showed a significant decrease in the entrainment rate, a strong decrease in the maximum velocity decay rate, a lower jet expansion and an overall increase in the values of second order moments of the Reynolds stress components. The time-resolved PIV analysis (10 kHz) shows a distorted and elongated topology of the Kelvin-Helmholtz (K-H) structures for (Ulf = 0,5 ms-1) and a detached topology for (Ulf = 1 ms-1). The results of the mutual interaction between the inner and outer layers indicate that the ELS partially breaks the vortex dipole formation mechanism which becomes irregular and less predictive, leading to the elongation of the transitional region and a lag effect in the beginning of the self-similarity region. POD technique reveals the role of the ELS in redistributing energy between the modes. The ELS also affects the K-H instabilities by disrupting their two-dimensional organization, topology, alignment and shedding frequency, highlighting the inhibitory effect exerted on the development of primary structures. The spatial correlations Rvv reflect the decrease of the length scales in the case of a perturbed jet.

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Pages: 159 p.

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  • Original title: Analyse des structures des écoulements et des instabilités développées par un rideau d'air cisaillé latéralement par un courant externe : application au cas des meubles frigorifiques de vente.
  • Record ID : 30032288
  • Languages: English
  • Subject: Technology
  • Publication: Université de valenciennes et du hainaut-cambrésis - Valenciennes - France
  • Publication date: 2017/02/16

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