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Control of Convective Heat Transfer in a Confined Laminar Impinging Jet by Low Amplitude Forcing

[+] Author Affiliations
Victor Adrian Chiriac

Motorola, Inc., Tempe, AZ

Alfonso Ortega

University of Arizona, Tucson, AZ

Paper No. IMECE2002-32909, pp. 31-39; 9 pages
doi:10.1115/IMECE2002-32909
From:
  • ASME 2002 International Mechanical Engineering Congress and Exposition
  • Heat Transfer, Volume 1
  • New Orleans, Louisiana, USA, November 17–22, 2002
  • Conference Sponsors: Heat Transfer Division
  • ISBN: 0-7918-3632-0 | eISBN: 0-7918-1691-5, 0-7918-1692-3, 0-7918-1693-1
  • Copyright © 2002 by ASME

abstract

A numerical finite-difference model, derived using a control-volume approach, was used to compute the flow and heat transfer characteristics in a two-dimensional confined laminar air jet impinging on an isothermal surface. Several cases were considered with Re=650, 750, and nozzle to plate spacing, H/W=5. The behavior of the jet and the attendant heat transfer from the target wall were investigated when the jet was forced by fluidic excitation at the nozzle exit. At Re between 585 and 610, the unforced jet exhibits a transition to an unsteady regime leading to asymmetric vortex shedding and jet flapping [1, 2]. Investigation of the velocity spectra indicate three distinct dominant modes; the lowest frequency is associated with the jet flapping while the highest frequency is associated with the asymmetric vortex formation which causes buckling of the jet column. As a result of the two combined modes, the peak heat transfer is enhanced and the lateral cooling extent is broadened. The jet was subjected to forcing by introduction of numerical excitation at each side of the jet that modeled fluidic excitation. The jet was forced on both opposing sides at its exit, both with in-phase and out-of-phase modes. Under some conditions, out of phase forcing at Re=650 at the highest frequency leads to stabilization of the normally separated flow on one side only. This unusual asymmetric flow field is unsteady but repeatable, and results in an enhancement of the heat transfer. At Reynolds number of 750, forcing with an out of phase mode at the highest frequency leads to a complete stabilization of the jet. The forcing suppresses the high-amplitude low frequency flapping mode leaving only a high frequency vortex formation mode. The suppression of the jet flapping leads to a decrease in the peak heat transfer, but because separation is suppressed, the average wall heat transfer is enhanced.

Copyright © 2002 by ASME

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