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The Pervasive Effect of the Calmed Region

[+] Author Affiliations
R. L. Thomas, J. P. Gostelow

University of Leicester, Leicester, UK

Paper No. GT2005-69125, pp. 1105-1112; 8 pages
doi:10.1115/GT2005-69125
From:
  • ASME Turbo Expo 2005: Power for Land, Sea, and Air
  • Volume 3: Turbo Expo 2005, Parts A and B
  • Reno, Nevada, USA, June 6–9, 2005
  • Conference Sponsors: International Gas Turbine Institute
  • ISBN: 0-7918-4726-8 | eISBN: 0-7918-3754-8
  • Copyright © 2005 by ASME

abstract

Experiments have been conducted relating to the interaction of imposed freestream wakes upon a flat plate laminar separation bubble under an adverse pressure gradient. Controlled wakes, representative of those seen in turbomachinery environments, were used to investigate unsteadiness effects upon a separating boundary layer that undergoes natural transition in the free shear layer under steady conditions. Hot-wire anemometry using a single hot-wire has shown leading edge boundary layer disturbances induced under each passing wake, which grow steadily via by-pass and natural transition methods into turbulent strips that convect with the flow. These disturbances are of such strength that the separated region is resisted and effectively swept away by the passing turbulence, momentarily giving rise to a wholly attached laminar boundary layer. Controlling the chord-wise proximity of neighboring wakes allowed for the investigation of the effect and extent of the calmed region behind each induced turbulent strip. Measurements have shown that a strong suppression of velocity fluctuations is seen related to the proximity of the turbulent strips. Turbulence level reductions of up to 40% have been demonstrated as wake spacing is reduced. Even for those cases where systematic wakes are sufficiently close together to prevent the development of a visible calmed region, very strong calming influences are seen in the wake induced turbulent domain that would have normally been occupied by the calmed flow.

Copyright © 2005 by ASME

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