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The effect of roughness on separating flow over two-dimensional hills

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Abstract

Two new experimental data sets for turbulent flow over a steep, rough hill are presented. These include detailed laser Doppler anemometry measurements obtained at the separation and reattachment points and, in particular, within the reverse flow region on the lee side of the hill. These results allow the development of a new parametrization for rough wall boundary layers and validate the use of Stratford’s solution for a separating rough flow. The experiments were conducted in a water channel for two different Reynolds numbers. In the first set of rough wall experiments, the flow conditions and the hill shape are similar to those presented in Loureiro et al. (Exp. Fluids, 42:441–457, 2007a) for a smooth surface, leading to a much reduced separation region. In the second set of experiments, the Reynolds number is raised ten times. The region of separated flow is then observed to increase, but still to a length shorter than that recorded by Loureiro et al. (Exp. Fluids, 42:441–457, 2007a). Detailed data on mean velocity and turbulent quantities are presented. To quantify the wall shear stress, global optimization algorithms are used. The merit function is defined in terms of a local solution that is shown to reduce to the classical law of the wall far away from a separation point and to the expression of Stratford at a separation point. The flow structure at the separation point is also discussed.

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Acknowledgments

JBRL benefited from a Research Fellowship from the Brazilian Ministry of Science and Technology through Programme Prometro (Grant no. 554391/2006-6). ASM benefited from a Research Scholarship from the Brazilian National Research Council (CNPq). ASM is also thankful to the Rio de Janeiro Research Foundation (FAPERJ) (Grant no. E-26/171.198/2003) for the concession of further financial help regarding his stay at Oporto University. APSF is grateful to the Brazilian National Research Council (CNPq) for the award of a Research Fellowship (Grant no. 306977/2006-0). The work was financially supported by CNPq through Grants no. 477392/2006-7 and no. 476091-2007/1, and by the Rio de Janeiro Research Foundation (FAPERJ) through Grants E-26/171.346/2005 and E-26/171.198/2003. ASM, JBRL and FTP are grateful to Prof. Maria Fernanda Proença of the Hydraulics Laboratory of Oporto University for all her help in setting up the flow rig, as well as for some very interesting technical discussions.

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Authors and Affiliations

  1. Mechanical Engineering Program (PEM/COPPE/UFRJ), C.P. 68503, Rio de Janeiro, 21945-970, Brazil

    J. B. R. Loureiro, A. S. Monteiro & A. P. Silva Freire

  2. Scientific Division, Brazilian National Institute of Metrology (INMETRO), Rio de Janeiro, Brazil

    J. B. R. Loureiro

  3. Universidade do Minho, Largo do Paço, 4704-553, Braga, Portugal

    F. T. Pinho

  4. Centro de Estudos de Fenómenos de Transporte, Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias s/n, 4200-465, Porto, Portugal

    F. T. Pinho

Authors
  1. J. B. R. Loureiro
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  2. A. S. Monteiro
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  3. F. T. Pinho
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  4. A. P. Silva Freire
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Correspondence to J. B. R. Loureiro.

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Loureiro, J.B.R., Monteiro, A.S., Pinho, F.T. et al. The effect of roughness on separating flow over two-dimensional hills. Exp Fluids 46, 577–596 (2009). https://doi.org/10.1007/s00348-008-0583-4

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  • DOI: https://doi.org/10.1007/s00348-008-0583-4

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