The effect of roughness on separating flow over two-dimensional hills |
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Authors: | J B R Loureiro A S Monteiro F T Pinho A P Silva Freire |
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Institution: | 1.Mechanical Engineering Program (PEM/COPPE/UFRJ),Rio de Janeiro,Brazil;2.Scientific Division,Brazilian National Institute of Metrology (INMETRO),Rio de Janeiro,Brazil;3.Universidade do Minho, Largo do Pa?o,Braga,Portugal;4.Centro de Estudos de Fenómenos de Transporte,Faculdade de Engenharia da Universidade do Porto,Porto,Portugal |
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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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