Spanwise variations in nominally two-dimensional rough-wall boundary layers
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Laboratory experiments have been conducted in two separate boundary layer facilities to investigate steady spanwise variations in mean velocity discovered during studies of developing flows over regular arrays of large roughness elements. Regular spanwise variation was found with a steady wavelength, moderated by the growing boundary layer, which was an integer multiple of the repeating unit of roughness. Amplitude variations greater than ±5% in the mean were found over the roughness and greater than ±10% in turbulence quantities. Due to the dominating nature of this phenomena throughout the layer, care should be taken in undertaking local measurements aimed at identifying flow variations caused by roughness heterogeneity.
Partial funding for this work was from the urban meteorology programme under the Universities Weather Research Network (Natural Environment Research Council Grant DST/26/39). RTR is grateful for support from the School of Engineering Sciences. We thank Mr. T. Lawton at the University of Surrey for consultation. The authors declare that these experiments were completed in compliance with the current laws of the United Kingdom.
- Blackwelder R, Swearingen J (1988) The role of inflectional velocity profiles in wall bounded flows. Near Wall Turb, Proceedings of Z Zariac Conference, pp 1–21Google Scholar
- Klebanoff P, Tidstrom K (1959) Evolution of amplified waves leading to transition in a boundary layer with zero pressure gradient. NASA Tech Note D 195:1–67Google Scholar
- Mehta R (1985) Turbulent boundary layer perturbed by a screen. AIAA J 23(9):1335–1342Google Scholar
- Reynolds R (2006) Measurements of the structure of urban-type boundary layers. Ph.D thesis, The University of Southampton, Southampton, United KingdomGoogle Scholar
- Reynolds R, Hayden P, Robins A, Castro I (2004) Spanwise variation in rough-wall boundary layers. Advances in Turb X. Proc 10th Euro Turb Conf 1:239–242Google Scholar