Observations of turbulent secondary flows in a rough-wall boundary layer. (10th June 2014)

• Record Type: Journal Article
• Authors: Barros, Julio M.; Christensen, Kenneth T.
• Is Part Of: Journal of fluid mechanics. Volume 748(2014:Jun.)
• Publication Date: 2014-06-10
• Subjects: Fluid mechanics -- Periodicals; 532.005
• DOI: 10.1017/jfm.2014.218
• Languages: English
• ISSNs: 0022-1120

Abstract

<abstract> <title>Abstract</title> <p>The characteristics of a turbulent boundary layer overlying a complex roughness topography were explored with stereo particle-image velocimetry measurements in the wall-normal–spanwise <inline-formula><alternatives><inline-graphic xlink:href="ark:/27927/pgh190mnhxz" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><tex-math><![CDATA[$(y\mbox{--}z)$]]></tex-math></alternatives></inline-formula> plane. The roughness under consideration was replicated from a turbine blade damaged by deposition of foreign materials containing a broad range of topographical scales arranged in a highly irregular manner. The single-point turbulence statistics displayed strong spanwise heterogeneity, in particular spanwise-alternating low- and high-momentum flow pathways in the mean flow marked by enhanced Reynolds stresses and turbulent kinetic energy. The spanwise regions between high- and low-momentum flow pathways were occupied by swirling motions, suggesting the generation and sustainment of turbulent secondary flows due to the spanwise heterogeneity of the complex roughness under consideration. Similar observations were recently reported for more ordered spanwise roughness transitions by Nugroho, Hutchins &amp; Monty (<italic>Intl J. Heat Fluid Flow</italic> vol. 41, 2013, pp. 90–102) and Willingham <italic>et al.</italic> (<italic>Phys. Fluids</italic> vol. 26, 2014, 025111).</p> </abstract>