Journal of Fluid Mechanics

Papers

Coherent structures in wave boundary layers. Part 2. Solitary motion

B. MUTLU SUMERa1 c1, PALLE M. JENSENa1, LONE B. SØRENSENa1, JØRGEN FREDSØEa1, PHILIP L.-F. LIUa2 and STEFAN CARSTENSENa1 p1

a1 Technical University of Denmark, DTU Mekanik, Section of Coastal, Maritime and Structural Engineering, Building 403, 2800 Kgs. Lyngby, Denmark

a2 School of Civil and Environmental Engineering, Cornell University, Ithaca, NY 14853, USA

Abstract

This study continues the investigation of wave boundary layers reported by Carstensen, Sumer & Fredsøe (J. Fluid Mech., 2010, part 1 of this paper). The present paper summarizes the results of an experimental investigation of turbulent solitary wave boundary layers, simulated by solitary motion in an oscillating water tunnel. Two kinds of measurements were made: bed shear stress measurements and velocity measurements. The experiments show that the solitary-motion boundary layer experiences three kinds of flow regimes as the Reynolds number is increased: (i) laminar regime; (ii) laminar regime where the boundary-layer flow experiences a regular array of vortex tubes near the bed over a short period of time during the deceleration stage; and (iii) transitional regime characterized with turbulent spots, revealed by single/multiple, or, sometimes, quite dense spikes in the bed shear stress traces. Supplementary synchronized flow visualization tests confirmed the presence of the previously mentioned flow features. Information related to flow resistance are also given in the paper.

(Received September 19 2008)

(Revised October 16 2009)

(Accepted October 18 2009)

Key Words:

  • Boundary layer stability;
  • Waves;
  • Turbulent transition

Correspondence:

c1 Email address for correspondence: bms@mek.dtu.dk

p1 Present address: DHI, Agern Alle 5, 2970 Hørsholm, Denmark.

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