Journal of Fluid Mechanics


Large-scale motions in a supersonic turbulent boundary layer

a1 Center for Aeromechanics Research, The University of Texas at Austin, 210 E. 24th Street, WRW220, Mail Code C0604, Austin, TX 78712, USA

Article author query
ganapathisubramani b   [Google Scholar] 
clemens nt   [Google Scholar] 
dolling ds   [Google Scholar] 


Wide-field particle image velocimetry measurements were performed in a Mach 2 turbulent boundary layer to study the characteristics of large-scale coherence at two wall-normal locations ($y/\delta\,{=}\,0.16$ and 0.45). Instantaneous velocity fields at both locations indicate the presence of elongated streamwise strips of uniform low- and high-speed fluid (length$\,{>}\,8\delta$). These long coherent structures exhibit strong similarities to those that have been found in incompressible boundary layers, which suggests an underlying similarity between the incompressible and supersonic regimes. Two-point correlations of streamwise velocity fluctuations show coherence over a longer streamwise distance at $y/\delta\,{=}\,0.45$ than at $y/\delta\,{=}\,0.16$, which indicates an increasing trend in the streamwise length scale with wall-normal location. The spanwise scale of these uniform-velocity strips increases with increasing wall-normal distance as found in subsonic boundary layers. The large-scale coherence observed is consistent with the very large-scale motion (VLSM) model proposed by Kim & Adrian (Phys. Fluids, vol. 11, 1999, p. 417) for incompressible boundary layers.

(Published Online May 24 2006)
(Received July 14 2005)
(Revised December 19 2005)