Characterization of coherent vortical structures in a supersonic turbulent boundary layer

• Published in: Journal of fluid mechanics Vol. 613; pp. 205 - 231
• Main Authors: PIROZZOLI, SERGIO, BERNARDINI, MATTEO, GRASSO, FRANCESCO
• Format: Journal Article
• Language: English
• Published: Cambridge, UK Cambridge University Press 25.10.2008
• Subjects: Boundary layer; Boundary layer and shear turbulence; Boundary layers; Compressible flows; shock and detonation phenomena; Exact sciences and technology; Fluid dynamics; Fluid mechanics; Fundamental areas of phenomenology (including applications); Physics; Supersonic and hypersonic flows; Turbulence; Turbulent flows, convection, and heat transfer; Supersonic flow; Compressible fluid; Turbulent flow; Digital simulation; Coherent structures; Modelling; Boundary layers; Turbulence structure; Navier-Stokes equations
• ISSN: 0022-1120; 1469-7645
• DOI: 10.1017/S0022112008003005

A spatially developing supersonic boundary layer at Mach 2 is analysed by means of direct numerical simulation of the compressible Navier--Stokes equations, with the objective of quantitatively characterizing the coherent vortical structures. The study shows structural similarities with the incompressible case. In particular, the inner layer is mainly populated by quasi-streamwise vortices, while in the outer layer we observe a large variety of structures, including hairpin vortices and hairpin packets. The characteristic properties of the educed structures are found to be nearly uniform throughout the outer layer, and to be weakly affected by the local vortex orientation. In the outer layer, typical core radii vary in the range of 5–6 dissipative length scales, and the associated circulation is approximately constant, and of the order of 180 wall units. The statistical properties of the vortical structures in the outer layer are similar to those of an ensemble of non-interacting closed-loop vortices with a nearly planar head inclined at an angle of approximately 20° with respect to the wall, and with an overall size of approximately 30 dissipative length scales.