Phase relationships between large and small scales in the turbulent boundary layer

• Published in: Experiments in fluids 2013-03, Vol.54 (3), p.1-13, Article 1481
• Main Authors: Jacobi, I., McKeon, B. J.
• Format: Article
• Language: English
• Subjects: Boundary layer and shear turbulence; Correlation analysis; Density; Engineering; Engineering Fluid Dynamics; Engineering Thermodynamics; Envelopes; Exact sciences and technology; Fluctuation; Fluid dynamics; Fluid- and Aerodynamics; Fundamental areas of phenomenology (including applications); Heat and Mass Transfer; Instrumentation for fluid dynamics; Modulation; Phase relationships; Physics; Research Article; Turbulence; Turbulent boundary layer; Turbulent flows, convection, and heat transfer
• ISSN: 0723-4864; 1432-1114
• DOI: 10.1007/s00348-013-1481-y

The apparent amplitude modulation effect between large- and small-scale motions in the turbulent boundary layer, including both streamwise and wall-normal velocity components, is explored by cross-correlation techniques. Single-point hotwire and planar PIV measurements are employed to consider the envelopes of small-scale fluctuations in both directions and their correlation with the fluctuations of large-scale motions in the streamwise direction. The degree of correlation is interpreted as a measure of phase lag between the different scale motions, and these phase measurements are used to demonstrate that the fluctuations in the envelope of small-scale motions in both directions tend to lead corresponding fluctuations in the large scales in the streamwise direction. The cospectral density of the cross-correlation between the different scales is used to identify the particular large-scale motions dominant in the modulation effect, and it is shown that the dominant interacting (or ‘modulating’) scale corresponds in size to the very large-scale motions observed in internal flows but not normally observed in the outer region of the boundary layer.