The spatial organization of small scales around large-scale coherent structures in a flat plate turbulent boundary layer is studied using a conditional-averaging technique applied to experimental and computational data. The technique averages the small-scale velocity conditioned on the projection coefficient between the instantaneous streamwise velocity field and a model for large-scale velocity structures in the wake and logarithmic regions. Two distinct scenarios are identified for the organization of the small scales: amplitude variation, in which at a given wall-normal location the small-scale intensity varies in amplitude across the streamwise extent of the large-scale structure, and height variation, in which the small-scale velocity intensity remains nearly constant along a curve that changed its wall-normal location across the streamwise extent of the large-scale structure. Small scales that are energetic at the wall-normal location where the large-scale structure is centered primarily show evidence of height variation, while small scales that are energetic at wall-normal locations far from the center of the large-scale structure primarily show evidence of amplitude variation. Connections can be drawn between the statistical observations characterized by the amplitude modulation statistic and the structural picture associated with vortex clusters.
ASJC Scopus subject areas
- Computational Mechanics
- Modeling and Simulation
- Fluid Flow and Transfer Processes