Abstract
Flow in a flat-plate zero-pressure-gradient boundary layer at Mach 3 was visualized via nanoparticle-based planar laser scattering (NPLS). Coherent structures such as an individual hairpin vortex and hairpin packet were identified in the streamwise-wall-normal plane on the basis of the now accepted hairpin model. Λ-shaped vortices were found in a staggered pattern in the streamwise-spanwise plane, which indicated H-type transition in the present experiments. This is the direct evidence (in the form of flow visualization) of such coherent structures in a supersonic boundary layer. A series of NPLS images taken in streamwise-spanwise planes at different heights is presented, and the three-dimensional structures of the supersonic boundary layer agree well with the hairpin model.
Highlights
Flow in a flat-plate zero-pressure-gradient boundary layer at Mach 3 was visualized via nanoparticle-based planar laser scattering (NPLS)
Flow visualization of a flat-plate zero-pressure-gradient boundary layer at Mach 3 is performed, and the coherent structures in streamwise-wall-normal and streamwisespanwise planes are shown in the NPLS images
Individual hairpins as well as a hairpin packet are identified in the streamwise-wall-normal plane
Summary
Flow in a flat-plate zero-pressure-gradient boundary layer at Mach 3 was visualized via nanoparticle-based planar laser scattering (NPLS). Coherent structures such as an individual hairpin vortex and hairpin packet were identified in the streamwise-wallnormal plane on the basis of the accepted hairpin model. Λ-shaped vortices were found in a staggered pattern in the streamwise-spanwise plane, which indicated H-type transition in the present experiments This is the direct evidence (in the form of flow visualization) of such coherent structures in a supersonic boundary layer. Ringuette et al [7] utilized a direct numerical simulation (DNS) database of Mach 3 turbulent boundary layers and found large-scale coherent structures similar to those observed in experiments under both supersonic and incompressible conditions. Using the recently developed nanoparticle-based planar laser scattering (NPLS) technique, the interaction between an oblique shock wave and turbu-
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