Three-Dimensional Large Scale Motions in Zero Pressure Gradient and Adverse Pressure Gradient Turbulent Boundary Layers

  • Student: Blake Melnick
  • Funding Agency:  Army Research Office

This work is focused on investigating three-dimensional structures in zero pressure gradient and adverse pressure gradient turbulent boundary layers.   While researchers have a pretty good picture some of the structures in a turbulent boundary layer (hairpin vortices, large scale motions, turbulent bulges, coherent structures, sweeps, and ejections), there is still much to be learned about the underlying physics of turbulent boundary layers.  In particular more investigation into the three-dimensional structures of an adverse pressure gradient turbulent boundary layer would be beneficial for many areas of fluid dynamics.

Boundary layer separation can have negative consequences in some situations (large total pressure losses, decreased heat transfer, loss of control, and loss of lift), so being able to give more information about these structures in an adverse pressure gradient that is on the verge of separation would be insightful.  How do these structures change their shape, size, orientation, and spacing as they get closer to separation?  Could detailing these changes give clues to the underlying physics, and possibly how can we prevent separation?

The Auburn University Advanced Laser Diagnostics Laboratory has two 3-D measurement techniques that we are using to investigate the turbulent boundary layer structures.  A 3-D flow visualization technique that utilizes a home-built pulse burst laser that emits 68 laser pulses at a rate of 500 kHz in conjunction with a scanning mirror and a high-speed camera captures instantaneous 3-D snapshots of the turbulent boundary layer as shown in Figure 1.  In addition, a newly developed plenoptic camera can capture a 3-D velocity field of the turbulent boundary layer as shown in Figure 2.

3D flow visualization of a turbulent boundary layer
Figure 1: 3-D flow visualization of a turbulent boundary layer (flow from left to right).

3D velocity field of a turbulent boundary layer
Figure 2: 3-D velocity field of a turbulent boundary layer (flow from left to right).

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Last Updated: Jul 26, 2013