Nonlinear wakes behind a row of elongated roughness elements.

Area of Science:

• Fluid dynamics
• Turbulence research

Background:

• Previous studies focused on smaller roughness elements and linear flow distortions.
• High Reynolds number flow over roughness elements is critical for understanding aerodynamic and hydrodynamic phenomena.

Purpose of the Study:

• To analyze the nonlinear behavior of downstream wakes generated by larger roughness elements.
• To investigate the novel triple-deck structure in roughness-scale flow.
• To establish a nonlinear wake flow as a basis for studying secondary instability and turbulence.

Main Methods:

• Analysis of high Reynolds number flow over spanwise-periodic roughness elements.
• Extension of previous work to larger roughness heights and elongated planform shapes.
• Identification of a novel triple-deck structure in the roughness scale flow.

Main Results:

• Discovery of a qualitatively different, nonlinear behavior in downstream wakes.
• Characterization of the flow with a novel triple-deck structure.
• Demonstration of formal nonlinearity in intermediate and far wake regions.

Conclusions:

• The nonlinear wake flow resulting from larger roughness elements is a key departure from previous linear models.
• This nonlinear flow provides a suitable foundation for investigating secondary instability and turbulence.
• The findings advance the understanding of complex flow phenomena in boundary layers.