Scale Modulations in the Zero-Pressure-Gradient Turbulent Boundary Layer Using Staggered Roughness Elements

An incompressible, zero-pressure-gradient flat-plate boundary-layer flow with surface modifications is studied experimentally. The shape and size of protruding roughness elements affect the characteristics of the immediate downstream turbulent boundary layer, and this effect can extend several times the boundary-layer outer scales. The impact of roughness elements on existing scales of turbulent boundary-layer flows affects turbulence production and energy dissipation. This study explores options for a staggered distribution of square roughness elements to modulate near-wall scales in turbulent boundary-layer flow. The careful parameter choices in this work aim to understand scale interactions/modulations in turbulent boundary-layer flows through staggered roughness elements, which have applications in developing passive drag-control methods.