Paper Title
Towards Effective Large-scale Real-time Control Scheme: Structural Identification of a High-Reynolds Number Turbulent Boundary Layer via Wall Sensors

The large-scale coherent structures in the outer region of a high-Reynolds-number turbulent boundary layer are highly energetic and have an influence on the wall and hence on the skin friction drag. To evaluate the accuracy of the structural manipulation for large-scale real-time control schemes, in which wall sensors are utilized as control components, the canonical effect of the outer-region structures onto the wall needs to be quantified. We conducted measurements of friction velocity fluctuations (u_τ), together with simultaneous measurements of streamwise velocity (u) fluctuations throughout a turbulent boundary layer with a friction Reynolds number of〖Re〗_τ≈14400. The streamwise locations for both of the measurements of theuand u_τ fluctuations were nominally the same. The coherence magnitude between the former and latter signals is evaluated as a function of the wall-normal height and the resolved streamwise wavelength. It is concluded that the most influential large-scale structures in the log-region of a high-Reynolds-number turbulent boundary layer on the wall-shear stress possess a characteristic lower bound of a streamwise wavelength of λ_x≈1.9δ (where δ is the boundary layer thickness). Index Terms - Turbulent boundary layer, Coherent structures, High-Reynolds-number, Large-scale control scheme.