Phase relationships between velocity, wall pressure, and wall shear stress in a forced turbulent boundary layer Kevin Rosenberg ∗ , Subrahmanyam Duvvuri † , Mitul Luhar ‡ , Beverley J. McKeon § California Institute of Technology, Pasadena, California, 91125 Casey Barnard ¶ , Brett Freidkes ‖ , Jessica Meloy ∗∗ , Mark Sheplak †† University of Florida, Gainesville, Florida, 32611 A large scale spatio-temporally periodic disturbance was excited in a turbulent boundary layer via a wall-actuated dynamic roughness. Streamwise velocity, wall pressure, and direct wall shear stress measurements were made with a hot wire, pressure microphone, and a micro-scale differential capacitive sensor, respectively. Phase-averaged fields for the three quantities were calculated and analyzed. A phase calibration between the various sensors was performed with an acoustic plane wave tube over a range of operating conditions to validate a direct phase comparison between the respective quantities. Results suggest encouraging agreement between the phase of the wall shear stress and velocity near the wall; however, more refined velocity measurements are needed to make quantitative comparisons to the wall pressure. Overall, this work highlights the potential for wall-based control with applications towards reducing turbulent drag. Nomenclature U ∞ Free stream velocity δ Boundary layer thickness ν Kinematic viscosity μ Dynamic viscosity ρ Density c Isentropic speed of sound η Stokes number k x Streamwise wavenumber u Streamwise velocity τ w Wall shear stress p w Wall pressure p + Incident pressure phasor p − Reflected pressure phasor x Axial location within plane wave tube y Transverse location within plane wave tube  () Phase-averaged quantity CSSS Capacitive shear-stress sensor ∗ PhD Candidate, Graduate Aerospace Laboratories, AIAA Student Member. † Postdoctoral Scholar, Graduate Aerospace Laboratories, AIAA Student Member. ‡ Current Affiliation: Assistant Professor, Aerospace & Mechanical Engineering, USC, AIAA Member. § Professor of Aeronautics, Graduate Aerospace Laboratories, AIAA Associate Fellow. ¶ PhD Candidate, Mechanical & Aerospace Engineering, AIAA Student Member. ‖ PhD Student, Mechanical & Aerospace Engineering ∗∗ Current Affiliation: Engineer, Boeing Test & Evaluation, AIAA Member. †† Professor, Mechanical & Aerospace Engineering, Computer & Electrical Engineering, AIAA Associate Fellow. 1 of 7 American Institute of Aeronautics and Astronautics