Development and analysis of a turbulent boundary layer under spatially and temporally varying unsteady adverse pressure gradients*

Unsteady adverse pressure gradients were imposed by an apparatus placed at the end of a boundary layer wind tunnel containing a 0.38 m long curving plate, rotary actuator, and pulley system. Varying pressure inputs to the actuator enabled achievable plate deflection speeds between 0.37 m/s and 0.97 m/s. The value k, a dimensionless unsteadiness parameter comparing the convective timescales to the imposed geometric timescales, was observed within the range of 0.29 to 3.42 when the freestream velocity was 7.5 m/s. Time-resolved planar particle image velocimetry (PIV) was used to analyze the behavior of the flow as the plate curved by collecting 500 phase-locked ensemble images at 3.75 kHz. This imaging was specifically done with a plate deformation speed of 0.74 m/s and k value of 2.78. The friction-based Reynolds number, Re_τ, of the incoming flow was approximately 956 in the center of the field of view with a boundary layer thickness, δ, of approximately 47.5 mm at the beginning of the field of view. This talk will primarily focus on the development and characterization of the experimental setup and preliminary PIV data. Opportunities for future work utilizing the full capabilities of the setup are also addressed.