Spatially and temporally resoved 2C-2D PIV in the inner layer of a high Reynolds number adverse pressure gradient turbulent boundary layer

A joint experiment was performed in May 2015 in the framework of the European Project EuHIT: "European High performance Infrastructures in Turbulence". One of the aims was a detailed study of a high Reynolds number turbulent boundary layer flow under adverse pressure gradient (APG-TBL) to determine the effect of the pressure gradient on the spatio-temporal character of structures in the inner layer. Highly spatially resolved time series of up to 38 s duration of the streamwise and wall-normal velocity component were measured using 2C-2D PIV with single-exposed image pairs acquired at frequencies up to 6.7 kHz. The domain of these 2C-2D velocity field measurements spanned 5 x 25 mm² corresponding to a domain of up to 85⁺ x 426⁺ with the spatial resolution of the velocity measurements ranging from 0.4⁺ to 0.7⁺. Using these highly spatially and temporally resolved velocity measurements, time series of the wall-shear stress, spectra of the velocities, statistics and other pertinent characteristics of the APG-TBL were extracted and analysed. 2C-2D PIV using a sCMOS camera with 2560 x 2160 px resolution and 16 bit dynamic range was undertaken in streamwise–spanwise planes spanning 14.6 x 17.3 mm², which corresponds to a domain of up to 250⁺ x 300⁺.The spatial resolution of these velocity measurements is 0.9⁺. The camera was equipped with a Zeiss lens of 100 mm focal length with a teleconverter. f2 was used for these experiments, resulting in an estimated depth of-field of 170 µm and a diffraction limited diameter of approximately 10 µm. These measurements provide pertinent spanwise characteristics of the low and high momentum zones at different wall-normal distances in the APG-TBL.