A large-format, digital, long-distance micro Particle Image Velocimetry system (µPIV) has been applied, to measure the wall-shear-stress and the logarithmic region of a canonical boundary layer flow along a flat plate, non-intrusively with high accuracy and spatial resolution. The fundamental aim was the accurate determination of the two universal constants k and B of the logarithmic law-of-the-wall for different Reynolds numbers. This is of fundamental interest in order to provide experimental evidence that k and B are not universal constants. To achieve the required measurement accuracy and spatial resolution all experimental limitations associated with the seeding, light-sheet, out-of-focus particles, optical aberrations and distortions and the spatial correlation image analysis were successfully solved. In addition, it is shown that systematic measurement errors caused by the strong illumination of the tracer particles (radiative and thermal effects) can be neglected.    «

A large-format, digital, long-distance micro Particle Image Velocimetry system (µPIV) has been applied, to measure the wall-shear-stress and the logarithmic region of a canonical boundary layer flow along a flat plate, non-intrusively with high accuracy and spatial resolution. The fundamental aim was the accurate determination of the two universal constants k and B of the logarithmic law-of-the-wall for different Reynolds numbers. This is of fundamental interest in order to provide...    »