Effects of external disturbances on turbulent boundary layers

The state of a turbulent boundary layer developing under the influence of different types of freestream turbulence (FST) is examined. Different FST conditions with different length scales and turbulence intensity levels are generated using an active grid. Experiments are performed using two different techniques allowing simultaneous measurements of the freestream and the boundary layer: single component hot-wire anemometry and multi-camera planar Particle Image Velocimetry (PIV). Penetration level of the freestream into the boundary layer and the effect on the near wall region are shown to depend on the turbulence characteristics of the freestream. These interactions will further be investigated using spectral analysis from hot-wire measurements and also coherent structures associated with these interactions will be studied using PIV data