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I describe two dimensional Lagrangian acceleration statistics of inertial particles in a turbulent boundary layer with free stream turbulence. These appear to be the first Lagrangian acceleration measurements of inertial particles in a shear flow. We find that at the the outer edge of the boundary layer, where the shear is weak, the acceleration probability density functions are similar to those previously observed in isotropic turbulence for inertial particles. As the boundary layer plate is approached, the tails of the probability density functions narrow, become negatively skewed, and their peak occurs at negative accelerations (decelerations in the stream-wise direction). The mean deceleration and its rms increase to large values close to the plate. A simple model suggests that the acceleration behavior is dominated by shear and inertia. The results are contrasted with inertial particles in isotropic turbulence and with fluid particle acceleration statistics in a boundary layer.
This work was carried out with S. Gerashchenko, N. Sharp, S. Neuscamman |
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