Transport of Inertial Droplets in a Turbulent Boundary Layer

The transport of highly inertial droplets in the presence of a turbulent boundary layer is studied experimentally inside a wind tunnel. Water droplets are injected into the boundary layer at free-stream velocities ranging from U_∞ = 2.4 to 6.6 m/s with a boundary layer thickness ranging from δ = 11.4 to 12.5 cm. The size, speed, and acceleration of droplets are measured using a high-speed cinematic in-line holographic system positioned 162 cm downstream from the nozzle and at many wall-normal streamwise locations spanning the full thickness of the boundary layer. Water droplets with diameters ranging from 30 to 1000 μm are measured with corresponding Stokes numbers ranging from St_η = 0.11 to 160. Wall-normal droplet concentration and velocity profiles are reported. Droplet statistics like velocity and acceleration are discussed as a function of droplet size and wall-normal location. The importance of turbulence on the motion of highly inertial droplets is discussed and compared to similar statistics obtained from inertial droplets produced by breaking wind-forced waves.