Convection Velocities in Turbulent Boundary Layers over Rough Surfaces

The time-resolved particle image velocimetry was used to asses the mean convection velocities of flow structures within the turbulent boundary layers above rough surfaces. The mean convection velocity was derived from the temporal-spatial correlation function. The mean convection velocities are larger than local mean velocities in the log layer and lower wake layer and vice versa in the upper wake layer. The cross-over height is higher for more rough surfaces. Larger structures are convected faster than smaller structures.