Statistical Characteristics of a Turbulent Boundary Layer over a d-Type Rough Surface

The turbulent structure of the turbulent boundary layer over a d-type rough surface was examined using both x type-hot wire and usual time averaged procedure, and hot-wire rakes and conditional sampling techniques. Results showed that even in the present rough boundary layer the almost same organized structure as found in the smooth surface boundary layer existed, and that this structure was at an oblique angle of about 23 deg. To the free stream and also indicated a high degree coherence over a considerable area in the direction normal to the wall. Conditional averaged results showed that the strong accelerations of the streamwise velocity occurred at y+=15 to y/δ=0.7. It could be deduced from this pattern that there existed the events associated with the bursting phenomenon.