INVESTIGATION OF WALL-BOUNDED TURBULENCE OVER REGULARLY DISTRIBUTED ROUGHNESS

Experiments were conducted in the fully-rough regime on surfaces consisting of regularly distributed Lego bricks of uniform height, arranged in different configurations. Measurements were made with high resolution planar Particle Image Velocimetry on six different configurations at different frontal solidity, λF , and fixed plan solidity, λP. Results indicate that mean velocity profiles in defect form conforms to outer-layer similarity. However, streamwise, wall-normal turbulent intensities and particularly Reynolds shear stresses show a lack of similarity across the different cases. Quadrant analysis reveals an increase in Q4 and in Q2 activities in the outer layer which is dependent on the frontal solidity. Proper Orthogonal Decomposition show an increase in fractional and cumulative turbulent kinetic energy contribution of the lowest-order modes with increasing the density of the elements, indicating a redistribution of the energy toward the larger-scales.