Highly-disturbed turbulent flow in a square channel with V-shaped ribs on one wall

We investigate highly-disturbed turbulent flows in a square channel with V-shaped ribs mounted on one wall. A planar particle image velocimetry (PIV) system is used to measure the fully developed turbulent flow at the channel midspan and two off-center planes. V-shaped rib configurations with three different inclinations (60°, 45° and 30°) are studied and compared to the perpendicular (90°) rib case. The highly-disturbed turbulent flow in the V-shaped rib cases are studied by investigating the statistics of first and second order moments, including the mean velocity, mean shear, mean vorticity and Reynolds stresses. Owing to the geometrical skewness of the V-shaped ribs, strong secondary flows are induced which appear in the pattern of a pair of streamwise counter-rotating roll cells and have a significant impact on the momentum transport process. Near the channel midspan of the V-shaped ribs, turbulent intensity is suppressed above the ribs but enhanced below the rib height, and turbulent vortical motions exhibit isotropic patterns due to the strong disturbances from the ribs. The coherent flow structures have been systematically analyzed based on studying two-point auto-correlation coefficient, quadrant decomposition of Reynolds stresses, swirling strength, and proper orthogonal decomposition of the turbulent flow.