Secondary motions above a staggered multi-scale rough wall

Wind tunnel experiments were performed to investigate turbulent flow over an array of heterogeneous roughness elements using stereoscopic particle image velocimetry. Nine streamwise planes, covering one periodic cell a multi-scale element that is arranged in staggered pattern, are combined quantify mean features and Reynolds stresses. Dispersive stresses, arising from spatial variations the temporally averaged velocity, also presented. The results highlight create large deficit pathway along surfaces. Outer scaling time-averaged velocity presents which nearly independent type, with parameters revealing values near those observed smooth wall boundary layers, such as wake strength parameter, opposing earlier work containing aligned patterns. secondary motion most accentuated at ridges roughness, showing formation structures sensitive location investigated spanwise direction.