Influence of Ridge Spacing on Secondary Currents in Turbulent Channel Flow over Triangular Ridges

Surfaces with spanwise variation of topology, such as ridge-type roughness, are known to generate secondary currents, which originate from turbulence anisotropy and spatial gradients of Reynolds stresses and represent Prandtl’s secondary flows of the second kind [1]. The presence of secondary currents is reflected in spanwise heterogeneity of the time-averaged streamwise velocity field in the form of alternating high- and low-momentum pathways (HMPs and LMPs), which correspond to downwash and upwash flow regions, respectively. In surfaces with ridge-type roughness, LMPs are typically observed above the ridges and HMPs occur in between them [2, 3]. However, a swap in their locations can be observed when ridge spacing exceeds channel half-height [4].