Effect of hemispherical roughness spacing on Double-averaged turbulence characteristics for different flow submergence

Abstract

The double-averaged (DA) turbulence characteristics over rough bed comprising of hemispherical elements with different spacing (p/r = 2, 4, 6, and 8; p = pitch distance; r = height of hemisphere) is quantified for three flow-submergences [h/r = 7.14, 5.35, 3.57; mean flow-depth (h)= 20 cm, 15 cm, and 10 cm]. The production and dissipation rates of turbulent kinetic energy are maximum at and below the crest level. Within interfacial sublayer, the degree of anisotropy is observed to be maximum for p/r = 4 and the tendency for the return to isotropy is strongest for p/r = 8 in the outer layer. The turbulence generated in the bottom region is still present in the outer region for low flow-submergences. The turbulence strength is maintained in the roughness order (descending) as p/r = 4 >2> 6 > 8 > plane bed; wherein the change in flow-submergence does not change this order.