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.