Low relative-submergence effects in a rough-bed open-channel flow

Maxime Rouzès (1) , Frédéric Moulin (1) , Emma Florens (1) , Olivier Eiff (2)

1 IMFT - Institut de mécanique des fluides de Toulouse
2 KIT - Karlsruhe Institute of Technology

Multi-plane stereoscopic PIV measurements were performed in an open-channel flume fitted with cubes to investigate very low submergence ratios, h/k = {1.5, 2, 3}, where h is the water depth and k the roughness height. The spatial standard deviation of the mean flow components reveals that the extent of the roughness sublayer increases drastically with the decrease in h/k to span the entire water column for the lowest h/k investigated. Despite this, the logarithmic law is still observed on the double-averaged velocity profiles for all h/k, first with a fixed von Kármán constant κ and, second, via the indicator function where κ is a free parameter. Also, the longitudinal and vertical normal stresses indicate a universal boundary layer behaviour independent of h/k. The results suggest that the logarithmic and wake-defect laws can still be applied at such low h/k. However, the lateral normal stress depends on h/k in the range investigated as well as on the geometry of the roughness pattern.

Mots clés: Double-averaging; Logarithmic law; Rough-wall boundary-layers; Roughness sublayer; Stereoscopic PIV; Turbulent openchannel flows; Relative submergence

Domaines: Mécanique des fluides [physics.class-ph]

Maxime Rouzès, Frédéric Moulin, Emma Florens, Olivier Eiff. Low relative-submergence effects in a rough-bed open-channel flow. Journal of Hydraulic Research, 2018, 56, pp.1-28. ⟨10.1080/00221686.2018.1478894⟩. ⟨hal-02135758⟩