Author(s): Farhad Bahmanpouri, Carlo Gualtieri, Hubert Chanson

Linked Author(s): Farhad Bahmanpouri, Carlo Gualtieri, Hubert Chanson

Keywords: Hydraulic jump; Air-Water Flow; Pebbled Rough Bed; Physical Modelling;

Abstract: The hydraulic jump is a sudden transition from a supercritical flow to a subcritical motion, characterised by strong turbulence, air entrainment and energy dissipation. A hydraulic jump results in strong interactions between turbulence, free-surface and air-water mixing. Past research on hydraulic jump with bed roughness focused on the identification of basic parameters including conjugate depth ratio, roller length and mean velocity. However, to date, only very few studies have addressed the air-water flow parameters. This paper aims to investigate the basic parameters of air-water flow in hydraulic jump on pebbled rough bed. The experiments were performed in a channel with partially-developed inflow conditions. The gravel materials, mixed natural river pebbles, were installed on the bed for the whole length of the flume. A phase-detection double-tip conductivity probe was used to measure the basic air-flow properties. The experiments were conducted for discharges ranging from 0.06 to 0.1 m3/s, corresponding to inflow Froude numbers Fr1 between 1.7 and 2.84 and Reynolds number Re1 from 170,000 to 220,000. Comparisons between rough and smooth bed data, as well as with the literature highlighted some distinctive effects of the non-uniform bed roughness. The results on rough pebble bed showed a shorter roller length and higher magnitudes of air-flow properties including void fraction and bubble count rate than those on smooth bed, especially in the region close to the jump toe.

DOI: https://doi.org/10.3850/38WC092019-0557

Year: 2019