Research on effect of contraction angle and ratio of flaring piers on impact pressure in stilling basin.

Chunqi Chen, Faxing Zhang

Friday 3 july 2015

12:00 - 12:15h at Amazon (level 1)

Themes: (T) Water engineering, (ST) River and coastal engineering

Parallel session: 15E. Engineering - River

The joint energy dissipater of flaring piers and stilling basin has been introduced into wide use in high dam constructions located in narrow valley areas, which often confront restricted discharge width and large discharge per unit width. At the end of the flaring piers, the overflow nappe is compelled to contract laterally as well as extend longitudinally and vertically. As a consequence, the contraction jet can meet the requirements of the discharge and energy dissipation. With inappropriate contraction ratio or contraction angle, however, the flaring piers may cause a rise in the impact pressure in the stilling basin. The influence of the contraction angle and ratio of flaring piers on the impact pressure downstream should thus be a cause of concern. A model of flaring piers with alterable contraction ratios and contraction angles was established in a circulating water system. The contraction ratios ranged from 0.2 to 0.8 with a gap of 0.2. The contraction angles were set to be 15, 20, 25 or 30 degrees. Experiments under three different discharge conditions were performed. The variation of the impact pressure in the stilling basin with different contraction angles and ratios of the flaring piers were summarized. As the results showed, the largest impact pressure, in most cases, decreased as the contraction angle increased from 15 to 25 degree. As the contraction angle increased to 30 degrees, the peak value of the impact pressure altered indistinctly. Meanwhile, the largest impact pressures varied in their sensitivity to the contraction ratio under different discharge. The contraction ratios of 0.6 and 0.4 were regarded as proper values according to the data analysis. The results may provide a reference for engineering design.