Keywords: hydraulic structures, vertical drop, brink depth, toe depth, impinging point, pool water depth, critical depth, multi–drop, stepped chutes, napped flow, skimming flow, volume of fluid, VOF, computational fluid dynamics, CFD, Fluent, expert systems, drop structure design
Investigation of the performance of single and multi–drop hydraulic structures
In this paper, the work is divided into two parts. First, the hydraulic performance of single and multi–drop structures is investigated and compared using two approaches. In the first approach, the empirical equations found in the literature are summarised and reanalysed to compare the dissipation of energy of single drop and multi–drop structures. The demarcation condition at which multi–drop structure behaves as a single drop is identified. In the second approach, a numerical investigation of the hydraulic performance of single vertical drop and multi–stepped channel has been conducted via the computational fluid dynamic (CFD) fluent package using the volume of fluid (VOF) technique. It is found that the CFD package is able to simulate the hydraulic performance of both structures (single and multi–drop) reasonably well; however, it has been noted that in some situations the CFD package did not detect the presence of air cavities underneath the nappe for the napped flow case. Second, an Excel solver called HSMD has been developed. The objective of this solver is to work as an expert system for the design of drop structures and to facilitate the use of the large number of the available empirical formulas for practicing engineers. A comparison between the previous laboratory empirical formula (adopted in HSMD model) and numerical simulations has been also carried out.