Investigation of Flow Energy Dissipation over Different Stepped Spillways

Sohrabipoor N,Barani G A,Rahnama M B

doi:10.3844/ajassp.2005.1101.1105

Abstract

In this study, to investigate energy dissipation of flow overstepped spillways of different step shapes, a physical wooden model has been built in the Shahid Bahonar Universitys hydraulics lab. This model with 41.41° slope has 84 cm height and 21 steps. Each step has 4 cm height, 4.5 cm width and 30 cm length. Experiments have been carried out for different types of step shapes (plain steps, end sill steps with thickness of 1, 2, 3 and 4 cm and steps with a bottom adverse slope of 15, 26, 36 and 45°). Overall, 131 experiments were done, the hydraulic parameters of flow over the model were measured and the energy dissipation of flow was calculated. Results show that the energy dissipation of flow on end sill and inclined stepped spillways are more than the plain one, it is increased by increasing the thickness of end sill or the adverse slope size. Comparison of flow energy dissipation over end sills stepped spillway and inclined type show that the inclined type has been dissipated more energy than the equivalent end sill type. Also for stepping spillway of different step shapes, flow energy dissipation decreases with increasing the flow rate. It is concluded that for a large stepped spillway with high flow rate the inclined type spillway is more effective than the other forms.

Highlights

Depth and h is the height of the steps[5]
Depend on the hydraulic conditions of flow and the geologic characteristics of the damُs site Spillways can be built with different types and shapes
Amount of the flow kinetic energy, such that the downstream stilling basin, where the residual energy is dissipated by hydraulic jump, can be largely reduced in dimensions

Summary

Introduction

Depth and h is the height of the steps[5]. Stepped spillways allow continuously dissipating a considerable. Design and contraction of spillways are very expensive and include a major part of the damُs contraction cost For large dams it is about 20 % of total damُs construction cost, and for small dams about 80 %[1]. Due to the high flow discharge over the spillways, their design and construction is very complicated and usually faced with difficulties such as cavitations and high flow kinetic energy. The cavitations risk along the spillway decreases significantly due to smaller flow velocities and the large air entertainment rate[4]. It becomes usual to protect the the limit of skimming flow, the stepped surface is very spillway surface from cavitations erosion by effective in dissipating energy. Stepped spillways can be designed as slopes, the transition from the (lower) jet flow to the multipurpose systems, as examples, river training,

Methods

Results

Conclusion