Numerical Modelling of Flow Over Aerator of Orifice Spillway

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv

Aerators on Spillways of Indian Dams

Spillways of high head dams are susceptible to cavitation damage due to surface deformities and high velocity. Aeration is the most effective method for mitigating cavitation damage. Design of aerators is complex. Hence, recourse is always taken to refer the existing designs while designing an aeration system for a dam. This paper highlights the details of aerators for five major projects in India viz. Sardar Sarovar, Tehri, Indirasagar, Karjan and Chamera Stage I. This data would be of immense use to the designers

Hydraulics of Aerator for Orifice Spillway

Orifice spillways are being designed for the diversion dams constructed in cascades. These spillways are designed for dual purpose of flood disposal as well as flushing of sediment. The spillways are located as near the river bed as possible so as to flush the sediment. Due to this the head over the spillway crest is of the order of 30–40 m. In exceptional cases the head increases to about 60 to 80 m. The spillway crest profile becomes very flat as compared to overflow spillways. High negative pressures leading to cavitation damage is the main concern. Design of aeration groove for orifice spillways is a grey area and needs considerable research. This paper highlights the need for aerator, design considerations, present practices and their limitations. Sample calculations along with model results are included for illustration

Hydraulic design of spillway aerators

Spillways for high head dams are subject to high velocity flows. Due to the inherent surface roughness and geometrical deformities usually associated with concrete structures, spillways are susceptible to cavitation damage. Aeration is one of the most effective methods for mitigation of cavitation. Design of aerators is a subject of continuing interest. The present study describes the present state of knowledge for spillway aerators. A comparative study is presented to assess the various methods available for the estimation of jet length, sub-pressure under the nappe, and the air velocity in the ducts. The limitations of the present methodologies for the design of aerators for overflow spillways have been conveyed with the help of a sample calculation for a 125m high dam, and the need for further research investigations for high head, high discharge, intensity spillways have been identified. Special considerations for aerators of orifice spillways have also been discussed. The need for physical and mathematical modelling and limitations encountered therein are then conveyed