INVESTIGATION OF FLOW OVER A PIANO KEY WEIR

Abstract

India is third in the world for the number of major dams with about 5700. They offer a variety of economic and social services, such as flood control, municipal and industrial water supply, hydro power, water supply, irrigation, etc. Spillways are hydraulic structures built in a dam to spill excess water from a reservoir. They are critical for reservoir operation and play a crucial role in the safe operation of the dam. However, to enhance the discharging capacity of the dam without changing the total length of the overflow section, non-linear types of spillways are used. A Piano Key Weir (PKW), a type of non-linear weir, is purposely used to enhance the discharging capacity of existing dams or new dams having geological/geometrical constraints. Due to hydrological changes and sedimentation that affects storage capacity, the old dams need to be upgraded or renovated. As a result, high-efficiency weirs and spillways must be installed in order to increase low head dams' capacity for discharge. PKWs are best suitable for this kind of rehabilitation purpose. This report covers the study of various types of piano key weirs, observation of various hydraulic parameters of PKW, and to correlate results obtained from Experimental values with the numerical modelling in order to understand the hydraulic behaviour of PKW. The Computational Fluid Dynamics (CFD) model selected ANSYS Fluent which simultaneously solves the three-dimensional (3D), transient Reynolds averaged Navier-Stokes equations, capable of resolving complex geometries and boundaries. The volume of fluid (VOF) method is employed in FLUENT tracking fluid-air or fluid-fluid interfaces. It has been observed that when head overflow increases, the discharge efficiency of PK weirs rapidly decreases after increasing at low heads. In the present study it has been observed that discharge equation shows better conformity with Cicero and Delisle (2013) and Crookston et al. (2018) with experimental values. Also the Discharge Coefficient of PKW calculated from experimentally and numerically shows that numerical modelling exhibits good conformity to the experimental values.